The influence of light and dark on the catecholamine content of the retina and choroid.

Recent histochemical studies with the use of a fluorescence method to detect catecholaminecontaining neurons have uncovered a system of dopamine-containing amacrine cells as toell as a plexus of norepinephrine-containing nerve terminals in the choroid. This study examined the effect of dark and light adaptation on the catecholamine content of the posterior segment of the eye of the albino guinea pig, rabbit, and rat by quantitative and histochemical means. In the rat and rabbit, there was a significant increase in the dopamine content with light adaptation. In the guinea pig, there was an increase, but this was not statistically significant. A significant increase in the norepinephrine content was observed in the posterior segment of the guinea pig and rabbit ivith light adaptation. The increase in norepinephrine appeared to be a direct effect on the choroidal nerve terminals, since with pigmented guinea pigs the increase was not observed. Likewise, decentralization of the choroid in albino guinea pigs did not alter the changes seen with light adaptation. Histochemical studies demonstrated a consistent increase in the fluorescence of the amacrine cells of the rabbit and guinea pig with light adaptation. It was not possible to show consistent changes in the rat.