The neuroendocrinology and neurochemistry of birdsong

Birdsong is a complex learned motor skill that is used in the context of territory defense and mate choice. Songbirds have evolved a specialized neural circuit that controls the learning, production, and perception of song. Studies of the hormonal regulation of neurotransmitter systems in this specialized circuit provide an opportunity for neuroscientists to investigate the cellular neurochemistry of complex behaviors. In this review, we review the hormonal regulation of seasonal neuroplasticity in this circuit with special emphasis on the action of androgens including their estrogenic and androgenic metabolites. One theme that emerges is that androgens can induce seasonal changes in the morphology of the song circuit but that the ability of testosterone to be metabolized into androgenic or estrogenic metabolites also changes seasonally. The basic chemical neuroanatomy of the song system is reviewed and possible sites for the modulation of these transmitter systems by androgens are identified.