Stereoselective, sex-dependent 5-HT2A receptor modulation of cortical plasticity by MDMA in mice.

The drug MDMA, also known as ecstasy, is being studied as a possible aid in psychotherapy for hard-to-treat mental health conditions, but how it works in the brain is not fully understood. In experiments with mice, the S(+) form of MDMA, but not the R(-) form, activated a specific serotonin receptor (5-HT2AR) and caused changes in brain cell connections in the frontal cortex of males. The R(-) form had little effect except for a head-twitch response in females. Blocking the serotonin transporter with fluoxetine prevented these effects, showing that MDMA works indirectly by increasing serotonin levels. These results reveal that MDMA's effects on brain plasticity depend on both the drug's chemical form and the sex of the animal.

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Abstract

The psychoactive entactogen 3,4-methylenedioxymethamphetamine (MDMA), widely known as a recreational drug, is gaining renewed attention as a potential psychotherapeutic adjunct for treatment-resistant psychiatric disorders, yet its neurobiological mechanisms - particularly those related to its stereoisomers and sex-specific effects - remain poorly understood. Here, we report stereoselective and sex-dependent actions of MDMA on serotonin (or 5-hydroxytryptamine) 2A receptor (5-HT2AR)-mediated signaling and dendritic structural plasticity in mouse frontal cortex. Using both in vitro and in vivo approaches, we found that racemic MDMA and S(+)-MDMA exhibit weak partial agonism at 5-HT2AR in HEK293 cells, whereas R(-)-MDMA shows negligible functional activity despite higher specific binding affinity. In vivo, S(+)-MDMA elicited a dose-dependent head-twitch response (HTR) in both sexes, while R(-)-MDMA-induced HTR only in females. Correspondingly, S(+)-MDMA increased inositol monophosphate (IP1) accumulation in the frontal cortex of male and female mice, whereas R(-)-MDMA showed minimal effects. Structurally, S(+)-MDMA enhanced dendritic spine density in male frontal cortex in a partially 5-HT2AR-dependent manner, while no spine remodeling was observed in females or with R(-)-MDMA. Pharmacological blockade of the serotonin transporter (SERT) with fluoxetine fully prevented S(+)-MDMA-induced HTR and IP1 signaling, without affecting responses to the direct 5-HT2AR agonist DOI. These findings indicate that MDMA engages 5-HT2AR signaling indirectly via serotonin efflux and that this effect is both stereoselective and sex-dependent in mice, uncovering a previously unrecognized interaction between sex, MDMA stereochemistry, and 5-HT2AR-mediated cortical plasticity, with important implications for the rational design of MDMA-based therapeutics.