The Development and Function of The Efferent Fibers in Rat Cochlea

Abstract

It is known that the efferent nerve fibers in the cochlea are either sympathetic or cholinergic and eachfiber distributes to the vessel wall of the modiolus, osseous spiral lamina and the outer hair cells, respectively.The cholinergic fibers innervates to the outer hair cells can modulate the active mechanism in the cochlea.The function of the sympathetic system remains unclear.In this study, we compared the distribution of thecholinergic terminal and noradrenergic fibers between those in the neonatal and adult rat cochlea.Mosttyrosine hydroxylase (TH) positive fibers in the cochlea disappeared after superior cervical ganglionectomy.VAT (vesicular acetylcholine transporter) immunoreaction could be found at the outer hair cells whichwere identified as 3 rows.Compared with the neonatal rat, the number of TH-immunoreactive fibers in theadult rat decreased in the cochlea, especially in the modiolus.No difference in VAT reaction was foundbetween the neonatal and adult rats.Moreover, to elucidate one of functions of the sympathetic system inthe cochlea after ipsilateral superior cervical ganglionectomy at neonatal stage, we examined the hearingchanges of both sides using the auditory brainstem response (ABR).The latency of wave I in the sympathectomyside was longer than that in the control side.We speculated that development is different foreach efferent fiber in the cochlea.Furthermore, fibers from the superior cervical ganglion influence thedevelopment of hearing.