AN ELECTROPHYSIOLOGICAL STUDY OF DEVELOPMENTAL-CHANGES IN THE INNERVATION OF THE GUINEA-PIG TAENIA-COLI

A sucrose-gap technique was used to study the development of neuromusc ular transmission in the taenia coli of fetal, 1- to 2-day-old, 3- to 4-week-old and 3-month-old guinea-pigs. In addition, the effects of ex ogenous, alpha,beta-methylene adenosine 5'-triphosphate (ATP), noradre naline, vasoactive intestinal polypeptide (VIP) and carbachol were exa mined. Taking the response to a single pulse of electrical field stimu lation as the index of a developed neuromuscular junction, it was appa rent that the non-adrenergic inhibitory system arose before, and matur ed more quickly than, the cholinergic system. The inhibitory system wa s present by 8 weeks of gestation in some fetuses, but, in contrast, e xcitatory cholinergic transmission was not seen until birth. As eviden ced by responses to carbachol, alpha,beta-methylene ATP and VIP, choli nergic, purinergic and VIP receptors were present on the smooth muscle at the earliest ages studied. No changes in sensitivity to these agen ts were noted throughout development, although in adults the level of the maximum responses increased.