Effects of Intracerebroventricular Administration of 5-(Glutathion-S-yl)-α-methyldopamine on Brain Dopamine, Serotonin, and Norepinephrine Concentrations in Male Sprague-Dawley Rats

The metabolite 5-(glutathion-S-yl)-alpha-methyldopamine, formed from the oxidation of alpha-methyldopamine in the presence of glutathione, reproduces several acute behavioral and neurochemical effects of the serotonergic neurotoxicants MDA and MDMA in rats. Intracerebroventricular injection of this conjugate caused hyperactivity, aggression, forepaw treading, and Straub tail—behaviors typical of serotonin release. It also produced short-term changes in dopaminergic, serotonergic, and noradrenergic systems, including increased dopamine synthesis and acute serotonin turnover, as well as depletion of brain norepinephrine similar to MDA's pressor effect. However, a single injection did not cause long-term serotonergic toxicity, suggesting that while acute dopamine turnover may be necessary for such toxicity, it is not sufficient on its own.

Study at a glance

Abstract

alpha-Methyldopamine (alpha-MeDA) is a metabolite of the serotonergic neurotoxicants 3,4-(+/-)-(methylenedioxy)amphetamine (MDA) and 3,4-(+/-)-(methylenedioxy)methamphetamine (MDMA). alpha-MeDA readily oxidizes, and in the presence of glutathione (GSH) it forms 5-(glutathion-S-yl)-alpha-methyldopamine [5-(glutathion-S-yl)-alpha-MeDA]. Since GSH conjugates of many polyphenols are biologically (re)active, we investigated the role of 5-(glutathion-S-yl)-alpha-MeDA in the acute and long-term neurochemical changes observed after administration of MDA. Intracerebroventricular (icv) administration of 5-(glutathion-S-yl)-alpha-MeDA (720 nmol) to male Sprague-Dawley rats produced behavioral changes similar to those reported after subcutaneous administration of MDA. Thus, animals became hyperactive and aggressive and displayed forepaw treading and Straub tails, behaviors usually seen after administration of serotonin (5-HT) releasers, and consistent with a role for 5-(glutathion-S-yl)-alpha-MeDA in some of the behavioral alterations seen after administration of MDA and MDMA. In addition to the behavioral changes, 5-(glutathion-S-yl)-alpha-MeDA also caused short-term alterations in the dopaminergic, serotonergic, and noradrenergic systems. An increase in dopamine synthesis appears to be a prerequisite for the long-term depletion of brain 5-HT following MDMA administration. However, although 5-(glutathion-S-yl)-alpha-MeDA reproduced some of the effects of MDA on the dopaminergic system and was capable of causing acute increases in 5-HT turnover, a single icv injection of 5-(glutathion-S-yl)-alpha-MeDA did not result in long-term serotonergic toxicity. Thus, although acute stimulation of dopamine turnover may be necessary for long-term serotonergic toxicity, such changes are not sufficient to produce these effects. The effects of a multiple dosing schedule of 5-(glutathion-S-yl)-alpha-MeDA will therefore require investigation before we can define a role for this metabolite in MDA and MDMA mediated neurotoxicity. MDA also produces a pressor response that is related to its ability to release neuronal norepinephrine stores, and 5-(glutathion-S-yl)-alpha-MeDA caused comparable depletions of brain norepinephrine concentrations, indicating that both compounds produce similar effects on the noradrenergic system.