The molecular mechanism of "ecstasy" [3,4-methylenedioxy-methamphetamine (MDMA)]: serotonin transporters are targets for MDMA-induced serotonin release

A conformationally sensitive residue on the cytoplasmic surface of serotonin transporter

Serotonin transporter (SERT) contains a single reactive external cysteine residue at position 109 (Chen, J. G., Liu-Chen, S., and Rudnick, G. (1997) Biochemistry 36, 1479-1486) and seven predicted cytoplasmic cysteines. A mutant of rat SERT (X8C) in which those eight cysteine residues were replaced by other amino acids retained approximately 32% of wild type transport activity and approximately 56% of wild type binding activity. In contrast to wild-type SERT or the C109A mutant, X8C was resistant to inhibition of high affinity cocaine analog binding by the cysteine reagent 2-(aminoethyl)methanethiosulfonate hydrobromide (MTSEA) in membrane preparations from transfected cells. Each predicted cytoplasmic cysteine residue was reintroduced, one at a time, into the X8C template. Reintroduction of Cys-357, located in the third intracellular loop, restored MTSEA sensitivity similar to that of C109A. Replacement of only Cys-109 and Cys-357 was sufficient to prevent MTSEA sensitivity. Thus, Cys-357 was the sole cytoplasmic determinant of MTSEA sensitivity in SERT. Both serotonin and cocaine protected SERT from inactivation by MTSEA at Cys-357. This protection was apparently mediated through a conformational change following ligand binding. Although both ligands bind in the absence of Na(+) and at 4 degrees C, their ability to protect Cys-357 required Na(+) and was prevented at 4 degrees C. The accessibility of Cys-357 to MTSEA inactivation was increased by monovalent cations. The K(+) ion, which is believed to serve as a countertransport substrate for SERT, was the most effective ion for increasing Cys-357 reactivity.

In vitro neuronal and vascular responses to 5-HT in rats chronically exposed to MDMA

1. This study examined the effects of chronic exposure of rats to 3,4-methylenedioxymethamphetamine (MDMA) on [(3)H]5-hydroxytryptamine ([(3)H]5-HT) re-uptake into purified rat brain synaptosomes, 5-HT-induced isometric contraction of aortic rings and [(3)H]5-HT re-uptake into rat aorta. 2. Rats were administered MDMA (20 mg kg(-1) i.p.) twice daily over 4 days. One, 7, 14 or 21 days post treatment, whole brain synaptosomes and descending thoracic aortic rings were prepared for investigation. 3. Chronic MDMA treatment significantly reduced the maximum rate (V(max)) of specific high-affinity [(3)H]5-HT re-uptake 1 day after treatment and for up to 21 days post-final administration of MDMA. Direct application of MDMA (100 microM) abolished synaptosomal re-uptake of [(3)H]5-HT in vitro. 4. Chronic MDMA administration significantly reduced the maximum contraction (E(max)) to 5-HT at 1 and 7 days after treatment, but not at 14 or 21 days. 5. Chronic MDMA administration had no effect on sodium-dependent [(3)H]5-HT re-uptake into aorta 1 day after treatment, nor did 100 microM MDMA have any direct effect on [(3)H]5-HT uptake into aortic rings in vitro. 6. These results show, for the first time, an altered responsiveness of vascular tissue to MDMA after chronic administration. In addition, they demonstrate a difference in the sensitivity of central and peripheral 5-HT uptake systems to chronic MDMA exposure, and suggest that the action of MDMA in the cardiovascular system does not arise from a direct effect of MDMA on peripheral 5-HT transport.

Which neuroreceptors mediate the subjective effects of MDMA in humans? A summary of mechanistic studies

In preclinical studies, 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') has been shown to release serotonin (5-HT), dopamine and norepinephrine. However, the role of these neurotransmitters and their corresponding receptor sites in mediating the subjective effects of MDMA has not yet been studied in humans. Therefore, we investigated the effects of three different neuroreceptor pretreatments on the subjective, cardiovascular and adverse effects of MDMA (1.5 mg/kg orally) in 44 healthy human volunteers. Pretreatments were: the selective serotonin reuptake inhibitor citalopram (40 mg intravenously) in 16 subjects, the 5-HT(2) antagonist ketanserin (50 mg orally) in 14 subjects, and the D(2) antagonist haloperidol (1.4 mg intravenously) in 14 subjects. Each of these studies used a double-blind placebo-controlled within-subject design and all subjects were examined under placebo, pretreatment, MDMA and pretreatment plus MDMA conditions. Citalopram markedly reduced most of the subjective effects of MDMA, including positive mood, increased extraversion and self-confidence. Cardiovascular and adverse effects of MDMA were also attenuated by citalopram. Haloperidol selectively reduced MDMA-induced positive mood but had no effect on other subjective effects of MDMA or the cardiovascular or adverse responses to MDMA. Ketanserin selectively reduced MDMA-induced perceptual changes and emotional excitation. These results indicate that the overall psychological effects of MDMA largely depend on carrier-mediated 5-HT release, while the more stimulant-like euphoric mood effects of MDMA appear to relate, at least in part, to dopamine D(2) receptor stimulation. The mild hallucinogen-like perceptual effects of MDMA appear to be due to serotonergic 5-HT(2) receptor stimulation. Copyright 2001 John Wiley & Sons, Ltd.

Labelled alpha-methyl-L-tryptophan as a tracer for the study of the brain serotonergic system

The alpha-methyl-L-trypotophan (alpha-MTrp) method for the study of the brain serotonergic system is based on the fact that labelled alpha-MTrp is taken up by and, in part, retained in the brain, and this retention (trapping) is proportional to brain serotonin (5-HT) synthesis. A 3-compartment model is proposed in which the plasma, the precursor and irreversible pools are mathematically distinct compartments. The irreversible compartment is assumed to be the one in which the tracer is trapped. By definition, the tracer from the irreversible compartment does not exchange directly with the plasma compartment. The rate at which labelled alpha-MTrp is trapped is converted to the rate of 5-HT synthesis by dividing it by a conversion factor, called the lumped constant, and multiplying it by the plasma-free tryptophan concentration. Our results revealed that brain 5-HT synthesis can be influenced by the extraneuronal concentration of 5-HT and that, generally, the influence is not uniform throughout the brain. They also suggest that brain trapping of labelled alpha-MTrp relates to 5-HT synthesis. The proposed procedure for converting the rate at which labelled alpha-MTrp is trapped to brain 5-HT synthesis rates is based on measurements that suggest that plasma-free Trp relates to brain 5-HT synthesis. However, as with all biological models, there is likely room for improvement in our approach.

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.

Pharmacological characterization and visualization of the glial serotonin transporter

Astrocytes contain transport systems that are capable of removing various neurotransmitters from the synaptic cleft by transporters present in the plasma membrane. Glial serotonin transporter (SERT) plays an important role in the re-uptake of 5-hydroxytryptamine (5-HT). We examined the pharmacological characterization of 5-HT uptake into rat cortical synaptosomes and cultured rat astrocytes, and the immunodetection of glial SERT proteins using specific site-directed monoclonal antibodies (MoAb). Furthermore, using a reverse transcriptase-polymerase chain reaction (RT-PCR) method, we addressed the expression of SERT mRNA in cultured rat astrocytes. We investigated the inhibitory effects of various monoamine uptake inhibitors on the uptake of [3H]5-HT into cultured astrocytes and cortical synaptosomes. Tricyclic antidepressants (clomipramine and imipramine) as well as selective serotonin re-uptake inhibitors (fluvoxamine, fluoxetine and zimelidine) were very potent inhibitors of [3H]5-HT uptake in both preparations. In contrast, the inhibitory effects of NE uptake inhibitors (nisoxetine and desipramine) and cocaine were weaker than those of 5-HT uptake inhibitors. In addition, dopamine (DA) uptake inhibitors (nomifensine and GBR-12935) exhibited a Ki value in the low micromolar range. The inhibitory potencies were in the order 5-HT uptake inhibitors (clomipramine, fluvoxamine, fluoxetine, imipramine and zimelidine) > NE uptake inhibitors (nisoxetine and desipramine) = cocaine > DA uptake inhibitors (nomifensine and GBR-12935). There was no difference in the order of the inhibitory effects of various monoamine uptake inhibitors between the two preparations. A correlation analysis of the potencies of various monoamine uptake inhibitors in the inhibition of [3H]5-HT into cultured astrocytes and cortical synaptosomes produced a highly significant correlation coefficient of 0.9893 (P < 0.0001). Immunocytochemical staining using anti-SERT MoAb in cultured astrocytes revealed that the plasma membrane, as well as intracellular, perinuclear compartments, presumably endoplasmic reticulum or golgi membranes, showed a considerable level of immunoreactivity. Extracts of astrocytes and synaptosomes from the cortex were immunoblotted with anti-SERT MoAb. SDS-PAGE/Western blots indicate that anti-SERT MoAb recognized two bands of 120 and 73 kDa in both preparations. RT-PCR demonstrated that astrocytes in cultured expressed mRNA for the cloned SERT protein, which has been characterized as the neuronal SERT. These pharmacological experiments indicate that this uptake process takes place through glial SERT that is very similar to neuronal SERT. Furthermore, the present data also indicate that the presence of the mRNA and protein for the neuronal SERT were established in cultured rat astrocytes, and the polypeptide portion of SERT in astrocytes and frontal cortex could be the same gene product.

Effect of temperature on dopamine transporter function and intracellular accumulation of methamphetamine: implications for methamphetamine-induced dopaminergic neurotoxicity

Hyperthermia exacerbates and hypothermia attenuates methamphetamine (METH)-induced dopamine (DA) neurotoxicity. The mechanisms underlying these temperature effects are unknown. Given the essential role of the DA transporter (DAT) in the expression of METH-induced DA neurotoxicity, we hypothesized that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT. To test this hypothesis, the effects of small, physiologically relevant temperature changes on DAT function were evaluated in two types of cultured neuronal cells: (1) a neuroblastoma cell line stably transfected with human DAT cDNA and (2) rat embryonic mesencephalic primary cells that naturally express the DAT. Temperatures for studies of DAT function were selected based on core temperature measurements in animals exposed to METH under usual ambient (22 degrees C) and hypothermic (6 degrees C) temperature conditions, where METH neurotoxicity was fully expressed and blocked, respectively. DAT function, determined by measuring accumulation of radiolabeled DA and 1-methyl-4-phenylpyridinium (MPP(+)), was found to directly correlate with temperature, with higher levels of substrate uptake at 40 degrees C, intermediate levels at 37 degrees C, and lower levels at 34 degrees C. DAT-mediated accumulation of METH also directly correlated with temperature, with greater accumulation at higher temperatures. These findings indicate that relatively small, physiologically relevant changes in temperature significantly alter DAT function and intracellular METH accumulation, and suggest that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT.

Quantitative analysis of inward and outward transport rates in cells stably expressing the cloned human serotonin transporter: inconsistencies with the hypothesis of facilitated exchange diffusion

Quantitative aspects of inward and outward transport of substrates by the human plasmalemmal serotonin transporter (hSERT) were investigated. Uptake and superfusion experiments were performed on human embryonic kidney 293 cells permanently expressing the hSERT using [(3)H]serotonin (5-HT) and [(3)H]1-methyl-4-phenylpyridinium (MPP(+)) as substrates. Saturation analyses rendered K(m) values of 0.60 and 17.0 microM for the uptake of [(3)H]5-HT and [(3)H]MPP(+), respectively. Kinetic analysis of outward transport was performed by prelabeling the cells with increasing concentrations of the two substrates and exposing them to a saturating concentration of p-chloroamphetamine (PCA; 10 microM). Apparent K(m) values for PCA induced transport were 564 microM and about 7 mM intracellular [(3)H]5-HT and [(3)H]MPP(+), respectively. Lowering the extracellular Na(+) concentrations in uptake and superfusion experiments revealed differential effects on substrate transport: at 10 mM Na(+) the K(m) value for [(3)H]5-HT uptake increased approximately 5-fold and the V(max) value remained unchanged. The K(m) value for [(3)H]MPP(+) uptake also increased, but the V(max) value was reduced by 50%. When efflux was studied at saturating prelabeling conditions of both substrates, PCA as well as unlabeled 5-HT and MPP(+) (all substances at saturating concentrations) induced the same efflux at 10 mM and 120 mM Na(+). Thus, notwithstanding a 50% reduction in the V(max) value of transport into the cell, MPP(+) was still able to induce maximal outward transport of either substrate. Thus, hSERT-mediated inward and outward transport seems to be independently modulated and may indicate inconsistencies with the classical model of facilitated exchange diffusion.

Intravenous administration of ecstasy (3,4-methylendioxymethamphetamine) enhances cortical and striatal acetylcholine release in vivo

The effect of intravenous administration of 3,4-methylendioxymethamphetamine (MDMA), in a range of doses (0.32-3.2 mg/kg) that have been shown to maintain self-administration behaviour in rats, on in vivo acetylcholine release from rat prefrontal cortex and dorsal striatum was studied by means of microdialysis with vertical concentric probes. Intravenous administration of MDMA dose-dependently increased basal acetylcholine release from the prefrontal cortex to 57+/-21%, 98+/-20%, 102+/-7% and 141+/-14% above baseline, at doses of 0.32, 0.64, 1.0 and 3.2 mg/kg, respectively. MDMA also stimulated striatal acetylcholine release at the dose of 3.2 mg/kg i.v. (the maximal increase being 32+/-3% above baseline) while at the dose of 1 mg/kg i.v., MDMA failed to affect basal acetylcholine output. Administration of MDMA also dose-dependently stimulated behaviour. The results of the present study show that MDMA affects measures of central cholinergic neurotransmission in vivo and suggest that at least some of the psychomotor stimulant actions of MDMA might be positively coupled with an increase in prefrontal cortical and striatal acetylcholine release.

The reverse transport of DA, what physiological significance?

It is well established that midbrain dopamine neurons innervating the striatum, release their neurotransmitter through an exocytotic process triggered by the neural firing and involving a transient calcium entry in the terminals. Long ago, it had been proposed, however, that another mechanism of release could co-exist with classical exocytosis, involving the reverse-transport of the cytosolic amine by the carrier, ordinarily responsible for uptake function. This atypical mode of release could be evoked directly at the preterminal level by multiple environmental endogenous factors involving transient alterations of the sodium gradient. It cannot be excluded that this mode of release participates in the firing-induced release. In contrast with the classical exocytosis of a preformed DA pool, the reverse-transport of DA requires simultaneous alterations of intraterminal amine metabolism including synthesis and displacement from storage compartment. The concept of a reverse-transport of dopamine is coming from the observations that releasing substances, such as amphetamine-related molecules, actually induce this type of transport. A large set of arguments advocates that reverse-transport plays a role in the maintenance of basal extracellular DA concentration in striatum. It was also often evoked in physiopathological situations including ischemia, neurodegenerative processes, etc. The most recent studies suggest that this release could occur mainly outside the synapses, and thus could constitute a major feature in the paracrine transmission, sometimes evoked for DA.

Compensatory responses in the aging hippocampal serotonergic system following neurodegenerative injury with 5,7-dihydroxytryptamine

This study utilized a multidisciplinary approach to examine injury-induced compensatory responses in the aging hippocampal serotonin transporter (5-HTT), a membrane protein implicated in a variety of neurodegenerative disorders. Age-dependent cellular, anatomical, and physiological changes of the 5-HTT were evaluated in female Fischer 344 rats (2 and 17 months) following denervation of the serotonergic afferents (fimbria-fornix and cingulum bundle) to the dorsal hippocampus using the neurotoxicant 5,7-dihydroxytryptamine (5,7-DHT). Seven days following 5,7-DHT administration, a uniform loss of the hippocampal 5-HTT immunoreactivity was observed in both age groups. However, at 21 days 5-HTT immunoreactivity in young 5,7-DHT-treated animals was similar to control levels, indicative of recovery, while older animals exposed to 5,7-DHT did not show recovery of hippocampal 5-HTT expression. 5-HTT binding site density, as determined by quantitative autoradiography ([3H]citalopram), supported the immunohistochemical results by demonstrating a recovery of 5-HTT binding sites in young, but not old animals, at 21 days following the lesion (P < 0.001). Furthermore, cellular electrophysiological function of hippocampal CA1 pyramidal neurons in 3- and 18-month-old F344 rats at 21 days following 5,7-DHT or vehicle treatment were assessed using in vivo microiontophoretic application of serotonin (5-HT). Independent of changes in sensitivity to the inhibitory effects of 5-HT application, the time to recovery of cell firing following application of 5-HT was significantly increased in the 18-month 5,7-DHT group compared to the 18-month vehicle and 3-month 5,7-DHT groups (60 and 59% increases, respectively; P < 0.05). Overall, these series of studies comprise a model which can be used to identify cellular events underlying both the formation of injury-induced compensatory processes in younger animals and the lack thereof with advancing age.

The role of recreational drugs in trauma

The association of trauma with illicit/recreational drugs is being increasingly recognized but is difficult to quantify. Significant amounts of these substances are readily available and may be taken alone, in combination with other drugs or with alcohol. The acute and chronic effects of these drugs result in numerous difficulties in management. Health-care workers involved in the treatment of trauma must have a high index of suspicion for the presence of drugs and a detailed knowledge of their effects. In this article we will review the scale of the problem, the common drugs abused and their effects, and we will discuss guidelines for management.

Effect of temperature on dopamine transporter function and intracellular accumulation of methamphetamine: implications for methamphetamine-induced dopaminergic neurotoxicity

Hyperthermia exacerbates and hypothermia attenuates methamphetamine (METH)-induced dopamine (DA) neurotoxicity. The mechanisms underlying these temperature effects are unknown. Given the essential role of the DA transporter (DAT) in the expression of METH-induced DA neurotoxicity, we hypothesized that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT. To test this hypothesis, the effects of small, physiologically relevant temperature changes on DAT function were evaluated in two types of cultured neuronal cells: (1) a neuroblastoma cell line stably transfected with human DAT cDNA and (2) rat embryonic mesencephalic primary cells that naturally express the DAT. Temperatures for studies of DAT function were selected based on core temperature measurements in animals exposed to METH under usual ambient (22 degrees C) and hypothermic (6 degrees C) temperature conditions, where METH neurotoxicity was fully expressed and blocked, respectively. DAT function, determined by measuring accumulation of radiolabeled DA and 1-methyl-4-phenylpyridinium (MPP(+)), was found to directly correlate with temperature, with higher levels of substrate uptake at 40 degrees C, intermediate levels at 37 degrees C, and lower levels at 34 degrees C. DAT-mediated accumulation of METH also directly correlated with temperature, with greater accumulation at higher temperatures. These findings indicate that relatively small, physiologically relevant changes in temperature significantly alter DAT function and intracellular METH accumulation, and suggest that the effect of temperature on METH-induced DA neurotoxicity is mediated, at least in part, at the level of the DAT.

Synaptosomes still viable after 25 years of superfusion

Superfused synaptosomes have been utilized in studies of neurotransmitter release during 25 years. This review summarizes the aspects of neurotransmission that have been and could be successfully investigated with this technique. The major aim of the article is to draw attention on the versatility of superfused synaptosomes and to suggest how the system could be exploited in clarifying several aspects of synaptic neurochemistry including neurotransmitter transport, receptor localization, receptor-receptor interactions, functional aspects of multi-sited receptor complexes, receptor heterogeneity and mechanisms of neurotransmitter exocytosis-endocytosis.

Aortic dissection after ingestion of "ecstasy" (MDMA)

The authors report a case of aortic dissection and cardiac tamponade in a 29-year-old man after ingestion of ecstasy (methylenedioxymethamphetamine, MDMA) at a "rave" party. There was no history of hypertension, myxoid heart disease, or other risk factors for aortic dissection in the deceased, although a minor degree of cystic medial necrosis was noted on histologic examination of the aorta. Autopsy toxicology revealed low residual levels of MDMA in the blood about 48 hours after ingestion of the drug. This case report describes a probable association between MDMA ingestion and aortic dissection in a previously well young adult. The likely mechanisms are discussed, and the difficulties in diagnosing this complication are highlighted.

Acute psychological and physiological effects of MDMA ("Ecstasy") after haloperidol pretreatment in healthy humans

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") releases serotonin and dopamine. The role for dopamine in mediating the effects of MDMA has not yet been examined in humans. We investigated the effect of pretreatment with the dopamine D(2) antagonist haloperidol (1.4 mg i.v.) on psychological and physiological responses to MDMA (1.5 mg/kg p.o.) in 14 healthy volunteers using a double-blind placebo-controlled within-subject design. Subjective peak effects were rated using standardised scales. The physiological effects measured were blood pressure, heart rate and body temperature. Side effects were assessed during the session, and after 1 and 3 days. Haloperidol attenuated MDMA-induced positive and mania-like mood but had no reducing effect on other subjective changes or on cardiovascular effects. Results are consistent with a partial dopaminergic mediation of the euphoriant effects of MDMA. In contrast, dopamine does not seem to contribute to the physiological effects of MDMA, indicating a role for serotonin and norepinephrine.

Raves: a review of the culture, the drugs and the prevention of harm

Raves are all-night dance parties attended by large numbers of youth, sometimes in excess of 20,000. The rave scene, which is international in scope, is distinguished by clandestine venues, hypnotic electronic music and the liberal use of drugs such as ecstasy (3,4-methylenedioxymethamphetamine), GHB (gamma-hydroxybutyrate) and ketamine. Several rave-related deaths in Canada in 1999 alerted health authorities, parents and police to the health risks of rave attendance. Family physicians, emergency physicians and pediatricians should have some understanding of raves, the drugs and the health risks so they can effectively counsel and treat patients. The rave culture in Canada and the drugs commonly used at raves are reviewed, and strategies and initiatives for harm reduction are discussed.

Prior experience of morphine application alters the c-fos response to MDMA ('ecstasy') and cocaine in the rat striatum

Repeated morphine application usually leads to the development of tolerance but under certain circumstances sensitization may arise simultaneously. This phenomenon becomes obvious in behavioral tests as increasing locomotor activity and increasing drug self-administration during a course of chronic morphine application. It was suggested recently that sensitization could contribute to addiction. The molecular mechanisms of sensitization may include the long lasting increase in neuronal responsiveness to morphine which was observed in defined brain areas after repeated morphine injections. In this work, we studied whether morphine-sensitized Wistar rats also display an enhanced neuronal activity in response to other drugs of abuse (so called co-sensitization). The substances to be tested were injected as single doses 4 weeks after completion of a 10-day morphine pretreatment. MDMA (3, 4-methylenedioxymethamphetamine, 6 mg/kg) as a single test dose yielded a c-fos response in a wide range of brain areas. In the caudate putamen, the expression pattern of c-fos was clearly altered if the rats had received repeated morphine application previously. In this case, the MDMA-induced c-fos expression was markedly confined to the centromedial, mesolimbic aspect of the striatum whereas it had a diffuse appearance in rats not exposed to the opiate earlier. Cocaine application (50 mg/kg) elicited an intense c-fos expression in the medial striatum if the animals were morphine-pretreated; it was virtually absent in drug-naive rats after the same cocaine dose. Ten mg/kg cocaine had a similar but weaker effect. No difference in the c-fos expression pattern between morphine and saline pretreated animals was observed in the case of a THC (Delta(9)-tetrahydrocannabinol, 25 mg/kg) or an LSD (lysergic acid diethylamide, 1 mg/kg) test application. These findings imply that morphine sensitizes the brain towards other addicting drugs. In consequence, morphine sensitization obviously does not solely reflect alterations in mu-opioid receptor signaling. Rather, it seems to reflect further rearrangements within the mesolimbic system.

MDMA ('ecstasy') enhances basal acetylcholine release in brain slices of the rat striatum

The pharmacological basis of acute (+/-)-MDMA (3, 4-methylenedioxymethamphetamine) intoxication still awaits full characterization. According to present knowledge, MDMA enhances the release of serotonin and dopamine in striatal slices and interacts with different types of receptors such as 5-HT2 (5-hydroxytryptamine or serotonin), M1 and M2 muscarinic acetylcholine (ACh), and histamine H1 receptors. Currently, no information is available about the influence of (+/-)-MDMA on striatal cholinergic neurotransmission. In the present study, we used the in vitro perfusion technique to investigate the effect of (+/-)-MDMA on ACh release in rat striatal slices. Perfusions with (+/-)-MDMA (10-300 microM) resulted in a dose-dependent increase of spontaneous ACh release (EC50 approximately 30 microM). The effect was reversible and Ca++- and tetrodotoxin-sensitive. To determine the neurochemical pathways underlying this response, we perfused with (+/-)-MDMA in the presence of various inhibitors of neurotransmitter receptors. Blockade of glutamate or muscarinic ACh receptors as well as 5-HT1, 5-HT2, 5-HT3C or dopamine D2 receptors did not modulate (+/-)-MDMA-induced ACh release. However, the presence of histamine H1 receptor antagonists in the perfusion medium abolished (+/-)-MDMA-induced ACh release. The present data clearly demonstrate that (+/-)-MDMA enhances the activity of striatal cholinergic neurons and suggest an involvement of histamine H1 receptors. The effect is not mediated by glutamate and does not involve the activation of receptors of dopamine D2, 5-HT1, 5-HT2, 5-HT3C or muscarinic ACh. Considering the relatively high affinity of (+/-)-MDMA for the H1 histamine receptor (Ki 6 microM), a direct activation of this type of receptor might represent a plausible mechanism for (+/-)-MDMA-induced ACh release.

Toxicity of drug abuse--amphetamine designer drugs (ecstasy): mental effects and consequences of single dose use

MDMA (3,4-methylendioxymethamphetamine) is the most commonly used substance within the 'ecstasy' group of drugs. MDMA interferes with serotonin and catecholamine transporters in the central nervous system to increase monoamine synaptic levels and thereby mediate the majority of its central nervous effects. These range from wanted effects like euphoria, central nervous stimulation, and feeling of closeness to mild hallucinations, impairment of cognition and co-ordination and further to serious reactions like agitation, disturbed and bizarre behaviour, and possibly psychosis. The full picture of the consequences of these transitory changes is not known. It has been assumed that the risk of being involved in fatalities and accidents during the state of MDMA influence is increased, but this possible risk increase has so far not been determined. Observations of the prevalence of MDMA involvement in cases of reckless driving and the MDMA blood concentrations measured indicate a risk increase comparable to that observed after use of amphetamines.

Comparative study of fluoxetine, sibutramine, sertraline and dexfenfluramine on the morphology of serotonergic nerve terminals using serotonin immunohistochemistry

We compared the effects of treatment with high doses of fluoxetine, sibutramine, sertraline, and dexfenfluramine for 4 days on brain serotonergic nerve terminals in rats. Methylenedioxymethamphetamine (MDMA) and 5,7-dihydroxytryptamine (5,7-DHT) were used as positive controls because both compounds deplete brain serotonin. Food intake and body weight changes were also monitored and yoked, pair-fed animals were used to control for possible changes in morphology due to nutritional deficits. Fluoxetine, sibutramine, sertraline and dexfenfluramine all produced a significant reduction in body weight. Fluoxetine, sibutramine and sertraline treatment resulted in no depletion of brain serotonin but produced morphological abnormalities in the serotonergic immunoreactive nerve network. In contrast, dexfenfluramine and MDMA depleted brain serotonin and produced morphological changes in the serotonin nerve network. These results indicate that even though fluoxetine, sibutramine and sertraline do not deplete brain serotonin, they do produce morphological changes in several brain regions (as identified by serotonin immunohistochemistry). Dexfenfluramine and MDMA, on the other hand, markedly deplete brain serotonin and also produce morphological changes. Collectively, these results lend support to the concept that all compounds acting on brain serotonin systems, whether capable of producing serotonin depletion or not, could produce similar effects on the morphology of cerebral serotonin systems.

An assessment of the acute effects of the serotonin releasers methylenedioxymethamphetamine, methylenedioxyamphetamine and fenfluramine on immunity in rats

The purpose of the present study was to examine the effect of the serotonin releasing amphetamine derivatives methylenedioxymethamphetamine (MDMA), methylenedioxyamphetamine (MDA) and fenfluramine (FEN) on immunity in rats. Similar to MDA and MDMA, FEN reduced the number of circulating lymphocytes, provoked a suppression of Con A-stimulated lymphocyte proliferation and total IFN-gamma and IL-10 production in diluted whole blood cultures. Thus the non-psychostimulant amphetamine derivative FEN, shares the ability of the psychostimulant methylenedioxy-substituted amphetamine derivatives to alter these indices of immune function in the rat. However, when Con A-stimulated cytokine production was normalised for the number of lymphocytes in culture in order to examine cytokine production at a cellular level, the effect of the amphetamine derivatives begins to diverge. FEN shares with MDMA and MDA the ability to suppress production of the Th2 type cytokine IL-10. However the effect of these drugs on Th1 type cytokine secretion was much more complex. While the methylendioxy-substituted amphetamines increases the secretion of the Th1 type cytokine IL-2 without altering the related Th1 type cytokine IFN-gamma, FEN did not alter IL-2 secretion, but suppressed IFN-gamma secretion. In addition to these effects on T-cell responses, all three drugs inhibited LPS-induced TNF-alpha secretion from diluted whole blood cultures suggesting that macrophage activity is impaired following treatment. In all, these data extend our previous findings concerning the effects of MDMA on the immune system and demonstrate that the related serotonin releasers MDA and FEN also provoke immunological changes in rats.

Long-lasting effects of (+/-)3,4-methylenedioxymethamphetamine (ecstasy) on serotonin system function in humans

BACKGROUND

Fifteen (+/-)3,4-Methylenedioxymethamphetamine (MDMA) users, who did not show other drug dependencies or prolonged alcohol abuse, and 15 control subjects were included in the study.

METHODS

Prolactin (PRL) and cortisol (CORT) responses to the serotonergic agonist d-fenfluramine (D-fen), clinical psychobehavioral changes, and psychometric measures were evaluated 3 weeks and then 12 months after MDMA discontinuation.

RESULTS

MDMA users showed significantly reduced PRL and CORT responses in comparison with control subjects at 3 weeks (respectively, p < .001; p < .005). The responses of PRL to D-fen were unmodified at 12 months after prolonged abstinence and were significantly reduced in comparison with controls (p < .001). In contrast, CORT responses in MDMA users were restored after 12 months of abstinence, with significantly higher responses to D-fen, in comparison with 3-week responses (p < .05). MDMA users' high scores on the Novelty Seeking (NS) scale on the Tridimensional Personality Questionnaire (TPQ) appeared unchanged by long-term abstinence. In contrast, Buss Durkee Hostility Inventory (BDHI) (Buss and Durkee 1957) direct and guilt scores decreased significantly after 12 months of abstinence. PRL AUCs at 12 months were inversely correlated with the measures of MDMA exposure (r = -.538).

CONCLUSIONS

Our data indicate long-lasting 5-HT system impairment in abstinent MDMA users although the hypothesis of serotonergic changes attributable to a premorbid condition cannot be excluded. CORT restored responses to D-fen at 12 months, and the correlation of neuroendocrine changes with MDMA exposure suggest that the neuroendocrine impairment may be due to a partially reversible neurotoxic action of MDMA on the human brain.

Modified structure of the human serotonin transporter promoter

Recently, several studies have reported an association between anxiety traits, affective disorders and autism and alleles of a functional promoter polymorphism (5HTT-LPR) in the human serotonin transporter (5HTT, SERT).1-3 The mechanistic basis for allelic differences in transporter transcription are presently unknown. To explore this issue, we cloned the human 5HTT promoter region from a PAC genomic library and now describe an unreported 381-bp insert between the polymorphic region and the transcription start site. We verified the presence of this novel sequence by Southern hybridization of genomic digests and PCR amplifications from multiple unrelated individuals. Sequence analysis of the novel region reveals a number of canonical transcription factor binding sites (eg AP1, Elk1, NFkappaB) that may be important in controlling the response of the 5HTT gene to regulatory factors. PCR studies of genomic templates reveal a low level of amplification of a deleted template matching the size of the originally reported 5HTT promoter. This deleted template is absent from PAC amplifications, suggesting that the human 5HTT promoter may exhibit in vivo instability. Molecular Psychiatry (2000) 5, 110-115.

Differential polarization of serotonin transporters in axons versus soma-dendrites: an immunogold electron microscopy study

In spite of the conventional belief that neurotransmitter uptake occurs at the synapses, we demonstrated previously that serotonin transporters and the high-affinity uptake of serotonin were not confined to the terminals but rather occurred throughout the axons [Zhou F. C. et al. (1998) Brain Res. 805, 241-254]. In the present study, the detailed distribution of serotonin transporters over various parts of the neuron was illustrated and analysed morphometrically using a pre-embedding immunogold method with a characterized serotonin transporter antibody at the electron microscopic level. Our findings reveal a highly polarized distribution of serotonin transporters between axons and soma-dendrites in two aspects. (1) On the plasma membrane, serotonin transporter-immunogold is extremely low on soma-dendrites and synaptic junctions, but consistently dense along the axons and perisynaptic area. (2) In contrast, serotonin transporter labeling in the cytoplasm is concentrated in soma and dendrites, particularly on the membranes of rough endoplasmic reticulum, Golgi complexes and tubulovesicular structures, but low in the axoplasm. The extensive distribution of serotonin transporter along the axolemma suggests a broad range of uptake sites beyond synaptic junctions, and is consistent with the notion that the major mode of transmission for serotonin neurons is through volume (extrasynaptic) transmission. The highly polarized distribution also indicates that the major serotonin uptake sites are on axons and not on soma-dendrites.

Inhibition of plasma membrane monoamine transporters by beta-ketoamphetamines

Methcathinone and methylone, the beta-ketone analogues of methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA), respectively, were tested for neurotransmitter uptake inhibition in vitro. The beta-ketones were threefold less potent than the nonketo drugs at inhibiting platelet serotonin accumulation, with IC(50)'s of 34.6+/-4.8 microM and 5.8+/-0.7 microM, respectively. Methcathinone and methylone were similar in potency to methamphetamine and MDMA at catecholamine transporters individually expressed in transfected glial cells. For dopamine uptake, IC(50)'s were 0.36+/-0.06 microM and 0.82+/-0.17 microM, respectively; for noradrenaline uptake, IC(50) values were 0.51+/-0.10 microM and 1. 2+/-0.1 microM, respectively. In chromaffin granules, IC(50)'s for serotonin accumulation were 112+/-8.0 microM for methcathinone and 166+/-12 microM for methylone, 10-fold higher than the respective values for methamphetamine and MDMA. Our results indicate that methcathinone and methylone potently inhibit plasma membrane catecholamine transporters but only weakly inhibit the vesicle transporter.

Membrane trafficking of neurotransmitter transporters in the regulation of synaptic transmission

Many psychoactive drugs influence the transport of neurotransmitters across biological membranes, suggesting that the physiological regulation of neurotransmitter transport might contribute to normal and perhaps abnormal behaviour. Over the past few years, molecular characterization of the neurotransmitter transporters has enabled investigation of their subcellular location and regulation. The analysis of location suggests that membrane trafficking has an important role in the normal function of these proteins. One of the major regulatory mechanisms also involves changes in localization that might contribute to synaptic plasticity. This article discusses recent work on the membrane trafficking of neurotransmitter transporters and its role in regulating their activity.

Acute injection of drugs with low addictive potential (delta(9)-tetrahydrocannabinol, 3,4-methylenedioxymethamphetamine, lysergic acid diamide) causes a much higher c-fos expression in limbic brain areas than highly addicting drugs (cocaine and morphine)

It is regarded as a common pharmacological property responsible for the addictive potential of drugs of abuse that they are able to activate brain areas involved in the sensation of pleasure, especially the nucleus accumbens. To investigate the connection between addictive potential and stimulation of critical brain areas in more detail, we studied c-fos accumulation in response to various addicting drugs in direct comparison. The substances were injected into drug-naive rats, and c-fos mRNA levels were measured throughout the brain by in situ hybridization. Cocaine in a high dose of 50 mg/kg yielded only a discrete c-fos expression in the medial and central striatum. Morphine (50 mg/kg) caused a weak c-fos synthesis in the lateral septum. THC (delta(9)-tetrahydrocannabinol), 25 mg/kg, induced c-fos mRNA again in the lateral septum and furthermore in large parts of the striatum including the nucleus accumbens. LSD (lysergic acid diamide), 1 mg/kg, elicited a similar c-fos expression pattern as THC, but there was additionally a very strong hybridization signal in the cerebral cortex, especially in the upper layers, and in the ventral part of the periaqueductal gray. The widest range of brain areas was activated by MDMA (3, 4-methylenedioxymethamphetamine, 'ecstasy'), 6 mg/kg. In addition to the regions that responded to LSD, there was a very pronounced c-fos signal in the nucleus accumbens core and shell and in the mammillary nuclei. Taken together, our study revealed that the drugs with the highest addictive potential, cocaine and morphine, yielded a very low c-fos synthesis throughout the brain whereas the brain regions closely linked to pleasure (especially the nucleus accumbens) responded strongly to drugs with an apparently lower addictive potential (THC, LSD, MDMA).

Phosphorylation and sequestration of serotonin transporters differentially modulated by psychostimulants

Many psychotropic drugs interfere with the reuptake of dopamine, norepinephrine, and serotonin. Transport capacity is regulated by kinase-linked pathways, particularly those involving protein kinase C (PKC), resulting in transporter phosphorylation and sequestration. Phosphorylation and sequestration of the serotonin transporter (SERT) were substantially impacted by ligand occupancy. Ligands that can permeate the transporter, such as serotonin or the amphetamines, prevented PKC-dependent SERT phosphorylation. Nontransported SERT antagonists such as cocaine and antidepressants were permissive for SERT phosphorylation but blocked serotonin effects. PKC-dependent SERT sequestration was also blocked by serotonin. These findings reveal activity-dependent modulation of neurotransmitter reuptake and identify previously unknown consequences of amphetamine, cocaine, and antidepressant action.

Effects of 5-HT-releasing agents on the extracellullar hippocampal 5-HT of rats. Implications for the development of novel antidepressants with a short onset of action

The effects of two selective 5-HT-releasing agents, 4-methylthioamphetamine (MTA) and 5-methoxy-6-methyl-2-aminoindan (MMAI), on the extracellular 5-HT concentration in the dorsal hippocampus was determined by microdialysis in anesthetized rats. After i.p. administration of 1 or 5 mg/kg of either compound, a rapid and significant increase of 5-HT basal release was observed. MTA (5 mg/kg) induced a maximal increase of about 2000% over the basal value 40 min after injection, which declined slowly, whereas MMAI (5 mg/kg) induced a maximal response of about 1350% which showed a rapid decline. Monoamine oxidase-A inhibitory properties of MTA, and MMAI's lack of similar properties might account for the difference between the two compounds. In agreement with previous information, a much lower increase in hippocampal 5-HT was observed in response to systemic fluoxetine. This difference in the magnitude of the response after MTA or MMAI and fluoxetine indicates that different mechanisms of action are operating. Based on evidence showing that an acute enhancement of 5-HT neurotransmission might result in the rapid appearance of therapeutic effects of serotonergic antidepressants, we suggest that MTA and MMAI might serve as leads for a novel family of compounds with a short onset of action useful for treating depression.

Transmembrane domain I contributes to the permeation pathway for serotonin and ions in the serotonin transporter

Mutation of a conserved Asp (D98) in the rat serotonin (5HT) transporter (rSERT) to Glu (D98E) led to decreased 5HT transport capacity, diminished coupling to extracellular Na+ and Cl-, and a selective loss of antagonist potencies (cocaine, imipramine, and citalopram but not paroxetine or mazindol) with no change in 5HT Km value. D98E, which extends the acidic side chain by one carbon, affected the rank-order potency of substrate analogs for inhibition of 5HT transport, selectively increasing the potency of two analogs with shorter alkylamine side chains, gramine, and dihydroxybenzylamine. D98E also increased the efficacy of gramine relative to 5HT for inducing substrate-activated currents in Xenopus laevis oocytes, but these currents were noticeably dependent on extracellular medium acidification. I-V profiles for substrate-independent and -dependent currents indicated that the mutation selectively impacts ion permeation coupled to 5HT occupancy. The ability of the D98E mutant to modulate selective aspects of substrate recognition, to perturb ion dependence as well as modify substrate-induced currents, suggests that transmembrane domain I plays a critical role in defining the permeation pathway of biogenic amine transporters.

Molecular chaperones stimulate the functional expression of the cocaine-sensitive serotonin transporter

The serotonin transporter (SERT) is an N-glycosylated integral membrane protein that is predicted to contain 12 transmembrane regions. SERT is the major binding site in the brain for antidepressant drugs, and it also binds amphetamines and cocaine. The ability of various molecular chaperones to interact with a tagged version of SERT (Myc-SERT) was investigated using the baculovirus expression system. Overexpression of Myc-SERT using the baculovirus system led to substantial quantities of inactive transporter, together with small amounts of fully active and, therefore, correctly folded molecules. The high levels of inactive Myc-SERT probably arose because folding was rate-limiting due, perhaps, to insufficient molecular chaperones. Therefore, Myc-SERT was co-expressed with the endoplasmic reticulum (ER) molecular chaperones calnexin, calreticulin and immunoglobulin heavy chain binding protein (BiP), and the foldase, ERp57. The expression of functional Myc-SERT, as determined by an inhibitor binding assay, was enhanced nearly 3-fold by co-expressing calnexin, and to a lesser degree on co-expression of calreticulin and BiP. Co-expression of ERp57 did not increase the functional expression of Myc-SERT. A physical interaction between Myc-SERT-calnexin and Myc-SERT-calreticulin was demonstrated by co-immunoprecipitation. These associations were inhibited in vivo by deoxynojirimycin, an inhibitor of N-glycan precusor trimming that is known to prevent the calnexin/calreticulin-N-glycan interaction. Functional expression of the unglycosylated SERT mutant, SERT-QQ, was also increased on co-expression of calnexin, suggesting that the interaction between calnexin and SERT is not entirely dictated by the N-glycan. SERT is the first member of the neurotransmitter transporter family whose folding has been shown to be assisted by the molecular chaperones calnexin, calreticulin, and BiP.

Transmembrane domain I contributes to the permeation pathway for serotonin and ions in the serotonin transporter

Mutation of a conserved Asp (D98) in the rat serotonin (5HT) transporter (rSERT) to Glu (D98E) led to decreased 5HT transport capacity, diminished coupling to extracellular Na+ and Cl-, and a selective loss of antagonist potencies (cocaine, imipramine, and citalopram but not paroxetine or mazindol) with no change in 5HT Km value. D98E, which extends the acidic side chain by one carbon, affected the rank-order potency of substrate analogs for inhibition of 5HT transport, selectively increasing the potency of two analogs with shorter alkylamine side chains, gramine, and dihydroxybenzylamine. D98E also increased the efficacy of gramine relative to 5HT for inducing substrate-activated currents in Xenopus laevis oocytes, but these currents were noticeably dependent on extracellular medium acidification. I-V profiles for substrate-independent and -dependent currents indicated that the mutation selectively impacts ion permeation coupled to 5HT occupancy. The ability of the D98E mutant to modulate selective aspects of substrate recognition, to perturb ion dependence as well as modify substrate-induced currents, suggests that transmembrane domain I plays a critical role in defining the permeation pathway of biogenic amine transporters.

Intraregional variation in expression of serotonin transporter messenger RNA by 5-hydroxytryptamine neurons

The distribution of the messenger RNA encoding the 5-hydroxytryptamine transporter was investigated in rat brain. 5-Hydroxytryptamine transporter messenger RNA was found exclusively in the B1-B9 cell groups containing the cell bodies of 5-hydroxytryptamine neurons. Combined in situ hybridization and 5-hydroxytryptamine immunocytochemistry demonstrated 5-hydroxytryptamine transporter gene expression in the majority of and exclusively in 5-hydroxytryptamine neurons. Cells differed in their levels of expression of 5-hydroxytryptamine transporter messenger RNA and 5-hydroxytryptamine immunofluorescence, but with a tight correlation between the two parameters. Image analysis of cells from B7, the dorsal raphe nucleus, and B8, the median raphe nucleus, revealed significant differences between groups in the mean cellular level of 5-hydroxytryptamine transporter gene expression. Cells in the ventromedial subdivision of B7 displayed higher levels of expression than cells in B8 or cells in the lateral wings of B7. There was also heterogeneity in the distribution of the cellular levels of expression for two other genes expressed by 5-hydroxytryptamine neurons: l-aromatic amino acid decarboxylase messenger RNA and tryptophan hydroxylase messenger RNA. However, the relative levels of expression of these two genes within the four regions studied differed from that of 5-hydroxytryptamine transporter messenger RNA. These results indicate intraregional differences between 5-hydroxytryptamine neurons with respect to 5-hydroxytryptamine transporter messenger RNA levels. Such differences may account for the differential sensitivity of 5-hydroxytryptamine neurons to cytotoxins.

Quantitation of N-ethyl-3,4-methylenedioxyamphetamine and its major metabolites in human plasma by high-performance liquid chromatography and fluorescence detection

A HPLC method has been developed for the analogue of Ecstasy MDE and its major metabolites N-ethyl-4-hydroxy-3-methoxyamphetamine (HME) and 3,4-methylenedioxyamphetamine (MDA) in human plasma. In the course of our investigations we found that the methylenedioxyamphetamines and HME exhibit fluorescence at 322 nm. Therefore the detection could be carried out with a fluorescence (FL) detector. Solid-phase extraction was used for sample preparation and yielded high recovery rates greater than 95%. The limit of quantitation for MDE and its metabolites in the extracts was between 1.5 and 8.9 ng/ml and the method standard deviations were less than 5%. This sensitive, rapid and reliable analytical method has been used successfully in the quantitation of the substances in plasma samples obtained from 14 volunteers in two clinical studies after p.o. administration of 100 to 140 mg MDE*HCI. The maximum plasma concentrations were 235-465 ng/ml (MDE), 67-673 ng/ml (HME) and 7-33 ng/ml (MDA), respectively. Pharmacokinetic parameters have been investigated using the plasma concentration curves.

The effect of MDMA (3,4-methylenedioxymethamphetamine) on the 5-HT synthesis rate in the rat brain: an autoradiographic study

The effect of MDMA (3,4-methylenedioxymethamphetamine), a psychotropic amphetamine derivative, treatment on the rate of serotonin (5-hydroxytryptamine; 5-HT) synthesis in the rat brain was studied by autoradiography using alpha-[14C]-methyl-l-tryptophan method. Three different treatment protocols were compared to the control (saline) treated rats: (1) rats treated twice with 10 mg/kg every 12 h (20 mg/kg total) and injected tracer for the synthesis measurements 15 h later; (2) rats treated with four injections of 5 mg/kg every 12 h (20 mg/kg total) and injected tracer for the synthesis measurement 17 h after the last dose; and (3) rats given eight injections of 5 mg/kg every 12 h for four days (40 mg/kg) and used in the synthesis study 14 days after the last dose. Results showed a significant decrease in the rate of synthesis in the majority of cerebral structures examined in the 10 mg/kg group. In contrast the group receiving the same total amount (20 mg/kg) of MDMA but over two days (4x5 mg/kg) showed a significant increase in 5-HT synthesis in comparison to controls. The 5-HT synthesis rates measured 14 days after the last dose (four days, 8x5 mg/kg) were significantly reduced. The findings suggest that MDMA can produce either an increase or a decrease in the 5-HT synthesis a short time after a total dose of 20 mg/kg depending on the dose fractionation. However, 14 days after total dose of 40 mg/kg given over four days the synthesis rate was significantly reduced in many brain structures. The latter suggests a possible effect of the MDMA neurotoxicity on the serotonergic neurons, in addition to a possible influence on 5-HT synthesis via a feedback mechanism.

Reserpine attenuates D-amphetamine and MDMA-induced transmitter release in vivo: a consideration of dose, core temperature and dopamine synthesis

Amphetamine releases dopamine through a transporter-mediated mechanism. The purpose of this report was to further our understanding of the intracellular pool from which amphetamine releases dopamine: the cytoplasmic pool, the vesicular pool, or both. Rats were treated with D-amphetamine (AMPH) (1.0 or 10.0 mg/kg) or an amphetamine analog, methylenedioxymethamphetamine (MDMA) (2.0, 5.0, or 10.0 mg/kg). Pre-treatment with 10.0 mg/kg reserpine (18 h prior to AMPH or MDMA) attenuated dopamine release for high and low AMPH doses; however the low-dose effect showed borderline significance. Pre-treatment with 10.0 mg/kg reserpine attenuated dopamine and serotonin release induced by MDMA. The dopamine effect was seen at all three MDMA doses; the effect on serotonin was only measured at the 10.0 mg/kg dose. Reserpine pre-treatment caused reductions in core body temperature; heating the rats to normal body temperature for 3 h prior to AMPH or MDMA, and during the 4 h post-treatment period partially reversed the reserpine-induced attenuation of dopamine release. However, the intermediate level of dopamine release for the reserpinized-heated animals was not significantly different from either the reserpine group (not heated) or the AMPH or MDMA alone groups. In a separate group of rats, the effects of reserpine and reserpine+heat on dopamine synthesis were measured. DOPA accumulation after treatment with the aromatic acid decarboxylase inhibitor NSD-1015 (100 mg/kg, 30 min before sacrifice), was greater in rats treated with reserpine compared to controls; heating the reserpinized rats did not significantly alter the amount of DOPA accumulation; however there was a trend towards further increase. These results suggest that D-amphetamine releases dopamine that is stored in both vesicles and the cytoplasm. Cooling may contribute to the attenuation of AMPH or MDMA-induced dopamine release observed after reserpine; however, AMPH or MDMA dependence upon vesicular stores most likely explains the diminished release after reserpine. The attenuation of AMPH or MDMA-induced transmitter release by reserpine is thought to be counteracted by a reserpine-induced replenishment of stores. Therefore, all doses of D-amphetamine may use vesicular stores; the degree to which new synthesis counteracts the vesicular depletion may be the variable which differentiates low from high doses of D-amphetamine.

Death by "ecstasy": the serotonin syndrome?

"Ecstasy" or 3,4-methylenedioxymethamphetamine (MDMA) is a popular drug of abuse and is generally regarded as safe by the lay public. There are an increasing number of reports of MDMA-induced toxicity that exhibit features of the serotonin syndrome. We report a case of severe hyperthermia, altered mental status, and autonomic dysfunction after a single recreational ingestion of MDMA.

The serotonin transporter: a primary target for antidepressant drugs

The serotoninergic system is known to modulate mood, emotion, sleep and appetite and thus is implicated in the control of numerous behavioural and physiological functions. Decreased serotoninergic neurotransmission has been proposed to play a key role in the aetiology of depression. The concentration of synaptic serotonin is controlled directly by its reuptake into the pre-synaptic terminal and, thus, drugs blocking serotonin transport have been successfully used for the treatment of depression. In addition to tricyclic antidepressants (TCAs; e.g. imipramine) which also block noradrenaline reuptake, highly specific serotonin reuptake inhibitors (SSRIs) such as fluoxetine and paroxetine have been developed, which are increasingly prescribed for depressed patients. The mode of action of these antidepressant drugs on their direct target, the serotonin transport protein, and possible regulatory mechanisms with respect to long-term alleviation of depression, although having been investigated both neurobiologically and clinically over the last years, are not yet understood. The cloning of the cDNA encoding the serotonin transporter has allowed a more precise characterization of this protein at the molecular level. This will show how antidepressants act at this target, thereby affecting the biochemical, pharmacological and electrophysiological properties of the serotoninergic system and give an introduction of how they might exert their therapeutic effect. This review gives an overview of the recent developments in this field, discusses mechanisms of antidepressant action on this target, and also possible interactions with other components of serotoninergic neurotransmission.

Small changes in ambient temperature cause large changes in 3,4-methylenedioxymethamphetamine (MDMA)-induced serotonin neurotoxicity and core body temperature in the rat

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA) is a drug of abuse and has been shown to be neurotoxic to 5-HT terminals in many species. MDMA-engendered neurotoxicity has been shown to be affected by both ambient temperature and core body temperature. We now report that small (2 degreesC) changes in ambient temperature produce changes in core temperature in MDMA-treated rats, but the same changes in ambient temperature do not affect core temperature of saline-treated animals. Furthermore, increases in core temperature of MDMA-treated animals increase neurotoxicity. Rats were given MDMA (20 or 40 mg/kg) or saline and placed in an ambient temperature of 20, 22, 24, 26, 28, or 30 degreesC using a novel temperature measurement apparatus that controls ambient temperature +/-0.5 degrees C. Two weeks after MDMA treatment, the rats were killed, and regional 5-HT and 5-hydroxyindole acetic acid levels were analyzed as a measure of neurotoxicity. Rats treated with MDMA at 20 and 22 degrees C showed a hypothermic core temperature response. Treatment with MDMA at 28 and 30 degreesC produced a hyperthermic response. At ambient temperatures of 20-24 degrees C, neurotoxicity was not observed in the frontal cortex, somatosensory cortex, hippocampus, or striatum. At ambient temperatures of 26-30 degrees C, neurotoxicity was seen and correlated with core temperature in all regions examined. These data indicate that ambient temperature has a significant affect on MDMA neurotoxicity, core temperature, and thermoregulation in rats. This finding has implications on both the temperature dependence of the mechanism of MDMA neurotoxicity and human use because fatal hyperthermia is associated with MDMA use in humans.

Small changes in ambient temperature cause large changes in 3,4-methylenedioxymethamphetamine (MDMA)-induced serotonin neurotoxicity and core body temperature in the rat

The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA) is a drug of abuse and has been shown to be neurotoxic to 5-HT terminals in many species. MDMA-engendered neurotoxicity has been shown to be affected by both ambient temperature and core body temperature. We now report that small (2 degreesC) changes in ambient temperature produce changes in core temperature in MDMA-treated rats, but the same changes in ambient temperature do not affect core temperature of saline-treated animals. Furthermore, increases in core temperature of MDMA-treated animals increase neurotoxicity. Rats were given MDMA (20 or 40 mg/kg) or saline and placed in an ambient temperature of 20, 22, 24, 26, 28, or 30 degreesC using a novel temperature measurement apparatus that controls ambient temperature +/-0.5 degrees C. Two weeks after MDMA treatment, the rats were killed, and regional 5-HT and 5-hydroxyindole acetic acid levels were analyzed as a measure of neurotoxicity. Rats treated with MDMA at 20 and 22 degrees C showed a hypothermic core temperature response. Treatment with MDMA at 28 and 30 degreesC produced a hyperthermic response. At ambient temperatures of 20-24 degrees C, neurotoxicity was not observed in the frontal cortex, somatosensory cortex, hippocampus, or striatum. At ambient temperatures of 26-30 degrees C, neurotoxicity was seen and correlated with core temperature in all regions examined. These data indicate that ambient temperature has a significant affect on MDMA neurotoxicity, core temperature, and thermoregulation in rats. This finding has implications on both the temperature dependence of the mechanism of MDMA neurotoxicity and human use because fatal hyperthermia is associated with MDMA use in humans.

Detection of designer drugs in human hair by ion mobility spectrometry (IMS)

Since its inception in the early 1970s under the name plasma chromatography, ion mobility spectrometry (IMS) has undergone great changes. It is now utilized more and more in forensic science laboratories where it is used to detect explosives and environmental pollutants [1-4] as well as its use in detecting drugs of abuse [5-8]. Although IMS is known for nearly 30 years now [9], relatively few cases of the application of ion mobility spectrometry to the analysis of human hair have been reported [10-12]. The authors report a new and quick method to rapidly screen and determine MDMA ('ecstasy', 'Adam') and MDEA ('Eve') in human hair. The proposed method using trihexylamine as internal standard resulted in a rapid procedure useful in screening human hair specimens for designer drugs.

Altered brain serotonin homeostasis and locomotor insensitivity to 3, 4-methylenedioxymethamphetamine ("Ecstasy") in serotonin transporter-deficient mice

The sodium-dependent, high affinity serotonin [5-hydroxytryptamine (5-HT)] transporter (5-HTT) provides the primary mechanism for inactivation of 5-HT after its release into the synaptic cleft. To further evaluate the function of the 5-HTT, the murine gene was disrupted by homologous recombination. Despite evidence that excess extracellular 5-HT during embryonic development, including that produced by drugs that inhibit the 5-HTT, may lead to severe craniofacial and cardiac malformations, no obvious developmental phenotype was observed in the 5-HTT-/- mice. High affinity [3H]5-HT uptake was completely absent in 5-HTT-/- mice, confirming a physiologically effective knockout of the 5-HTT gene. 5-HTT binding sites labeled with [125I] 3 beta-(4'-iodophenyl)tropan-2 beta-carboxylic acid methyl ester were reduced in a gene dose-dependent manner, with no demonstrable binding in 5-HTT-/- mutants. In adult 5-HTT-/- mice, marked reductions (60-80%) in 5-HT concentrations were measured in several brain regions. While (+)-amphetamine-induced hyperactivity did not differ across genotypes, the locomotor enhancing effects of (+)-3, 4-methylenedioxymethamphetamine, a substituted amphetamine that releases 5-HT via a transporter-dependent mechanism, was completely absent in 5-HTT-/- mutants. Together, these data suggest that the presence of a functional 5-HTT is essential for brain 5-HT homeostasis and for 3,4-methylenedioxymethamphetamine-induced hyperactivity.

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.

Phosphorylation and regulation of antidepressant-sensitive serotonin transporters

Antidepressant-sensitive serotonin (5-hydroxytryptamine, 5HT) transporters (SERTs) are responsible for efficient synaptic clearance of extracellular 5HT. Previously (Qian, Y., Galli, A., Ramamoorthy, S., Risso, S., DeFelice, L. J., and Blakely, R. D. (1997) J. Neurosci. 17, 45-47), we demonstrated that protein kinase (PKC)-linked pathways in transfected HEK-293 cells lead to the internalization of cell-surface human (h) SERT protein and a reduction in 5HT uptake capacity. In the present study, we report that PKC activators rapidly, and in a concentration-dependent manner, elevate the basal level of hSERT phosphorylation 5-6-fold. Similarly, protein phosphatase (PP1/PP2A) inhibitors down-regulate 5HT transport and significantly elevate hSERT 32P incorporation, effects that are additive with those of PKC activators. Moreover, hSERT phosphorylation induced by beta-phorbol 12-myristate 13-acetate is abolished selectively by the PKC inhibitors staurosporine and bisindolylmaleimide I, whereas hSERT phosphorylation induced by phosphatase inhibitors is insensitive to these agents at comparable concentrations. Protein kinase A and protein kinase G activators fail to acutely down-regulate 5HT uptake but significantly enhance hSERT phosphorylation. Basal hSERT and okadaic acid-induced phosphorylation were insensitive to chelation of intracellular calcium and Ca2+/calmodulin-dependent protein kinase inhibitors. Together these results reveal hSERT to be a phosphoprotein whose phosphorylation state is likely to be tightly controlled by multiple kinase and phosphatase pathways that may also influence the transporter's regulated trafficking.

Cellular localization and expression of the serotonin transporter in mouse brain

The high-affinity serotonin (5-HT) transporter (5-HTT) plays an important role in the removal of extracellular serotonin, thereby modulating and terminating the action of this neurotransmitter at various pre- and post-synaptic serotonergic receptors and heteroreceptors. In order to characterize the anatomical distribution of the 5-HTT in mouse brain, in situ hybridization histochemistry using 35S-labeled riboprobes was performed. These results were compared with 5-HTT binding site distribution as evaluated by [125I]RTI-55 autoradiography. High levels of 5-HTT mRNA were detected in all brain stem raphe nuclei, with variations in labeling among the various subnuclei. Those brain areas known to possess serotonergic cell bodies stained intensely for both 5-HTT mRNA and 5-HTT binding sites. In contrast to previous findings in rat brain, the highest densities of 5-HTT sites were found in areas outside the raphe complex, particularly in the substantia nigra, globus pallidus, and superior colliculi.

Vesicular transport regulates monoamine storage and release but is not essential for amphetamine action

To assess the role of exocytotic release in signaling by monoamines, we have disrupted the neuronal vesicular monoamine transporter 2 (VMAT2) gene. VMAT2-/- mice move little, feed poorly, and die within a few days after birth. Monoamine cell groups and their projections are indistinguishable from those of wild-type littermates, but the brains of mutant mice show a drastic reduction in monoamines. Using midbrain cultures from the mutant animals, amphetamine but not depolarization induces dopamine release. In vivo, amphetamine increases movement, promotes feeding, and prolongs the survival of VMAT2-/- animals, indicating that precise, temporally regulated exocytotic release of monoamine is not required for certain complex behaviors. In addition, the brains of VMAT2 heterozygotes contain substantially lower monoamine levels than those of wild-type littermates, and depolarization induces less dopamine release from heterozygous than from wild-type cultures, suggesting that VMAT2 expression regulates monoamine storage and release.

Pharmacokinetic and pharmacodynamic principles of illicit drug use and treatment of illicit drug users

Many clinicians are confronted by the use of illicit drugs on a daily basis. The unsanctioned use of opioids, psychostimulants, benzodiazepines, alcohol and nicotine is a major cause of morbidity and mortality. Multiple factors have inhibited the scientific study of these agents including prohibition, public denial and lack of commercial interests. In dealing with problems related to these drugs, clinicians need a scientific understanding of their pharmacology, quantifiable effects and potential adverse effects. Illicit drug users select drugs with particular pharmacokinetic parameters and pharmacodynamic properties. Generally, rapid absorption, rapid entry into the central nervous system, high bioavailability, short half-life, small volume of distribution and high free drug clearance are pharmacokinetic characteristics which predict a high potential for harmful use because these factors increase positive reinforcement. Drug users adapt the method and route of drug administration to optimise the delivery of the drug to the brain while attempting to maximise the bioavailability of the drug. Inhalation and smoking are the routes of administration which allow the most rapid delivery of drug to the brain, while intravenous injection maximises the bioavailability of an administered drug. Each route of administration results in attendant complications related to mucosal damage, carcinogenesis and risk of infection. Negative reinforcement or withdrawal is a major drive to recurrent use. Many illicit drugs have pharmacological features that promote dependence, including long half-life, low free drug clearance and sufficient drug exposure to allow development of tolerance. The preventive or reductive pharmacotherapeutics of illicit drug use makes use of several subsets of agents: those which act on the same receptor or system as the illicit drug (such as methadone), those which produce an adverse reaction on consumption of the illicit drug (such as disulfiram) and those which symptomatically attenuate illicit drug withdrawal symptoms (such as clonidine). Many new agents are being trialled as potential preventive or reductive agents. It is important to consider pharmacotherapy as only one potential part of the treatment of illicit drug users. The complications of illicit drug use present many therapeutic challenges. As with all patients consuming multiple drugs, illicit drug users are prone to developing drug interactions. The most common interactions seen in practice are pharmacodynamic in nature, most often due to the additive effects of different drugs on the central nervous system. However, alcohol, cocaine, disulfiram, methadone and tricyclic antidepressants may be involved in important pharmacokinetic interactions. Of these the effect of long term alcohol consumption in increasing the hepatotoxicity of paracetamol and of cytochrome P450 3A microsomal enzyme stimulating drugs in diminishing the efficacy of methadone are the most commonly encountered.