Noradrenergic Inputs Mediate State Dependence of Auditory Responses in the Avian Song System

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Abstract
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 manipulationsin vivo, we show that infusion of α-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.

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