MDMA (ecstasy) effects on cultured serotonergic neurons: evidence for Ca2(+)-dependent toxicity linked to release

Transcriptomic Analysis of Glycosylation and Neuroregulatory Pathways in Rodent Models in Response to Psychedelic Molecules

The potential for psychedelic molecules in impacting cognitive flexibility has long been supported and acknowledged across scientific reports. In the current study, an approach leveraging knowledge-based gene-set information analysis has been adopted to explore the potential impact of psychedelic molecules on both glycosylation, (a post-translational modifications (PTM)) and on neuro-regulatory pathways. Though limitations and restrictions rise from the scarcity of publicly available 'omics' data, targeted analysis enabled us to identify a number of key glycogenes (Hexb, Hs6st2, Col9a2, B3gat2, Mgat5, Bgn) involved the structural organization of extracellular matrix and neuroprotective factors (Kl, Pomc, Oxt, Gal, Avp, Cartpt) which play vital roles in neuron protection, development as well as synaptic stability. In response to psychedelic molecules, we found that these genes and associated pathways are transcriptional altered in rodent models. The approach used indicates the potential to exploit existing datasets for hypothesis generation and testing for the molecular processes which play a role in the physiological response to psychedelic molecule effects. These reported findings, which focused on alterations in glycogenes and neuro-regulatory factors may provide a novel range of biomarkers to track the beneficial, as well as potential toxicological effects of psychedelic molecules.

p-Chloroamphetamine decreases serotonin and induces apoptosis in granulosa cells and follicular atresia in prepubertal female rats

Amphetamine derivatives negatively impact serotonin (5-HT) production, which triggers apoptosis in different tissues, depending on the receptor they bind. 5-HT in the ovary stimulates estradiol secretion, a survival factor of granulosa cells. The effect of amphetamine derivatives on the serotonergic system of the ovary and follicular development is unknown. Therefore, in this study, we investigated the effects of p-chloroamphetamine (pCA), derived from amphetamines, on estradiol production, follicular development, apoptosis of granulosa cells, and serotonin 5-HT₇ receptor (R5-HT₇) expression. Female rats (30 days old) were injected with 10mg/kg of pCA intraperitoneally and were euthanized 48 or 120h after treatment. The concentration of 5-HT in the hypothalamus decreased at 48 and 120h after treatment and in the ovary at 120h. The serum concentration of estradiol decreased at all times studied. Follicular atresia, TUNEL-positive (apoptotic) granulosa cells and Bax expression were elevated by pCA, but none of these effects was associated with R5-HT₇ expression. These results suggest that pCA induces the dysregulation of the serotonergic system in the hypothalamus and the ovary, negatively impacting estradiol production and follicular development.

New Insights on Different Response of MDMA-Elicited Serotonin Syndrome to Systemic and Intracranial Administrations in the Rat Brain

In spite of the fact that systemic administration of MDMA elicits serotonin syndrome, direct intracranial administration fails to reproduce the effect. To reconcile these findings, it has been suggested that the cause of serotonin syndrome is attributed mainly to MDMA hepatic metabolites, and less likely to MDMA itself. Recently, however, this explanation has been challenged, and alternative hypotheses need to be explored. Here, we tested the hypothesis that serotonin syndrome is the result of excessive 5HT simultaneously in many brain areas, while MDMA administered intracranially fails to cause serotonin syndrome because it produces only a localized effect at the delivery site and not to other parts of the brain. This hypothesis was examined using adult male Sprague Dawley rats by comparing 5HT responses in the right and left hemispheric frontal cortices, right and left hemispheric diencephalons, and medullar raphe nucleus. Occurrence of serotonin syndrome was confirmed by measuring change in body temperature. Administration routes included intraperitoneal (IP), intracerebroventricular (ICV) and reverse microdialysis. First, we found that IP administration caused excessive 5HT in all five sites investigated and induced hypothermia, suggesting the development of the serotonin syndrome. In contrast, ICV and reverse microdialysis caused excessive 5HT only in regions of delivery sites without changes in body-core temperature, suggesting the absence of the syndrome. Next, chemical dyes were used to trace differences in distribution and diffusion patterns between administration routes. After systemic administration, the dyes were found to be evenly distributed in the brain. However, the dyes administered through ICV or reverse microdialysis injection still remained in the delivery sites, poorly diffusing to the brain. In conclusion, intracranial MDMA administration in one area has no or little effect on other areas, which must be considered a plausible reason for the difference in MDMA-elicited serotonin syndrome between systemic and intracranial administrations.

Chronic SSRI stimulation of astrocytic 5-HT2B receptors change multiple gene expressions/editings and metabolism of glutamate, glucose and glycogen: a potential paradigm shift

It is firmly believed that the mechanism of action of SSRIs in major depression is to inhibit the serotonin transporter, SERT, and increase extracellular concentration of serotonin. However, this undisputed observation does not prove that SERT inhibition is the mechanism, let alone the only mechanism, by which SSRI's exert their therapeutic effects. It has recently been demonstrated that 5-HT2B receptor stimulation is needed for the antidepressant effect of fluoxetine in vivo. The ability of all five currently used SSRIs to stimulate the 5-HT2B receptor equipotentially in cultured astrocytes has been known for several years, and increasing evidence has shown the importance of astrocytes and astrocyte-neuronal interactions for neuroplasticity and complex brain activity. This paper reviews acute and chronic effects of 5-HT2B receptor stimulation in cultured astrocytes and in astrocytes freshly isolated from brains of mice treated with fluoxetine for 14 days together with effects of anti-depressant therapy on turnover of glutamate and GABA and metabolism of glucose and glycogen. It is suggested that these events are causally related to the mechanism of action of SSRIs and of interest for development of newer antidepressant drugs.

The effects of Psychotropic drugs On Developing brain (ePOD) study: methods and design

BACKGROUND

Animal studies have shown that methylphenidate (MPH) and fluoxetine (FLX) have different effects on dopaminergic and serotonergic system in the developing brain compared to the developed brain. The effects of Psychotropic drugs On the Developing brain (ePOD) study is a combination of different approaches to determine whether there are related findings in humans.

METHODS/DESIGN

Animal studies were carried out to investigate age-related effects of psychotropic drugs and to validate new neuroimaging techniques. In addition, we set up two double-blind placebo controlled clinical trials with MPH in 50 boys (10-12 years) and 50 young men (23-40 years) suffering from ADHD (ePOD-MPH) and with FLX in 40 girls (12-14 years) and 40 young women (23-40 years) suffering from depression and anxiety disorders (ePOD-SSRI). Trial registration numbers are: Nederlands Trial Register NTR3103 and NTR2111. A cross-sectional cohort study on age-related effects of these psychotropic medications in patients who have been treated previously with MPH or FLX (ePOD-Pharmo) is also ongoing. The effects of psychotropic drugs on the developing brain are studied using neuroimaging techniques together with neuropsychological and psychiatric assessments of cognition, behavior and emotion. All assessments take place before, during (only in case of MPH) and after chronic treatment.

DISCUSSION

The combined results of these approaches will provide new insight into the modulating effect of MPH and FLX on brain development.

Roles of 3,4-methylenedioxymethamphetamine (MDMA)-induced alteration of connexin43 and intracellular Ca(2+) oscillation in its cardiotoxicity

Although it is well known that 3,4-methylenedioxymethamphetamine (MDMA) can cause various cardiovascular abnormalities and even sudden death from cardiac arrhythmia, whether it has any effect on myocardial gap junctions, which might be one of the targets mediating MDMA-induced cardiotoxicity, remains unclear.

OBJECTIVE

To test the hypothesis that MDMA may affect the myocardial gap junction protein connexin43 (Cx43) and induce cardiac dysrhythmia.

METHOD

(1) In vivo study: adult rats were treated with a single dose MDMA administration (20mg/kg, i.p.). Electrocardiogram detection and immunohistochemical analysis were performed to evaluate cardiac function and expression of Cx43, respectively; (2) in vitro study: cultured ventricular myocytes of neonatal rats were treated with MDMA (10, 100, 1000μmol/L) for 1h. Western blotting and real-time quantitative polymerase chain reaction (RT-qPCR) were performed to investigate the total Cx43 mRNA expression. Immunofluorescent analysis was used to evaluate the amount of junctional Cx43. The phosphorylation status of Cx43 at site Ser368 and intracellular Ca(2+) oscillation were also studied.

RESULTS

Obvious changes in electrocardiographic patterns were found in rats following MDMA administration. They were characterized by prolonged QRS duration associated with increased amplitude of QRS complex. The heart rates in treated rats were significantly decreased compared to the rats in the control group. The immunohistochemical findings revealed a significant decrease in Cx43 expression. The in vitro study also showed a marked decline in total Cx43 protein associated with reduction of Cx43 mRNA, whereas the phosphorylated Cx43 at Ser368 was increased. Decrease of junctional Cx43 was found correlated with reduction in N-cadherin induced by high concentration of MDMA. Additionally, confocal microscopy findings revealed alteration of intracellular calcium oscillation patterns characterized by high frequency and increasing influx Ca(2+).

CONCLUSIONS

MDMA reduces expression of cardiac gap junction protein Cx43. The increase of phosphorylation status of Cx43 at Ser368 induced by MDMA is attributed, at least in part, to the Ca(2+)-dependent regulation of protein kinase C (PKC) activity. Our findings provide first evidence of MDMA-mediated changes in those cardiac gap junctions that may underlie MDMA-induced cardiac arrhythmia.

The effects of ecstasy (MDMA) on brain serotonin transporters are dependent on age-of-first exposure in recreational users and animals

Rationale and Objective

Little is known on the effects of ecstasy (MDMA, a potent 5-HT-releaser and neurotoxin) exposure on brain development in teenagers. The objective of this study was to investigate whether in humans, like previous observations made in animals, the effects of MDMA on the 5-HT system are dependent on age-of-first exposure.

Methods

5-HT transporter (SERT) densities in the frontal cortex and midbrain were assessed with [¹²³I]β-CIT single photon emission computed tomography in 33 users of ecstasy. Subjects were stratified for early-exposed users (age-at-first exposure 14–18 years; developing brain), and late-exposed users (age-at-first exposure 18–36 years; mature brain). In parallel, we investigated the effects of age experimentally with MDMA in early-exposed (adolescent) rats and late-exposed (adult) rats using the same radioligand.

Results

On average, five years after first exposure, we found a strong inverse relationship, wherein age-at-first exposure predicted 79% of the midbrain SERT variability in early (developing brain) exposed ecstasy users, whereas this was only 0.3% in late (mature brain) exposed users (p = 0.007). No such effect was observed in the frontal cortex. In rats, a significant age-BY-treatment effect (p<0.01) was observed as well, however only in the frontal cortex.

Conclusions

These age-related effects most likely reflect differences in the maturational stage of the 5-HT projection fields at age-at-first exposure and enhanced outgrowth of the 5-HT system due to 5-HT’s neurotrophic effects. Ultimately, our findings stress the need for more knowledge on the effects of pharmacotherapies that alter brain 5-HT levels in the pediatric population.

Toxicity of amphetamines: an update

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

Synthesis and serotonin transporter activity of 1,3-bis(aryl)-2-nitro-1-propenes as a new class of anticancer agents

Structural derivatives of 4-MTA, an illegal amphetamine analogue have been previously shown to have anticancer effects in vitro. In this study we report the synthesis of a series of novel 1,3-bis(aryl)-2-nitro-1-propene derivatives related in structure to 4-MTA. A number of these compounds containing a classic nitrostyrene structure are shown to have antiproliferative activities in vitro in a range of malignant cell lines, particularly against Burkitt's lymphoma derived cell lines, whilst having no effect on 'normal' peripheral blood mononuclear cells. Such effects appear to be independent of the serotonin transporter, a high affinity target for amphetamines and independent of protein tyrosine phosphatases and tubulin dynamics both of which have been previously associated with nitrostyrene-induced cell death. We demonstrate that a number of these compounds induce caspase activation, PARP cleavage, chromatin condensation and membrane blebbing in a Burkitt's lymphoma derived cell line, consistent with these compounds inducing apoptosis in vitro. Although no specific target has yet been identified for the action of these compounds, the cell death elicited is potent, selective and worthy of further investigation.

The neurotrophic and neuroprotective effects of psychotropic agents

Accumulating evidence suggests that psychotropic agents such as mood stabilizers, antidepressants, and antipsychotics realize their neurotrophic/neuroprotective effects by activating the mitogen activated protein kinaselextracellular signal-related kinase, PI3-kinase, and winglesslglycogen synthase kinase (GSK) 3 signaling pathways. These agents also upregulate the expression of trophic/protective molecules such as brain-derived neurotrophic factor, nerve growth factor, B-cell lymphoma 2, serine-threonine kinase, and Bcl-2 associated athanogene 1, and inactivate proapoptotic molecules such as GSK-3, They also promote neurogenesis and are protective in models of neurodegenerative diseases and ischemia. Most if not all, of this evidence was collected from animal studies that used clinically relevant treatment regimens. Furthermore, human imaging studies have found that these agents increase the volume and density of brain tissue, as well as levels of N-acetyl aspartate and glutamate in selected brain regions. Taken together, these data suggest that the neurotrophic/neuroprotective effects of these agents have broad therapeutic potential in the treatment, not only of mood disorders and schizophrenia, but also neurodegenerative diseases and ischemia.

Actions of 3,4-methylenedioxymethamphetamine (MDMA) on cerebral dopaminergic, serotonergic and cholinergic neurons

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative and a popular drug of abuse that exhibits mild hallucinogenic and rewarding properties and engenders feelings of connectedness and openness. The unique psychopharmacological profile of this drug of abuse most likely is derived from the property of MDMA to promote the release of dopamine and serotonin (5-HT) in multiple brain regions. The present review highlights primarily data from studies employing in vivo microdialysis that detail the actions of MDMA on the release of these neurotransmitters. Data from in vivo microdialysis experiments indicate that MDMA, like most amphetamine derivatives, increases the release of dopamine in the striatum, n. accumbens and prefrontal cortex. However, the release of dopamine evoked by MDMA in each of these brain regions appears to be modulated by concomitantly released 5-HT and the subsequent activation of 5-HT2A/C or 5-HT2B/C receptors. In addition to its stimulatory effect on the release of monoamines, MDMA also enhances the release of acetylcholine in the striatum, hippocampus and prefrontal cortex, and this cholinergic response appears to be secondary to the activation of histaminergic, dopaminergic and/or serotonergic receptors. Beyond the acute stimulatory effect of MDMA on neurotransmitter release, MDMA also increases the extracellular concentration of energy substrates, e.g., glucose and lactate in the brain. In contrast to the acute stimulatory actions of MDMA on the release of monoamines and acetylcholine, the repeated administration of high doses of MDMA is thought to result in a selective neurotoxicity to 5-HT axon terminals in the rat. Additional studies are reviewed that focus on the alterations in neurotransmitter responses to pharmacological and physiological stimuli that accompany MDMA-induced 5-HT neurotoxicity.

Prior exposure to chronic stress and MDMA potentiates mesoaccumbens dopamine release mediated by the 5-HT(1B) receptor

(+) 3,4,-Methylenedioxymethamphetamine (MDMA) is an abused drug that acutely releases serotonin (5-HT) and dopamine (DA) but produces long-term damage to 5-HT terminals. MDMA-induced DA release has been shown to be dampened by 5-HT. Although stress also activates the mesolimbic DA pathway, it is unknown if chronic stress after exposure to neurotoxic doses of MDMA will augment MDMA-induced DA release in the nucleus accumbens shell (NAcc(sh)). Rats were pretreated with MDMA (10 mg/kg x 4, intraperitoneal (i.p.)). After 7 days, rats were subjected to 10 days of chronic unpredictable stress. DA release in the NAcc(sh) and 5-HT in the ventral tegmental area (VTA) were measured after a challenge injection of MDMA (5 mg/kg, i.p.). The combination of pretreatment with MDMA+stress decreased basal concentrations of 5-HT in the VTA and DA in the NAcc(sh) and enhanced MDMA-stimulated DA release in the NAcc(sh). Pretreatment with MDMA or stress alone blunted MDMA-induced 5-HT release in the VTA. The augmentation of MDMA-induced DA release in rats pretreated with MDMA+chronic stress was attenuated by perfusion of the 5-HT(1B) antagonist, GR127935 into the VTA before the MDMA challenge injection. These results suggest that prior exposure to both MDMA and stress can produce a long-term augmentation in mesolimbic DA transmission and enhanced drug abuse vulnerability that is mediated, in part, by the 5-HT(1B) receptor in the VTA.

(±)3,4-Methylenedioxyamphetamine elicits action potential bursts in a central snail neuron

The effects of (+/-)3,4-methylenedioxyamphetamine (MDA) were studied in an identifiable RP4 neuron of the African snail, Achatina fulica Ferussac, using the two-electrode voltage-clamp method. The RP4 neuron generated spontaneous action potentials. Extracellular or intracellular application of MDA elicited action potential bursts of the central RP4 neuron. The action potential bursts elicited by MDA were not blocked when neurons were immersed in high-Mg2+ solution, Ca2+-free solution, nor after continuous perfusion with atropine, d-tubocurarine, propranolol, prazosin, haloperidol, sulpiride or methiothepin. Notably, the induction of action potential bursts was blocked by pretreatment with protein kinase C (PKC) inhibitors, chelerythrine and Ro 31-8220, but not by protein kinase A (PKA) inhibitors, KT-5720 and H89, nor by the phospholipase C (PLC) inhibitor, U73122. PKC activators, i.e., phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acety-sn-glycerol (OAG; a membrane-permeant DAG analog), facilitate the induction of action potential bursts elicited by MDA. Voltage-clamp studies revealed that MDA decreased the delayed rectifying K+ current (I(KD)) of the RP4 neuron. Further, although Ro 31-8220 did not affect the I(KD), Ro 31-8220 decreased the inhibitory effect of MDA on the I(KD). These results suggest that the generation of action potential bursts elicited by MDA was not due to (1) the synaptic effects of neurotransmitters, (2) the cholinergic, adrenergic, dopaminergic or serotoninergic receptors of the excitable membrane. Instead, the MDA-elicited action potential bursts are closely related to PKC activity and the inhibitory effects on the I(KD).

Modulation of electrically evoked serotonin release in cultured rat raphe neurons

Electrically evoked release of serotonin (5-HT) and its modulation via 5-HT autoreceptors and alpha(2)-heteroreceptors was studied in primary cell cultures prepared from the embryonic (ED 15) rat mesencephalic brain region comprising the raphe nuclei. Cultures were grown for up to 3 weeks on circular glass coverslips. They developed a dense network of non-neuronal and neuronal cells, some of which were positive for tryptophan hydroxylase. To measure 5-HT release, the cultures were pre-incubated with [(3)H]5-HT (in the presence of the selective noradrenaline reuptake inhibitor oxaprotiline [1 micromol/L]), superfused with modified Krebs-Henseleit medium containing 6-nitroqipazine [1 micromol/L] and electrically stimulated using two conditions. Condition A: 360 pulses, 3 Hz, 0.5 ms, 90 mA, or condition B: 4 pulses 100 Hz, 0.5 ms, 90 mA (a condition which diminishes interactions with endogenously released transmitters during ongoing stimulation). After only 1 week in culture, the electrically evoked overflow of [(3)H] was Ca(2+) dependent and tetrodotoxin sensitive, suggesting an action-potential-induced exocytotic release of 5-HT. Using stimulation condition A in cultures grown for 2 weeks, both basal and evoked 5-HT release were strongly enhanced by methiotepine (1 micromol/L) but unaffected by the 5-HT(1B) autoreceptor agonist CP-93, 129 (1 micromol/L) and the alpha(2)-adrenoceptor agonist UK-14, 304 (1 micromol/L). Conversely, using stimulation condition B, not only CP-93, 129 (IC(50) 8.1 +/- 1.4 nmol/L) and UK-14, 304 (IC(50) 14.9 +/- 1.6 nmol/L) had inhibitory effects on cells grown for 2 weeks, but also the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin. In conclusion, we describe for the first time electrically evoked release of 5-HT from primary cultures of fetal raphe cells and its modulation via 5-HT(1B) and 5-HT(1A) auto- and alpha(2)-heteroreceptors. Such cultured raphe cells may represent a suitable model to study expression and development of presynaptic receptors on serotonergic neurons in-vitro.

A Potent Serotonin-Modulating Compound AP-267 Attenuates Morphine Withdrawal-Induced Blood-Brain Barrier Dysfunction in Rats

The possibility that a serotonin 5-HT2c receptor-modulating compound, AP-267, will influence spontaneous morphine withdrawal symptoms and the alterations in the brain fluid microenvironment was examined in a rat model. Daily administration of morphine (10 mg/kg, i.p.) for 10 days resulted in dependence of rats as seen by loss of analgesic response. On the 11th day, no morphine administration was given. This resulted in profound withdrawal symptoms 24 h after morphine withdrawal. The magnitude and severity of these symptoms were increased further 48 h after withdrawal. Measurement of the blood-brain barrier (BBB) permeability, a measure of perturbed brain fluid microenvironment showed leakage of Evans blue and radioiodine tracers in several parts of the brain in rats showing withdrawal symptoms. Whereas, rats treated with AP-267 either on the 1st day or 2nd day morphine withdrawal showed much less symptoms and leakage of the BBB. Taken together, these observations suggest that (a) stress associated with the withdrawal symptoms are sufficient enough to induce breakdown of the BBB function, and (b) modulation of serotonin 5-HT2c receptors may have some protective influence on the stress symptoms and the BBB disruption.

Serotonin transporter expression is not sufficient to confer cytotoxicity to 3,4-methylenedioxymethamphetamine (MDMA) in vitro

There is much evidence from animal studies that the recreational drug MDMA is a selective toxin which damages serotonin nerve terminals and axons. These in vivo studies show that an interaction between MDMA and the serotonin transporter protein (SERT) is the .rst step in toxicity. To further our understanding of the biochemical processes of MDMA toxicity we wished to use an in vitro model for toxicity. We produced two COS-7 cell lines with different levels of expression of recombinant rat SERT, as determined by 5-HT uptake assays, and compared them to human SERT expressing JAR cells and to untransfected COS-7 cells which do not express SERT. Cultured cells were exposed to MDMA (0.1 microM-1 mM) for 24 or 48 h at 37 degrees C before assessing cytotoxicity by LDH release and MTT turnover. Only at the highest concentration used, 1 mM, was MDMA cytotoxic, and this toxicity was found in all cell lines. Cytotoxicity caused by 48 h exposure to 1 mM MDMA at 37 degrees C was not related to the level of SERT expression, not blocked by the SERT-blocking drugs paroxetine or fluoxetine and not enhanced, in JAR cells, by forskolin preincubation that increased 5-HT uptake capacity by 50%. We conclude that SERT expression is not sufficient to confer MDMA toxicity to cell lines. Therefore SERT-expressing cell lines do not offer a simple model system to elucidate the mechanisms underlying MDMA toxicity.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

Methylenedioxymethamphetamine (MDMA, Ecstasy) neurotoxicity: cellular and molecular mechanisms

Methylenedioxymethamphetamine (MDMA, Ecstasy) is a very popular drug of abuse. This has led to new intense concerns relevant to its nefarious neuropsychiatric effects. These adverse events might be related to the neurotoxic effects of the drug. Although the mechanisms of MDMA-induced neurotoxicity remain to be fully characterized, exposure to the drug can cause acute and long-term neurotoxic effects in animals and nonhuman primates. Recent studies have also documented possible toxic effects in the developing fetus. Nevertheless, there is still much debate concerning the effects of the drug in humans and how to best extrapolate animal and nonhuman primate data to the human condition. Herein, we review the evidence documenting the adverse effects of the drug in some animal models. We also discuss possible mechanisms for the development of MDMA neurotoxicity. Data supporting deleterious effects of this drug on the developing fetus are also described. Much remains to be done in order to clarify the molecular and biochemical pathways involved in the long-term neuroplastic changes associated with MDMA abuse.

Stereochemical analysis of 3,4-methylenedioxymethamphetamine and its main metabolites by gas chromatography/mass spectrometry

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is consumed as the racemate but some metabolic steps are enantioselective. In addition, chiral properties are preserved during MDMA biotransformation. A quantitative analytical methodology using gas chromatography/mass spectrometry (GC/MS) to determine enantioselective disposition in the body of MDMA and its main metabolites including 3,4-methylenedioxyamphetamine (MDA), 4-hydroxy-3-methoxymethamphetamine (HMMA), and 4-hydroxy-3-methoxyamphetamine (HMA) was developed. Plasma and urine samples were collected from a male volunteer. The analysis of MDMA, MDA, and 4-hydroxy-3-methoxy metabolites by GC/MS required a two-step derivatization procedure. The first step consisted of derivatization of the amine with enantiomerically pure Mosher's reagent ((R)-MTPCl). Triethylamine was used as a base to neutralize hydrochloric acid formed during the reaction allowing quantitative derivatization, which resulted in a substantial improvement in the sensitivity of the method compared with other previously described techniques. Further treatment with ammonium hydroxide was required since both amine and hydroxyl groups underwent derivatization in the reaction. Ammonium hydroxide breaks bonds formed with hydroxyl groups without affecting amine derivatives. The second derivatization step using hexamethyldisilazane was needed for metabolites containing phenol residues. This derivatization method permitted the stereochemically specific study of MDMA and its main monohydroxylated metabolites by GC/MS. A detailed study of the chemical reactions involved in the derivatization steps was indispensable to develop a straightforward, sensitive, and reproducible method for the analysis of the parent drug compound and its metabolites.

Fetal exposure to (+/-)-methylenedioxymethamphetamine in utero enhances the development and metabolism of serotonergic neurons in three-dimensional reaggregate tissue culture

Methylenedioxymethamphetamine (MDMA, Ecstasy) is a potent psychomotor stimulant with neurotoxic potential which is widely abused by females of childbearing age raising serious public health concerns in terms of exposure of the fetus to the drug. The current study was conducted using the three-dimensional reaggregate tissue culture system as an approach to the assessment of risk to fetal brain cells following exposure to MDMA during early to mid-gestation. In this culture system, the serotonergic and dopaminergic mesencephalic-striatal projections are reconstructed and develop with a time course similar to that observed in vivo. Pregnant C57Bl/6J mice were injected twice daily with 40 mg/kg MDMA or saline from gestational day 6 to 13. On gestational day 14, mesencephalic and striatal cells from MDMA- and saline-exposed embryos were used to prepare reaggregate cultures. Levels of neurotransmitters and their metabolites in the reaggregates and culture medium were assessed at 22 and 36 days of culture. There was a long-term enhancement of serotonergic development and metabolism by fetal exposure to MDMA as evidenced by increased reaggregate serotonin levels as well as the elevated production and release of 5-hydroxyindoleacetic acid in cultures prepared from MDMA-exposed embryos which persisted for up to 36 days of culture. Dopaminergic neurons in such cultures also exhibited increased metabolism as indicated by elevated levels of dihydroxyphenylacetic acid in reaggregate tissue and culture medium. The data obtained suggest that exposure to MDMA in utero during early to mid-gestation may result in more active serotonergic and dopaminergic neurons.

Fetal exposure to methamphetamine in utero stimulates development of serotonergic neurons in three-dimensional reaggregate tissue culture

Methamphetamine is a potent psychomotor stimulant with neurotoxic potential which is widely abused by females of childbearing age, raising serious public health concerns in terms of exposure of the fetus to the drug. The current study was conducted to determine the effect of maternal administration of methamphetamine on developing monoaminergic neurons using three-dimensional reaggregate tissue cultures prepared from fetal mesencephalic and striatal cells. In this culture system, the dopaminergic and serotonergic mesencephalic-striatal projections are reconstructed and develop with a time course similar to that observed in vivo. Pregnant C57Bl/6J mice were injected twice daily with 40 mg/kg methamphetamine or saline from gestational days 6-13. On gestational day 14, cells from methamphetamine and saline-exposed embryos were used to prepare reaggregate cultures. Levels of neurotransmitters and their metabolites in the reaggregates and culture medium were monitored at 14, 29, 43, and 64 days of culture. Reaggregates prepared from methamphetamine-exposed embryos showed a significant elevation in serotonin levels at all culture ages compared to reaggregates prepared from saline-treated embryos. Levels of 5-HIAA in reaggregates and culture medium were also elevated in 14- and 29-day-old cultures derived from drug-exposed embryos. The development of the dopaminergic nigrostriatal projection was resistant to repeated in utero exposure to methamphetamine. In contrast, exposure of the fetus to methamphetamine, during early to midgestation, produced a long-lasting stimulatory effect on serotonergic development in culture.

Modern views on an ancient chemical: serotonin effects on cell proliferation, maturation, and apoptosis

Evolutionarily, serotonin existed in plants even before the appearance of animals. Indeed, serotonin may be tied to the evolution of life itself, particularly through the role of tryptophan, its precursor molecule. Tryptophan is an indole-based, essential amino acid which is unique in its light-absorbing properties. In plants, tryptophan-based compounds capture light energy for use in metabolism of glucose and the generation of oxygen and reduced cofactors. Tryptophan, oxygen, and reduced cofactors combine to form serotonin. Serotonin-like molecules direct the growth of light-capturing structures towards the source of light. This morphogenic property also occurs in animal cells, in which serotonin alters the cytoskeleton of cells and thus influences the formation of contacts. In addition, serotonin regulates cell proliferation, migration and maturation in a variety of cell types, including lung, kidney, endothelial cells, mast cells, neurons and astrocytes). In brain, serotonin has interactions with seven families of receptors, numbering at least 14 distinct proteins. Of these, two receptors are important for the purposes of this review. These are the 5-HT1A and 5-HT2A receptors, which in fact have opposing functions in a variety of cellular and behavioral processes. The 5-HT1A receptor develops early in the CNS and is associated with secretion of S-100beta from astrocytes and reduction of c-AMP levels in neurons. These actions provide intracellular stability for the cytoskeleton and result in cell differentiation and cessation of proliferation. Clinically, 5-HT1A receptor drugs decrease brain activity and act as anxiolytics. The 5-HT2A receptor develops more slowly and is associated with glycogenolysis in astrocytes and increased Ca(++) availability in neurons. These actions destabilize the internal cytoskeleton and result in cell proliferation, synaptogenesis, and apoptosis. In humans, 5-HT2A receptor drugs produce hallucinations. The dynamic interactions between the 5-HT1A and 5-HT2A receptors and the cytoskeleton may provide important insights into the etiology of brain disorders and provide novel strategies for their treatment.

The mechanisms involved in the long-lasting neuroprotective effect of fluoxetine against MDMA ('ecstasy')-induced degeneration of 5-HT nerve endings in rat brain

1. It has been reported that co-administration of fluoxetine with 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') prevents MDMA-induced degeneration of 5-HT nerve endings in rat brain. The mechanisms involved have now been investigated. 2. MDMA (15 mg kg(-1), i.p.) administration produced a neurotoxic loss of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in cortex, hippocampus and striatum and a reduction in cortical [3H]-paroxetine binding 7 days later. 3. Fluoxetine (10 mg kg(-1), i.p., x2, 60 min apart) administered concurrently with MDMA or given 2 and 4 days earlier provided complete protection, and significant protection when given 7 days earlier. Fluvoxamine (15 mg kg(-1), i.p., x2, 60 min apart) only produced neuroprotection when administered concurrently. Fluoxetine (10 mg kg(-1), x2) markedly increased the K(D) and reduced the B(max) of cortical [3H]-paroxetine binding 2 and 4 days later. The B(max) was still decreased 7 days later, but the K(D) was unchanged. [3H]-Paroxetine binding characteristics were unchanged 24 h after fluvoxamine (15 mg kg(-1), x2). 4. A significant cerebral concentration of fluoxetine plus norfluoxetine was detected over the 7 days following fluoxetine administration. The fluvoxamine concentration had decreased markedly by 24 h. 5. Pretreatment with fluoxetine (10 mg kg(-1), x2) failed to alter cerebral MDMA accumulation compared to saline pretreated controls. 6. Neither fluoxetine or fluvoxamine altered MDMA-induced acute hyperthermia. 7. These data demonstrate that fluoxetine produces long-lasting protection against MDMA-induced neurodegeneration, an effect apparently related to the presence of the drug and its active metabolite inhibiting the 5-HT transporter. Fluoxetine does not alter the metabolism of MDMA or its rate of cerebral accumulation.

Altered serotonin innervation patterns in the forebrain of monkeys treated with (+/-)3,4-methylenedioxymethamphetamine seven years previously: factors influencing abnormal recovery

The recreational drug (+/-)3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") is a potent and selective brain serotonin (5-HT) neurotoxin in animals and, possibly, in humans. The purpose of the present study was to determine whether brain 5-HT deficits persist in squirrel monkeys beyond the 18-month period studied previously and to identify factors that influence recovery of injured 5-HT axons. Seven years after treatment, abnormal brain 5-HT innervation patterns were still evident in MDMA-treated monkeys, although 5-HT deficits in some regions were less severe than those observed at 18 months. No loss of 5-HT nerve cell bodies in the rostral raphe nuclei was found, indicating that abnormal innervation patterns in MDMA-treated monkeys are not the result of loss of a particular 5-HT nerve cell group. Factors that influence recovery of 5-HT axons after MDMA injury are (1) the distance of the affected axon terminal field from the rostral raphe nuclei, (2) the degree of initial 5-HT axonal injury, and possibly (3) the proximity of damaged 5-HT axons to myelinated fiber tracts. Additional studies are needed to better understand these and other factors that influence the response of primate 5-HT neurons to MDMA injury and to determine whether the present findings generalize to humans who use MDMA for recreational purposes.

Causes and consequences of the loss of serotonergic presynapses elicited by the consumption of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") and its congeners

The massive and prolonged stimulation of serotonin (5-HT)-release and the increased dopaminergic activity are responsible for the acute psychomimetic and psychostimulatory effects of 3,4-methylenedioxy-methamphetamine (MDMA, "ecstasy") and its congeners. In vulnerable subjects, at high doses or repeated use, and under certain unfavorable conditions (crowding, high ambient temperature), severe, in some cases fatal, averse systemic reactions (hyperthermia, serotonin-syndrome) may occur during the first few hours. Animal experiments revealed the existence of similar differences in vulnerability and similar dose- and context-related influences on a similar sequence of acute responses. The severity of these acute systemic responses is closely related to the severity of the long-term damage to 5-HT axon terminals caused by the administration of substituted amphetamines. Attempts to identify the mechanisms involved in this selective degeneration of 5-HT presynapses brought to light a multitude of different factors and conditions which either attenuate or potentiate the loss of 5-HT terminals caused by MDMA and related amphetamine derivatives. These puzzling observations suggest that the degeneration of 5-HT presynapses represents only the final step in a sequence of events which compromise the ability of 5-HT terminals to maintain their functional and structural integrity. Substituted amphetamines selectively tax energy metabolism in 5-HT presynapses through their ability to exchange with 5-HT and to dissipate transmembrane ion gradients. The active carrier systems in the vesicular and presynaptic membrane operate at a permanently activated state. The resulting energy deficit can no longer adequately restored by the 5-HT presynapses when their availability of substrates for ATP production is additionally reduced by the hyperthermic and other energy consuming reactions which are elicited by the systemic administration of substituted amphetamines. The exhaustion of energy in 5-HT nerve terminals compromised all energy-requiring endogenous mechanisms involved in the regulation of transmembrane-ion exchange, internal Ca(++)-homeostasis, prevention of oxidative stress, detoxification, and repair. Above a critical threshold the failure of these self-protective mechanisms will lead to the degeneration of the 5-HT axon terminals. Based on the role of 5-HT as a global modulatory transmitter-system involved in the stabilization and integration of impulse flow between distributed multifocal neuronal networks, the partial loss of 5-HT presynapses must be expected to impair the ability of these networks to maintain the integrity of signal flow pattern, and increase the likelihood of switching to unstable information processing. Behavioral responding may therefore become more dominated by activities generated in individual networks, and hitherto "buffered" personality traits and predisposition may become manifested as defined psychiatric syndromes in certain predisposed subjects.

Release of serotonin induced by 3,4-methylenedioxymethamphetamine (MDMA) and other substituted amphetamines in cultured fetal raphe neurons: further evidence for calcium-independent mechanisms of release

The substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), p-chloro-amphetamine (PCA) and fenfluramine (FEN) all exert their effects by releasing serotonin (5-HT) from presynaptic nerve terminals. In the current study, we examined the ability of these agents to induce the release of 5-HT in culture fetal raphe neurons. The data indicate that the rank order of release potencies for these agents was (+/-)PCA>(+)MDMA=(+)MDA=(+/-)FEN. Studies examining the role fo calcium in 5-HT release demonstrate that preventing calcium influx with L- and N-type calcium channel blockers inhibits potassium-stimulated release of -3H-5-HT but has no effect on release induced by the substituted amphetamines. Furthermore, omitting calcium from the extracellular media or depleting the vesicular pool of neurotransmitter with continual potassium stimulation did not affect the release of -3H-5-HT induced by these compounds. Administration of fluoxetine prior to the substituted amphetamines significantly attenuated the releasing effects of these agents, while producing no effect on potassium-stimulated release. These results are consistent with the notion that the amphetamines induce release of cytoplasmic 5-HT via the plasma membrane transporter.

3,4-Methylenedioxymethamphetamine ('Ecstasy') promotes the translocation of protein kinase C (PKC): requirement of viable serotonin nerve terminals

The metabolic effects of the neurotoxic, ring-substituted amphetamine 3,4-methylenedioxy-methamphetamine (MDMA or 'Ecstasy') were examined in vivo. In this study, we focused on the ability of MDMA to induce a translocation of the calcium and phospholipid-dependent protein kinase C (PKC) from the cytosol to the cortical plasma membrane. Two injections of MDMA (20 mg/kg; 10 h apart; s.c.) increased the density of membrane bound PKC sites by 48.0% over saline treated animals without mediating a significant change in ligand ([3H]phorbol 12,13 dibutyrate; [3H]PDBu) affinity. Longer drug treatments (8 x 20 mg/kg) induced a lasting (up to 5 days post-treatment) increase in the density of membrane-bound PKC. Prior destruction of cortical 5-HT nerve terminals with p-chloroamphetamine (PCA) prevents this effect and suggests that viable 5-HT uptake sites are essential for MDMA-induced PKC translocation. These results demonstrate that MDMA-induced PKC translocation is mediated by viable cortical 5-HT nerve terminals, and that prolonged kinase activation may contribute to MDMA-induced serotonergic neurotoxicity.

Activation of glycogen phosphorylase by serotonin and 3,4-methylenedioxymethamphetamine in astroglial-rich primary cultures: involvement of the 5-HT2A receptor

Neurotransmitters, neuropeptides, and ions regulate glycogen levels in the brain by modulating the activity of glycogen synthase (GSase) and glycogen phosphorylase (GPase). GPase is co-localized with glial fibrillary acidic protein (GFAP), an astroglia-specific marker, suggesting that glycogen is localized in astroglial cells. Additionally, functional serotonin (5-HT) receptors are found in both neurons and glia, and 5-HT is known to stimulate glycogenolysis. It is reported that 3,4-methylenedioxymethamphetamine (MDMA), a drug of abuse, stimulates the release and inhibits the reuptake of 5-HT, and selectively inhibits the activity of MAO-A. These biochemical consequences of MDMA lead to increased extra-cellular 5-HT levels. This study investigates the effects of MDMA(+) and serotonin (5-HT) on glycogen metabolism in the rat brain. A histochemical method was designed to visualize active glycogen phosphorylase (GPase) in an astroglial-rich primary culture. Serotonin activated GPase in a concentration-dependent manner (100 nM-100 microM). Maximal activation by 5-HT was achieved by 50 microM and resulted in a 167% increase in the number of reactive sites (P < 0.001). MDMA(+) (500 nM-50 microM) directly stimulated GPase activity with maximal activation induced by 5 microM, which caused a 70% increase in the number of reactive sites (P < 0.001). The 5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-bromophenyl)-2-aminopropane (DOB), also displayed a concentration-dependent increase in the number of GPase reactive sites. Maximal stimulation by DOB occurred at 100 nM which increased the number of reactive sites by 166% (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Tryptophan pretreatment augmentation of p-chloroamphetamine-induced serotonin and dopamine release and reduction of long-term neurotoxicity

The impact of tryptophan (TRP) pretreatment on the neurochemical effects of p-chloroamphetamine (PCA) was investigated. The neurotoxic effects of PCA on serotonin (5-HT) neurons, the acute effects of PCA on extracellular 5-HT and dopamine (DA), and the displacement by PCA of whole blood 5-HT were examined. TRP pretreatment (400 mg/kg of the methyl ester) significantly reduced the long-term (1 week) decrease in tissue 5-HT resulting from PCA (2 mg/kg, i.p., of the hydrochloride salt) in the prefrontal cortex and striatum, but not in the dorsal hippocampus. Microdialysis studies in awake animals showed that this pretreatment regimen resulted in augmented PCA-induced increases in extracellular 5-HT (4-fold) and DA (2-fold). TRP pretreatment also resulted in increased displacement of 5-HT from whole blood. The implications of these results toward possible mechanisms of action of PCA-induced neurotoxicity are discussed.

A study of the mechanism of MDMA ('ecstasy')-induced neurotoxicity of 5-HT neurones using chlormethiazole, dizocilpine and other protective compounds

1. An investigation has been made in rats into the neurotoxic effect of the relatively selective 5-hydroxytryptamine (5-HT) neurotoxin, 3,4-methylenedioxymethamphetamine (MDMA or 'Ecstasy') using chlormethiazole and dizocilpine, both known neuroprotective compounds and also gamma-butyrolactone, ondansetron and pentobarbitone. 2. Administration of MDMA (20 mg kg-1, i.p.) resulted in a 50% loss of cortical and hippocampal 5-HT and 5-hydroxyindole acetic acid (5-HIAA) 4 days later. This reflects the long term neurotoxic loss of 5-HT that occurs. Injection of gamma-butyrolactone (GBL; 400 mg kg-1, i.p.) 5 min before and 55 min after the MDMA provided substantial protection. Pentobarbitone (25 mg kg-1, i.p.) using the same dose regime was also protective, but ondansetron (0.5 mg kg-1 or 0.1 mg kg-1, i.p.) was without effect. 3. MDMA (20 mg kg-1) had no significant effect on striatal dopamine concentration 4 days later but did produce a small decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) content. There were few significant changes in rats given MDMA plus GBL, ondansetron or pentobarbitone. 4. A single injection of MDMA (20 mg kg-1, i.p.) resulted in a greater than 80% depletion of 5-HT in hippocampus and cortex 4 h later, reflecting the initial rapid release that had occurred. None of the neuroprotective compounds (chlormethiazole, 50 mg kg-1; dizocilpine, 1 mg kg-1; GBL, 400 mg kg-1; pentobarbitone, 25 mg kg-1) given 5 min before and 55 min after the MDMA injection, altered the degree of 5-HT loss. 5. Acute MDMA injection increased striatal dopamine content (28%) and decreased the DOPAC content. In general, administration of the drugs under investigation did not significantly alter these MDMA-induced changes. Both chlormethiazole and GBL produced a greater increase in dopamine than MDMA alone, but this was apparently an additive effect to the action of either drug alone. 6. The 5-HT loss 4 h following administration of the neurotoxin p-chloroamphetamine (2.5 mg kg-1,i.p.) was not affected by chlormethiazole or dizocilpine. p-Chloroamphetamine did not appear to alter striatal dopamine metabolism.7. None of the protective drugs inhibited the initial 5-HT loss following MDMA, rendering unlikely any proposal that they are protective because they inhibit 5-HT release and the subsequent formation ofa toxic indole derivative. All the protective compounds (unlike ondansetron) probably inhibit dopamine release in the striatum. Since the neurotoxic action of some substituted amphetamines is dependent on the integrity of nigro-striatal neurones, this fact may go some way to explain the protective action of this diverse group of compounds.

Hyperthermia associated with 3,4-methylenedioxyethamphetamine ('Eve')

A patient was admitted with hyperthermia, muscle rigidity, rhabdomyolysis and disseminated intravascular coagulation. He was initially thought to have taken 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy'), but subsequent toxicology revealed the presence of 3,4-methylenedioxyethamphetamine (MDEA, 'Eve'), its sister drug, in his blood. Subsequent in vitro testing for malignant hyperthermia proved to be negative.

Integrative transporter-mediated release from cytoplasmic and vesicular 5-hydroxytryptamine stores in cultured neurons

The direct effects of 3,4-methylenedioxymethamphetamine (MDMA) and p-chloroamphetamine (PCA) were studied in microculture of fetal 5-hydroxytryptamine (5-HT) neurons. Both MDMA and PCA released 5-HT with the potency of PCA > MDMA by a mechanism inhibited by fluoxetine, and inhibitor of the 5-HT transporter. The transporter-mediated release by MDMA and PCA reduced intracellular stores of 5-HT. Both MDMA and PCA inhibit MAO-A activities, which also contributes to the increase of extracellular 5-HT levels. Deprenyl (10(-7) M) increased the amount of intracellular 5-HT and potentiated the MDMA- or PCA-induced release of 5-HT. Conversely, reserpine (10(-9) M) reduced the intracellular 5-HT levels and attenuated the transporter-mediated release. In addition, MDMA- or PCA-mediated release was attenuated by nimodipine (10(-8) M), an L-type Ca2+ channel antagonist. Our results indicate that MDMA- or PCA-induced release of 5-HT occurs from the cytoplasm to the media through the 5-HT transporter, and that the release may incorporate 5-HT from the vesicular stores.

Stimulant-induced alterations in dopaminergic and serotonergic function in fetal raphe neurons

Methamphetamine and its structural analogues have been demonstrated to be neurotoxic to CNS dopamine (DA) and serotonin (5-HT) neurons both in vivo and in vitro. Our laboratory has been actively characterizing mesencephalic cultures and the effects of methamphetamine exposure on neurochemical and immunochemical indices. The purpose of the present studies was to extend our findings with mesencephalic cultures and compare them with methamphetamine-induced alterations in fetal raphe cultures that contain both DA and 5-HT cells. Methamphetamine (10 and 100 microM) was added to the cultures 24 h after plating and fresh daily thereafter. The effects of chronic methamphetamine exposure on [3H]-DA and [3H]-5-HT uptake were determined after 5 days of drug treatment. Additional cultures were immunochemically analyzed for the presence of DA- and 5-HT-containing cells and total neuronal density. Results indicate that repeated methamphetamine exposure decreased DA and 5-HT uptake. Furthermore, repeated exposure to the higher concentration of methamphetamine (100 microM) caused a significant reduction in the number of DA and 5-HT cells as well as reducing the total neuronal density. This would suggest that this higher concentration of methamphetamine results in generalized neurotoxicity. Exposure to 10 microM methamphetamine resulted in more specific effects on dopaminergic function. These findings indicate that repeated methamphetamine administration can induce similar alterations in both dopaminergic and serotonergic neurons in raphe cultures.

Neurotoxic amphetamine analogues: effects in monkeys and implications for humans

A wealth of evidence has accrued over the last 20 years indicating that certain amphetamine analogues have the potential to damage central monoaminergic neurons. For example, amphetamine has been shown to be toxic to dopamine neurons, MDMA to serotonin neurons, and methamphetamine to both (Table 1). In rodents, the toxic effects of amphetamines appear to be limited to axon terminals, and regenerative sprouting tends to be the rule. By contrast, in primates, nerve cell bodies appear to be affected, and the deleterious effects of amphetamine derivatives tend to be longer lasting, and possibly permanent (Fig. 2). Although findings in animals are compelling, observations in humans are less clear. In particular, it remains to be determined whether amphetamine analogues damage central monoaminergic neurons in humans and, if they do, whether functional consequences ensue. Also, the mechanism by which amphetamines damage monoaminergic neurons remains to be defined. Further insight into these basic and clinical aspects of amphetamine neurotoxicity should enhance our understanding of central monoaminergic systems in normal brain function, and their role in the pathophysiology of neuropsychiatric disorders.

The substituted amphetamines 3,4-methylenedioxymethamphetamine, methamphetamine, p-chloroamphetamine and fenfluramine induce 5-hydroxytryptamine release via a common mechanism blocked by fluoxetine and cocaine

The abilities of the substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine, p-chloroamphetamine (PCA) and fenfluramine to induce synaptosomal [3H]serotonin (5-HT) release were compared using a novel microassay system. The rank order of release potencies was found to be (+/-)PCA congruent to (+)-fenfluramine greater than (+)-MDMA much greater than (+)-methamphetamine. Combination of two drugs at their EC50 did not cause more release than either drug alone at an equivalent concentration. In addition, the 5-HT uptake blockers fluoxetine and cocaine inhibited the release induced by MDMA, methamphetamine, PCA and fenfluramine to the same percentage. However, threshold concentrations of the substituted amphetamines known to inhibit uptake did not attenuate the release caused by higher concentrations of these compounds. These results suggests that MDMA, methamphetamine, PCA and fenfluramine cause 5-HT release via a common mechanism. Furthermore, these results indicate that the 5-HT uptake blockade induced by these substituted amphetamines in vitro is different from that induced by either fluoxetine or cocaine.

Lack of serotonin neurotoxicity after intraraphe microinjection of (+)-3,4-methylenedioxymethamphetamine (MDMA)

Systemic administration of 3,4-methylenedioxymethamphetamine (MDMA) produces depletions of serotonin (5-HT) and its primary metabolite, 5-hydroxyindoleacetic acid (5-HIAA), decreases 5-HT reuptake sites and diminishes tryptophan hydroxylase activity in various forebrain regions. MDMA has been shown to be neurotoxic to the fine fibers originating from dorsal raphe (DR) 5-HT neurons but not the beaded fibers from the median raphe (MR) nucleus. In the present experiment, MDMA was microinjected directly into the DR or MR to determine whether differential neurotoxicity developed in the DR versus MR fiber systems as measured by 5-HT levels and immunocytochemistry. Two weeks following stereotaxic injection with either vehicle or (+)MDMA (50 micrograms base in 2 microliters) into the DR or MR, rat brains were assayed for 5-HT and catecholamine content or 5-HT immunocytochemistry. HPLC analysis revealed no significant changes in monoamine or metabolite concentrations in the hippocampus and striatum of rats administered intra-DR or -MR (+)MDMA. Raphe sections stained for 5-HT also did not reveal any apparent neurotoxicity. A single cerebral injection of (+)MDMA does not produce neurotoxicity to 5-HT neuronal systems originating in the raphe, although neurotoxicity of multiple MDMA injections into these raphe nuclei cannot be ruled out.

Dextromethorphan protects against the neurotoxic effects of p-chloroamphetamine in rats

Dextromethorphan, an agent that blocks the neuronal-damaging effects of hypoxemia in vitro, was tested for its ability to prevent the neurotoxic effects of p-chloroamphetamine (PCA). Rats were treated with either saline, PCA, dextromethorphan, or the combination of PCA and increasing doses of dextromethorphan. Dextromethorphan provided a dose-related protection against the serotonin (5-HT)-depleting effects of PCA. These observations may offer a clue as to the mechanism responsible for PCA-induced neurotoxicity.

Major metabolites of (+/-)3,4-methylenedioxyamphetamine (MDA) do not mediate its toxic effects on brain serotonin neurons

The two major metabolites of (+/-)3,4-methylenedioxyamphetamine (MDA), alpha-methyldopamine (alpha-MeDA) and 3-O-methyl-alpha-methyldopamine (3-O-Me-alpha-MeDA), were administered to rats intracerebroventricularly and into brain parenchyma. In addition, their precursors, (alpha-MeDOPA and 3-O-Me-alpha-MeDOPA, respectively) were administered systemically, individually and in combination. None of these treatments produced a lasting depletion of brain serotonin (5-HT). These findings suggest that neither of MDA's major metabolites mediate its toxic effects on 5-HT neurons and that either a minor metabolite is responsible or that alternate mechanisms are involved.

Dose-related effects of prenatal 5-methoxytryptamine (5-MT) on development of serotonin terminal density and behavior

Our previous studies with a tissue culture model of neuronal development have shown that the development of serotonin neurons is dependent, at least in part, on the stimulation of high affinity serotonin receptors. One receptor inhibits the outgrowth of neurons, while the other promotes it. The present study was therefore undertaken to replicate these findings in a whole animal model system. Pregnant Sprague-Dawley rats were treated from gestational day 12 until birth with 0.1, 1.0 or 3.0 mg/kg 5-methoxytryptamine (5-MT). The pups were assessed for serotonin outgrowth by the selective synaptosomal uptake of [3H]serotonin at postnatal days 1, 15 and 30 (D1, D15, D30). In addition, the pups were tested behaviorally for the neonatal serotonin syndrome at D5 (induced by quipazine), spontaneous alternation and open field activity at day 15 and lick suppression at day 30. At 1.0 mg/kg, the terminal outgrowth of serotonin neurons was inhibited, while the highest dose, 3.0 mg/kg, showed stimulation of outgrowth. The highest dose caused behavioral alterations which had abated by 30 days, while the intermediate dose (1.0 mg/kg) showed behavioral changes throughout. Interestingly, the lowest dose, 0.1 mg/kg, showed changes in uptake only at D1 and behavioral changes only at later timepoints, principally at D30. This suggests that serotonin not only plays a role in regulating the development of the neurons which produce it, but that it may also play a role in neurochemical imprinting--that is, changes in behavior in the adult may be due to changes in neurochemistry during development, even though that neurochemistry may have been corrected by the time the animal becomes an adult.