EFFECTS OF UNILATERAL VAGOTOMY ON NITRIC-OXIDE SYNTHASE AND HISTAMINEH-3 RECEPTORS IN THE RAT DORSAL VAGAL COMPLEX

Nitric oxide synthase (NOS) and histamine H-3 receptors are both marke dly increased by neuronal injuries. To examine whether peripheral axot omy produced differential changes in NOS and H-3 receptors, both NOS a nd H-3 receptors were measured in the dorsal vagal complex after unila teral vagotomy. The presence of NOS-positive neurons was examined usin g both NADPH-diaphorase histochemistry and neuronal NOS-immunohistoche mistry in rats vagotomized at the mid-cervical level. NADPH-diaphorase activity and NOS-immunoreactivity were markedly enhanced on the dorsa l motor nucleus of the vagus (DMX) and in the ambiguus nucleus at the denervated side. Intraperitoneal injection of NOS inhibitors, N-omega- nitro-L-arginine (10 mg/kg) or dexamethasone (0.5 mg/kg) attenuated th e increase in NADPH-diaphorase activity. Glial fibrillary acidic prote in (GFAP) was similarly induced 2 weeks after vagotomy in the vagal co mplex and surrounding area. Histamine H-3 receptors in the vagal compl ex were visualized with [H-3]N-alpha-methylhistamine. The ligand-label ed H-3 receptors were mainly located at the nucleus of the solitary tr act (NST). The densities of H-3 receptors did not change in the NST af ter unilateral vagotomy. These results suggest that peripheral axotomy such as mid-cervical vagotomy preferentially induces NOS in damaged n eurons without affecting the level of H-3 receptors.