Development of sympathetic nerve--muscle transmission in chick.

The development of sympathetic nerve--muscle transmission was investigated pharmacologically by using the nerve-expansor secundariorum muscle preparation of 2- to 35-day-old chicks. The nerve-induced muscle contraction was not affected by atropine and neostigmine after hatch but was slightly depressed by phentolamine and completely depressed by guanethidine. Since the responsiveness of the muscle to some adrenomimetic drugs remained constant after hatch, adrenergic receptor function does not change during development. The nerve-induced muscle response was scarcely influenced by cocaine or reserpine in neonatal chick while it was potentiated by cocaine and changed by reserpine in mature chicks. These results suggest that cocaine- and reserpine-sensitive mechanisms gradually develop in sympathetic nerve function after hatch. The presence of a potentiating effect of cocaine on the nerve-induced muscle response in dimethylphenylpiperazinium-treated neonatal chick suggests that the development of sympathetic nerve function is regulated by nerve activity itself.