REFLEX PUPILLODILATOR MECHANISMS AN EXPERIMENTAL ANALYSIS

Abstract

In expts. carried out on cats and dogs, reflex dilatation of the pupil elicited by peripheral pain producing stimulation was not altered by sympathetic denervation of the eye, but was abolished by section of the oculomotor nerve or extirpation of the ciliary ganglion. This reaction, therefore, was mediated through the parasympathetic nerves. Following transection of the spinal cord in the lower cervical region, strong stimulation of the sciatic nerve resulted in slight enlargement of the pupil in some animals under nembutal anesthesia but not in unanesthetized animals. The excitability of the ciliospinal center apparently was increased by the action of the anesthetic agent. While the pupil was dilated due to atropine depression of the cholinergic innervation of the iris, moderate stimulation of the oculomotor nerve elicited further pupillary dilatation. While the adrenergic nerves were depressed due to the intravenous admn. of ergo-toxine, peripheral stimulation elicited only slight dilatation of the pupil. These results support the assumption that the pupillodilator reaction mediated through the mesencephalic center is actively integrated and controlled. The inhibition of the circular muscle is brought about, not by inhibition of the parasympathetic center, but by activation of this center which results in the discharge of efferent nerve impulses through adrenergic fibers arising in the ciliary ganglion.