Glutamatergic hyperactivity in the nucleus striatum, the main basal ganglia input, has been invol... more Glutamatergic hyperactivity in the nucleus striatum, the main basal ganglia input, has been involved in the progression of Parkinson's disease (PD) and the onset of L-Dopa-induced dyskinesias (LIDs). Abnormalities in the spiny projection neurons (SPNs) excitability and firing, and in the overactivity of glutamate transmission found in animal models of PD, pointed to the synaptic dysfunctions as a primary target to counteract alterations before overt neurodegeneration, conferring a key role to striatal glutamatergic transmission in the early phases of the disease. The present paper will provide an overview of the evidence that glutamatergic overactivity is a critical mechanism underlying different PD-associated striatal alterations in early and advanced symptomatic stages of the disease. These aberrant changes, under L-Dopa therapy, lead to a more complex synaptopathy that involves other neurotransmitter systems and persistent modifications to generate LIDs. The review will discuss the main changes in glutamatergic functions found in PD preclinical models and clinical studies and an update of the current pharmacological strategies to modulate the glutamatergic systems at the pre- and postsynaptic levels will be provided.
Levodopa (L-DOPA) treatment is the main gold-standard therapy for Parkinson disease (PD). Besides... more Levodopa (L-DOPA) treatment is the main gold-standard therapy for Parkinson disease (PD). Besides good antiparkinsonian effects, prolonged use of this drug is associated to the development of involuntary movements known as L-DOPA-induced dyskinesia (LID). L-DOPA-induced dyskinesia is linked to a sensitization of dopamine (DA) D1 receptors located on spiny projection neurons (SPNs) of the dorsal striatum. Several evidences have shown that the emergence of LID can be related to striatal D1/cAMP/PKA/DARPP-32 and extracellular signal-regulated kinases (ERK1/2) pathway overactivation associated to aberrant N-methyl-d-aspartate (NMDA) receptor function. In addition, within striatum, ERK1/2 is also able to modulate in a D1 receptor-dependent manner the activity of the mammalian target of rapamycin complex 1 (mTORC1) pathway under DA depletion and L-DOPA therapy. Consistently, increased mTORC1 signaling appears during chronic administration of L-DOPA and shows a high correlation with the severity of dyskinesia. Furthermore, the abnormal activation of the D1/PKA/DARPP-32 cascade is paralleled by increased phosphorylation of the GluA1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor at the PKA Ser845 site. The GluA1 promotes excitatory AMPA receptor-mediated transmission and may be implicated in the alterations found at the corticostriatal synapses of dyskinetic animals. In our study, we investigated the role of mTORC1 pathway activation in modulating bidirectional striatal synaptic plasticity in L-DOPA-treated parkinsonian rats. Inhibition of mTORC1 by coadministration of rapamycin to L-DOPA was able to limit the magnitude of LID expression, accounting for a therapeutic effect of this
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal ... more Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal dopamine (DA)–glutamate interactions, severe alterations in motor control, and reduced behavioral flexibility. Experimental models of disease show that during symptomatic phases, HD shares with other hyperkinetic disorders the loss of synaptic depotentiation in the striatal spiny projection neurons (SPNs). Here we test the hypothesis that corticostriatal long‐term depression (LTD), a well‐conserved synaptic scaling down response to environmental stimuli, is also altered in symptomatic male R6/1 mice, a HD model with gradual development of symptoms. In vitro patch‐clamp and intracellular recordings of corticostriatal slices from R6/1 mice confirm that, similar to other models characterized by hyperkinesia and striatal DA D1 receptor pathway dysregulation, once long‐term potentiation (LTP) is induced, synaptic depotentiation is lost. Our new observations show that activity‐dependent LTD wa...
BackgroundProlonged dopaminergic replacement therapy in PD results in pulsatile dopamine receptor... more BackgroundProlonged dopaminergic replacement therapy in PD results in pulsatile dopamine receptors stimulation in both dorsal and ventral striatum causing wearing off, motor fluctuations, and nonmotor side effects such as behavioral addictions. Among impulse control disorders, binge eating can be easily modeled in laboratory animals.ObjectivesWe hypothesize that manipulation of dopamine levels in a 6‐hydroxydopamine–lesioned rats, as a model of PD characterized by a different extent of dopamine denervation between dorsal and ventral striatum, would influence both synaptic plasticity of the nucleus accumbens and binge‐like eating behavior.MethodsFood preference, food intake, and weight gain were monitored in sham‐operated and unilaterally lesioned rats, subjected to a modified version of Corwin's limited access protocol, modelling binge eating disorder. Electrophysiological properties and long‐term potentiation of GABAergic spiny projection neurons of the nucleus accumbens core w...
A BS TRACT: Objective: Spreading depolarization (SD) is a transient self-propagating wave of neur... more A BS TRACT: Objective: Spreading depolarization (SD) is a transient self-propagating wave of neuronal and glial depolarization coupled with large membrane ionic changes and a subsequent depression of neuronal activity. Spreading depolarization in the cortex is implicated in migraine, stroke, and epilepsy. Conversely, spreading depolarization in the striatum, a brain structure deeply involved in motor control and in Parkinson's disease (PD) pathophysiology, has been poorly investigated. Methods: We characterized the participation of glutamatergic and dopaminergic transmission in the induction of striatal spreading depolarization by using a novel approach combining optical imaging, measurements of endogenous DA levels, and pharmacological and molecular analyses. Results: We found that striatal spreading depolarization requires the concomitant activation of D1-like DA and Nmethyl-D-aspartate receptors, and it is reduced in experimental PD. Chronic L-dopa treatment, inducing dyskinesia in the parkinsonian condition, increases the occurrence and speed of propagation of striatal spreading depolarization, which has a direct impact on one of the signaling pathways downstream from the activation of D1 receptors. Conclusion: Striatal spreading depolarization might contribute to abnormal basal ganglia activity in the dyskinetic condition and represents a possible therapeutic target.
In the striatum, specific N-methyl-D-aspartate receptor (NMDAR) subtypes are found in different n... more In the striatum, specific N-methyl-D-aspartate receptor (NMDAR) subtypes are found in different neuronal cells. Spiny projection neurons (SPNs) are characterized by NMDARs expressing GluN2A and GluN2B subunits, while GluN2D is exclusively detected in striatal cholinergic interneurons (ChIs). In Parkinson's disease (PD), dopamine depletion and prolonged treatment with levodopa (L-DOPA) trigger adaptive changes in the glutamatergic transmission from the cortex to the striatum, also resulting in the aberrant function of striatal NMDARs. While modifications of GluN2A-and GluN2B-NMDARs in SPNs have been extensively documented, only few studies reported GluN2D dysfunction in PD and no data are available in L-DOPA-induced dyskinesia (LID). Here we investigate the contribution of a specific NMDAR subtype (GluN2D-NMDAR) to PD and LID, and whether this receptor could represent a candidate for future pharmacological interventions. Our results show that GluN2D synaptic abundance is selectively augmented in the striatum of L-DOPA-treated male parkinsonian rats displaying a dyskinetic phenotype. This event is associated to a dramatic increase in GluN2D binding to the postsynaptic protein scaffold PSD-95. Moreover, immunohistochemistry and electrophysiology experiments reveal that GluN2D-NMDARs are expressed not only by striatal ChIs but also by SPNs in dyskinetic rats. Notably, in vivo treatment with a well-characterized GluN2D antagonist ameliorates the severity of established dyskinesia in L-DOPA-treated animals. Our findings support a role for GluN2D-NMDARs in LID, and they confirm that celltype and subunit specific modifications of NMDARs underlie the pathophysiology of LID.
Absence of functional presynaptic scaffolding protein Bassoon (Bsn) in mutant mice is associated ... more Absence of functional presynaptic scaffolding protein Bassoon (Bsn) in mutant mice is associated with the development of pronounced spontaneous seizures and with consistent alterations in neuronal activity and morphology of hippocampus and cerebral cortex. The basal ganglia network receives a strong glutamatergic series of inputs from cortical regions through the striatum and it has been involved in the pathophysiology of epilepsy. However its functions, and in particular the role of the striatal microcircuit, in limiting epileptogenesis is still debated. To further investigate on the role of BG in limiting epileptic activity, we hypothesized that the spreading of epileptic seizures from the cortex to the striatum may alter both short and long-term excitability in two neuronal subtypes, the striatal fast-spiking GABAergic interneurons (FS) and the medium spiny (MS) neurons as an adaptive mechanism. To this end we first planned to study the epileptic phenotype and the learning skills of mutants. We then propose to characterize the plastic changes by electrophysiological recordings, molecular analyses and morphological studies. Epileptic seizures in mutant mice were video-recorded, classified and procedural learning and hippocampal-based learning skills were evaluated with a battery of behavioral tests. In vitro intracellular recordings were performed from corticostriatal slices obtained from Bsn mutants and WT mice while extracellular recordings were performed in hippocampal slices. Postsynaptic proteins were analyzed by Western blotting while morphological studies of FS and MS were performed in epileptic mice brain with Golgi-staining and unbiased immunohystochemical technique. Bsn mutant mice showed early-onset epileptic seizure development, which in adults were associated to a rearrangement of synaptic plasticity within the striatal microcircuit. In fact, although long-term depression (LTD) was equally expressed in both genotypes, the amplitude of long-term potentiation (LTP) induced in MS neurons of Bsn mutant mice was reduced compared to control, while hippocampal LTP was completely lost. The alteration in striatal plasticity was associated to differences in dendrite branching and spine maturation of MS neurons and to profound modifications of postsynaptic components expression in the whole striatum. In particular, in the striatum of epileptic mice, the NMDA subunit composition was found altered, the BDNF expression decreased and TrkB receptor upregulated. Interestingly, following high frequency stimulation protocol, GABAergic FS recorded from Bsn mutant mice expressed a NMDA and BDNF-dependent short-term potentiation that was absent in WT animals. Moreover FS interneurons were increased in number in the epileptic genotype. Behavioral tests for assessment of learning skills demonstrated that procedural learning capabilities are intact while hippocampal-based functions are compromised in epileptic mice providing evidences for a competition between the two memory systems. Our results indicate that while hippocampal synaptic plasticity is lost, striatal neuronal subtypes are differentially sensitive to continuous seizures and to the associated alterations of BDNF/TrkB signaling. These data suggest that changes of corticostriatal activity develop in early-onset epileptic conditions associated to the lack of functional Bsn. The reorganization of plasticity between neuronal subtypes may protect striatum and downstream BG nuclei from continuous cortical seizures in order to preserve striatal functions.
Hippocampus and striatum play distinctive roles in memory processes since declarative and non-dec... more Hippocampus and striatum play distinctive roles in memory processes since declarative and non-declarative memory systems may act independently. However, hippocampus and striatum can also be engaged to function in parallel as part of a dynamic system to integrate previous experience and adjust behavioral responses. In these structures the formation, storage, and retrieval of memory require a synaptic mechanism that is able to integrate multiple signals and to translate them into persistent molecular traces at both the corticostriatal and hippocampal/limbic synapses. The best cellular candidate for this complex synthesis is represented by long-term potentiation (LTP). A common feature of LTP expressed in these two memory systems is the critical requirement of convergence and coincidence of glutamatergic and dopaminergic inputs to the dendritic spines of the neurons expressing this form of synaptic plasticity. In experimental models of Parkinson's disease abnormal accumulation of α-synuclein affects these two memory systems by altering two major synaptic mechanisms underlying cognitive functions in cholinergic striatal neurons, likely implicated in basal ganglia dependent operative memory, and in the CA1 hippocampal region, playing a central function in episodic/declarative memory processes.
Multiple sclerosis, one of the main causes of non-traumatic neurological disability in young adul... more Multiple sclerosis, one of the main causes of non-traumatic neurological disability in young adults, is an inflammatory and neurodegenerative disorder of the central nervous system. Although the pathogenesis of neuroaxonal damage occurring during the course of the disease is still largely unknown, there is accumulating evidence highlighting the potential role of mitochondria in multiple sclerosis-associated neuronal degeneration. The aim of the present study was to investigate, by utilizing electrophysiological techniques in brain striatal slices, the potential protective effects of interferon-β1a, one of the most widely used medication for multiple sclerosis, against acute neuronal dysfunction induced by mitochondrial toxins. Interferon-β1a was found to exert a dosedependent protective effect against the progressive loss of striatal field potential amplitude induced by the mitochondrial complex I inhibitor rotenone. Interferon-β1a also reduced the generation of the rotenone-induced inward current in striatal spiny neurons. Conversely, interferon-β1a did not influence the electrophysiological effects of the mitochondrial complex II inhibitor 3-nitropropionic acid. The protective effect of interferon-β1a against mitochondrial complex I inhibition was found to be dependent on the activation of STAT1 signaling. Conversely, endogenous dopamine depletion and the modulation of the p38 MAPK and mTOR pathways did not influence the effects of interferon-β1a. During experimental autoimmune encephalomyelitis (EAE) striatal rotenone toxicity was enhanced but the protective effect of interferon-β1a was still evident. These results support future studies investigating the role played by specific intracellular signaling pathways in mediating the potential link among inflammation, mitochondrial impairment and neuroaxonal degeneration in multiple sclerosis.
Functional and structural interactions between D1 receptor (D1R) and NMDA receptor (NMDAR) have b... more Functional and structural interactions between D1 receptor (D1R) and NMDA receptor (NMDAR) have been shown to play a critical role in many functions of the brain. Interestingly, when these subtle interactions become abnormal, they might contribute to several diseases.Here we show that prolonged activation of D1R by SKF 38393 is able, in vitro as well as in vivo, to significantly reduce the quantity of NR2A subunit at the postsynaptic site. Interestingly, this molecular effect was in agreement with the reduction in the NMDA-AMPA ratio and specifically in NMDA(NR2A)-AMPA ratio as demonstrated by electrophysiological recordings. Considering the effect of this pharmacological approach on the NMDA subunit composition, we used SKF38393 in a model of \u201cearly\u201d Parkinson's Disease (PD), the so called \u201cpartial lesion\u201d model. In this condition, mild motor impairments were observed, compared to the more severe alterations occurring in the full lesion model. In addition, in corticostriatal slices recorded from partial lesioned animals (PL) a lack of Long Term Potentiation (LTP) was found, as well as a strong increase in the NR2A subunit abundance at the postsynaptic site. In the attempt to restore synaptic plasticity in PL, SKF38393 was administered in vivo. Surprisingly, the treatment successfully restored LTP in striatal neurons, by reducing the NR2A subunit levels at the postsynaptic site and it improved the motor performances. Finally, in order to avoid the typical side effects deriving from the dopaminergic treatment in PD, we used an alternative tool able to mimic the effect of the D1 agonist on the NMDAR subunit composition. To this end, we directly targeted NMDAR via a cell permeable peptide, TAT2A, acting towards the interruption of the NR2A subunit delivery to the NMDAR complex. Notably, TAT2A determined a significant improvement in motor behaviour and it rescued LTP thus representing a new therapeutic strategy in P
The basal ganglia are subcortical nuclei controlling voluntary actions and have been implicated i... more The basal ganglia are subcortical nuclei controlling voluntary actions and have been implicated in Parkinson's disease (PD). The prevailing model of basal ganglia function states that two circuits, the direct and indirect pathways, originate from distinct populations of striatal medium spiny neurons (MSNs) and project to different output structures. These circuits are believed to have opposite effects on movement. Specifically, the activity of direct pathway MSNs is postulated to promote movement, whereas the activation of indirect pathway MSNs is hypothesized to inhibit it. Recent findings have revealed that this model might not fully account for the concurrent activation of both pathways during movement. Accordingly, we propose a model in which intrastriatal connections are critical and the two pathways are structurally and functionally intertwined. Thus, all MSNs might either facilitate or inhibit movement depending on the form of synaptic plasticity expressed at a certain moment. In PD, alterations of dopamine-dependent synaptic plasticity could alter this coordinated activity.
N-methyl-D-aspartate (NMDA) receptors have been implicated as a mediator of neuronal injury assoc... more N-methyl-D-aspartate (NMDA) receptors have been implicated as a mediator of neuronal injury associated with many neurological disorders including ischemia, epilepsy, brain trauma, dementia and neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. To this, non-selective NMDA receptor antagonists have been tried and have been shown to be effective in many experimental animal models of disease, and some of these compounds have moved into clinical trials. However, the initial enthusiasm for this approach has waned, because the therapeutic index for most NMDA antagonists is quite poor, with significant adverse effects at clinically effective doses, thus limiting their utility. More recently, the concept that the exact pathways downstream NMDA receptor activation could represent a key variable element among neurological disorders has been put forward. In particular, variations in NMDA receptor subunit composition could be important in different disorders, both in the pathophysiological mechanisms of cell death and in the application of specific symptomatic therapies. As to PD, NMDA receptor complex has been shown to be altered in experimental models of parkinsonism and in PD in humans. Further, it has become increasingly evident that the NMDA receptor complex is intimately involved in the regulation of corticostriatal long-term potentiation, which is altered in experimental parkinsonism. The following sections will examine the modifications of specific NMDA receptor subunits as well as post-synaptic associated signalling complex including kinases and scaffolding proteins in experimental parkinsonism. These findings may allow the identification of specific molecular targets whose pharmacological or genetic manipulation might lead to innovative therapies for PD.
In humans, nicotine is self administered by inhalation of tobacco smoke as opposed to animal mode... more In humans, nicotine is self administered by inhalation of tobacco smoke as opposed to animal models, where nicotine is administered via systemic injection. The aim of the present study was to clarify whether tobacco smoke inhalation would affect dopaminergic projections differently from the reported activation after the systemic administration of nicotine. For this purpose, tobacco smoke from cigarettes containing 1.0 or 0.1 mg nicotine was delivered by inhalation to rats, while recording from antidromically identi®ed nigrostriatal and mesolimbic dopamine neurons. Smoke inhalation from 1.0 mg nicotine cigarettes caused a peculiar abrupt increase of discharge activity of mesolimbic dopamine neurons, while nigrostriatal cells were less responsive. This activation was promptly antagonized by mecamylamine (2.0 mg/kg, i.v.). In contrast, smoke delivered from 0.1 mg nicotine cigarettes was ineffective. These ®ndings suggest that the boosting activation of mesolimbic dopamine neurons by inhaled nicotine might be relevant for the rewarding properties of tobacco smoking and also for the effectiveness of new treatments to stop smoking.
Huntington&am... more Huntington's disease (HD) is a fatal hereditary neurodegenerative disease causing degeneration of striatal spiny neurons, whereas cholinergic interneurons are spared. This cell-type specific pathology produces an array of abnormalities including involuntary movements, cognitive impairments, and psychiatric disorders. Although the genetic mutation responsible for HD has been identified, little is known about the early synaptic changes occurring within the striatal circuitry at the onset of clinical symptoms. We therefore studied the synaptic plasticity of spiny neurons and cholinergic interneurons in two animal models of early HD. As a pathogenetic model, we used the chronic subcutaneous infusion of the mitochondrial toxin 3-nitropropionic acid (3-NP) in rats. This treatment caused striatal damage and impaired response flexibility in the cross-maze task as well as defective extinction of conditioned fear suggesting a perseverative behavior. In these animals, we observed a loss of depotentiation in striatal spiny neurons and a lack of long-term potentiation (LTP) in cholinergic interneurons. These abnormalities of striatal synaptic plasticity were also observed in R6/2 transgenic mice, a genetic model of HD, indicating that both genetic and phenotypic models of HD show cell-type specific alterations of LTP. We also found that in control rats, as well as in wild-type (WT) mice, depotentiation of spiny neurons was blocked by either scopolamine or hemicholinium, indicating that reversal of LTP requires activation of muscarinic receptors by endogenous acetylcholine. Our findings suggest that the defective plasticity of cholinergic interneurons could be the primary event mediating abnormal functioning of striatal circuits, and the loss of behavioral flexibility typical of early HD might largely depend on cell-type specific plastic abnormalities.
Huntington's disease (HD) is a late-onset neurodegenerative disorder that follows an autosomal-do... more Huntington's disease (HD) is a late-onset neurodegenerative disorder that follows an autosomal-dominant pattern of inheritance. In human cases of HD and experimental models of the disease, multiple alterations in neurotransmitters and post-receptor machineries have been described. Dopamine, acetylcholine and glutamate signalling, which usually cooperate in the induction of physiological synaptic plasticity, are all disrupted. Impairment of the induction and reversal of the main forms of neuronal synaptic plasticity influences the computational function of complex neural circuits that mediate essential cognitive and motor functions. As long-term potentiation and long-term depression represent the accepted model for neuronal learning processes, their impairment could account for the onset and progression of both motor and cognitive symptoms of HD.
Background: Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retarda... more Background: Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS. Methods: Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated. Results: The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum. Conclusions: The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS.
Glutamatergic hyperactivity in the nucleus striatum, the main basal ganglia input, has been invol... more Glutamatergic hyperactivity in the nucleus striatum, the main basal ganglia input, has been involved in the progression of Parkinson's disease (PD) and the onset of L-Dopa-induced dyskinesias (LIDs). Abnormalities in the spiny projection neurons (SPNs) excitability and firing, and in the overactivity of glutamate transmission found in animal models of PD, pointed to the synaptic dysfunctions as a primary target to counteract alterations before overt neurodegeneration, conferring a key role to striatal glutamatergic transmission in the early phases of the disease. The present paper will provide an overview of the evidence that glutamatergic overactivity is a critical mechanism underlying different PD-associated striatal alterations in early and advanced symptomatic stages of the disease. These aberrant changes, under L-Dopa therapy, lead to a more complex synaptopathy that involves other neurotransmitter systems and persistent modifications to generate LIDs. The review will discuss the main changes in glutamatergic functions found in PD preclinical models and clinical studies and an update of the current pharmacological strategies to modulate the glutamatergic systems at the pre- and postsynaptic levels will be provided.
Levodopa (L-DOPA) treatment is the main gold-standard therapy for Parkinson disease (PD). Besides... more Levodopa (L-DOPA) treatment is the main gold-standard therapy for Parkinson disease (PD). Besides good antiparkinsonian effects, prolonged use of this drug is associated to the development of involuntary movements known as L-DOPA-induced dyskinesia (LID). L-DOPA-induced dyskinesia is linked to a sensitization of dopamine (DA) D1 receptors located on spiny projection neurons (SPNs) of the dorsal striatum. Several evidences have shown that the emergence of LID can be related to striatal D1/cAMP/PKA/DARPP-32 and extracellular signal-regulated kinases (ERK1/2) pathway overactivation associated to aberrant N-methyl-d-aspartate (NMDA) receptor function. In addition, within striatum, ERK1/2 is also able to modulate in a D1 receptor-dependent manner the activity of the mammalian target of rapamycin complex 1 (mTORC1) pathway under DA depletion and L-DOPA therapy. Consistently, increased mTORC1 signaling appears during chronic administration of L-DOPA and shows a high correlation with the severity of dyskinesia. Furthermore, the abnormal activation of the D1/PKA/DARPP-32 cascade is paralleled by increased phosphorylation of the GluA1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor at the PKA Ser845 site. The GluA1 promotes excitatory AMPA receptor-mediated transmission and may be implicated in the alterations found at the corticostriatal synapses of dyskinetic animals. In our study, we investigated the role of mTORC1 pathway activation in modulating bidirectional striatal synaptic plasticity in L-DOPA-treated parkinsonian rats. Inhibition of mTORC1 by coadministration of rapamycin to L-DOPA was able to limit the magnitude of LID expression, accounting for a therapeutic effect of this
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal ... more Huntington's disease (HD) is a genetic neurodegenerative condition characterized by abnormal dopamine (DA)–glutamate interactions, severe alterations in motor control, and reduced behavioral flexibility. Experimental models of disease show that during symptomatic phases, HD shares with other hyperkinetic disorders the loss of synaptic depotentiation in the striatal spiny projection neurons (SPNs). Here we test the hypothesis that corticostriatal long‐term depression (LTD), a well‐conserved synaptic scaling down response to environmental stimuli, is also altered in symptomatic male R6/1 mice, a HD model with gradual development of symptoms. In vitro patch‐clamp and intracellular recordings of corticostriatal slices from R6/1 mice confirm that, similar to other models characterized by hyperkinesia and striatal DA D1 receptor pathway dysregulation, once long‐term potentiation (LTP) is induced, synaptic depotentiation is lost. Our new observations show that activity‐dependent LTD wa...
BackgroundProlonged dopaminergic replacement therapy in PD results in pulsatile dopamine receptor... more BackgroundProlonged dopaminergic replacement therapy in PD results in pulsatile dopamine receptors stimulation in both dorsal and ventral striatum causing wearing off, motor fluctuations, and nonmotor side effects such as behavioral addictions. Among impulse control disorders, binge eating can be easily modeled in laboratory animals.ObjectivesWe hypothesize that manipulation of dopamine levels in a 6‐hydroxydopamine–lesioned rats, as a model of PD characterized by a different extent of dopamine denervation between dorsal and ventral striatum, would influence both synaptic plasticity of the nucleus accumbens and binge‐like eating behavior.MethodsFood preference, food intake, and weight gain were monitored in sham‐operated and unilaterally lesioned rats, subjected to a modified version of Corwin's limited access protocol, modelling binge eating disorder. Electrophysiological properties and long‐term potentiation of GABAergic spiny projection neurons of the nucleus accumbens core w...
A BS TRACT: Objective: Spreading depolarization (SD) is a transient self-propagating wave of neur... more A BS TRACT: Objective: Spreading depolarization (SD) is a transient self-propagating wave of neuronal and glial depolarization coupled with large membrane ionic changes and a subsequent depression of neuronal activity. Spreading depolarization in the cortex is implicated in migraine, stroke, and epilepsy. Conversely, spreading depolarization in the striatum, a brain structure deeply involved in motor control and in Parkinson's disease (PD) pathophysiology, has been poorly investigated. Methods: We characterized the participation of glutamatergic and dopaminergic transmission in the induction of striatal spreading depolarization by using a novel approach combining optical imaging, measurements of endogenous DA levels, and pharmacological and molecular analyses. Results: We found that striatal spreading depolarization requires the concomitant activation of D1-like DA and Nmethyl-D-aspartate receptors, and it is reduced in experimental PD. Chronic L-dopa treatment, inducing dyskinesia in the parkinsonian condition, increases the occurrence and speed of propagation of striatal spreading depolarization, which has a direct impact on one of the signaling pathways downstream from the activation of D1 receptors. Conclusion: Striatal spreading depolarization might contribute to abnormal basal ganglia activity in the dyskinetic condition and represents a possible therapeutic target.
In the striatum, specific N-methyl-D-aspartate receptor (NMDAR) subtypes are found in different n... more In the striatum, specific N-methyl-D-aspartate receptor (NMDAR) subtypes are found in different neuronal cells. Spiny projection neurons (SPNs) are characterized by NMDARs expressing GluN2A and GluN2B subunits, while GluN2D is exclusively detected in striatal cholinergic interneurons (ChIs). In Parkinson's disease (PD), dopamine depletion and prolonged treatment with levodopa (L-DOPA) trigger adaptive changes in the glutamatergic transmission from the cortex to the striatum, also resulting in the aberrant function of striatal NMDARs. While modifications of GluN2A-and GluN2B-NMDARs in SPNs have been extensively documented, only few studies reported GluN2D dysfunction in PD and no data are available in L-DOPA-induced dyskinesia (LID). Here we investigate the contribution of a specific NMDAR subtype (GluN2D-NMDAR) to PD and LID, and whether this receptor could represent a candidate for future pharmacological interventions. Our results show that GluN2D synaptic abundance is selectively augmented in the striatum of L-DOPA-treated male parkinsonian rats displaying a dyskinetic phenotype. This event is associated to a dramatic increase in GluN2D binding to the postsynaptic protein scaffold PSD-95. Moreover, immunohistochemistry and electrophysiology experiments reveal that GluN2D-NMDARs are expressed not only by striatal ChIs but also by SPNs in dyskinetic rats. Notably, in vivo treatment with a well-characterized GluN2D antagonist ameliorates the severity of established dyskinesia in L-DOPA-treated animals. Our findings support a role for GluN2D-NMDARs in LID, and they confirm that celltype and subunit specific modifications of NMDARs underlie the pathophysiology of LID.
Absence of functional presynaptic scaffolding protein Bassoon (Bsn) in mutant mice is associated ... more Absence of functional presynaptic scaffolding protein Bassoon (Bsn) in mutant mice is associated with the development of pronounced spontaneous seizures and with consistent alterations in neuronal activity and morphology of hippocampus and cerebral cortex. The basal ganglia network receives a strong glutamatergic series of inputs from cortical regions through the striatum and it has been involved in the pathophysiology of epilepsy. However its functions, and in particular the role of the striatal microcircuit, in limiting epileptogenesis is still debated. To further investigate on the role of BG in limiting epileptic activity, we hypothesized that the spreading of epileptic seizures from the cortex to the striatum may alter both short and long-term excitability in two neuronal subtypes, the striatal fast-spiking GABAergic interneurons (FS) and the medium spiny (MS) neurons as an adaptive mechanism. To this end we first planned to study the epileptic phenotype and the learning skills of mutants. We then propose to characterize the plastic changes by electrophysiological recordings, molecular analyses and morphological studies. Epileptic seizures in mutant mice were video-recorded, classified and procedural learning and hippocampal-based learning skills were evaluated with a battery of behavioral tests. In vitro intracellular recordings were performed from corticostriatal slices obtained from Bsn mutants and WT mice while extracellular recordings were performed in hippocampal slices. Postsynaptic proteins were analyzed by Western blotting while morphological studies of FS and MS were performed in epileptic mice brain with Golgi-staining and unbiased immunohystochemical technique. Bsn mutant mice showed early-onset epileptic seizure development, which in adults were associated to a rearrangement of synaptic plasticity within the striatal microcircuit. In fact, although long-term depression (LTD) was equally expressed in both genotypes, the amplitude of long-term potentiation (LTP) induced in MS neurons of Bsn mutant mice was reduced compared to control, while hippocampal LTP was completely lost. The alteration in striatal plasticity was associated to differences in dendrite branching and spine maturation of MS neurons and to profound modifications of postsynaptic components expression in the whole striatum. In particular, in the striatum of epileptic mice, the NMDA subunit composition was found altered, the BDNF expression decreased and TrkB receptor upregulated. Interestingly, following high frequency stimulation protocol, GABAergic FS recorded from Bsn mutant mice expressed a NMDA and BDNF-dependent short-term potentiation that was absent in WT animals. Moreover FS interneurons were increased in number in the epileptic genotype. Behavioral tests for assessment of learning skills demonstrated that procedural learning capabilities are intact while hippocampal-based functions are compromised in epileptic mice providing evidences for a competition between the two memory systems. Our results indicate that while hippocampal synaptic plasticity is lost, striatal neuronal subtypes are differentially sensitive to continuous seizures and to the associated alterations of BDNF/TrkB signaling. These data suggest that changes of corticostriatal activity develop in early-onset epileptic conditions associated to the lack of functional Bsn. The reorganization of plasticity between neuronal subtypes may protect striatum and downstream BG nuclei from continuous cortical seizures in order to preserve striatal functions.
Hippocampus and striatum play distinctive roles in memory processes since declarative and non-dec... more Hippocampus and striatum play distinctive roles in memory processes since declarative and non-declarative memory systems may act independently. However, hippocampus and striatum can also be engaged to function in parallel as part of a dynamic system to integrate previous experience and adjust behavioral responses. In these structures the formation, storage, and retrieval of memory require a synaptic mechanism that is able to integrate multiple signals and to translate them into persistent molecular traces at both the corticostriatal and hippocampal/limbic synapses. The best cellular candidate for this complex synthesis is represented by long-term potentiation (LTP). A common feature of LTP expressed in these two memory systems is the critical requirement of convergence and coincidence of glutamatergic and dopaminergic inputs to the dendritic spines of the neurons expressing this form of synaptic plasticity. In experimental models of Parkinson's disease abnormal accumulation of α-synuclein affects these two memory systems by altering two major synaptic mechanisms underlying cognitive functions in cholinergic striatal neurons, likely implicated in basal ganglia dependent operative memory, and in the CA1 hippocampal region, playing a central function in episodic/declarative memory processes.
Multiple sclerosis, one of the main causes of non-traumatic neurological disability in young adul... more Multiple sclerosis, one of the main causes of non-traumatic neurological disability in young adults, is an inflammatory and neurodegenerative disorder of the central nervous system. Although the pathogenesis of neuroaxonal damage occurring during the course of the disease is still largely unknown, there is accumulating evidence highlighting the potential role of mitochondria in multiple sclerosis-associated neuronal degeneration. The aim of the present study was to investigate, by utilizing electrophysiological techniques in brain striatal slices, the potential protective effects of interferon-β1a, one of the most widely used medication for multiple sclerosis, against acute neuronal dysfunction induced by mitochondrial toxins. Interferon-β1a was found to exert a dosedependent protective effect against the progressive loss of striatal field potential amplitude induced by the mitochondrial complex I inhibitor rotenone. Interferon-β1a also reduced the generation of the rotenone-induced inward current in striatal spiny neurons. Conversely, interferon-β1a did not influence the electrophysiological effects of the mitochondrial complex II inhibitor 3-nitropropionic acid. The protective effect of interferon-β1a against mitochondrial complex I inhibition was found to be dependent on the activation of STAT1 signaling. Conversely, endogenous dopamine depletion and the modulation of the p38 MAPK and mTOR pathways did not influence the effects of interferon-β1a. During experimental autoimmune encephalomyelitis (EAE) striatal rotenone toxicity was enhanced but the protective effect of interferon-β1a was still evident. These results support future studies investigating the role played by specific intracellular signaling pathways in mediating the potential link among inflammation, mitochondrial impairment and neuroaxonal degeneration in multiple sclerosis.
Functional and structural interactions between D1 receptor (D1R) and NMDA receptor (NMDAR) have b... more Functional and structural interactions between D1 receptor (D1R) and NMDA receptor (NMDAR) have been shown to play a critical role in many functions of the brain. Interestingly, when these subtle interactions become abnormal, they might contribute to several diseases.Here we show that prolonged activation of D1R by SKF 38393 is able, in vitro as well as in vivo, to significantly reduce the quantity of NR2A subunit at the postsynaptic site. Interestingly, this molecular effect was in agreement with the reduction in the NMDA-AMPA ratio and specifically in NMDA(NR2A)-AMPA ratio as demonstrated by electrophysiological recordings. Considering the effect of this pharmacological approach on the NMDA subunit composition, we used SKF38393 in a model of \u201cearly\u201d Parkinson's Disease (PD), the so called \u201cpartial lesion\u201d model. In this condition, mild motor impairments were observed, compared to the more severe alterations occurring in the full lesion model. In addition, in corticostriatal slices recorded from partial lesioned animals (PL) a lack of Long Term Potentiation (LTP) was found, as well as a strong increase in the NR2A subunit abundance at the postsynaptic site. In the attempt to restore synaptic plasticity in PL, SKF38393 was administered in vivo. Surprisingly, the treatment successfully restored LTP in striatal neurons, by reducing the NR2A subunit levels at the postsynaptic site and it improved the motor performances. Finally, in order to avoid the typical side effects deriving from the dopaminergic treatment in PD, we used an alternative tool able to mimic the effect of the D1 agonist on the NMDAR subunit composition. To this end, we directly targeted NMDAR via a cell permeable peptide, TAT2A, acting towards the interruption of the NR2A subunit delivery to the NMDAR complex. Notably, TAT2A determined a significant improvement in motor behaviour and it rescued LTP thus representing a new therapeutic strategy in P
The basal ganglia are subcortical nuclei controlling voluntary actions and have been implicated i... more The basal ganglia are subcortical nuclei controlling voluntary actions and have been implicated in Parkinson's disease (PD). The prevailing model of basal ganglia function states that two circuits, the direct and indirect pathways, originate from distinct populations of striatal medium spiny neurons (MSNs) and project to different output structures. These circuits are believed to have opposite effects on movement. Specifically, the activity of direct pathway MSNs is postulated to promote movement, whereas the activation of indirect pathway MSNs is hypothesized to inhibit it. Recent findings have revealed that this model might not fully account for the concurrent activation of both pathways during movement. Accordingly, we propose a model in which intrastriatal connections are critical and the two pathways are structurally and functionally intertwined. Thus, all MSNs might either facilitate or inhibit movement depending on the form of synaptic plasticity expressed at a certain moment. In PD, alterations of dopamine-dependent synaptic plasticity could alter this coordinated activity.
N-methyl-D-aspartate (NMDA) receptors have been implicated as a mediator of neuronal injury assoc... more N-methyl-D-aspartate (NMDA) receptors have been implicated as a mediator of neuronal injury associated with many neurological disorders including ischemia, epilepsy, brain trauma, dementia and neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease. To this, non-selective NMDA receptor antagonists have been tried and have been shown to be effective in many experimental animal models of disease, and some of these compounds have moved into clinical trials. However, the initial enthusiasm for this approach has waned, because the therapeutic index for most NMDA antagonists is quite poor, with significant adverse effects at clinically effective doses, thus limiting their utility. More recently, the concept that the exact pathways downstream NMDA receptor activation could represent a key variable element among neurological disorders has been put forward. In particular, variations in NMDA receptor subunit composition could be important in different disorders, both in the pathophysiological mechanisms of cell death and in the application of specific symptomatic therapies. As to PD, NMDA receptor complex has been shown to be altered in experimental models of parkinsonism and in PD in humans. Further, it has become increasingly evident that the NMDA receptor complex is intimately involved in the regulation of corticostriatal long-term potentiation, which is altered in experimental parkinsonism. The following sections will examine the modifications of specific NMDA receptor subunits as well as post-synaptic associated signalling complex including kinases and scaffolding proteins in experimental parkinsonism. These findings may allow the identification of specific molecular targets whose pharmacological or genetic manipulation might lead to innovative therapies for PD.
In humans, nicotine is self administered by inhalation of tobacco smoke as opposed to animal mode... more In humans, nicotine is self administered by inhalation of tobacco smoke as opposed to animal models, where nicotine is administered via systemic injection. The aim of the present study was to clarify whether tobacco smoke inhalation would affect dopaminergic projections differently from the reported activation after the systemic administration of nicotine. For this purpose, tobacco smoke from cigarettes containing 1.0 or 0.1 mg nicotine was delivered by inhalation to rats, while recording from antidromically identi®ed nigrostriatal and mesolimbic dopamine neurons. Smoke inhalation from 1.0 mg nicotine cigarettes caused a peculiar abrupt increase of discharge activity of mesolimbic dopamine neurons, while nigrostriatal cells were less responsive. This activation was promptly antagonized by mecamylamine (2.0 mg/kg, i.v.). In contrast, smoke delivered from 0.1 mg nicotine cigarettes was ineffective. These ®ndings suggest that the boosting activation of mesolimbic dopamine neurons by inhaled nicotine might be relevant for the rewarding properties of tobacco smoking and also for the effectiveness of new treatments to stop smoking.
Huntington&am... more Huntington's disease (HD) is a fatal hereditary neurodegenerative disease causing degeneration of striatal spiny neurons, whereas cholinergic interneurons are spared. This cell-type specific pathology produces an array of abnormalities including involuntary movements, cognitive impairments, and psychiatric disorders. Although the genetic mutation responsible for HD has been identified, little is known about the early synaptic changes occurring within the striatal circuitry at the onset of clinical symptoms. We therefore studied the synaptic plasticity of spiny neurons and cholinergic interneurons in two animal models of early HD. As a pathogenetic model, we used the chronic subcutaneous infusion of the mitochondrial toxin 3-nitropropionic acid (3-NP) in rats. This treatment caused striatal damage and impaired response flexibility in the cross-maze task as well as defective extinction of conditioned fear suggesting a perseverative behavior. In these animals, we observed a loss of depotentiation in striatal spiny neurons and a lack of long-term potentiation (LTP) in cholinergic interneurons. These abnormalities of striatal synaptic plasticity were also observed in R6/2 transgenic mice, a genetic model of HD, indicating that both genetic and phenotypic models of HD show cell-type specific alterations of LTP. We also found that in control rats, as well as in wild-type (WT) mice, depotentiation of spiny neurons was blocked by either scopolamine or hemicholinium, indicating that reversal of LTP requires activation of muscarinic receptors by endogenous acetylcholine. Our findings suggest that the defective plasticity of cholinergic interneurons could be the primary event mediating abnormal functioning of striatal circuits, and the loss of behavioral flexibility typical of early HD might largely depend on cell-type specific plastic abnormalities.
Huntington's disease (HD) is a late-onset neurodegenerative disorder that follows an autosomal-do... more Huntington's disease (HD) is a late-onset neurodegenerative disorder that follows an autosomal-dominant pattern of inheritance. In human cases of HD and experimental models of the disease, multiple alterations in neurotransmitters and post-receptor machineries have been described. Dopamine, acetylcholine and glutamate signalling, which usually cooperate in the induction of physiological synaptic plasticity, are all disrupted. Impairment of the induction and reversal of the main forms of neuronal synaptic plasticity influences the computational function of complex neural circuits that mediate essential cognitive and motor functions. As long-term potentiation and long-term depression represent the accepted model for neuronal learning processes, their impairment could account for the onset and progression of both motor and cognitive symptoms of HD.
Background: Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retarda... more Background: Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS. Methods: Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated. Results: The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum. Conclusions: The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS.
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Papers by V. Ghiglieri