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

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.

Pharmacological aspects of the combined use of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and gamma-hydroxybutyric acid (GHB): a review of the literature

Epidemiological studies show that the use of club drugs is on the rise. Furthermore, the last few decades have seen a rise in patterns of polydrug use. One of the combinations frequently used is ecstasy (MDMA) with gammahydroxybutyrate (GHB). For effective prevention it is important to be aware of this phenomenon and of the pharmacology of these drugs. The effects of the combination extend to different neurotransmitter systems, including serotonin, dopamine and noradrenaline. Studies investigating the effects of combinations of psychoactive substances are limited. In this review we describe the subjective effects of the MDMA/GHB combination. Furthermore, we review the individual actions of MDMA on serotonin, dopamine and noradrenaline systems. In addition, actions of GHB on these systems are discussed as a possible pharmacological basis for the interaction of both drugs. It is postulated that GHB attenuates the unpleasant or dysphoric effects of MDMA by its effect on the central dopaminergic system.

Locomotor stimulation produced by 3,4-methylenedioxymethamphetamine (MDMA) is correlated with dialysate levels of serotonin and dopamine in rat brain

(+/-)-3,4-Methylenedioxymethamphetamine (MDMA, or Ecstasy) is an illicit drug that evokes transporter-mediated release of monoamines, including serotonin (5-HT) and dopamine (DA). Here we monitored the effects of MDMA on neurochemistry and motor activity in rats, as a means to evaluate relationships between 5-HT, DA, and behavior. Male rats undergoing in vivo microdialysis were housed in chambers equipped with photobeams for measurement of ambulation (i.e., forward locomotion) and stereotypy (i.e., head weaving and forepaw treading). Microdialysis probes were placed into the n. accumbens, striatum or prefrontal cortex in separate groups of rats. Dialysate samples were assayed for 5-HT and DA by microbore HPLC-ECD. Rats received two i.v. injections of MDMA, 1 mg/kg followed by 3 mg/kg 60 min later; neurochemical and locomotor parameters were measured concurrently. MDMA produced dose-related elevations in extracellular 5-HT and DA in all regions, with the magnitude of 5-HT release always exceeding that of DA release. MDMA-induced ambulation was positively correlated with dialysate DA levels in all regions (P<0.05-0.0001) and with dialysate 5-HT in striatum and cortex (P<0.001-0.0001). Stereotypy was strongly correlated with dialysate 5-HT in all areas (P<0.001-0.0001) and with dialysate DA in accumbens and striatum (P<0.001-0.0001). These data support previous work and suggest the complex spectrum of behaviors produced by MDMA involves 5-HT and DA in a region- and modality-specific manner.

Administration of SCH 23390 into the medial prefrontal cortex blocks the expression of MDMA-induced behavioral sensitization in rats: an effect mediated by 5-HT2C receptor stimulation and not by D1 receptor blockade

Akin to what has been reported for cocaine, systemic administration of the dopamine D1 receptor antagonist, SCH 23390 ((R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride), blocks the expression but not the induction of 3,4-methylenedioxymethamphetamine (MDMA)-induced behavioral sensitization. Since the medial prefrontal cortex (mPFC) appears to regulate the expression of sensitization to cocaine, this study examined whether microinjection of SCH 23390 into the mPFC would alter the expression of MDMA sensitization. Saline or MDMA was administered for 5 consecutive days. After 12 days of withdrawal, rats received a bilateral intra-mPFC microinjection of SCH 23390 or saline followed by an intraperitoneal (i.p.) challenge dose of MDMA. While SCH 23390 enhanced locomotion in MDMA-naïve rats, it completely suppressed the expression of sensitization in MDMA-pretreated animals. Since, SCH 23390 has a fairly good affinity for 5-HT(2C) receptors, we went further to study the role of mPFC D1 and 5-HT(2C) receptors in this, apparently, paradoxical effect shown by SCH 23390. Thus, the microinjection of both SKF 81297 (R-(+)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide) and MK 212 (6-chloro-2-(1-piperazinyl)pyrazine hydrochloride), a D1 and 5-HT(2C) receptor agonist, respectively, blocked MDMA sensitization. By contrast, the 5-HT(2C) receptor antagonist, RS 102221 (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulfonamido)phenyl-5-oxopentyl]-1,3,8-triazaspiro[4,5]decane-2,4-dione hydrochloride), had no effect in MDMA-naïve or MDMA-sensitized animals, but reversed the effects of SCH 23390 in MDMA-pretreated rats. These results demonstrate that suppression of MDMA-induced sensitization by SCH 23390 is mediated by 5-HT(2C) receptor stimulation in the mPFC and not by the blockade of mPFC D1 receptors. Furthermore, these data indicate that stimulation of 5-HT(2C) receptors by SCH 23390 is not a minor issue and should be considered when interpreting future data.

Ibotenic acid lesions of the medial prefrontal cortex block the development and expression of 3,4-methylenedioxymethamphetamine-induced behavioral sensitization in rats

There is ample evidence that plastic changes in the nervous system require the excitatory amino acid transmission. This appears to be also the case for psychostimulant-induced behavioral sensitization. More specifically the glutamatergic input from the medial prefrontal cortex (mPFC) to the VTA and the NAc appears to be involved in behavioral sensitization processes. However, dissociations regarding the role of the mPFC with respect to the development and expression of sensitization, as well as with respect to the psychostimulant being studied (amphetamine versus cocaine) appear to exist. The present study examined the role of the dorsal mPFC in the development and expression of 3,4-methylenedioxymethamphetamine (MDMA)-induced sensitization. Bilateral ibotenic acid or sham lesions of the dorsal mPFC were performed 7 days prior to or 4 days after a context-dependent sensitization-inducing regimen of MDMA (15 mg/kg i.p.) or saline. Rats were then challenged with MDMA (5 mg/kg i.p.) after 12 days of withdrawal. Ibotenic acid lesions did not affect the activating effects of MDMA, but prevented the development and expression of MDMA sensitization. Thus, the distance traveled during the development phase of sensitization increased in sham-lesioned rats but not in ibotenic-lesioned animals. Similarly, sham-lesioned rats showed a sensitized response when challenged with MDMA after the withdrawal period, an effect not observed in ibotenic-lesioned animals. These data reinforce the view that the dorsal mPFC is involved in psychostimulant sensitization and more specifically they indicate that the dorsal mPFC plays a key role in the development and expression of MDMA-induced behavioral sensitization.

Studies on the role of dopamine D1 receptors in the development and expression of MDMA-induced behavioral sensitization in rats

RATIONALE

There is a large body of evidence indicating that the mesoaccumbens dopamine pathway is critically involved in the expression of behavioral sensitization to amphetamine and cocaine, but its role in the development of sensitization to psychostimulants is not that sound. Very few studies, however, have examined the role of dopamine transmission in 3,4-methylenedioxymethamphetamine (MDMA)-induced sensitization.

OBJECTIVES

The effects of the D1 receptor antagonist SCH 23390 on the development and expression of MDMA-induced behavioral sensitization were investigated in rats.

METHODS

During the development phase of sensitization, SCH 23390 was administered 15 min before every administration of MDMA. After 12 days of withdrawal, a MDMA challenge dose was given and locomotor activity was measured. In separate experiments, 15 min before the challenge injection of MDMA, SCH 23390 was administered either systemically or directly into the core of the nucleus accumbens (NAc) of MDMA-pretreated rats.

RESULTS

SCH 23390 did not prevent the development of MDMA-induced behavioral sensitization but completely blocked the expression when given before the challenge dose of MDMA. The same results were obtained when SCH 23390 was locally applied into the core of the NAc.

CONCLUSIONS

The present data suggest that D1 receptor stimulation is not critical for the development of long-term MDMA sensitization, in agreement with what has been reported for cocaine. By contrast, expression of sensitization depends on the activation of D1 receptors located in the NAc core.

The pre-clinical behavioural pharmacology of 3,4-methylenedioxymethamphetamine (MDMA)

3,4-Methylenedioxymethamphetamine (MDMA) is a relatively novel drug of abuse and as such little is currently known of its behavioural pharmacology. This review aims to examine whether MDMA represents a novel class of abused drug. MDMA is known as a selective serotonergic neurotoxin in a variety of animal species but acutely it is a potent releaser and/or reuptake inhibitor of presynaptic serotonin, dopamine, noradrenaline, and acetylcholine. Interaction of these effects contributes to its behavioural pharmacology, in particular its effects on body temperature. Drug discrimination studies indicate that MDMA and related drugs produce unique interoceptive effects which have led to their classification as entactogens. This is supported by results from other behavioural paradigms although there is evidence for dose dependency of MDMA-specific effects. MDMA also produces conditioned place preference but is not a potent reinforcer in self-administration studies. These unique behavioural effects probably underlie its current popularity. MDMA is found in the street drug ecstasy but it may not be appropriate to equate the two as other drugs are routinely found in ecstasy tablets

Methylenedioxymethamphetamine-induced inhibition of neuronal firing in the nucleus accumbens is mediated by both serotonin and dopamine

Methylenedioxymethamphetamine (MDMA) is a mood-altering, legally restricted drug that has been reported to inhibit glutamate-evoked firing of cells in the nucleus accumbens. This study used extracellular recording combined with microiontophoresis to examine whether the inhibitory effect of MDMA on neuronal firing in the nucleus accumbens is mediated by serotonin and/or dopamine. Serotonin and serotonin agonists with relative selectivity for the receptor subtypes 5-HT1A, 5-HT1B, 5-HT2A/2C and 5-HT3 all significantly (P < 0.01) inhibited glutamate-evoked firing of cells in the nucleus accumbens compared to the effects of an acidic saline control solution (30-60 nA, 60 s ejection currents for all). The current (dose)-dependent inhibition produced by the serotonin agonists did not differ significantly from the inhibition produced by MDMA except for the 5-HT1A agonist 8-hydroxy-(2-di-n-propylamino) tetralin, which inhibited glutamate-evoked firing significantly more than MDMA or any of the other serotonin agonists. At the highest ejection current tested (60 nA, 60 s), glutamate-evoked firing was inhibited by MDMA in 94% of tested cells, by serotonin in 80% of tested cells and by the serotonin receptor subtype agonists in 95-100% of the tested cells. In addition to being mimicked by serotonin and serotonin agonists, MDMA-induced inhibition of glutamate-evoked firing in the nucleus accumbens was partially blocked by the serotonin antagonists ketanserin (100% of tested cells), methysergide (80% of tested cells), methiothepin (100% of tested cells) and WAY100135 (100% of tested cells). Furthermore, application of the serotonin uptake blocker fluoxetine, which prevents MDMA-induced serotonin release, also significantly attenuated MDMA-induced inhibition of glutamate-evoked firing in all of the cells that were tested. These observations suggest that MDMA-induced inhibition of nucleus accumbens cell firing is at least partially mediated by serotonin. Depletion of dopamine by pretreatment with the neurotoxin 6-hydroxydopamine and the synthesis inhibitor alpha-methyl-p-tyrosine blocked the inhibition of glutamate-evoked firing produced by MDMA applied with low ejection currents (30-40 nA, 60 s). However, this dopamine depletion had no effect on inhibition of glutamate-evoked firing produced by serotonin ejected with low or high currents (20-60 nA, 60 s). These results suggest that both dopamine release and an intermediate step of MDMA-induced serotonin release are necessary for the inhibitory effects of MDMA on neuronal excitability in the nucleus accumbens. The dopamine- and serotonin-mediated inhibitory effects of MDMA on glutamate-evoked firing of nucleus accumbens cells may play a role in the mood-altering properties of this increasingly popular drug.

Comparison of the action of the stereoisomers of the psychostimulant 4-methylaminorex (4-MAX) on midbrain dopamine cells in the rat: an extracellular single unit study

In this study, we examined and characterized the action of the stereoisomers of 2-amino-4-methyl-delta 2-5-phenyl-oxazoline (4-methylaminorex, 4-MAX) on spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC or A9) and ventral tegmental area (VTA or A10) in anesthetized male rats. This was accomplished using the technique of extracellular single unit recording. The intravenous (i.v.) administration of the stereoisomers of 4-MAX (0.1-6.4 mg/kg) produced a dose-dependent suppression of the basal firing rate of A10 DA cells with the following rank order of potency: trans 4S,5S > cis 4R,5S approximately cis 4S,5R >> trans 4S,5S 4-MAX. The rank order of potency of the isomers of 4-MAX to suppress the firing of A9 DA cells was trans 4S,5S = cis 4R,5S = cis 4S,5R >> trans 4R,5R. The trans 4S,5S isomer was 5-fold more potent in suppressing DA cell firing in the A10 compared to the A9 area. The suppressant action of the isomers on A9 and A10 DA cells was reversed by the i.v. administration of haloperidol and the D2/D3 receptor antagonists (-)-sulpiride and (-)-eticlopride but not by the D1 receptor antagonists SCH 23390 and SCH 39166. In addition, the suppressant action of the trans 4S,5S isomer on A10 DA cells was not antagonized or reversed by the i.v. administration of the receptor antagonists granisetron (5-HT3), ritanserin (5-HT2A,C), idazoxan (alpha 2), phentolamine (peripheral alpha 1), (+/-)-pindolol (5-HT1A,B beta) or prazosin (alpha 1). The pretreatment of animals with either alpha-methyl-p-tyrosine (AMPT) or reserpine, but not p-chlorophenylalanine (PCPA), (+/-)-fluoxetine or tomoxetine, significantly attenuated the suppression of A10 DA cell firing produced by trans 4S,5S 4-MAX. Overall, our results suggest that the suppressant action of 4-MAX on midbrain DA cell firing may be mediated by the release of DA, which subsequently interacts with D2/D3 receptors.

The induction of serotonin3-like receptor supersensitivity and dopamine receptor subsensitivity in the rat medial prefrontal cortex after the intraventricular administration of the neurotoxin 5,7-dihydroxytryptamine: a microiontophoretic study

This study examines the effect of intraventricular administration of the neurotoxin 5,7-dihydroxytryptamine on serotonin1A, serotonin2 and serotonin3 receptors in the rat medial prefrontal cortex using in vivo extracellular single cell recording and iontophoresis. Iontophoresis of the serotonin1A, serotonin1C,2 and serotonin3 receptor agonists (+-)-8-hydroxy-(di-n-propyl)aminotetralin, (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and 2-methylserotonin, respectively, produces a current-dependent (5-80 nA) suppression of the basal firing rate of medial prefrontal cortical cells in sham- and 5,7-dihydroxytryptamine-lesioned rats. The suppression produced by 2-methylserotonin and serotonin was significantly greater in 5,7-dihydroxytryptamine-lesioned rats than in control rats. No significant difference in the spontaneous activity of medial prefrontal cortex cells was observed between experimental and control rats after iontophoresis of (+-)-8-hydroxy-(di-n-propyl)aminotetralin or (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane. There was no significant difference between the groups regarding the response of medial prefrontal cortex cells to the iontophoresis of GABA, whereas the response of medial prefrontal cortex cells to the iontophoresis of dopamine was significantly attenuated in animals pretreated with 5,7-dihydroxytryptamine compared to controls. Our results indicate that 5,7-dihydroxytryptamine-induced denervation selectively enhances the sensitivity of serotonin3-like receptors in the medial prefrontal cortex, which could, at least partially, account for the serotonin denervation supersensitivity. Moreover, the finding that the response of medial prefrontal cortical cells to the iontophoresis of dopamine is attenuated in 5,7-dihydroxytryptamine pretreated rats is consistent with the view that the inhibitory action of dopamine in the medial prefrontal cortex is dependent upon serotonin tone.

Further studies on N-methyl-1(3,4-methylenedioxyphenyl)-2-aminopropane as a discriminative stimulus: antagonism by 5-hydroxytryptamine3 antagonists

Using a standard two-lever operant paradigm, male Sprague-Dawley rats were trained to discriminate 1.5 mg/kg N-methyl-1(3,4-methylenedioxyphenyl)-2- aminopropane (MDMA) from saline using a variable-interval 15-s schedule of reinforcement for food reward. Tests of stimulus antagonism were conducted to further define the mechanism of action of MDMA as a discriminative stimulus. Low doses of the 5-hydroxytryptamine1A (5-HT1A) antagonist NAN-190, the 5-HT2 antagonist pirenperone, and the dopamine antagonist haloperidol were able to somewhat attenuate the MDMA stimulus; however, none of these agents decreased MDMA-appropriate responding to less than 46%. The 5-HT3 antagonists zacopride and LY 278584 (ID50 = 0.02 micrograms/kg) antagonized the MDMA discriminative stimulus. Zacopride also attenuated the stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) in DOM-trained animals but not those of (+)amphetamine in (+)amphetamine-trained animals. Several possible mechanistic interpretations are provided but it is concluded that MDMA produces its stimulus effects via a complex mechanism involving both dopaminergic and serotonergic components.

M.D.M.A. ("Ecstasy"); a case of possible drug-induced psychosis

3, 4, Methylenedioxymetamphetamine (M.D.M.A., Ecstasy) is a modified amphetamine with stimulant and hallucinogenic properties. Ecstasy has been increasingly abused in Dublin in recent years. It is commonly perceived by users as a safe drug. We report a case of prolonged psychosis following brief recreational use of Ecstasy.