Long-term effects of repeated methylamphetamine administration on monoamine neurons in the rhesus monkey brain

Previous studies indicate that the repeated administration of D-methylamphetamine (MA) produces a long-lasting depletion of dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) in various brain regions of a number of species. The objectives of the present study were: (1) to establish a short, subcutaneous injection regimen which would reliably produce the neuronal alterations; (2) to evaluate MA-induced NE depletions produced by this new regimen; and (3) to determine whether central MA-induced neuronal changes are reflected in changes in cerebrospinal fluid monoamine metabolite concentrations. It was observed that high doses of MA administered (s.c.) over a 2-week period to rhesus monkeys produced decreases in DA and 5-HT, but not NE levels, in various brain regions. The decrease in caudate DA levels was accompanied by a decrease in the number of DA uptake sites, a decrease in the level of homovanillic acid (HVA) and an increase in DA turnover. This decrease in brain DA was also accompanied by a decrease in the cerebrospinal fluid concentration of HVA.     

Evaluation of the neurotoxicity of N-methyl-1-(4-methoxyphenyl)-2-aminopropane (para-methoxymethamphetamine, PMMA)

These studies assessed the neurotoxic potential of N-methyl-1-(4-methoxyphenyl)-2-aminopropane (para-methoxymethamphetamine; PMMA), an amphetamine analog that has surfaced in the illicit drug market. Repeated subcutaneous injections of PMMA caused lasting, dose-related reductions in regional brain concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), and in the density of [³H]paroxetine-labelled 5-HT uptake sites. Comparison of the neurotoxic potential of PMMA to that of para-methoxyamphetamine (PMA) and 3,4-methyl-enedioxymethamphetamine (MDMA) showed that equivalent doses of PMMA and PMA (80 mg/kg) produced comparable depletions of 5-HT, but that these depletions were not as pronounced as those induced by a lower dose of MDMA (20 mg/kg). Striatal DA was not affected on a long-term basis by any of the ring-substituted amphetamines evaluated in this study. These data suggest that PMMA, like PMA and MDMA, produces long-term (possibly neurotoxic) effects on brain serotonin neurons, but that PMMA is less potent than MDMA as a 5-HT neurotoxin. Further, they raise concern over the illicit use of PMMA since humans could be more sensitive than rodents to the 5-HT neurotoxic effects of PMMA and related drugs.     

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

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

Altered prolactin response to M-chlorophenylpiperazine in monkeys previously treated with 3,4-methylenedioxymethamphetamine (MDMA) or fenfluramine

3,4-Methylenedioxymethamphetamine ("Ecstasy," MDMA) and fenfluramine, widely used by humans, are potent brain serotonin (5-HT) neurotoxins in animals. Thus, there is concern that humans previously exposed to these amphetamine derivatives may have incurred brain 5-HT neurotoxicity. However, assessing the status of brain 5-HT neurons in the living organism is challenging. To determine whether MDMA- and/or fenfluramine-induced 5-HT neurotoxicity can be detected during life using neuroendocrine methods, groups of monkeys previously treated with neurotoxic regimens of MDMA or fenfluramine, along with saline-treated controls, underwent neuroendocrine challenge with the direct 5-HT agonist and 5-HT-releasing drug, m-chlorophenylpiperazine (m-CPP). Animals treated 2 weeks previously with MDMA exhibited a nonsignificant reduction in the prolactin response to m-CPP. In contrast, monkeys treated 3 1/2 years previously with MDMA or 2 years previously with fenfluramine exhibited significantly increased prolactin responses to m-CPP. No significant differences in cortisol concentrations were noted between groups at any time point. These data indicate that neuroendocrine challenge with m-CPP is capable of detecting substituted amphetamine-induced 5-HT neurotoxicity in living primates, but that the recency of drug exposure is an important consideration. Changes in the neuroendocrine response to m-CPP over time in animals with substituted amphetamine-induced neurotoxicity may be related to aberrant 5-HT reinnervation of the basal forebrain that occurs over time in monkeys previously treated with neurotoxic doses of MDMA or fenfluramine.     

Methamphetamine neurotoxicity and striatal glutamate release: comparison to 3,4-methylenedioxymethamphetamine.

The effect of repeated administration of either methamphetamine (MA), 3,4-methylenedioxymethamphetamine (MDMA) or vehicle on the extracellular concentrations of glutamate (GLU), aspartate, taurine, dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), was studied in awake, freely moving rats using in vivo microdialysis. MA (7.5 mg/kg, i.p.) administered every 2 h for a total of 3 injections, increased the extracellular concentration of GLU in the anteromedial striatum. By contrast, neither vehicle nor MDMA (9.2 and 13.8 mg/kg) increased GLU efflux following repeated administration. Both MA and MDMA increased the extracellular concentration of DA in the striatum. However, the cumulative increase in DA was significantly greater in the MDMA treated animals as compared to the MA group. The concentrations of DA, serotonin (5-HT) and their metabolites were determined in the striatum 7 days following the repeated administration of MA, MDMA and vehicle. MA, but not MDMA or vehicle, decreased the concentration of DA in the striatum. Conversely, MDMA (13.8 mg/kg) decreased the concentration of 5-HT, whereas MA, MDMA (9.2 mg/kg) and vehicle had no effect on striatal 5-HT content. These data are suggestive that the long-term (7 day) DA neurotoxicity produced by the repeated administration of MA is mediated, in part, by a delayed increase in extracellular concentrations of GLU. In contrast, repeated administration of MDMA, at a dose which produced a long-term (7 day) depletion of striatal 5-HT content, had no effect on GLU efflux in the striatum.     

Long-lasting neuroprotective effect of sildenafil against 3,4-methylenedioxymethamphetamine- induced 5-hydroxytryptamine deficits in the rat brain

Sildenafil, given shortly before 3,4-methylenedioxymethamphetamine (MDMA), affords protection against 5-hydroxytryptamine (5-HT) depletions caused by this amphetamine derivative by an acute preconditioning-like mechanism. Because acute and delayed preconditionings do not share the same mechanisms, we investigated whether sildenafil would also protect the 5-HT system of the rat if given 24 hr before MDMA. For this, MDMA (3 × 5 mg/kg i.p., every 2 hr) was administered to rats previously treated with sildenafil (8 mg/kg p.o.). One week later, 5-HT content and 5-HT transporter density were measured in the striatum, frontal cortex, and hippocampus of the rats. Our findings indicate that sildenafil afforded significant protection against MDMA-induced 5-HT deficits without altering the acute hyperthermic response to MDMA or its metabolic disposition. Sildenafil promoted ERK1/2 activation an effect that was paralleled by an increase in MnSOD expression that persisted 24 hr later. In addition, superoxide and superoxide-derived oxidants, shown by ethidium fluorescence, increased after the last MDMA injection, an effect that was prevented by sildenafil pretreatment. Similarly, MDMA increased nitrotyrosine concentration in the hippocampus, an effect not shown by sildenafil-pretreated rats. In conclusion, our data demonstrate that sildenafil produces a significant, long-lasting neuroprotective effect against MDMA-induced 5-HT deficits. This effect is apparently mediated by an increased expression of MnSOD and a subsequent reduced susceptibility to the oxidative stress caused by MDMA.     

Neonatal citalopram treatment inhibits the 5-HT depleting effects of MDMA exposure in rats

Neonatal exposure to 3,4-methylenedioxymethamphetamine (MDMA) produces long-term learning and memory deficits and increased anxiety-like behavior. The mechanism underlying these behavioral changes is unknown but we hypothesized that it involves perturbations to the serotonergic system as this is the principle mode of action of MDMA in the adult brain. During development 5-HT is a neurotrophic factor involved in neurogenesis, synaptogenesis, migration, and target region specification. We have previously showed that MDMA exposure (4×10 mg/kg/day) from P11-20 (analogous to human third trimester exposure) induces ~50% decreases in hippocampal 5-HT throughout treatment. To determine whether MDMA-induced 5-HT changes are determinative, we tested if these changes could be prevented by treatment with a selective serotonin reuptake inhibitor (citalopram: CIT). In a series of experiments we evaluated the effects of different doses and dose regimens of CIT on MDMA-induced 5-HT depletions in three brain regions (hippocampus, entorhinal cortex, and neostriatum) at three time-points (P12, P16, P21) during the treatment interval (P11-20) known to induce behavioral alterations when animals are tested as adults. We found that 5 mg/kg CIT administered twice daily significantly attenuated MDMA-induced 5-HT depletions in all three regions at all three ages but that the protection was not complete at all ages. Striatal dopamine was unaffected. We also found increases in hippocampal NGF and plasma corticosterone following MDMA treatment on P16 and P21, respectively. No changes in BDNF were observed. CIT treatment may be a useful means of interfering with MDMA-induced 5-HT reductions and thus permit tests of the hypothesis that the drug's cognitive and/or anxiety effects are mediated through early disruptions to 5-HT dependent developmental processes.     

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in the rat: characterization and age-dependent effects

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a potent dopaminergic toxin that has been found to produce Parkinson's disease-like symptoms in humans and monkeys. The neurotoxic effects of MPTP appear to be reduced in rodents where multiple dosing procedures are required to demonstrate long-lasting neuronal deficits. In the present study, the neurotoxic effects of MPTP were further characterized in the rat. Following the repeated administration of MPTP, pronounced (60-80%) and dose-dependent depletions of striatal dopamine and serotonin concentrations were found in the rat brain. Time-course studies revealed that while striatal dopamine concentrations remained consistently reduced for at least 8 weeks following MPTP treatment, striatal serotonin depletions as well as MPTP-induced monoamine depletions in other brain regions were transient in nature. Pretreatment with the MAO-B inhibitor pargyline afforded a selective and complete protection of striatal dopamine levels without significantly affecting MPTP-induced striatal serotonin depletions. Similarly, treatment with ascorbic acid was found to selectively attenuate MPTP-induced dopamine depletions in rats. The neurotoxic effects of MPTP were also found to increase in the developing rat. No significant brain monoamine depletions were observed in neonatal rats following the repeated administration of MPTP. However, MPTP-induced neurotoxicity progressively increased in older rats. The present results indicate that when appropriate treatment procedures are used, a pronounced, selective, age-dependent, and long-lasting MPTP-induced reduction in striatal dopamine concentrations can be observed in the rat brain. The present results are discussed in reference to the putative mechanisms and species differences of MPTP-induced neurotoxicity.     

Toxic effects of MDMA on central serotonergic neurons in the primate: importance of route and frequency of drug administration

This study compared the toxic effects of oral versus subcutaneous and single versus multiple doses of 3,4-methylenedioxymethamphetamine (MDMA) on central serotonergic neurons in non-human primates. Orally administered MDMA was approximately one-half as effective as subcutaneously administered drug. Multiple doses were more effective than single doses, but a single 5 mg/kg dose of MDMA given orally still produced a long-lasting depletion of serotonin in the monkey brain. These results indicate that when MDMA is given to monkeys in a manner similar to that employed by humans, it exerts toxic effects on central serotonergic neurons. This suggests that humans using MDMA may be at risk for incurring central serotonergic neuronal damage.     

Neuroanatomic specificity and time course of alterations in rat brain serotonergic pathways induced by MDMA (3,4-methylenedioxymethamphetamine): assessment using quantitative autoradiography.

The widely abused "designer" drug MDMA (3,4-methylenedioxymethamphetamine) has been shown to cause marked and long-lasting changes in brain serotonergic systems. The present study uses quantitative in vitro autoradiography of 3H-paroxetine labeled 5-HT uptake sites to assess the time-dependent effects of MDMA on 5-HT neurons in specific neuroanatomic loci. Following treatment with MDMA (20 mg/kg, b.i.d. for 4 days), marked decreases in 5-HT uptake sites were observed in a number of brain regions known to receive projections of 5-HT neurons. These regions included cerebral cortex, caudate nucleus, hippocampus, nucleus accumbens, olfactory tubercle, superior and inferior colliculi, geniculate nuclei, and most thalamic nuclei. In contrast, other areas such as the septal nuclei and some thalamic nuclei which also receive 5-HT projections were not substantially affected by this drug. In most regions, decreases in 5-HT uptake sites occurred within 24 hours of the last dose of MDMA and persisted at the 2 week time point. Some regions such as dorsal striatum exhibited a time-dependent reduction with greater reductions occurring at 2 weeks rather than immediately following the MDMA treatment regimen. The density of 5-HT uptake sites in other regions such as endopiriform nucleus and substantia nigra at the 2 week versus 18 hour time point indicated some degree of region-specific recovery. Regions which demonstrated no significant reduction in 5-HT uptake sites included the dorsal and median raphe nuclei, ventral tegmental area, central grey, interpeduncular nucleus, locus coerulus, pontine reticular formation and cerebellum. Likewise, regions containing 5-HT axons of passage (e.g., indusium griseum and lateral hypothalamus) appeared to be insensitive to the neurotoxic effects of MDMA on 5-HT neurons. Furthermore, the neurotoxic effects of MDMA showed specificity in that the catecholamine neurons labeled by 3H-mazindol were unaffected by the treatment regimen. These data indicate that the preferential degeneration of serotonergic neurons by MDMA is mediated primarily at 5-HT terminal regions, whereas regions containing 5-HT perikarya and axons of passage remain relatively unaffected. In addition, the observed time-dependent reductions and recovery of 5-HT uptake sites which were detected within 2 weeks of the treatment regimen in certain brain regions suggest region-specific differences in recovery of 5-HT systems from MDMA-induced lesion.     

Lack of long-term monoamine depletions following repeated or continuous exposure to cocaine

Cocaine was administered to rats for prolonged periods either by repeated injections (10 mg/kg twice daily for 10 days and 12.5 mg/kg 8 times daily for 10 days) or by continuous intravenous infusion (100 mg/kg/day for 21 days). None of the regimens produced long-lasting depletions of dopamine (DA), serotonin (5-HT), or major metabolites in striatum, hippocampus, hypothalamus, or somatosensory cortex. These results suggest that prolonged exposure to cocaine does not produce neurotoxicity like that observed with d-amphetamine or d-methylamphetamine.     

Reduced efficacy of fluoxetine following MDMA ("Ecstasy")-induced serotonin loss in rats

Long-term serotonin (5-HT) neuronal loss is currently a major cause of concern associated with recreational use of the substituted amphetamine 3,4 methylenedioxymethamphetamine (MDMA; "Ecstasy"). Such loss may be problematic considering that psychiatric disorders such as depression and anxiety and responses to first line treatments for these disorders are associated with 5-HT. In this study the effects of prior exposure to MDMA on behavioural and central neurochemical changes induced by the serotonin (5-HT) re-uptake inhibitor and antidepressant fluoxetine were examined in rats. Animals were administered MDMA (10 mg/kg. i.p.) four times daily for two consecutive days. One week later the animals were subjected to treatment with fluoxetine (10 mg/kg, i.p.). Fluoxetine treatment groups received either acute (saline injections for 20 days followed by 3 fluoxetine treatments over 24 h) or chronic (once daily fluoxetine for 21 days) drug administration. Prior exposure to MDMA resulted in an attenuation of fluoxetine-induced swimming behaviour in the modified forced swimming test (FST); a behavioural test of antidepressant action. In parallel MDMA treatment resulted in significant regional depletions of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) accompanied by a reduction in cortical [3H] paroxetine binding to nerve terminal 5-HT transporters. MDMA-induced 5-HT loss was enhanced in animals following chronic fluoxetine administration. Elimination of fluoxetine and its metabolite norfluoxetine from the brain abolished this interaction between MDMA and fluoxetine treatment. Fluoxetine administration reduced both 5-HIAA and the 5-HIAA:5-HT metabolism ratio, which was attenuated in animals pre-treated with MDMA. Overall the results show that MDMA induces long-term 5-HT loss in the rodent brain and consequently diminishes behaviour and reductions in 5-HT metabolism induced by the antidepressant fluoxetine. These results have potential clinical relevance, suggesting that 5-HT re-uptake inhibitors such as fluoxetine may be less effective at treating depression in chronic abusers of MDMA.     

Evidence for a role of energy dysregulation in the MDMA-induced depletion of brain 5-HT

Although the exact mechanism involved in the long-term depletion of brain serotonin (5-HT) produced by substituted amphetamines is not completely known, evidence suggests that oxidative and/or bioenergetic stress may contribute to 3,4-methylenedioxymethamphetamine (MDMA)-induced 5-HT toxicity. In the present study, the effect of supplementing energy substrates was examined on the long-term depletion of striatal 5-HT and dopamine produced by the local perfusion of MDMA (100 microM) and malonate (100 mM) and the depletion of striatal and hippocampal 5-HT concentrations produced by the systemic administration of MDMA (10 mg/kg i.p. x4). The effect of systemic administration of MDMA on ATP levels in the striatum and hippocampus also was examined. Reverse dialysis of MDMA and malonate directly into the striatum resulted in a 55-70% reduction in striatal concentrations of 5-HT and dopamine, and these reductions were significantly attenuated when MDMA and malonate were co-perfused with nicotinamide (1 mM). Perfusion of nicotinamide or ubiquinone (100 microM) also attenuated the depletion of 5-HT in the striatum and hippocampus produced by the systemic administration of MDMA. Finally, the systemic administration of MDMA produced a 30% decrease in the concentration of ATP in the striatum and hippocampus. These results support the conclusion that MDMA produces a dysregulation of energy metabolism which contributes to the mechanism of MDMA-induced 5-HT neurotoxicity.     

A Study on the Mechanisms by Which Minocycline Protects Against MDMA (‘Ecstasy’)-Induced Neurotoxicity of 5-HT Cortical Neurons

3,4-Methylenedioxymethamphetamine (MDMA, ‘ecstasy’) is a selective 5-HT neurotoxin in rat brain which has been shown to produce acute neuroinflammation characterized by activation of microglia and release of interleukin-1beta (IL-1β). We aimed to determine whether or not minocycline, a semi-synthetic tetracycline antibiotic capable of inhibiting microglial activation, could prevent the inflammatory response and reduce the toxicity induced by MDMA. Adult male Dark Agouti rats were given minocycline twice a day for 2 days (45 mg/kg on the first day and 90 mg/kg on the second day; 12-h apart, i.p.). MDMA (12.5 mg/kg; i.p.) was given after the third minocycline injection and animals were killed either 1 h later for the determination of NFκB binding activity, 3 h later for the determination of IL-1β, 24 h later for the determination of microglial activation or 7 days later for the determination of [³H]-paroxetine binding as a measure of 5-HT neurotoxicity. MDMA increased NFκB activation, IL-1β release and microglial activation both in the frontal cortex and in the hypothalamus and 7 days later produced a reduction in the density of 5-HT uptake sites in both these brain areas. Minocycline prevented the MDMA-induced increase in NFκB activation, IL-1β release and microglial activation in the frontal cortex and prevented the 5-HT neurotoxicity 7 days later. However, in the hypothalamus, in spite of preventing MDMA-induced microglial activation, minocycline failed to prevent MDMA-induced NFκB activation, IL-1β release and neurotoxicity. This suggests that the protective mechanism of minocycline against MDMA-induced neurotoxicity in frontal cortex involves inhibition of MDMA-induced NFκB activation possibly through a reduction in IL-1β signalling.     

Neonatal 3,4-methylenedioxymethamphetamine (ecstasy) alters dopamine and serotonin neurochemistry and increases brain-derived neurotrophic factor in the forebrain and brainstem of the rat

Growing concerns surround the risk of fetal exposure to 3,4-methylenedioxymethamphetamine (MDMA; ecstasy). Prior animal studies using neonatal rats administered MDMA from postnatal days (P) 11-20 (a period approximating third trimester brain development in humans) have demonstrated long-lasting decrements in serotonin (5-HT) and learning; however, no studies have examined the acute post-MDMA response of the brain at this early age. Specifically, it is of interest whether MDMA administration to neonatal rats produces the expected depletion of monoamines and whether the brain exhibits any ameliorative response to the pharmacologic insult. In the current study, this model was employed to determine whether forebrain and brainstem dopamine (DA) and 5-HT neurochemistry were altered 24 h after the last injection (P21), and whether brain-derived neurotrophic factor (BDNF) was upregulated in response to MDMA exposure. All forebrain structures examined (frontal cortex, hippocampus, and striatum) showed significant MDMA-induced reductions in 5-HT and its metabolite, 5-HIAA, and significant increases in the DA metabolite, HVA, as well as DA turnover (HVA/DA). In the brainstem, there were significant increases in 5-HIAA, HVA and DA turnover. BDNF was significantly increased (19-38%) in all forebrain structures and in the brainstem in MDMA-exposed neonates versus saline controls. These data suggest that MDMA exposure to the developing rat brain from P11-20 produces similar alterations in serotonin and dopamine neurochemistry to those observed from adult administrations. In addition, a compensatory increase in BDNF was observed and may be the brains ameliorative response to minimize MDMA effects. This is the first report demonstrating that MDMA exposure results in increased levels of BDNF and that such increases are correlated with changes in monoamine levels. Future research is needed to elucidate any deleterious effects MDMA-induced increases in trophic activity might have on the developing brain and to examine earlier gestational exposure periods in order to assess the risk throughout pregnancy.     

Behavioral and neurochemical effects of orally administered MDMA in the rodent and nonhuman primate

MDMA (methylenedioxymethamphetamine) is a recreational drug of abuse known as "Ecstasy" which markedly decreases regional brain serotonin (5-HT) content and produces 5-HT nerve terminal degeneration in forebrain areas of the rat. In order to determine the acute and chronic behavioral effects of MDMA, adult rats were given MDMA at 0, 5 or 10 mg/kg, po for 4 consecutive days. Alternatively, parachloroamphetamine (PCA) at 5 mg/kg was administered under the same regimen. Within 30 min after the first dose, the MDMA-treated rats exhibited the serotonin motor syndrome consisting of straub tail and splayed hindlimbs comparable to that seen in the PCA-treated rats. This serotonin motor syndrome, with a duration of about 2 hr, was less pronounced after subsequent doses. At 2-4 wk after the last dose, no significant differences between control and treated rats were seen in emergence, hot plate response, auditory startle response or complex maze behavior even though a significant dose-related decrease (50%) in 5-HT concentration was observed in the frontal cortex and hippocampus of these rats 4 wks after the last dose. Adult female monkeys dosed po with 5 or 10 mg/kg of MDMA twice/day for 4 consecutive days demonstrated no spontaneous behavioral changes or weight loss compared to controls, but forebrain 5-HT concentration was reduced by 80% 1 mon after dosing. These data indicate that at doses only 2-3 times the human dose, MDMA produces significant forebrain 5-HT decreases but does not produce detectable residual behavioral alterations as assessed by these behavioral paradigms.     

Effects of benzylpiperazine derivatives on the neurotoxicity of 3,4-methylenedioxymethamphetamine in rat brain

The neurotoxicity of 3,4-methylenedioxymethamphetamine (MDMA) in rat brain was attenuated significantly by coadministration of several benzylpiperazines (p-nitrobenzylpiperazine, p-chlorobenzylpiperazine and 1-piperonylpiperazine), which were weak inhibitors for [³H]6-nitroquipazine binding to the 5-hydroxytryptamine (5-HT) transporter in rat brain. These results suggest that these benzylpiperazines may inhibit the MDMA-induced neurotoxicity by a novel neuropharmacological effect other than 5-HT uptake inhibition.     

Fenfluramine-induced loss of serotonin transporters in baboon brain visualized with PET

The present study sought to determine whether or not Positron Emission Tomography (PET) with the newly developed positron emitting serotonin (5-HT) transporter ligand, (+)[11C]McN-5652, could be used to detect fenfluramine-induced 5-HT neurotoxicity in the brain of living primates (baboons). Six PET imaging studies were performed: three before treatment with fenfluramine (5 mg/kg, s.c., twice daily for 4 days) and three after (18, 45, and 81 days after treatment). The dose of fenfluramine used in this study (5 mg/kg) is known to produce 5-HT neurotoxicity in primates, and to be approximately two times higher than a dose of fenfluramine reported to produce small and inconsistent weight loss in baboons (2 mg/kg). Following fenfluramine treatment, marked lasting reductions in regional brain specific binding of (+)[11C]McN-5652 were found by means of PET. Findings with PET corresponded well with post-mortem neurochemical findings indicative of serotonergic neurotoxicity (lasting depletions of regional brain 5-HT, 5-HIAA, and 5-HT uptake sites). These results suggest that PET imaging with (+)[11C]McN-5652 will be useful for evaluating the 5-HT neurotoxic potential of fenfluramine and related drugs in living humans.     

Enhancement of morphine-induced analgesia after repeated injections of methylenedioxymethamphetamine

Repeated administration of methylenedioxymethamphetamine (MDMA) to rats results in long-term depletion of serotonin (5-hydroxytryptamine; 5-HT) in several brain regions. Because of the apparent role of 5-HT in morphine-induced antinociception, the present experiment was designed to determine the effects of repeated MDMA injections on morphine-induced analgesia. Rats (n = 48) received 8 s.c. injections (one every 12 h for 4 days) of MDMA (20 mg/kg) or saline (1.0 ml/kg). Two weeks after the last injection, the groups were divided into 4 subgroups that received either saline, or morphine 2.5, 3.55 or 5.0 mg/kg (s.c.). Nociception was assayed before and after saline or morphine administration by the method of tail immersion in warm water (55 degrees C). The day after analgesia testing, the animals were sacrificed, brains and spinal cords removed and 5-HT, norepinephrine (NE) and dopamine (DA) levels in various brain and spinal cord regions were assayed. The analgesic effect of morphine was enhanced in rats that had received repeated MDMA injections. MDMA selectively depleted 5-HT in the cortex, hippocampus, striatum, brainstem and in the cervical portion of spinal cord. However, 5-HT levels were not changed in the thoracic and lumbar segments of the spinal cord. Thus, a functional consequence of repeated MDMA administration in rats was to enhance morphine-induced antinociception in association with reductions in brain and cervical spinal cord 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)     

The designer methcathinone analogs, mephedrone and methylone, are substrates for monoamine transporters in brain tissue

The nonmedical use of 'designer' cathinone analogs, such as 4-methylmethcathinone (mephedrone) and 3,4-methylenedioxymethcathinone (methylone), is increasing worldwide, yet little information is available regarding the mechanism of action for these drugs. Here, we employed in vitro and in vivo methods to compare neurobiological effects of mephedrone and methylone with those produced by the structurally related compounds, 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine. In vitro release assays using rat brain synaptosomes revealed that mephedrone and methylone are nonselective substrates for plasma membrane monoamine transporters, similar to MDMA in potency and selectivity. In vivo microdialysis in rat nucleus accumbens showed that i.v. administration of 0.3 and 1.0 mg/kg of mephedrone or methylone produces dose-related increases in extracellular dopamine and serotonin (5-HT), with the magnitude of effect on 5-HT being greater. Both methcathinone analogs were weak motor stimulants when compared with methamphetamine. Repeated administrations of mephedrone or methylone (3.0 and 10.0 mg/kg, s.c., 3 doses) caused hyperthermia but no long-term change in cortical or striatal amines, whereas similar treatment with MDMA (2.5 and 7.5 mg/kg, s.c., 3 doses) evoked robust hyperthermia and persistent depletion of cortical and striatal 5-HT. Our data demonstrate that designer methcathinone analogs are substrates for monoamine transporters, with a profile of transmitter-releasing activity comparable to MDMA. Dopaminergic effects of mephedrone and methylone may contribute to their addictive potential, but this hypothesis awaits confirmation. Given the widespread use of mephedrone and methylone, determining the consequences of repeated drug exposure warrants further study.