THE REACTION OF THE ISOLATED CAT IRIS TO SEROTONIN

¹ Laboratory of Neurophysiology, Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts

The effects of serotonin (5-HT) and a number of other substances were tested on the isolated ntact cat iris and on the isolated iris sphincter and dilator muscle. The reaction of the pupillary opening on the intact iris was recorded by means of a photoelectric technique. The reaction of the isolated muscles was measured by means of ("isometric") mechanoelectric transducers.

The isolated iris reacted to serotonin with miosis. Concentrations of 0.3 µg per ml of Ringer solution were effective. The pupillary constriction and ensuing dilation lasted up to 15 and more minutes. Two-peaked patterns occurred often with larger doses. Serotonin treatment desensitized the preparation to later injections of 5-HT. The isolated constrictor muscle reacted to 5-HT with contraction; the dilator strip, with relaxation often followed by contraction when larger doses were used.

Epinephrine and norepinephrine induced dilation of the pupil. Norepinephrine led to contraction of the dilator muscle. Atropine was of small influence upon the serotonin reactions but in moderate doses eliminated the acetylcholine effect upon the intact iris and the constrictor muscle completely.