Single dose of MDMA causes extensive decrement of serotoninergic fibre density without blockage of the fast axonal transport in Dark Agouti rat brain and spinal cord

Prolonged neurotoxicity of the recreational drug, MDMA (3,4-methylenedioxymethamphetamine) on serotoninergic axon terminals has been suggested. The effect of a single (15 mg/kg) dose of intraperitoneally administered MDMA on serotoninergic fibre density, defined by tryptophan hydroxylase (TpH) and serotonin transporter (5-HTT) immunoreactivity, has been evaluated in the spinal cord and brain areas in Dark Agouti rats, 7 and 180 days after MDMA applications. Immunostaining for amyloid precursor protein (APP) has been performed to examine possible defects of the fast axonal transport, and 5-HTT mRNA expressions were quantified in neurones of medullary raphe nuclei. Seven days after MDMA treatment, a substantial decrease in the density of TpH-immunoreactive fibres was detectable in the frontal cortex, the caudate-putamen, the CA1 region of the hippocampus, and marked decreases were found in the spinal cord. These changes in TpH density showed a high correlation with 5-HTT densities. In contrast, APP-immunoreactive axonal bulbs were not detected in any of the brain regions studied. Seven days after MDMA administrations, significantly elevated 5-HTT mRNA expressions were found in the raphe pallidus and obscurus. Our results suggest that a single dose of MDMA elicits widespread depletion of TpH and 5-HTT immunoreactivity in serotoninergic axons without morphological sign of the blockage of the fast anterograde axonal transport. Our results do not support the notion of MDMA-induced axotomy of serotoninergic neurones. The up-regulation of 5-HTT mRNA expressions 1 week after MDMA injections might indicate the potential recovery of the serotonin system.