EFFECTS OF NOREPINEPHRINE ON [H-3] DOPAMINE RELEASE AND HORIZONTAL CELL RECEPTIVE-FIELD SIZE IN THE GOLDFISH RETINA

Norepinephrine increased the release of pre-loaded [H-3]dopamine from goldfish retinas. Pharmacological studies suggested that the norepinep hrine-induced [H-3]dopamine release was due to an exchange mechanism b etween norepinephrine and pre-loaded [H-3]dopamine. Norepinephrine als o depolarized and reduced the receptive-field size of horizontal cells in goldfish retinas. The action of norepinephrine on horizontal cells was probably not due to the release of endogeneous dopamine because t he effect of norepinephrine was not abolished in retinas in which all dopaminergic neurons had been destroyed by prior treatment with 6-hydr oxydopamine. The pharmacology of the effect of norepinephrine on horiz ontal cells suggested that it was due to an agonist action of norepine phrine acting at horizontal cell dopamine receptors. It is still uncle ar whether endogenous norepinephrine is a regulator of dopamine releas e in the fish retina. Consequently, the function of the putative norep inephrine-containing amacrine cells of the fish retina remains to be e lucidated.