Nitric oxide cyclic guanosine monophosphate pathway in the peripheral and central auditory system of the rat

The neuronal isoform of nitric oxide synthase (nNOS) and soluble guanylate cyclase (sGC) were localized in the cochlea, the cochlear nucleus (CN), and the superior olivary complex (SOC) of Fisher 344 rats. In the cochlea, nNO S was identified in spiral ganglion cells by using nicotinamide adenine din ucleotide phosphate (NADPH)-diaphorase histochemistry and in situ hybridiza tion. NADPH-diaphorase staining also was detected in blood vessels of the m odiolus. By using immunohistochemistry against cyclic guanosine monophospha te, cochlear sGC activity was localized to pericytes in the spiral ligament as well as nerve fibers innervating outer hair cells. In the lower auditor y brainstem, nNOS was localized to principal cells of the medial nucleus of the trapezoid body (MNTB) with NADPH-diapharase histochemistry and in situ hybridization. NADPH-diaphorase activity also was observed in the lateral and medial superior olive (LSO and MSG, respectively), the superior perioli vary nucleus (SPN), the ventral and lateral nuclei of the trapezoid body (V NTB and LNTB, respectively), and the ventral cochlear nucleus (VCN). Transc ripts of the beta-subunit of sGC were localized in rat brainstem by using i n situ hybridization. mRNA for sGC was expressed in neurons within the SPN, LSO, MSO, LNTB, MNTB, VNTB, and VCN. Highest levels of sGC expression were seen in the SPN. These results suggest that the NO/cGMF pathway is involve d in both the ascending and descending pathways of the auditory brainstem. J. Comp. Neurol. 404:52-63, 1999. (C) 1999 Wiley-Liss, inc.