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

MDMA (ecstasy) modulates locomotor and prefrontal cortex sensory evoked activity

Ingestion of 3, 4-methylenedioxymethamphetamine (MDMA) leads to heightened response to sensory stimulation; thus, MDMA is referred to as "ecstasy" because it produces pleasurable enhancement of such sensation. There have been no electrophysiological studies that report the consequences of MDMA on sensory input. The present study was initiated to study the effects of acute and chronic MDMA on locomotor activity and sensory evoked field potential from freely behaving rats previously implanted with permanent electrodes in the prefrontal cortex (PFC). The main findings of this study are that: (1) acute MDMA augments locomotor behavior and attenuates the incoming sensory input, (2) chronic treatment of MDMA elicits behavioral sensitization, (3) chronic administration of MDMA results in attenuation of the baseline activity of the sensory evoked field potential, and (4) administration of rechallenge MDMA result in enhancement of the PFC sensory evoked field potential.

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.

Functional MRI study of working memory in MDMA users

RATIONALE

Methylene-dioxymethamphetamine (MDMA) is known to cause degeneration of serotonin nerve terminals after acute doses in animals. Similarly, behavioral studies in human MDMA users regularly find abnormalities in memory, mood, and impulse control. However, studies of brain function using brain imaging in MDMA users have been less consistent.

OBJECTIVES

The purpose of this study was to determine, using functional magnetic resonance imaging (fMRI), whether individuals with a self-reported history of MDMA use would differ from non-MDMA using controls on activation while performing a working memory task.

METHODS

Fifteen MDMA using subjects and 19 non-MDMA using controls underwent fMRI scanning while performing the immediate and delayed memory task (IMT/DMT). The study was based on a block design in which the delayed memory task (DMT) alternated with the immediate memory task (IMT), which served as a control condition. FMRI scans were acquired on a 1.5 T scanner, using a gradient echo echoplanar pulse sequence.

RESULTS

Random effects SPM99 analysis showed significantly greater activation (whole volume corrected cluster P<0.05) during the DMT relative to the IMT in the MDMA subjects compared with the control subjects in the medial superior frontal gyrus, in the thalamus extending into putamen, and in the hippocampus.

CONCLUSIONS

Although these effects could be due to other drugs used by MDMA users, these results are consistent with behavioral problems that are associated with MDMA use, and with animal studies on the effects of MDMA on brain function.

Impaired executive function in male MDMA ("ecstasy") users

RATIONALE

Long-term users of ecstasy have shown impaired performance on a multitude of cognitive abilities (most notably memory, attention, executive function). Research into the pattern of MDMA effects on executive functions remains fragmented, however.

OBJECTIVES

To determine more systematically what aspects of executive function are affected by a history of MDMA use, by using a model that divides executive functions into cognitive flexibility, information updating and monitoring, and inhibition of pre-potent responses.

METHODS

MDMA users and controls who abstained from ecstasy and other substances for at least 2 weeks were tested with a computerized cognitive test battery to assess their abilities on tasks that measure the three submodalities of executive function, and their combined contribution on two more complex executive tasks. Because of sex-differential effects of MDMA reported in the literature, data from males and females were analyzed separately.

RESULTS

Male MDMA users performed significantly worse on the tasks that tap on cognitive flexibility and on the combined executive function tasks; no differences were found on the other cognitive tasks. Female users showed no impairments on any of the tasks.

CONCLUSIONS

The present data suggest that a history of MDMA use selectively impairs executive function. In male users, cognitive flexibility was impaired and increased perseverative behavior was observed. The inability to adjust behavior rapidly and flexibly may have repercussions for daily life activities.

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

Repeated exposure to methylenedioxymethamphetamine (MDMA) alters nucleus accumbens neuronal responses to dopamine and serotonin

The purpose of this experiment was to investigate the effects of repeated exposure to methylenedioxymethamphetamine (MDMA) on responses of neurons in the nucleus accumbens of anesthetized rats to microiontophoretically-applied dopamine and serotonin. In tests conducted 1-4 days or 9-15 days following the last injection of MDMA (20 mg/kg, s.c., twice daily for 4 days), the inhibitory effects of both dopamine and serotonin on glutamate-evoked firing of nucleus accumbens cells were significantly attenuated compared to effects in control rats that were pretreated with saline injections. The inhibitory effect of the D1 receptor agonist SKF38393 was also significantly attenuated in the MDMA-pretreated rats. In contrast, the amount of inhibition of glutamate-evoked firing produced by application of GABA did not significantly differ between the MDMA-pretreated and the saline-pretreated rats. The neurotoxicity of the MDMA treatment regimen was confirmed by demonstrating that 3H-paroxetine binding was significantly decreased in the medial prefrontal cortex and the nucleus accumbens of the MDMA-pretreated rats. The mechanisms that produce the attenuated inhibitory responses to dopamine and serotonin following repeated injections of MDMA are not known. However, the results of these experiments indicate that repeated MDMA administration induces long-lasting changes in dopaminergic as well as serotonergic neurotransmission in the nucleus accumbens.

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.

Methylenedioxymethamphetamine depresses glutamate-evoked neuronal firing and increases extracellular levels of dopamine and serotonin in the nucleus accumbens in vivo

The nucleus accumbens has been implicated as an important site for the actions of many drugs that are used recreationally. This study examined the effects of methylenedioxymethamphetamine (MDMA), a euphoric and hallucinogenic drug, on glutamate-evoked neuronal firing and on extracellular levels of dopamine and serotonin in the nucleus accumbens of the rat. Microiontophoretic application of MDMA inhibited glutamate-evoked firing of most of the nucleus accumbens cells that were tested (83 of 86), as did microiontophoretic application of dopamine and serotonin. MDMA-induced inhibition of glutamate-evoked firing was partially blocked by the dopamine antagonist SCH39166 and was attenuated by combined pretreatment with inhibitors of both serotonin and catecholamine synthesis, p-chlorophenylalanine and alpha-methyl-p-tyrosine. MDMA applied directly into the nucleus accumbens and adjacent regions of the ventral striatum through a dialysis probe increased extracellular levels of both dopamine and serotonin. These results indicate that MDMA has inhibitory effects on glutamate-evoked neuronal firing in the nucleus accumbens and suggest that the inhibition is mediated by increased extracellular dopamine and serotonin. Furthermore, these results permit MDMA to be added to the extensive list of abused drugs that have been demonstrated to elevate extracellular levels of dopamine and serotonin in the nucleus accumbens.

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.