Pineal response to light: mediation by the accessory optic system in the monkey.

Abstract

THE activity of the melatonin-forming enzyme in the rat pineal gland, hydroxyindole-O-methyl-transferase (HIOMT), is high in animals kept in constant darkness and low when they are kept in constant light1. The response to light depends on the integrity of one component of the central retinal projections, the accessory optic system. Rats subjected to bilateral section of the inferior accessory optic tracts do not show a pineal HIOMT response to light although their visual behaviour is otherwise normal2,3. In contrast, animals with bilateral transection of the primary optic tracts behave as though they were blind but exhibit a normal pineal response to light2,3. There seem to be two separate functions carried out by the central retinal projections in the rat; one projection, the primary optic tracts, maintains visually guided behaviour, and the other, the accessory optic system, shares in the control of a pineal response to light.