The present study was designed to elucidate the role of dopamine (DA) metabolism in the serotonergic neurotoxicity induced by 3,4-methylenedioxymethamphetamine (MDMA). An antisense (AS) oligonucleotide (ODN) sequence targeted at monoamine oxidase-B (MAO-B) was utilized to attenuate MAO-B activity prior to MDMA administration. Sprague-Dawley rats were surgically implanted with intracerebroventricular (icv) cannulae and received a continuous infusion of MAO-B AS-ODN via an osmotic minipump. Constant AS ODN infusion for 7 days at a rate of 0.5 microl/h (total daily dose 600 pmol) resulted in a 63% knockdown of MAO-B activity. MDMA (40 mg/kg, sc) produced a rise in body temperature within 1 h of MDMA administration and a reduction in striatal serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) levels 7 days later. Pretreatment with the MAO-B AS ODN prior to MDMA attenuated this reduction in serotonergic markers, yet had no effect on MDMA-induced hyperthermia. Furthermore, in vivo microdialysis revealed that previous AS ODN treatment failed to alter the acute DA release induced by MDMA (10 mg/kg, sc) within the striatum. These results indicate that MAO-B plays an integral role in the development of MDMA-induced neurotoxicity while not affecting MDMA-induced hyperthermia or acute DA release.