Development of innervation in cat gastrointestinal sphincters during the postnatal period. (Functional studies)

The development of function in the intramural nerves was investigated by evaluating the mechanical responses of the smooth muscle of cat gastrointestinal sphincters to transmural electrical stimulation (2-20 Hz, 0.5 msec, supramaximal intensity for 20 sec) between 1 and 60 days postnatal. The intramural nervous system of the gastrointestinal sphincters was found to develop functionally in a cranio-caudal sequence. The cholinergic innervation in the lower esophageal sphincter (LES) was well developed in the first postnatal days. The development of the non-cholinergic, non-adrenergic innervation, however, proceeded further. An age-determined increase in the amplitude of the adrenoblocker-resistant primary relaxation of LES evoked by switching on the electrical stimulation, was established. The cholinergic innervation in the pyloric sphincter (PS) and ileocecal sphincter (ICS) was developed in the first postnatal days. The non-cholinergic, non-adrenergic innervation appeared in PS between 10- and 15-days postnatal and in ICS between 15- and 60-days postnatal. Noradrenaline (1 mumol) elicited responses typical of adult cats as early as the first postnatal days: contraction in LES and relaxation in PS. In ICS it did not evoke the typical response, contraction, until 15 days after birth.