5-HT2C receptors in the nucleus accumbens constrain the rewarding effects of MDMA
Matthew B. Pomrenze, Sam Vaillancourt, Juliana S. Salgado, Kendall B. Raymond, Pierre Llorach, Hiroaki Sacai, Daniel Ryskamp Rijsketic, Tuuli M. Hietamies, Gavin Touponse, Daniel F. Cardozo Pinto, Z. Rastegar, Austen B. Casey, Neir Eshel, Robert C. Malenka, Boris D. Heifets
Abstract
MDMA is a promising adjunct to psychotherapy and has well-known abuse liability, although less than other amphetamine analogs. While the reinforcing dopamine (DA)-releasing properties of MDMA are on par with methamphetamine (METH), MDMA is a far more potent serotonin (5-HT) releaser, via the 5-HT transporter (SERT). MDMA-mediated 5-HT release in a major reward center, the nucleus accumbens (NAc), drives prosocial behaviors via 5-HT1BR activation. We hypothesized that this prosocial mechanism contributes to the reduced reinforcing properties of MDMA compared to METH and used a platform of assays to predict the balance of prosocial and abuse-linked effects of (R)-MDMA, a novel entactogen in clinical development. NAc DA release, measured by GRAB-DA photometry in vivo, increased in proportion to MDMA (7.5 and 15 mg/kg, i.p.) and METH (2 mg/kg i.p.)-conditioned place preference (CPP). Using conditional knockouts (cKOs) for DAT and SERT, microdialysis, and photometry, we found that MDMA-released 5-HT limited MDMA-released DA through actions in the NAc, rather than at ventral tegmental area DAergic cell bodies. SERT cKO reduced the MDMA dose required for CPP three-fold. This enhanced MDMA-CPP and increased DA release were replicated by intra-NAc infusion of either a 5-HT reuptake inhibitor (escitalopram) to prevent MDMA interaction with SERT, or a 5-HT2CR antagonist (SB242084), but not by the 5-HT1BR antagonist NAS-181. These data support separate mechanisms for the low abuse potential versus prosocial effect of MDMA. Using this platform of assays, (R)-MDMA is predicted to have prosocial effects and low abuse potential.