Neuroendocrine evidence that (S)-2-(chloro-5-fluoro-indol- l-yl)-1-methylethylamine fumarate (Ro 60-0175) is not a selective 5-hydroxytryptamine(2C) receptor agonist.

The 5-hydroxytryptamine(2A) and (2C) (5-HT(2A) and 5-HT(2C)) receptors are so closely related that selective agonists have not been developed until recently with the advent of (S)-2-(chloro-5-fluoro-indol-l-yl)-1-methylethylamine fumarate (Ro 60-0175), a putatively selective 5-HT(2C) receptor agonist. In the present study, Ro 60-0175 was used to analyze the importance of 5-HT(2C) receptors in hormone secretion. Injection of Ro 60-0175 (5 mg/kg s.c.) produced a maximum increase in plasma levels of adrenocorticotrophic hormone, oxytocin, and prolactin at 15 min postinjection and a maximum increase in plasma corticosterone levels at 60 min postinjection. Ro 60-0175-mediated increases in plasma hormone levels were dose-dependent (corticosterone ED(50) = 2.43 mg/kg; oxytocin ED(50) = 4.19 mg/kg; and prolactin ED(50) = 4.03 mg/kg). To assess the role of 5-HT(2C) and 5-HT(2A) receptors in mediating the hormone responses to Ro 60-0175, rats were pretreated with the 5-HT(2C) antagonist 6-chloro-5-methyl-1-[2-(2-methylpyridyl-3-oxy)-pyrid-5-yl carbonyl] indoline (SB 242084) or 5-HT(2A) antagonists (+/-)-2,3-dimethoxyphenyl-1-[2-4-(piperidine)-methanol] (MDL 100,907) before injection of Ro 60-0175 (5 mg/kg s.c.). Neither SB 242084 (0.1, 0.5, 1, and 5 mg/kg i.p.) nor MDL 100,907 (1, 5, and 10 microg/kg s.c.) significantly inhibited the Ro 60-0175-induced increases in plasma hormone levels. The data suggest that Ro 60-0175 increases hormone secretion by mechanisms independent of the activation of 5-HT(2C) and/or 5-HT(2A) receptors and suggest that Ro 60-0175 is not a highly selective 5-HT(2C) receptor agonist.

Ascorbic acid prevents 3,4-methylenedioxymethamphetamine (MDMA)-induced hydroxyl radical formation and the behavioral and neurochemical consequences of the depletion of brain 5-HT.

MDMA-induced 5-HT neurotoxicity has been proposed to involve oxidative stress due to increased formation of hydroxyl radicals. Recently, MDMA-induced 5-HT neurotoxicity has been shown to be accompanied by a suppression of behavioral and neurochemical responses to a subsequent injection of MDMA. The intent of the present study was to examine whether suppression of the MDMA-induced formation of hydroxyl radicals by an antioxidant, ascorbic acid, attenuates both the MDMA-induced depletion of 5-HT and the functional consequences associated with this depletion. Treatment of rats with ascorbic acid suppressed the generation of hydroxyl radicals, as evidenced by the production of 2,3-dihydroxybenzoic acid from salicylic acid, in the striatum during the administration of a neurotoxic regimen of MDMA. Ascorbic acid also attenuated the MDMA-induced depletion of striatal 5-HT content. In rats treated with a neurotoxic regimen of MDMA, the ability of a subsequent injection of MDMA to increase the extracellular concentration of 5-HT in the striatum, elicit the 5-HT behavioral syndrome, and produce hyperthermia was markedly reduced compared to the responses in control rats. The concomitant administration of ascorbic acid with the neurotoxic regimen of MDMA prevented the diminished neurochemical and behavioral responses to a subsequent injection of MDMA. Finally, a neurotoxic regimen of MDMA produced significant reductions in the concentrations of vitamin E and ascorbic acid in the striatum and hippocampus. Thus, the MDMA-induced depletion of brain 5-HT and the functional consequences thereof appear to involve the induction of oxidative stress resulting from an increased generation of free radicals and diminished antioxidant capacity of the brain.

A neurotoxic regimen of MDMA suppresses behavioral, thermal and neurochemical responses to subsequent MDMA administration.

RATIONALE: 3,4-Methylenedioxymethamphetamine (MDMA) produces a long-term depletion of serotonin (5-HT) in the rat brain; this depletion may have some functional consequences. OBJECTIVE: The aim of the present study was to evaluate the acute effects of MDMA on the extracellular concentrations of dopamine and 5-HT, body temperature and the 5-HT behavioral syndrome in rats 7 days following a neurotoxic regimen of MDMA. METHODS: One week after the rats were treated with a neurotoxic regimen of MDMA (10 mg/kg, i.p., every 2 h for a total of four injections), the rats were injected with a subsequent injection of MDMA. In vivo microdialysis combined with HPLC was utilized to measure the extracellular concentration of 5-HT and dopamine in the striatum. The increase in body temperature was determined by rectal temperature measurements, and the 5-HT behavioral syndrome was scored using a rating scale following the administration of MDMA. RESULTS: The neurotoxic regimen produced a 45% reduction in brain 5-HT concentrations. The magnitude of the MDMA-induced increase in the extracellular concentration of 5-HT, but not dopamine, in the striatum produced by an acute injection of MDMA (7.5 mg/kg, i.p.) was reduced in rats treated previously with the neurotoxic regimen of MDMA when compared with that in control animals. In addition, the magnitude of the 5-HT behavioral syndrome, as well as the hyperthermic response, produced by MDMA was markedly diminished in rats that had previously received the neurotoxic regimen of MDMA. CONCLUSIONS: It is concluded that the long-term depletion of brain 5-HT produced by MDMA is accompanied by impairments in 5-HT function, as evidenced by the deficits in the neurochemical, thermal and behavioral responses to subsequent MDMA administration.

Involvement of the serotonin transporter in the formation of hydroxyl radicals induced by 3,4-methylenedioxymethamphetamine.

The mechanism of 3,4-methylenedioxymethamphetamine (MDMA)-induced depletion of brain serotonin (5-hydroxytryptamine, 5-HT) has been proposed to involve the generation of reactive oxygen species. In the present study, quantification of the extracellular concentration of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid was used as an index of hydroxyl radical generation. Although both MDMA and D-amphetamine markedly increased the extracellular concentration of dopamine in the striatum, only MDMA increased the extracellular concentration of 2,3-DHBA. Treatment with fluoxetine either 1 h prior to or 4 h following the administration of MDMA reduced the MDMA-induced formation of 2,3-DHBA and also attenuated the MDMA-induced depletion of 5-HT in the striatum. These results are supportive of the view that the MDMA-induced generation of hydroxyl radicals and, ultimately, the long-term depletion of 5-HT, is dependent, in part, on the activation of the 5-HT transporter.

Mazindol attenuates the 3,4-methylenedioxymethamphetamine-induced formation of hydroxyl radicals and long-term depletion of serotonin in the striatum.

The formation of hydroxyl radicals following the systemic administration of 3,4-methylenedioxymethamphetamine (MDMA) was studied in the striatum of the rat by quantifying the stable adducts of salicylic acid and D-phenylalanine, namely, 2,3-dihydroxybenzoic acid (2,3-DHBA) and p-tyrosine, respectively. The repeated administration of MDMA produced a sustained increase in the extracellular concentration of 2,3-DHBA and p-tyrosine, as well as dopamine. The MDMA-induced increase in the extracellular concentration of both dopamine and 2,3-DHBA was suppressed in rats treated with mazindol, a dopamine uptake inhibitor. Mazindol also attenuated the long-term depletion of serotonin (5-HT) in the striatum produced by MDMA without altering the acute hyperthermic response to MDMA. These results are supportive of the view that MDMA produces a dopamine-dependent increase in the formation of hydroxyl radicals in the striatum that may contribute to the mechanism whereby MDMA produces a long-term depletion of brain 5-HT content.

Effect of 3,4-methylenedioxymethamphetamine (MDMA) on hippocampal dopamine and serotonin.

The 3,4-methylenedioxymethamphetamine (MDMA)-induced increase in the extracellular concentration of dopamine and the long-term depletion of 5-HT were studied in the hippocampus of the rat brain. MDMA produced a dose-dependent increase in the extracellular concentration of dopamine in the hippocampus, as well as in the striatum. The MDMA-induced increase in the extracellular concentration of dopamine in the hippocampus, but not in the striatum, was suppressed in rats treated with the norepinephrine uptake inhibitor, desipramine, and in rats in which noradrenergic neurons in the hippocampus were lesioned with DSP4 (N-(2- chloroethyl)-N-ethyl-2-bromo benzylamine). However, the long-term depletion of 5-HT in the hippocampus produced by MDMA was unaltered in desipramine-treated rats. These results are supportive of the view that the MDMA-induced increase in the extracellular concentration of dopamine in the hippocampus is the result of an enhanced release of dopamine from noradrenergic neurons. In addition, the MDMA-induced depletion of 5-HT in the hippocampus appears not to involve dopamine-initiated processes, because suppression of MDMA-induced dopamine release did not attenuate the long-term depletion of 5-HT in the hippocampus.