The action of (+/-)-MDMA on medial prefrontal cortical neurons is mediated through the serotonergic system.

The mechanism of action of systemically administered (+/-)-MDMA (3,4-methylenedioxymethamphetamine) on spontaneously active neurons in the medial prefrontal cortex (mPFc) of chloral hydrate anesthetized rats was examined using standard single unit extracellular recording techniques. Intravenously administered MDMA dose-dependently decreased the firing rates of the majority of mPFc neurons in control rats. In contrast, in rats that were pretreated with p-chlorophenylalanine (PCPA), which depletes the brain serotonin (5-hydroxytryptamine, 5-HT) content by inhibiting tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of 5-HT, MDMA was largely ineffective in inhibiting the firing of mPFc cells. In PCPA-treated animals, the administration of 5-hydroxytryptophan (5-HTP), which presumably restored the brain 5-HT content, but not L-DOPA, reinstated MDMA's inhibitory action in PCPA-treated rats. In rats that were pretreated with alpha-methyl-p-tyrosine (AMPT), which depletes the brain dopamine (DA) content by inhibiting tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of DA, MDMA inhibited the firing of all of the mPFc cells. MDMA's effect on mPFc neurons was reversed by 5-HT receptor antagonists such as granisetron and metergoline. These results strongly suggest that MDMA exerts its action on mPFc cells indirectly by releasing endogenous 5-HT.     

Electrophysiologic changes in ventral midbrain dopaminergic neurons resulting from (+/-) -3,4-methylenedioxymethamphetamine (MDMA-"Ecstasy").

BACKGROUND: Although dopamine (DA) has been implicated in the psychostimulant properties of 3,4-methylenedioxymethamphetamine (MDMA), there is no detailed information on its modalities of action on single ventral midbrain dopaminergic neurons. METHODS: We examined the actions of MDMA on intracellularly recorded dopaminergic neurons maintained in slices. RESULTS: At 1 micromol/L, MDMA depolarized and excited the cells; at 3 micromol/L, either excited or inhibited the neurons. Interestingly, higher concentrations (10-30 micromol/L) inhibited firing through membrane hyperpolarization or caused an outward current. Whereas MDMA's excitatory effects were antagonized by pindolol, indicating involvement of 5-HT 1B receptors, the inhibitory effects were counteracted by sulpiride indicating involvement D2 receptors. Treatment of the cells with carbidopa eliminated MDMA-induced firing inhibition and membrane hyperpolarization. MDMA enhanced DA-induced cellular responses but reduced those of amphetamine. Cocaine-induced outward currents were not affected by MDMA. These actions are consistent with inhibition of the DA transporter. Moreover, MDMA depressed the GABA(B) IPSP by activating 5-HT 1B receptors. CONCLUSIONS: Our data demonstrate that 3-30 micromol/L MDMA preferentially inhibits the dopaminergic cells via indirect activation of D2 autoreceptors due to increased extracellular concentration of DA. In contrast, reduction of the GABA(B) IPSP could partially account for excitation caused by 1-3 micromol/L drug.     

MDMA: further evidence that its action in the medial prefrontal cortex is mediated by the serotonergic system.

Systemically administered (+/-)-MDMA (3,4-methylenedioxymethamphetamine, 'Ecstasy') suppressed the firing rates of the majority of neurons in the medial prefrontal cortex (mPFc). The responses of mPFc cells to (+/-)-MDMA is mimicked by (+)-MDMA but not (-)-MDMA. Furthermore, pretreatment with fluoxetine (a specific 5-HT uptake blocker) but not GBR 12909 (a specific dopamine uptake blocker) prevented the suppressant action of MDMA. These data support the notion that the 5-HT system mediates (+/-)-MDMA's action.     

Examination of the action of 3,4-methylenedioxymethamphetamine on rat A10 dopamine neurons

Extracellular single cell recording was used to examine the effect of intravenous administration of (−), (+), and (±)-3,4-methylenedioxymethamphetamine (MDMA) on A10 dopamine (DA) neurons in chloral hydrate anesthetized male rats. Both (±)-MDMA and (+)-MDMA inhibited the firing rate of most (79%) A10 DA cells. By contrast, (−)-MDMA induced either no effect or a slight increase in the firing rate of these cells. Analysis of the effects of (±)-MDMA on the firing pattern of the DA cells revealed an overall decrease in the percentage of spikes in bursts but both increases and decreases were seen in the coefficient of variation of interspike intervals. To determine the contribution of 5-HT and DA to the (±)-MDMA-induced inhibition of A10 DA cells rats were pretreated either with the 5-HT synthesis inhibitor p-chlorophenylalanine (PCPA) or the DA synthesis inhibitor α-methyl-p-tyrosine (AMPT). Pretreatment of rats with PCPA did not reduce the ability of (±)-MDMA to inhibit the DA cells. However, in rats pretreated with AMPT, the (±)-MDMA-induced inhibition was blocked and some cells (44%) showed instead an increase in firing rate following administration of (±)-MDMA. The administration of l-3,4-dihydroxyphenylalanine (L -DOPA) to AMPT-treated rats rapidly restored the inhibition of cell firing by (±)-MDMA. In conclusion, the results reported here demonstrate that MDMA has an overall inhibitory effect on A10 DA cells. Despite MDMA's greater potency in releasing 5-HT compared to DA, the inhibitory effect of this drug on A10 DA cells appears to be mediated by the latter transmitter. © 1996 Wiley-Liss, Inc.     

Effects of short-term serotonin depletion on the efficacy of serotonin neurotransmission: electrophysiological studies in the rat central nervous system

The effects of short-term serotonin (5-HT) depletion by p-chlorophenylalanine (PCPA) on the firing activity of dorsal raphe nucleus 5-HT neurons, on the responsiveness of dorsal hippocampus pyramidal neurons to microiontophoretically applied 5-HT and on the efficacy of the electrical stimulation of the ascending 5-HT pathway in suppressing the firing activity of CA3 dorsal hippocampus pyramidal neurons were assessed in chloral hydrate-anesthetized rats. PCPA (250 mg/kg/day i.p. for 2 days) reduced the 5-HT content of the dorsal hippocampus by 90%. However, the number of spontaneously active 5-HT neurons per microelectrode trajectory through the dorsal raphe or their average rate of firing was unaltered. The effect of afferent 5-HT pathway stimulation was reduced in only 40% of treated rats, whereas the sensitivity of CA3 pyramidal neurons to microiontophoretic 5-HT was not modified. The function of the terminal 5-HT autoreceptor was assessed using methiothepin, an autoreceptor antagonist. Methiothepin (1 mg/kg, i.v.) significantly enhanced the efficacy of the stimulation in PCPA-treated rats, although the degree of enhancement was much less than in controls. A greater reduction of the effectiveness of the stimulation was obtained by increasing the dose of PCPA (350 mg/kg/day i.p. for 2 days). This regimen reduced the 5-HT content of the dorsal hippocampus by 95%. In these rats, the sensitivity of the terminal 5-HT autoreceptor was assessed by increasing the frequency of the stimulation from 1 to 5 Hz. This procedure reduced to a similar extent the efficacy of the stimulation in treated and control rats, suggesting that the reduced effectiveness of methiothepin in enhancing 5-HT synaptic transmission in PCPA-treated rats is due to a lower degree of activation of the terminal 5-HT autoreceptor. The present results showing that the 350 mg/kg/day regimen of PCPA, but not the 250 mg/kg/day regimen, reduced the efficacy of the stimulation of the ascending 5-HT pathway suggest that a greater than 90% depletion is required to affect 5-HT neurotransmission significantly. The reduced level of activation of terminal 5-HT autoreceptors in rats treated with the lower dose of PCPA may facilitate the release of the remaining 5-HT per stimulation-triggered action potential, ensuring a virtually unaltered synaptic efficacy.     

MDMA-induced c-Fos expression in oxytocin-containing neurons is blocked by pretreatment with the 5-HT-1A receptor antagonist WAY 100635

The popular party drug MDMA (3,4-methylenedioxymethamphetamine, "Ecstasy") increases sociability in both humans and laboratory animals. Recent research suggests that these prosocial effects may involve serotonin (5-HT)-stimulated hypothalamic release of the neuropeptide oxytocin. WAY 100635, a 5-HT(1A) receptor antagonist, prevents MDMA-induced increases in plasma oxytocin and also reduces MDMA-mediated increases in social interaction in rats. The present study used c-Fos immunohistochemistry to determine the possible role of 5-HT(1A) receptors in MDMA-mediated activation of oxytocin synthesizing neurons. Male Wistar rats (n=8/group) were administered MDMA (10 mg/kg, i.p.) with or without WAY 100635 (1 mg/kg, i.p.) pre-treatment and c-Fos expression was then assessed throughout the brain. MDMA significantly increased locomotor activity and this effect was partly prevented by WAY 100635, in agreement with previous studies. WAY 100635 significantly reduced MDMA-induced c-Fos expression in a subset of brain regions examined. A particularly prominent reduction was seen in the oxytocin-positive neurons of the supraoptic nucleus and paraventricular hypothalamus, with more modest reductions in the Islands of Calleja, median preoptic nucleus, somatosensory cortex and nucleus of the solitary tract. WAY 100635 did not alter MDMA-induced c-Fos expression in the striatum, thalamus, or central amygdala. These results indicate that MDMA's action on oxytocin producing cells in the hypothalamus is mediated through 5-HT(1A) receptors and that certain specific cortical, limbic and brainstem sites are also activated by MDMA via these receptors.     

Neurochemical and Neurotoxic Effects of MDMA (Ecstasy) and Caffeine After Chronic Combined Administration in Mice

MDMA (3,4-methylenedioxymethamphetamine) is a psychostimulant popular as a recreational drug because of its effect on mood and social interactions. MDMA acts at dopamine (DA) transporter (DAT) and serotonin (5-HT) transporter (SERT) and is known to induce damage of dopamine and serotonin neurons. MDMA is often ingested with caffeine. Caffeine as a non-selective adenosine A1/A2A receptor antagonist affects dopaminergic and serotonergic transmissions. The aim of the present study was to determine the changes in DA and 5-HT release in the mouse striatum induced by MDMA and caffeine after their chronic administration. To find out whether caffeine aggravates MDMA neurotoxicity, the content of DA and 5-HT, density of brain DAT and SERT, and oxidative damage of nuclear DNA were determined. Furthermore, the effect of caffeine on MDMA-induced changes in striatal dynorphin and enkephalin and on behavior was assessed. The DA and 5-HT release was determined with in vivo microdialysis, and the monoamine contents were measured by HPLC with electrochemical detection. DNA damage was assayed with the alkaline comet assay. DAT and SERT densities were determined by immunohistochemistry, while prodynorphin (PDYN) and proenkephalin were determined by quantitative PCR reactions. The behavioral changes were measured by the open-field (OF) test and novel object recognition (NOR) test. Caffeine potentiated MDMA-induced DA release while inhibiting 5-HT release in the mouse striatum. Caffeine also exacerbated the oxidative damage of nuclear DNA induced by MDMA but diminished DAT decrease in the striatum and worsened a decrease in SERT density produced by MDMA in the frontal cortex. Neither the striatal PDYN expression, increased by MDMA, nor exploratory and locomotor activities of mice, decreased by MDMA, were affected by caffeine. The exploration of novel object in the NOR test was diminished by MDMA and caffeine. Our data provide evidence that long-term caffeine administration has a powerful influence on functions of dopaminergic and serotonergic neurons in the mouse brain and on neurotoxic effects evoked by MDMA.     

(+/-)3,4-Methylenedioxymethamphetamine ('Ecstasy')-induced serotonin neurotoxicity: studies in animals

The popular recreational drug, (+/-)3, 4-methylenedioxymethamphetamine (MDMA; 'Ecstasy') is a potent and selective brain serotonin (5-HT) neurotoxin in animals. MDMA-induced 5-HT neurotoxicity can be demonstrated using a variety of neurochemical, neuroanatomical and, more recently, functional measures of 5-HT neurons. Although the neurotoxic effects of MDMA in animals are widely accepted, the relevance of the animal data to human MDMA users has been questioned, largely because dosages of drugs used in animals are perceived as being much higher than those used by humans. In the present paper, we review the extensive body of data demonstrating that MDMA produced toxic effects on brain 5-HT neurons in animals and present new data indicating that levels of the type 2 vesicular monoamine transporter are reduced in MDMA-treated animals, providing further indication of MDMA's 5-HT neurotoxic potential. Further, we demonstrate, using principles of interspecies scaling, that dosages of MDMA known to be neurotoxic in animals fall squarely in the range of dosages used typically by recreational MDMA users.     

Increased CRE-binding activity and tryptophan hydroxylase mRNA expression induced by 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") in the rat frontal cortex but not in the hippocampus

A single administration of either 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") or p-chloroamphetamine (PCA) produced a rapid and marked reduction of serotonin (5-HT) content in rat frontal cortex and hippocampus. In the cortex of MDMA-treated rats, 5-HT levels returned to control values 48 h after drug administration. This recovery was correlated with an induction of CRE-binding activity and an enhanced expression of tryptophan hydroxylase (TPH) mRNA, the rate-limiting enzyme in 5-HT biosynthesis, suggesting that MDMA may up-regulate the TPH gene through a CREB-dependent mechanism. In the cortex of PCA-treated rats, neither a recovery of 5-HT levels nor changes in DNA-binding or TPH mRNA were found at the same time point. In the hippocampus of rats receiving either PCA or MDMA a decrease in TPH mRNA levels was found at all times, along with a reduced CRE-binding at the 8-h time point. The results show region-specific effects of MDMA. In the frontal cortex, the increased TPH expression suggests a compensatory response to MDMA-induced loss of serotonergic function.     

Modulation of the ability of clozapine to facilitate NMDA- and electrically evoked responses in pyramidal cells of the rat medial prefrontal cortex by dopamine: pharmacological evidence

Previous studies have shown that dopamine (DA) may play an important role in mediating or modulating the facilitating action of clozapine in glutamatergic transmission. This possibility was tested further in the present study by pharmacological manipulation of the DA system. When rats were pretreated with reserpine (which blocks storage of biogenic amines) and alpha-methyl para-tyrosine (AMPT, which inhibits tyrosine hydroxylase, the rate-limiting enzyme for the DA synthesis), the ability of clozapine to augment glutamatergic transmission in pyramidal cells of the medial prefrontal cortex (mPFC) was totally abolished. Furthermore, the application of l-dihydroxyphenylalanine (L-DOPA, the immediate precursor of DA which bypasses the synthesis step inhibited by AMPT) reversed the effect produced by reserpine plus AMPT and reinstated the facilitating action of clozapine, whereas administration of 5-hydroxytryptophan (5-HTP), the immediate precursor of 5-HT, was ineffective. In addition, DA D1 receptor antagonist SCH 23390 also completely prevented clozapine-induced facilitating action in the mPFC pyramidal cells. The present results demonstrate that newly synthesized DA and DA D1 receptors are required for clozapine to elicit its facilitating action on glutamatergic neurotransmission in the mPFC.     

Altered neuronal responsiveness to biogenic amines in rat cerebral cortex after serotonin denervation or depletion

To further investigate monoaminergic mechanisms in cerebral cortex, responsiveness of cortical neurons to microiontophoretic applications of serotonin (5-HT), dopamine (DA) or noradrenaline (NA) was examined in the frontoparietal region of control, 5,7-dihydroxytryptamine (5,7-DHT)- and p-chlorophenylalanine (PCPA)-treated rats anesthetized with urethane. As a rule, 100 nA applications of either one of these biogenic amines induced marked slowings or total interruptions of ‘spontaneous’ firing overlasting the 30s periods of ejection. Given the large amounts of monoamines ejected, it could be inferred that such microiontophoretic applications produced a maximal activation of receptors. In control rats, the responses to 5-HT, DA and NA were of approximately equal duration ( 5 min). Two to 4 weeks after denervation with 5,7-DHT, most neurons (75%) exhibited greatly prolonged responses to 5-HT( 14 min), and marked depressions of firing could be induced by small ejection currents (2 nA) having little or no effect in the controls. In addition, 85% of the units supersensitive to 5-HT showed considerably shortened responses to DA and NA( 1 min). After 2–14 days of depletion with PCPA, there was no change in the responsiveness to 5-HT in spite of a 91% lowering of cortical 5-HT content equivalent to that measured after denervation. Nevertheless, responsiveness to DA and NA was again diminished in a majority (80%) of the units tested. In control or PCPA-treated rats, acute administration of the 5-HT re-uptake blocker fluoxetine increased the duration of depressions induced by 100 nA applications of 5-HT but did not enhance responsiveness to low ejection currents. This suggested that, after 5-HT denervation, the suppression of re-uptake was mainly responsible for the prolongation of 5-HT responses (‘presynaptic’ component of supersentivity), whereas a modification of 5-HT receptors accounted for the greater efficacy of small doses of 5-HT (‘postsynaptic’ component). Responsiveness to the microiontophoretic application of phenylephrine (PHE), a noradrenergic α-agonist, was comparable with that to NA in PCPA- and 5,7-DHT-treated as well as in control rats. Therefore, the hyposensitivity to DA and NA appeared indicative of a desensitization of catecholamine receptors caused by the absence of 5-HT. Such a desensitization may be viewed as an adaptive change resulting from an increased release of endogenous DA and NA. This interpretation would in turn imply that, normally, 5-HT regulates catecholamine release in the neocortex.     

Comparison of the effects of various typical and atypical antipsychotic drugs on the suppressant action of 2-methylserotonin on medial prefrontal cortical cells in the rat.

In this study, we report the effects of various typical and atypical antipsychotic drugs (APDs) on the suppressant action of microiontophoretically applied 2-methylserotonin (2-Me-5HT, a 5-HT3 agonist) on medial prefrontal cortical (mPFc) cells. The microiontophoresis of 2-Me-5HT (10-80 nA) produced a current-dependent suppression of mPFc cells' firing, and this effect was blocked by various 5-HT3 antagonists. The microiontophoresis of the atypical APDs clozapine and a structurally related compound, RMI 81,582, mimicked the action of the 5-HT3 antagonists. In addition, the intravenous administration of clozapine and RMI 81,582 antagonized the suppressant action produced by the iontophoretic application of 2-Me-5HT on mPFc cells. However, the suppressant action of 2-Me-5HT was not blocked by the typical APDs haloperidol and chlorpromazine. The putative atypical APDs risperidone, setoperone, CL 77328, SCH 23390, CGS 10746B, 1-sulpiride, and thioridazine were ineffective in antagonizing 2-Me-5HT's action. Overall, our results suggest that the majority of putative atypical APDs do not interact with 5-HT3 binding sites in the brain. Whether the interaction of clozapine and RMI 81,582 with 5-HT3 sites is correlated with their therapeutic efficacy or lower potential to induce neurological side effects remains to be determined.     

Neonatal 3,4-methylenedioxymethamphetamine (MDMA) exposure alters neuronal protein kinase A activity, serotonin and dopamine content, and [35S]GTPgammaS binding in adult rats

Recreational use of methylenedioxymethamphetamine (MDMA) has dramatically increased among juveniles and young adults of child-bearing age, and the potential for fetal exposure has increased. For this reason, it is surprising that comparatively few studies have assessed the long-term impact of early MDMA exposure on serotonin (5-HT) and dopamine (DA) neurotransmitter systems. The purpose of this study was to determine whether repeated exposure to MDMA during the preweanling period would cause long-term changes in 5-HT and DA functioning. Rats were treated with saline or 20 mg/kg MDMA (two injections per day) from postnatal day (PD) 11-20. At PD 90, rats were killed, and their dorsal striatum, prefrontal cortex, and hippocampus were removed. 5-HT and DA content, as well as their metabolites, were measured using HPLC. In addition, cAMP-dependent protein kinase A (PKA) activity and agonist-stimulated [35S]GTPgammaS binding was assayed using tissue homogenates from each brain region. Results indicated that early MDMA exposure caused a decrease in PKA activity and 5-HT content in the prefrontal cortex and hippocampus while increasing the efficacy of 5-HT1A receptors as measured by agonist-stimulated [35S]GTPgammaS binding. Additionally, DA content was reduced in the dorsal striatum and prefrontal cortex. These data indicate that early MDMA exposure has long-term effects on the 5-HT and DA neurotransmitter systems that may be mediated, at least partially, by changes in 5-HT1A receptor sensitivity.     

MDMA and fenfluramine alter the response of the circadian clock to a serotonin agonist in vitro

The substituted amphetamine drugs, 3,4-methylenedioxymethamphetamine (MDMA or ‘Ecstasy’) and fenfluramine, are known to damage 5-HT neurons in the brain of animals. However, little is known about the drugs’ effects on circadian rhythmicity which is known to be influenced by serotonergic input to the suprachiasmatic nuclei. In the present study, we tested the ability of MDMA and fenfluramine treatment to alter the ability of the circadian clock to reset in response to an agonist of the 5-HT1A and 5-HT7 receptor subtypes soon after treatment with the drugs, and then again at 20 weeks. Coronal hypothalamic slices containing the suprachiasmatic nuclei (SCN) were prepared from rats and 3-min recordings of the firing rate of individual cells were performed throughout a 12-h period. The ability of the 5-HT agonist, 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT), to cause a phase advance in the firing pattern of SCN neurons was assessed in slices from control animals and those pretreated with MDMA or fenfluramine (10, 15 and 20 mg/kg administered on successive days) 6–10 days or 20 weeks previously. Phase advances to 8-OH-DPAT in the slice were attenuated by pretreatment with MDMA or fenfluramine at both drug-test intervals. Our study demonstrates that repeated exposure to MDMA or fenfluramine may interfere with the ability of serotonin to phase shift the circadian clock in the rat. It is possible that such an effect may be responsible for some of the clinical changes, such as sleep disorders and mood changes, sometimes reported by human users of the substituted amphetamines.     

Action of serotonin in the medial prefrontal cortex: mediation by serotonin3-like receptors.

In the present study, we investigated the effects of various serotonin (5-HT) antagonists on 5-HT's action on medial prefrontal cortical cells (mPFc) using the techniques of single cell recording and microiontophoresis. The microiontophoretic application of 5-HT (10-80 nA) produced a current-dependent suppression of mPFc cell firing and this effect was blocked by the selective 5-HT3 receptor antagonists (+/-)-zacopride, ICS 205930 and granisetron at currents of 5-20 nA. Furthermore, the intravenous (i.v.) administration of (+/-)-zacopride (5-50 micrograms/kg) markedly attenuates the suppressive action of 5-HT on mPFc cell firing. In contrast, the microiontophoresis of 5-HT1 and 5-HT2 receptor antagonists such as (+/-)-pindolol, spiperone, metergoline, and ritanserin (10-20 nA) failed to block 5-HT's effect. In fact, in some cells, spiperone and ritanserin potentiated 5-HT's action and prolonged neuronal recovery. In addition, the intravenous administration of either ritanserin (5-2,000 micrograms/kg) or metergoline (4-2,400 micrograms/kg) failed to alter 5-HT's action. The electrical stimulation of the caudal linear raphe nucleus (CLi) suppressed the spontaneous activity of 83% of the mPFc cells tested by 45 +/- 2%. This suppression was significantly attenuated by the iontophoresis of granisetron (2.5-5 nA) but not by the 5-HT2 and 5-HT1C receptor antagonist ritanserin or the relatively selective 5-HT2 receptor antagonist (+)-MDL 11,939 (10-40 nA). However, the i.v. administration of ritanserin (0.5-1.5 mg/kg) or S-zacopride (0.1 mg/kg) significantly blocked the suppression of mPFc cell firing produced by CLi stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prenatal 3,4-methylenedioxymethamphetamine (ecstasy) exposure induces long-term alterations in the dopaminergic and serotonergic functions in the rat

We investigated several aspects of the dopaminergic and serotonergic functions throughout brain development in rats prenatally exposed to MDMA ("ecstasy"). Pregnant rats were treated with MDMA (10 mg/kg s.c.) or saline from the 13th to the 20th day of gestation and studies were conducted on the progeny from both groups: (i) quantification of whole brain contents of DA, 5-HT and metabolites from the 14th day of embryonic life (E14) to weaning (21st day of postnatal life, P21); (ii) quantification of DA and 5-HT membrane transporters by autoradiography from E18 to adult age (P70); (iii) measurement of pharmacologically induced release of DA and 5-HT using microdialysis on adult (P70) freely moving rats; (iv) measurement of sucrose preference in adults (P70). Prenatally MDMA-exposed rats showed (i) a two-fold decrease of whole brain levels of 5-HT and 5-HIAA at P0; (ii) no effect on the DAT and SERT density; (iii) a strongly reduced pharmacologically induced release of DA and 5-HT at P70 in the striatum and hippocampus; and (iv) a significant 20% decrease in sucrose preference at P70. This study suggests that a prenatal exposure to MDMA induces transient and long-term neurochemical and behavioural modifications in dopaminergic and serotonergic functions.     

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.     

Modulatory role for biogenic amines in the cerebral cortex. Microiontophoretic studies

In order to investigate the mode of action of biogenic amines in rat cerebral cortex, the unitary activity of spontaneously firing neurons and their excitatory response to acetylcholine (ACh) were examined using microiontophoretic administration of dopamine (DA), noradrenaline (NA) and serotonin (5-HT). The predominant effect of these biogenic amines on the spontaneous activity was a profound and prolonged inhibition of firing (2–4 min), which attained its maximum within 15–120 sec. This response was generally more abrupt in onset and of greater magnitude with NA and 5-HT than with DA. Most units inhibited by DA, NA and 5-HT also showed marked depression of their excitatory response to ACh when pretreated with these biogenic amines. With repetitive administration of ACh, it could be shown that the total duration of inhibition of ACh responses by DA and NA was not as prolonged as the inhibition of the spontaneous firing of the same cells. With 5-HT, the initial ACh responses of many neurons could be completely blocked, and this inhibitory effect lasted as long as the inhibition of spontaneous firing.In view of the anatomical data demonstrating a relative sparsity of monoamine nerve terminals in cerebral cortex, the strong inhibition induced by DA, NA or 5-HT may have reflected slow inactivation of the biogenic amines. However, it could also be indicative of underlying mechanisms of action dependent on metabolic changes. Indeed, the interaction between biogenic amines and ACh might imply a balance between the intracellular pools of cAMP and cGMP is directly or indirectly influenced by the biogenic amines and ACh, respectively. This hypothesis would not exclude other modes of local interaction between DA, NA, 5-HT and ACh, and appears compatible with the modulatory role of biogenic amines in cerebral cortex.     

Auditory stimuli enhance MDMA-conditioned reward and MDMA-induced nucleus accumbens dopamine, serotonin and locomotor responses

MDMA (3,4-methylenedioxymethamphetamine), also known as ecstasy, is a popular drug often taken in environments rich in audio and visual stimulation, such as clubs and dance parties. The present experiments were conducted to test the notion that auditory stimulation influences the rewarding effects of MDMA. In Experiment 1, a conditioned place preference (CPP) procedure was conducted in which rats received MDMA (1.5mg/kg, s.c.) in a distinctive environment accompanied by music (65-75dB), white noise (70dB), or no added sound. Animals were pretreated with saline on alternating days in an alternate environment. Results revealed CPP in animals exposed to white noise during MDMA trials. For Experiment 2, rats from Experiment 1 had access to operant levers that delivered intravenous MDMA (0.5mg/kg/inj) or saline (0.1ml) on alternate days in the presence or absence of the same types of auditory stimuli as previously experienced. After three each of MDMA and non-reinforced (saline) sessions, animals were tested for NAcc DA and 5-HT responses to MDMA (1.5mg/kg) or saline under the same stimulus conditions. Findings revealed that NAcc DA and 5-HT increased after an MDMA injection, and both DA and 5-HT were significantly highest in animals exposed to music during the test session. These results indicate that paired sensorial stimuli can engage the same systems activated during drug use and enhance neurochemical and behavioral responses to MDMA administration.     

Clozapine modulates midbrain dopamine neuron firing via interaction with the NMDA receptor complex

The mode of action by which the atypical antipsychotic drug clozapine exerts its superior efficacy to ameliorate both positive and negative symptoms is still relatively unknown. A recent study shows that a pharmacologically increased concentration of brain kynurenic acid, an endogenous antagonist at the glycine-site of the NMDA receptor as well as at the alpha7* nicotinic receptor, reverses the excitatory effects of clozapine on ventral tegmental area (VTA) dopamine (DA) neurons into an inhibitory action. In the present in vivo electrophysiological study, we further investigated the mechanisms of action of clozapine on VTA DA neurons. In control rats intravenously administered clozapine (1.25-10 mg/kg) was associated with increased firing rate and burst firing activity of VTA DA neurons. However, administration of the N-methyl-D-aspartate (NMDA)-receptor antagonist MK 801 blocked the excitatory action of clozapine. Moreover, in rats pretreated with the antagonist of the glycine-site of the NMDA receptor, L-701,324, the effects of clozapine on VTA DA neurons were converted to purely inhibitory responses, including a decrease in firing rate and burst firing activity. Pretreatment with the alpha7* nicotinic receptor antagonist MLA did not affect the excitatory action of clozapine on VTA DA neurons. The results of the present study suggest that clozapine interacts with the NMDA receptor complex. In this regard, clozapine could affect the glycine site of the NMDA receptor or tentatively inhibit the glycine transporter. The inhibitory action of clozapine on VTA DA neurons may account for its beneficial effects in ameliorating symptoms of schizophrenia and may suggest further studies to investigate a role of the glycine site of the NMDA receptor as a target for novel antipsychotics.