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, nNOS was identified in spiral ganglion cells by using nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry and in situ hybridization. NADPH-diaphorase staining also was detected in blood vessels of the modiolus. By using immunohistochemistry against cyclic guanosine monophosphate, cochlear sGC activity was localized to pericytes in the spiral ligament as well as nerve fibers innervating outer hair cells. In the lower auditory brainstem, nNOS was localized to principal cells of the medial nucleus of the trapezoid body (MNTB) with NADPH-diaphorase histochemistry and in situ hybridization. NADPH-diaphorase activity also was observed in the lateral and medial superior olive (LSO and MSO, respectively), the superior periolivary nucleus (SPN), the ventral and lateral nuclei of the trapezoid body (VNTB and LNTB, respectively), and the ventral cochlear nucleus (VCN). Transcripts of the beta-subunit of sGC were localized in rat brainstem by using in 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/cGMP pathway is involved in both the ascending and descending pathways of the auditory brainstem.