Evidence for increased nitric oxide production in the auditory brain stem of the aged dwarf hamster ( Phodopus sungorus): an NADPH-diaphorase histochemical study

Age-related changes of the auditory system such as presbyacusis are believed to be due, at least in part, to alterations of central structures. The superior olivary complex (SOC), a group of interrelated brain stem nuclei, projects to a variety of neuronal structures including the cochlea and the inferior colliculus (IC). The soluble gas nitric oxide (NO), believed to function as a neuroactive substance within the SOC and cochlea, is thought to be involved in ageing processes. Since it is unknown whether NO-production is altered in the ageing auditory system, the present study was conducted to investigate whether the number of NO-producing cells in the SOC is changed with increasing age. The histochemical detection of NADPH-diaphorase activity (NADPH-d), a marker for neurons containing NOS, was utilized to investigate the numbers of NO-producing cells in the SOC of adult and senile Djungarian dwarf hamsters ( Phodopus sungorus). Our results demonstrate that the number of stained neurons was almost doubled in the SOC of senile hamsters. The most distinct changes were observed in the medial nucleus of the trapezoid body. In contrast, NO-producing preganglionic sympathetic neurons of the spinal intermediolateral nucleus, which was studied for comparison, did not exhibit significant differences between adult and senile animals. It is concluded that the increase of NO-production in the ageing auditory brain stem, as revealed by our data, may be related to hearing impairments with increasing age.