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 neuromuscular 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 exogenous, alpha,beta-methylene adenosine 5'-triphosphate (ATP), noradrenaline, vasoactive intestinal polypeptide (VIP) and carbachol were examined. Taking the response to a single pulse of electrical field stimulation as the index of a developed neuromuscular junction, it was apparent that the non-adrenergic inhibitory system arose before, and matured more quickly than, the cholinergic system. The inhibitory system was present by 8 weeks of gestation in some fetuses, but, in contrast, excitatory cholinergic transmission was not seen until birth. As evidenced by responses to carbachol, alpha,beta-methylene ATP and VIP, cholinergic, purinergic and VIP receptors were present on the smooth muscle at the earliest ages studied. No changes in sensitivity to these agents were noted throughout development, although in adults the level of the maximum responses increased.