Immunohistochemical localization of adrenergic receptors in the rat organ of corti and spiral ganglion

α₁-, β₁-, and β₂- adrenergic receptors (ARs), which mediate responses to adrenergic input, have been immunohistochemically identified within the organ of Corti and spiral ganglion with polyclonal antibodies of established specificity. α₁-AR was immunolocalized to sites overlapping supranuclear regions of inner hair cells as well as to nerve fibers approaching the base of inner hair cells, most evident in the basal cochlear turn. A similar preponderance across cochlear turns for α₁-AR in afferent cell bodies in the spiral ganglion pointed to type I afferent dendrites as a possible neural source of α₁-AR beneath the inner hair cell. Foci of immunoreactivity for α₁-AR, putatively neural, were found overlapping supranuclear and basal sites of outer hair cells for all turns, β₁- and β₂-ARs were immunolocalized to sites overlapping apical and basal poles of the inner and outer hair cells, putatively neural in part, with immunoreactive nerve fibers observed passing through the habenula perforata. β₁- and β₂-ARs were also detected in the cell bodies of Deiters' and Hensen's cells. Within the spiral ganglion, β₁,- and β₂-ARs were immunolocalized to afferent cell bodies, with highest expression in the basal cochlear turn, constituting one possible neural source of receptors within the organ of Corti, specifically on type I afferent dendrites. β₁- and β₂-ARs in Hensen's and Deiters' cells would couple to Gas, known to be present specifically in the supporting cells. Overall, adrenergic modulation of neural/supporting cell function within the organ of Corti represents a newly considered mechanism for modifying afferent signaling.