Immunohistochemical localization of α2-adrenergic receptors in the neonatal rat cochlea and the vestibular labyrinth.

The α2-adrenergic receptors (α2-ARs), which mediate physiological responses to noradrenaline and adrenaline, are encoded by three different genes but all are coupled to the Gi/Go subfamily of G proteins. The present study investigated the localization of three subtypes, i.e., α2a-, α2b-, and α2c-ARs, in cochlea and vestibular labyrinth in rat in the early postnatal period by immunohistochemistry. The results showed that α2-ARs were widely distributed in regions, including the organ of Corti, spiral ganglion neurons, stria vascularis, crista ampullaris, Scarpa's ganglion, utricle, and Reissner's membrane. Furthermore, the cellular locations of α2-ARs between different cell subtypes as well as receptor subtypes and different observed time points also had diversity. α2a-AR mainly targeted to nuclei at postnatal ages (P)3. While at P(8), only ganglion neurons maintained this character whereas other cell types expressed α2a-AR mainly in plasma membrane. The α2b- and α2c-ARs exhibited predominantly in plasma membrane. Compared with P(8), α2c-AR was not present at stria vascularis at P(3). Overall, our observations indicated that there was region-specific regulation of α2-ARs development in cochlea and vestibular labyrinth. In addition, the extensive expressions of α2-ARs established a significant foundation for the exploration of the function of α2-ARs in cochlea and vestibular labyrinth.