Nitric oxide synthase in the auditory brain stem.

: The auditory superior olivary complex (SOC), a group of inter-related brain stem nuclei, sends efferents to a variety of neuronal structures including the cochlea and the inferior colliculus. The present study conducted in rats and hamsters sought to investigate whether the neuroactive substance nitric oxide (NO) is produced in the rodent SOC. Immunohisto- and cytochemistry of the NO-synthesizing enzyme neuronal NO-synthase (nNOS), and histochemistry (NADPH-diaphorase activity of nNOS) was used. Perikarya stained by either method were found in the medial nucleus of the trapezoid body and in periolivary nuclei projecting to the cochlea, while terminals were observed mainly in the lateral superior olivary nucleus and in the superior paraolivary nucleus. These data demonstrate the existence of nNOS in the rodent SOC and provide evidence that nitric oxide acts as neuroactive substance in the auditory brain stem and the organ of Corti.