Noradrenergic inputs mediate state dependence of auditory responses in the avian song system.

Norepinephrine (NE) plays a complex role in the behavioral state-dependent regulation of sensory processing. However, the role of forebrain NE action in modulating high-order sensory activity has not been directly addressed. In this study, we take advantage of the discrete, feedforward organization of the avian song system to identify a site and mechanism of NE action underlying state-dependent modulation of sensory processing. We have developed an experimental paradigm in which brief arousal repeatedly suppresses song system auditory responsiveness. Using pharmacological manipulations in vivo, we show that infusion of alpha-adrenergic antagonists into the NIf (nucleus interfacialis of the nidopallium), an auditory forebrain area, blocks this state-dependent modulation. We also demonstrate dose-dependent enhancement and suppression of song system auditory response properties by NE and adrenergic agonists. Our results demonstrate that noradrenergic release in a single forebrain area is a mechanism underlying behavioral state-dependent regulation of auditory processing in a neural system specialized for vocal learning.