Papers by Charles Breckenridge
Http Dx Doi Org 10 1080 15287399409531912, Oct 19, 2009
Reviews of environmental contamination and toxicology, 2008
More than 40 publications have described results of atrazine responses in 17 estrogen-dependent s... more More than 40 publications have described results of atrazine responses in 17 estrogen-dependent systems and in more than a dozen different reporter and estrogen receptor-binding studies in vitro. Results from these studies have consistently failed to demonstrate that atrazine acts as an estrogen agonist. Moreover, a variety of indices of estrogen-dependent activity, in models that encompass cell incubations to whole animals, have failed to respond to atrazine. Researchers in more than a dozen laboratories have examined rats, rat tissues, human and prokaryotic cells, in addition to tissues from reptile, fish, amphibian, avian, molluscan, and insect sources, without eliciting estrogenic-like responses from atrazine. In contrast, studies of atrazine ability to antagonize estrogen-mediated responses have yielded equivocal results. Results of several studies show inhibition of estrogen-like activities by atrazine, yet many other tests have yielded negative results. Generally, in vivo mod...
Atrazine (ATZ) was administered daily by gavage to pregnant female Sprague Dawley rats at doses o... more Atrazine (ATZ) was administered daily by gavage to pregnant female Sprague Dawley rats at doses of 0, 6.25, 25 or 50 mg/kg/day, either during gestation, lactation and post-weaning (G/L/PW cohort) to F 1 generation female offspring or only from postnatal day (PND 21) until five days after sexual maturation (vaginal opening) when the estrogen-primed, luteinizing hormone (LH) surge was evaluated (PW cohort). Additional subgroups of F 1 females received the vehicle or ATZ from PND 21–133 or from PND 120–133. Slight reductions in fertility and the percentage of F 1 generation pups surviving to PND 21 in the gestationally exposed 50 mg/kg dose group were accompanied by decreased food intake and body weight of dams and F 1 generation offspring. The onset of puberty was delayed in of the F 1 generation G/L/PW females at doses of 25 and 50 mg/kg/day. F 1 generation females in the PW high-dose ATZ group also experienced a delay in the onset of puberty. ATZ had no effect on peak LH or LH AUC in ovariectomized rats 5 days after sexual maturation, irrespective of whether the F 1 generation females were treated from gestation onward or only peripubertally. There was no effect of ATZ treatment on the estrous cycle, peak LH or LH AUC of F 1 generation females exposed from gestation through to PND 133 or only for two weeks from PND 120–133. These results indicate that developing females exposed to ATZ are not more sensitive compared to animals exposed to ATZ as young adults. Birth Defects Res (Part B) 104:204–217, 2015. C 2015 Wiley Periodicals, Inc.
In this study, we quantified the effects of in utero exposure to the herbicide atrazine on subseq... more In this study, we quantified the effects of in utero exposure to the herbicide atrazine on subsequent mammary gland development. Atrazine was administered to pregnant female Long Evans rats from gestation days 13–19 at doses of 0, 6.5, 50, or 100 mg/kg/ day. A pair-fed control group was yoked to the high-dose atrazine-treated group. Litter size was standardized to 10 pups on postnatal day (PND) 4. Whole mounts of the left fourth mammary gland and histologic sections of the right fourth gland were obtained from a subgroup of offspring on PND1, 21, 33, on day of vaginal opening (VO), or around PND65 at diestrus. A blinded, quantitative analysis of key morphological features in mammary gland whole mounts (ductal elongation, ductal network area, epithelial area, terminal end bud [TEB] incidence, and epithelial density) as well as epithelial proliferation within different parenchymal structures was conducted. There was no effect of atrazine exposure on any of the measures of mammary gland development at the maternal dose of 6.5 mg/kg/day. On PND1, ductal elongation was increased by approximately 20% (p < 0.05) in the female offspring born to dams exposed to 50 and 100 mg/kg/ day atrazine, coincident with decreased epithelial proliferation in the 100 mg/kg/day group at this age. These differences were not present on PND21, or thereafter. An increased incidence of TEB in the mammary glands from females that were born to both the pair-fed and 50 mg/kg/day–treated dams at the time of VO indicated that this response was a specific result of maternal caloric restriction. Collectively, these data indicate that maternal atrazine exposure has no long-term effects on mammary gland development in female offspring beyond a transitory response to high doses at PND1.
Male and female C57BL/6J mice were administered diquat dibromide (DQ • Br 2) in their diets at co... more Male and female C57BL/6J mice were administered diquat dibromide (DQ • Br 2) in their diets at concentrations of 0 (control), 12.5 and 62.5 ppm for 13 weeks to assess the potential effects of DQ on the nigrostriatal dopaminergic system. Achieved dose levels at 62.5 ppm were 6.4 and 7.6 mg DQ (ion)/kg bw/day for males and females, respectively. A separate group of mice was administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) ip as a positive control. The comparative effects of DQ and MPTP on the substantia nigra pars compacta (SNpc) and/or striatum were assessed using neurochemical, neuropathological and stereological endpoints. Morphological and stereological assessments were performed by investigators who were " blinded " to dose group. DQ had no effect on striatal dopamine concentration or dopamine turnover. There was no evidence of neuronal degeneration, astrocytic or microglial activation, or a reduction in the number of tyrosine hydroxylase positive (TH þ) neurons in the SNpc or neuronal processes in the striatum of DQ-treated mice. These results are consistent with the rapid clearance of DQ from the brain following a single dose of radiolabeled DQ. In contrast, MPTP-treated mice exhibited decreased striatal dopamine concentration, reduced numbers of TH þ neurons in the SNpc, and neuropathological changes, including neuronal necrosis, as well as astrocytic and microglial activation in the striatum and SNpc.
The previously-published physiologically based pharmacokinetic model for atrazine (ATZ), deisopro... more The previously-published physiologically based pharmacokinetic model for atrazine (ATZ), deisopropylatrazine (DIA), deethylatrazine (DEA), and diaminochlorotriazine (DACT), which collectively comprise the total chlorotriazines (TCT) as represented in this study, was modified to allow for scaling to humans. Changes included replacing the fixed dose-dependent oral uptake rates with a method that represented delayed absorption observed in rats administered ATZ as a bolus dose suspended in a methylcellulose vehicle. Rate constants for metabolism of ATZ to DIA and DEA, followed by metabolism of DIA and DEA to DACT were predicted using a compartmental model describing the metabolism of the chlorotriazines by rat and human hepatocytes in vitro. Overall, the model successfully predicted both the 4-day plasma time-course data in rats administered ATZ by bolus dose (3, 10, and 50 mg/kg/day) or in the diet (30, 100, or 500 ppm). Simulated continuous daily exposure of a 55-kg adult female to ATZ at a dose of 1.0 mg/kg/day resulted in steady-state urinary concentrations of 0.6, 1.4, 2.5, and 6.0 mg/L for DEA, DIA, DACT, and TCT, respectively. The TCT (ATZ þ DEA þ DIA þ DACT) human urinary biomonitoring equivalent concentration following continuous exposure to ATZ at the chronic point of departure (POD ¼ 1.8 mg/kg/day) was 360.6 lg/L.
The risk of human exposure to total chlorotriazines (TCT) in drinking water was evaluated using a... more The risk of human exposure to total chlorotriazines (TCT) in drinking water was evaluated using a physiologically based pharmacokinetic (PBPK) model. Daily TCT (atrazine, deethylatrazine, deisopropylatrazine, and diaminochlorotriazine) chemographs were constructed for 17 frequently monitored community water systems (CWSs) using linear interpolation and Krieg estimates between observed TCT values. Synthetic chemographs were created using a conservative bias factor of 3 to generate intervening peaks between measured values. Drinking water consumption records from 24-h diaries were used to calculate daily exposure. Plasma TCT concentrations were updated every 30 minutes using the PBPK model output for each simulated calendar year from 2006 to 2010. Margins of exposure (MOEs) were calculated (MOE ¼ [Human Plasma TCT POD ] Ä [Human Plasma TCT EXP ]) based on the toxicological point of departure (POD) and the drinking water-derived exposure to TCT. MOEs were determined based on 1, 2, 3, 4, 7, 14, 28, or 90 days of rolling average exposures and plasma TCT C max , or the area under the curve (AUC). Distributions of MOE were determined and the 99.9th percentile was used for risk assessment. MOEs for all 17 CWSs were >1000 at the 99.9 th percentile. The 99.9 th percentile of the MOE distribution was 2.8-fold less when the 3-fold synthetic chemograph bias factor was used. MOEs were insensitive to interpolation method, the consumer's age, the water consumption database used and the duration of time over which the rolling average plasma TCT was calculated, for up to 90 days. MOEs were sensitive to factors that modified the toxicological, or hyphenated appropriately no-observed-effects level (NOEL), including rat strain, endpoint used, method of calculating the NOEL, and the pharmacokinetics of elimination, as well as the magnitude of exposure (CWS, calendar year, and use of bias factors).
NeuroToxicology, 2009
Neurotoxicity and mechanistic data were collected for six a-cyano pyrethroids (b-cyfluthrin, cype... more Neurotoxicity and mechanistic data were collected for six a-cyano pyrethroids (b-cyfluthrin, cypermethrin, deltamethrin, esfenvalerate, fenpropathrin and l-cyhalothrin) and up to six non-cyano containing pyrethroids (bifenthrin, S-bioallethrin [or allethrin], permethrin, pyrethrins, resmethrin [or its cis-isomer, cismethrin] and tefluthrin under standard conditions. Factor analysis and multivariate dissimilarity analysis were employed to evaluate four independent data sets comprised of (1) fifty-six behavioral and physiological parameters from an acute neurotoxicity functional observatory battery (FOB), (2) eight electrophysiological parameters from voltage clamp experiments conducted on the Na v 1.8 sodium channel expressed in Xenopus oocytes, (3) indices of efficacy, potency and binding calculated for calcium ion influx across neuronal membranes, membrane depolarization and glutamate released from rat brain synaptosomes and (4) changes in chloride channel open state probability using a patch voltage clamp technique for membranes isolated from mouse neuroblastoma cells.
Journal of comparative and physiological psychology, 1973
ABSTRACT In Exp. I, rats with hippocampal lesions were severely impaired in learning a fixed resp... more ABSTRACT In Exp. I, rats with hippocampal lesions were severely impaired in learning a fixed response sequence in a complex maze. Following subsequent manipulations, it was found that hippocampally damaged rats could learn the sequence as well as cortical and operated control Ss in the presence of highly conspicuous cues. Performance of hippocampally damaged Ss, unlike that of the control groups, deteriorated following removal of the cue used in original learning. In Exp. V, Ss with medial thalamic lesions also exhibited maze-learning impairment, but they benefited less than the hippocampal groups from an enhancement of cue conditions. The hippocampus is discussed in terms of its importance in processing relevant stimulus cues and in the organization of appropriate response strategies. (24 ref.)
Biochemical medicine, 1975
ABSTRACT A reliable method is described for long-term blood sampling or intravenous infusion in t... more ABSTRACT A reliable method is described for long-term blood sampling or intravenous infusion in the freely behaving rat. Using this technique, the authors have been able to maintain cannula patency over a period of one year. During this time two daily blood samples were taken from each of four cannulated rats.
It is known that human subjects deprived of meaningful visual, auditory and somatosensory stimula... more It is known that human subjects deprived of meaningful visual, auditory and somatosensory stimulation (sensory deprivation), spend a larger portion of their time asleep (increased Stage I &amp; II) than when in a normal environment. Furthermore, that phase of sleep which is characterized by the presence of rapid eye movements (REM sleep) is altered under these conditions, with REM density
Birth Defects Research Part B: Developmental and Reproductive Toxicology, 2014
Atrazine (ATR) blunts the hormone-induced luteinizing hormone (LH) surge, when administered by ga... more Atrazine (ATR) blunts the hormone-induced luteinizing hormone (LH) surge, when administered by gavage (50-100 mg/kg/day for 4 days), in ovariectomized rats. In this study, we determined if comparable doses delivered either by gavage (bolus dose) or distributed in diet would reduce the LH surge and subsequently affect fertility in the intact female rat. ATR was administered daily to intact female Sprague-Dawley (SD) or Long Evans (LE) rats by gavage (0, 0.75 1.5, 3, 6, 10, 12, 50, or 100 mg/kg/day) or diet (0, 30, 100, 160, 500, 660, or 1460 ppm) during one complete 4-day estrous cycle, starting on day of estrus. Estrous status, corpora lutea, ova, and LH plasma concentrations were evaluated. A second cohort of animals was mated on the fourth treatment day. Fertility metrics were assessed on gestational day 20. A higher portion of LE rats had asynchronous estrous cycles when compared to SD rats both during pretreatment and in response to ATR (ࣙ50 mg/kg). In contrast, bolus doses of ATR (ࣙ50 mg/kg) inhibited the peak and area under the curve for the preovulatory LH surge in SD but not LE animals. Likewise, only bolus-treated SD, not LE, rats displayed reduced mean number of corpora lutea and ova. There were no effects of ATR administered by gavage on mating, gravid number, or fetus number. Dietary administration had no effect on any reproductive parameter measured. These findings indicate that short duration, high-bolus doses of ATR can inhibit the LH surge and reduce the number of follicles ovulated; however, dietary administration has no effect on any endocrine or reproductive outcomes. Birth Defects Res (Part B) 101:262-275, 2014. C 2014 Wiley Periodicals, Inc.
Birth Defects Research Part B: Developmental and Reproductive Toxicology, 2015
Atrazine (ATZ) was administered daily by gavage to pregnant female Sprague Dawley rats at doses o... more Atrazine (ATZ) was administered daily by gavage to pregnant female Sprague Dawley rats at doses of 0, 6.25, 25 or 50 mg/kg/day, either during gestation, lactation and post-weaning (G/L/PW cohort) to F 1 generation female offspring or only from postnatal day (PND 21) until five days after sexual maturation (vaginal opening) when the estrogen-primed, luteinizing hormone (LH) surge was evaluated (PW cohort). Additional subgroups of F 1 females received the vehicle or ATZ from PND 21-133 or from PND 120-133. Slight reductions in fertility and the percentage of F 1 generation pups surviving to PND 21 in the gestationally exposed 50 mg/kg dose group were accompanied by decreased food intake and body weight of dams and F 1 generation offspring. The onset of puberty was delayed in of the F 1 generation G/L/PW females at doses of 25 and 50 mg/kg/day. F 1 generation females in the PW high-dose ATZ group also experienced a delay in the onset of puberty. ATZ had no effect on peak LH or LH AUC in ovariectomized rats 5 days after sexual maturation, irrespective of whether the F 1 generation females were treated from gestation onward or only peripubertally. There was no effect of ATZ treatment on the estrous cycle, peak LH or LH AUC of F 1 generation females exposed from gestation through to PND 133 or only for two weeks from PND 120-133. These results indicate that developing females exposed to ATZ are not more sensitive compared to animals exposed to ATZ as young adults. Birth Defects Res (Part B) 00:1-14,
Birth Defects Research Part B Developmental and Reproductive Toxicology
Atrazine (ATR), hydroxyatrazine (OH-ATR), and the three chloro metabolites of ATR (deethylatrazin... more Atrazine (ATR), hydroxyatrazine (OH-ATR), and the three chloro metabolites of ATR (deethylatrazine [DEA], deisopropylatrazine [DIA], diaminochlorotriazine [DACT]) were evaluated for developmental effects in rats and rabbits. Three developmental toxicity studies were conducted on ATR in rats (two studies) and rabbits and a developmental toxicity study was conducted in rats for each of the four ATR metabolites DEA, DIA, DACT, and OH-ATZ. ATR administration by gavage to pregnant rats and rabbits from implantation (gestation day [GD] 6 in rat, GD 7 in rabbit) through closure of the palate (GD 15 in rat and GD 19 in rabbit) did not statistically significantly alter the incidence of developmental abnormalities or malformations at dose levels up to 100 (rat) or 75 (rabbit) mg/kg bw/day. There were no effects on developmental toxicity parameters for DEA, DIA, DACT, or OH-ATR at oral dose levels up to 100, 100, 150, or 125 mg/kg bw/day, respectively, with the exception of reductions in fetal...
Birth Defects Research Part B Developmental and Reproductive Toxicology
BACKGROUND Reproductive toxicity of Atrazine (ATR) was evaluated in two rat multigenerational stu... more BACKGROUND Reproductive toxicity of Atrazine (ATR) was evaluated in two rat multigenerational studies. Development of male reproductive parameters was evaluated in separate studies after prenatal or postnatal exposure.METHODS In multigenerational studies, rats received dietary concentrations of 0, 10, 50, 100 or 500 ppm ATR. In separate studies in female rats, ATR was administered by gavage at 0, 1, 5, 25 or 125 mg/kg/day during pregnancy (GD6–21) or lactation (LD2–21). Plasma testosterone concentration, testicular and epididymal weights, and sperm counts were measured in male offspring on PND70 and 170.RESULTSIn the multigenerational studies, parental systemic toxicity occurred at 500 ppm (38.7 mg/kg/day), but reproductive endpoints were unaffected. In the prenatal study, maternal toxicity and embryo-fetal mortality occurred at 125 mg/kg/day. In male offspring, testosterone levels and sperm counts were unaffected, although the percentage of abnormal sperm increased at 125 mg/kg/day...
Reviews of environmental contamination and toxicology, 2008
More than 40 publications have described results of atrazine responses in 17 estrogen-dependent s... more More than 40 publications have described results of atrazine responses in 17 estrogen-dependent systems and in more than a dozen different reporter and estrogen receptor-binding studies in vitro. Results from these studies have consistently failed to demonstrate that atrazine acts as an estrogen agonist. Moreover, a variety of indices of estrogen-dependent activity, in models that encompass cell incubations to whole animals, have failed to respond to atrazine. Researchers in more than a dozen laboratories have examined rats, rat tissues, human and prokaryotic cells, in addition to tissues from reptile, fish, amphibian, avian, molluscan, and insect sources, without eliciting estrogenic-like responses from atrazine. In contrast, studies of atrazine ability to antagonize estrogen-mediated responses have yielded equivocal results. Results of several studies show inhibition of estrogen-like activities by atrazine, yet many other tests have yielded negative results. Generally, in vivo mod...
Scandinavian journal of work, environment & health, 2005
An innovative approach to dose-response modeling provides statistical insight into the relative l... more An innovative approach to dose-response modeling provides statistical insight into the relative likelihood of different mechanisms of action in cancer dose-response studies. Two illustrative examples are given based on time-to-tumor data on mammary fibroadenoma and adenocarcinoma in female Sprague-Dawley rats using 34 different dose metrics. The likelihood for the study outcome was calculated for each dose metric and compared with the background likelihood using a likelihood-ratio test. In the first example, fibroadenomas were strongly related to the presence or absence of mammary secretory activity, galactoceles, pituitary tumors, and abnormal diestrous days in weeks 1 to 26. Adenocarcinomas were the most strongly related to the number and percentage of abnormal estrous days. In these examples, the usual dose metric based on the dietary concentration of the pesticide had some explanatory ability but not nearly as much as the dose metrics more directly related to hormonal mechanisms...
Journal of andrology
Previous studies have reported that atrazine, a widely used herbicide that selectively inhibits p... more Previous studies have reported that atrazine, a widely used herbicide that selectively inhibits photosynthesis in broadleaf and grassy weeds, has adverse effects on reproductive function in the male, suggesting a direct effect of atrazine on the hypothalamicpituitary-testicular axis. As yet, however, no studies have critically examined the doses of atrazine that elicit such effects, and few have focused on the mechanism by which atrazine acts. Herein we report a dose-response study of the effects of atrazine ingestion on reproductive function in male Sprague-Dawley rats during a critical developmental period, the peripubertal period. Atrazine was administered by gavage to rats from day 22 to day 47 of age, at doses of 1-200 mg/kg body weight per day. Atrazine administration of up to 50 mg/kg per day had no effect on any of the measured variables. Serum testosterone concentration was reduced by atrazine at doses of 100 and 200 mg/kg per day, as were seminal vesicle and ventral prosta...
Regulatory Toxicology and Pharmacology, 2014
Several investigations have reported that mice administered paraquat dichloride (PQÁCl 2 ) by int... more Several investigations have reported that mice administered paraquat dichloride (PQÁCl 2 ) by intraperitoneal injection exhibit a loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). In this study, male and female C57BL/6J mice were administered PQÁCl 2 in the diet at concentrations of 0 (control), 10, and 50 ppm for a duration of 13 weeks. A separate group of mice were administered 1-methyl-4phenyl-1,2,3,6-tetrahydropyridine (MPTP) during week 12 as positive controls to produce a loss of dopaminergic neurons in the SNpc. The comparative effects of PQ and MPTP on the SNpc and/or striatum were assessed using neurochemical, neuropathological, and stereological endpoints. Morphological and stereological assessments were performed by investigators 'blinded' to the origin of the tissue. Neither dose of PQÁCl 2 (10 or 50 ppm in the diet) caused a loss of striatal dopamine or dopamine metabolite concentrations in the brains of mice. Pathological assessments of the SNpc and striatum showed no evidence of neuronal degeneration or astrocytic/microglial activation. Furthermore, the number of tyrosine hydroxylase-positive (TH + ) neurons in the SNpc was not reduced in PQ-treated mice. In contrast, MPTP caused a decrease in striatal dopamine concentration, a reduction in TH + neurons in the SNpc, and significant pathological changes including astrocytic and microglial activation in the striatum and SNpc. The MPTPinduced effects were greater in males than in females. It is concluded that 13 weeks of continuous dietary exposure of C57BL/6J mice to 50 ppm PQÁCl 2 (equivalent to 10.2 and 15.6 mg PQ ion/kg body weight/day for males and females, respectively) does not result in the loss of, or damage to, dopaminergic neurons in the SNpc.
Regulatory Toxicology and Pharmacology, 2002
The mammalian hazard assessment of the herbicide atrazine (ATR) has focused on the induction of m... more The mammalian hazard assessment of the herbicide atrazine (ATR) has focused on the induction of mammary tumors and accelerated reproductive aging of adult rats, and the relationship of these effects to the inhibition of leutinizing hormone (LH) release from the pituitary, an effect itself caused by inhibition of GnRH signaling by the adult rat hypothalamus. In earlier studies, Laws et al. (Toxicol. Sci., 58, 366-376, 2000) demonstrated a delay in female rat sexual maturation induced by ATR, effects that could equally have been caused by inhibition of hypothalamic GnRH release. The present studies were designed to compare the doses that interfere with GnRH signaling seen in previous studies in adult Sprague-Dawley (SD) rats (LH surge suppression) with doses that impair GnRH signaling in peripubertal rats, as indicated by delayed sexual maturation. The studies evaluated the effects of ATR treatment on the timing of uterine growth and vaginal opening (VO) in peripubertal female Wistar (Alderley Park, AP) and SD rats. Doses of 10, 30, and 100 mg/kg ATR were administered daily from postnatal day (pnd) 21 to up to pnd 46. Determinations of uterine weight were made at pnd 30, 33, 43 (AP), and 46 (SD) and the timing of VO was also assessed in the last two of these experiments. The centrally acting GnRH antagonist Antarelix (ANT) was used as a positive control agent as it has previously been shown to prevent uterine growth and to delay VO in peripubertal AP rats. Uterine growth and VO were completely prevented in AP rats exposed to ANT. Uterine growth was delayed at pnd 30 and 33 in AP rats exposed to 100 mg/kg ATR, but this growth inhibition had been overcome by pnd 43. VO was significantly delayed in AP rats for the 100 mg/kg ATR dose. By pnd 46, VO was significantly delayed in SD rats exposed to both 30 and 100 mg/kg ATR, but uterine weights were unaffected by that time (as for AP rats). It is concluded that the no-effect level for the effects of ATR on sexually immature rats (10 mg/kg in SD; 30 mg/kg AP) is approximately the same as reported previously by Laws et al. in peripubertal Wistar rats (25 mg/kg). However, the no-effect level in peripubertal female SD rats is nearly an order of magnitude greater than the no-observed effect level observed in female SD rats fed ATR for 6 months (1.8 mg/kg) where LH suppression was used as an indicator of effect on the pituitary/hypothalamic axis (USEPA, Atrazine-DACT Fourth Report of the Hazard Identification and Review Committee, April 5, 2002). These results support the conclusion that the pituitary/hypothalamic axis in peripubertal female SD rats is less sensitive than that in adult female SD rats. C 2002 Elsevier Science (USA) Key Words: delayed sexual maturation; GnRH inhibition; no observed adverse effect level (NOAEL). 468 0273-2300/02 $35.00 C 2002 Elsevier Science (USA) All rights reserved.
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Papers by Charles Breckenridge