Adrenergic receptors are differentially expressed in the rat cochlea

Abstract

Norepinephrine and nerve fibers containing dopamine β‐hydroxylase are present in the organ of Corti (OC) (ARO Abstr. 26: 12, 2003; 28: 226, 2005). However, the identity and localization of adrenergic receptors (ARs) in the cochlea are uncertain. Here we present the immunolocalization of α1, β1, and β2 AR subtypes in the cochlea of rat. For the α1 AR subtype, immunoreactivity (IR) was detected overlapping apical and basal sites of the inner hair cells (IHCs) in the basal turn, but no IR was detected in relation to the IHCs in the middle and apical turns. IR was observed in close association with the outer hair cells (OHCs) in middle and apical turns, occasionally overlapping Deiters’ cells. For the β1 AR subtype, IR was detected in close association with the IHCs in all turns. IR was also present in presumed nerve fibers at the base of the OHCs, but the OHCs themselves appeared devoid of IR. For the β2 AR subtype IR was associated with IHCs. IR was detected around the basal poles of the OHCs in the middle and apical turns, possibly associated with nerve fibers in all three turns. Within the spiral ganglion, type I afferent cell bodies showed IR for α1 and β1 ARs, whereas a subpopulation of cell bodies exhibited IR for the β2 AR. To our knowledge, this is the first report localizing α1 and β2 AR IR in the OC. ARs in the cochlea may modulate afferent neural activity, control OHC contractility, monitor intracellular Ca2+, and K+ transport.