D1-like dopamine receptor density in nuclei involved in social behavior correlates with song in a context-dependent fashion in male European starlings

Research in songbirds shows that singing behavior is regulated by both brain areas involved in vocal behavior as well as those involved in social behavior. Interestingly, the precise role of these regions in song can vary as a function of the social, environmental and breeding context. To date, little is known about the neurotransmitters underlying such context-dependent regulation of song. Dopamine (DA) modulates highly motivated, goal-directed behaviors (including sexually motivated song) and emerging data implicate DA in the context-dependent regulation of singing behavior. This study was performed to begin to examine whether differences in DA receptors may underlie, in part, context-dependent differences in song production. We used autoradiographic procedures to label D1-like and D2-like DA receptors to examine the relationship between DA receptor density and singing behavior in multiple contexts in male European starlings (Sturnus vulgaris). Within a breeding context (when testosterone (T) was high), D1-like receptor density in the medial preoptic nucleus (POM) and midbrain central gray (GCt) negatively correlated with song used to attract a female. Additionally in this context, D1-like receptor density in POM, GCt, medial bed nucleus of the stria terminalis (BSTm), and lateral septum (LS) negatively correlated with song likely used to defend a nest box. In contrast, in a non-breeding context (when T was low), D1-like receptor density in POM and LS positively correlated with song used to maintain social flocks. No relationships were identified between song in any context and D2-like receptor densities. Differences in the brain regions and directional relationships between D1-like receptor binding and song suggest that dopaminergic systems play a region and context-specific role in song. These data also suggest that individual variation in singing behavior may, in part, be explained by individual differences in D1-like receptor density in brain regions implicated in social behavior.