Neurotoxic amphetamine analogues: effects in monkeys and implications for humans

Different Doses of Methamphetamine Are Needed to Produce Locomotor or Blood Pressure Sensitization in Mice

Methamphetamine (METH) exposure increases locomotor sensitization. However, no study has explored the occurrence of cardiovascular sensitization. The present study, carried out in mice, analyzed the following: (i) METH sensitization extending to systolic blood pressure (SBP); (ii) a potential correlation between ambulatory and cardiovascular sensitization; and (iii) morphological alterations within meso-striatal, meso-limbic and pontine catecholamine systems including c-fos expression. Locomotor activity, SBP and occurrence of morphological alterations of catecholaminergic neurons were assessed in C57Bl/6J mice following daily i.p. injections of either saline or METH (1, 2 or 5 mg/kg) for 5 consecutive days and following 6 days of withdrawal. Reiterated exposure to the lower doses of METH (1 mg/kg and 2 mg/kg) produced in mice locomotor sensitization without altering SBP. In contrast, repeated treatment with the highest dose of METH (5 mg/kg) produced sensitization of SBP in the absence of locomotor sensitization. No morphological alterations but increases in c-fos expression within neurons of locus coeruleus and nucleus accumbens were detected. The present data suggest that METH produces plastic changes that extend beyond the motor systems to alter autonomic regulation. This cardiovascular sensitization occurs independently of locomotor sensitization. The persistency of increased blood pressure may underlie specific mechanisms operating in producing hypertension.

Neurotrophic Factors in Cannabis-induced Psychosis: An Update

BACKGROUND

Cannabis is the most widely used illicit substance. Numerous scientific evidence confirm the strong association between cannabis and psychosis. Exposure to cannabis can induce the development of psychosis and schizophrenia in vulnerable individuals. However, the neurobiological processes underlying this relationship are unknown. Neurotrophins are a class of proteins that serve as survival factors for central nervous system (CNS) neurons. In particular, Nerve Growth Factor (NGF) plays an important role in the survival and function of cholinergic neurons while Brain Derived Neurotrophic Factor (BDNF) is involved in synaptic plasticity and the maintenance of midbrain dopaminergic and cholinergic neurons. Glial Cell Derived Neurotrophic Factor (GDNF) promotes the survival of midbrain dopaminergic neurons and Neuregulin 1 (NrG- 1) contributes to glutamatergic signals regulating the N-methyl-D-aspartate (NMDA). They have a remarkable influence on the neurons involved in the Δ-9-THC (tethra-hydro-cannabinol) action, such as dopaminergic and glutamatergic neurons, and can play dual roles: first, in neuronal survival and death, and, second, in activity-dependent plasticity.

METHODS

In this brief update, reviewing in a narrative way the relevant literature, we will focus on the effects of cannabis on this class of proteins, which may be implicated, at least in part, in the mechanism of the psychostimulant-induced neurotoxicity and psychosis.

CONCLUSION

Since altered levels of neurotrophins may participate in the pathogenesis of psychotic disorders which are common in drug users, one possible hypothesis is that repeated cannabis exposure can cause psychosis by interfering with neurotrophins synthesis and utilization by CNS neurons.

Neurotoxicity of MDMA: Main effects and mechanisms

Preclinical and clinical studies indicate that 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy'), in addition to having abuse potential, may elicit acute and persistent abnormalities of varying severity at the central level. Importantly, neurotoxic effects of MDMA have been demonstrated in experimental animals. Accordingly, central toxicity induced by MDMA may pose a serious harm for health, since MDMA is among the substances that are used for recreational purposes by young and adult people. This review provides a concise overview of recent findings from preclinical and clinical studies that evaluated the central effects of MDMA, and the mechanisms involved in the neurotoxicity induced by this amphetamine-related drug.

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.

Cognitive Effects of MDMA in Laboratory Animals: A Systematic Review Focusing on Dose

±3,4-Methylenedioxymethamphetamine (MDMA) is a synthetic, psychoactive drug that is primarily used recreationally but also may have some therapeutic value. At low doses, MDMA produces feelings of relaxation, empathy, emotional closeness, and euphoria. Higher doses can produce unpleasant psychostimulant- and hallucinogen-like adverse effects and therefore are usually not taken intentionally. There is considerable evidence that MDMA produces neurotoxicity and cognitive deficits at high doses; however, these findings may not generalize to typical recreational or therapeutic use of low-dose MDMA. Here, we systematically review 25 years of research on the cognitive effects of MDMA in animals, with a critical focus on dose. We found no evidence that doses of less than 3 mg/kg MDMA-the dose range that users typically take-produce cognitive deficits in animals. Doses of 3 mg/kg or greater, which were administered most often and frequently ranged from 5 to 20 times greater than an average dose, also did not produce cognitive deficits in a slight majority of experiments. Overall, the preclinical evidence of MDMA-induced cognitive deficits is weak and, if anything, may be the result of unrealistically high dosing. While factors associated with recreational use such as polydrug use, adulterants, hyperthermia, and hyponatremia can increase the potential for neurotoxicity, the short-term, infrequent, therapeutic use of ultra low-dose MDMA is unlikely to pose significant cognitive risks. Future studies must examine any adverse cognitive effects of MDMA using clinically relevant doses to reliably assess its potential as a psychotherapeutic.

Binge-like acquisition of α-pyrrolidinopentiophenone (α-PVP) self-administration in female rats

RATIONALE

The synthetic cathinone α-pyrrolidinopentiophenone (α-PVP) has been associated with bizarre public behavior in users. Association of such behavior with extended binges of drug use motivates additional investigation, particularly since a prior study found that half of male rats experience a binge of exceptionally high intake, followed by sustained lower levels of self-administration during the acquisition of intravenous self-administration (IVSA) of a related drug, 3,4-methylenedioxypyrovalerone.

OBJECTIVES

The binge-like acquisition pattern is novel for rat IVSA; thus, the present study sought to determine if this effect generalizes to IVSA of α-PVP in female rats.

METHODS

Female Wistar rats were trained in IVSA of α-PVP (0.05 mg/kg/inf) in experimental chambers containing an activity wheel. Groups were trained with the wheels fixed (No-Wheel group), fixed for the initial 5 days of acquisition or free to move throughout acquisition (Wheel group). The groups were next subjected to a wheel access switch and then all animals to dose-substitution (0.0125-0.3 mg/kg/inf) with the wheels alternately fixed and free to move.

RESULTS

Approximately half of the rats initiated their IVSA pattern with a binge day of exceptionally high levels of drug intake, independent of wheel access condition. Wheel activity was much lower in the No-Wheel group in the wheel switch post-acquisition. Dose-effect curves were similar for wheel access training groups, for binge/no binge phenotypic subgroups and were not altered with wheel access during the dose-substitution.

CONCLUSION

This confirms the high reinforcer effectiveness of α-PVP in female rats and the accompanying devaluation of wheel activity as a naturalistic reward.

Striatal Reinnervation Process after Acute Methamphetamine-Induced Dopaminergic Degeneration in Mice

Methamphetamine (METH), an amphetamine derivate, may increase the risk of developing Parkinson's disease (PD). Human and animal studies have shown that METH produces persistent dopaminergic neurotoxicity in the nigrostriatal pathway, despite initial partial recovery. To determine the processes leading to early compensation, we studied the detailed morphology and distribution of tyrosine hydroxylase immunoreactive fibers (TH-ir) classified by their thickness (types I-IV) before and after METH. Applying three established neurotoxic regimens of METH: single high dose (1 × 30 mg/kg), multiple lower doses (3 × 5 mg/kg) or (3 × 10 mg/kg), we show that METH primarily damages type I fibers (the thinner ones), and to a much lesser extend types II-IV fibers including sterile axons. The striatal TH terminal partial recovery process, consisting of a progressive regrowth increases in types II, III, and IV fibers, demonstrated by co-localization of GAP-43, a sprouting marker, was observed 3 days post-METH treatment. In addition, we demonstrate the presence of growth-cone-like TH-ir structures, indicative of new terminal generation as well as improvement in motor functions after 3 days. A temporal relationship was observed between decreases in TH-expression and increases in silver staining, a marker of degeneration. Striatal regeneration was associated with an increase in astroglia and decrease in microglia expression, suggesting a possible role for the neuroimmune system in regenerative processes. Identification of regenerative compensatory mechanisms in response to neurotoxic agents could point to novel mechanisms in countering the neurotoxicity and/or enhancing the regenerative processes.

Progression and Persistence of Neurotoxicity Induced by MDMA in Dopaminergic Regions of the Mouse Brain and Association with Noradrenergic, GABAergic, and Serotonergic Damage

The amphetamine-related drug 3,4-methylenedioxymethamphetamine (MDMA) is known to induce neurotoxic damage in dopaminergic regions of the mouse brain. In order to characterize how the number of administrations influenced the severity of MDMA-induced dopaminergic damage and to describe the localization and persistence of this damage, we evaluated the changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) in different regions of the mouse brain. Moreover, we investigated whether dopaminergic damage was associated with noradrenergic, GABAergic, and serotonergic damage, by evaluating the changes in noradrenaline transporter (NET), glutamic acid decarboxylase-67 (GAD-67), and serotonin transporter (SERT). Mice received 14, 28, or 36 MDMA administrations (10 mg/kg twice a week) and were sacrificed at different time points (postnatal days 85, 110, 138, or 214) for immunohistochemical evaluation. Mice receiving 28 administrations showed reduced levels of DAT-positive fibers in caudate-putamen (CPu) and medial prefrontal cortex (mPFC) and reduced levels of TH-positive nigral neurons. These mice also displayed increased NET-positive hippocampal fibers, reduced GAD-67-positive neurons in CPu and hippocampus, and reduced GAD-67-positive fibers in mPFC. Similar effects of MDMA on DAT, TH, and GAD-67 were found in mice receiving 36 administrations, which also displayed reduced levels of striatal, cortical, and hippocampal TH-immunoreactive fibers. The reductions in dopaminergic markers and GAD-67 persisted at 3 months after MDMA discontinuation. Finally, MDMA never modified the levels of SERT. These results provide further insight into the localization and persistence of MDMA-induced dopaminergic damage and show that this effect may associate with GABAergic but not noradrenergic or serotonergic damage.

Vascular-directed responses of microglia produced by methamphetamine exposure: indirect evidence that microglia are involved in vascular repair?

Background

Brain microglial activations and damage responses are most commonly associated with neurodegeneration or systemic innate immune system activation. Here, we used histological methods to focus on microglial responses that are directed towards brain vasculature, previously undescribed, after a neurotoxic exposure to methamphetamine.

Methods

Male rats were given doses of methamphetamine that produce pronounced hyperthermia, hypertension, and toxicity. Identification of microglia and microglia-like cells (pericytes and possibly perivascular cells) was done using immunoreactivity to allograft inflammatory factor 1 (Aif1 a.k.a Iba1) and alpha M integrin (Itgam a.k.a. Cd11b) while vasculature endothelium was identified using rat endothelial cell antigen 1 (RECA-1). Regions of neuronal, axonal, and nerve terminal degeneration were determined using Fluoro-Jade C.

Results

Dual labeling of vasculature (RECA-1) and microglia (Iba1) showed a strong association of hypertrophied cells surrounding and juxtaposed to vasculature in the septum, medial dorsal hippocampus, piriform cortex, and thalamus. The Iba1 labeling was more pronounced in the cell body while Cd11b more so in the processes of activated microglia. These regions have been previously identified to have vascular leakage after neurotoxic methamphetamine exposure. Dual labeling with Fluoro-Jade C and Iba1 indicated that there was minimal or no evidence of neuronal damage in the septum and hippocampus where many hypertrophied Iba1-labeled cells were found to be associated with vasculature. Although microglial activation around the prominent neurodegeneration was found in the thalamus, there were also many examples of activated microglia associated with vasculature.

Conclusions

The data implicate microglia, and possibly related cell types, in playing a major role in responding to methamphetamine-induced vascular damage, and possibly repair, in the absence of neurodegeneration. Identifying brain regions with hypertrophied/activated microglial-like cells associated with vasculature has the potential for identifying regions of more subtle examples of vascular damage and BBB compromise.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0526-6) contains supplementary material, which is available to authorized users.

Fragment C Domain of Tetanus Toxin Mitigates Methamphetamine Neurotoxicity and Its Motor Consequences in Mice

BACKGROUND

The C-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) is a nontoxic peptide with demonstrated in vitro and in vivo neuroprotective effects against striatal dopaminergic damage induced by 1-methyl-4-phenylpyridinium and 6-hydoxydopamine, suggesting its possible therapeutic potential in Parkinson's disease. Methamphetamine, a widely abused psychostimulant, has selective dopaminergic neurotoxicity in rodents, monkeys, and humans. This study was undertaken to determine whether Hc-TeTx might also protect against methamphetamine-induced dopaminergic neurotoxicity and the consequent motor impairment.

METHODS

For this purpose, we treated mice with a toxic regimen of methamphetamine (4mg/kg, 3 consecutive i.p. injections, 3 hours apart) followed by 3 injections of 40 ug/kg of Hc-TeTx into grastrocnemius muscle at 1, 24, and 48 hours post methamphetamine treatment.

RESULTS

We found that Hc-TeTx significantly reduced the loss of dopaminergic markers tyrosine hydroxylase and dopamine transporter and the increases in silver staining (a well stablished degeneration marker) induced by methamphetamine in the striatum. Moreover, Hc-TeTx prevented the increase of neuronal nitric oxide synthase but did not affect microglia activation induced by methamphetamine. Stereological neuronal count in the substantia nigra indicated loss of tyrosine hydroxylase-positive neurons after methamphetamine that was partially prevented by Hc-TeTx. Importantly, impairment in motor behaviors post methamphetamine treatment were significantly reduced by Hc-TeTx.

CONCLUSIONS

Here we demonstrate that Hc-TeTx can provide significant protection against acute methamphetamine-induced neurotoxicity and motor impairment, suggesting its therapeutic potential in methamphetamine abusers.

The effects of ecstasy on neurotransmitter systems: a review on the findings of molecular imaging studies

RATIONALE

Ecstasy is a commonly used psychoactive drug with 3,4-methylenedioxymethamphetamine (MDMA) as the main content. Importantly, it has been suggested that use of MDMA may be neurotoxic particularly for serotonergic (5-hydroxytryptamine (5-HT)) neurons. In the past decades, several molecular imaging studies examined directly in vivo the effects of ecstasy/MDMA on neurotransmitter systems.

OBJECTIVES

The objective of the present study is to review the effects of ecstasy/MDMA on neurotransmitter systems as assessed by molecular imaging studies in small animals, non-human primates and humans.

METHODS

A search in PubMed was performed. Eighty-eight articles were found on which inclusion and exclusion criteria were applied.

RESULTS

Thirty-three studies met the inclusion criteria; all were focused on the 5-HT or dopamine (DA) system. Importantly, 9 out of 11 of the animal studies that examined the effects of MDMA on 5-HT transporter (SERT) availability showed a significant loss of binding potential. In human studies, this was the case for 14 out of 16 studies, particularly in heavy users. In abstinent users, significant recovery of SERT binding was found over time. Most imaging studies in humans that focused on the DA system did not find any significant effect of ecstasy/MDMA use.

CONCLUSIONS

Preclinical and clinical molecular imaging studies on the effects of ecstasy/MDMA use/administration on neurotransmitter systems show quite consistent alterations of the 5-HT system. Particularly, in human studies, loss of SERT binding was observed in heavy ecstasy users, which might reflect 5-HT neurotoxicity, although alternative explanations (e.g. down-regulation of the SERT) cannot be excluded.

Cognitive judgment bias in the psychostimulant-induced model of mania in rats

RATIONALE

Animal models of mania lack genuine cognitive parameters. The present gold standard of mania models, amphetamine-induced hyperlocomotion, is rather unspecific and does not necessarily target its cardinal symptoms. Therefore, alternative behavioral markers that are sensitive to stimulants are required.

OBJECTIVES

In the present study, by combining the psychostimulant-induced model of mania in rodents with the recently developed ambiguous-cue interpretation (ACI) tests, we investigated the effects of chronic administration of D-amphetamine and cocaine on the cognitive judgment bias of rats.

METHODS

To accomplish this goal, in two separate experiments, previously trained animals received chronic, daily injections of either D-amphetamine (2 mg/kg) or cocaine (10 mg/kg) for 2 weeks and were subsequently tested with the ACI procedure.

RESULTS

Chronic treatment with both psychostimulants did not make rats more "optimistic."

CONCLUSIONS

The results are discussed in terms of behavioral and pharmacological actions of the tested compounds and their implications for modeling mania in animals.

Effects of a short-course MDMA binge on dopamine transporter binding and on levels of dopamine and its metabolites in adult male rats

Although the recreational drug 3,4-methylenedioxymethamphetamine (MDMA) is often described as a selective serotonergic neurotoxin, some research has challenged this view. The objective of this study was to determine the influence of MDMA on subsequent levels of two different markers of dopaminergic function, the dopamine transporter (DAT) as well as dopamine and its major metabolites. In experiment I, adult male Sprague-Dawley rats were administered either a low or moderate dose MDMA binge (2.5 or 5.0mg/kg×4 with an inter-dose interval of 1h) or saline, and were killed 1 week later. The moderate dose dramatically reduced [(3)H]WIN 35,428 binding to striatal DAT by 73.7% (P≤0.001). In experiment II, animals were binged with a higher dose of MDMA (10mg/kg×4) to determine the drug's effects on concentrations of serotonin (5-HT), dopamine, and their respective major metabolites 5-hydroxyindoleacetic acid (5-HIAA), dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in the striatum and frontal cortex 1 week later. As expected, MDMA significantly reduced 5-HT and 5-HIAA (≥50%) in these structures, while only a marginal decrease in dopamine was noted in the striatum. In contrast, levels of DOPAC (34.3%, P<0.01) and HVA (33.5%, P<0.001) were reduced by MDMA treatment, suggesting a decrease in dopamine turnover. Overall, these findings indicate that while serotonergic markers are particularly vulnerable to MDMA-induced depletion, significant dopaminergic deficits may also occur under some conditions. Importantly, DAT expression may be more vulnerable to perturbation by MDMA than dopamine itself.

Methylenedioxymethamphetamine (MDMA, 'Ecstasy'): Neurodegeneration versus Neuromodulation

The amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) is widely abused as a recreational drug due to its unique psychological effects. Of interest, MDMA causes long-lasting deficits in neurochemical and histological markers of the serotonergic neurons in the brain of different animal species. Such deficits include the decline in the activity of tryptophan hydroxylase in parallel with the loss of 5-HT and its main metabolite 5-hydoxyindoleacetic acid (5-HIAA) along with a lower binding of specific ligands to the 5-HT transporters (SERT). Of concern, reduced 5-HIAA levels in the CSF and SERT density have also been reported in human ecstasy users, what has been interpreted to reflect the loss of serotonergic fibers and terminals. The neurotoxic potential of MDMA has been questioned in recent years based on studies that failed to show the loss of the SERT protein by western blot or the lack of reactive astrogliosis after MDMA exposure. In addition, MDMA produces a long-lasting down-regulation of SERT gene expression; which, on the whole, has been used to invoke neuromodulatory mechanisms as an explanation to MDMA-induced 5-HT deficits. While decreased protein levels do not necessarily reflect neurodegeneration, the opposite is also true, that is, neuroregulatory mechanisms do not preclude the existence of 5-HT terminal degeneration.

Impact of methamphetamine on dopamine neurons in primates is dependent on age: implications for development of Parkinson's disease

Methamphetamine is a CNS stimulant with limited therapeutic indications, but is widely abused. Short-term exposure to higher doses, or long-term exposure to lower doses, of methamphetamine induces lasting damage to nigrostriatal dopamine neurons in man and animals. Strong evidence indicates that the mechanism for this detrimental effect on dopamine neurons involves oxidative stress exerted by reactive oxygen species. This study investigates the relative susceptibility of dopamine neurons in mid-gestation, young, and adult (not aged) monkeys to four treatments with methamphetamine over 2 days. Primate dopamine neurons undergo natural cell death at mid-gestation, and we hypothesized that during this event they are particularly vulnerable to oxidative stress. The results indicated that at mid-gestation and in adults, dopamine neurons were susceptible to methamphetamine-induced damage, as indicated by loss of striatal tyrosine hydroxylase (TH) immunoreactivity and dopamine concentration. However, dopamine neurons in young animals appeared totally resistant to the treatment, despite this group having higher brain levels of methamphetamine 3 h after administration than the adults. As a possible explanation for the protection, striatal glial-derived neurotrophic factor (GDNF) levels were elevated in young animals 1 week after treatment, but not in adults following methamphetamine treatment. Implications of these primate studies are: (1) the susceptibility of dopamine neurons at mid-gestation to methamphetamine warns against the risk of exposing pregnant women to the drug or oxidative stressors, and supports the hypothesis of Parkinson's disease being associated with oxidative stress during development, (2) elucidation of the mechanism of resistance of dopamine neurons in the young animals to methamphetamine-induced oxidative stress may provide targets for slowing or preventing age- or disease-related loss of adult nigrostriatal dopamine (DA) neurons, and (3) the increased striatal production of GDNF in young animals, but not in adults, in response to methamphetamine, suggests the possibility of an age-related change in the neurotrophic capacity of the striatal dopamine system.

Methamphetamine and lentivirus interactions: reciprocal enhancement of central nervous system disease

Use of methamphetamine is increasingly a significant factor for the spread of human immunodeficiency virus type 1, for in certain populations, there is a convergence of methamphetamine abuse with human immunodeficiency virus type 1 infection. Methamphetamine and human immunodeficiency virus type 1 are both individually neuropathogenic, and the neuropathology caused by these two agents occurs in overlapping brain regions. However, the biological interaction of methamphetamine with lentiviruses remains unknown. Here, we investigate the effects of simultaneous exposure of these two agents on disease progression using the feline immunodeficiency virus model. The study models the bingeing methamphetamine user with sequential and repeated episodes of use, which were interrupted by periods of abstinence. Methamphetamine exposure significantly accelerated and enhanced the severity of the feline immunodeficiency virus model-induced central nervous system functional pathology, as measured in delays in brainstem auditory evoked potentials. Reciprocally, feline immunodeficiency virus enhanced the severity of the methamphetamine-induced effects on brain monoamine neurotransmitter and dopamine transporter levels. The results of this study indicate that a dual potentiation occurred. That is, methamphetamine enhanced feline immunodeficiency virus model-induced central nervous system disease and feline immunodeficiency virus model enhanced the toxic effects of methamphetamine, heralding a significant concern for those individuals that are exposed to both agents.

Neurochemistry of drug action: insights from proton magnetic resonance spectroscopic imaging and their relevance to addiction

Proton magnetic resonance spectroscopy ((1)H MRS) is a noninvasive imaging technique that permits measurement of particular compounds or metabolites within the tissue of interest. In the brain, (1)H MRS provides a snapshot of the neurochemical environment within a defined volume of interest. A search of the literature demonstrates the widespread utility of this technique for characterizing tumors, tracking the progress of neurodegenerative disease, and for understanding the neurobiological basis of psychiatric disorders. As of relatively recently, (1)H MRS has found its way into substance abuse research, and it is beginning to become recognized as a valuable complement in the brain imaging toolbox that also contains positron emission tomography, single-photon-emission computed tomography, and functional magnetic resonance imaging. Drug abuse studies using (1)H MRS have identified several biochemical changes in the brain. The most consistent alterations across drug class were reductions in N-acetylaspartate and elevations in myo-inositol, whereas changes in choline, creatine, and amino acid transmitters also were abundant. Together, the studies discussed herein provide evidence that drugs of abuse may have a profound effect on neuronal health, energy metabolism and maintenance, inflammatory processes, cell membrane turnover, and neurotransmission, and these biochemical changes may underlie the neuropathology within brain tissue that subsequently gives rise to the cognitive and behavioral impairments associated with drug addiction.

White-matter abnormalities in brain during early abstinence from methamphetamine abuse

BACKGROUND

Previous studies revealed microstructural abnormalities in prefrontal white matter and corpus callosum of long-term abstinent chronic methamphetamine abusers. In view of the importance of the early abstinence period in treatment retention, we compared 23 methamphetamine-dependent subjects abstinent from methamphetamine for 7-13 days with 18 healthy comparison subjects. As certain metabolic changes in the brain first manifest after early abstinence from methamphetamine, it is also possible that microstructural white-matter abnormalities are not yet present during early abstinence.

METHODS

Using diffusion tensor imaging at 1.5 T, fractional anisotropy (FA) was measured in prefrontal white matter at four inferior-superior levels parallel to the anterior commissure-posterior commissure (AC-PC) plane. We also sampled FA in the corpus callosum at the midline and at eight bilateral, fiber-tract sites in other regions implicated in effects of methamphetamine.

RESULTS

The methamphetamine group exhibited lower FA in right prefrontal white matter above the AC-PC plane (11.9% lower; p = 0.007), in midline genu corpus callosum (3.9%; p = 0.019), in left and right midcaudal superior corona radiata (11.0% in both hemispheres, p's = 0.020 and 0.016, respectively), and in right perforant fibers (7.3%; p = 0.025). FA in left midcaudal superior corona radiata was correlated with depressive and generalized psychiatric symptoms within the methamphetamine group.

CONCLUSIONS

The findings support the idea that methamphetamine abuse produces microstructural abnormalities in white matter underlying and interconnecting prefrontal cortices and hippocampal formation. These effects are already present during the first weeks of abstinence from methamphetamine and are linked to psychiatric symptoms assessed during this period.

Equivalent effects of acute tryptophan depletion on REM sleep in ecstasy users and controls

INTRODUCTION

This study sought to test the association between 3,4-methylenedioxymethamphetamine use, serotonergic function and sleep.

MATERIALS AND METHODS

Ambulatory polysomnography was used to measure three nights sleep in 12 ecstasy users and 12 controls after screening (no intervention), a tryptophan-free amino acid mixture (acute tryptophan depletion (ATD)) and a tryptophan-supplemented control mixture.

RESULTS

ATD significantly decreased rapid eye movement (REM) sleep onset latency, increased the amount of REM sleep and increased the amount of stage 2 sleep in the first 3 h of sleep. There was no difference between ecstasy users' and controls' sleep on the screening night or after ATD.

DISCUSSION

These findings imply that the ecstasy users had not suffered significant serotonergic damage as indexed by sleep.

Fetal effects of psychoactive drugs

Psychoactive drug use by pregnant women has the potential to effect fetal development; the effects are often thought to be drug-specific and gestational age dependent. This article describes the effects of three drugs with similar molecular targets that involve monoaminergic transmitter systems: cocaine, methamphetamine, and selective serotonin re-uptake inhibitors (SSRIs) used to treat maternal depression during pregnancy. We propose a possible common epigenetic mechanism for their potential effects on the developing child. We suggest that exposure to these substances acts as a stressor that affects fetal programming, disrupts fetal placental monoamine transporter expression and alters neuroendocrine and neurotransmitter system development. We also discuss neurobehavioral techniques that may be useful in the early detection of the effects of in utero drug exposure.

Acute inhalation exposure to vaporized methamphetamine causes lung injury in mice

Methamphetamine (MA) is currently the most widespread illegally used stimulant in the United States. Use of MA by smoking is the fastest growing mode of administration, which increases concerns about potential pulmonary and other medical complications. A murine exposure system was developed to study the pulmonary affects of inhaled MA. Mice were exposed to 25-100 mg vaporized MA and assessments were made 3 h following initiation of exposure to model acute lung injury. Inhalation of MA vapor resulted in dose-dependent increases in MA plasma levels that were in the range of those experienced by MA users. At the highest MA dose, histological changes were observed in the lung and small but significant increases in lung wet weight to body weight ratios (5.656 +/- 0.176 mg/g for the controls vs. 6.706+/- 0.135 mg/g for the 100 mg MA-exposed mice) were found. In addition, there was 53% increase in total protein in bronchoalveolar lavage (BAL) fluid, greater than 20% increase in albumin levels in the BAL fluid, greater than 2.5-fold increase in lactate dehydrogenase levels in the BAL fluid, and reduced total BAL cell numbers (approximately 77% of controls). Levels of the early response cytokines tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 were dose-dependently increased in BAL fluid of MA-exposed mice. Exposure to 100 mg MA significantly increased free radical generation in the BAL cells to 107-146% of controls and to approximately 135% of the controls in lung tissue in situ. Together, these data show that acute inhalation exposure to relevant doses of volatilized MA is associated with elevated free radical formation and significant lung injury.

Ecstasy produces left ventricular dysfunction and oxidative stress in rats

AIMS

Our aim was to determine whether the repeated, binge administration of 3,4-methylenedioxymethamphetamine (ecstasy; MDMA) produces structural and/or functional changes in the myocardium that are associated with oxidative stress.

METHODS AND RESULTS

Echocardiography and pressure-volume conductance catheters were used to assess left ventricular (LV) structure and function in rats subjected to four ecstasy binges (9 mg/kg i.v. for 4 days, separated by a 10 day drug-free period). Hearts from treated and control rats were used for either biochemical and proteomic analysis or the isolation of adult LV myocytes. After the fourth binge, treated hearts showed eccentric LV dilation and diastolic dysfunction. Systolic function was not altered in vivo; however, the magnitude of the contractile responses to electrical stimulation was significantly smaller in myocytes from rats treated in vivo with ecstasy compared with myocytes from control rats. The magnitude of the peak increase in intracellular calcium (measured by Fura-2) was also significantly smaller in myocytes from ecstasy-treated vs. control rats. The relaxation kinetics of the intracellular calcium transients were significantly longer in myocytes from ecstasy-treated rats. Ecstasy significantly increased nitrotyrosine content in the left ventricle. Proteomic analysis revealed increased nitration of contractile proteins (troponin-T, tropomyosin alpha-1 chain, myosin light polypeptide, and myosin regulatory light chain), mitochondrial proteins (Ub-cytochrome-c reductase and ATP synthase), and sarcoplasmic reticulum calcium ATPase.

CONCLUSION

The repeated binge administration of ecstasy produces eccentric LV dilation and dysfunction that is accompanied by oxidative stress. These functional responses may result from the redox modification of proteins involved in excitation-contraction coupling and/or mitochondrial energy production. Together, these results indicate that ecstasy has the potential to produce serious cardiac toxicity and ventricular dysfunction.

Effect of N-acetylcysteine and/or deferoxamine on oxidative stress and hyperactivity in an animal model of mania

Studies have consistently reported the participation of free radicals in Bipolar Disorder. Administration of d-amphetamine (d-AMPH) is a relevant animal model of mania and it increases oxidative stress in rat brain. Evidences indicate that the antioxidants N-acetylcysteine (NAC) and Deferoxamine (DFX) exert protective effects in the brain. The present study was designed to evaluate the effects of NAC, DFX or their combination on AMPH-induced hyperactivity. The protein oxidation levels were analyzed in prefrontal cortex and hippocampus. In the first animal model (reversal treatment), adult male Wistar rats received saline or d-AMPH for 14 days, and from the 8th to the 14th day, they were treated with saline, NAC, DFX, or NAC plus DFX. In the second animal model (prevention treatment), rats were pretreated with saline or antioxidant regime, and from the 8th to the 14th day, they also received saline or d-AMPH. In the prefrontal cortex, the protein carbonyls were not affected by the treatment with antioxidants alone but it was increased by treatment with NAC plus DFX. At the same model, NAC plus DFX reversed the protein damage in the hippocampus, but NAC alone increased this damage. In the prevention treatment, it was observed that the protein damage in the prefrontal cortex was prevented by DFX or NAC plus DFX. In the hippocampus, the pretreatment with all antioxidant regime prevented protein damage induced by d-AMPH. At both treatments (reversal or prevention) the antioxidants did not present any effect against d-AMPH-induced hyperactivity. In conclusion, NAC or DFX and the combination of NAC plus DFX reverse and protect against d-AMPH-induced oxidative protein damage. Using these protocols we could not observe affects on locomotion, however this effect varies depending on the brain region and the treatment regime.

Ecstasy (MDMA) and memory function: a meta-analytic update

A meta-analysis was conducted to examine the impact of recreational ecstasy use on short-term memory (STM), long-term memory (LTM), verbal and visual memory. We located 26 studies containing memory data for ecstasy and non-ecstasy users from which effect sizes could be derived. The analyses provided measures of STM and LTM in 610 and 439 ecstasy users and revealed moderate-to-large effect sizes (Cohen's d) of d = -0.63 and d = -0.87, respectively. The difference between STM versus LTM was non-significant. The effect size for verbal memory was large (d = -1.00) and significantly larger than the small effect size for visual memory (d = -0.27). Indeed, our analyses indicate that visual memory may be affected more by concurrent cannabis use. Finally, we found that the total lifetime number of ecstasy tablets consumed did not significantly predict memory performance.

MDMA (Ecstasy) and human dopamine, norepinephrine, and serotonin transporters: implications for MDMA-induced neurotoxicity and treatment

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA, designated as "Ecstasy" if illicitly marketed in tablet form) induces significant decrements in neuronal serotonin (5-HT) markers in humans, nonhuman primates, and rats as a function of dosing and dosing regimen. In rats, MDMA-mediated effects are attributed, in part, to selective high-affinity transport of MDMA into 5-HT neurons by the 5-HT transporter (SERT), followed by extensive 5-HT release.

OBJECTIVES

To clarify whether SERT-selective effects of MDMA at human monoamine transporters can account for the reported MDMA-induced selective toxicity of serotonin neurons in primate brain.

METHODS

We investigated the interaction of [(3)H](+/-, RS)- (+, S)- and (-, R)-MDMA with the human SERT, dopamine (DA) transporter (DAT), and norepinephrine (NE) transporter (NET) in stably transfected human embryo kidney (HEK)-293 cells.

RESULTS

The human DAT, NET, and SERT actively transported [(3)H]RS(+/-)-MDMA saturably, stereoselectively, and in a temperature-, concentration-, and transporter-dependent manner. MDMA exhibited the highest affinity for the NET>>SERT>or=DAT, the same rank order for MDMA inhibition of [(3)H]DA, [(3)H]NE, and [(3)H]5-HT transport and stimulated release of the [(3)H]monoamines, which differed from reports derived from rodent monoamine transporters. The extent of MDMA-induced release of 5-HT was higher compared with release of DA or NE.

CONCLUSIONS

The affinity of MDMA for the human SERT in transfected cells does not clarify the apparent selective toxicity of MDMA for serotonin neurons, although conceivably, its higher efficacy for stimulating 5-HT release may be a distinguishing factor. The findings highlight the need to investigate MDMA effects in DAT-, SERT-, and NET-expressing neurons in the primate brain and the therapeutic potential of NET or DAT inhibitors, in addition to SERT-selective inhibitors, for alleviating the pharmacological effects of MDMA.

Dopamine transporters and cognitive function in methamphetamine abuser after a short abstinence: A SPECT study

The purpose of this study was to examine the change of dopamine transporters (DAT) binding in methamphetamine (METH) abusers in a two-week period of abstinence and its association with cognitive function. Seven healthy subjects and seven METH abusers were recruited. At baseline conditions, the values of specific uptake ratio (SUR) of DAT binding measured by single photon emission computed tomography were lower in METH abusers than in controls. After a two-week period of abstinence, DAT binding was partially recovered and there were no statistic differences in SUR between METH abusers and controls. There was a borderline correlation between the changes of DAT binding in the right, but not the left, striatum and the %Error of Wisconsin Card Sorting Test. These findings indicate that DAT binding in METH abusers can be reversed in a short period of abstinence. The recovery of DAT binding was asymmetric and possibly parallel with the improvement of cognitive function.

Increased oxidative stress in submitochondrial particles after chronic amphetamine exposure

Previous studies have suggested that reactive oxygen species (ROS) production may play a role in the pathophysiology of many neuropsychiatric disorders, such as bipolar disorder (BD) and schizophrenia (SCZ). In addition, there is an emerging body of data indicating that BD and SCZ may be associated with mitochondrial dysfunction. We studied the effects of acute and chronic d-amphetamine on ROS production in submitochondrial particles of rat brain. Male Wistar rats were divided in two experimental groups: acute and chronic treatment. In the acute treatment, rats received one single IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline (control group). In the chronic treatment, rats received one daily IP injection of d-amphetamine (1, 2 or 4 mg/kg) or saline for 7 days. Locomotor activity was assessed with the open field task, and thiobarbituric acid reactive substances (TBARS) and superoxide production were measured in submitochondrial particles of the prefrontal cortex and hippocampus. Both acute and chronic amphetamine treatment increased locomotor behavior. Chronic amphetamine exposure induced a 3- to 6-fold increase of TBARS and a 1.5- to 2-fold increase of superoxide production in submitochondrial particles of prefrontal cortex and hippocampus (P < 0.05). No effects on superoxide or TBARS were observed with acute treatment. These findings suggest that amphetamine-induced mitochondrial ROS generation may be a useful model to investigate the hypothesis of altered brain energy metabolism associated with BD and SCZ. Further studies assessing the effects of mood stabilizers and antipsychotics in preventing mitochondrial oxidative stress are necessary.

Ecstasy: are animal data consistent between species and can they translate to humans?

The number of 3,4-methylenedioxymethamphetamine (ecstasy or MDMA) animal research articles is rapidly increasing and yet studies which place emphasis on the clinical significance are limited due to a lack of reliable human data. MDMA produces an acute, rapid release of brain serotonin and dopamine in experimental animals and in the rat this is associated with increased locomotor activity and the serotonin behavioural syndrome in rats. MDMA causes dose-dependent hyperthermia, which is potentially fatal, in humans, primates and rodents. Subsequent serotonergic neurotoxicity has been demonstrated by biochemical and histological studies and is reported to last for months in rats and years in non-human primates. Relating human data to findings in animals is complicated by reports that MDMA exposure in mice produces selective long-term dopaminergic impairment with no effect on serotonin. This review compares data obtained from animal and human studies and examines the acute physiological, behavioural and biochemical effects of MDMA as well as the long-term behavioural effects together with serotonergic and dopaminergic impairments. Consideration is also given to the role of neurotoxic metabolites and the influence of age, sex and user groups on the long-term actions of MDMA.

Role of nitrergic system in behavioral and neurotoxic effects of amphetamine analogs

Several amphetamine analogs are potent psychostimulants and major drugs of abuse. In animal models, the psychomotor and reinforcing effects of amphetamine, methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy), and methylphenidate (MPD; Ritalin) are thought to be dependent on increased extracellular levels of dopamine (DA) in mesocorticolimbic and mesostriatal pathways. However, amphetamine analogs that increase primarily serotonergic transmission, such as p-chloroamphetamine (PCA) and fenfluramine (FEN), have no potential for abuse. High doses of METH, MDMA, PCA, and FEN produce depletions of dopaminergic and serotonergic nerve terminal markers and are considered as potential neurotoxicants. The first part of this review briefly summarizes the behavioral and neurotoxic effects of amphetamines that have a different spectrum of activity on dopaminergic and serotonergic systems. The second part discusses evidence supporting involvement of the nitrergic system in dopamine-mediated effects of amphetamines. The nitrergic system in this context corresponds to nitric oxide (NO) produced from neuronal nitric oxide synthase (nNOS) that has roles in nonsynaptic interneuronal communication and excitotoxic neuronal injury. Increasing evidence now suggests cross talk between dopamine, glutamate, and NO. Results from our laboratory indicate that dopamine-dependent psychomotor, reinforcing, and neurotoxic effects of amphetamines are diminished by pharmacological blockade of nNOS or deletion of the nNOS gene. These findings, and evidence supporting the role of NO in synaptic plasticity and neurotoxic insults, suggest that NO functions as a neuronal messenger and a neurotoxicant subsequent to exposure to amphetamine-like psychostimulants.

The differential effects of ecstasy/polydrug use on executive components: shifting, inhibition, updating and access to semantic memory

RATIONALE/OBJECTIVES

Recent theoretical models suggest that the central executive may not be a unified structure. The present study explored the nature of central executive deficits in ecstasy users.

METHODS

In study 1, 27 ecstasy users and 34 non-users were assessed using tasks to tap memory updating (computation span; letter updating) and access to long-term memory (a semantic fluency test and the Chicago Word Fluency Test). In study 2, 51 ecstasy users and 42 non-users completed tasks that assess mental set switching (number/letter and plus/minus) and inhibition (random letter generation).

RESULTS

MANOVA revealed that ecstasy users performed worse on both tasks used to assess memory updating and on tasks to assess access to long-term memory (C- and S-letter fluency). However, notwithstanding the significant ecstasy group-related effects, indices of cocaine and cannabis use were also significantly correlated with most of the executive measures. Unexpectedly, in study 2, ecstasy users performed significantly better on the inhibition task, producing more letters than non-users. No group differences were observed on the switching tasks. Correlations between indices of ecstasy use and number of letters produced were significant.

CONCLUSIONS

The present study provides further support for ecstasy/polydrug-related deficits in memory updating and in access to long-term memory. The surplus evident on the inhibition task should be treated with some caution, as this was limited to a single measure and has not been supported by our previous work.

Long-term effects of MDMA (Ecstasy) on the human central nervous system revealed by visual evoked potentials

Several studies indicate long-term cognitive impairment of MDMA (ecstasy) users. In the present study we attempted to establish whether electrophysiological correlates of low-level cognitive processes present a long-term alteration, dependent on the level of use of ecstasy. We addressed this issue by investigating amplitude and latency of VEPs related to a very simple discrimination task involving sustained attention (arousal). Eight heavy-MDMA users, eight moderate-MDMA users and 18 drug-free control subjects were asked to discriminate whether the digit at the centre of the screen was 1 or 2. None of the subjects (except one) had used MDMA in the 6 months previous testing. We measured psychophysical performance and EEG, recorded in Oz and Fz during task execution. The heavy-MDMA users made significantly more errors than the other two groups (p < .05). Moreover, they presented reduced amplitude but not latency of VEPs in both Oz and Fz. The effect in Oz is present in P200 (for heavy users only, p < .05) and in P300 components (for both MDMA groups; heavy users: p < .001, moderate users: p < .0.5). In Fz, the amplitude effect is present in N250 (for heavy users only, p < .05) and in P300 components (for both MDMA groups; heavy users: p < .05, moderate users: p < .05). The three groups do not differ in early components, reflecting low-level processing. These results provide evidence of long-term electrophysiological abnormality displayed by ecstasy users and agree with the suggestion that even typical recreational doses of ecstasy are sufficient to cause long-term altered cortical activity in humans.

Human and animal hepatocytes in vitro with extrapolation in vivo

Human and animal hepatocytes are now being used as an in vitro technique to aid drug discovery by predicting the in vivo metabolic pathways of drugs or new chemical entities (NCEs), identifying drug-metabolizing enzymes and predicting their in vivo induction. Because of the difficulty of establishing whether the cytotoxic susceptibility of human hepatocytes to xenobiotics/drugs in vitro could be used to predict in vivo human hepatotoxicity, a comparison of the susceptibility of the hepatocytes of human and animal models to six chemical classes of drugs/xenobiotics in vitro have been related to their in vivo hepatotoxicity and the corresponding activity of their metabolizing enzymes. This study showed that the cytotoxic effectiveness of 16 halobenzenes towards rat hepatocytes in vitro using higher doses and short incubation times correlated well with rat hepatotoxic effectiveness in vivo with lower doses/longer times. The hepatic/hepatocyte xenobiotic metabolizing enzyme activities of various animal species and human have been reviewed for use by veterinarians and research scientists. Where possible, recommendations have been made regarding which animal hepatocyte model is most applicable for modeling the susceptibility to xenobiotic induced hepatotoxicity of those humans with slow versus rapid metabolizing enzyme polymorphisms. These recommendations are based on the best human fit for animal drug/xenobiotic metabolizing enzymes in terms of activity, kinetics and substrate/inhibitor specificity. The use of human hepatocytes from slow versus rapid metabolizing individuals for drug metabolism/cytotoxicity studies; and the research use of freshly isolated rat hepatocytes and "Accelerated Cytotoxicity Mechanism Screening" (ACMS) techniques for identifying drug/xenobiotic reactive metabolites are also described. Using these techniques the molecular hepatocytotoxic mechanisms found in vitro for seven classes of xenobiotics/drugs were found to be similar to the rat hepatotoxic mechanisms reported in vivo.

Lobeline Attenuates Methamphetamine-Induced Changes in Vesicular Monoamine Transporter 2 Immunoreactivity and Monoamine Depletions in the Striatum

L-Lobeline is an alkaloid that inhibits the behavioral effects of methamphetamine (METH) in rats. No studies have examined the effects of lobeline on the acute and long-term neurochemical changes produced by neurotoxic doses of METH. The effects of lobeline on METH-induced dopamine release, alterations in vesicular monoamine transporter 2 (VMAT-2) distribution, and long-term depletions of dopamine and serotonin (5-HT) content in the rat striatum were examined. METH increased body temperature and dopamine release, decreased VMAT-2 immunoreactivity at 1 and 24 h after METH, and decreased dopamine and 5-hydroxytryptamine (5-HT) content in striatum when examined 7 days later. Prevention of METH-induced hyperthermia attenuated the decrease in VMAT-2 as well as dopamine and 5-HT content. Lobeline pretreatment did not affect METH-induced dopamine release but attenuated the decreases in VMAT-2 after METH and the long-term decreases in striatal dopamine and 5-HT content. These effects of lobeline were due partly to the attenuation of METH-induced hyperthermia. The maintenance of hyperthermia during lobeline + METH exposure restored the effects of METH on decreases in VMAT-2 as well as dopamine and 5-HT content. To examine the effects of lobeline independent of its effects on METH-induced hyperthermia, lobeline was administered after METH when body temperature returned to normal. Lobeline treatment at 5 and 7 h after METH attenuated the METH-induced decreases in synaptosomal, membrane-associated, and vesicular VMAT-2 24 h after METH, as well as the METH-induced decreases in dopamine and 5-HT content 7 days later. Therefore, lobeline has both temperature-dependent and -independent neuroprotective effects against METH toxicity.

Acute and long-term effects of MDMA on cerebral dopamine biochemistry and function

RATIONALE AND OBJECTIVES

The majority of experimental and clinical studies on the pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) tend to focus on its action on 5-HT biochemistry and function. However, there is considerable evidence for MDMA having marked acute effects on dopamine release. Furthermore, while MDMA produces long-term effects on 5-HT neurones in most species examined, in mice its long-term effects appear to be restricted to the dopamine system. The objective of this review is to examine the actions of MDMA on dopamine biochemistry and function in mice, rats, guinea pigs, monkeys and humans.

RESULTS AND DISCUSSION

MDMA appears to produce a major release of dopamine from its nerve endings in all species investigated. This release plays a significant role in the expression of many of the behaviours that occur, including behavioural changes, alterations of the mental state in humans and the potentially life-threatening hyperthermia that can occur. While MDMA appears to be a selective 5-HT neurotoxin in most species examined (rats, guinea pigs and primates), it is a selective dopamine neurotoxin in mice. Selectivity may be a consequence of what neurotoxic metabolites are produced (which may depend on dosing schedules), their selectivity for monoamine nerve endings, or the endogenous free radical trapping ability of specific nerve endings, or both. We suggest more focus be made on the actions of MDMA on dopamine neurochemistry and function to provide a better understanding of the acute and long-term consequences of using this popular recreational drug.

Multiple molecular and neuropharmacological effects of MDMA (Ecstasy)

3,4-Methylenedioxymethamphetamine (MDMA), commonly referred to as Ecstasy, is a widely abused, psychoactive recreational drug, which induces short- and long-term neuropsychiatric behaviors. This drug is neurotoxic to serotonergic neurons in vivo, and induces programmed cell death in cultured human serotonergic cells and rat neocortical neurons. Over the years it has been shown that MDMA alters the release of several neurotransmitters in the brain, it induces recompartmentation of intracellular serotonin and c-fos, and modifies the expression of a few genes. Recently, we observed changes in gene expression in mice treated with MDMA, and cloned and sequenced 11 cDNAs thus affected (4 correspond to known and 7 to unknown genes). The effect of MDMA on two of these genes, GABA transporter 1 and synaptotagmin IV was studied in detail. Characterization of the relationship between a given gene and certain physiological or behavioral effects of MDMA could shed light on the mechanism of the drug's action. However, establishing such a connection is difficult for several reasons, including that serotonergic neurons are not the only cells affected by MDMA. In this review, molecular and neurochemical events that occur in the brain following exposure to MDMA, and link between the observed molecular changes with known physiological effects of the drug are discussed. It is indicated that MDMA alters the expression of several proteins involved in GABA neurotransmission, thus having critical effect on thermoregulation and MDMA acute toxicity. This analysis should facilitate development of novel approaches to prevent deleterious effects, especially mortality induced by MDMA and other abused psychostimulants.

Why is parkinsonism not a feature of human methamphetamine users?

For more than 50 years, methamphetamine has been a widely used stimulant drug taken to maintain wakefulness and performance and, in high doses, to cause intense euphoria. Animal studies show that methamphetamine can cause short-term and even persistent depletion of brain levels of the neurotransmitter dopamine. However, the clinical features of Parkinson's disease, a dopamine deficiency disorder of the brain, do not appear to be characteristic of human methamphetamine users. We compared dopamine levels in autopsied brain tissue of chronic methamphetamine users with those in patients with Parkinson's disease and in a control group. Mean dopamine levels in the methamphetamine users were reduced more in the caudate (-61%) than in the putamen (-50%), a pattern opposite to that of Parkinson's disease. Some methamphetamine users had severely decreased dopamine levels, within the parkinsonian range, in the caudate (up to 97% dopamine loss) but not in the putamen. As the putamen and caudate subserve aspects of motor and cognitive function, respectively, our data suggest that methamphetamine users are not parkinsonian because dopamine levels are not sufficiently decreased in the motor component of the striatum. However, the near-total reduction in the caudate could explain reports of cognitive disturbances, sometimes disabling, in some drug users, and suggests that treatment with dopamine substitution medication (e.g. levodopa) during drug rehabilitation might be helpful.

The Neuropsychopharmacology and Toxicology of 3,4-methylenedioxy-N-ethyl-amphetamine (MDEA)

This paper reviews the pharmacology and toxicology of 3,4-methylenedioxy-N-ethylamphetamine (MDEA, "eve"). MDEA is a ring-substituted amphetamine (RSA) like MDMA, its well known N-methyl analog. Both have become very popular substances of abuse in the techno- and house-music scene. They can evoke psychomotor stimulation, mild alterations of perception, sensations of closeness and a positive emotional state as well as sympathomimetic physical effects. At present, the name "ecstasy" is no longer used only for MDMA, but for the whole group of RSAs (MDA, MDMA, MDEA and MBDB) as they are chemically and pharmacologically nearly identical; moreover, many ecstasy pills contain mixtures of the RSAs. Hence, for a selective review on MDEA, it is crucial to strictly differentiate between: 1) street and chemical names, and 2) studies with or without chemically defined substances. In order to present MDEA-specific information, the pharmacodynamics and kinetics are described on the basis of MDEA challenge studies in animals and humans. In the toxicology section, we present a collection of case reports on fatalities where MDEA was toxicologically confirmed. On the question of serotonergic neurotoxicity and possible long-term consequences, however, MDEA-specific information is available from animal studies only. The neurotoxic potential of MDEA in humans is difficult to estimate, as ecstasy users do not consume pure substances. For future research, challenge studies in animals using dosing regimens adapted to human consumption patterns are needed. Such challenge studies should directly compare individual RSAs. They will represent the most viable and fruitful approach to the resolution of the highly controversial issues of serotonergic neurotoxicity and its functional consequences.

Chronic stress augments the long-term and acute effects of methamphetamine

There is growing evidence that exposure to stress alters the acute effects of abused drugs on the CNS. However, it is not known whether stress augments the longer-term neurotoxic effects of psychostimulant drugs, such as methamphetamine. Methamphetamine at high doses decreases forebrain dopamine concentrations. The current study tested the hypothesis that 10 days of unpredictable stress augmented striatal dopamine depletions 7 days following four injections of either 7.5 or 10 mg/kg methamphetamine (1 injection every 2 h). Furthermore, to assess the effects of chronic stress on immediate responses to methamphetamine, extracellular striatal dopamine and methamphetamine concentrations, and rectal temperature were monitored during the methamphetamine injection regimen. Seven days following either a 7.5 mg/kg or 10 mg/kg methamphetamine injection regimen, male rats exposed to unpredictable stress showed greater depletions in striatal dopamine tissue content compared with non-stressed controls injected with methamphetamine. Stressed rats had increased hyperthermic responses and dopamine efflux in the striatum during the methamphetamine injections when compared with non-stressed control rats. Moreover, stressed rats had an increased mortality rate (33%) compared with non-stressed controls (16.7%) following four injections of 10 mg/kg methamphetamine. The enhanced acute and longer-term effects of methamphetamine in stressed rats was not due to a greater concentrations of methamphetamine in the striatum, as extracellular levels of methamphetamine during the injection regimen did not differ between the two groups. In summary, exposure to 10 days of chronic unpredictable stress augments longer-term depletions of dopamine in the striatum, as well as acute methamphetamine-induced hyperthermia and extracellular dopamine levels. These findings suggest that chronic stress increases the responsiveness of the brain to the acute pharmacological effects of methamphetamine and enhances the vulnerability of the brain to the neurotoxic effects of psychostimulants.

Chronic cannabis abuse raises nerve growth factor serum concentrations in drug-naive schizophrenic patients

Long-term cannabis abuse may increase the risk of schizophrenia. Nerve growth factor (NGF) is a pleiotropic neurotrophic protein that is implicated in development, protection and regeneration of NFG-sensitive neurones. We tested the hypothesis that damage to neuronal cells in schizophrenia is precipitated by the consumption of cannabis and other neurotoxic substances, resulting in raised NGF serum concentrations and a younger age for disease onset. The NGF serum levels of 109 consecutive drug-naive schizophrenic patients were measured and compared with those of healthy controls. The results were correlated with the long-term intake of cannabis and other illegal drugs. Mean (+/- SD) NGF serum levels of 61 control persons (33.1 +/- 31.0 pg/ml) and 76 schizophrenics who did not consume illegal drugs (26.3 +/- 19.5 pg/ml) did not differ significantly. Schizophrenic patients with regular cannabis intake (> 0.5 g on average per day for at least 2 years) had significantly raised NGF serum levels of 412.9 +/- 288.4 pg/ml (n = 21) compared to controls and schizophrenic patients not consuming cannabis (p < 0.001). In schizophrenic patients who abused not only cannabis, but also additional substances, NGF concentrations were as high as 2336.2 +/- 1711.4 pg/ml (n = 12). On average, heavy cannabis consumers suffered their first episode of schizophrenia 3.5 years (n = 21) earlier than schizophrenic patients who abstained from cannabis. These results indicate that cannabis is a possible risk factor for the development of schizophrenia. This might be reflected in the raised NGF-serum concentrations when both schizophrenia and long-term cannabis abuse prevail.

Neuroimaging in drug abuse

Neuroimaging techniques, including positron emission tomography (PET), are ideally suited for studies of addiction. These minimally invasive modalities yield information about acute and long-term drug-induced structural and functional changes in the brain over time. Changes can be observed in the brains of human and animal subjects during drug self-administration. Neuroimaging with PET allows precise quantification and visualization of the drug and its rates of movement in the body. In addition, imaging reveals recovery of function and reappearance of neuronal markers in abstinent drug users. Evidence that suggests that PET may have use in identifying individuals predisposed to become addicted is emerging. Finally, candidate pharmacotherapies for drug addiction can be critically evaluated. These unique assets clearly point to the use of these strategies for addiction studies.

Speed kills: cellular and molecular bases of methamphetamine‐induced nerve terminal degeneration and neuronal apoptosis

Methamphetamine (METH) is a drug of abuse that has long been known to damage monoaminergic systems in the mammalian brain. Recent reports have provided conclusive evidence that METH can cause neuropathological changes in the rodent brain via apoptotic mechanisms akin to those reported in various models of neuronal death. The purpose of this review is to provide an interim account for a role of oxygen-based radicals and the participation of transcription factors and the involvement of cell death genes in METH-induced neurodegeneration. We discuss data suggesting the participation of endoplasmic reticulum and mitochondria-mediated activation of caspase-dependent and -independent cascades in the manifestation of METH-induced apoptosis. Studies that use more comprehensive approaches to gene expression profiling should allow us to draw more instructive molecular portraits of the complex plastic and degenerative effects of this drug.

The pharmacology and clinical pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")

The amphetamine derivative (+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug among young people, particularly those involved in the dance culture. MDMA produces an acute, rapid enhancement in the release of both serotonin (5-HT) and dopamine from nerve endings in the brains of experimental animals. It produces increased locomotor activity and the serotonin behavioral syndrome in rats. Crucially, it produces dose-dependent hyperthermia that is potentially fatal in rodents, primates, and humans. Some recovery of 5-HT stores can be seen within 24 h of MDMA administration. However, cerebral 5-HT concentrations then decline due to specific neurotoxic damage to 5-HT nerve endings in the forebrain. This neurodegeneration, which has been demonstrated both biochemically and histologically, lasts for months in rats and years in primates. In general, other neurotransmitters appear unaffected. In contrast, MDMA produces a selective long-term loss of dopamine nerve endings in mice. Studies on the mechanisms involved in the neurotoxicity in both rats and mice implicate the formation of tissue-damaging free radicals. Increased free radical formation may result from the further breakdown of MDMA metabolic products. Evidence for the occurrence of MDMA-induced neurotoxic damage in human users remains equivocal, although some biochemical and functional data suggest that damage may occur in the brains of heavy users. There is also some evidence for long-term physiological and psychological changes occurring in human recreational users. However, such evidence is complicated by the lack of knowledge of doses ingested and the fact that many subjects studied are or have been poly-drug users.

Methamphetamine rapidly decreases mouse vesicular dopamine uptake: role of hyperthermia and dopamine D2 receptors

Multiple high-dose administrations of the dopamine-releasing agent, methamphetamine, rapidly and persistently decrease vesicular dopamine uptake in purified vesicles prepared from striata of treated rats. Because important differences in the neurotoxic effects of stimulants have been documented in rats and mice, the purpose of this study was to determine if methamphetamine-induced effects in rats occur in mice and to elucidate mechanisms underlying these effects. Results reveal methamphetamine treatment rapidly decreased mouse striatal vesicular dopamine uptake; a phenomenon associated with a subcellular redistribution of vesicular monoamine transporter-2 (VMAT-2) immunoreactivity. Both methamphetamine-induced hyperthermia and dopamine D2 receptor activation contributed to the stimulant-induced deficits in vesicular dopamine uptake. Unlike methamphetamine, the dopamine reuptake inhibitors, methylphenidate and cocaine, rapidly increased vesicular dopamine uptake. The implications of these phenomena are discussed.