A single sentence summary is not possible because the abstract contains multiple distinct findings. Four weeks after administering MDMA to mice, the potency of a 5-HT1A receptor agonist to inhibit serotonin neuron firing in the dorsal raphe nucleus doubled, and the hypothermic response to 8-OH-DPAT increased, indicating supersensitivity of 5-HT1A autoreceptors. Brain serotonin levels decreased without changes in citalopram binding. MDMA treatment also reduced hippocampal cell proliferation by 30% and increased immobility in the forced swim test, suggesting depressive-like behavior. These effects were absent in mice lacking the serotonin transporter, indicating the transporter is required for these delayed, antidepressant-opposite effects that may contribute to MDMA-induced mood disorders.
The serotonin 5-HT2A receptor plays a crucial role in the reinforcing and addictive properties of MDMA. In experiments with mice, those lacking the 5-HT2A receptor showed reduced self-administration of MDMA at both 0.125 and 0.25 mg/kg per infusion compared to normal mice. MDMA increased horizontal locomotion more in the knockout mice than in normal mice. Dopamine release in the nucleus accumbens was lower in knockout mice both at baseline and after MDMA challenge. Cue-induced reinstatement of MDMA-seeking behavior was blocked by a selective 5-HT2A receptor antagonist at 0.5 mg/kg. These findings suggest that 5-HT2A receptors are essential for MDMA's reinforcing effects and for relapse triggered by drug-associated cues, likely through modulation of dopamine activity in the brain's reward pathway.