Repeated exposure to methamphetamine causes long-lasting presynaptic corticostriatal depression that is renormalized with drug readministration

Amphetamine-induced sensitization has little effect on multiple learning paradigms and fails to rescue mice with a striatal learning defect

Behavioral sensitization to psychostimulants such as amphetamine (AMPH) is associated with synaptic modifications that are thought to underlie learning and memory. Because AMPH enhances extracellular dopamine in the striatum where dopamine and glutamate signaling are essential for learning, one might expect that the molecular and morphological changes that occur in the striatum in response to AMPH, including changes in synaptic plasticity, would affect learning. To ascertain whether AMPH sensitization affects learning, we tested wild-type mice and mice lacking NMDA receptor signaling in striatal medium spiny neurons in several different learning tests (motor learning, Pavlovian association, U-maze escape test with strategy shifting) with or without prior sensitization to AMPH. Prior sensitization had minimal effect on learning in any of these paradigms in wild-type mice and failed to restore learning in mutant mice, despite the fact that the mutant mice became sensitized by the AMPH treatment. We conclude that the changes in synaptic plasticity and many other signaling events that occur in response to AMPH sensitization are dissociable from those involved in learning the tasks used in our experiments.

Overinhibition of corticostriatal activity following prenatal cocaine exposure

OBJECTIVE

Prenatal cocaine exposure (PCE) can cause persistent neuropsychological and motor abnormalities in affected children, but the physiological consequences of PCE remain unclear. Conclusions drawn from clinical studies can sometimes be confounded by polysubstance abuse and nutritional deprivation. However, existing observations suggest that cocaine exposure in utero, as in adults, increases synaptic dopamine and promotes enduring dopamine-dependent plasticity at striatal synapses, altering behaviors and basal ganglia function.

METHODS

We used a combination of behavioral measures, electrophysiology, optical imaging, and biochemical and electrochemical recordings to examine corticostriatal activity in adolescent mice exposed to cocaine in utero.

RESULTS

We show that PCE caused abnormal dopamine-dependent behaviors, including heightened excitation following stress and blunted locomotor augmentation after repeated treatment with amphetamine. These abnormal behaviors were consistent with abnormal γ-aminobutyric acid (GABA) interneuron function, which promoted a reversible depression in corticostriatal activity. PCE hyperpolarized and reduced tonic GABA currents in both fast-spiking and persistent low-threshold spiking type GABA interneurons to increase tonic inhibition at GABAB receptors on presynaptic corticostriatal terminals. Although D2 receptors paradoxically increased glutamate release following PCE, normal corticostriatal modulation by dopamine was reestablished with a GABAA receptor antagonist.

INTERPRETATION

The dynamic alterations at corticostriatal synapses that occur in response to PCE parallel the reported effects of repeated psychostimulants in mature animals, but differ in being specifically generated through GABAergic mechanisms. Our results indicate approaches that normalize GABA and D2 receptor-dependent synaptic plasticity may be useful for treating the behavioral effects of PCE and other developmental disorders that are generated through abnormal GABAergic signaling.

Regulation of prefrontal excitatory neurotransmission by dopamine in the nucleus accumbens core

Interactions between dopamine and glutamate signalling within the nucleus accumbens core are required for behavioural reinforcement and habit formation. Dopamine modulates excitatory glutamatergic signals from the prefrontal cortex, but the precise mechanism has not been identified. We combined optical and electrophysiology recordings in murine slice preparations from CB1 receptor-null mice and green fluorescent protein hemizygotic bacterial artificial chromosome transgenic mice to show how dopamine regulates glutamatergic synapses specific to the striatonigral and striatopallidal basal ganglia pathways. At low cortical frequencies, dopamine D1 receptors promote glutamate release to both D1 and D2 receptor-expressing medium spiny neurons while D2 receptors specifically inhibit excitatory inputs to D2 receptor-expressing cells by decreasing exocytosis from cortical terminals with a low probability of release. At higher cortical stimulation frequencies, this dopaminergic modulation of presynaptic activity is occluded by adenosine and endocannabinoids. Glutamatergic inputs to both D1 and D2 receptor-bearing medium spiny neurons are inhibited by adenosine, released upon activation of NMDA and AMPA receptors and adenylyl cyclase in D1 receptor-expressing cells. Excitatory inputs to D2 receptor-expressing cells are specifically inhibited by endocannabinoids, whose release is dependent on D2 and group 1 metabotropic glutamate receptors. The convergence of excitatory and inhibitory modulation of corticoaccumbal activity by dopamine, adenosine and endocannabinoids creates subsets of corticoaccumbal inputs, selectively and temporally reinforces strong cortical signals through the striatonigral pathway while inhibiting the weak, and may provide a mechanism whereby continued attention might be focused on behaviourally salient information.

Circadian modulation of osmoregulated firing in rat supraoptic nucleus neurones

The antidiuretic hormone vasopressin (VP) promotes water reabsorption from the kidney and levels of circulating VP are normally related linearly to plasma osmolality, aiming to maintain the latter close to a predetermined set point. Interestingly, VP levels rise also in the absence of an increase in osmolality during late sleep in various mammals, including rats and humans. This circadian rhythm is functionally important because the absence of a late night VP surge results in polyuria and disrupts sleep in humans. Previous work has indicated that the VP surge may be caused by facilitation of the central processes mediating the osmotic control of VP release, and the mechanism by which this occurs was recently studied in angled slices of rat hypothalamus that preserve intact network interactions between the suprachiasmatic nucleus (SCN; the biological clock), the organum vasculosum lamina terminalis (OVLT; the central osmosensory nucleus) and the supraoptic nucleus (SON; which contains VP-releasing neurohypophysial neurones). These studies confirmed that the electrical activity of SCN clock neurones is higher during the middle sleep period (MSP) than during the late sleep period (LSP). Moreover, they revealed that the excitation of SON neurones caused by hyperosmotic stimulation of the OVLT was greater during the LSP than during the MSP. Activation of clock neurones by repetitive electrical stimulation, or by injection of glutamate into the SCN, caused a presynaptic inhibition of glutamatergic synapses made between the axon terminals of OVLT neurones and SON neurones. Consistent with this effect, activation of clock neurones with glutamate also reduced the excitation of SON neurones caused by hyperosmotic stimulation of the OVLT. These results suggest that clock neurones in the SCN can mediate an increase in VP release through a disinhibition of excitatory synapses between the OVLT and the SON during the LSP.

Major depression among methamphetamine users entering drug treatment programs

OBJECTIVE

To determine the prevalence of major depression among people entering treatment for methamphetamine use.

DESIGN, SETTING AND PARTICIPANTS

The study was a cross-sectional survey involving 41 specialised drug and alcohol treatment agencies in Brisbane and Sydney. Services provided by these agencies included residential rehabilitation, detoxification and counselling. Participants were 400 people entering treatment for methamphetamine use who were recruited from participating treatment agencies between January 2006 and November 2007. Participants underwent a structured, face-to-face, 1.5-hour interview. Assessment instruments included the Composite International Diagnostic Interview and the Short Form 12.

MAIN OUTCOME MEASURE

Diagnosis of a major depressive episode in the year prior to the study.

RESULTS

The prevalence of major depression in the year prior to the study was 40% (95% CI, 35%-44%). A noteworthy post-hoc observation was that a further 44% of participants met the symptom criteria for major depression but were excluded from a diagnosis because their symptoms were better accounted for by psychoactive substance use. Both major depression and these latter cases of "substance-induced depression" were associated with severe symptoms of depression, high levels of disability and suicidal ideation.

CONCLUSION

Most people entering treatment programs for methamphetamine use have levels of depression that require clinical management. Making a diagnosis of major depression in the context of heavy methamphetamine use is problematic because of substance-induced symptoms of depression.

Molecular substrates of action control in cortico-striatal circuits

The purpose of this review is to describe the molecular mechanisms in the striatum that mediate reward-based learning and action control during instrumental conditioning. Experiments assessing the neural bases of instrumental conditioning have uncovered functional circuits in the striatum, including dorsal and ventral striatal sub-regions, involved in action-outcome learning, stimulus-response learning, and the motivational control of action by reward-associated cues. Integration of dopamine (DA) and glutamate neurotransmission within these striatal sub-regions is hypothesized to enable learning and action control through its role in shaping synaptic plasticity and cellular excitability. The extracellular signal regulated kinase (ERK) appears to be particularly important for reward-based learning and action control due to its sensitivity to combined DA and glutamate receptor activation and its involvement in a range of cellular functions. ERK activation in striatal neurons is proposed to have a dual role in both the learning and performance factors that contribute to instrumental conditioning through its regulation of plasticity-related transcription factors and its modulation of intrinsic cellular excitability. Furthermore, perturbation of ERK activation by drugs of abuse may give rise to behavioral disorders such as addiction.

HIV and chronic methamphetamine dependence affect cerebral blood flow

Human immunodeficiency virus (HIV) and methamphetamine (METH) dependence are independently associated with neuronal dysfunction. The coupling between cerebral blood flow (CBF) and neuronal activity is the basis of many task-based functional neuroimaging techniques. We examined the interaction between HIV infection and a previous history of METH dependence on CBF within the lenticular nuclei (LN). Twenty-four HIV-/METH-, eight HIV-/METH+, 24 HIV+/METH-, and 15 HIV+/METH+ participants performed a finger tapping paradigm. A multiple regression analysis of covariance assessed associations and two-way interactions between CBF and HIV serostatus and/or previous history of METH dependence. HIV+ individuals had a trend towards a lower baseline CBF (-10%, p = 0.07) and greater CBF changes for the functional task (+32%, p = 0.01) than HIV- subjects. Individuals with a previous history of METH dependence had a lower baseline CBF (-16%, p = 0.007) and greater CBF changes for a functional task (+33%, p = 0.02). However, no interaction existed between HIV serostatus and previous history of METH dependence for either baseline CBF (p = 0.53) or CBF changes for a functional task (p = 0.10). In addition, CBF and volume in the LN were not correlated. A possible additive relationship could exist between HIV infection and a history of METH dependence on CBF with a previous history of METH dependence having a larger contribution. Abnormalities in CBF could serve as a surrogate measure for assessing the chronic effects of HIV and previous METH dependence on brain function.

Repeated mirtazapine nullifies the maintenance of previously established methamphetamine-induced conditioned place preference in rats

The atypical antidepressant mirtazapine enhances monoaminergic transmission; thus, mirtazapine therapy may counter the hypo-activation of monoamine systems associated with withdrawal from methamphetamine abuse. Human addiction therapy will likely require chronic administration that is given after brain and behavioral maladaptations are established. To emulate this scenario in rats, we ascertained if acute or repeated mirtazapine treatments could antagonize previously established consequences of repeated methamphetamine. Methamphetamine-induced conditioned place preference (CPP) was used, wherein methamphetamine (1mg/kg, i.p.) was administered in a unique environmental context once-daily for three days interposed by saline injections in an alternate context. Subsequently, mirtazapine (5mg/kg, i.p.) was administered in the home cage either as 10 once-daily injections or a single injection. The expression of CPP was determined in drug-free rats three days after the last mirtazapine injection. Expression of methamphetamine-induced CPP was inhibited by 10 home cage administrations of mirtazapine but not by a single injection of mirtazapine. These findings reveal that mirtazapine can inhibit the maintenance of methamphetamine-induced CPP and that treatment duration and/or treatment timing contributes to this effect of mirtazapine.

Chronic methamphetamine exposure suppresses the striatal expression of members of multiple families of immediate early genes (IEGs) in the rat: normalization by an acute methamphetamine injection

RATIONALE

Repeated injections of cocaine cause blunted responses to acute cocaine challenge-induced increases in the expression of immediate early genes (IEGs).

OBJECTIVES

The aim of this study was to test if chronic methamphetamine (METH) exposure might cause similar blunting of acute METH-induced increases in IEG expression.

RESULTS

Repeated saline or METH injections were given to rats over 14 days. After 1 day of withdrawal, they received a single injection of saline or METH (5 mg/kg). Acute injection of METH increased c-fos, fosB, fra2, junB, Egr1-3, Nr4a1 (Nur77), and Nr4a3 (Nor-1) mRNA levels in the striatum of saline-pretreated rats. Chronic METH treatment alone reduced the expression of AP1, Erg1-3, and Nr4a1 transcription factors below control levels. Acute METH challenge normalized these values in METH-pretreated rats. Unexpectedly, acute METH challenge to METH-pretreated animals caused further decreases in Nr4a2 (Nurr1) mRNA levels. In contrast, the METH challenge caused significant but blunted increases in Nr4a3 and Arc expression in METH-pretreated rats. There were also chronic METH-associated decreases in the expression of cAMP responsive element binding protein (CREB) which modulates IEG expression via activation of the cAMP/PKA/CREB signal transduction pathway. Chronic METH exposure also caused significant decreases in preprotachykinin, but not in prodynorphin, mRNA levels.

CONCLUSIONS

These results support the accumulated evidence that chronic administration of psychostimulants is associated with blunting of their acute stimulatory effects on IEG expression. The METH-induced renormalization of the expression of several IEGs in rats chronically exposed to METH hints to a potential molecular explanation for the recurrent self-administration of the drug by human addicts.

Safety of stimulant treatment in attention deficit hyperactivity disorder: part II

IMPORTANCE OF THE FIELD

Attention deficit hyperactivity disorder (ADHD) is the most common childhood psychiatric disorder and in at least 50% of cases persists into adulthood. Treatment of ADHD with stimulants is one of the oldest and most effective pharmacological treatments in psychiatry. Yet, there continues to be controversy over the safety of stimulant medications in the treatment of ADHD.

AREAS COVERED IN THIS REVIEW

This paper is a continuation of an earlier paper that reviewed the safety profile of newer stimulant agents, especially in relation to special populations. This part II reviews, through essentially an organ-system approach, the various clinical concerns that have been raised over the safety of stimulant medications. This includes neuropsychiatric, cardiovascular effects on growth and development, and a number of other less common concerns.

WHAT THE READER WILL GAIN

A thorough review of safety concerns in stimulants that emphasizes clinical information, case reports, open series or controlled trials relating to stimulant use in the treatment of ADHD.

TAKE HOME MESSAGE

While many safety concerns have been raised in the use of stimulants, the vast majority of treatment complications are either quickly reversible or easily manageable with appropriate clinical care. The negative consequences of untreated ADHD clearly outweigh the risks of the stimulant medicines when used in an appropriate and careful manner.

The risk of psychotic symptoms associated with recreational methamphetamine use

INTRODUCTION AND AIMS

To determine whether recreational methamphetamine use is associated with an increased risk of psychotic symptoms.

DESIGN AND METHOD

A cross-sectional survey of 157 people attending dance events in Sydney, Australia. Participants were assessed for psychotic symptoms in the past year using items from the Psychosis Screen. Participants with and without psychotic symptoms were compared on methamphetamine use, polydrug use and other demographic factors. An ordinal logistic regression was used to determine the probability of psychotic symptoms by methamphetamine use and level of polydrug use.

RESULTS

Psychotic symptoms in the past year were predicted by methamphetamine use and heavier polydrug use in the past year, and a history of a psychotic disorder (schizophrenia, schizoaffective or bipolar affective disorder). After removing participants with a history of a psychotic disorder (n = 16) and adjusting for polydrug use, methamphetamine use increased the probability of two or more psychotic symptoms (indicative of psychosis risk) from 9% to 21%. There was a non-significant increase in the risk of psychotic symptoms with higher levels of polydrug use. Methamphetamine use was typically monthly or less often (83%), and most users described their use as recreational (85%).

DISCUSSION AND CONCLUSIONS

Within the context of polydrug use, recreational methamphetamine use is associated with a twofold to threefold increase in the probability of psychotic symptoms.

How addictive drugs disrupt presynaptic dopamine neurotransmission

The fundamental principle that unites addictive drugs appears to be that each enhances synaptic dopamine by means that dissociate it from normal behavioral control, so that they act to reinforce their own acquisition. This occurs via the modulation of synaptic mechanisms that can be involved in learning, including enhanced excitation or disinhibition of dopamine neuron activity, blockade of dopamine reuptake, and altering the state of the presynaptic terminal to enhance evoked over basal transmission. Amphetamines offer an exception to such modulation in that they combine multiple effects to produce nonexocytic stimulation-independent release of neurotransmitter via reverse transport independent from normal presynaptic function. Questions about the molecular actions of addictive drugs, prominently including the actions of alcohol and solvents, remain unresolved, but their ability to co-opt normal presynaptic functions helps to explain why treatment for addiction has been challenging.

Methamphetamine self-administration produces attentional set-shifting deficits and alters prefrontal cortical neurophysiology in rats

BACKGROUND

Chronic methamphetamine abusers exhibit deficits in tasks requiring intact prefrontal cortex function, and prefrontal cortex dysfunction has been implicated in the loss of control over drug use. This study used a combination of behavioral and electrophysiologic assessments in rats with a history of long access methamphetamine self-administration to determine methamphetamine-induced changes in prefrontal cortex-dependent attentional set-shifting performance, drug-seeking, and prefrontal cortex neuronal activity.

METHODS

Male Long-Evans rats self-administered methamphetamine (.02 mg/infusion, intravenous) or received yoked saline infusions for 6 hours a day for 14 days. Cognitive flexibility was assessed using an attentional set-shifting task before 2 weeks of self-administration and 1 day after self-administration. Animals then underwent 11 days of abstinence, followed by three subsequent tests for context-induced drug seeking. Finally, animals were anesthetized, and single-unit in vivo extracellular recordings were performed in the dorsomedial prefrontal cortex.

RESULTS

Methamphetamine-experienced rats showed escalated drug intake and context-induced drug-seeking following abstinence. During the extradimensional set-shift component, meth-experienced rats showed selective impairments that were identical to deficits produced by excitotoxic lesions of the prefrontal cortex. Rats with a history of chronic methamphetamine intake also exhibited higher basal firing frequency and a significantly greater proportion of burst-firing cells in the prefrontal cortex compared with yoked-saline controls.

CONCLUSIONS

Prefrontal cortex-specific alterations in neuronal function may play a key role in methamphetamine-induced attentional deficits and drug-seeking. These data support the possibility that targeting prefrontal cortex pathology may improve treatment outcome in methamphetamine addiction.

Imaging presynaptic exocytosis in corticostriatal slices

Optical imaging is a valuable tool for investigating alterations in membrane turnover and vesicle trafficking. Established techniques can easily be adapted to study the mechanisms of synaptic dysfunction in models of neuropsychiatric disorders and neurodegenerative diseases, such as drug addiction, Parkinsonism, and Huntington's disease. Fluorescent endocytic tracers, including FM1-43, have been used to optically monitor synaptic vesicle fusion and measure synaptic function in various preparations, including chromaffin cells, dissociated cell cultures, and brain slices. In this chapter, we describe a technique that provides a direct measure of pathway-specific exocytosis from glutamatergic corticostriatal terminals.

Presynaptic regulation of dopamine transmission in schizophrenia

A role for dopamine (DA) release in the hallucinations and other positive symptoms associated with schizophrenia has long been inferred from the antipsychotic response to D2 DA receptor antagonists and because the DA releaser amphetamine can be psychotogenic. Recent studies suggest that patients with schizophrenia, including those never exposed to antipsychotic drugs, maintain high presynaptic DA accumulation in the striatum. New laboratory approaches are elucidating mechanisms that control the level of presynaptic DA stores, thus contributing to fundamental understanding of the basic pathophysiologic mechanism in schizophrenia.

Enhanced striatal cholinergic neuronal activity mediates L-DOPA-induced dyskinesia in parkinsonian mice

Treatment of Parkinson disease (PD) with L-3,4-dihydroxyphenylalanine (L-DOPA) dramatically relieves associated motor deficits, but L-DOPA-induced dyskinesias (LID) limit the therapeutic benefit over time. Previous investigations have noted changes in striatal medium spiny neurons, including abnormal activation of extracellular signal-regulated kinase1/2 (ERK). Using two PD models, the traditional 6-hydroxydopamine toxic lesion and a genetic model with nigrostriatal dopaminergic deficits, we found that acute dopamine challenge induces ERK activation in medium spiny neurons in denervated striatum. After repeated L-DOPA treatment, however, ERK activation diminishes in medium spiny neurons and increases in striatal cholinergic interneurons. ERK activation leads to enhanced basal firing rate and stronger excitatory responses to dopamine in striatal cholinergic neurons. Pharmacological blockers of ERK activation inhibit L-DOPA-induced changes in ERK phosphorylation, neuronal excitability, and the behavioral manifestation of LID. In addition, a muscarinic receptor antagonist reduces LID. These data indicate that increased dopamine sensitivity of striatal cholinergic neurons contributes to the expression of LID, which suggests novel therapeutic targets for LID.

Striatal structure and function in mood disorders: a comprehensive review

OBJECTIVES

  A large and diverse literature has implicated abnormalities of striatal structure and function in both unipolar and bipolar disorder. Recent functional imaging studies have greatly expanded this body of research. The aim of this review is to provide a comprehensive and critical appraisal of the relevant literature.

METHODS

  A total of 331 relevant articles were reviewed to develop an integrated overview of striatal function in mood disorders.

RESULTS

  There is compelling evidence from multiple studies that functional abnormalities of the striatum and greater corticostriatal circuitry exist in at least some forms of affective illness. The literature does not yet provide data to determine whether these aberrations represent primary pathology or they contribute directly to symptom expression. Finally, there is considerable evidence that bipolar disorder may be associated with striatal hyperactivity and some suggestion that unipolar illness may be associated with hypoactivation.

CONCLUSIONS

  Additional research investigating striatal function in affective disorders will be critical to the development of comprehensive models of the neurobiology of these conditions.

Cortico-basal ganglia circuitry: a review of key research and implications for functional connectivity studies of mood and anxiety disorders

There is considerable evidence that dysfunction of the cortico-basal ganglia circuits may be associated with several mood and anxiety disorders. However, it is unclear whether circuit abnormalities contribute directly either to the neurobiology of these conditions or to the manifestation of symptoms. Understanding the role of these pathways in psychiatric illness has been limited by an incomplete characterization of normal function. In recent years, studies using animal models and human functional imaging have greatly expanded the literature describing normal cortico-basal ganglia circuit function. In this paper, recent key studies of circuit function using human and animal models are reviewed and integrated with findings from other studies conducted over the previous decades. The literature suggests several hypotheses of cortico-basal ganglia circuitry function in mood and anxiety disorders that warrant further exploration. Hypotheses are proposed herein based upon the cortico-basal ganglia mechanisms of: (1) feedforward and feedback control, (2) circuit integration and (3) emotional control. These are presented as models of circuit function, which may be particularly relevant to future investigations using neuroimaging and functional connectivity analyses.

Smoking-induced change in intrasynaptic dopamine concentration: effect of treatment for Tobacco Dependence

The aim of this study was to determine whether standard treatments for Tobacco Dependence affect smoking-induced changes in intrasynaptic dopamine (DA) concentration. Forty-three otherwise healthy adult cigarette smokers (10 to 40 cigarettes per day) were treated with either practical group counseling (PGC) psychotherapy (n=14), bupropion HCl (n=14), or matching pill placebo (n=15) (random assignment) for 8 weeks. Before and after treatment, each subject underwent a bolus-plus-continuous-infusion (11)C-raclopride positron emission tomography (PET) scanning session, during which he or she smoked a regular cigarette. The PET scanning outcome measure of interest was percent change in smoking-induced (11)C-raclopride binding potential (BP(ND)) in the ventral caudate/nucleus accumbens (VCD/NAc), as an indirect measure of DA release. Although the entire study sample had a smaller mean smoking-induced reduction in VCD/NAc BP(ND) after treatment (compared to before treatment), this change was highly correlated with smaller total cigarette puff volumes (and not other treatment variables). These data indicate that smoking-induced DA release is dose-dependent, and is not significantly affected by reductions in daily smoking levels or treatment type.

Risky decisions and their consequences: neural processing by boys with Antisocial Substance Disorder

BACKGROUND

Adolescents with conduct and substance problems ("Antisocial Substance Disorder" (ASD)) repeatedly engage in risky antisocial and drug-using behaviors. We hypothesized that, during processing of risky decisions and resulting rewards and punishments, brain activation would differ between abstinent ASD boys and comparison boys.

METHODOLOGY/PRINCIPAL FINDINGS

We compared 20 abstinent adolescent male patients in treatment for ASD with 20 community controls, examining rapid event-related blood-oxygen-level-dependent (BOLD) responses during functional magnetic resonance imaging. In 90 decision trials participants chose to make either a cautious response that earned one cent, or a risky response that would either gain 5 cents or lose 10 cents; odds of losing increased as the game progressed. We also examined those times when subjects experienced wins, or separately losses, from their risky choices. We contrasted decision trials against very similar comparison trials requiring no decisions, using whole-brain BOLD-response analyses of group differences, corrected for multiple comparisons. During decision-making ASD boys showed hypoactivation in numerous brain regions robustly activated by controls, including orbitofrontal and dorsolateral prefrontal cortices, anterior cingulate, basal ganglia, insula, amygdala, hippocampus, and cerebellum. While experiencing wins, ASD boys had significantly less activity than controls in anterior cingulate, temporal regions, and cerebellum, with more activity nowhere. During losses ASD boys had significantly more activity than controls in orbitofrontal cortex, dorsolateral prefrontal cortex, brain stem, and cerebellum, with less activity nowhere.

CONCLUSIONS/SIGNIFICANCE

Adolescent boys with ASD had extensive neural hypoactivity during risky decision-making, coupled with decreased activity during reward and increased activity during loss. These neural patterns may underlie the dangerous, excessive, sustained risk-taking of such boys. The findings suggest that the dysphoria, reward insensitivity, and suppressed neural activity observed among older addicted persons also characterize youths early in the development of substance use disorders.

Central clock excites vasopressin neurons by waking osmosensory afferents during late sleep

Osmoregulated vasopressin release is facilitated during the late sleep period (LSP) to prevent dehydration and enuresis. Previous work has shown that clock neurons in the suprachiasmatic nucleus (SCN) have low firing rates during the LSP, but it is not known how this reduced activity enhances vasopressin release. We found that synaptic excitation of rat supraoptic nucleus neurons by osmosensory afferents is facilitated during the LSP. Stimulation of the SCN at this time inhibited excitatory synaptic currents induced in supraoptic neurons by activation of osmosensory afferents. This effect was associated with an increased rate of synaptic failures and occurred without changes in frequency facilitation, quantal size or in the ratio of postsynaptic responses mediated by AMPA and NMDA receptors. We conclude that clock neurons mediate an activity-dependent presynaptic silencing of osmosensory afferent synapses onto vasopressin neurons and that osmoregulatory gain is enhanced by removal of this effect during late sleep.

Age-dependent alterations of corticostriatal activity in the YAC128 mouse model of Huntington disease

Huntington disease is a genetic neurodegenerative disorder that produces motor, neuropsychiatric, and cognitive deficits and is caused by an abnormal expansion of the CAG tract in the huntingtin (htt) gene. In humans, mutated htt induces a preferential loss of medium spiny neurons in the striatum and, to a lesser extent, a loss of cortical neurons as the disease progresses. The mechanisms causing these degenerative changes remain unclear, but they may involve synaptic dysregulation. We examined the activity of the corticostriatal pathway using a combination of electrophysiological and optical imaging approaches in brain slices and acutely dissociated neurons from the YAC128 mouse model of Huntington disease. The results demonstrated biphasic age-dependent changes in corticostriatal function. At 1 month, before the behavioral phenotype develops, synaptic currents and glutamate release were increased. At 7 and 12 months, after the development of the behavioral phenotype, evoked synaptic currents were reduced. Glutamate release was decreased by 7 months and was markedly reduced by 12 months. These age-dependent alterations in corticostriatal activity were paralleled by a decrease in dopamine D(2) receptor modulation of the presynaptic terminal. Together, these findings point to dynamic alterations at the corticostriatal pathway and emphasize that therapies directed toward preventing or alleviating symptoms need to be specifically designed depending on the stage of disease progression.

Behavioral sensitization to amphetamine is not accompanied by changes in glutamate receptor surface expression in the rat nucleus accumbens

We examined whether behavioral sensitization to amphetamine is associated with redistribution of glutamate receptors (GluR) in the rat nucleus accumbens (NAc) or dorsolateral striatum (DLSTR). Following repeated amphetamine treatment and 21 days of withdrawal, surface and intracellular levels of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) or NMDA receptor subunits were determined using a protein cross-linking assay. In contrast to our previous results in cocaine-sensitized rats, we did not observe redistribution of GluR1 or GluR2 to the cell surface in the NAc after amphetamine withdrawal, although a small increase in total GluR1 was found in the shell subregion. Nor did we observe activation of signaling pathways associated with cocaine-induced AMPA receptor trafficking or changes in NMDA receptor subunits. No significant changes were observed in the DLSTR. We also investigated the effect of administering a challenge injection of amphetamine to amphetamine-sensitized rats 24 h prior to biochemical analysis based on prior studies showing that cocaine challenge decreases AMPA receptor surface expression in the NAc of cocaine-sensitized rats. GluR1 and GluR2 were not significantly altered in either NAc or DLSTR, although a modest effect on GluR3 cannot be ruled out. Our results suggest that glutamate transmission in the NAc is dramatically different in rats sensitized to amphetamine versus cocaine.

Striatal plasticity and basal ganglia circuit function

The dorsal striatum, which consists of the caudate and putamen, is the gateway to the basal ganglia. It receives convergent excitatory afferents from cortex and thalamus and forms the origin of the direct and indirect pathways, which are distinct basal ganglia circuits involved in motor control. It is also a major site of activity-dependent synaptic plasticity. Striatal plasticity alters the transfer of information throughout basal ganglia circuits and may represent a key neural substrate for adaptive motor control and procedural memory. Here, we review current understanding of synaptic plasticity in the striatum and its role in the physiology and pathophysiology of basal ganglia function.

N-Acetylcysteine reverses cocaine-induced metaplasticity

Cocaine addiction is characterized by an impaired ability to develop adaptive behaviors that can compete with cocaine seeking, implying a deficit in the ability to induce plasticity in cortico-accumbens circuitry critical for regulating motivated behavior. RWe found that rats withdrawn from cocaine self-administration had a marked in vivo deficit in the ability to develop long-term potentation (LTP) and depression (LTD) in the nucleus accumbens core subregion following stimulation of prefrontal cortex. N-acetylcysteine treatment prevents relapse in animal models and craving in humans by activating cystine-glutamate exchange and thereby stimulating extrasynaptic metabotropic glutamate receptors (mGluR). N-acetylcysteine treatment restored the ability to induce LTP and LTD by indirectly stimulating mGluR2/3 and mGluR5, respectively. Cocaine self-administration induces metaplasticity that inhibits the further induction of synaptic plasticity, and this impairment can be reversed by N-acetylcysteine, a drug that also prevents relapse.

Short-term and long-term plasticity at corticostriatal synapses: implications for learning and memory

The striatum is the major division of the basal ganglia, representing the input station of the circuit and arguably the principal site within the basal ganglia where information processing occurs. Striatal activity is critically involved in motor control and learning. Many parts of the striatum are involved in reward processing and in various forms of learning and memory, such as reward-association learning. Moreover, the striatum appears to be a brain center for habit formation and is likely to be involved in advanced stages of addiction. The critical role played by the striatum in learning and cognitive processes is thought to be based on changes in neuronal activity when specific behavioral tasks are being learned. Accordingly, excitatory corticostriatal synapses onto both striatal projecting spiny neurons and interneurons are able to undergo the main forms of synaptic plasticity, including long-term potentiation, long-term depression, short-term forms of intrinsic plasticity and spike timing-dependent plasticity. These specific forms of neuroplasticity allow the short-term and long-term selection and differential amplification of cortical neural signals modulating the processes of motor and behavioral selection within the basal ganglia neural circuit.

Methamphetamine induces chronic corticostriatal depression: too much of a bad thing

Leading theories of drug addiction propose that repeated drug exposure produces a long-lasting homeostatic dysregulation in brain reward processing that is normalized by drug readministration. In this issue of Neuron, Bamford and colleagues describe a novel neurobiological substrate that may contribute to this effect.