Sexually-motivated song correlates with opioid- and dopamine-related gene expression in the rostral nucleus accumbens of male European starlings

Recent studies on songbirds reveal that the nucleus accumbens (NAc) plays a role in facilitating and rewarding “gregarious” singing behavior, a form of communication produced outside a mating context that plays a role in flock cohesion. In addition to its role in reward, the NAc and both opioids and dopamine in this region are known to modulate incentively-motivated behaviors, including sexually-motivated behaviors. This raises the possibility that in addition to gregarious birdsong, the NAc may also play a role in “sexually-motivated” male courtship song. The goal of the present study was to provide insight into this hypothesis using RNAscope and behavioral observations to identify relationships between the expression of opioid- and dopamine-related genes, song, and other social behaviors. Negative correlations were identified between a principal behavioral component containing sexually-motivated song and preening and the expression of both pre-proenkephalin [PENK] and the dopamine D1 receptor [DRD1] gene in NAc. The expression of the mu opioid receptor [OPRM1] gene in NAc correlated negatively with social motivation, reflected in the propensity to spend time near a large compared to a small group, with a similar trend observed for DRD2. Results are the first to reveal a potential role for the NAc in sexually-motivated song and to suggest that specific patterns of opioid- and dopamine-related gene expression within a rostral portion of the songbird NAc may play distinct roles in sexually-motivated song, preening and social motivation.