Damage of serotonergic axons and immunolocalization of Hsp27, Hsp72, and Hsp90 molecular chaperones after a single dose of MDMA administration in Dark Agouti rat: Temporal, spatial, and cellular patterns

In utero exposure to dexamethasone causes a persistent and age-dependent exacerbation of the neurotoxic effects and glia activation induced by MDMA in dopaminergic brain regions of C57BL/6J mice

Clinical and preclinical evidence indicates that prenatal exposure to glucocorticoids may induce detrimental effects in the offspring, including reduction in fetal growth and alterations in the CNS. On this basis, the present study investigated whether in utero exposure to high levels of glucocorticoids is a risk factor that may lead to an exacerbation of the central noxious effects induced by psychoactive drugs consumed later in life. To this end, pregnant C57BL6/J dams were treated with dexamethasone (DEX, 0.05 mg/kg per day) from gestational day 14 until delivery. Thereafter, the male offspring were evaluated to ascertain the magnitude of dopaminergic damage, astrogliosis and microgliosis elicited in the nigrostriatal tract by the amphetamine-related drug 3,4--methylenedioxymethamphetamine (MDMA, 4 × 20 mg/kg, 2 h apart, sacrificed 48 h later) administered at either adolescence or adulthood. Immunohistochemistry was performed in the substantia nigra pars compacta (SNc) and striatum, to evaluate dopaminergic degeneration by measuring tyrosine hydroxylase (TH), as well as astrogliosis and microgliosis by measuring glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA-1), respectively. Moreover, immunohistochemistry was used to ascertain the co-localization of IBA-1 with either the pro-inflammatory interleukin (IL) IL-1β or the anti-inflammatory IL IL-10, in order to determine the microglial phenotype. In utero administration of DEX induced dopaminergic damage by decreasing the density of TH-positive fibers in the striatum, although only in adult mice. MDMA administration induced dopaminergic damage and glia activation in the nigrostriatal tract of adolescent and adult mice. Mice exposed to DEX in utero and treated with MDMA later in life showed a more pronounced loss of dopaminergic neurons (adolescent mice) and astrogliosis (adolescent and adult mice) in the SNc, compared with control mice. These results suggest that prenatal exposure to glucocorticoids may induce an age-dependent and persistent increase in the susceptibility to central toxicity of amphetamine-related drugs used later in life.

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.

Downregulation of the Vitamin D Receptor Regulated Gene Set in the Hippocampus After MDMA Treatment

The active ingredient of ecstasy, ±3,4-methylenedioxymethamphetamine (MDMA), in addition to its initial reinforcing effects, induces selective and non-selective brain damage. Evidences suggest that the hippocampus (HC), a central region for cognition, may be especially vulnerable to impairments on the long-run, nevertheless, transcription factors that may precede and regulate such chronic changes remained uninvestigated in this region. In the current study, we used gene-set enrichment analysis (GSEA) to reveal possible transcription factor candidates responsible for enhanced vulnerability of HC after MDMA administration. Dark Agouti rats were intraperitoneally injected with saline or 15 mg/kg MDMA. Three weeks later HC gene expression was measured by Illumina whole-genome beadarrays and GSEA was performed with MSigDB transcription factor sets. The number of significantly altered genes on the genome level (significance < 0.001) in up/downregulated sets was also counted. MDMA upregulated one, and downregulated 13 gene sets in the HC of rats, compared to controls, including Pax4, Pitx2, FoxJ2, FoxO1, Oct1, Sp3, AP3, FoxO4, and vitamin D receptor (VDR)-regulated sets (q-value <0.05). VDR-regulated set contained the second highest number of significantly altered genes, including among others, Camk2n2, Gria3, and Grin2a. Most identified transcription factors are implicated in the response to ischemia confirming that serious hypoxia/ischemia occurs in the HC after MDMA administration, which may contribute to the selective vulnerability of this brain region. Moreover, our results also raise the possibility that vitamin D supplementation, in addition to the commonly used antioxidants, could be a potential alternative method to attenuate MDMA-induced chronic hippocampal impairments.

Gene expression analysis indicates reduced memory and cognitive functions in the hippocampus and increase in synaptic reorganization in the frontal cortex 3 weeks after MDMA administration in Dark Agouti rats

BACKGROUND

3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") is a widely used entactogenic drug known to impair cognitive functions on the long-run. Both hippocampal and frontal cortical regions have well established roles in behavior, memory formation and other cognitive tasks and damage of these regions is associated with altered behavior and cognitive functions frequently described in otherwise healthy MDMA users. Meanwhile, in post-traumatic stress disorder (PTSD) patients seem to benefit from therapeutic application of the drug, where damage in hippocampal cue extinction may play a role. The aim of this study was to examine the hippocampus, frontal cortex and dorsal raphe of Dark Agouti rats with gene expression arrays (Illumina RatRef bead arrays) looking for possible mechanisms and new candidates contributing to the consequences of a single dose of MDMA (15 mg/kg) 3 weeks earlier.

RESULTS

The number of differentially expressed genes in the hippocampus, frontal cortex and the dorsal raphe were 481, 155, and 15, respectively. Gene set enrichment analysis of the microarray data revealed reduced expression of 'memory' and 'cognition', 'dendrite development' and 'regulation of synaptic plasticity' gene sets in the hippocampus, parallel to the downregulation of CaMK II subunits, glutamate-, CB1 cannabinoid- and EphA4, EphA5, EphA6 receptors. Downregulated gene sets in the frontal cortex were related to protein synthesis, chromatin organization, transmembrane transport processes, while 'dendrite development', 'regulation of synaptic plasticity' and 'positive regulation of synapse assembly' gene sets were upregulated besides elevated levels of a CaMK II subunit and NMDA2B glutamate receptor. Changes in the dorsal raphe region were mild and in most cases not significant.

CONCLUSION

The present data raise the possibility of new synapse formation / synaptic reorganization in the frontal cortex 3 weeks after a single neurotoxic dose of MDMA. In contrast, a prolonged depression of new neurite formation in the hippocampus is proposed by downregulations of members in long-term potentiation pathway and synaptic plasticity emphasizing the particular vulnerability of this brain region and proposing a mechanism responsible for cognitive problems in healthy individuals. At the same time, these results underpin benefits of MDMA in PTSD, where the drug may help memory extinction.

Involvement of autophagy upregulation in 3,4-methylenedioxymethamphetamine ('ecstasy')-induced serotonergic neurotoxicity

It has been suggested that autophagy plays pathogenetic roles in cerebral ischemia, brain trauma, and neurodegenerative disorders. 3,4-Methylenedioxymethamphetamine (MDMA or ecstasy) is an illicit drug that causes long-term serotonergic neurotoxicity in the brain. Apoptosis and necrosis have been implicated in MDMA-induced neurotoxicity, but the role of autophagy in MDMA-elicited serotonergic toxicity has not been investigated. The present study aimed to examine the contribution of autophagy to neurotoxicity in serotonergic neurons in in vitro and in vivo animal models challenged with MDMA. Here, we demonstrated that in cultured rat serotonergic neurons, MDMA exposure induced LC3B-densely stained autophagosome formation, accompanying by a decrease in neurite outgrowth. Autophagy inhibitor 3-methyladenine (3-MA) significantly attenuated MDMA-induced autophagosome accumulation, and ameliorated MDMA-triggered serotonergic neurite damage and neuron death. In contrast, enhanced autophagy flux by rapamycin or impaired autophagosome clearance by bafilomycin A1 led to more autophagosome accumulation in serotonergic neurons and aggravated neurite degeneration. In addition, MDMA-induced autophagy activation in cultured serotonergic neurons might be mediated by serotonin transporter (SERT). In an in vivo animal model administered MDMA, neuroimaging showed that 3-MA protected the serotonin system against MDMA-induced downregulation of SERT evaluated by animal-PET with 4-[(18)F]-ADAM, a SERT radioligand. Taken together, our results demonstrated that MDMA triggers upregulation of autophagy in serotonergic neurons, which appears to be detrimental to neuronal growth.

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.

Attenuation of ecstasy-induced neurotoxicity by N-acetylcysteine

Exposure to 3, 4-methylenedioxymethamphetamine (MDMA) can lead to spatial memory impairments and hippocampal cell death. Numerous evidence indicates that the antioxidant N-acetylcysteine (NAC) exerts protective effects in the brain. The present study evaluates the effects of NAC on MDMA-induced neurotoxicity.

METHODS

We intraperitoneally injected 28 adult male Sprague-Dawley rats (200-250 g) with either 0, 10 mg/kg of MDMA, or 10 mg/kg of MDMA plus 100 mg/kg of NAC. Spatial memory was assessed with a Morris Water Maze (MWM). At the end of the study, rats' brains were removed to study the structure and ultrastructure of CA1, and measure Bcl-2 and Bax expressions in the hippocampus. In the MWM, NAC treatment significantly attenuated the MDMA-induced increase in distance traveled (p < 0.05) and escape latency (p < 0.001). The decreased time spent in the target quadrant in MDMA-treated animals was attenuated by NAC (p < 0.01). NAC significantly protected against MDMA-induced apoptosis and the up- and down-regulation of Bax and Bcl-2, respectively. These data have suggested that NAC could protect against behavioral changes and apoptosis in the hippocampus following administration of MDMA. NAC might be useful for the treatment of neurotoxicity in MDMA users.

Transcriptional evidence for the role of chronic venlafaxine treatment in neurotrophic signaling and neuroplasticity including also Glutamatergic [corrected] - and insulin-mediated neuronal processes

OBJECTIVES

Venlafaxine (VLX), a serotonine-noradrenaline reuptake inhibitor, is one of the most commonly used antidepressant drugs in clinical practice for the treatment of major depressive disorder (MDD). Despite being more potent than its predecessors, similarly to them, the therapeutical effect of VLX is visible only 3-4 weeks after the beginning of treatment. Furthermore, recent papers show that antidepressants, including also VLX, enhance the motor recovery after stroke even in non depressed persons. In the present, transcriptomic-based study we looked for changes in gene expressions after a long-term VLX administration.

METHODS

Osmotic minipumps were implanted subcutaneously into Dark Agouti rats providing a continuous (40 mg/kg/day) VLX delivery for three weeks. Frontal regions of the cerebral cortex were isolated and analyzed using Illumina bead arrays to detect genes showing significant chances in expression. Gene set enrichment analysis was performed to identify specific regulatory networks significantly affected by long term VLX treatment.

RESULTS

Chronic VLX administration may have an effect on neurotransmitter release via the regulation of genes involved in vesicular exocytosis and receptor endocytosis (such as Kif proteins, Myo5a, Sv2b, Syn2 or Synj2). Simultaneously, VLX activated the expression of genes involved in neurotrophic signaling (Ntrk2, Ntrk3), glutamatergic transmission (Gria3, Grin2b and Grin2a), neuroplasticity (Camk2g/b, Cd47), synaptogenesis (Epha5a, Gad2) and cognitive processes (Clstn2). Interestingly, VLX increased the expression of genes involved in mitochondrial antioxidant activity (Bcl2 and Prdx1). Additionally, VLX administration also modulated genes related to insulin signaling pathway (Negr1, Ppp3r1, Slc2a4 and Enpp1), a mechanism that has recently been linked to neuroprotection, learning and memory.

CONCLUSIONS

Our results strongly suggest that chronic VLX treatment improves functional reorganization and brain plasticity by influencing gene expression in regulatory networks of motor cortical areas. These results are consonant with the synaptic (network) hypothesis of depression and antidepressant-induced motor recovery after stroke.

Is brain gliosis a characteristic of chronic methamphetamine use in the human?

Animal data show that high doses of the stimulant drug methamphetamine can damage brain dopamine neurones; however, it is still uncertain whether methamphetamine, at any dose, is neurotoxic to human brain. Since gliosis is typically associated with brain damage and is observed in animal models of methamphetamine exposure, we measured protein levels (intact protein and fragments, if any) of markers of microgliosis (glucose transporter-5, human leukocyte antigens HLA-DRα [TAL.1B5] and HLA-DR/DQ/DPβ [CR3/43]) and astrogliosis (glial fibrillary acidic protein, vimentin, and heat shock protein-27) in homogenates of autopsied brain of chronic methamphetamine users (n=20) and matched controls (n=23). Intact protein levels of all markers were, as expected, elevated (+28%-1270%, P<0.05) in putamen of patients with the neurodegenerative disorder multiple system atrophy (as a positive control) as were concentrations of fragments of glial fibrillary acidic protein, vimentin and heat shock protein-27 (+170%-4700%, P<0.005). In contrast, intact protein concentrations of the markers were normal in dopamine-rich striatum (caudate, putamen) and in the frontal cortex of the drug users. However, striatal levels of cleaved vimentin and heat shock protein-27 were increased (by 98%-211%, P<0.05), with positive correlations (r=0.41-0.60) observed between concentrations of truncated heat shock protein-27 and extent of dopamine loss (P=0.006) and levels of lipid peroxidation products 4-hydroxynonenal (P=0.046) and malondialdehyde (P=0.11). Our failure to detect increased intact protein levels of commonly used markers of microgliosis and astrogliosis could be explained by exposure to methamphetamine insufficient to cause a toxic process associated with overt gliosis; however, about half of the subjects had died of drug intoxication suggesting that "high" drug doses might have been used. Alternatively, drug tolerance to toxic effects might have occurred in the subjects, who were all chronic methamphetamine users. Nevertheless, the finding of above-normal levels of striatal vimentin and heat shock protein-27 fragments (which constituted 10-28% of the intact protein), for which changes in the latter correlated with those of several markers possibly suggestive of damage, does suggest that some astrocytic "disturbance" had occurred, which might in principle be related to methamphetamine neurotoxicity or to a neuroplastic remodeling process. Taken together, our neurochemical findings do not provide strong evidence for either marked microgliosis or astrogliosis in at least a subgroup of human recreational methamphetamine users who used the drug chronically and shortly before death. However, a logistically more difficult quantitative histopathological study is needed to confirm whether glial changes occur or do not occur in brain of human methamphetamine (and amphetamine) users.

Effects of stress and MDMA on hippocampal gene expression

MDMA (3,4-methylenedioxymethamphetamine) is a substituted amphetamine and popular drug of abuse. Its mood-enhancing short-term effects may prompt its consumption under stress. Clinical studies indicate that MDMA treatment may mitigate the symptoms of stress disorders such as posttraumatic stress syndrome (PTSD). On the other hand, repeated administration of MDMA results in persistent deficits in markers of serotonergic (5-HT) nerve terminals that have been viewed as indicative of 5-HT neurotoxicity. Exposure to chronic stress has been shown to augment MDMA-induced 5-HT neurotoxicity. Here, we examine the transcriptional responses in the hippocampus to MDMA treatment of control rats and rats exposed to chronic stress. MDMA altered the expression of genes that regulate unfolded protein binding, protein folding, calmodulin-dependent protein kinase activity, and neuropeptide signaling. In stressed rats, the gene expression profile in response to MDMA was altered to affect sensory processing and responses to tissue damage in nerve sheaths. Subsequent treatment with MDMA also markedly altered the genetic responses to stress such that the stress-induced downregulation of genes related to the circadian rhythm was reversed. The data support the view that MDMA-induced transcriptional responses accompany the persistent effects of this drug on neuronal structure/function. In addition, MDMA treatment alters the stress-induced transcriptional signature.

Gene expression analysis indicates CB1 receptor upregulation in the hippocampus and neurotoxic effects in the frontal cortex 3 weeks after single-dose MDMA administration in Dark Agouti rats

BACKGROUND

3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") is a widely used recreational drug known to impair cognitive functions on the long-run. Both hippocampal and frontal cortical regions have well established roles in behavior, memory formation and other cognitive tasks and damage of these regions is associated with altered behavior and cognitive functions, impairments frequently described in heavy MDMA users. The aim of this study was to examine the hippocampus, frontal cortex and dorsal raphe of Dark Agouti rats with gene expression arrays (Illumina RatRef bead arrays) looking for possible mechanisms and new candidates contributing to the effects of a single dose of MDMA (15 mg/kg) 3 weeks earlier.

RESULTS

The number of differentially expressed genes in the hippocampus, frontal cortex and the dorsal raphe were 481, 155, and 15, respectively. Gene set enrichment analysis of the microarray data revealed reduced expression of 'memory' and 'cognition', 'dendrite development' and 'regulation of synaptic plasticity' gene sets in the hippocampus, parallel to the upregulation of the CB1 cannabinoid- and Epha4, Epha5, Epha6 ephrin receptors. Downregulated gene sets in the frontal cortex were related to protein synthesis, chromatin organization, transmembrane transport processes, while 'dendrite development', 'regulation of synaptic plasticity' and 'positive regulation of synapse assembly' gene sets were upregulated. Changes in the dorsal raphe region were mild and in most cases not significant.

CONCLUSION

The present data raise the possibility of new synapse formation/synaptic reorganization in the frontal cortex three weeks after a single neurotoxic dose of MDMA. In contrast, a prolonged depression of new neurite formation in the hippocampus is suggested by the data, which underlines the particular vulnerability of this brain region after the drug treatment. Finally, our results also suggest the substantial contribution of CB1 receptor and endocannabinoid mediated pathways in the hippocampal impairments. Taken together the present study provides evidence for the participation of new molecular candidates in the long-term effects of MDMA.

"Ecstasy"-induced toxicity in SH-SY5Y differentiated cells: role of hyperthermia and metabolites

3,4-Methylenedioxymethamphetamine (MDMA; "ecstasy") is a recreational hallucinogenic drug of abuse known to elicit neurotoxic properties. Hepatic formation of neurotoxic metabolites is thought to play a major role in MDMA-related neurotoxicity, though the mechanisms involved are still unclear. Here, we studied the neurotoxicity mechanisms and stability of MDMA and 6 of its major human metabolites, namely α-methyldopamine (α-MeDA) and N-methyl-α-methyldopamine (N-Me-α-MeDA) and their correspondent glutathione (GSH) and N-acetyl-cysteine (NAC) conjugates, under normothermic (37 °C) or hyperthermic conditions (40 °C), using cultured SH-SY5Y differentiated cells. We showed that MDMA metabolites exhibited toxicity to SH-SY5Y differentiated cells, being the GSH and NAC conjugates more toxic than their catecholic precursors and MDMA. Furthermore, whereas the toxicity of the catechol metabolites was potentiated by hyperthermia, NAC-conjugated metabolites revealed higher toxicity under normothermia and GSH-conjugated metabolites-induced toxicity was temperature-independent. Moreover, a time-dependent decrease in extracellular concentration of MDMA metabolites was observed, which was potentiated by hyperthermia. The antioxidant NAC significantly protected against the neurotoxic effects of MDMA metabolites. MDMA metabolites increased intracellular glutathione levels, though depletion in thiol content was observed in MDMA-exposed cells. Finally, the neurotoxic effects induced by the MDMA metabolite N-Me-α-MeDA involved caspase 3 activation. In conclusion, this study evaluated the stability of MDMA metabolites in vitro, and demonstrated that the catechol MDMA metabolites and their GSH and NAC conjugates, rather than MDMA itself, exhibited neurotoxic actions in SH-SY5Y differentiated cells, which were differently affected by hyperthermia, thus highlighting a major role for reactive metabolites and hyperthermia in MDMA's neurotoxicity.

3,4-methylenedioxymethamphetamine induces gene expression changes in rats related to serotonergic and dopaminergic systems, but not to neurotoxicity

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is an amphetamine derivative widely abused by young adults. Although many studies have reported that relatively high doses of MDMA deplete serotonin (5-HT) content and decrease the availability of serotonin transporters (5-HTT), limited evidence is available as to the adaptive mechanisms taking place in gene expression levels in the brain following a dosing regimen of MDMA comparable to human consumption. In order to further clarify this issue, we used quantitative PCR to study the long-term changes induced by acute administration of MDMA (5 mg/kg × 3) in the expression of genes related to serotonergic and dopaminergic systems, as well as those related to cellular toxicity in the cortex, hippocampus, striatum, and brain stem of rats. Seven days after MDMA administration, we found a significantly lower expression of the 5-HTT (Slc6a4) and the vesicular monoamine transporter (Slc18a2) genes in the brain stem area. In the hippocampus, monoamine oxidase B (Maob) and tryptophan hydroxylase 2 (Tph2) gene expressions were increased. In the striatum, tyrosine hydroxylase (Th) expression was decreased, and a lower expression of α-synuclein (Snca) was observed in the cortex. In contrast, no significant changes were observed in the genes considered to be biomarkers of toxicity including the glial fibrillary acidic protein (Gfap) and the heat-shock 70 kD protein 1A (Hspa1a) in any of the structures assayed. These results suggest that MDMA promotes adaptive changes in genes related to serotonergic and dopaminergic functionality, but not in genes related to neurotoxicity.

The neurotoxicity of hallucinogenic amphetamines in primary cultures of hippocampal neurons

3,4-Methylenedioxymethamphetamine (MDMA or "Ecstasy") and 2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) are hallucinogenic amphetamines with addictive properties. The hippocampus is involved in learning and memory and seems particularly vulnerable to amphetamine's neurotoxicity. We evaluated the neurotoxicity of DOI and MDMA in primary neuronal cultures of hippocampus obtained from Wistar rat embryos (E-17 to E-19). Mature neurons after 10 days in culture were exposed for 24 or 48 h either to MDMA (100-800 μM) or DOI (10-100 μM). Both the lactate dehydrogenase (LDH) release and the tetrazolium-based (MTT) assays revealed a concentration- and time-dependent neuronal death and mitochondrial dysfunction after exposure to both drugs. Both drugs promoted a significant increase in caspase-8 and caspase-3 activities. At concentrations that produced similar levels of neuronal death, DOI promoted a higher increase in the activity of both caspases than MDMA. In the mitochondrial fraction of neurons exposed 24h to DOI or MDMA, we found a significant increase in the 67 kDa band of apoptosis inducing factor (AIF) by Western blot. Moreover, 24h exposure to DOI promoted an increase in cytochrome c in the cytoplasmatic fraction of neurons. Pre-treatment with an antibody raised against the 5-HT(2A)-receptor (an irreversible antagonist) greatly attenuated neuronal death promoted by 48 h exposure to DOI or MDMA. In conclusion, hallucinogenic amphetamines promoted programmed neuronal death involving both the mitochondria machinery and the extrinsic cell death key regulators. Death was dependent, at least in part, on the stimulation of the 5-HT(2A)-receptors.

Implications of central immune signaling caused by drugs of abuse: mechanisms, mediators and new therapeutic approaches for prediction and treatment of drug dependence

In the past two decades a trickle of manuscripts examining the non-neuronal central nervous system immune consequences of the drugs of abuse has now swollen to a significant body of work. Initially, these studies reported associative evidence of central nervous system proinflammation resulting from exposure to the drugs of abuse demonstrating key implications for neurotoxicity and disease progression associated with, for example, HIV infection. However, more recently this drug-induced activation of central immune signaling is now understood to contribute substantially to the pharmacodynamic actions of the drugs of abuse, by enhancing the engagement of classical mesolimbic dopamine reward pathways and withdrawal centers. This review will highlight the key in vivo animal, human, biological and molecular evidence of these central immune signaling actions of opioids, alcohol, cocaine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA). Excitingly, this new appreciation of central immune signaling activity of drugs of abuse provides novel therapeutic interventions and opportunities to identify 'at risk' individuals through the use of immunogenetics. Discussion will also cover the evidence of modulation of this signaling by existing clinical and pre-clinical drug candidates, and novel pharmacological targets. Finally, following examination of the breadth of central immune signaling actions of the drugs of abuse highlighted here, the current known common immune signaling components will be outlined and their impact on established addiction neurocircuitry discussed, thereby synthesizing a common neuroimmune hypothesis of addiction.

The Nature of 3, 4-Methylenedioxymethamphetamine (MDMA)-Induced Serotonergic Dysfunction: Evidence for and Against the Neurodegeneration Hypothesis

High doses of the recreational drug 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") have been well-documented to reduce the expression of serotonergic markers in several forebrain regions of rats and nonhuman primates. Neuroimaging studies further suggest that at least one of these markers, the plasma membrane serotonin transporter (SERT), may also be reduced in heavy Ecstasy users. Such effects, particularly when observed in experimental animal models, have generally been interpreted as reflecting a loss of serotonergic fibers and terminals following MDMA exposure. This view has been challenged, however, based on the finding that MDMA usually does not elicit glial cell reactions known to occur in response to central nervous system (CNS) damage. The aim of this review is to address both sides of the MDMA-neurotoxicity controversy, including recent findings from our laboratory regarding the potential of MDMA to induce serotonergic damage in a rat binge model. Our data add to the growing literature implicating neuroregulatory mechanisms underlying MDMA-induced serotonergic dysfunction and questioning the need to invoke a degenerative response to explain such dysfunction.

Low ambient temperature reveals distinct mechanisms for MDMA-induced serotonergic toxicity and astroglial Hsp27 heat shock response in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is a widely used recreational drug known to cause selective long-term serotonergic damage. In our recent paper we described region-specific, dose-dependent increase in the protein expression of astroglial Hsp27 and neuronal Hsp72 molecular chaperones after MDMA administration of rats. Here, we examined the possible interaction of elevated Hsp27 protein level to hyperthermic responses after MDMA administration and its separation from drug-induced serotonergic neurotoxicity. For this, 7-8 week old male Dark Agouti rats were treated with 15 mg/kg i.p. MDMA. Treatment at an ambient temperature of 22 ± 1°C caused a significant elevation of the rectal temperature, an increase of Hsp27 immunoreactive protoplasmic astrocytes in the hippocampus, the parietal and cingulate cortices, and a significant decrease in the density of tryptophan hydroxylase immunoreactive fibers in the same brain regions, 8h as well as 24h after drug administrations. In addition, serotonergic axons exhibited numerous swollen varicosities and fragmented morphology. MDMA treatment at low ambient temperature (10 ± 2°C) almost completely abolished the elevation of body temperature and the increased astroglial Hsp27 expression but failed to alter - or just slightly attenuated - the depletion in the density of tryptophan hydroxylase immunoreactive fibers. These results suggest that the increased astroglial Hsp27 protein expression is rather related to the hyperthermic response after the drug administration and it could be separated from the serotonergic neurotoxicity caused by MDMA. In addition, the induction of Hsp27 per se is uneffective to protect serotonergic fibers after MDMA administration. Our results also suggest that Tph immunohistochemistry is an early and sensitive method to demonstrate MDMA-caused vulnerability.

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.

Ultrastructural characterization of tryptophan hydroxylase 2-specific cortical serotonergic fibers and dorsal raphe neuronal cell bodies after MDMA treatment in rat

RATIONALE

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is a widely used recreational drug known to cause selective long-term serotonergic damage.

OBJECTIVES

The aim of this study was to characterize the ultrastructure of serotonergic pericarya and proximal neurites in the dorsal raphe nucleus as well as the ultrastructure of serotonergic axons in the frontal cortex of adolescent Dark Agouti rats 3 days after treatment with 15 mg/kg i.p. MDMA.

METHODS

Light microscopic immunohistochemistry and pre-embedding immunoelectron microscopy with a novel tryptophan hydroxylase-2 (Tph2) specific antibody, as a marker of serotonergic structures.

RESULTS

Light microscopic analysis showed reduced serotonergic axon density and aberrant swollen varicosities in the frontal cortex of MDMA-treated animals. According to the electron microscopic analysis, Tph2 exhibited diffuse cytoplasmic immunolocalization in dorsal raphe neuronal cell bodies. The ultrastructural-morphometric analysis of these cell bodies did not indicate pathological changes or significant alteration in the cross-sectional areal density of any examined organelles. Proximal serotonergic neurites in the dorsal raphe exhibited no ultrastructural alteration. However, in the frontal cortex among intact fibers, numerous serotonergic axons with destructed microtubules were found. Most of their mitochondria were intact, albeit some injured axons also contained degenerating mitochondria; moreover, a few of them comprised confluent membrane whorls only.

CONCLUSIONS

Our treatment protocol does not lead to ultrastructural alteration in the serotonergic dorsal raphe cell bodies and in their proximal neurites but causes impairment in cortical serotonergic axons. In these, the main ultrastructural alteration is the destruction of microtubules although a smaller portion of these axons probably undergo an irreversible damage.

Enzymatic-nonenzymatic cellular antioxidant defense systems response and immunohistochemical detection of MDMA, VMAT2, HSP70, and apoptosis as biomarkers for MDMA (Ecstasy) neurotoxicity

3,4-Methylenedioxymethamphetamine (MDMA)-induced neurotoxicity leads to the formation of quinone metabolities and hydroxyl radicals and then to the production of reactive oxygen species (ROS). We evaluated the effect of a single dose of MDMA (20 mg/kg, i.p.) on the enzymatic and nonenzymatic cellular antioxidant defense system in different areas of rat brain in the early hours (<6 hr) of the administration itself, and we identified the morphological expressions of neurotoxicity induced by MDMA on the vulnerable brain areas in the first 24 hr. The acute administration of MDMA produces a decrease of reduced and oxidized glutathione ratio, and antioxidant enzyme activities were significantly reduced after 3 hr and after 6 hr in frontal cortex. Ascorbic acid levels strongly increased in striatum, hippocampus, and frontal cortex after 3 and 6 hr. High levels of malonaldehyde with respect to control were measured in striatum after 3 and 6 hr and in hippocampus and frontal cortex after 6 hr. An immunohistochemical investigation on the frontal, thalamic, hypothalamic, and striatal areas was performed. A strong positive reaction to the antivesicular monoamine transporter 2 was observed in the frontal section, in the basal ganglia and thalamus. Cortical positivity, located in the most superficial layer was revealed only for heat shock protein 70 after 24 hr.

Effects of 3,4-methylenedioxymethamphetamine (MDMA) on serotonin transporter and vesicular monoamine transporter 2 protein and gene expression in rats: implications for MDMA neurotoxicity

3,4-Methylenedioxymethamphetamine (MDMA; 'Ecstasy') is a popular recreational drug used worldwide. This study aimed to determine the effects of this compound on the expression of nerve terminal serotonergic markers in rats. Experiment 1 investigated MDMA-induced changes in levels of the serotonin transporter (SERT) and the vesicular monoamine transporter 2 (VMAT-2) in the hippocampus, a region with sparse dopaminergic innervation, after lesioning noradrenergic input with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). Adult male Sprague-Dawley rats were administered 100 mg/kg DSP-4 or saline 1 week prior to either an MDMA (10 mg/kg x 4) or saline binge. Two weeks following the binge treatment, the DSP-4/MDMA group unexpectedly showed little change in hippocampal VMAT-2 protein expression compared with DSP-4/Saline controls, despite large reductions in SERT levels in all regions examined in the MDMA-treated animals. Furthermore, animals treated with binge MDMA (Experiment 2) showed a striking decrease in SERT gene expression (and a lesser effect on VMAT-2) measured by quantitative RT-PCR in pooled dorsal and median raphe tissue punches, when compared with saline-treated controls. These results demonstrate that MDMA causes substantial regulatory changes in the expression of serotonergic markers, thus questioning the need to invoke distal axotomy as an explanation of MDMA-related serotonergic deficits.

Acute SSRI-induced anxiogenic and brain metabolic effects are attenuated 6 months after initial MDMA-induced depletion

To assess the functional state of the serotonergic system, the acute behavioural and brain metabolic effect of SSRI antidepressants were studied during the recovery period after MDMA-induced neuronal damage. The effects of the SSRI fluoxetine and the serotonin receptor agonist meta-chloro-phenylpiperazine (m-CPP) were investigated in the social interaction test in Dark Agouti rats, 6 months after treatment with a single dose of MDMA (15 or 30 mg kg(-1), i.p.). At earlier time points these doses of MDMA have been shown to cause 30-60% loss in axonal densities in several brain regions. Densities of the serotonergic axons were assessed using serotonin-transporter and tryptophan-hydroxylase immunohistochemistry. In a parallel group of animals, brain function was examined following an acute challenge with either fluoxetine or citalopram, using 2-deoxyglucose autoradiographic imaging. Six months after MDMA treatment the densities of serotonergic axons were decreased in only a few brain areas including hippocampus and thalamus. Basal anxiety was unaltered in MDMA-treated animals. However, the acute anxiogenic effects of fluoxetine, but not m-CPP, were attenuated in animals pretreated with MDMA. The metabolic response to both citalopram and fluoxetine was normal in most of the brain areas examined with the exception of ventromedial thalamus and hippocampal sub-fields where the response was attenuated. These data provide evidence that 6 months after MDMA-induced damage serotonergic axons show recovery in most brain areas, but serotonergic functions to challenges with SSRIs including anxiety and aggression remain altered.

MDMA treatment 6 months earlier attenuates the effects of CP-94,253, a 5-HT1B receptor agonist, on motor control but not sleep inhibition

The possible long-term effects of the recreational drug "ecstasy" (3,4-methylenedioxymethamphetamine, MDMA) on the function of 5-hydroxytryptamine-1B (5-HT(1B)) receptor in sleep and motor control were investigated using a selective 5-HT(1B) receptor agonist, 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyrinzidyl)-1H-pyrrolo([3,2-b])pyridine hydrochloride (CP-94,253; 5 mg/kg). CP-94,253 or vehicle was administered to freely moving rats pre-treated with MDMA (15 mg/kg) or vehicle 6 months earlier, and polygraphic recording for 24 h and motor activity measurements were performed. Active wake (AW), passive wake (PW), light slow wave sleep (SWS-1), deep slow wave sleep (SWS-2), paradoxical sleep (PS), and diurnal rhythm were analyzed for the whole period. In additional, the EEG power spectrum was calculated for the second hour after the acute treatment for AW, PW, SWS-1, and SWS-2. 5-HT transporter (5-HTT) immunohistochemistry was measured in brain areas related to sleep and motor control 6 months after MDMA treatment. CP-94,253 increased AW and PW, decreased SWS-2 and PS, and altered parameters of diurnal rhythm in control animals. CP-94,253 decreased the EEG power spectra at higher frequencies. The effects of CP-94,253 on AW and diurnal rhythm were reduced or eliminated in MDMA-treated animals. MDMA treatment decreased 5-HTT fibre density in posterior hypothalamus, tuberomammillary nucleus, caudate putamen and ventrolateral striatum. These data suggest that long-term changes in 5-HT(1B) receptor function occur after serotonergic damage caused by a single dose of MDMA.

3,4-Methylenedioxymethamphetamine induces differential regulation of tryptophan hydroxylase 2 protein and mRNA levels in the rat dorsal raphe nucleus

Previous investigations with 3,4-methylenedioxymethamphetamine (MDMA) have suggested that administration of this drug results in a degeneration of 5-HT nerve terminals and subsequent alterations in 5-HT neurotransmission. However, only limited investigations have examined the effects of MDMA on the dorsal raphe nucleus. The present study was designed to assess the effect of MDMA on the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), by measuring TPH2 protein and mRNA levels in rat dorsal raphe (DR) nucleus. Rats were administered MDMA (20 mg/kg, s.c.) or saline twice daily for 4 days and killed 14 days later. Tissue sections of the DR were processed for quantitative immunoautoradiography and in situ hybridization histochemistry for measurements of the levels of TPH2-immunoreactivity (IR) and TPH2 mRNA. To assess 5-HT axon terminal integrity after MDMA treatment, the density of 5-HT transporter (SERT) binding sites was measured by quantitative autoradiography using [125I]RTI-55 ((-)-2beta-carbomethoxy-3 beta-(4-iodophenyl) tropane) ((125)I-RTI-55) as a ligand. TPH2-IR levels were significantly decreased by 45% in the mid DR and by 40% in the caudal DR in the MDMA-treated rats compared with saline-injected rats. In contrast, TPH2 mRNA levels were significantly increased by 24% in the mid DR and by 12% in the caudal DR. MDMA treatment significantly decreased (125)I-RTI-55 labeled SERT binding sites in the striatum, nucleus accumbens and cingulate cortex demonstrating a loss of 5-HT terminals. The increase in TPH2 mRNA levels in both the mid DR and caudal DR of MDMA-treated rats may reflect a compensatory mechanism in the injured 5-HT neurons to increase TPH2 protein synthesis. Taken together, our results suggest that a serious defect occurs in the biosynthesis of TPH2 in the DR following MDMA administration.

Incidental use of ecstasy: no evidence for harmful effects on cognitive brain function in a prospective fMRI study

RATIONALE

Heavy ecstasy use in humans has been associated with cognitive impairments and changes in cognitive brain function supposedly due to damage to the serotonin system. There is concern that even a single dose of 3,4-methylenedioxymethamphetamine may be neurotoxic, but very little is known about the consequences of a low dose of ecstasy for cognitive brain function.

OBJECTIVES

The objective of the study was to assess the effects of a low dose of ecstasy on human cognitive brain function using functional magnetic resonance imaging (fMRI).

MATERIALS AND METHOD

We prospectively studied, as part of the NeXT (Netherlands XTC toxicity) study, sustained effects of a low dose of ecstasy on brain function in 25 subjects before and after their first episode of ecstasy use (mean 2.0 +/- 1.4 ecstasy pills, on average 11.1 +/- 12.9 weeks since last ecstasy use), compared to 24 persistent ecstasy-naive controls, also measured twice and matched with the novice users on age, gender, IQ, and cannabis use. Cognitive brain function was measured in the domains of working memory, selective attention, and associative memory using fMRI.

RESULTS

No significant effects were found of a low dose of ecstasy on working memory, selective attention, or associative memory neither at the behavioral level nor at the neurophysiological level.

CONCLUSIONS

This study yielded no firm evidence for sustained effects of a low dose of ecstasy on human cognitive brain function. The present findings are relevant for the development of prevention and harm reduction strategies. Furthermore, the study is relevant to the discussion concerning potential therapeutic use of ecstasy.

Evidence for a role of Hsp70 in the neuroprotection induced by heat shock pre-treatment against 3,4-methylenedioxymethamphetamine toxicity in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') produces acute hyperthermia which increases the severity of the selective serotoninergic neurotoxicity produced by the drug in rats. Heat shock protein 70 (Hsp70) is a major inducible cellular protein expressed in stress conditions and which is thought to exert protective functions. MDMA (12.5 mg/kg, i.p.), given to rats housed at 22 degrees C, produced an immediate hyperthermia and increased Hsp70 in frontal cortex between 3 h and 7 days after administration. MDMA, given to rats housed at low ambient temperature (4 degrees C) produced transient hypothermia followed by mild hyperthermia but no increase in Hsp70 expression, while rats treated at elevated room temperature (30 degrees C) showed enhanced hyperthermia and similar expression of Hsp70 to that seen in rats housed at 22 degrees C. Fluoxetine-induced inhibition of 5-HT release and hydroxyl radical formation did not modify MDMA-induced Hsp70 expression 3 h later. Four- or 8-day heat shock (elevation of basal rectal temperature by 1.5 degrees C for 1 h) or geldanamycin pre-treatment induced Hsp70 expression and protected against MDMA-induced serotoninergic neurotoxicity without affecting drug-induced hyperthermia. Thus, MDMA-induced Hsp70 expression depends on the drug-induced hyperthermic response and not on 5-HT release or hydroxyl radical formation and pre-induction of Hsp70 protects against the long-term serotoninergic damage produced by MDMA.

Single dose of MDMA causes extensive decrement of serotoninergic fibre density without blockage of the fast axonal transport in Dark Agouti rat brain and spinal cord

Prolonged neurotoxicity of the recreational drug, MDMA (3,4-methylenedioxymethamphetamine) on serotoninergic axon terminals has been suggested. The effect of a single (15 mg/kg) dose of intraperitoneally administered MDMA on serotoninergic fibre density, defined by tryptophan hydroxylase (TpH) and serotonin transporter (5-HTT) immunoreactivity, has been evaluated in the spinal cord and brain areas in Dark Agouti rats, 7 and 180 days after MDMA applications. Immunostaining for amyloid precursor protein (APP) has been performed to examine possible defects of the fast axonal transport, and 5-HTT mRNA expressions were quantified in neurones of medullary raphe nuclei. Seven days after MDMA treatment, a substantial decrease in the density of TpH-immunoreactive fibres was detectable in the frontal cortex, the caudate-putamen, the CA1 region of the hippocampus, and marked decreases were found in the spinal cord. These changes in TpH density showed a high correlation with 5-HTT densities. In contrast, APP-immunoreactive axonal bulbs were not detected in any of the brain regions studied. Seven days after MDMA administrations, significantly elevated 5-HTT mRNA expressions were found in the raphe pallidus and obscurus. Our results suggest that a single dose of MDMA elicits widespread depletion of TpH and 5-HTT immunoreactivity in serotoninergic axons without morphological sign of the blockage of the fast anterograde axonal transport. Our results do not support the notion of MDMA-induced axotomy of serotoninergic neurones. The up-regulation of 5-HTT mRNA expressions 1 week after MDMA injections might indicate the potential recovery of the serotonin system.