Development of substance P- and vasoactive intestinal polypeptide-containing neurones in the rat stomach

The ontogeny and distribution of nerve fibres containing immunoreactive substance P (SP) and vasoactive intestinal polypeptide (VIP) were studied in the fetal and neonatal rat stomach, using immunohistochemistry and radioimmunoassay. Dimly fluorescent SP- and VIP-immunoreactive fibres began to appear in the myenteric plexus from embryonic day (ED) 17 and 18, respectively, and then in the circular muscle layer from ED 19. VIP-immunoreactive fibres increased in the mucosal layer after birth but not SP-immunoreactive fibres. Both immunoreactive fibres seemed to arise from intrinsic neurones in the stomach. SP and VIP were detectable from ED 15 and 18 in the rat stomach, respectively, by radioimmunoassay. The concentration of SP in the stomach increased until ED 18, but it tended to decrease somewhat thereafter. The concentration of VIP in the stomach increased throughout the period from ED 18 to 7 days post-natal. The results suggest that the development of VIP-containing neurones lags about 2 days behind that of SP-containing neurones in the rat stomach.