The transcriptome of playfulness is sex-biased in the juvenile rat medial amygdala: a role for inhibitory neurons

Social play is a well-conserved, dynamic behavior known to be sexually differentiated. In most species, males play more than females, a sex difference largely driven by the medial amygdala (MeA) yet the full mechanism establishing this bias is unknown. Here, we explore “the transcriptome of playfulness” in both sexes for the first time, demonstrating that the transcriptomic profile in the juvenile rat MeA associated with playfulness is markedly distinct in males and females. Parallel single-cell RNA-sequencing experiments from newborn rats suggest that inhibitory neurons drive this sex difference. Furthermore, we show that inhibitory neurons comprise the majority of play-active cells in the juvenile MeA, with males having more play-active cells than females, of which a greater proportion are GABAergic. Through integrative bioinformatic analyses, we further explore the expression, function, and cell-type specificity of key play-associated gene modules, providing valuable insight into the sex-biased mechanisms underlying this fundamental social behavior. In this study, we generated bulk RNA-seq data from the amygdala of P30 (30 days of age; juvenile) high- and low-playing male and female rats. Playfulness was assessed once daily from P26-29, and animals that exhibited an average play score that was in the top third per sex (n=6 per group) were sacrificed, amygdalas dissected, and sequenced using RNA-seq. MHI = male high-players; MLO = male low-players; FHI = female high-players; FLO = female low-players