Long-term methamphetamine administration in the vervet monkey models aspects of a human exposure: brain neurotoxicity and behavioral profiles

Repeated methamphetamine exposure decreases plasma brain-derived neurotrophic factor levels in rhesus monkeys

Background

Brain-derived neurotrophic factor (BDNF) is known to prevent methamphetamine (METH)-induced neurotoxicity and plays a role in various stages of METH addiction. However, there is a lack of research with longitudinal design on changes in plasma BDNF levels in active METH-dependent individuals.

Aims

The aim of the study was to investigate changes in BDNF levels during METH self-administration in monkeys.

Methods

This study measured plasma BDNF levels in three male rhesus monkeys with continuous METH exposure and four male control rhesus monkeys without METH exposure. Changes in plasma BDNF levels were then assessed longitudinally during 40 sessions of METH self-administration in the three monkeys.

Results

Repeated METH exposure decreased plasma BDNF levels. Additionally, plasma BDNF decreased with long-term rather than short-term accumulation of METH during METH self-administration.

Conclusions

These findings may indicate that the changes in peripheral BDNF may reflect the quantity of accumulative METH intake during a frequent drug use period.

Does chronic use of amphetamine-type stimulants impair interference control? - A meta-analysis

In substance use and addiction, inhibitory control is key to ignoring triggers, withstanding craving and maintaining abstinence. In amphetamine-type stimulant (ATS) users, most research focused on behavioral inhibition, but largely neglected the equally important subdomain of cognitive interference control. Given its crucial role in managing consumption, we investigated the relationship between interference control and chronic ATS use in adults. A database search (Pubmed & Web of Science) and relevant reviews were used to identify eligible studies. Effect sizes were estimated with random effects models. Subgroup, meta-regression, and sensitivity analyses explored heterogeneity in effect sizes. We identified 61 studies (53 datasets) assessing interference control in 1873 ATS users and 1905 controls. Findings revealed robust small effect sizes for ATS-related deficits in interference control, which were mainly seen in methamphetamine, as compared to MDMA users. The differential effects are likely due to tolerance-induced dopaminergic deficiencies (presumably most pronounced in methamphetamine users). Similarities between different ATS could be due to noradrenergic deficiencies; but elucidating their functional role in ATS users requires further/more research.

Goofballing of Opioid and Methamphetamine: The Science Behind the Deadly Cocktail

Globally, millions of people suffer from various substance use disorders (SUD), including mono-and polydrug use of opioids and methamphetamine. Brain regions such as the cingulate cortex, infralimbic cortex, dorsal striatum, nucleus accumbens, basolateral and central amygdala have been shown to play important roles in addiction-related behavioral changes. Clinical and pre-clinical studies have characterized these brain regions and their corresponding neurochemical changes in numerous phases of drug dependence such as acute drug use, intoxication, craving, withdrawal, and relapse. At present, many studies have reported the individual effects of opioids and methamphetamine. However, little is known about their combined effects. Co-use of these drugs produces effects greater than either drug alone, where one decreases the side effects of the other, and the combination produces a prolonged intoxication period or a more desirable intoxication effect. An increasing number of studies have associated polydrug abuse with poorer treatment outcomes, drug-related deaths, and more severe psychopathologies. To date, the pharmacological treatment efficacy for polydrug abuse is vague, and still at the experimental stage. This present review discusses the human and animal behavioral, neuroanatomical, and neurochemical changes underlying both morphine and methamphetamine dependence separately, as well as its combination. This narrative review also delineates the recent advances in the pharmacotherapy of mono- and poly drug-use of opioids and methamphetamine at clinical and preclinical stages.

Dopamine dysfunction in stimulant use disorders: mechanistic comparisons and implications for treatment

Dopamine system deficiencies and associated behavioral phenotypes may be a critical barrier to success in treating stimulant use disorders. Similarities in dopamine dysfunction between cocaine and methamphetamine use disorder but also key differences may impact treatment efficacy and outcome. This review will first compare the epidemiology of cocaine and methamphetamine use disorder. A detailed account of the pharmacokinetic and pharmacodynamic properties associated with each drug will then be discussed, with an emphasis on effects on the dopamine system and associated signaling pathways. Lastly, treatment results from pharmacological clinical trials will be summarized along with a more comprehensive review of the involvement of the trace amine-associated receptor on dopamine signaling dysfunction among stimulants and its potential as a therapeutic target.

Neurotoxicity of methamphetamine: Main effects and mechanisms

Methamphetamine (METH) is an illicit psychostimulant that is abused throughout the world. METH addiction is also a major public health concern and the abuse of large doses of the drug is often associated with serious neuropsychiatric consequences that may include agitation, anxiety, hallucinations, paranoia, and psychosis. Some human methamphetamine users can also suffer from attention, memory, and executive deficits. METH-associated neurological and psychiatric complications might be related, in part, to METH-induced neurotoxic effects. Those include altered dopaminergic and serotonergic functions, neuronal apoptosis, astrocytosis, and microgliosis. Here we have endeavored to discuss some of the main effects of the drug and have presented the evidence supporting certain of the molecular and cellular bases of METH neurotoxicity. The accumulated evidence suggests the involvement of transcription factors, activation of dealth pathways that emanate from mitochondria and endoplasmic reticulum (ER), and a role for neuroinflammatory mechanisms. Understanding the molecular processes involved in METH induced neurotoxicity should help in developing better therapeutic approaches that might also serve to attenuate or block the biological consequences of use of large doses of the drug by some humans who meet criteria for METH use disorder.

Methamphetamine and heightened risk for early-onset stroke and Parkinson's disease: A review

INTRODUCTION

Methamphetamine users are typically young adults, placing them at risk for significant drug-related harms. Neurological harms include stroke and Parkinson's disease, both of which may develop prematurely in the context of methamphetamine use.

MATERIAL AND METHODS

We conducted a narrative review examining the evidence first, for stroke under 45 years and second, early onset of Parkinson's disease (PD) and parkinsonism related to methamphetamine use. We summarise epidemiological factors and common clinical features, before examining in detail the underlying pathology and causal mechanisms.

RESULTS AND DISCUSSION

Methamphetamine use among young people (<45 years) is associated with heightened risk for haemorrhagic stroke. Compared to age-matched all-cause fatal stroke, haemorrhage secondary to aneurysmal rupture is more common among young people with methamphetamine-related stroke and is associated with significantly poorer prognosis. Aetiology is related primarily to both acute and chronic hypertension associated with methamphetamine's sympathomimetic action. Evidence from a variety of sources supports a link between methamphetamine use and increased risk for the development of PD and parkinsonism, and with their early onset in a subset of individuals. Despite this, direct evidence of degeneration of dopaminergic neurons in methamphetamine users has not been demonstrated to date.

CONCLUSIONS

Stroke and Parkinson's Disease/parkinsonism are neurological harms observed prematurely in methamphetamine users.

Is Attention-Deficit/Hyperactivity Disorder a Risk Syndrome for Parkinson's Disease?

Recent epidemiological evidence indicates that diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with increased risk for diseases of the basal ganglia and cerebellum, including Parkinson's disease (PD). The evidence reviewed here indicates that deficits in striatal dopamine are a shared component of the causal chains that produce these disorders. Neuropsychological studies of adult ADHD, prodromal PD, and early-stage PD reveal similar deficits in executive functions, memory, attention, and inhibition that are mediated by similar neural substrates. These and other findings are consistent with the possibility that ADHD may be part of the PD prodrome. The mechanisms that may mediate the association between PD and ADHD include neurotoxic effects of stimulants, other environmental exposures, and Lewy pathology. Understanding the nature of the association between PD and ADHD may provide insight into the etiology and pathogenesis of both disorders. The possible contribution of stimulants to this association may have important clinical and public health implications.

Activation of proline biosynthesis is critical to maintain glutamate homeostasis during acute methamphetamine exposure

Methamphetamine (METH) is a highly addictive psychostimulant that causes long-lasting effects in the brain and increases the risk of developing neurodegenerative diseases. The cellular and molecular effects of METH in the brain are functionally linked to alterations in glutamate levels. Despite the well-documented effects of METH on glutamate neurotransmission, the underlying mechanism by which METH alters glutamate levels is not clearly understood. In this study, we report an essential role of proline biosynthesis in maintaining METH-induced glutamate homeostasis. We observed that acute METH exposure resulted in the induction of proline biosynthetic enzymes in both undifferentiated and differentiated neuronal cells. Proline level was also increased in these cells after METH exposure. Surprisingly, METH treatment did not increase glutamate levels nor caused neuronal excitotoxicity. However, METH exposure resulted in a significant upregulation of pyrroline-5-carboxylate synthase (P5CS), the key enzyme that catalyzes synthesis of proline from glutamate. Interestingly, depletion of P5CS by CRISPR/Cas9 resulted in a significant increase in glutamate levels upon METH exposure. METH exposure also increased glutamate levels in P5CS-deficient proline-auxotropic cells. Conversely, restoration of P5CS expression in P5CS-deficient cells abrogated the effect of METH on glutamate levels. Consistent with these findings, P5CS expression was significantly enhanced in the cortical brain region of mice administered with METH and in the slices of cortical brain tissues treated with METH. Collectively, these results uncover a key role of P5CS for the molecular effects of METH and highlight that excess glutamate can be sequestered for proline biosynthesis as a protective mechanism to maintain glutamate homeostasis during drug exposure.

Neuronal and peripheral damages induced by synthetic psychoactive substances: an update of recent findings from human and animal studies

Preclinical and clinical studies indicate that synthetic psychoactive substances, in addition to having abuse potential, may elicit toxic effects of varying severity at the peripheral and central levels. Nowadays, toxicity induced by synthetic psychoactive substances poses a serious harm for health, since recreational use of these substances is on the rise among young and adult people. The present review summarizes recent findings on the peripheral and central toxicity elicited by “old” and “new” synthetic psychoactive substances in humans and experimental animals, focusing on amphetamine derivatives, hallucinogen and dissociative drugs and synthetic cannabinoids.

Psychostimulant use and the brain

Psychostimulant users are typically young adults. We have conducted a narrative review of neuropsychiatric harms associated with the psychostimulants methamphetamine/amphetamine, cocaine and 3,4-methylenedioxymethamphetamine (MDMA), focusing on epidemiological factors, common clinical presentations, underlying causal mechanisms and treatment options. The major neuropsychiatric harms of psychostimulant use are stroke, neurocognitive impairment, Parkinson's disease, seizures and psychotic illness. These arise through a combination of acute monoamine release, longer-term neurotransmitter effects and indirect effects. These effects are moderated by factors in the individual and in the pattern of substance use. Neuropsychiatric harms associated with psychostimulant use can thus lead to severe long-term impairment.

Methamphetamine use and future risk for Parkinson's disease: Evidence and clinical implications

BACKGROUND

Methamphetamine use has been posited to be a risk factor for the development of Parkinson's disease (PD) and parkinsonism. The clinical implications of a potential association between methamphetamine use and PD are considered.

METHODS

A review of methamphetamine and PD and parkinsonism was conducted, including evidence from animal models, clinical and population studies.

RESULTS

There is biological plausibility to a link between methamphetamine use and PD. Though clinical and epidemiological evidence in this area is scant, a number of studies suggest that methamphetamine is associated with a moderately increased risk of PD and parkinsonism, and may also lead to premature onset of PD. The long lag time between exposure to methamphetamine and onset of PD, the potential for recovery from neurotoxic effects, and tobacco smoking each may attenuate the association. Individual and drug use characteristics that may modulate a user's risk remain poorly understood.

CONCLUSIONS

The use of methamphetamine may be an initiating event in the development of PD and parkinsonism, in addition to other risk factors that a given individual may hold. Clinicians should be vigilant to signs of prodromal and emerging PD among methamphetamine users. In individuals with premature onset illness, information on current or prior exposure to methamphetamine should be sought.

Estradiol and the control of feeding behavior

This review lays out the evidence for the role of E2 in homeostatic and hedonic feeding across several species. While significant effort has been expended on homeostatic feeding research, more studies for hedonic feeding need to be conducted (i.e. are there increases in meal size and enhanced motivation to natural food rewards). By identifying the underlying neural circuitry involved, one can better delineate the mechanisms by which E2 influences feeding behavior. By utilizing more selective neural targeting techniques, such as optogenetics, significant progress can be made toward this goal. Together, behavioral and physiological techniques will help us to better understand neural deficits that can increase the risk for obesity in the absence of E2 (menopause) and aid in developing therapeutic strategies.

The Effects of Housing Density on Social Interactions and Their Correlations with Serotonin in Rodents and Primates

Population density has been suggested to affect social interactions of individuals, but the underlying neural mechanisms remain unclear. In contrast, neurotransmission of monoamines such as serotonin (5-HT) and dopamine (DA) has been demonstrated to play important roles in social behaviors. Here, we investigated whether housing density affected social interactions of rodents and non-human primates housed in groups, and its correlations with monoamines. Japanese macaques exhibited higher plasma 5-HT, but not DA, concentrations than rhesus macaques. Similarly, C57BL/6 mice exhibited higher plasma and brain tissue 5-HT concentrations than DBA2 mice. Under crowding, C57BL/6 mice and Japanese macaques exhibited more prominent social avoidance with mates than DBA2 mice and rhesus macaques, respectively. Although DBA2 mice and rhesus macaques in crowding exhibited elevated plasma stress hormones, such stress hormone elevations associated with crowding were absent in C57BL/6 mice and Japanese macaques. Administration of parachlorophenylalanine, which inhibits 5-HT synthesis, increased social interactions and stress hormones in C57BL/6 mice under crowding. These results suggest that, animals with hyperserotonemia may exhibit social avoidance as an adaptive behavioral strategy to mitigate stress associated with crowding environments, which may also be relevant to psychiatric disorder such as autism spectrum disorder.

Modeling human methamphetamine use patterns in mice: chronic and binge methamphetamine exposure, reward function and neurochemistry

Different methamphetamine use patterns in human subjects may contribute to inconsistent findings regarding the effects of methamphetamine abuse on brain and behavior. The present study investigated whether human-derived chronic and binge methamphetamine use patterns have differential effects on reward and neurochemistry in mice. Brain reward function in mice was evaluated during acute/prolonged withdrawal, and in response to methamphetamine challenge using the intracranial self-stimulation procedure. Brain dopaminergic, serotonergic and glutamatergic neurochemistry was determined with high-performance liquid chromatography. Chronic and binge regimens induced withdrawal-related decreases in reward function that were more severe during the binge regimen during cycles 1-2. Despite large differences in methamphetamine dose, both regimens induced similar reward deficits during cycles 3-4. Neither methamphetamine regimen led to persistent alterations in the sensitivity to the reward-enhancing effects of acute methamphetamine challenge. The binge regimen severely depleted striatal dopamine levels and increased brain glutamine levels. The chronic regimen had milder effects on striatal dopamine levels and altered cortical dopamine and serotonin levels. This work highlights that the magnitude of acute/prolonged withdrawal may not reflect amount or frequency of methamphetamine intake. In contrast, the array of underlying neurochemical alterations was methamphetamine regimen dependent. Thus, stratifying methamphetamine-dependent individuals based on use pattern may help to cater therapeutic interventions more appropriately by targeting use pattern-specific neurotransmitter systems.

Role of Mitochondria in Methamphetamine-Induced Dopaminergic Neurotoxicity: Involvement in Oxidative Stress, Neuroinflammation, and Pro-apoptosis-A Review

Methamphetamine (MA), an amphetamine-type psychostimulant, is associated with dopaminergic toxicity and has a high abuse potential. Numerous in vivo and in vitro studies have suggested that impaired mitochondria are critical in dopaminergic toxicity induced by MA. Mitochondria are important energy-producing organelles with dynamic nature. Evidence indicated that exposure to MA can disturb mitochondrial energetic metabolism by inhibiting the Krebs cycle and electron transport chain. Alterations in mitochondrial dynamic processes, including mitochondrial biogenesis, mitophagy, and fusion/fission, have recently been shown to contribute to dopaminergic toxicity induced by MA. Furthermore, it was demonstrated that MA-induced mitochondrial impairment enhances susceptibility to oxidative stress, pro-apoptosis, and neuroinflammation in a positive feedback loop. Protein kinase Cδ has emerged as a potential mediator between mitochondrial impairment and oxidative stress, pro-apoptosis, or neuroinflammation in MA neurotoxicity. Understanding the role and underlying mechanism of mitochondrial impairment could provide a molecular target to prevent or alleviate dopaminergic toxicity induced by MA.

Methamphetamine and psychiatry: A story of the colourless substance of abuse

OBJECTIVE

The current paper aims to provide an overview of methamphetamine in its historical context, integrated with a current understanding derived from animal studies and clinical experience.

CONCLUSION

Despite over a century of clinical experience, methamphetamine remains a troublesome substance. There remains an urgent need at multiple levels from various sectors to combat this ongoing problem, and psychiatry has an essential role in this endeavour.

Association of Stimulant Use With Dopaminergic Alterations in Users of Cocaine, Amphetamine, or Methamphetamine: A Systematic Review and Meta-analysis

Importance

Stimulant use disorder is common, affecting between 0.3% and 1.1% of the population, and costs more than $85 billion per year globally. There are no licensed treatments to date. Several lines of evidence implicate the dopamine system in the pathogenesis of substance use disorder. Therefore, understanding the nature of dopamine dysfunction seen in stimulant users has the potential to aid the development of new therapeutics.

Objective

To comprehensively review the in vivo imaging evidence for dopaminergic alterations in stimulant (cocaine, amphetamine, or methamphetamine) abuse or dependence.

Data Sources

The entire PubMed, EMBASE, and PsycINFO databases were searched for studies from inception date to May 14, 2016.

Study Selection

Case-control studies were identified that compared dopaminergic measures between stimulant users and healthy controls using positron emission tomography or single-photon emission computed tomography to measure striatal dopamine synthesis or release or to assess dopamine transporter availability or dopamine receptor availability.

Data Extraction and Synthesis

Demographic, clinical, and imaging measures were extracted from each study, and meta-analyses and sensitivity analyses were conducted for stimulants combined, as well as for cocaine and for amphetamine and methamphetamine separately if there were sufficient studies.

Main Outcomes and Measures

Differences were measured in dopamine release (assessed using change in the D2/D3 receptor availability after administration of amphetamine or methylphenidate), dopamine transporter availability, and dopamine receptor availability in cocaine users, amphetamine and methamphetamine users, and healthy controls.

Results

A total of 31 studies that compared dopaminergic measures between 519 stimulant users and 512 healthy controls were included in the final analysis. In most of the studies, the duration of abstinence varied from 5 days to 3 weeks. There was a significant decrease in striatal dopamine release in stimulant users compared with healthy controls: the effect size was -0.84 (95% CI, -1.08 to -0.60; P < .001) for stimulants combined and -0.87 (95% CI, -1.15 to -0.60; P < .001) for cocaine. In addition, there was a significant decrease in dopamine transporter availability: the effect size was -0.91 (95% CI, -1.50 to -0.32; P < .01) for stimulants combined and -1.47 (95% CI, -1.83 to -1.10; P < .001) for amphetamine and methamphetamine. There was also a significant decrease in D2/D3 receptor availability: the effect size was -0.76 (95% CI, -0.92 to -0.60; P < .001) for stimulants combined, -0.73 (95% CI, -0.94 to -0.53; P < .001) for cocaine, and -0.81 (95% CI, -1.12 to -0.49; P < .001) for amphetamine and methamphetamine. Consistent alterations were not found in vesicular monoamine transporter, dopamine synthesis, or D1 receptor studies.

Conclusions and Relevance

Data suggest that both presynaptic and postsynaptic aspects of the dopamine system in the striatum are down-regulated in stimulant users. The commonality and differences between these findings and the discrepancies with the preclinical literature and models of drug addiction are discussed, as well as their implications for future drug development.

Pair housing of Vervets/African Green Monkeys for biomedical research

Vervets, also known as African green monkeys, are a nonhuman primate species widely used in biomedical research. However, there are currently few references available describing techniques and rates of success for pair-housing this species. We present data from four cohorts of vervets from three different facilities: (i) the Wake Forest Vervet Research Colony (VRC; n = 72 female pairs, n= 52 male pairs), (ii) the University of Louisiana at Lafayette-New Iberia Research Center (UL-NIRC; n = 57 female pairs, n = 54 male pairs), (iii) the Tulane National Primate Research Center (TNRPC; n = 18 male pairs), and (iv) a cohort of imported males (n = 18 pairs) at Wake Forest. Compatibility was measured at 14, 30, and 60 days following introduction. Success rates for pair-housing at 14 days ranged from 96% to 98% for females and 96% to 100% for males at the VRC and UL-NIRC but were lower in the smaller imported male cohorts (TNPRC: 50%; WF: 28%). Among the UL-NIRC cohort and VRC male cohort, most of the pair separations after 14 days were due to reasons unrelated to social incompatibility. In contrast, a large proportion of TNPRC and imported male pairs successful at 14 days required separation within 60 days due to incompatibility. Multiple logistic regressions were performed using cohort, mean age of pair and weight difference between pair-mates as potential predictors of compatibility at 14 days. All three predicted the 14-day outcome in males but not females. A separate analysis in the VRC cohort found no evidence that prior familiarity in a group setting influenced outcomes. Variations in success rates across cohorts may have been influenced by introduction methodology. Behavioral differences between vervets and macaques, coupled with our findings, lead us to theorize that the gradual introduction techniques commonly implemented to pair house macaques may not be beneficial or suitable for this species. Am. J. Primatol. 79:e22501, 2017. © 2015 Wiley Periodicals, Inc.

Effects of chronic methamphetamine on psychomotor and cognitive functions and dopamine signaling in the brain

Methamphetamine (MA) studies in animals usually involve acute, binge, or short-term exposure to the drug. However, addicts take substantial amounts of MA for extended periods of time. Here we wished to study the effects of MA exposure on brain and behavior, using an animal model analogous to this pattern of MA intake. MA doses, 4 and 8mg/kg/day, were based on previously reported average daily freely available MA self-administration levels. We examined the effects of 16 week MA treatment on psychomotor and cognitive function in the rat using open field and novel object recognition tests and we studied the adaptations of the dopaminergic system, using in vitro and in vivo receptor imaging. We show that chronic MA treatment, at doses that correspond to the average daily freely available self-administration levels in the rat, disorganizes open field activity, impairs alert exploratory behavior and anxiety-like state, and downregulates dopamine transporter in the striatum. Under these treatment conditions, dopamine terminal functional integrity in the nucleus accumbens is also affected. In addition, lower dopamine D1 receptor binding density, and, to a smaller degree, lower dopamine D2 receptor binding density were observed. Potential mechanisms related to these alterations are discussed.

The Roles of Dopamine D1 Receptor on the Social Hierarchy of Rodents and Nonhuman Primates

BACKGROUND

Although dopamine has been suggested to play a role in mediating social behaviors of individual animals, it is not clear whether such dopamine signaling contributes to attributes of social groups such as social hierarchy.

METHODS

In this study, the effects of the pharmacological manipulation of dopamine D1 receptor function on the social hierarchy and behavior of group-housed mice and macaques were investigated using a battery of behavioral tests.

RESULTS

D1 receptor blockade facilitated social dominance in mice at the middle, but not high or low, social rank in the groups without altering social preference among mates. In contrast, the administration of a D1 receptor antagonist in a macaque did not affect social dominance of the drug-treated animal; however, relative social dominance relationships between the drug-treated and nontreated subjects were altered indirectly through alterations of social affiliative relationships within the social group.

CONCLUSIONS

These results suggest that dopamine D1 receptor signaling may be involved in social hierarchy and social relationships within a group, which may differ between rodents and primates.

Blunted Dopamine Transmission in Addiction: Potential Mechanisms and Implications for Behavior

Positron emission tomography (PET) imaging consistently shows blunted striatal dopamine release and decreased dopamine D2 receptor availability in addiction. Here, we review the preclinical and clinical studies indicating that this neurobiological phenotype is likely to be both a consequence of chronic drug consumption and a vulnerability factor in the development of addiction. We propose that, behaviorally, blunted striatal dopamine transmission could reflect the increased impulsivity and altered cost/benefit computations that are associated with addiction. The factors that influence blunted striatal dopamine transmission in addiction are unknown. Herein, we give an overview of various factors, genetic, environmental, and social, that are known to affect dopamine transmission and that have been associated with the vulnerability to develop addiction. Altogether, these data suggest that blunted dopamine transmission and decreased D2 receptor availability are biomarkers both for the development of addiction and resistance to treatment. These findings support the view that blunted dopamine reflects impulsive behavior and deficits in motivation, which lead to the escalation of drug use.

Mechanisms of amphetamine action illuminated through optical monitoring of dopamine synaptic vesicles in Drosophila brain

Amphetamines elevate extracellular dopamine, but the underlying mechanisms remain uncertain. Here we show in rodents that acute pharmacological inhibition of the vesicular monoamine transporter (VMAT) blocks amphetamine-induced locomotion and self-administration without impacting cocaine-induced behaviours. To study VMAT's role in mediating amphetamine action in dopamine neurons, we have used novel genetic, pharmacological and optical approaches in Drosophila melanogaster. In an ex vivo whole-brain preparation, fluorescent reporters of vesicular cargo and of vesicular pH reveal that amphetamine redistributes vesicle contents and diminishes the vesicle pH-gradient responsible for dopamine uptake and retention. This amphetamine-induced deacidification requires VMAT function and results from net H⁺ antiport by VMAT out of the vesicle lumen coupled to inward amphetamine transport. Amphetamine-induced vesicle deacidification also requires functional dopamine transporter (DAT) at the plasma membrane. Thus, we find that at pharmacologically relevant concentrations, amphetamines must be actively transported by DAT and VMAT in tandem to produce psychostimulant effects.

Amphetamines are known to enhance extracellular dopamine levels, but the underlying mechanisms are unclear. Utilising a new pH biosensor for synaptic vesicles, the authors show that amphetamines diminish vesicle pH gradients, disrupting dopamine packaging and leading to increased neurotransmitter release.

Effects of self-administered methamphetamine on discrimination learning and reversal in nonhuman primates

RATIONALE

Frequent exposure to methamphetamine has been reported to adversely influence cognitive behavior and, in particular, inhibitory control processes.

OBJECTIVE

The present studies were conducted in squirrel monkeys to assess the effects of daily intravenous methamphetamine self-administration on touch screen-based repeated acquisition and discrimination reversal tasks thought to reflect behavioral dimensions of, respectively, learning and response inhibition.

METHODS

First, stable methamphetamine-maintained behavior was established in each subject (0.35-1.6 mg/kg/session), and subsequently, a second daily session of discrimination learning was conducted (20 h later). Subjects first learned to discriminate between two simultaneously presented stimuli (acquisition) and, subsequently, to re-learn the discrimination with the contingencies switched (reversal). The role of the interval between self-administration and touch screen sessions was evaluated, as well as the effects of abrupt methamphetamine discontinuation.

RESULTS

Results indicate that daily methamphetamine self-administration markedly disrupted the development of discrimination learning, initially requiring nearly twice the number of trials to master discriminations. The magnitude of adverse effects in individual subjects correlated to the level of daily methamphetamine intake. Importantly, however, behavioral disruption of discrimination learning was surmounted following remedial training. Once criterion levels of discrimination performance were achieved, subsequent development of reversal performance was largely unaffected except when the interval between self-administration and touch screen session was short and, thus, likely a result of methamphetamine’s direct effects. Discontinuation of methamphetamine produced no disruption in acquisition or reversal.

CONCLUSION

These results indicate that self-administered methamphetamine can markedly disrupt learning processes and highlight key differences in its effects on different aspects of discrimination learning.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

Dopamine in socioecological and evolutionary perspectives: implications for psychiatric disorders

Dopamine (DA) transmission in brain areas such as the prefrontal cortex (PFC) and nucleus accumbens (NAcc) plays important roles in cognitive and affective function. As such, DA deficits have been implicated in a number of psychiatric disorders such as schizophrenia and attention deficit/hyperactivity disorder (ADHD). Accumulating evidence suggests that DA is also involved in social behavior of animals and humans. Although most animals organize and live in social groups, how the DA system functions in such social groups of animals, and its dysfunction causes compromises in the groups has remained less understood. Here we propose that alterations of DA signaling and associated genetic variants and behavioral phenotypes, which have been normally considered as “deficits” in investigation at an individual level, may not necessarily yield disadvantages, but even work advantageously, depending on social contexts in groups. This hypothesis could provide a novel insight into our understanding of the biological mechanisms of psychiatric disorders, and a potential explanation that disadvantageous phenotypes associated with DA deficits in psychiatric disorders have remained in humans through evolution.

Relationship of impulsivity and depression during early methamphetamine withdrawal in Han Chinese population

OBJECTIVE

High level of impulsivity as well as depression is thought to be involved in the maintenance and development of methamphetamine (METH) addiction. However, the relationship between impulsivity and depression has not been studied thoroughly in METH dependence subjects, especially in early METH abstinent subjects. In this study, our objective is to explore the interplay between the depressive symptoms and impulsivity in early METH abstinent subjects.

METHODS

A total of 182 early abstinent METH dependent subjects (abstinence for 1-7 days) were recruited and the level of impulsivity was measured by the Barratt Impulsiveness Scale (BIS-11). Depressive symptoms and anxiety symptoms were assessed by the short 13-item Beck Depression Inventory (BDI-13) and Beck Anxiety Inventory (BAI) respectively.

RESULTS

Global impulsivity of BIS-11 was significantly correlated with depressive symptoms among early METH abstinent subjects (r=0.283, p=0.001). Moreover, all subscales of BIS-11 were also found to be correlated with depressive symptoms: correlation with attentional impulsivity (r=0.202, p=0.006); correlation with motor impulsivity (r=0.267, p=0.001); and correlation with non-planning impulsivity (r=0.177, p=0.017).

CONCLUSIONS

This study showed a relationship between impulsivity and depression, which may further the comprehension of motivational elements contributing to the maintenance and development of METH use disorder. Future research would be dedicated to exploring underlying mechanisms of association between impulsivity and depression.

Enhanced methamphetamine metabolism in rhesus macaque as compared with human: an analysis using a novel method of liquid chromatography with tandem mass spectrometry, kinetic study, and substrate docking

Methamphetamine (MA), which remains one of the widely used drugs of abuse, is metabolized by the cytochrome P450 (P450) family of enzymes in humans. However, metabolism of methamphetamine in macaques is poorly understood. Therefore, we first developed and validated a very sensitive liquid chromatography with tandem mass spectrometry (LC-MS/MS) method using solid phase extraction of rhesus plasma with a lower limit of quantitation at 1.09 ng/ml for MA and its metabolites, 4-hydroxy methamphetamine (4-OH MA), amphetamine (AM), 4-OH amphetamine (4-OH AM), and norephedrine. We then analyzed plasma samples of MA-treated rhesus, which showed >10-fold higher concentrations of AM (∼29 ng/ml) and 4-OH AM (∼28 ng/ml) than MA (∼2 ng/ml). Because the plasma levels of MA metabolites in rhesus were much higher than in human samples, we examined MA metabolism in human and rhesus microsomes. Interestingly, the results showed that AM and 4-OH AM were formed more rapidly and that the catalytic efficiency (Vmax/Km) for the formation of AM was ∼8-fold higher in rhesus than in human microsomes. We further examined the differences in these kinetic characteristics using three selective inhibitors of each human CYP2D6 and CYP3A4 enzymes. The results showed that each of these inhibitors inhibited both d- and l-MA metabolism by 20%-60% in human microsomes but not in rhesus microsomes. The differences between human and rhesus CYP2D6 and CYP3A4 enzymes were further assessed by docking studies for both d and l-MA. In conclusion, our results demonstrated an enhanced MA metabolism in rhesus compared with humans, which is likely to be caused by differences in MA-metabolizing P450 enzymes between these species.

Systems biology of the vervet monkey

Nonhuman primates (NHP) provide crucial biomedical model systems intermediate between rodents and humans. The vervet monkey (also called the African green monkey) is a widely used NHP model that has unique value for genetic and genomic investigations of traits relevant to human diseases. This article describes the phylogeny and population history of the vervet monkey and summarizes the use of both captive and wild vervet monkeys in biomedical research. It also discusses the effort of an international collaboration to develop the vervet monkey as the most comprehensively phenotypically and genomically characterized NHP, a process that will enable the scientific community to employ this model for systems biology investigations.

Acute and sub-chronic effects of purified cathinone from khat (Catha edulis) on behavioural profiles in vervet monkeys (Chlorocebus aethiops)

We investigated the cumulative effects of cathinone on behavioural alterations in single-caged vervet monkeys. Fourteen adult vervets were divided into tests (12 animals) and controls (2 animals), and exposed to escalating doses of cathinone at alternate days of each week for 4 months in presence and absence of cage enrichment. One month of pre-treatment phase served to establish baseline values. Composite behavioural scores of aggression, anxiety, abnormal responses, withdrawal and appetite loss were done. A series of repeated measures analysis of variances were conducted to examine the extent to which cathinone administration was associated with patterns of changes in behavioural data. Results indicate a dose-dependent effect of cathinone on increases of aggression, anxiety, abnormal responses, withdrawal, and appetite loss. The findings demonstrate that at high doses and long-term exposure, cathinone causes behavioural alterations probably via changes in presynaptic striatal dopamine system.

Effects of length of abstinence on decision-making and craving in methamphetamine abusers

Rationale

The majority of drug abusers are incapable of sustaining abstinence over any length of time. Accumulating evidence has linked intense and involuntary craving, Impulsive decision-making and mood disturbances to risk for relapse. However, little is known about temporal changes of these neuropsychological functions in methamphetamine (METH)-dependent individuals.

Objectives

To investigate the effect of length of abstinence on decision-making, craving (baseline and cue-induced), and emotional state in METH-addicted individuals.

Methods

In this cross-sectional study, 183 adult METH-dependent patients at an addiction rehabilitation center who were abstinent for 6 days (n = 37), 14 days (n = 33), 1 month (n = 31), 3 months (n = 30), 6 months (n = 26), or 1 year (n = 30) and 39 healthy subjects were administered the Iowa Gambling Task (IGT) to assess decision-making performance. Depression, anxiety, and impulsivity were also examined. One hundred thirty-nine METH abusers who were abstinent for the aforementioned times then underwent a cue session, and subjective and physiological measures were assessed.

Results

METH dependent individuals who were abstinent for longer periods of time exhibited better decision-making than those who were abstinent for shorter periods of time. And self-reported emotional symptoms improved with abstinence. METH abusers’ ratings of craving decreased with the duration of abstinence, while cue-induced craving increased until 3 months of abstinence and decreased at 6 months and 1 year of abstinence.

Conclusions

We present time-dependent alterations in decision-making, emotional state, and the incubation of cue-induced craving in METH-dependent individuals, which might have significant clinical implications for the prevention of relapse.

Imaging addiction: D2 receptors and dopamine signaling in the striatum as biomarkers for impulsivity

Dependence to drugs of abuse is closely associated with impulsivity, or the propensity to choose a lower, but immediate, reward over a delayed, but more valuable outcome. Here, we review clinical and preclinical studies showing that striatal dopamine signaling and D2 receptor levels - which have been shown to be decreased in addiction - directly impact impulsivity, which is itself predictive of drug self-administration. Based on these studies, we propose that the alterations in D2 receptor binding and dopamine release seen in imaging studies of addiction constitute neurobiological markers of impulsivity. Recent studies in animals also show that higher striatal dopamine signaling at the D2 receptor is associated with a greater willingness to expend effort to reach goals, and we propose that this same relationship applies to humans, particularly with respect to recovery from addiction. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Development of amyloid burden in African Green monkeys

The vervet is an old world monkey increasingly being used as a model for human diseases. In addition to plaques and tangles, an additional hallmark of Alzheimer's disease is damage to neurons that synthesize noradrenaline (NA). We characterized amyloid burden in the posterior temporal lobe of young and aged vervets, and compared that with changes in NA levels and astrocyte activation. Total amyloid beta (Aβ)40 and Aβ42 levels were increased in the aged group, as were numbers of amyloid plaques detected using antibody 6E10. Low levels of Aβ42 were detected in 1 of 5 younger animals, although diffusely stained plaques were observed in 4 of these. Increased glial fibrillary acidic protein staining and messenger RNA levels were significantly correlated with increased age, as were cortical NA levels. Levels of Aβ42 and Aβ40, and the number of 6E10-positive plaques, were correlated with NA levels. Interestingly messenger RNA levels of glial derived neurotrophic factor, important for noradrenergic neuronal survival, were reduced with age. These findings suggest that amyloid pathology in aged vervets is associated with astrocyte activation and higher NA levels.

Alterations in the striatal dopamine system during intravenous methamphetamine exposure: effects of contingent and noncontingent administration

The continuing spread of methamphetamine (METH) abuse has stimulated research aimed at understanding consequences of its prolonged exposure. Alterations in nigrostriatal dopamine (DA) system parameters have been characterized in experimental studies after discontinuation of long-term METH but fewer studies have included similar assessments during METH exposure. Here, we report METH plasma pharmacokinetics and striatal DA system alterations in rat after noncontingent and contingent METH administration for 7.5 weeks. Escalating METH exposure was delivered by dynamic infusion (DI) that incorporated a "humanized" plasma METH half life or by intravenous self-administration (IVSA) that included binge intakes. Kinetic modeling of DI and IVSA for 24 h periods during the final week of METH exposure showed that plasma METH levels remained between 0.7 and 1.5 µM. Animals were sacrificed during their last METH administration for autoradiography assessment using [³H]ligands and D2 agonist-induced [³⁵S]GTPγS binding. DA transporter binding was decreased (DI, 34%; IVSA, 15%) while vesicular monoamine transporter binding and substantia nigra DA cell numbers were unchanged. Decreases were measured for D2 receptor (DI and IVSA, 15-20%) and [³⁵S]GTPγS binding (DI, 35%; IVSA, 18%). These similar patterns of DI and IVSA associated decreases in striatal DA markers reflect consequences of cumulative METH exposure and not the drug delivery method. For METH IVSA, individual differences were observed, yet each animal's total intake was similar within and across three 24-h binges. IVSA rodent models may be useful for identifying molecular mechanisms that are associated with METH binges in humans.

Functional and structural brain changes associated with methamphetamine abuse

Methamphetamine (MA) is a potent psychostimulant drug whose abuse has become a global epidemic in recent years. Firstly, this review article briefly discusses the epidemiology and clinical pharmacology of methamphetamine dependence. Secondly, the article reviews relevant animal literature modeling methamphetamine dependence and discusses possible mechanisms of methamphetamine-induced neurotoxicity. Thirdly, it provides a critical review of functional and structural neuroimaging studies in human MA abusers; including positron emission tomography (PET) and functional and structural magnetic resonance imaging (MRI). The effect of abstinence from methamphetamine, both short- and long-term within the context of these studies is also reviewed.

Dysregulation of D₂-mediated dopamine transmission in monkeys after chronic escalating methamphetamine exposure

Compulsive drug-seeking and drug-taking are important substance-abuse behaviors that have been linked to alterations in dopaminergic neurotransmission and to impaired inhibitory control. Evidence supports the notions that abnormal D₂ receptor-mediated dopamine transmission and inhibitory control may be heritable risk factors for addictions, and that they also reflect drug-induced neuroadaptations. To provide a mechanistic explanation for the drug-induced emergence of inhibitory-control deficits, this study examined how a chronic, escalating-dose regimen of methamphetamine administration affected dopaminergic neurochemistry and cognition in monkeys. Dopamine D₂-like receptor and dopamine transporter (DAT) availability and reversal-learning performance were measured before and after exposure to methamphetamine (or saline), and brain dopamine levels were assayed at the conclusion of the study. Exposure to methamphetamine reduced dopamine D₂-like receptor and DAT availability and produced transient, selective impairments in the reversal of a stimulus-outcome association. Furthermore, individual differences in the change in D₂-like receptor availability in the striatum were related to the change in response to positive feedback. These data provide evidence that chronic, escalating-dose methamphetamine administration alters the dopamine system in a manner similar to that observed in methamphetamine-dependent humans. They also implicate alterations in positive-feedback sensitivity associated with D₂-like receptor dysfunction as the mechanism by which inhibitory control deficits emerge in stimulant-dependent individuals. Finally, a significant degree of neurochemical and behavioral variation in response to methamphetamine was detected, indicating that individual differences affect the degree to which drugs of abuse alter these processes. Identification of these factors ultimately may assist in the development of individualized treatments for substance dependence.

Protective role for the disulfide isomerase PDIA3 in methamphetamine neurotoxicity

Methamphetamine abuse continues to be a worldwide problem, damaging the individual user as well as society. Only minimal information exists on molecular changes in the brain that result from methamphetamine administered in patterns typical of human abusers. In order to investigate such changes, we examined the effect of methamphetamine on the transcriptional profile in brains of monkeys. Gene expression profiling of caudate and hippocampus identified protein disulfide isomerase family member A3 (PDIA3) to be significantly up-regulated in the animals treated with methamphetamine as compared to saline treated control monkeys. Methamphetamine treatment of mice also increased striatal PDIA3 expression. Treatment of primary striatal neurons with methamphetamine revealed an up-regulation of PDIA3, showing a direct effect of methamphetamine on neurons to increase PDIA3. In vitro studies using a neuroblastoma cell line demonstrated that PDIA3 expression protects against methamphetamine-induced cell toxicity and methamphetamine-induced intracellular reactive oxygen species production, revealing a neuroprotective role for PDIA3. The current study implicates PDIA3 to be an important cellular neuroprotective mechanism against a toxic drug, and as a potential target for therapeutic investigations.

Cognitive control and the dopamine D₂-like receptor: a dimensional understanding of addiction

The phenotypic complexity of psychiatric conditions is revealed by the dimensional nature of these disorders, which consist of multiple behavioral, affective, and cognitive dysfunctions that can result in substantial psychosocial impairment. The high degree of heterogeneity in symptomatology and comorbidity suggests that simple categorical diagnoses of "affected" or "unaffected" may fail to capture the true characteristics of the disorder in a manner relevant to individualized treatment. A particular dimension of interest is cognitive control ability because impairments in the capacity to control thoughts, feelings, and actions are key to several psychiatric disorders. Here, we describe evidence suggesting that cognitive control over behavior is a crucial dimension of function relevant to addictions. Moreover, dopamine (DA) D(2)-receptor transmission is increasingly being identified as a point of convergence for these behavioral and cognitive processes. Consequently, we argue that measures of cognitive control and D(2) DA receptor function may be particularly informative markers of individual function and treatment response in addictions.

Toxicity of amphetamines: an update

Amphetamines represent a class of psychotropic compounds, widely abused for their stimulant, euphoric, anorectic, and, in some cases, emphathogenic, entactogenic, and hallucinogenic properties. These compounds derive from the β-phenylethylamine core structure and are kinetically and dynamically characterized by easily crossing the blood-brain barrier, to resist brain biotransformation and to release monoamine neurotransmitters from nerve endings. Although amphetamines are widely acknowledged as synthetic drugs, of which amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are well-known examples, humans have used natural amphetamines for several millenniums, through the consumption of amphetamines produced in plants, namely cathinone (khat), obtained from the plant Catha edulis and ephedrine, obtained from various plants in the genus Ephedra. More recently, a wave of new amphetamines has emerged in the market, mainly constituted of cathinone derivatives, including mephedrone, methylone, methedrone, and buthylone, among others. Although intoxications by amphetamines continue to be common causes of emergency department and hospital admissions, it is frequent to find the sophism that amphetamine derivatives, namely those appearing more recently, are relatively safe. However, human intoxications by these drugs are increasingly being reported, with similar patterns compared to those previously seen with classical amphetamines. That is not surprising, considering the similar structures and mechanisms of action among the different amphetamines, conferring similar toxicokinetic and toxicological profiles to these compounds. The aim of the present review is to give an insight into the pharmacokinetics, general mechanisms of biological and toxicological actions, and the main target organs for the toxicity of amphetamines. Although there is still scarce knowledge from novel amphetamines to draw mechanistic insights, the long-studied classical amphetamines-amphetamine itself, as well as methamphetamine and MDMA, provide plenty of data that may be useful to predict toxicological outcome to improvident abusers and are for that reason the main focus of this review.

AC927, a σ receptor ligand, blocks methamphetamine-induced release of dopamine and generation of reactive oxygen species in NG108-15 cells

Methamphetamine is a highly addictive psychostimulant drug of abuse that causes neurotoxicity with high or repeated dosing. Earlier studies demonstrated the ability of the selective σ receptor ligand N-phenethylpiperidine oxalate (AC927) to attenuate the neurotoxic effects of methamphetamine in vivo. However, the precise mechanisms through which AC927 conveys its protective effects remain to be determined. With the use of differentiated NG108-15 cells as a model system, the effects of methamphetamine on neurotoxic endpoints and mediators such as apoptosis, necrosis, generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), and dopamine release were examined in the absence and presence of AC927. Methamphetamine at physiologically relevant micromolar concentrations caused apoptosis in NG108-15 cells. At higher concentrations of methamphetamine, necrotic cell death was observed. At earlier time points, methamphetamine caused ROS/RNS generation, which was detected with the fluorigenic substrate 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescin diacetate, acetyl ester, in a concentration- and time-dependent manner. N-Acetylcysteine, catalase, and l-N(G)-monomethyl arginine citrate inhibited the ROS/RNS fluorescence signal induced by methamphetamine, which suggests the formation of hydrogen peroxide and RNS. Exposure to methamphetamine also stimulated the release of dopamine from NG108-15 cells into the culture medium. AC927 attenuated methamphetamine-induced apoptosis, necrosis, ROS/RNS generation, and dopamine release in NG108-15 cells. Together, the data suggest that modulation of σ receptors can mitigate methamphetamine-induced cytotoxicity, ROS/RNS generation, and dopamine release in cultured cells.

Methamphetamine toxicity and its implications during HIV-1 infection

Over the past two decades methamphetamine (MA) abuse has seen a dramatic increase. The abuse of MA is particularly high in groups that are at higher risk for HIV-1 infection, especially men who have sex with men (MSM). This review is focused on MA toxicity in the CNS as well as in the periphery. In the CNS, MA toxicity is comprised of numerous effects, including, but not limited to, oxidative stress produced by dysregulation of the dopaminergic system, hyperthermia, apoptosis, and neuroinflammation. Multiple lines of evidence demonstrate that these effects exacerbate the neurodegenerative damage caused by CNS infection of HIV perhaps because both MA and HIV target the frontostriatal regions of the brain. MA has also been demonstrated to increase viral load in the CNS of SIV-infected macaques. Using transgenic animal models, as well as cultured cells, the HIV proteins Tat and gp120 have been demonstrated to have neurotoxic properties that are aggravated by MA. In addition, MA has been shown to exhibit detrimental effects on the blood-brain barrier (BBB) that have the potential to increase the probability of CNS infection by HIV. Although the effects of MA in the periphery have not been as extensively studied as have the effects on the CNS, recent reports demonstrate the potential effects of MA on HIV infection in the periphery including increased expression of HIV co-receptors and increased expression of inflammatory cytokines.

Neuroimaging and drug taking in primates

RATIONALE

Neuroimaging techniques have led to significant advances in our understanding of the neurobiology of drug taking and the treatment of drug addiction in humans. Neuroimaging approaches provide a powerful translational approach that can link findings from humans and laboratory animals.

OBJECTIVE

This review describes the utility of neuroimaging toward understanding the neurobiological basis of drug taking and documents the close concordance that can be achieved among neuroimaging, neurochemical, and behavioral endpoints.

RESULTS

The study of drug interactions with dopamine and serotonin transporters in vivo has identified pharmacological mechanisms of action associated with the abuse liability of stimulants. Neuroimaging has identified the extended limbic system, including the prefrontal cortex and anterior cingulate, as important neuronal circuitry that underlies drug taking. The ability to conduct within-subject longitudinal assessments of brain chemistry and neuronal function has enhanced our efforts to document long-term changes in dopamine D2 receptors, monoamine transporters, and prefrontal metabolism due to chronic drug exposure. Dysregulation of dopamine function and brain metabolic changes in areas involved in reward circuitry have been linked to drug taking behavior, cognitive impairment, and treatment response.

CONCLUSIONS

Experimental designs employing neuroimaging should consider well-documented determinants of drug taking, including pharmacokinetic considerations, subject history, and environmental variables. Methodological issues to consider include limited molecular probes, lack of neurochemical specificity in brain activation studies, and the potential influence of anesthetics in animal studies. Nevertheless, these integrative approaches should have important implications for understanding drug taking behavior and the treatment of drug addiction.

The ugly side of amphetamines: short- and long-term toxicity of 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy'), methamphetamine and D-amphetamine

Amphetamine ('Speed'), methamphetamine ('Ice') and its congener 3,4-methylenedioxymethamphetamine (MDMA; 'Ecstasy') are illicit drugs abused worldwide for their euphoric and stimulant effects. Despite compelling evidence for chronic MDMA neurotoxicity in animal models, the physiological consequences of such toxicity in humans remain unclear. In addition, distinct differences in the metabolism and pharmacokinetics of MDMA between species and different strains of animals prevent the rationalisation of realistic human dose paradigms in animal studies. Here, we attempt to review amphetamine toxicity and in particular MDMA toxicity in the pathogenesis of exemplary human pathologies, independently of confounding environmental factors such as poly-drug use and drug purity.

Repeated co-administrations of alcohol- and methamphetamine-produced anxiogenic effect could be associated with the neurotoxicity in the dentate gyrus

To date, joint use of alcohol (EtOH) and methamphetamine (MA) represents a specific combination of polydrug abuse. Repeated administrations of EtOH, MA, and combined EtOH and MA were assessed for their effects on brain cell toxicity, cell mitosis and anxiety/depression-like behavior. We found that repeated co-administrations of EtOH and MA produced profound anxiogenic effects. Specifically, combined EtOH and MA decreased open arm exploratory responses in the elevated plus maze test. Moreover, combined EtOH and MA significantly decreased immobile responses in the tail suspension test. MA, EtOH, and their combination all reduced the number of NeuN-positive cells in amygdala (Amg), while neither of them altered the number of NeuN-positive cells in striatum (St) or prefrontal cortex (PFC). Combined EtOH and MA decreased the number of NeuN-positive cells in dentate gyrus (DG). EtOH, MA, and combined EtOH and MA all diminished comparable number of GFAP-positive cells in Amg, DG, and St. Neither of these treatment affected the number of GFAP-positive cells in PFC. EtOH, MA, and combined EtOH and MA generated comparable inhibiting effects on cell proliferation in the subventricular zone (SVZ) and DG. These results, taken together, suggest that repeated co-administrations of MA and EtOH may produce an observable anxiogenic effect. This combination-produced anxiogenic effect could be associated with neuronal loss in the dentate gurus. In contrast, such an anxiogenic effect is less likely related to this combination-caused glial toxicity in limbic regions or cell proliferation-inhibiting effect in the SVZ or DG.

Nonhuman primate positron emission tomography neuroimaging in drug abuse research

Positron emission tomography (PET) neuroimaging in nonhuman primates has led to significant advances in our current understanding of the neurobiology and treatment of stimulant addiction in humans. PET neuroimaging has defined the in vivo biodistribution and pharmacokinetics of abused drugs and related these findings to the time course of behavioral effects associated with their addictive properties. With novel radiotracers and enhanced resolution, PET neuroimaging techniques have also characterized in vivo drug interactions with specific protein targets in the brain, including neurotransmitter receptors and transporters. In vivo determinations of cerebral blood flow and metabolism have localized brain circuits implicated in the effects of abused drugs and drug-associated stimuli. Moreover, determinations of the predisposing factors to chronic drug use and long-term neurobiological consequences of chronic drug use, such as potential neurotoxicity, have led to novel insights regarding the pathology and treatment of drug addiction. However, similar approaches clearly need to be extended to drug classes other than stimulants. Although dopaminergic systems have been extensively studied, other neurotransmitter systems known to play a critical role in the pharmacological effects of abused drugs have been largely ignored in nonhuman primate PET neuroimaging. Finally, the study of brain activation with PET neuroimaging has been replaced in humans mostly by functional magnetic resonance imaging (fMRI). There has been some success in implementing pharmacological fMRI in awake nonhuman primates. Nevertheless, the unique versatility of PET imaging will continue to complement the systems-level strengths of fMRI, especially in the context of nonhuman primate drug abuse research.

A web-based brain atlas of the vervet monkey, Chlorocebus aethiops

Vervet monkeys are a frequently studied animal model in neuroscience research. Although equally distantly related to humans, the ancestors of vervets diverged from those of macaques and baboons more than 11 million years ago, antedating the divergence of the ancestors of humans, chimpanzees and gorillas. To facilitate anatomic localization in the vervet brain, two linked on-line electronic atlases are described, one based on registered MRI scans from hundreds of vervets (http://www.loni.ucla.edu/Research/Atlases/Data/vervet/vervetmratlas/vervetmratlas.html) and the other based on a high-resolution cryomacrotome study of a single vervet (http://www.loni.ucla.edu/Research/Atlases/Data/vervet/vervetatlas/vervetatlas.html). The averaged MRI atlas is also available as a volume in Neuroimaging Informatics Technology Initiative format. In the cryomacrotome atlas, various sulcal and subcortical structures have been anatomically labeled and surface rendered views are provided along the primary planes of section. Both atlases simultaneously provide views in all three primary planes of section, rapid navigation by clicking on the displayed images, and stereotaxic coordinates in the averaged MRI atlas space. Despite the extended time period since their divergence, the major sulcal and subcortical landmarks in vervets are highly conserved relative to those described in macaques.

Effect of D1-like and D2-like receptor antagonists on methamphetamine and 3,4-methylenedioxymethamphetamine self-administration in rats

It has been suggested that activation of dopamine D1-like and D2-like receptors contribute equally to the maintenance of drug self-administration. This study compared the contribution of these receptor subtypes to 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (MA) self-administration. Effects of pretreatment with the D2-like receptor antagonist, eticlopride (0.0, 0.0125, 0.025 or 0.05 mg/kg, intraperitoneal), on responding maintained by several doses of MDMA (0.5, 1.0 and 2.0 mg/kg/infusion) and MA (0.05, 0.1 and 0.2 mg/kg/infusion) were determined. As we have published data showing the effects of the D1-like receptor antagonist, SCH23390 (0.0, 0.01 or 0.02 mg/kg, subcutaneous), on MDMA self-administration, effects of this dose range on the MA dose-response curve were determined. In our previous study, 0.02 mg/kg SCH23390 produced a rightward shift in the MDMA dose response curve, whereas in the present results, this dose decreased responding maintained by most doses of MA. Eticlopride increased the responding maintained by most doses of MDMA but failed to alter MA self-administration. The present results suggest that both D1-like and D2-like receptors contribute to the maintenance of MDMA self-administration, whereas MA self-administration was more sensitive to D1-like receptor blockade.