Effects of intracranial stimulation on denervated nictitating membrane of the cat

¹ Departments of Anatomy and Pharmacology, Albert Einstein College of Medicine, New York City
² Department of Anatomy and Pharmacology, Albert Einstein College of Medicine, New York City

The effect of intracranial stimulation on the chronically denervated nictitating membrane of the encéphale isolé cat has been studied. After eliminating sympathoadrenal discharge, we found that the nictitating membrane responds to direct stimulation of the brain stem and certain cranial nerves through: 1) an intrinsic sensitivity to direct mechanical stimulation which develops in the smooth-muscle fibers of the nictitating membrane after chronic denervation; 2) an effect by way of the greater superficial petrosal nerve, producing retraction of the nictitating membrane from diffusion of acetylcholine onto the sensitized smooth muscle from secretomotor fibers innervating nearby orbital glands; and 3) finally, after exclusion of cranial nerve effects, one can still, under optimal conditions, obtain retraction of the nictitating membrane after stimulation of the reticular formation, an effect that is tentatively ascribed to the release of a humoral factor from some intracranial source. The bearing of these findings on previous work in which the nictitating membrane has been used as an indicator of circulating neurohumors is discussed.