Seasonal and individual variation in singing behavior correlates with alpha 2-noradrenergic receptor density in brain regions implicated in song, sexual, and social behavior

In seasonally breeding male songbirds, both the function of song and the stimuli that elicit singing behavior change seasonally. The catecholamine norepinephrine (NE) modulates attention and arousal across behavioral states, yet the role of NE in seasonally-appropriate vocal communication has not been well-studied. The present study explored the possibility that seasonal changes in alpha 2-noradrenergic receptors (α ₂-R) within song control regions and brain regions implicated in sexual arousal and social behavior contribute to seasonal changes in song behavior in male European starlings (Sturnus vulgaris). We quantified singing behavior in aviary housed males under spring breeding season conditions and fall conditions. α ₂-R were identified with the selective ligand [ ³H]RX821002 using autoradiographic methods. The densities of α ₂-R in song control regions (HVC and the robust nucleus of the arcopallium [RA]) and the lateral septum (LS) were lower in Spring Condition males. α ₂-R densities in the caudal portion of the medial preoptic nucleus (POM) related negatively to singing behavior. Testosterone concentrations were highest in Spring Condition males and correlated with α ₂-R in LS and POM. Results link persistent seasonal alterations in the structure or function of male song to seasonal changes in NE α ₂-Rs in HVC, RA, and LS. Individual differences in α ₂-R in the POM may in part explain individual differences in song production irrespective of the context in which a male is singing, perhaps through NE modification of male sexual arousal.