Re-emergence of striatal cholinergic interneurons in movement disorders

Allosteric modulation of GluN2C/GluN2D-containing NMDA receptors bidirectionally modulates dopamine release: implication for Parkinson's disease

BACKGROUND AND PURPOSE

Allosteric modulators of ionotropic receptors and GPCRs might constitute valuable therapeutic tools for intervention in several diseases, including Parkinson's disease (PD). However, the possibility that some of these compounds could alter neurotransmission in health and disease has not been thoroughly examined. Hence, we determined whether CIQ, a positive allosteric modulator of NMDA receptors that contain the GluN2C or GluN2D subunits, modulates dopamine release in the striatum of control mice and of a mouse model of presymptomatic Parkinsonism.

EXPERIMENTAL APPROACH

We used amperometry to measure, in mouse brain slices containing the dorsal striatum, dopamine release evoked by stimulations that mimicked tonic (single pulses) or phasic (trains) activity. We used control mice and mice with a partial, 6-hydroxydopamine-induced, degeneration of dopaminergic neurons in the substantia nigra.

KEY RESULTS

In control mice, CIQ inhibited tonic dopamine release and induced an initial inhibition followed by a long-lasting increase in phasic release. Pirenzepine, a muscarinic receptor antagonist, blocked the depression of release induced by CIQ, but not the long-lasting potentiation. CIQ also increased action potential firing in striatal cholinergic interneurons. In the partially dopamine-depleted striatum, CIQ induced an inhibition followed by a potentiation of both tonic and phasic release, but did not significantly increase the firing of cholinergic interneurons.

CONCLUSIONS AND IMPLICATIONS

CIQ has bidirectional, activity- and ACh-dependent, modulatory effects on dopamine release in the striatum. This study suggests a potentially valuable means to enhance dopamine release in presymptomatic Parkinsonism.

Whole-brain mapping of inputs to projection neurons and cholinergic interneurons in the dorsal striatum

The dorsal striatum integrates inputs from multiple brain areas to coordinate voluntary movements, associative plasticity, and reinforcement learning. Its projection neurons consist of the GABAergic medium spiny neurons (MSNs) that express dopamine receptor type 1 (D1) or dopamine receptor type 2 (D2). Cholinergic interneurons account for a small portion of striatal neuron populations, but they play important roles in striatal functions by synapsing onto the MSNs and other local interneurons. By combining the modified rabies virus with specific Cre- mouse lines, a recent study mapped the monosynaptic input patterns to MSNs. Because only a small number of extrastriatal neurons were labeled in the prior study, it is important to reexamine the input patterns of MSNs with higher labeling efficiency. Additionally, the whole-brain innervation pattern of cholinergic interneurons remains unknown. Using the rabies virus-based transsynaptic tracing method in this study, we comprehensively charted the brain areas that provide direct inputs to D1-MSNs, D2-MSNs, and cholinergic interneurons in the dorsal striatum. We found that both types of projection neurons and the cholinergic interneurons receive extensive inputs from discrete brain areas in the cortex, thalamus, amygdala, and other subcortical areas, several of which were not reported in the previous study. The MSNs and cholinergic interneurons share largely common inputs from areas outside the striatum. However, innervations within the dorsal striatum represent a significantly larger proportion of total inputs for cholinergic interneurons than for the MSNs. The comprehensive maps of direct inputs to striatal MSNs and cholinergic interneurons shall assist future functional dissection of the striatal circuits.

Involvement of cholinergic system in hyperactivity in dopamine-deficient mice

Dopaminergic systems have been known to be involved in the regulation of locomotor activity and development of psychosis. However, the observations that some Parkinson's disease patients can move effectively under appropriate conditions despite low dopamine levels (eg, kinesia paradoxia) and that several psychotic symptoms are typical antipsychotic resistant and atypical antipsychotic sensitive indicate that other systems beyond the dopaminergic system may also affect locomotor activity and psychosis. The present study showed that dopamine-deficient (DD) mice, which had received daily L-DOPA injections, could move effectively and even be hyperactive 72 h after the last L-DOPA injection when dopamine was almost completely depleted. Such hyperactivity was ameliorated by clozapine but not haloperidol or ziprasidone. Among multiple actions of clozapine, muscarinic acetylcholine (ACh) activation markedly reduced locomotor activity in DD mice. Furthermore, the expression of choline acetyltransferase, an ACh synthase, was reduced and extracellular ACh levels were significantly reduced in DD mice. These results suggest that the cholinergic system, in addition to the dopaminergic system, may be involved in motor control, including hyperactivity and psychosis. The present findings provide additional evidence that the cholinergic system may be targeted for the treatment of Parkinson's disease and psychosis.

Rhes regulates dopamine D2 receptor transmission in striatal cholinergic interneurons

Ras homolog enriched in striatum (Rhes) is highly expressed in striatal medium spiny neurons (MSNs) of rodents. In the present study, we characterized the expression of Rhes mRNA across species, as well as its functional role in other striatal neuron subtypes. Double in situ hybridization analysis showed that Rhes transcript is selectively localized in striatal cholinergic interneurons (ChIs), but not in GABAergic parvalbumin- or in neuropeptide Y-positive cell populations. Rhes is closely linked to dopamine-dependent signaling. Therefore, we recorded ChIs activity in basal condition and following dopamine receptor activation. Surprisingly, instead of an expected dopamine D2 receptor (D2R)-mediated inhibition, we observed an aberrant excitatory response in ChIs from Rhes knockout mice. Conversely, the effect of D1R agonist on ChIs was less robust in Rhes mutants than in controls. Although Rhes deletion in mutants occurs throughout the striatum, we demonstrate that the D2R response is altered specifically in ChIs, since it was recorded in pharmacological isolation, and prevented either by intrapipette BAPTA or by GDP-β-S. Moreover, we show that blockade of Cav2.2 calcium channels prevented the abnormal D2R response. Finally, we found that the abnormal D2R activation in ChIs was rescued by selective PI3K inhibition thus suggesting that Rhes functionally modulates PI3K/Akt signaling pathway in these neurons. Our findings reveal that, besides its expression in MSNs, Rhes is localized also in striatal ChIs and, most importantly, lack of this G-protein, significantly alters D2R modulation of striatal cholinergic excitability.

Identification and characterization of ML352: a novel, noncompetitive inhibitor of the presynaptic choline transporter

The high-affinity choline transporter (CHT) is the rate-limiting determinant of acetylcholine (ACh) synthesis, yet the transporter remains a largely undeveloped target for the detection and manipulation of synaptic cholinergic signaling. To expand CHT pharmacology, we pursued a high-throughput screen for novel CHT-targeted small molecules based on the electrogenic properties of transporter-mediated choline transport. In this effort, we identified five novel, structural classes of CHT-specific inhibitors. Chemical diversification and functional analysis of one of these classes identified ML352 as a high-affinity (K_i = 92 nM) and selective CHT inhibitor. At concentrations that fully antagonized CHT in transfected cells and nerve terminal preparations, ML352 exhibited no inhibition of acetylcholinesterase (AChE) or cholineacetyltransferase (ChAT) and also lacked activity at dopamine, serotonin, and norepinephrine transporters, as well as many receptors and ion channels. ML352 exhibited noncompetitive choline uptake inhibition in intact cells and synaptosomes and reduced the apparent density of hemicholinium-3 (HC-3) binding sites in membrane assays, suggesting allosteric transporter interactions. Pharmacokinetic studies revealed limited in vitro metabolism and significant CNS penetration, with features predicting rapid clearance. ML352 represents a novel, potent, and specific tool for the manipulation of CHT, providing a possible platform for the development of cholinergic imaging and therapeutic agents.

Acute vocal fold dystonic reaction to propofol: a case report

A 67-year old male underwent uneventful robotic-assisted thoracoscopic resection of a solitary pulmonary fibrous tumor. Immediately following extubation at the completion of the surgical procedure, the patient developed respiratory distress that did not resolve with treatment. Benadryl provided only temporary relief. Midazolam and hydromorphone were given for anxiolysis and analgesia respectively, which provided transient relief of symptoms. Propofol was given to decrease upper airway reflexes. Adequate reversal from nondepolarizing neuromuscular blockade was confirmed with nerve stimulator. A flexible laryngoscope was introduced nasally to visualize the vocal cords, which revealed intermittent tremulousness of the vocal cords, adduction of bilateral vocal cords to the midline, and minimal to absent opening with inspiration, without any apparent injury or blood, saliva, or vomit noted in or around the glottic opening. The patient was then given diazepam and reintubated. Given the patient's history of difficulty breathing after previous surgery and the lack of vocal cord movement, dystonic reaction to propofol was suspected. The patient remained intubated for two hours in the post-anesthesia care unit before being extubated uneventfully.

Enhanced GABAergic Inputs Contribute to Functional Alterations of Cholinergic Interneurons in the R6/2 Mouse Model of Huntington's Disease

Although large cholinergic interneurons (LCIs) in striatum are spared in Huntington's disease (HD), deficits in cholinergic function have been described. Here we demonstrate in a mouse model of HD that the firing patterns of LCIs are disrupted and this is due to aberrant GABAergic neurotransmission. This explains cholinergic deficits in HD.

In Huntington’s disease (HD), a hereditary neurodegenerative disorder, striatal medium-sized spiny neurons undergo degenerative changes. In contrast, large cholinergic interneurons (LCIs) are relatively spared. However, their ability to release acetylcholine (ACh) is impaired. The present experiments examined morphological and electrophysiological properties of LCIs in the R6/2 mouse model of HD. R6/2 mice show a severe, rapidly progressing phenotype. Immunocytochemical analysis of choline acetyltransferase-positive striatal neurons showed that, although the total number of cells was not changed, somatic areas were significantly smaller in symptomatic R6/2 mice compared to wild-type (WT) littermates, For electrophysiology, brain slices were obtained from presymptomatic (3-4 weeks) and symptomatic (>8 weeks) R6/2 mice and their WT littermates. Striatal LCIs were identified by somatic size and spontaneous action potential firing in the cell-attached mode. Passive and active membrane properties of LCIs were similar in presymptomatic R6/2 and WT mice. In contrast, LCIs from symptomatic R6/2 animals displayed smaller membrane capacitance and higher input resistance, consistent with reduced somatic size. In addition, more LCIs from symptomatic mice displayed irregular firing patterns and bursts of action potentials. They also displayed a higher frequency of spontaneous GABAergic IPSCs and larger amplitude of electrically evoked IPSCs. Selective optogenetic stimulation of somatostatin- but not parvalbumin-containing interneurons also evoked larger amplitude IPSCs in LCIs from R6/2 mice. In contrast, glutamatergic spontaneous or evoked postsynaptic currents were not affected. Morphological and electrophysiological alterations, in conjunction with the presence of mutant huntingtin in LCIs, could explain impaired ACh release in HD mouse models.

Striatal cholinergic dysfunction as a unifying theme in the pathophysiology of dystonia

Dystonia is a movement disorder of both genetic and non-genetic causes, which typically results in twisted posturing due to abnormal muscle contraction. Evidence from dystonia patients and animal models of dystonia indicate a crucial role for the striatal cholinergic system in the pathophysiology of dystonia. In this review, we focus on striatal circuitry and the centrality of the acetylcholine system in the function of the basal ganglia in the control of voluntary movement and ultimately clinical manifestation of movement disorders. We consider the impact of cholinergic interneurons (ChIs) on dopamine-acetylcholine interactions and examine new evidence for impairment of ChIs in dysfunction of the motor systems producing dystonic movements, particularly in animal models. We have observed paradoxical excitation of ChIs in the presence of dopamine D2 receptor agonists and impairment of striatal synaptic plasticity in a mouse model of DYT1 dystonia, which are improved by administration of recently developed M1 receptor antagonists. These findings have been confirmed across multiple animal models of DYT1 dystonia and may represent a common endophenotype by which to investigate dystonia induced by other types of genetic and non-genetic causes and to investigate the potential effectiveness of pharmacotherapeutics and other strategies to improve dystonia.

On the role of adenosine (A)₂A receptors in cocaine-induced reward: a pharmacological and neurochemical analysis in rats

RATIONALE

Several studies have suggested the inhibitory control of adenosine (A)2A receptor stimulation in cocaine-induced behavioral actions.

OBJECTIVES

A combination of systemic or local drug injections and in vivo neurochemical analysis investigated A2A receptors in cocaine and food reward.

METHODS

Rats, trained to self-administer cocaine or food, were tested with the selective A2A receptor antagonists KW 6002 and SCH 58261 or the selective A2A receptor agonist CGS 21680. Extracellular dopamine, glutamate, and GABA levels in the nucleus accumbens and ventral pallidum were determined following intra-accumbal CGS 21680 administration during cocaine self-administration.

RESULTS

Neither KW 6002 nor SCH 58261 (0.25-1 mg/kg) altered cocaine self-administration (0.125-0.5 mg/kg/infusion), while CGS 21680 (0.2-0.4 mg/kg) produced a downward shift in the cocaine dose-response curve under a fixed ratio schedule of reinforcement and decreased the cocaine breaking point. CGS 21680 blocked also operant responding for food, while the A2A receptor antagonists were inactive. Local steady-state infusion of CGS 21680 (10 μM) during cocaine self-administration increased the active level pressing that was accompanied with reduced dopamine and increased GABA in the nucleus accumbens in the absence of changes in GABA and glutamate levels in the ventral pallidum. Pretreatment with systemic KW 6002 counteracted the increases in number of cocaine infusions seen after intra-accumbal administration of CGS 21680.

CONCLUSION

The findings support a role of A2A receptors in modulating goal-maintained behaviors. They also indicate that increased accumbal GABA release involving an antagonistic A2A-D2 receptor interaction can participate in mediating the inhibitory effects of the A2A agonist on cocaine reward.

Dopamine regulates distinctively the activity patterns of striatal output neurons in advanced parkinsonian primates

Nigrostriatal dopamine denervation plays a major role in basal ganglia circuitry disarray and motor abnormalities of Parkinson's disease (PD). Studies in rodent and primate models have revealed that striatal projection neurons, namely, medium spiny neurons (MSNs), increase the firing frequency. However, their activity pattern changes and the effects of dopaminergic stimulation in such conditions are unknown. Using single-cell recordings in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated primates with advanced parkinsonism, we studied MSN activity patterns in the transition to different motor states following levodopa administration. In the "off" state (baseline parkinsonian disability), a burst-firing pattern accompanied by prolonged silences (pauses) was found in 34% of MSNs, and 80% of these exhibited a levodopa response compatible with dopamine D1 receptor activation (direct pathway MSNs). This pattern was highly responsive to levodopa given that bursting/pausing almost disappeared in the "on" state (reversal of parkinsonism after levodopa injection), although this led to higher firing rates. Nonbursty MSNs fired irregularly with marked pausing that increased in the on state in the MSN subset with a levodopa response compatible with dopamine D2 receptor activation (indirect pathway MSNs), although the pause increase was not sustained in some units during the appearance of dyskinesias. Data indicate that the MSN firing pattern in the advanced parkinsonian monkey is altered by bursting and pausing changes and that dopamine differentially and inefficiently regulates these behaviorally correlated patterns in MSN subpopulations. These findings may contribute to understand the impact of striatal dysfunction in the basal ganglia network and its role in motor symptoms of PD.

Nicotinic, glutamatergic and dopaminergic synaptic transmission and plasticity in the mesocorticolimbic system: focus on nicotine effects

Cigarette smoking is currently the leading cause of preventable deaths and disability throughout the world, being responsible for about five million premature deaths/year. Unfortunately, fewer than 10% of tobacco users who try to stop smoking actually manage to do so. The main addictive agent delivered by cigarette smoke is nicotine, which induces psychostimulation and reward, and reduces stress and anxiety. The use of new technologies (including optogenetics) and the development of mouse models characterised by cell-specific deletions of receptor subtype genes or the expression of gain-of-function nAChR subunits has greatly increased our understanding of the molecular mechanisms and neural substrates of nicotine addiction first revealed by classic electrophysiological, neurochemical and behavioural approaches. It is now becoming clear that various aspects of nicotine dependence are mediated by close interactions of the glutamatergic, dopaminergic and γ-aminobutyric acidergic systems in the mesocorticolimbic system. This review is divided into two parts. The first provides an updated overview of the circuitry of the ventral tegmental area, ventral striatum and prefrontal cortex, the neurotransmitter receptor subtypes expressed in these areas, and their physiological role in the mesocorticolimbic system. The second will focus on the molecular, functional and behavioural mechanisms involved in the acute and chronic effects of nicotine on the mesocorticolimbic system.

Anticholinergic drugs rescue synaptic plasticity in DYT1 dystonia: role of M1 muscarinic receptors

Broad-spectrum muscarinic receptor antagonists have represented the first available treatment for different movement disorders such as dystonia. However, the specificity of these drugs and their mechanism of action is not entirely clear. We performed a systematic analysis of the effects of anticholinergic drugs on short- and long-term plasticity recorded from striatal medium spiny neurons from DYT1 dystonia knock-in (Tor1a(+/Δgag) ) mice heterozygous for ΔE-torsinA and their controls (Tor1a(+/+) mice). Antagonists were chosen that had previously been proposed to be selective for muscarinic receptor subtypes and included pirenzepine, trihexyphenydil, biperiden, orphenadrine, and a novel selective M1 antagonist, VU0255035. Tor1a(+/Δgag) mice exhibited a significant impairment of corticostriatal synaptic plasticity. Anticholinergics had no significant effects on intrinsic membrane properties and on short-term plasticity of striatal neurons. However, they exhibited a differential ability to restore the corticostriatal plasticity deficits. A complete rescue of both long-term depression (LTD) and synaptic depotentiation (SD) was obtained by applying the M1 -preferring antagonists pirenzepine and trihexyphenidyl as well as VU0255035. Conversely, the nonselective antagonist orphenadrine produced only a partial rescue of synaptic plasticity, whereas biperiden and ethopropazine failed to restore plasticity. The selectivity for M1 receptors was further demonstrated by their ability to counteract the M1 -dependent potentiation of N-methyl-d-aspartate (NMDA) current recorded from striatal neurons. Our study demonstrates that selective M1 muscarinic receptor antagonism offsets synaptic plasticity deficits in the striatum of mice with the DYT1 dystonia mutation, providing a potential mechanistic rationale for the development of improved antimuscarinic therapies for this movement disorder.

Aging, motor skill, and the energy cost of walking: implications for the prevention and treatment of mobility decline in older persons

BACKGROUND

Age-associated neural changes profoundly affect the biomechanics and energetics of walking, increase energy cost, and require novel approaches to exercise that focus on motor learning theory.

METHODS

We present a conceptual framework for motor skill in walking, its effect on the energy cost of walking, and the influence of the aging brain.

RESULTS

Motor learning theory and practice can be incorporated into interventions to promote skilled, energy efficient walking in older people.

CONCLUSIONS

An extensive literature on motor skill and motor learning, derived from neuroscience, sports medicine, and neurorehabilitation, can be applied to problems of walking in late life.

Inherited isolated dystonia: clinical genetics and gene function

Isolated inherited dystonia-formerly referred to as primary dystonia-is characterized by abnormal motor functioning of a grossly normal appearing brain. The disease manifests as abnormal involuntary twisting movements. The absence of overt neuropathological lesions, while intriguing, has made it particularly difficult to unravel the pathogenesis of isolated inherited dystonia. The explosion of genetic techology enabling the identification of the causative gene mutations is transforming our understanding of dystonia pathogenesis, as the molecular, cellular and circuit level consequences of these mutations are identified in experimental systems. Here, I review the clinical genetics and cell biology of three forms of inherited dystonia for which the causative mutation is known: DYT1 (TOR1A), DYT6 (THAP1), DYT25 (GNAL).

Multiphasic modulation of cholinergic interneurons by nigrostriatal afferents

The motor and learning functions of the striatum are critically dependent on synaptic transmission from midbrain dopamine neurons and striatal cholinergic interneurons (CINs). Both neural populations alter their discharge in vivo in response to salient sensory stimuli, albeit in opposite directions. Whereas midbrain dopamine neurons respond to salient stimuli with a brief burst of activity, CINs exhibit a distinct pause in firing that is often followed by a period of increased excitability. Although this "pause-rebound" sensory response requires dopaminergic signaling, the precise mechanisms underlying the modulation of CIN firing by dopaminergic afferents remain unclear. Here, we show that phasic activation of nigrostriatal afferents in a mouse striatal slice preparation is sufficient to evoke a pause-rebound response in CINs. Using a combination of optogenetic, electrophysiological, and pharmacological approaches, we demonstrate that synaptically released dopamine inhibits CINs through type 2 dopamine receptors, while another unidentified transmitter mediates the delayed excitation. These findings imply that, in addition to their direct effects on striatal projection neurons, midbrain dopamine neurons indirectly modulate striatal output by dynamically controlling cholinergic tone. In addition, our data suggest that phasic dopaminergic activity may directly participate in the characteristic pause-rebound sensory response that CINs exhibit in vivo in response to salient and conditioned stimuli.

Novel AAV-based rat model of forebrain synucleinopathy shows extensive pathologies and progressive loss of cholinergic interneurons

Synucleinopathies, characterized by intracellular aggregation of α-synuclein protein, share a number of features in pathology and disease progression. However, the vulnerable cell population differs significantly between the disorders, despite being caused by the same protein. While the vulnerability of dopamine cells in the substantia nigra to α-synuclein over-expression, and its link to Parkinson's disease, is well studied, animal models recapitulating the cortical degeneration in dementia with Lewy-bodies (DLB) are much less mature. The aim of this study was to develop a first rat model of widespread progressive synucleinopathy throughout the forebrain using adeno-associated viral (AAV) vector mediated gene delivery. Through bilateral injection of an AAV6 vector expressing human wild-type α-synuclein into the forebrain of neonatal rats, we were able to achieve widespread, robust α-synuclein expression with preferential expression in the frontal cortex. These animals displayed a progressive emergence of hyper-locomotion and dysregulated response to the dopaminergic agonist apomorphine. The animals receiving the α-synuclein vector displayed significant α-synuclein pathology including intra-cellular inclusion bodies, axonal pathology and elevated levels of phosphorylated α-synuclein, accompanied by significant loss of cortical neurons and a progressive reduction in both cortical and striatal ChAT positive interneurons. Furthermore, we found evidence of α-synuclein sequestered by IBA-1 positive microglia, which was coupled with a distinct change in morphology. In areas of most prominent pathology, the total α-synuclein levels were increased to, on average, two-fold, which is similar to the levels observed in patients with SNCA gene triplication, associated with cortical Lewy body pathology. This study provides a novel rat model of progressive cortical synucleinopathy, showing for the first time that cholinergic interneurons are vulnerable to α-synuclein over-expression. This animal model provides a powerful new tool for studies of neuronal degeneration in conditions of widespread cortical α-synuclein pathology, such as DLB, as well an attractive model for the exploration of novel biomarkers.

Famotidine, a Histamine H2 Receptor Antagonist, Does Not Reduce Levodopa-Induced Dyskinesia in Parkinson's Disease: A Proof-of-Concept Study

The neural mechanisms underlying levodopa-induced dyskinesia (LID) in Parkinson's disease (PD) may involve histamine (H₂) receptors on striatopallidal pathways. We recently demonstrated that the clinically available oral histamine H₂ receptor antagonist (H₂ RA), famotidine, can reduce l-dopa-induced chorea in MPTP-lesioned macaques. We hypothesized that famotidine may be useful in the treatment of LID in PD patients. We performed a proof-of-concept, double-blind, randomized, multiple cross-over (4×) trial. Seven PD subjects with bothersome dyskinesia were randomized to oral famotidine 80, 120, and 160 mg/day and placebo. Each subject was randomized to receive each of the four treatment phases for 14 days followed by a 7-day wash-out period between each treatment phase. The primary outcome measure was change in the Unified Dyskinesia Rating Scale (UDysRS; part III) between placebo and famotidine. Secondary outcomes were UDysRS (parts I and II), Global Impression of Change, Lang-Fahn Activities of Daily Living Dyskinesia Scale, Unified Parkinson's Disease Rating part III, and adverse events (AEs). Outcomes were evaluated pre- and post-treatment per dose and analyzed using a mixed-effects linear model. There was no significant effect of famotidine treatment on any of the primary or secondary outcome measures compared to placebo (each dose and all doses combined). There were no significant AEs. Even though the sample size of the current study is limited, famotidine seems to be safe in patients with PD and LID, but showed no potential as an antidyskinetic agent.

Distribution and morphological characteristics of striatal interneurons expressing calretinin in mice: a comparison with human and nonhuman primates

Striatal interneurons display a morphological and chemical heterogeneity that has been particularly well characterized in rats, monkeys and humans. By comparison much less is known of striatal interneurons in mice, although these animals are now widely used as transgenic models of various neurodegenerative diseases. The present immunohistochemical study aimed at characterizing striatal interneurons expressing calretinin (CR) in mice compared to those in squirrel monkeys and humans. The mouse striatum contains both small (9-12 μm) and medium-sized (15-20 μm) CR+ cells. The small cells are intensely stained with a single, slightly varicose and moderately arborized process. They occur throughout the striatum (77±9 cells/mm(3)), but prevail in the area of the subventricular zone and subcallosal streak, with statistically significant anteroposterior and dorsoventral decreasing gradients. The medium-sized cells are less intensely immunoreactive and possess 2-3 long, slightly varicose and poorly branched dendrites. They are rather uniformly scattered throughout the striatum and three times more numerous (224±31 cells/mm(3)) than the smaller CR+ cells. Double immunostaining experiments with choline acetyltransferase (ChAT) as a cholinergic marker in normal and Drd1a-tdTomato/Drd2-EGFP double transgenic mice reveal that none of the small or medium-sized CR+ cells express ChAT or D1 and D2 dopamine receptors. In contrast, the striatum in human and nonhuman primates harbors small and medium-sized CR+/ChAT- cells, as well as large CR+/ChAT+ interneurons that are absent in mice. Such a difference between rodents and primates must be taken into consideration if one hopes to better understand the striatal function in normal and pathological conditions.

Negative allosteric modulation of mGlu5 receptor rescues striatal D2 dopamine receptor dysfunction in rodent models of DYT1 dystonia

Early onset torsion dystonia (DYT1) is an autosomal dominantly inherited disorder caused by deletion in TOR1A gene. Evidence suggests that TOR1A mutation produces dystonia through an aberrant neuronal signalling within the striatum, where D2 dopamine receptors (D2R) produce an abnormal excitatory response in cholinergic interneurons (ChIs) in different models of DYT1 dystonia. The excitability of ChIs may be modulated by group I metabotropic glutamate receptor subtypes (mGlu1 and 5). We performed electrophysiological and calcium imaging recordings from ChIs of both knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) and transgenic mice overexpressing human torsinA (hMT1). We demonstrate that the novel negative allosteric modulator (NAM) of metabotropic glutamate 5 (mGlu) receptor, dipraglurant (ADX48621) counteracts the abnormal membrane responses and calcium rise induced either by the D2R agonist quinpirole or by caged dopamine (NPEC-Dopamine) in both models. These inhibitory effects were mimicked by two other well-characterized mGlu5 receptor antagonists, SIB1757 and MPEP, but not by mGlu1 antagonism. D2R and mGlu5 post-receptor signalling may converge on PI3K/Akt pathway. Interestingly, we found that the abnormal D2R response was prevented by the selective PI3K inhibitor, LY294002, whereas PLC and PKC inhibitors were both ineffective. Currently, no satisfactory pharmacological treatment is available for DYT1 dystonia patients. Our data show that negative modulation of mGlu5 receptors may counteract abnormal D2R responses, normalizing cholinergic cell excitability, by modulating the PI3K/Akt post-receptor pathway, thereby representing a novel potential treatment of DYT1 dystonia.

TRPC3 channel mediates excitation of striatal cholinergic interneurons

Striatal cholinergic interneurons exhibit tonic firing and more positive membrane potentials, however, the mechanism is unclear. In the present study, we found that intracellular perfusion of TRPC3 antibody induced outward current in striatal cholinergic interneurons identified by electrophysiological characteristics. The TRPC3 channel blocker flufenamic acid induced hyperpolarization, and reduced firing rate and outward current which was similar to the effect of TRPC3 channel antibody. Furthermore, by using single-cell RT-PCR we confirmed the co-existence of TRPC3 channel and D5 receptor mRNA in striatal cholinergic interneurons identified by electrophysiological characteristics and expression of choline acetyltransferase (Chat) mRNA. These results implied that the TRPC3 channel is involved in modulating the depolarization of cholinergic interneurons.

Striatal cholinergic cell ablation attenuates L-DOPA induced dyskinesia in Parkinsonian mice

3,4-Dihydroxyphenyl-L-alanine (L-DOPA)-induced dyskinesia (LID) is a debilitating side effect of long-term dopamine replacement therapy in Parkinson's Disease. At present, there are few therapeutic options for treatment of LID and mechanisms contributing to the development and maintenance of these drug-induced motor complications are not well understood. We have previously shown that pharmacological reduction of cholinergic tone attenuates the expression of LID in parkinsonian mice with established dyskinesia after chronic L-DOPA treatment. The present study was undertaken to provide anatomically specific evidence for the role of striatal cholinergic interneurons by ablating them before initiation of L-DOPA treatment and determining whether it decreases LID. We used a novel approach to ablate striatal cholinergic interneurons (ChIs) via Cre-dependent viral expression of the diphtheria toxin A subunit (DT-A) in hemiparkinsonian transgenic mice expressing Cre recombinase under control of the choline acetyltransferase promoter. We show that Cre recombinase-mediated DT-A ablation selectively eliminated ChIs when injected into striatum. The depletion of ChIs markedly attenuated LID without compromising the therapeutic efficacy of L-DOPA. These results provide evidence that ChIs play a key and selective role in LID and that strategies to reduce striatal cholinergic tone may represent a promising approach to decreasing L-DOPA-induced motor complications in Parkinson's disease.

Allosteric modulation of NMDA receptors alters neurotransmission in the striatum of a mouse model of Parkinson's disease

The GluN2 subunits that compose N-methyl-d-aspartate receptors (NMDARs) are attractive drug targets for therapeutic intervention in several diseases, in particular Parkinson's disease (PD). The precise roles and possible dysfunctions of NMDARs attributed to specific GluN2 subunits are however unresolved. Through the use of CIQ, a novel positive allosteric modulator of GluN2C/GluN2D-containing NMDARs, we have examined the functions and dysfunctions of NMDARs made of GluN2D in the striatum of control mice and of the 6-hydroxydopamine (6-OHDA)-lesioned mouse model of PD. We found that CIQ (20μM), applied to corticostriatal brain slices, increased the firing rate of spontaneously active cholinergic interneurons in the striatum of control mice and in the intact striatum of 6-OHDA-lesioned mice. CIQ also presynaptically depressed GABAergic neurotransmission through a cholinergic mechanism, but had no effect on glutamatergic neurotransmission, in medium spiny projection neurons (MSNs) of control and intact striatum. In the dopamine-depleted striatum, the effect of CIQ on the firing of cholinergic interneurons and GABAergic neurotransmission was lost. However, CIQ increased glutamatergic neurotransmission in MSNs. We also found that the protein levels of GluN2D were increased in the dopamine-depleted striatum as compared to the intact striatum. However, the contribution of GluN2D-containing NMDARs to whole-cell NMDA currents was reduced in cholinergic interneurons and increased in MSNs. These results demonstrate an impaired modulatory role of GluN2D-containing NMDARs on the activity of cholinergic interneurons and inhibitory transmission in the dopamine-depleted striatum. However, potentiation of excitatory neurotransmission occurs upon activation of these receptors. Thus, altered functions of GluN2D-containing NMDARs might contribute to adaptive changes in experimental Parkinsonism.

The potency and efficacy of anticholinergics to inhibit haloperidol-induced catalepsy in rats correlates with their rank order of affinities for the muscarinic receptor subtypes

Extrapyramidal syndromes (EPS) caused by antipsychotic therapy are currently treated with anticholinergics that lack selectivity for the five muscarinic receptor subtypes. Since these receptors are heterogeneously expressed among the different classes of striatal neurons and their afferents, it can be expected that their simultaneous blockade will cause distinct, sometimes opposed, effects within the striatal circuitry. In order to test the hypothesis that the differential blockade of the muscarinic receptor subtypes would influence their potency and efficacy to prevent EPS, here we tested four anticholinergics with varying order of affinities for the muscarinic receptor subtypes, and compared their dose-response curves to inhibit haloperidol-induced catalepsy in male rats. Drugs were applied into the lateral ventricle 15 min before haloperidol (2 mg/kg, s.c.). Catalepsy was measured in the bar test at 15 min intervals during 5 h. The preferential M1/M4 antagonist pirenzepine (3, 10, 30, 100, and 300 nmol) caused a dose-dependent inhibition of catalepsy intensity: ED50 = 5.6 nmol [95% CI, 3.9-8.1], and latency: ED50 = 5.6 nmol [95% CI, 3.7-8.6]. Pirenzepine had the steepest dose-response curve, producing maximal inhibition (84 ± 5%) at the dose of 10 nmol, while its effect tended to reverse at higher doses (62 ± 11%). The purported M1/M3 antagonist 4-DAMP (30, 100, and 300 nmol) also caused a dose-dependent inhibition of catalepsy intensity: ED50 = 29.5 nmol [95% CI, 7.0 to 123.0], and latency: ED50 = 28.5 nmol [95% CI, 2.2 to 362.0]. However, the curve for 4-DAMP had a less pronounced slope, reaching its maximal effect (63 ± 14%) at the dose of 300 nmol. The M2/M4 antagonist AF-DX 116 (10, 30, and 300 nmol) only caused a partial inhibition of catalepsy (30 ± 11%) at the dose of 30 nmol, but this changed to a non-significant increment (15 ± 10%) at the dose of 100 nmol. The alleged M4 antagonist tropicamide (30, 100, 300, and 600 nmol) produced a partial inhibition of catalepsy (36 ± 12%) at the dose of 300 nmol, but lacked effect at higher or lower doses. Concurrent treatment with pirenzepine (10 nmol) and tropicamide (300 nmol) produced an effect similar to that of tropicamide alone. The greater potency and efficacy of pirenzepine for catalepsy inhibition could be due to its higher affinity for M1 receptors and, to a lesser extent, for M4 receptors. It is suggested that selective M1 antagonists would be more effective than M2, M3 or M4 antagonists to prevent EPS caused by antipsychotic drugs.

GABAergic synaptic transmission onto striatal cholinergic interneurons in dopamine D2 receptor knock-out mice

Whole-cell or cell-attached analysis was carried out in dopamine (DA) D2 receptor (D2R) knock-out (KO) mice to elucidate the function of this receptor in the regulation of GABAergic synaptic transmission onto striatal cholinergic interneurons as well as their spontaneous firing. In slice preparation obtained from wild-type mice, evoked GABAergic inhibitory postsynaptic currents (IPSCs) showed frequency-dependent suppression, and this suppression significantly decreased in the presence of a D2-like receptor antagonist or in D2R KO mice. Contribution of N-type calcium channel was also significantly reduced in the striatal cholinergic interneurons of the D2R KO mice compared with that in the wild-type mice. Spontaneous firing of striatal cholinergic interneurons was inhibited by 5- or 10-Hz stimulation, and the suppression was decreased in the presence of a D2-like receptor antagonist or in D2R KO mice. These findings substantiate the physiological role of D2R in the regulation of GABAergic synaptic transmission onto striatal cholinergic interneurons as well as their excitability, confirming the tight coupling between D2R and N-type calcium channels in the regulation of GABA release.

Designing clinical trials for dystonia

With advances in the understanding of the pathophysiology of dystonia, novel therapeutics are being developed. Such therapies will require clinical investigation ranging from exploratory studies to examine safety, tolerability, dosage selection, and preliminary efficacy to confirmatory studies to evaluate efficacy definitively. As dystonia is a rare and complex disorder with clinical and etiological heterogeneity, clinical trials will require careful consideration of the trial design, including enrollment criteria, concomitant medication use, and outcome measures. Given the complexities of designing and implementing efficient clinical trials, it is important for clinicians and statisticians to collaborate closely throughout the clinical development process and that each has a basic understanding of both the clinical and statistical issues that must be addressed. To facilitate designing appropriate clinical trials in this field, we review important general clinical trial and regulatory principles, and discuss the critical components of trials with an emphasis on considerations specific to dystonia. Additionally, we discuss designs used in early exploratory, late exploratory, and confirmatory phases, including adaptive designs.

Mouse models of neurodevelopmental disease of the basal ganglia and associated circuits

This chapter focuses on neurodevelopmental diseases that are tightly linked to abnormal function of the striatum and connected structures. We begin with an overview of three representative diseases in which striatal dysfunction plays a key role--Tourette syndrome and obsessive-compulsive disorder, Rett's syndrome, and primary dystonia. These diseases highlight distinct etiologies that disrupt striatal integrity and function during development, and showcase the varied clinical manifestations of striatal dysfunction. We then review striatal organization and function, including evidence for striatal roles in online motor control/action selection, reinforcement learning, habit formation, and action sequencing. A key barrier to progress has been the relative lack of animal models of these diseases, though recently there has been considerable progress. We review these efforts, including their relative merits providing insight into disease pathogenesis, disease symptomatology, and basal ganglia function.

Ranitidine reduced levodopa-induced dyskinesia in a rat model of Parkinson's disease

BACKGROUND

Chronic administration of levodopa in Parkinson's disease leads to debilitating involuntary movements, termed levodopa-induced dyskinesia (LID). The pathogenesis of LID is poorly understood. Previous research has shown that histamine H2 receptors are highly expressed in the input (striatum) and output (globus pallidus, substantia nigra) regions of the basal ganglia, particularly in the GABAergic striatopallidal and striatonigral pathways. Therefore, a histamine H2 receptor antagonist could be used to reduce LID. In the present work, we investigated whether ranitidine has the potential to diminish LID in rats with dyskinesia and explored the underlying mechanisms involved.

METHODS

A rat model of PD was induced by 6-hydroxydopamine. Valid PD rats were then treated with levodopa (25 mg/kg, intraperitoneally) and benserazide (12.5 mg/kg, intraperitoneally) for 21 days to induce a rat model of LID. The acute and chronic effects of administration of ranitidine at different doses (5 mg/kg, 10 mg/kg, and 20 mg/kg) on abnormal involuntary movements, levodopa-induced rotations, and the forelimb adjusting steps test were investigated in LID rats. The chronic effect of ranitidine (10 mg/kg) on the expression of Arc and proenkephalin was also evaluated.

RESULTS

Levodopa elicited increased dyskinesia in PD rats. Acute ranitidine treatment had no effect on LID, but chronic ranitidine administration (10 mg/kg, 20 mg/kg) reduced LID in rats with dyskinesia. Importantly, levodopa-induced rotations were not affected by chronic treatment with ranitidine. In addition, chronic ranitidine (10 mg/kg, 20 mg/kg) significantly improved stepping of the lesioned forepaw. Real-time polymerase chain reaction showed that Arc and proenkephalin levels were reduced by chronic ranitidine (10 mg/kg) in dyskinetic rats.

CONCLUSION

These data indicate that ranitidine is a good adjunct for reducing LID in rats with dyskinesia. Inhibition of dopamine D1-mediated activation in the medium spiny neurons may account for the antidyskinetic effects of ranitidine in rats with dyskinesia.

Development of allosteric modulators of GPCRs for treatment of CNS disorders

The discovery of allosteric modulators of G protein-coupled receptors (GPCRs) provides a promising new strategy with potential for developing novel treatments for a variety of central nervous system (CNS) disorders. Traditional drug discovery efforts targeting GPCRs have focused on developing ligands for orthosteric sites which bind endogenous ligands. Allosteric modulators target a site separate from the orthosteric site to modulate receptor function. These allosteric agents can either potentiate (positive allosteric modulator, PAM) or inhibit (negative allosteric modulator, NAM) the receptor response and often provide much greater subtype selectivity than orthosteric ligands for the same receptors. Experimental evidence has revealed more nuanced pharmacological modes of action of allosteric modulators, with some PAMs showing allosteric agonism in combination with positive allosteric modulation in response to endogenous ligand (ago-potentiators) as well as "bitopic" ligands that interact with both the allosteric and orthosteric sites. Drugs targeting the allosteric site allow for increased drug selectivity and potentially decreased adverse side effects. Promising evidence has demonstrated potential utility of a number of allosteric modulators of GPCRs in multiple CNS disorders, including neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, as well as psychiatric or neurobehavioral diseases such as anxiety, schizophrenia, and addiction.

Dystonia as a network disorder: what is the role of the cerebellum?

The dystonias are a group of disorders defined by sustained or intermittent muscle contractions that result in involuntary posturing or repetitive movements. There are many different clinical manifestations and causes. Although they traditionally have been ascribed to dysfunction of the basal ganglia, recent evidence has suggested dysfunction may originate from other regions, particularly the cerebellum. This recent evidence has led to an emerging view that dystonia is a network disorder that involves multiple brain regions. The new network model for the pathogenesis of dystonia has raised many questions, particularly regarding the role of the cerebellum. For example, if dystonia may arise from cerebellar dysfunction, then why are there no cerebellar signs in dystonia? Why are focal cerebellar lesions or degenerative cerebellar disorders more commonly associated with ataxia rather than dystonia? Why is dystonia more commonly associated with basal ganglia lesions rather than cerebellar lesions? Can answers obtained from animals be extrapolated to humans? Is there any evidence that the cerebellum is not involved? Finally, what is the practical value of this new model of pathogenesis for the neuroscientist and clinician? This article explores potential answers to these questions.

Minimal Change in the cytoplasmic calcium dynamics in striatal GABAergic neurons of a DYT1 dystonia knock-in mouse model

DYT1 dystonia is the most common hereditary form of primary torsion dystonia. This autosomal-dominant disorder is characterized by involuntary muscle contractions that cause sustained twisting and repetitive movements. It is caused by an in-frame deletion in the TOR1A gene, leading to the deletion of a glutamic acid residue in the torsinA protein. Heterozygous knock-in mice, which reproduce the genetic mutation in human patients, have abnormalities in synaptic transmission at the principal GABAergic neurons in the striatum, a brain structure that is involved in the execution and modulation of motor activity. However, whether this mutation affects the excitability of striatal GABAergic neurons has not been investigated in this animal model. Here, we examined the excitability of cultured striatal neurons obtained from heterozygous knock-in mice, using calcium imaging as indirect readout. Immunofluorescence revealed that more than 97% of these neurons are positive for a marker of GABAergic neurons, and that more than 92% are also positive for a marker of medium spiny neurons, indicating that these are mixed cultures of mostly medium spiny neurons and a few (~5%) GABAergic interneurons. When these neurons were depolarized by field stimulation, the calcium concentration in the dendrites increased rapidly and then decayed slowly. The amplitudes of calcium transients were larger in heterozygous neurons than in wild-type neurons, resulting in ~15% increase in cumulative calcium transients during a train of stimuli. However, there was no change in other parameters of calcium dynamics. Given that calcium dynamics reflect neuronal excitability, these results suggest that the mutation only slightly increases the excitability of striatal GABAergic neurons in DYT1 dystonia.

Spectral evolution of a photochemical protecting group for orthogonal two-color uncaging with visible light

Caged compounds are molecules rendered functionally inert by derivatization with a photochemical protecting group. We describe the design logic behind the development of a diethylaminocoumarin (DEAC) caging chromophore, DEAC450, that absorbs blue light strongly (ε450 = 43,000 M(-1) cm(-1)) and violet light 11-fold more weakly. The absorption minimum is in the wavelength range (340-360 nm) that is traditionally used for photolysis of many widely used nitroaromatic caged compounds (e.g., 4-carboxymethoxy-5,7-dinitroindolinyl(CDNI)-GABA). We used this chromophore to synthesize DEAC450-caged cAMP and found this probe was very stable toward aqueous hydrolysis in the electronic ground state but was photolyzed with a quantum efficiency of 0.78. When DEAC450-cAMP and CDNI-GABA where co-applied to striatal cholinergic interneurons, the caged compounds were photolyzed in an chromatically orthogonal manner using blue and violet light so as to modulate the neuronal firing rate in a bidirectional way.

Glycogen synthase kinase-3 reduces acetylcholine level in striatum via disturbing cellular distribution of choline acetyltransferase in cholinergic interneurons in rats

Cholinergic interneurons, which provide the main source of acetylcholine (ACh) in the striatum, control the striatal local circuits and deeply involve in the pathogenesis of neurodegenerative diseases. Glycogen synthase kinase-3 (GSK-3) is a crucial kinase with diverse fundamental functions and accepted that deregulation of GSK-3 activity also plays important roles in diverse neurodegenerative diseases. However, up to now, there is no direct proof indicating whether GSK-3 activation is responsible for cholinergic dysfunction. In the present study, with combined intracerebroventricular injection of Wortmannin and GF-109203X, we activated GSK-3 and demonstrated the increased phosphorylation level of microtubule-associated protein tau and neurofilaments (NFs) in the rat striatum. The activated GSK-3 consequently decreased ACh level in the striatum as a result of the reduction of choline acetyltransferase (ChAT) activity. The alteration of ChAT activity was due to impaired ChAT distribution rather than its expression. Furthermore, we proved that cellular ChAT distribution was dependent on low phosphorylation level of NFs. Nevertheless, the cholinergic dysfunction in the striatum failed to induce significant neuronal number reduction. In summary, our data demonstrates the link between GSK-3 activation and cholinergic dysfunction in the striatum and provided beneficial evidence for the pathogenesis study of relevant neurodegenerative diseases.

Different correlation patterns of cholinergic and GABAergic interneurons with striatal projection neurons

The striatum is populated by a single projection neuron group, the medium spiny neurons (MSNs), and several groups of interneurons. Two of the electrophysiologically well-characterized striatal interneuron groups are the tonically active neurons (TANs), which are presumably cholinergic interneurons, and the fast spiking interneurons (FSIs), presumably parvalbumin (PV) expressing GABAergic interneurons. To better understand striatal processing it is thus crucial to define the functional relationship between MSNs and these interneurons in the awake and behaving animal. We used multiple electrodes and standard physiological methods to simultaneously record MSN spiking activity and the activity of TANs or FSIs from monkeys engaged in a classical conditioning paradigm. All three cell populations were highly responsive to the behavioral task. However, they displayed different average response profiles and a different degree of response synchronization (signal correlation). TANs displayed the most transient and synchronized response, MSNs the most diverse and sustained response and FSIs were in between on both parameters. We did not find evidence for direct monosynaptic connectivity between the MSNs and either the TANs or the FSIs. However, while the cross correlation histograms of TAN to MSN pairs were flat, those of FSI to MSN displayed positive asymmetrical broad peaks. The FSI-MSN correlogram profile implies that the spikes of MSNs follow those of FSIs and both are driven by a common, most likely cortical, input. Thus, the two populations of striatal interneurons are probably driven by different afferents and play complementary functional roles in the physiology of the striatal microcircuit.

GABAergic inputs from direct and indirect striatal projection neurons onto cholinergic interneurons in the primate putamen

Striatal cholinergic interneurons (ChIs) are involved in reward-dependent learning and the regulation of attention. The activity of these neurons is modulated by intrinsic and extrinsic γ-aminobutyric acid (GABA)ergic and glutamatergic afferents, but the source and relative prevalence of these diverse regulatory inputs remain to be characterized. To address this issue, we performed a quantitative ultrastructural analysis of the GABAergic and glutamatergic innervation of ChIs in the postcommissural putamen of rhesus monkeys. Postembedding immunogold localization of GABA combined with peroxidase immunostaining for choline acetyltransferase showed that 60% of all synaptic inputs to ChIs originate from GABAergic terminals, whereas 21% are from putatively glutamatergic terminals that establish asymmetric synapses, and 19% from other (non-GABAergic) sources of symmetric synapses. Double pre-embedding immunoelectron microscopy using substance P and Met-/Leu-enkephalin antibodies to label GABAergic terminals from collaterals of "direct" and "indirect" striatal projection neurons, respectively, revealed that 47% of the indirect pathway terminals and 36% of the direct pathway terminals target ChIs. Together, substance P- and enkephalin-positive terminals represent 24% of all synapses onto ChIs in the monkey putamen. These findings show that ChIs receive prominent GABAergic inputs from multiple origins, including a significant contingent from axon collaterals of direct and indirect pathway projection neurons.

Powerful inhibitory action of mu opioid receptors (MOR) on cholinergic interneuron excitability in the dorsal striatum

Cholinergic interneurons (ChIs) of dorsal striatum play a key role in motor control and in behavioural learning. Neuropeptides regulate cholinergic transmission and mu opioid receptor (MOR) activation modulates striatal acetylcholine release. However, the mechanisms underlying this effect are yet uncharacterized. Here, we examined the electrophysiological responses of ChIs to the selective MOR agonist, DAMGO {[D-Ala2-MePhe4-Gly(ol)5] enkephalin}. We observed a robust, dose-dependent inhibition of spontaneous firing activity (0.06-3 μM) which was reversible upon drug washout and blocked by the selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) (1 μM). Voltage-clamp analysis of the reversal potential of the DAMGO effect did not provide univocal results, indicating the involvement of multiple membrane conductances. The MOR-dependent effect persisted in the presence of GABAA and ionotropic glutamate receptor antagonists, ruling out an indirect effect. Additionally, it depended upon G-protein activation, as it was prevented by intrapipette GDP-β-S. Because D2 dopamine receptors (D2R) and MOR share a common post-receptor signalling pathway, occlusion experiments were performed with maximal doses of both D2R and MOR agonists. The D2R agonist quinpirole decreased spike discharge, which was further reduced by adding DAMGO. Then, D2R or MOR antagonists were used to challenge the response to the respective agonists, DAMGO or quinpirole. No cross-effect was observed, suggesting that the two receptors act independently. Our findings demonstrate a postsynaptic inhibitory modulation by MOR on ChIs excitability. Such opioidergic regulation of cholinergic transmission might contribute to shape information processing in basal ganglia circuits, and represent a potential target for pharmacological intervention.

Subtle microstructural changes of the striatum in a DYT1 knock-in mouse model of dystonia

The dystonias are comprised of a group of disorders that share common neurological abnormalities of involuntary twisting or repetitive movements and postures. The most common inherited primary dystonia is DYT1 dystonia, which is due to loss of a GAG codon in the TOR1A gene that encodes torsinA. Autopsy studies of brains from patients with DYT1 dystonia have revealed few abnormalities, although recent neuroimaging studies have implied the existence of microstructural defects that might not be detectable with traditional histopathological methods. The current studies took advantage of a knock-in mouse model for DYT1 dystonia to search for subtle anatomical abnormalities in the striatum, a region often implicated in studies of dystonia. Multiple abnormalities were identified using a combination of quantitative stereological measures of immunohistochemical stains for specific neuronal populations, morphometric studies of Golgi-stained neurons, and immuno-electron microscopy of synaptic connectivity. In keeping with other studies, there was no obvious loss of striatal neurons in the DYT1 mutant mice. However, interneurons immunoreactive for choline acetyltransferase or parvalbumin were larger in the mutants than in control mice. In contrast, interneurons immunoreactive for neuronal nitric oxide synthase were smaller in the mutants than in controls. Golgi histochemical studies of medium spiny projection neurons in the mutant mice revealed slightly fewer and thinner dendrites, and a corresponding loss of dendritic spines. Electron microscopic studies showed a reduction in the ratio of axo-spinous to axo-dendritic synaptic inputs from glutamatergic and dopaminergic sources in mutant mice compared with controls. These results suggest specific anatomical substrates for altered signaling in the striatum and potential correlates of the abnormalities implied by human imaging studies of DYT1 dystonia.

Response of striosomal opioid signaling to dopamine depletion in 6-hydroxydopamine-lesioned rat model of Parkinson's disease: a potential compensatory role

The opioid peptide receptors consist of three major subclasses, namely, μ, δ, and κ (MOR, DOR, and KOR, respectively). They are involved in the regulation of striatal dopamine functions, and increased opioid transmissions are thought to play a compensatory role in altered functions of the basal ganglia in Parkinson's disease (PD). In this study, we used an immunohistochemistry with tyramide signal amplification (TSA) protocols to determine the distributional patterns of opioid receptors in the striosome-matrix systems of the rat striatum. As a most striking feature of striatal opioid anatomy, MORs are highly enriched in the striosomes and subcallosal streak. We also found that DORs are localized in a mosaic pattern in the dorsal striatum (caudate-putamen), with heightened labeling for DOR in the striosomes relative to the matrix compartment. In the 6-hydroxydopamine-lesioned rat model of PD, lesions of the nigrostriatal pathways caused a significant reduction of striatal labeling for both the MOR and DOR in the striosomes, but not in the matrix compartment. Our results suggest that the activities of the striosome and matrix compartments are differentially regulated by the opioid signals involving the MORs and DORs, and that the striosomes may be more responsive to opioid peptides (e.g., enkephalin) than the matrix compartment. Based on a model in which the striosome compartment regulates the striatal activity, we propose a potent compensatory role of striosomal opioid signaling under the conditions of the striatal dopamine depletion that occurs in PD.

Epigenetic regulation of cholinergic receptor M1 (CHRM1) by histone H3K9me3 impairs Ca(2+) signaling in Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by an expanded trinucleotide CAG repeat in the gene coding for huntingtin. Deregulation of chromatin remodeling is linked to the pathogenesis of HD but the mechanism remains elusive. To identify what genes are deregulated by trimethylated histone H3K9 (H3K9me3)-dependent heterochromatin, we performed H3K9me3-ChIP genome-wide sequencing combined with RNA sequencing followed by platform integration analysis in stable striatal HD cell lines (STHdhQ7/7 and STHdhQ111/111) cells. We found that genes involving neuronal synaptic transmission including cholinergic receptor M1 (CHRM1), cell motility, and neuronal differentiation pathways are downregulated while their promoter regions are highly occupied with H3K9me3 in HD. Moreover, we found that repression of CHRM1 gene expression by H3K9me3 impairs Ca(2+)-dependent neuronal signal transduction in stable cell lines expressing mutant HD protein. Thus, our data indicate that the epigenetic modifications, such as aberrant H3K9me3-dependent heterochromatin plasticity, directly contribute to the pathogenesis of HD.

Nucleus accumbens neurotransmission and effort-related choice behavior in food motivation: effects of drugs acting on dopamine, adenosine, and muscarinic acetylcholine receptors

Mesolimbic dopamine (DA) is a critical component of the brain circuitry regulating behavioral activation and effort-related processes. Although nucleus accumbens (NAc) DA depletions or antagonism leave aspects of appetite and primary food motivation intact, rats with impaired DA transmission reallocate their instrumental behavior away from food-reinforced tasks with high response requirements, and instead select less effortful food-seeking behaviors. Previous work showed that adenosine A2A antagonists can reverse the effects of DA D2 antagonists on effort-related choice, and that stimulation of adenosine A2A receptors produces behavioral effects that are similar to those induced by DA antagonism. The present review summarizes the literature on the role of NAc DA and adenosine in effort-related processes, and also presents original data on the effects of local stimulation of muscarinic acetylcholine receptors in NAc core. Local injections of the muscarinic agonist pilocarpine directly into NAc core produces shifts in effort-related choice behavior similar to those induced by DA antagonism or A2A receptor stimulation, decreasing lever pressing but increasing chow intake in rats responding on a concurrent fixed ratio/chow feeding choice task. In contrast, injections into a neostriatal control site dorsal to the NAc were ineffective. The actions of pilocarpine on this task were attenuated by co-administration of the muscarinic antagonist scopolamine. Thus, drugs that act on DA, adenosine A2A, and muscarinic receptors regulate effort-related choice behavior, which may have implications for the treatment of psychiatric symptoms such as psychomotor slowing, fatigue or anergia that can be observed in depression and other disorders.

Behavioral and structural effects of unilateral intrastriatal injections of botulinum neurotoxin a in the rat model of Parkinson's disease

Botulinum neurotoxin (BoNT) inhibits the release of acetylcholine from presynaptic vesicles through its proteinase activity cleaving the SNARE complex. Parkinson's disease (PD) is associated with locally increased cholinergic activity in the striatum. Therefore, the present study investigates the effect of unilateral intrastriatal BoNT-A injection in naïve rats on striatal morphology; i.e., the total number of Nissl-stained neurons and the volume of caudate-putamen (CPu) were estimated. Furthermore, stainings for markers of gliosis (glial fibrillary acidic protein) and microglia (Iba1) were performed. In addition, the potential beneficial effects of a unilateral intrastriatal injection of BoNT-A on motor activity in the rat model of hemi-PD were evaluated. Hemi-PD was induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle. Six weeks later, rats received an ipsilateral intrastriatal injection of BoNT-A. Behaviorally, motor performance was tested. The total number of CPu neurons and the striatal volume were not significantly different between the BoNT-A-injected right and the intact left hemispheres of naïve rats. In hemi-PD rats, intrastriatal BoNT-A abolished apomorphine-induced rotations, increased amphetamine-induced rotations, and tended to improve left forelimb usage. Forced motor function in the accelerod test was not significantly changed by BoNT-A, and open field activity was also unaltered compared with sham treatment. Thus, intrastriatal BoNT-A affects spontaneous motor activity of hemi-PD rats to a minor degree compared with drug-induced motor function. In the future, tests assessing the cognitive and emotional performance should be performed to ascertain finally the potential therapeutic usefulness of intrastriatal BoNT-A for PD.

Target selectivity of feedforward inhibition by striatal fast-spiking interneurons

The striatal microcircuitry consists of a vast majority of projection neurons, the medium spiny neurons (MSNs), and a small yet diverse population of interneurons. To understand how activity is orchestrated within the striatum, it is essential to unravel the functional connectivity between the different neuronal types. Fast-spiking (FS) interneurons provide feedforward inhibition to both direct and indirect pathway MSNs and are important in sculpting their output to downstream basal ganglia nuclei. FS interneurons are also interconnected with each other via electrical and chemical synapses; however, whether and how they inhibit other striatal interneuron types remains unknown. In this study we combined multineuron whole-cell recordings with optogenetics to determine the target selectivity of feedforward inhibition by striatal FS interneurons. Using transgenic and viral approaches we directed expression of channelrhodopsin 2 (ChR2) to FS interneurons to study their connectivity within the mouse striatal microcircuit. Optogenetic stimulation of ChR2-expressing FS interneurons generated strong and reliable GABA(A)-dependent synaptic inputs in MSNs. In sharp contrast, simultaneously recorded neighboring cholinergic interneurons did not receive any synaptic inputs from photostimulated FS cells, and a minority of low-threshold spiking (LTS) interneurons responded weakly. We further tested the synaptic connectivity between FS and LTS interneurons using paired recordings, which showed only sparse connectivity. Our results show that striatal FS interneurons form a feedforward inhibitory circuit that is target selective, inhibiting projection neurons while avoiding cholinergic interneurons and sparsely contacting LTS interneurons, thus supporting independent modulation of MSN activity by the different types of striatal interneurons.

Prevention of haloperidol-induced alterations in brain acetylcholinesterase activity by vitamins B co-administration in a rodent model of tardive dyskinesia

Tardive dyskinesia (TD) is an iatrogenic syndrome being a significant adverse outcome of typical and atypical antipsychotic therapy. Recently we demonstrated that vitamins B (B1, B6, B12 alone or in combination) were able to prevent haloperidol-induced orofacial dyskinesia (OD) possibly by their antioxidant activity in the striatum, using a well-established model of TD. Here, based on the fact that alterations in cholinergic neurotransmission are related to TD pathophysiology and that vitamins B seems to influence brain cholinergic neurotransmission, we decided to investigate the effects of vitamins B1, B6, B12 and their association, vitamin B cocktail in haloperidol-induced cholinergic alterations, evaluated by alterations in acetylcholinesterase (AChE) activity, in striatum, prefrontal cortex and hippocampus, as a way to determine the participation of cholinergic neurotransmission, in these vitamins antidyskinetic mechanism. Haloperidol 1 mg/kg i.p. daily administration during 21 days to Wistar rats caused OD while decreased AChE activity in all brain areas studied. Vitamins B administration (B1:B6:B12 at 60:60:0.6 mg/kg, s.c) alone and vitamin B cocktail co-administered with haloperidol prevented OD development and increased AChE activity in all brain areas studied, with the maximum activity increment observed in the hippocampus of the animals co-treated with vitamin B12 and vitamin B cocktail. The antidyskinetic drug, clozapine did not induce OD and increased AChE activity similarly to the groups coadministered with vitamin B and HAL. The present data suggest that vitamins B can prevent haloperidol-induced alterations in AChE activity what can be related to the mechanism underlying their antidyskinetic effect.

Mice with selective elimination of striatal acetylcholine release are lean, show altered energy homeostasis and changed sleep/wake cycle

Cholinergic neurons are known to regulate striatal circuits; however, striatal-dependent physiological outcomes influenced by acetylcholine (ACh) are still poorly under;?>stood. Here, we used vesicular acetylcholine transporter (VAChT)(D2-Cre-flox/flox) mice, in which we selectively ablated the vesicular acetylcholine transporter in the striatum to dissect the specific roles of striatal ACh in metabolic homeostasis. We report that VAChT(D) (2-Cre-flox/flox) mice are lean at a young age and maintain this lean phenotype with time. The reduced body weight observed in these mutant mice is not attributable to reduced food intake or to a decrease in growth rate. In addition, changed activity could not completely explain the lean phenotype, as only young VAChT(D) (2-Cre-flox/flox) mice showed increased physical activity. Interestingly, VAChT(D) (2-Cre-flox/flox) mice show several metabolic changes, including increased plasma levels of insulin and leptin. They also show increased periods of wakefulness when compared with littermate controls. Taken together, our data suggest that striatal ACh has an important role in the modulation of metabolism and highlight the importance of striatum cholinergic tone in the regulation of energy expenditure. These new insights on how cholinergic neurons influence homeostasis open new avenues for the search of drug targets to treat obesity.

Therapeutic Strategies for Huntington's Disease

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease, caused by expansion of the CAG repeat in the huntingtin (HTT) gene and characterized pathologically by the loss of pyramidal neurons in several cortical areas, of striatal medium spiny neurons, and of hypothalamic neurons. Clinically, a distinguishing feature of the disease is uncontrolled involuntary movements (chorea, dyskensias) accompanied by progressive cognitive, motor, and psychiatric impairment. This review focuses on the current state of therapeutic development for the treatment of HD, including the preclinical and clinical development of small molecules and molecular therapies.

Chemical modification of the M(1) agonist VU0364572 reveals molecular switches in pharmacology and a bitopic binding mode

We previously reported the discovery of VU0364572 and VU0357017 as M(1)-selective agonists that appear to activate M(1) through actions at an allosteric site. Previous studies have revealed that chemical scaffolds for many allosteric modulators contain molecular switches that allow discovery of allosteric antagonists and allosteric agonists or positive allosteric modulators (PAMs) based on a single chemical scaffold. Based on this, we initiated a series of studies to develop selective M(1) allosteric antagonists based on the VU0364572 scaffold. Interestingly, two lead antagonists identified in this series, VU0409774 and VU0409775, inhibited ACh-induced Ca(2+) responses at rat M(1-5) receptor subtypes, suggesting they are nonselective muscarinic antagonists. VU0409774 and VU0409775 also completely displaced binding of the nonselective radioligand [(3)H]-NMS at M(1) and M(3) mAChRs with affinities similar to their functional IC(50) values. Finally, Schild analysis revealed that these compounds inhibit M(1) responses through a fully competitive interaction at the orthosteric binding site. This surprising finding prompted further studies to determine whether agonist activity of VU0364572 and VU0357017 may also engage in previously unappreciated actions at the orthosteric site on M(1). Surprisingly, both VU0364572 and VU0357017 completely displaced [(3)H]-NMS binding to the orthosteric site of M(1)-M(5) receptors at high concentrations. Furthermore, evaluation of agonist activity in systems with varying levels of receptor reserve and Furchgott analysis using a cell line expressing M(1) under control of an inducible promotor was consistent with an action of these compounds as weak orthosteric partial agonists of M(1). However, consistent with previous studies suggesting actions at a site that is distinct from the orthosteric binding site, VU0364572 or VU0357017 slowed the rate of [(3)H]-NMS dissociation from CHO-rM(1) membranes. Together, these results suggest that VU0364572 and VU0357017 act as bitopic ligands and that novel antagonists in this series act as competitive orthosteric site antagonists.

Targeting selective activation of M(1) for the treatment of Alzheimer's disease: further chemical optimization and pharmacological characterization of the M(1) positive allosteric modulator ML169

The M(1) muscarinic acetylcholine receptor is thought to play an important role in memory and cognition, making it a potential target for the treatment of Alzheimer's disease (AD) and schizophrenia. Moreover, M(1) interacts with BACE1 and regulates its proteosomal degradation, suggesting selective M(1) activation could afford both palliative cognitive benefit as well as disease modification in AD. A key challenge in targeting the muscarinic acetylcholine receptors is achieving mAChR subtype selectivity. Our lab has previously reported the M(1) selective positive allosteric modulator ML169. Herein we describe our efforts to further optimize this lead compound by preparing analogue libraries and probing novel scaffolds. We were able to identify several analogues that possessed submicromolar potency, with our best example displaying an EC(50) of 310 nM. The new compounds maintained complete selectivity for the M(1) receptor over the other subtypes (M(2)-M(5)), displayed improved DMPK profiles, and potentiated the carbachol (CCh)-induced excitation in striatal MSNs. Selected analogues were able to potentiate CCh-mediated nonamyloidogenic APPsα release, further strengthening the concept that M(1) PAMs may afford a disease-modifying role in the treatment of AD.