EFFECTS OF SUBSTANCE-P AND DISTRIBUTION OF SUBSTANCE P-LIKE IMMUNOREACTIVITY IN NERVES SUPPLYING THE STOMACH OF THE COD, GADUS-MORHUA

The innervation of the cod stomach by neurons showing substance P-like immunoreactivity (SPLI), and the effect and mechanism of action of su bstance P (SP) on the vascularly perfused cod stomach and on isolated muscle strip preparations from the pyloric sphincter have been investi gated. Infusion of SP produced a contraction of the stomach wall, whic h could not be blocked by tetrodotoxin, atropine or methysergide, indi cating a direct effect on the stomach smooth muscle. Similarly, the co ntraction produced by SP on preparations from the pyloric sphincter wa s unaffected by tetrodotoxin. Nerves showing SPLI were frequent in the myenteric plexus of the whole stomach, and in the submucosa and mucos a of the pyloric part of the stomach. SPLI was also observed in fibres in the intestinal branch of the vagus and occasionally in the splanch nic nerves. Ligation of the nerves showed an accumulation of SPLI abov e as well as below the ligature, being more prominent proximal to the ligature in the vagus and distal to the ligature in the splanchnic ner ve. In the vagus nerve, descending and ascending SPLI-fibres were seen surrounding non-reactive cell bodies. No reduction in intensity of th e immunoreaction of the neurons in the stomach wall was observed after ligation or sectioning of the vagosympathetic trunk or the splanchnic nerves, nor were SP-levels measured by radioimmunoassay reduced. Afte r denervation of vagal branches close to the stomach wall an insignifi cant decrease of immunoreactivity was observed in the myenteric plexus . Capsaicin treatment had no conclusive effect on the distribution of SPLI. It is concluded that the innervation showing SPLI may be of intr insic as well as extrinsic origin, with pathways in both vagal and spl anchnic branches. Only a direct effect of SP on the smooth muscle coul d be demonstrated.