Supersensitivity induced by trigeminal (substance P-ergic) nerve denervation in the rabbit iris sphincter muscle

Abstract

In the rabbit iris sphincter muscle, electrical transmural stimulation produced a substance P-ergic response, in addition to a cholinergic one (Jpn. J. Pharmacol, 31. 1071-1079, 1981). This substance P-ergic response was abolished after trigeminal nerve section, suggesting that the iris sphincter muscle is innervated by the trigeminal, substance P-ergic nerve (Life Sci. 31. 369-375, 1982). In the present study, we examined the effects of trigeminal nerve denervation on the responses of rabbit iris sphincter muscle. For the denervation, the left ophthalmic nerve was cut at the intracranial, peripheral site of the trigeminal ganglion. Five to forty-one days later, the sphincter muscles were isolated from the left and right eyes and were used as the denervated and innervated preparations, respectively. As compared with the innervated preparations, the denervated preparations produced a supersensitivity in response to exogenously applied substance P and carbachol. This supersensitivity was characterized as both an increase in maximal response and a decrease in EC50 and their extents developed with increasing days after the denervation. In contrast, the response to 10-20mM KCl was markedly attenuated by the denervation. The denervated muscle was about twice of the innervated muscle in length and extended well in response to stretch. These results suggest that physiological and physical properties of the rabbit iris sphincter muscle are influenced neurotrophically by the trigeminal, probably substance P-ergic, nerve.