RESUMO
(+) 3,4-Methylenedioxymethamphetamine (MDMA) is a psychedelic drug of abuse that causes selective degeneration of serotonergic fibers of dorsal raphe neurons that project throughout the forebrain. Previous studies using pharmacological and behavioral approaches suggested that MDMA treatment leads to desensitization of 5-HT1B receptors. We proposed to test whether this occurs by downregulation of 5-HT1B messenger RNA in dorsal raphe, striatum or CA1 hippocampal neurons and/or 5-HT1B binding site density in hippocampus and basal ganglia. In Experiment I, rats were treated with MDMA using several dosing protocols (2.5 or 10 mg kg-1 day-1 s.c. given a single time or twice daily for 4 days). The animals were killed 24 h after the last dose. [3H]-citalopram binding to serotonin transporters in hippocampus was reduced in the high dose protocol, indicating degeneration of forebrain serotonergic fibers. Despite the extensive reduction in serotonergic content, 5-HT1B mRNA did not change from control levels in any region when measured by in situ hybridization. [125I]-Iodocyanopindolol binding to 5-HT1B sites in hippocampus was also not changed. In Experiment II, high dose MDMA had no effect on 5-HT1B mRNA in any brain region either 1 or 14 days after treatment. However, [125I]-iodocyanopindolol binding more than doubled in striatum 1 day after MDMA treatment but returned to control levels by 14 days. This may have been a transient compensation to early neuronal damage caused by MDMA exposure. These results suggest that previously described changes in 5-HT1B function following MDMA treatment involve only posttranscriptional changes in receptor regulation and do not alter 5-HT1B mRNA levels.