C-type natriuretic peptide-like immunoreactivity in the rat inner ear

C-type natriuretic peptide (CNP) is a member of the atrial natriuretic pept ide family (ANP family). The family also includes ANP and brain natriuretic peptide (BNP). These peptides regulate the homeostasis of body fluid and b lood pressure as a neuropeptide in the central nervous system as well as a cardiac hormone in the periphery. We have recently reported the expression of CNP mRNA in the inner ear. To assess the possible physiological role of CNP in the inner ear, we investigated the localization of CNP peptide in th e rat inner ear by immunohistochemistry at the light and electron microscop ic level. CNP-like immunoreactivity was widely distributed in the secretory and the neuronal portion of the inner ear. i.e. the spiral ligament, the d ark cell region of the utriculus, the epithelium of the endolymphatic sac, the spiral ganglion cells and the vestibular ganglion cells. The results su ggest that CNP may play a role in the homeostasis of the perilymph and endo lymph and may also influence nerve activities in the inner ear. (C) 2000 El sevier Science B.V. All rights reserved.