Development of non-cholinergic, non-adrenergic excitatory and inhibitory responses to intramural nerve stimulation in rat stomach.

1. The onset and development of functional innervation of intramural neurones were examined by transmural nerve stimulation in circular muscle strips isolated from the rat stomach during the period from embryonic day (ED) 15 to 7-days postnatal. 2. At ED 15, transmural stimulation elicited an atropine-sensitive contraction in about half of the preparations. From ED 16, it caused a frequency-dependent contraction in all preparations. Physostigmine significantly potentiated the amplitude of the nerve-mediated contraction until ED 18. 3. Atropine inhibited but failed to abolish the contractile response to nerve stimulation in all preparations from ED 16. 4. During the contraction induced by carbamylcholine (CCh), transmural stimulation caused a biphasic response consisting of a contraction followed by a relaxation at ED 18 and ED 19, but caused a triphasic response consisting of a rapid relaxation followed by the biphasic response after birth. 5. CCh and substance P (SP) elicited contractions at ED 15 and vasoactive intestinal polypeptide (VIP) caused a relaxation at ED 16. The sensitivity to CCh and VIP increased with development but that to SP did not change. 6. The results suggest that functional intramural cholinergic and non-cholinergic excitatory innervations in the rat stomach are established almost simultaneously by ED 16, and the onset of functional intramural non-adrenergic inhibitory innervation lags about 2 days behind that of functional excitatory innervations.