Neural regulation of muscarinic receptors in chick expansor secundariorum muscle.

Abstract

We have recently observed the loss of muscarinic receptors from a smooth muscle of the chicken wing, the expansor secundariorum, during post-hatch development1. The nerve supplying the muscle has been shown to consist mainly of sympathetic fibres that, when stimulated, cause muscle contraction by the release of noradrenaline and subsequent activation of α-adrenoreceptors. Although no acetylcholine release has been detected in isolated nerve–muscle preparations2, the presence of a cholinergic input has not been clearly excluded. Kuromi and Hagihara2 observed that atropine was ineffective in blocking the nerve stimulation-induced contraction of the muscle, whereas phentolamine partly and guanethedine totally abolished the contraction. We have now examined the effect of denervation of the muscle 1 day after hatch on the binding of 3H-quinuclidinyl benzilate (3H-QNB), a radioligand for muscarinic receptors3,4. Our results indicate that the normal loss of muscarinic receptors from the expansor secundariorum is prevented by denervation. This observation is important as it demonstrates the regulation of a receptor population by a nerve supply that apparently does not release the corresponding transmitter.