TL neuro

August 30, 2024

On generating many research proposal ideas, part 1.

Filed under: Animal Models, Cannabis, E-cigarettes, Opiates, Tobacco/Nicotine, Vape inhalation, Vapor Inhalation — mtaffe @ 1:24 pm

I have occasionally done career-related presentations to new faculty through various mechanisms, most recently a NIH-funded program run by investigators at SDSU called ASSET. One of the things I always try to emphasize is the amount of work it takes to sustain a NIH-funded research laboratory. Work, meaning the number of grant proposals it is necessary to submit for consideration. Elements of this can be found in a recording of a presentation I did for UCSD’s Center for Faculty Diversity and Inclusion in 2021. Back in 2016 I wrote a blog post attempting to outline my grant submission and success numbers up to that point in time. As I always say, I don’t know how hard anyone else works at this, but I get a lot of rejections for every precious interval of funding.

The DrugMonkey blog has discussed the cumulative probability of getting one NIH R01 award in the service of making similar points about the necessary grant-submitting vigor. The latter one mentioned 15-18 R01 proposals over a four year period as being a reasonable target. Apparently this freaks some people out.

These discussions, in person and online, have a tendency to include newer scientists, postdocs and Assistant Professors, who wonder with dismay how one can have so many grant ideas as to support this rate of application to the NIH. In another post on this blog quite a time ago, I addressed how I navigated our interest in the cathinone stimulants from a first proposal submitted in October 2010 to our first R01 award on the topic in September of 2016.

I thought I would review how one of the through lines of my grant writing activity came about.

It summarizes my interest in examining the consequences of drug exposure in the adolescent developmental period.

This was initially crystallized as grant-fundable by the appearance of an RFA which was right in my lab wheelhouse at the time. It was about lasting behavioral consequences of adolescent alcohol exposure in non-human primate models. Literally the only part of this that we were not already working on was the alcohol part, and a alcohol focused postdoc had just joined my lab. I put in a R21 (Exploratory / Developmental) proposal. It was not funded, but the amended version put into a regular section was funded. Eventually we managed one interval of R01 support (after 3 tries) which was not continued (one try, then abandoned). These interests naturally led to pursuit of funding on the lasting behavioral impact of adolescent cannabis exposure, leading to one interval of funding of a component of a P20 Center (two tries) and one R01 (plus a substantive Supplement adding alcohol to the THC). There were two tries at a P50 Center follow-on (P20 awards can be viewed as the R21 of Centers) that were not funded and my R01 was in essence my component for the P50 attempts.

The alcohol R21 era was accompanied by three R21 attempts to examine the lasting effects of ADHD medications, all of which failed to be funded. A colleague of mine landed a U-mech more or less in the same space so I never really threw down on this. So much for my attempt to diversify* into another IC, the NIMH.

It was thus no surprise that my interest in the lasting effects of drug exposure during adolescence would continue to fuel my NIH grant proposals. This came back once my laboratory had switched over to rat models and a bigger interest in drug self-administration as the key outcome consequence. As far as I can tell, I put in my first proposal on the lasting effects of adolescent THC exposure in rats in for October 2019, of course including a relevant NIDA Notice of Special Interest (NOSI). I was busy with other submissions so the amended version only went in for July 2021, under a new NOSI. Both Not Discussed.

Not only were these linked to my prior interests from the monkey lab years, we’d also been working on e-cigarette vapor inhalation methods of drug delivery. So this method of exposure, and the corresponding translational link to what the kids these days were doing, was an overlapping and supporting (read: preliminary data) interest.

Proposals on the lasting effects of nicotine (July 2020, ND) and nicotine and THC were submitted (Oct 2021, ND; a new one for Fall 2022, ND). Again, Venn diagram overlap with the e-cigarette interest and the reality that adolescent nicotine exposure was zooming up because of the coolness of vaping. At this point I was also pursuing funding on partially overlapping interests from the TRDRP. I was fortunate enough to get funded in July of 2023, ending attempts at NIH funding on this topic. For now.

By this time we had one (rat) publication and much preliminary data on the basic structure of examining the consequences of adolescent vapor inhalation drug exposure which lasted into adulthood. So why not keep it rolling? We had been pursuing some work on oxycodone self-administration and it seemed useful to broaden the research program within the three headed dragon of the opioid crisis.

We decided to start looking at the lasting effects of adolescent heroin vapor exposure, leading to a grant proposal submitted Oct 2022 (53%ile, amended version July 2023, ND).

There are many aspects of this core line of research that appear very intentional and scripted from the outside.

I would say rather that the notion of lasting harms caused by adolescent drug use is just a basic, core, fundamental question of our field with high relevance to the human condition. It is an area that is immensely concerning and distressful to parents and IMO we do not have fantastic answers from the science side. Sure, lots of work exists but we could use more. There are always more things to address. This is why I lean on these types of structures to some of my NIH grant proposals.

But some of this also has an element of random walk, particularly considering we have to generate proposals supported in some way by prior work. Prior work funded under other projects that may not be directly applicable. But they have overlap and areas of intersection. Yes, I have to be creative about how available preliminary data support new proposals. But…that’s the job.

In behavioral work, there are several domains of outcome measure. Drug self-administration is one of our important focal outcomes. And we’re also interested in different drugs, all of which are self-administered. So maybe the adolescent exposure to one drug might be applied to the lasting self-administration of several other drugs. Maybe we have a bunch of overlapping circles of interest such as how THC may or may not alter the self-administration of opioids. THC-nicotine, THC-THC, and THC-heroin could be three separate proposals and lines of research. Or they could be integrated in some fashion. Every line of research has a little bud or a branch that points off in another direction. Sometimes, often I find, these directions form themselves into a coherent new R01-sized program of research. So I write another grant.

*this is a highly recommended strategy, btw. Staying essentially captive to one IC of the NIH throughout your career is not a good idea. Do as I say, not as I’ve done.

August 29, 2024

MDMA-induced hyperthermia in humans and animals

Filed under: Animal Models, MDMA, Thermoregulation — mtaffe @ 12:20 pm

The drug 3,4-methylenedioxymethamphetamine (MDMA) has been in the news lately, summer of 2024, what with the FDA having a hearing about the potential approval of MDMA for treatment of PTSD. That hearing did not go well and apparently the company Lykos (descended from MAPS) has kicked Rick Doblin off the board and reduced staff by 75% while it retrenches.

A new study from the Liechti laboratory (Straumann et al., 2024) examines the subjective and physiological effects of S- and R- isomers in comparison with the racemic mixture in human subjects. You can think of the isomers (enantiomers) as the left hand and right hand reflections of the molecule. The racemate (or racemic mixture), which most recreational consumers would experience, is made up of roughly half of each isomer. The study examined the effects at an oral dose of 125 mg, and the R-MDMA was also examined at 250 mg, p.o.. The background here is overtly the march towards drug approval and is within a context of proposals that one of the isomers might be safer and/or more effective as a therapy. The study was a double blind, crossover design with a placebo control, so all subjects participated in all five sessions. There were a minimum of 10 days between sessions.

Human subjects dosing can be a little frustrating to those of us on the animal research side who most often dose in mg of drug per kg of bodyweight. The usual pharmacology assumption of a 70 kg human should be expanded to a range of 50 (~110 lbs) to 90 (~200 lbs) kg when there are both men and women in the sample, as in this study. This lets us ballpark a possible dose range of 1.4 mg/kg to 5 mg/kg.

My interest was immediately drawn to the “safety” part and, in particular the Introductory comments that “R-MDMA induces less hyperthermia and less neurotoxicity” for which they cite Fantegrossi et al. 2003, among others. Since recreational MDMA consumers who die or get into serious clinical distress almost always present with very high body temperature, the temperature response is of significant interest. Somewhat relatedly, lasting changes in serotonin transporter expression (“neurotoxicity”) associated with repeated MDMA dosing in rats has been shown to depend on elevations in body temperature (Malberg and Seiden, 1998). If the body temperature doesn’t go up, the rats brains tend to express less lasting disruption of serotonin transporter expression. There has been, however, relatively scant data on the body temperature response to MDMA in controlled human laboratory studies. Freedman et al., 1995 was one of the few examples and it showed elevations of gastric body temperature of about 0.5 degrees Celsius after oral consumption of a 2 mg/kg (thank you!) racemic MDMA dose.

Adapted from Fig 3, Straumann et al., 2024. Black: placebo; Lt Blue: R-MDMA 125 mg; Blue: R-MDMA 250 mg; Red: S-MDMA 125 mg; Purple: MDMA 125 mg.

As you can see from this subpanel from Figure 3 in the Straumann et al. paper, all MDMA conditions increased body temperature compared with the placebo. The racemate and S-isomer produced identical responses at 125 mg, but it required a 250 mg dose of the R-isomer to induce the same ~0.6 degree Celsius effect. The Discussion merely says “Animal studies reported no hyperthermic effects of R-MDMA in mice or rats [14–16]. However, we found similar minimal increases in body temperature after S-MDMA and R-MDMA in the present human study.”. And it is true that the Fantegrossi et al., 2003 paper did not find any change in mouse body temperature after either 10 or 100 mg/kg, i.p., doses of R-MDMA, whereas S-MDMA and the racemic mixture elevated body temperature approximately equivalently at 32-56 mg/kg doses.

However.

Figure 1 from Taffe et al., 2005.

Straumann and colleagues apparently missed a paper from our lab (Taffe et al., 2005) which examined the temperature response to MDMA isomers and the racemate in nonhuman primates. We found that a 1.78 mg/kg, i.m. dose of the isomers and the racemate produced a roughly equivalent temperature elevation. In fact these responses are remarkably similar in magnitude and duration to the effects reported for humans by Straumann and colleagues. Interestingly, all three papers pose a bit of a pharmacological conundrum with respect to the enantiomers, but this is probably explained by a flat dose-effect function at the critical doses. In all three cases the effect of the same doses of the racemate and the S-MDMA isomer are identical. In our monkey study, each enantiomer was similarly active so you would predict a similar efficacy of the 50:50 mixture in the racemate. It all makes sense, but only if you ignore other evidence showing the R-MDMA is less potent. This also makes some sense in the mice (Fantegrossi et al., 2003) because there was no impact of the R-MDMA isomer. However, the fact that it was only half of the active dose (i.e., of the S-MDMA) included in the racemate is concerning. Only partially so, given that 32 and 54 mg/kg did roughly the same thing in the mice. Perhaps halving the active S-MDMA by administering the racemate didn’t drop the dose low enough from the key range to cause a partial response. The human data are a little weirder given that they showed the R-MDMA was maybe half as potent as the S-MDMA. So one would predict that the racemic mixture would produce a reduced effect. Still, by the same logic as the mouse study, it is possible the dose-effect function for the temperature response is just flat across this dose range.

One of our followup studies contrasted the effects of orally administered racemic MDMA at 1.78 and 5.0 mg/kg doses (Crean et al., 2007). Each dose significantly elevated body temperature and the peak only differed by about 0.2 degrees Celsius (there was a 0.5 vs 0.7 degree change from baseline for the two doses). The oral dosing is an even better match for the Straumann et al. data and addresses complaints from those that think the route of administration differences (humans usually swallow MDMA, animal studies typically inject the drug) precludes translational inferences. (That’s a fancy way of saying the animal data cannot apply to the human situation.) Our data also show a potentially compressed average temperature response that hits a ceiling around a 0.7 degree elevation. This is almost certainly due to the robust physiological regulation of temperature in larger bodied mammals.

Overall, it is nice to see such a close confirmation of our work in the human. We had reported a few things that perhaps differed enough from the rodent models to emphasize species would be critical to translational inferences. In one aspect, for example, the larger body size of the monkey probably makes their temperature responses less sensitive to the ambient temperature compared with rodents. In this case, the new work confirms our finding that the R-MDMA entantiomer increases body temperature at doses very near the doses required for the racemic mixture, and that S-MDMA is not more potent than the racemic mixture.

One implication of this is that it further validates the translation of some of our other findings to the human condition.

Crean, R.D., Davis, S.A. and Taffe M.A. Oral administration of (±)3,4-methylenedioxymethamphetamine and (+)methamphetamine alters temperature and activity in rhesus macaques, Pharmacol Biochem Behav, 2007, 87(1): 11-19.

Straumann, I., Avedisian, I., Klaiber, A., Varghese, N., Eckert, A., Rudin, D., Luethi, D., and Liechti, M.E. Acute effects of R-MDMA, S-MDMA, and racemic MDMA in a randomized double-blind cross-over trial in healthy participants, Neuropsychopharmacology, 2024 Aug 23. doi: 10.1038/s41386-024-01972-6. Online ahead of print.

Taffe, M.A., Lay, C.C., Von Huben, S.N., Davis, S.A., Crean, R.D. and Katner, S.N. Hyperthermia induced by 3,4-methylenedioxymethamphetamine in rhesus monkeys, Drug Alcohol Depend, 2006, 82(3):276-281.

May 16, 2024

Rescheduling of cannabis to Schedule III

Filed under: Cannabidiol, Cannabis, NIH — mtaffe @ 1:36 pm

The Biden administration has recently (5/16/2024) announced that it will move to re-schedule cannabis (“marijuana” in Federal Government terms) from Schedule I to Schedule III. Ryan Marino, MD, has posted a nice review with links, if you are interested in the timeline of Administration steps leading up to this point.

I’m immediately interested in the selfish question.

What does this mean for researchers such as myself who use the active constituents of cannabis in their research?

For reference, my experience is derived from holding a Schedule I researcher license from the DEA. We have had occasion to use delta9-tetrahydrocannabinol (THC), cannabidiol, and crude cannabis extracts in our work, approved under this licensure.

At present time the DEA lists [PDF] marihuana (sic; other names Cannabis, marijuana) under drug code 7360 and marihuana extract under drug code 7350. This latter was a relatively recent distinction, previously* extracts were covered under 7360. It also lists Tetrahydrocannabinols (other names THC, Delta-8 THC, Delta-9 THC, dronabinol and others) under drug code 7370. I have all three codes listed on my license at present**.

FORM DEA-225 (04-12)

Cannabidiol (CBD) is not mentioned on the schedules I’ve ever seen from the DEA website, but it was considered a Schedule I controlled substance. In terms of obtaining it, CBD was, to my recollection, originally covered under 7360 before 7350 was used. I am not sure how CBD was handled when 7350 was activated for extracts. My recollection is that the only reason I have 7360 on my license at all is because I had to do it for extracts, CBD or possibly both when I first became interested in using those substances. We have never been all that interested in using the plant material in our research. One interesting twist in the CBD story is that at one point there was a drug code 7372 introduced for Cannabidiol but it only ever appeared on the application for a license. My copy where this appears is FORM DEA-225 (04-12). I recall asking the DEA contact about this as it seemed at the time they were preparing to perhaps down-schedule CBD but nothing ever seemed to come of it. There was never a way to add 7372 to the actual license as far as I can recall. I have a shipping document for CBD from 2015 that indicates my license was checked for drug code of 7360, confirming my recollection CBD was covered under marihuana and not extracts.

The Agricultural Improvement Act of 2018 (aka the Farm Bill) championed by Senator Mitch McConnell effectively removed CBD from the Schedule. Those of us who wished to use CBD in research were in a little bit of limbo for many years because this window likely only applied to CBD derived from the Farm Bill defined hemp and not CBD derived Farm Bill defined non-hemp Cannabis. It was also unclear where synthetic CBD might fall. In early 2024, we obtained CBD from NIDA Drug Supply which was described as “synthetic” and as requiring no DEA license. It was also listed with a DEA code of 7350.

Back to THC. The PR from the Biden Administration DOJ, and press coverage, only mentions marijuana. This immediately got me curious about whether the DEA was going to do the sensible thing for us researchers, or to conveniently leave drug code 7370 for Tetrahydrocannabinols intact in Schedule I.

I started reading the notice of proposed rulemaking [PDF] which was some tough going. You have to get all the way to Page 82 and the Determination to Propose Rescheduling Marijuana to Schedule III header to find out what is actually being proposed. The key for us researcher types comes on Page 83.

In addition, this proposal would apply to Δ9-THC derived from the marijuana plant (other than the mature stalks and seeds) that falls outside the definition of hemp, because it meets the statutory definition of marijuana. …. This proposal would not apply to synthetically derived THC, which is outside the CSA’s definition of marijuana. Those tetrahydrocannabinols that can be derived only through a process of artificial synthesis (e.g., delta-10-tetrahydrocannabinol) are excluded. HHS provided a recommendation only relating to “marijuana” as defined in the CSA. That definition is limited to the plant (other than the mature stalks and seeds) and derivatives of the plant. Therefore, synthetic THC will remain in schedule I.

I am…relieved.

My understanding is that the usual sources of THC for researchers is plant derived, although I am checking up on this with NIDA drug supply, believe me. But it appears to be the case that THC will go along with cannabis plant material in this pending re-scheduling action.

This is great news for researchers.

“But it is still Scheduled?”, you wonder. Yes, but permission to use Schedule III and higher designations are almost always covered at the institutional level. In many of the more active research institutions, Schedule II is covered as well. This means individual researchers have no need for a license to be permitted to use those substances, although there may still be some internal approvals/trainings/processes required. This makes it a whole lot easier to conduct research with cannabis and with cannabinoid compounds.

*I have DEA schedule lists up through August 2016 which do not have 7350 listed. It does appear on a list from January 2018. I did not include 7350 on my annual renewal in Nov 2017 but I did in Nov 2018, suggesting this was added ~2018.

**For those who are unaware, the Schedule I researcher license is not blanket permission to use everything that is scheduled. One is required to apply for permission for every drug code covering the specific substances one wishes to use in the laboratory.

March 4, 2021

DEI work, the NIH funding gap, scholarly credit and career advancement

Filed under: DEI, NIH — mtaffe @ 10:52 am

I recently published a Feature Article in eLife, with Nick Gilpin, on the NIH’s dismal response to the funding disparity which was identified in 2011. I also put in a small comment at Neuropsychopharmacology addressing the ACNP’s breast beating about diversity, equity and inclusion within the ranks of this highly selective academic society. It is not that I just noticed this issue all of a sudden. But I never really had the motivation to supply something formal in a traditional academic outlet.

Part of this is that it is a lot of work. The Correspondence to Neuropsychopharmacology, which ran only about a page, had to be crafted to make the essential points within the allowable limits for the publication type. It went to peer review and there was an editing and re-submission phase not unlike that for any manuscript. The eLife article started out as as massive beast of unruly text, which we eventually posted on psyArXiv. It took at least 6 months from when my co-author started kicking my butt into gear to write it until we were ready to post a pre-print and seek a publication venue. Sure, I’m a notorious procrastinator when it comes to getting manuscripts into final form for submission but part of this was the work involved. It’s all well and good to have ideas and the framework for a manuscript, but beating it into submittable shape takes effort. We selected a venue and a publication type that involved very heavy editorial input and requests for revisions. This took a lot more work.

All of this is work that could be spent on my “real” job, i.e., preparing scientific manuscripts for publication and writing yet more grant applications for NIH funding.

Others have been doing the same work in past years. My colleagues Carl Hart and Jean-Lud Cadet addressed the ACNP issue. Kafui Dzirasa has addressed these issues here and here. Stevens and colleagues published the very well-received Fund Black Scientists call. Valentine. Starbird. Guy and colleagues. There has been a growing number of publications from scientists in the past year or so.

These are not enough. It is my view that we need even more. Sure, the NIH Director’s statement on structural racism which was published March 1, 2021 is very welcome. But NIH is still punting this to committee work and further bureacratic responses. It is essential to keep the heat and our eyes on the NIH to redress the lack of equity in their research funding.

Every academic society and every academic journal should be publishing material on diversity, equity and inclusion within their subfields. Particularly all of the ones that receive funding from the NIH, but I am sure we will start seeing reports on the lack of equity across many funding bodies. Cancer Research UK seems to be admitting to a Ginther / Hoppe style problem, for example [PDF]. So who is going to do the work?

It’s up to us. Which returns me to the amount of work it takes to publish even the shortest commentary and certainly a lengthy review or feature article. We cannot expect people to engage in these activities as a sort of career charity. My point of the day is that we do not have to.

I have linked DEI publications in this post that all show up in a PubMed search. This is the first aspect of credit. If they show up in a PubMed search on your name, then they go into the total count that someone might be glancing at when giving you a look-see. (Note that this will not necessarily always be the case at every possible academic journal, depending on the type of publication format you are using.)

But there is another key factor which I am just verifying lately. These items go into the Web of Science database of citable content with their citations counted. This is huge. Yes, I know lots of you like Google Scholar but when you are dealing with the long established traditions and expectations of your Department and University, WoS is key. These DEI works will go into your publication counts. Any citations will go into your citation totals, including your h-index. I think this should be encouraging for anyone trying to decide whether writing a piece on the NIH’s efforts to respond to the inequities of grant award will be helpful or harmful to their career.

July 7, 2020

CB1 contributions to THC-induced hypothermia after vapor inhalation

Filed under: Cannabis, E-cigarettes, Vape inhalation, Vapor Inhalation — mtaffe @ 1:03 pm

By this point the laboratory has published a number of papers showing that the vapor inhalation of Δ9-tetrahydrocannabinol (THC) reduces body temperature of rats. This was mostly done to validate our e-cigarette based method of drug delivery since hypothermia, along with anti-nociception, hypolocomotion and catalepsy, is a key marker of cannabinoid action in the rat (or mouse). This tetrad of signs was developed as a laboratory readout of THC-like effects before it was known where THC acted in the brain, before the endocannabinoid receptors were identified and before specific pharmacological tools were available to target the cannabinoid type 1 (CB1) receptor.  Since we are a behavioral pharmacological lab one of the primary ways to validate is to show that effects depend on the dose of the drug that is administered, and we have done that using both time of exposure and concentration of the drug in the vapor to control dose. The pharmacological tools are available now so the secondary go-to validation for  a behavioral pharmacological laboratory is to determine if antagonist drugs which block the ability of THC to interact with, e.g., the CB1 receptor, inhibit or block the effects of the inhaled drug.

A new paper (a pre-print version is available here) from the laboratory describes a several year journey of confusion about why a very simple experiment that “should” work, did not.

Nguyen, J.D., Creehan, K.M., Grant, Y., Vandewater, S.A., Kerr, T.M. and Taffe, M.A. Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats. Drug Alcohol Depend, 2020, in press.

The compound SR141716 (it was approved as a treatment medication as “Rimonabant” but pulled from the market for suicidal ideation reasons) interacts with the CB1 receptor, both preventing THC and other agonists from working (i.e., as an antagonist) and potentially reducing constitutive activity of that receptor (called an “inverse agonist” effect). SR141716 works fine for the prevention of some THC-induced effects including the aforementioned tetrad of signs in rats. Most specifically including hypothermia. So long as the THC is injected. It also blocks anti-nociceptive effects of THC when injected OR when inhaled.

Nguyen20-Fig1-tailflick

Figure 1 from this new paper shows the speed with which the rat tail is withdrawn from a 52 degree C water bath after a 30 minute inhalation session. When the vapor is from the PG vehicle, the tail is withdrawn within about 3 sec (open bar). After THC (grey bars) inhalation this slows to over 6 seconds in male and female rats. This is the anti-nociceptive effect of THC when delivered by inhalation but the magnitude is similar to what is produced by THC injection. Pretreatment with SR141716 (black bars) before the inhalation session entirely prevents the anti-nociceptive effect of THC in male rats entirely and greatly reduces it in female rats.  So far, so good, and actually we showed something similar in our very first paper, Nguyen et al 2016 (see Figure 4B).

Dating back to our very original studies, this is not what happens with the temperature response. Figure 2 from the new paper shows (Panels A, B, D) that SR141716 administered prior to THC inhalation does not affect the initial drop in body temperature, observed immediately after the 20-30 minute session.

What SR does do is slightly accelerate the return of body temperature to the normal range. To walk through the logic of these first panels, the study in A suggested perhaps the SR simply wasn’t effective until 90 minutes later so in B we moved the pre-treatment interval to 90 minutes before inhalation. No difference. There’s always a concern about dose so in Panel D we increased from 4 mg/kg SR141716 to a 10 mg/kg dose, and had no change. In Panel C, we injected the SR after the vapor session and again, no change in the overall picture, suggesting that even with pre-vapor administration of the SR141716, essentially the same level of activity was present in the post-vapor monitoring period.

The rest of the paper describes more experiments along the same theme- trying to give the antagonist the best chance to “work” and further confirming that it does work to prevent body temperature changes…..just so long as the THC is injected (either intraperitoneally or intravenously).

None of the usual pharmacological explanations related to antagonist/agonist dose, speed of uptake into the brain or competition for binding sites seem to be at work here. We’ve altered dose and injection route. We’ve evaluated both sexes and two different rat strains. Studies range across animal age (and therefore size) and their treatment history, including a chronic THC dosing group that exhibited partial tolerance to the THC inhalation. We have conducted vehicle inhalation controls, which do not alter body temperature, and thus there cannot be any role of the vapor exposure by itself. We used an alternate antagonist/inverse agonst drug and produced similar qualitative results.

Nguyen20-Fig2-temperature

Most convincingly, of course, the effects of the antagonist differ between the temperature and the nociceptive effects of THC inhalation.

Scientifically this is a nagging mystery. We’ve thrown effort at these studies over several years now, and have tried other manipulations that fail to resolve the question to our satisfaction. The literature on injected THC is reasonably robust but there are few investigations reported for inhaled exposure. What exists is limited by the experimental design. For example, Wilson and colleagues (2002) showed that the temperature response to inhaled THC could be attenuated by SR141716 pre-treatment in mice, but they only measured temperature at a single time-point after inhalation, with locomotor, nociception and catalepsy tests being performed first. It cannot be determined, therefore, if the temperature response at some earlier timepoint was unaffected by the SR141716 pre-treatment. This partial effect also conflicts with a complete blockade of the temperature response to inhaled THC in a different strain of mice reported by Marshell and colleagues (2014).

Sadly, this is the sort of mystery that doesn’t really justify a lot more effort and money to resolve. While important and useful for validation purposes, the hypothermic response to THC does not appear to have much translational value. It is not clear that human body temperature is affected by THC ingestion at all, nor what health implications this might have even if humans do experience temperature reductions.

This paper is one that I feared might not ever be publishable. It presents a bit of a mystery and does not actually solve it. This is not typically what is found to be publishable in academic science reporting. But from a conduct of science perspective it is really important to get out there. Just as we followed this frustrating path after starting from a expectation of rapid pharmacological validation of our method, others might likewise wish to validate their inhalation models. E-cigarette use for delivering cannabinoids continues to be very popular with both medical and recreational consumers of cannabis (via extracts). This encourages researchers to try to adopt similar methods to explore any possible implications for health or well being. There are other labs doing similar work already and they are, in many cases, rooted in behavioral pharmacological thinking as much as we are. At the very least, our paper serves as a warning that things may not be simple.

More usefully, perhaps someone will come up with a brilliant insight about where our thinking has led us astray. We could be missing something incredibly simple that explains all of this in a satisfying way. That is the absolute brilliance of the grand enterprise of science, i.e., that publishing work leads to someone else either confirming, contradicting or explaining our current state of knowledge.

July 19, 2019

Cannabidiol by vapor inhalation in rats

Filed under: Cannabidiol, Cannabis, E-cigarettes, Tobacco/Nicotine, Vapor Inhalation — mtaffe @ 2:37 pm

Cannabidiol is increasingly popular, occurring in a dizzying array of products in a highly unregulated retail market. This includes creams, oils, lotions, capsules and e-cigarette liquids, among many other items. A simple search for CBD on google will give you a taste of what I mean, if this is new to you. Just about every single senior person I talk to, it seems, is using CBD or knows another person who is using CBD  for various ailments.

The following has just been accepted for publication:

Javadi-Paydar, M.,  Creehan, K.M., Kerr, T.M.  and Taffe, M.A. Vapor inhalation of cannabidiol (CBD) in rats.  Pharmacol Biochem Behav, 2019 Jul 20:172741. doi: 10.1016/j.pbb.2019.172741. [ Publisher Site ][ PubMed ]

Figure 1: This figure has been adapted from Taffe et al. 2015. Click to enlarge.

We have been interested in studying the effects of CBD ever since reading a paper [Morgan et al., 2010] that appeared to show that the presence of CBD in cannabis protected users against the memory impairing effects of acute THC intoxication, subsequent to smoking their preferred cannabis. This led to our interest in the potentially interactive effects of CBD and THC and, in particular, tests of the hypothesis that CBD would reduce the effects of THC. Our initial papers on this were Wright et al 2013 and Taffe et al 2015. Of primary relevance for the discussion of our new work, the latter paper showed that CBD did not alter the body temperature (see Figure 1 C, D; blue bars) or activity of rats when injected at doses of 30 or 60 mg/kg, i.p.. Our new work confirms our prior finding that this may be due to the route of administration since, when male or female Wistar rats experience CBD by vapor inhalation, their body temperature does go down, albeit not as severely as when exposed to THC [Javadi-Paydar et al, 2018].

This finding required some follow-up, extraordinary claims requiring extraordinary evidence and all that. Although in the Taffe et al 2015 paper, CBD did appear to increase the magnitude of the hypothermia associated with THC when each were injected, i.p., (red trace and summary bars in Figure 1) there are data suggesting that this may be due to metobolic interference whereby CBD merely prolongs the activity of THC. Another thing that was slightly strange was the fact we observed that CBD reduces temperature of Wistar rats. We used Sprague-Dawley rats for the Taffe et al 2015 paper because initial pilot experiments suggested that perhaps Wistar (male) rats were less sensitive to the body temperature lowering effects of THC [a follow up to that is available in a pre-print]. Yet Javadi-Paydar et al (2018) found effects of vaporized CBD in male and female Wistar rats. Perhaps this is due to the difference between CB1 receptor mediated effects and serotonin 1a (5-HT1a) receptor mediated effects. There is growing evidence that CBD works in part by activating 5-HT1a receptors, and activation of this receptor (e.g., by injecting the agonist 8-OH-DPAT) drops the body temperature of rats precipitously. As an example we had published a figure on this as a positive control in the Wright et al 2012 paper focused on the activity of the cathinone mephedrone [blog post summary]. To further complicate matters, the response of male Wistar rats to 8-OH-DPAT in that paper seemed to be slightly greater than the response of male Sprague-Dawley rats.

Figure 2: Plasma CBD in male and female Wistar rats after vapor inhalation (top panels) or injection (bottom panels).Click to enlarge.

An earlier version of this manuscript was posted as a pre-print on June 04, 2019, and updated with a version almost identical to the final submitted manuscript on Jul 18, 2019.

The first critical thing in this new paper was to get a point of reference for the doses the animals were getting through vaporized CBD versus i.p. injection. This figure shows the plasma levels experienced at the end of vapor sessions are within the range of plasma levels observed 35 minutes after an injection. This was in male and female Wistar rats, making it a follow-up to the thermoregulatory data in the Javadi-Paydar et al (2018) paper. One of the major ways that we control dose with our inhalation model is to alter the concentration of the drug in the e-liquid vehicle (we use propylene glycol; PG), while holding other parameter fixed. So for CBD we have used concentrations of 100 and 400 mg per mL of the PG. Now admittedly we have only published the effects of 30 mg/kg CBD when injected, at the lower end of the dose range. But based on some pilot work I doubt that we’ll find out that lower dose of CBD are causing hypothermia when injected- but it could still be about dose. Our time-point here for injection was designed for comparison with the inhalation model but levels were likely much higher at 5 minutes after injection whereas they were increasing essentially linearly across the inhalation interval. Nevertheless, we are clearly not getting much, much higher plasma loads of CBD via inhalation, at least not in the blood.

The next step for this paper was to replicate the body temperature effect, which we did in a group of male Wistar rats.

Figure 3: Temperature responses to vapor inhalation of CBD and nicotine in male Sprague-Dawley rats. Open and grey symbols depict statistical differences summarized in the manuscript. Adapted from Javadi-Paydar et al 2019. Click to enlarge.

We then went on to evaluate the effect of CBD inhalation on body temperature in male Sprague-Dawley rats and found a similar (perhaps slightly increased relative to the Wistar male rats) degree of hypothermia under identical vaping conditions.

Figure 3 shows that CBD concentration-dependent reductions in body temperature are found in male Sprague-Dawley rats (blue data series), thereby replicating and extending to an additional rat strain. The next experiment showed that the effect of CBD (at the 100 mg/mL concentration) is attenuated when animals are pre-treated with the 5-HT1a antagonist WAY 100,635. This shows that the 5-HT1a receptor is very likely involved in the hypothermic response to vaporized CBD, further adding to the growing evidence that CBD acts at this receptor.

You may have noticed that the top two panels of Figure 3 include a nicotine inhalation condition and a CBD + nicotine inhalation condition. There are a couple of reasons for this. Most generally, CBD has been shown to attenuate relapse to alcohol and cocaine self-administration in rats and may reduce the salience of cigarette-associated cues in humans. Reviews of the potential of CBD as an anti-drug abuse treatment can be found here and here. The second rationale is that human substance users often use more than one drug at a time. THC and CBD co-occur in cannabis. People frequently use cannabis along with tobacco and/or alcohol. Our work in Javadi-Paydar et al 2019 examined potential interactive effects of THC with nicotine thus it was an obvious followup to see if CBD interacted with nicotine. As you can see in Figure 3, the effect of nicotine alone on body temperature is not obvious in this group (although it did enhance locomotor activity). Nicotine did, however, increase the effect of CBD when the two were co-administered. Interestingly CBD also suppressed the locomotor activating effects of vaporized nicotine inhalation in this study. So the combined effect appears to be independent, not interactive- i.e., an opposition when the two independent drug effects are in the opposite direction (locomotor activity) and add together when the two independent drug effects are in the same direction (see Javadi-Paydar et al 2019 for more on this interactive drug logic and on the hypothermia caused by nicotine inhalation).

CBD is often described as non-psychoactive constituent of cannabis because it does not appear to have the same dramatic subjective properties as delta-9-tetrahydrocannabinol. Also because there are a lot of studies where it does not appear to do much to a rodent when administered by itself. There are exceptions, but I think a fair take away is that often enough it has been found inactive. This may very well be due to investigating CBD in assays that are tuned to detect THC-like effects that are presumably mediated by the CB1 or CB2 receptors. Our thermoregulatory assay, fortunately, is sensitive to both CB1 and 5-HT1a agonists. It may also be the case that the route of administration is a fundamental contributor to observing or not observing effects of CBD in a rat. There are several pharmacokinetic possibilities that may explain this. Our plasma data are fairly limited in a temporal sense and we don’t know from plasma levels what the kinetics look like in the brain. It could be that there is a much different blood/brain ratio associated with the two routes of administration. It may be that the speed of initial brain entry of a threshold amount of drug varies as well. Additional work will be necessary to full determine how the route of administration alters the effects of CBD in rats and how this might translate to the human condition.

 

April 30, 2019

Obtaining the Opioid Overdose Rescue Medication Narcan “Over the Counter” Isn’t Simple

Filed under: Drug Overdose, Opiates — mtaffe @ 11:12 am

The news is full of accounts of the opioid crisis, most pointedly on deaths and near-lethal overdose events. There has been a long and steady increase in opioid-related deaths as depicted on graphs like this one from the CDC. The trend started in 2000 and mostly involved prescription opioids such as oxycodone and hydrocodone. These deaths stayed elevated increased less quickly in the past decade. Unfortunately, deaths associated with the non-prescription illicit opioid heroin started to increase in 2010, eventually reaching the levels associated with prescription opioids in 2016. Despite this long and steady increase in opioid-related deaths (and other indicators of harm were in parallel to this, ranging from epidemiological evidence of non-medical use to a demand for addiction treatment), it took until the recent Phase 3 to gain broad media and political attention. This more recent phase has been characterized by a rapid increase in deaths associated with highly potent synthetic opioids- most commonly fentanyl and, occasionally, derivatives of fentanyl. Much of this appears to be driven by illicit drug suppliers using fentanyl as a boosting agent without actually informing users that they are getting fentanyl. Fentanyl, and related derivatives, are popping up in association with heroin, in pressed pills faking the appearance of prescription opioid products (like Oxycontin) and in other non-opioid drugs such as cocaine. In September, my neighborhood had a small cluster of opioid-related overdoses (including 3 fatalities and 2 survivals) from an adulterated cocaine supply.

Although it took far too long to gain traction with first responders, there is an antidote to opioid overdose that can be helpful in preventing deaths. It is the compound called naloxone, which is an antagonist (blocker) of the mu opioid receptor. This is the brain receptor that is most involved in the respiratory suppression effects of opioids that leads to overdose deaths. If an individual who is intoxicated with an opioid is given a dose of naloxone, it can prevent death all by itself or it can slow the respiratory effects long enough to bring additional medical interventions to bear.  The wikipedia article reminds us “Naloxone was patented in 1961 and approved for opioid overdose in the United States in 1971“. So what’s the problem?

Availability. By the time anyone in the vicinity notices that a person is in respiratory suppression subsequent to their opioid use, this person may not have a lot of time before death. It may take time to get emergency services to the person or the person into the emergency room. There may not be anyone around who cares to intervene beyond calling 911. Which means that equipping first responders (EMS, firefighters, police) with an easily administered version of naloxone is a key component. This has been gradually accomplished with the Narcan nasal spray. There was resistance. In the waning years of the Bush administration there was still resistance to the idea of equipping first responders but this changed a lot during the Obama administration (overview from health affairs). First responders can only do so much, so in parallel there have been efforts to get Narcan into the hands of private citizens so that they can intervene in a suspected overdose. Naloxone by itself has minimal to no effects on an otherwise healthy individual and will not increase health problems brought about by overdose on many other non-opioid drugs so the dangers of a false alarm good Samaritan dosing with Narcan are pretty minimal. Many states have taken action to allow Narcan to be sold without a prescription and the major pharmacy chains Rite Aid, Walgreens and CVS have stepped up to provide this service. So the antidote is “available” to anyone. The next phase is to get this into more people’s medicine cabinets, just in case. And I am writing up my experience, below, to show you why this medication is not truly “over the counter” in the way you expect and why it is a good idea for you to go out and get it. Apparently it has a 12 month expiration date and is probably still highly effective for 18-24 months and even expired Narcan is probably better than no intervention when someone is overdosing on an opioid.

My experience obtaining “over the counter” Narcan.

I had been meaning to secure a Narcan kit for my medicine cabinet for a few years and just never go around to it. I’m a parent of teens and a friend and neighbor to other parents of teens. Teens, as they do, have a chance of coming in contact with opiods, of using opioids and of being around other kids who are using opioids. Intentionally or, as we saw in the fatalities in my neighborhood in 2018, unintentionally due to contamination of other drugs with fentanyl. And the surgeon general issued an Advisory reminding us that “You have an important role to play in addressing this public health crisis“. So I went down to my local CVS and tried to obtain a nasal Narcan kit.

The first thing to understand is that it is not “over the counter” like ibuprofen or condoms. You have to go to the pharmacist and ask for it. I did so and it was clear to me that this was the first time this particular pharmacist had dealt with the process. She was informed and super great about it but it was not a familiar process. She had to first print out some warning / informational page. This took time and made me wonder why they don’t print out a few and stick them under the supply on the shelf. I don’t think I would have had to show identification but I am not entirely sure, I was there for sudafed and had already shown it to her for that purpose.

What I did find out is that one has to be 18 years of age or older to purchase. This is a problem and a big one, if you ask me. Teens are a clear risk group and their peers should be able to obtain Narcan. As a related issue, I was informed it would be $130 for the two-dose nasal spray kit. No big deal for me, but you can imagine that this may be a HUGE barrier for kids or for street / homeless people. These are details you will want to check in your local jurisdiction because I would not be surprised if there are significant variations in the state laws and differences across drug store / pharmacy chain policies. Teen access and cost are barriers in my city, making it even more important in my view for parents to obtain the Narcan, put it in their medicine cabinet and tell their teens where it is and how to use it. It may help to review a youtube video on what overdose looks like (such as this one). I even made my kid take it to Coachella and there was very little fussing about that. It doesn’t have to be some huge thing, just a recognition that stuff can happen and it is better to be prepared.

Okay, back to the pharmacy process. I was told they have to “treat it like a prescription” in their system. Okay, no biggie for me but could be a little off-putting for teens, homeless and the illicit drug using community generally. The pharmacist asked me three questions- did I use drugs (no), was I in contact with anyone using drugs (I said no since I wasn’t thinking of some specific person) and a third similar question I can’t recall but also answered “no”. The pharmacist next informed me that she could not sell me Narcan if I answered no to all three questions. Which is another barrier- apparently the CVS policy in my city is to not sell it to anyone for ill defined general prophylaxis safety reasons. This was of course my actual reason. So I said “whoa, whoa, back up, I’ll give you a yes on the second question”. Okay phew, back on track. I was next asked “What is the name of this individual?” WHAT? As you can see, this is another huge barrier to the way Narcan is provided “over the counter”. At least in my city / state and at the CVS pharmacy. Again, YMMV in your location.

As I said the pharmacist was totally helpful. She fully realized what I was doing and did not give me any static when I reversed my “no” to the second question and answered her person query with “John Doe”. She did ask for an address (!) which I made up from the surrounding streets- I don’t know what would have happened if she had entered an address that didn’t exist. I also had to give a phone number for this person! I also made that one up but…..in the final stages of the process  got queried about text messages and it was clear that I’d accidentally made up a phone number that was already in the CVS database for a real customer. The pharmacist kindly deleted the phone number from the record.

I eventually walked out with a Narcan kit. $130 poorer and about 30 minutes after starting the process. There was no line at the pharmacy that particular day but it would not be unusual to be waiting in line. This is not a process that facilitates a rapid response to an overdosing individual.

You can see, that in addition to the time it takes, all of the process to obtain Narcan that I experiences presents several barriers. A person seeking Narcan under the stress of an overdosing friend might simply walk away if they didn’t have the money, weren’t 18 yet or were scared off by the requests for information on the victim and didn’t think to lie. For all I know this particular pharmacist was cool but another one might get sticky about my obvious lying with respect to the “John Doe” that they needed to enter as the patient in their database for the sale.

 

Additional Reading: Dose Makes the Poison blog fentanyl archive.

March 31, 2019

Taffe Laboratory 2.0

Filed under: Careerism, Lab Alumni — mtaffe @ 1:39 pm

Following 19 years of operation at The Scripps Research Institute, the Taffe Laboratory is moving to the Department of Psychiatry at the University of California, San Diego, effective April 1, 2019.

I was first appointed Assistant Professor at TSRI in August of 2000.  I had been a postdoc at TSRI from December 1996 and my lab head departed the institute in early 2000, leaving me in charge. TSRI provided the opportunity for me to be promoted to faculty if I could get a major grant funded. My first NIH R01 was funded September 11, 2000 and I have been running a laboratory ever since. In that time I have published 69 items indexed on PubMed, including a few datasets leftover from my postdoctoral work, a couple of commentaries and a couple of reviews. The laboratory survived a major change in research models somewhere around 2008 and has remained (touch wood) funded by the NIH. I am intensely grateful to the taxpayers of the United States for supporting our work over the years.

In February of 2019, I accepted the UCSD Chancellor’s offer of a Full Professor position in the Department of Psychiatry. This offer capped an 18 month recruiting effort spearheaded by the Chair and Vice-Chair for Research of the Department of Psychiatry. It required considerable effort on their part, was far more complicated than just the part that affects me and my laboratory and I am grateful that they sustained the effort. It has been…illuminating.

EmptyOffice

My new work home

Today is my last formal day at TSRI and tomorrow I begin the next stage of my career as an academic scientist. This is a fantastic opportunity and will be a tremendous step for my Laboratory as it is now, and as it will be in the future. It is almost unbelievable that I have been able to avoid the nearly inevitably academic nomad requirement through two postdoctoral appointments, an initial faculty appointment and, now, the mid-career jump. This just does not happen in academic scientific careers.

As I said on a Facebook post, I am brought to this new opportunity by the contributions of everyone who has worked in my laboratory over the years.

The Taffe Lab has always been a group effort and I would never be in this position without the heroic work of my technical staff including Amber and Stef and Chris and Glen and PK and Yanabel and Kevin and of course (cue fanfare) Sophia. Simon was a great first postdoc to help a noob prof. Becky and Jerry and Michelle and Shawn and Jacques and Mehrak and Eric and Arnold have all built this Lab with their efforts. We would not have accomplished much without them.

For those less familiar with the academic career in science, my job will not change all that much. I am still expected to get extramural research grants, to generate data, publish papers and help to advance the careers of younger scientists. I will continue to have a heavy focus of my laboratory on the problems associated with recreational drugs, including opioids, stimulants and cannabis.

June 22, 2018

An oxycodone vaccine prevents the acquisition of self-administration

Filed under: Opiates, Vaccines — mtaffe @ 2:59 pm

A paper from the laboratory has recently been accepted for publication .

Nguyen*, J.D., Hwang*, C.S., Grant, Y., Janda, K.D.. and Taffe, M.A. Prophylactic vaccination protects against the development of oxycodone self-administration.  Neuropharmacology, 2018, 138:292-303. [ Publisher Link ][ Free Author Share ]

This paper reflects joint effort with members of the Janda laboratory in our ongoing collaboration [ related posts ] to evaluate their anti-drug vaccines for efficacy in rat models of drug exposure and abuse. In this study we focused on a vaccine that induced antibodies that bind to oxycodone and evaluated the efficacy of this active vaccine (Oxy-TT) versus the carrier protein tetanus toxoid (TT). Our primary goal was to examine the intravenous self-administration of oxycodone in the rats.

This reorganization of Figure 2 from the paper depicts one of the key findings. The right panel shows the average number of infusions of oxycodone (0.06 mg/kg/infusion) obtained by subgroups of the Oxy-TT and TT rats. This median split analysis divides the Upper from Lower halves of the distribution based on average oxycodone responding across the 18 session acquisition interval. The distribution for the Oxy-TT group was more bimodal compared with the TT control group, indicating that some Oxy-TT rats took very little oxycodone across the acquisition period and some self-administered more. We defined successful acquisition as an average of 7 or more infusions obtained across two sequential days and the left panel reflects the proportion of the entire distributions of TT versus Oxy-TT that met this standard. Combined, we can infer that about 40% of the Oxy-TT animals essentially failed to acquire stable self-administration behavioral whereas all of the TT group did under these conditions. While it may seem disappointing to some eyes that the vaccine “worked” to prevent the establishment of stable self-administration in only 40% of the animals, this needs to be viewed in the context of human substance abuse. Only minorities of the individuals who try a given drug will go on to develop a habitual use pattern. This can be observed (cross-sectionally) in the Monitoring the Future data [vol 1 adolescents; vol 2 adults], in Schramm-Sapyta et al 2009 and in Anthony et al, 1994. The best way to reduce harm from repetitive use problems with drugs is to prevent it from progressing to this stage in the first place. Our study shows that the Oxy-TT vaccine is potentially capable of protecting a substantial subset of those individuals who sample a drug enough to become habitual users.

These panels from Figure 5 of the paper show that there was basic biological efficacy of the vaccine. These data show the plasma (left panel) and brain (right panel) amounts of oxycodone in the two vaccine groups after administration of 1.0 or 2.0 mg/kg subcutaneously. This shows that considerably more oxycodone is in the plasma of the Oxy-TT groups (as is expected since the antibodies should retain drug in the bloodstream and not let it get into other tissues. Lesser amounts of oxycodone were in the brains of the Oxy-TT group as well which is again consistent with the anticipated effects of successful anti-drug vaccination.

The second major behavioral finding is a bit more subtle. As you can see from the first figure, above, the Oxy-TT rats that did acquire self-administration responded for more drug than did the TT control animals. This is consistent with the second figure, i.e., that less of each infusion of drug was reaching the brain. Thus, assuming the rats on average seek the same approximate amount of drug in their brain, the vaccine resulted in an increase in self-administration behavior. In order to probe the extent to which the rats prefer to self-administer oxycodone we increased the workload. In training the rats only had to make one lever response for each infusion of drug, known as a Fixed Ratio 1 (FR1) contingency. But the Progressive Ratio procedure makes each successive infusion within the daily session cost more. When we did that, the Oxy-TT animals decreased their intake to a greater extent than did the TT rats. This figure is from a second cohort of rat groups that were trained to self-administer a

higher per-infusion dose (0.15 mg/kg/inf) of oxycodone. Under these conditions the Lower half of the Oxy-TT group self-administered about the same amount of drug as the entire TT group and the Upper half self-administered more. The figure depicts mean intake, post-acquisition, in four different workload conditions, starting and ending with the FR1 training condition. The two middle bars depict the oxycodone intake under two PR schedules which differ in steepness of the incrementing workload. There was a change for the TT group only in the hardest PR condition but this did not reach statistical significance. In contrast the overall number of infusions in a session that were obtained by the Oxy-TT animals (this is for the entire group) were reduced when it took more responses to obtain successive infusions. This shows that despite self-administering slightly more oxycodone when it is easy to get (FR1), the Oxy-TT animals are more likely to reduce their intake when the conditions are made slightly more difficult. Making drugs more difficult to obtain is, of course, one of the population level strategies we use to combat drug addiction. This is reflected in taxes and the regulation of sales of alcohol and tobacco that have been proven to reduce problematic use of these legal substances. Parents routinely use different strategies to make it more difficult for their teenagers to access drugs of all types. Many therapeutic interventions for drug abusers involve lifestyle changes that make getting access to drug more laborious. Thus, a strategy that makes an individual more liable to reduce their drug use when the costs increase has the potential for success in reducing drug use harms.

This last finding also has important implications for the design of human clinical trials that attempt to test the efficacy of anti-drug vaccines. The default approach has been to use measures of drug use as the measure of “success” of the trial. These data suggest that vaccinated people could use the same or even slightly more drug and still be getting a protective effect. That is, they might become more susceptible to other interventions which, for example, raise the cost or effort of getting drug.

__

*authors contributed equally

Funding for this work provided by USPHS Grants R01 DA035281, R01 DA024705, UH3 DA041146 (K.D.J.) and F32 AI126628 (C.S.W.).

October 16, 2017

High ambient temperature facilitates MDMA self-administration

Filed under: IVSA, MDMA, Thermoregulation — mtaffe @ 1:02 pm

The following has recently been accepted for publication:

Aarde, S.M., Huang, P-K  and Taffe, M.A. High Ambient Temperature Facilitates The Acquisition Of 3,4-Methylenedioxymethamphetamine (MDMA) Self-Administration. Pharmacol Biochem Behav, 2017, in press.  [ Publisher Site ][ PubMed ]

This study was motivated by a finding from Cornish and colleagues in 2003 where they showed that rats trained to self-administer MDMA at 21 °C ambient temperature will significantly increase their drug intake when placed in a 30 °C ambient temperature. This finding was of interest to our lab because of our longstanding interest in the role of the body temperature response to MDMA. In brief, the effect of a given dose of MDMA at ~21-24 °C is generally to lower a rat’s body temperature whereas the same dose given at ~27-30 °C elevates body temperature. The typical laboratory ambient temperature of about 21-24 °C is actually somewhat cold for a rat since their point of thermoneutrality is up around 30 °C.  This led us to think that perhaps one of the reasons why MDMA is a poor reinforcer in the intravenous self-administration (IVSA) paradigm is because it lowers body temperature. If this effect is aversive to the rat, this may oppose the rewarding properties of the drug. Consequently, the Cornish finding may have illustrated increased IVSA due to a blunted hypothermia (but that study didn’t measure it). This rationale formed the basis for an entire Aim of a grant proposal which was submitted in original form in 2007 and eventually funded in 2011 (R01 DA024105-01A2).

In this figure from the paper we present the number of MDMA infusions (1.0 mg/kg/infusion) obtained by the groups of rats trained to self-administer under Cold (20 °C; N=12) or Hot (30 °C; N=11) ambient conditions in two-hour sessions. The schedule of reinforcement was FR5 for these studies meaning that each infusion required that the rat make five lever presses. As is obvious from the figure, the Hot group obtained more infusions of MDMA than did the Cold group. On session 16 only the drug-free vehicle was available and the increased responding (“saline bursting”) can be interpreted as a sign of drug-seeking behavior. This is particularly important for the Cold group given their very low (but consistent) numbers of infusions obtained. So to this point of the study, the behavior replicates and extends the work of Cornish and colleagues in 2003. They trained their rats in a lower ambient condition and then did post-acquisition tests at a higher ambient temperature and so the effect of ongoing experience in cold versus hot conditions could not be assessed. Interestingly, however, Feduccia and colleagues (2010) did a study much more like ours in design and failed to find any difference in the acquisition of IVSA in cold versus hot ambient conditions. There are a few procedural differences which may explain the difference in outcome but additional experiments would be required for firm conclusions. One potential difference is the selection of FR1 reward contingency which led to similar behavior in the MDMA groups and the groups allowed to self-administer saline only in that study. Although we did not have saline-only controls, our lever discrimination remained over 80% in both groups. In Aarde et al (2013) we ran a saline-only control group, pretrained to lever press for food at FR5, at normal laboratory ambient temperature (24 °C) and showed that lever discrimination breaks down significantly within the first 10 sessions of saline IVSA.

As outlined above, we were interested in the nature of the body temperature response during self-administration and how this might be changed by different ambient temperature conditions. Feduccia and colleagues had found no change in body temperature induced by MDMA IVSA at all, but their monitoring was via pre- and post-session rectal sampling. The temperature response to MDMA in rats is transient and it was likely that the sampling at 2 hours after the start of the session missed the dynamic response. This technique also requires handling the rats which can cause a stress response which may increase the body temperature. Our study used implanted radiotelemetry to observe the temperature response during the session. This adaptation of a figure from the paper presents 30 min averages (data collected every 5 minutes) of body temperature across the self-administration session and for one hour after the drug was no longer available. The daily responses are collapsed across blocks of 5-6 sequential training days. The takeaway here is that body temperature decreased in both Hot and Cold groups during the initial hour of the self-administration session and this response was gradually blunted in the Hot group across the self-administration training. The similar degree of hypothermia early in the acquisition phase and the course of tolerance versus drug intake in the Hot group was not consistent with our original hypothesis. It looked much more as though MDMA caused hypothermia under all training conditions and any attenuation of that response followed, rather than caused, increased drug intake over time.

To further probe the role of ambient temperature we next switched the temperature conditions and found that MDMA IVSA was unchanged within the groups. As if they’d been set on a preference trajectory. The failure to increase drug intake in the Cold group when placed in higher ambient temperature conditions was discordant with the original Cornish finding and we do not know why this might be the case. Most importantly, the Hot-trained group self-administered more drug in Cold ambient then did the Cold-trained group in Hot ambient and developed a more pronounced drop in body temperature. This showed that the ongoing self-administration training did not categorically alter the temperature response to MDMA in these animals.

The last study in the self-administering groups examined the effect of non-contingent administration of a range of MDMA doses (1-5 mg/kg, i.v.) on the body temperature response under Hot and Cold ambient temperature conditions. Up to this point, the animals self-selected their doses and so the interaction of dose with the temperature responses could not be easily disentangled. This last study found that hypothermia depended on dose, ambient temperature and the prior MDMA intake of the rat. Those individuals who self-administered very low amounts across the study (regardless of ambient temperature condition) were most sensitive to MDMA-induced hypothermia. Hypothermia was produced in both subgroups under Cold ambient, albeit to a greater degree in the animals with less cumulative MDMA intake. The takeaway from this part of the study is less clear cut. Clearly the hypothermic response to  MDMA under low ambient temperature conditions was only quantitatively, not categorically, altered in rats that self-administered more MDMA. Temperature responses under higher ambient temperature conditions were blunted- to the point that 3-5 mg/kg MDMA, i.v., did not change body temperature from baseline in the higher preference subgroup and while 2-3 mg/kg lowered body temperature in the lower-preference subgroup, 4-5 mg/kg did not.  [In general, the dose-effect relationship for MDMA-induced hypothermia does not reflect across Cold and Hot ambient temperatures. A high MDMA dose produces both less hypothermia under Cold conditions and increased hyperthermia under Hot conditions. Likewise, a moderate dose produces less hyperthermia in Hot conditions and more hypothermia in Cold ambient temperature conditions.] Thus, these data allow for the possibility that incremental blunting of the hypothermic response to MDMA may have some effect on sustaining IVSA behavior. Still, the overall thrust of this study suggests that the body temperature response is not a primary driver of self-administration of MDMA.

An additional study examined the effect of MDMA on intracranial self-stimulation (ICSS) reward in a different group of animals with no MDMA self-administration history. In ICSS the animal makes behavioral responses in response to small amounts of electrical current delivered to a specific region of the brain. We used a thresholding procedure in which the amount of current required for the animal to feel a rewarding effect can be determined from day to day. This procedure has been used by many laboratories over decades to show that treatments that make the animal feel good (such as an injection of methamphetamine) lower reward thresholds whereas conditions that make the animal feel bad (such as drug withdrawal in a dependent rat) lead to increased reward thresholds. Our study found that thresholds were increased merely by being placed in a hot environment (these data are all relative to individual thresholds from a 24 °C uninjected test session). Under Cold conditions, a 2.5 mg/kg MDMA, i.p., injection reduced reward thresholds in a manner consistent with the effects of methamphetamine, MDPV or mephedrone (Nguyen et al, 2016). Under Hot conditions, the same MDMA dose only returned reward thresholds to a baseline established under 24 °C without producing a pro-reward effect.

 

This ICSS experiment supports an interpretation of increased MDMA self-administration under high ambient temperature conditions as a normalization of negative affect, rather than an enhancement of the positive, feel-good subjective effects of MDMA.

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