Concurrent Inhibition of Vesicular Monoamine Transporter 2 Does Not Protect Against 3,4-Methylenedioxymethamphetamine...

3, 4-Methylenedioxymethamphetamine (MDMA) is a hallucinogenic amphetamine derivative. The acute effects of MDMA are hyperthermia, hyperactivity, and behavioral changes, followed by long-term serotonergic neurotoxicity in rats and primates. However, the underlying mechanisms of MDMA neurotoxicity remain elusive. We reported that pretreatment of rats with Ro 4-1284, a reversible inhibitor of the vesicular monoamine transporter 2 (VMAT2), reduced MDMA-induced hyperactivity in rats, abolished the hyperthermic response, and the long-term neurotoxicity. Current studies focused on the effects of co- and/or postinhibition of VMAT2 on the acute and chronic effects of MDMA and on the dose-response relationship between MDMA-induced elevations in body temperature and subsequent reductions in indolamine concentrations. Sprague Dawley rats were treated with MDMA (20, 25, or 27.5 mg/kg sc), and either co- and/or posttreatment with the VMAT2 inhibitor (10 mg/kg ip). Rats simultaneously treated with Ro 4-1284 and MDMA exhibited a more rapid increase in body temperature compared to just MDMA. However, the duration of the elevated body temperature was significantly shortened (approximately 3 h vs approximately 8 h, respectively). A similar body temperature response was observed in rats posttreated (7 h after MDMA) with Ro 4-1284. Despite decreases in the area under the curve (Δtemp X time) of body temperature caused by Ro 4-1284, there were no significant differences in the degree of indolamine depletion between any of the MDMA-treated groups. The results suggest that the neuroprotective effects of VMAT2 inhibition is likely due to the indirect monoamine depleting effects of the Ro 4-1284 pretreatment, rather than by the direct inhibition of VMAT2 function.