Acute and chronic effects of MDMA on molecular mechanisms implicated in memory formation in rat hippocampus: surface expression of CaMKII and NMDA receptor subunits

Abstract

Acute 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") treatment induces learning deficits in different animal models. In a passive avoidance learning task in rats, previous studies suggested a role for Ca2+/calmodulin-dependent protein kinase II (CaMKII) and N-methyl-D-aspartate (NMDA) receptors in the acute learning impairment. As cognitive deficits by "ecstasy" in humans have been only reported in frequent recreational users, we examined whether a repeated MDMA treatment could induce in rats lasting molecular changes related to memory consolidation of passive avoidance. In rats with a pronounced 5-HT depletion by MDMA, the effect of another drug challenge was also examined. The surface expression in the hippocampus of NMDA receptor subunits, the scaffolding postsynaptic density protein PSD-95, phosphorylated CaMKII and protein phosphatase 1 (PP1) was measured. In rats repeatedly treated with MDMA (10 mg/kg) twice daily for 4 consecutive days, hippocampal 5-HT levels were markedly reduced 1 week later. At this time, neither learning performance was affected nor changes in membrane levels of NMDA receptor subunits, PSD-95, CaMKII and PP1 were found. In these rats, however, another drug challenge produced a rapid reduction in PSD-95 immunoreactivity and prevented the learning-specific increase in the NMDA receptor NR1 subunit and phosphorylated CaMKII. The results show no lasting change in learning-associated molecular events after a neurotoxic MDMA treatment. This drug only produces transient effects on early molecular events involved in memory consolidation, which do not appear to depend on endogenous 5-HT levels.