The consequences of loss followed by recovery of noradrenergic nerve function on muscarinic receptors in the chick expansor secundariorum muscle.

The effects of chemical sympathectomy with 6-hydroxydopamine on the response of the expansor secundariorum muscle to noradrenergic nerve stimulation, noradrenaline and acetylcholine have been investigated. Expansor muscles from 60 day old chicks were sensitive to noradrenergic nerve stimulation and exogenous noradrenaline but virtually unresponsive to acetylcholine. Chemical sympathectomy with 6-hydroxydopamine caused loss of function of noradrenergic nerves of the expansor muscle, induced supersensitivity to exogenous noradrenaline and gradually increased the response of the expansor muscle to acetylcholine. As the patency of noradrenergic nerves reappeared there was a decline in the extent of supersensitivity to noradrenaline and the response to acetylcholine gradually declined. The time courses of these changes differed, indicating that the mechanisms responsible for changes in response to noradrenaline and acetycholine are different.