Reciprocal Inhibition During One Type of Pupillary Dilatation.

Abstract

In this investigation cats and rabbits under light ether anesthesia were used. The cervical sympathetic nerves were isolated on both sides of the neck, and the sciatic nerves were so prepared that their central ends could be stimulated with a tetanizing current. An attempt was made to keep the degree of anesthesia, as well as the intensity of the illumination, constant.

One sciatic nerve was stimulated and a dilatation of both pupils was obtained. The cervical sympathetic on one side of the neck was now sectioned and the central end of the sciatic stimulated with the same strength of current. A bilateral pupillary dilatation was again obtained, but the extent of dilatation seen in the eye, which had its cervical sympathetic cut, was less than that seen in the normal eye. In some animals a 1% solution of pilocarpine was instilled into the partially denervated eye. After the drug produced its maximum myosis the sciatic was stimulated as well as the peripheral (head end) of the cervical sympathetic. In the pilocarpinized, partially denervated, eye no effect was obtained from stimulation of the sciatic nerve, while stimulation of the peripheral end of the cervical sympathetic produced a maximum mydriasis.

In other animals the pilocarpine instillation was omitted, and 1% atropine substituted in its stead. In those animals which had received pilocarpine the atropine was later administered. In both sets the results were identical. When the atropine produces its maximum effects by paralyzing the endings of the oculomotor fibres, we can say the pupil is in a position of rest, that is, both sets of nerves are “sectioned”, one by drugs and the other anatomically, and the muscles assume their position of rest. Stimulation of the sciatic nerve now produced the usual dilatation of the normal eye, but the pupil of the completely denervated eye remained entirely quiet and unaffected. The size of the normal dilated pupil exceeded that of the opposite one. The remaining cervical sympathetic was now cut and the pupil became smaller than the atropinized one. Stimulation of the sciatic nerve now produced a dilatation on that side, but the size of the dilated pupil did not equal that of the atropinized one.