DEVELOPMENT OF CHOLINERGIC AND INHIBITORY NONADRENERGIC NONCHOLINERGIC RESPONSES IN THE RAT GASTRIC FUNDUS

1 Cholinergic contractions and inhibitory non-adrenergic non-cholinerg ic (NANC) relaxations were studied in longitudinal muscle strips of th e gastric fundus of 2, 4 and 8 week old rats. 2 Contractions induced b y electrical stimulation of the cholinergic neurones and by administra tion of acetylcholine decreased during development. The potentiating e ffect of physostigmine was similar in the 3 age groups. 3 Short train stimulation in NANC conditions induced fast relaxations, which were mo re pronounced in 4 and 8 week than in 2 week old rats. These relaxatio ns were almost completely inhibited by N-G-nitro-L-arginine methyl est er (L-NAME) in the 3 age groups. The nitric oxide-induced relaxations did not change during development. 4 Sustained electrical stimulation in NANC conditions induced an initial relaxation, which was almost tot ally blocked by L-NAME, followed by an almost complete recovery of ton e at lower frequencies of stimulation. At higher frequencies of stimul ation, the recovery of tone was incomplete or absent. This sustained r elaxation was only partially reduced by L-NAME and almost abolished by L-NAME plus alpha-chymotrypsin. The initial relaxations increased dur ing development, while the sustained relaxations remained similar duri ng this period. Vasoactive intestinal polypeptide-induced relaxations were also similar in the 3 age groups. 5 These results show that the s ensitivity of the gastric fundus to acetylcholine decreases from 2 wee ks to 8 weeks postnatally, while the importance of the nitrergic inner vation increases during this period.