Effects of norepinephrine on [3H]dopamine release and horizontal cell receptive-field size in the goldfish retina
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Norepinephrine increased the release of pre-loaded [3H]dopamine from goldfish retinas. Pharmacological studies suggested that the norepinephrine-induced [3H]dopamine release was due to an exchange mechanism between norepinephrine and pre-loaded [3H]dopamine. Norepinephrine also 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 endogenous dopamine because the effect of norepinephrine was not abolished in retinas in which all dopaminergic neurons had been destroyed by prior treatment with 6-hydroxydopamine. The pharmacology of the effect of norepinephrine on horizontal cells suggested that it was due to an agonist action of norepinephrine acting at horizontal cell dopamine receptors. It is still unclear whether endogenous norepinephrine is a regulator of dopamine release in the fish retina. Consequently, the function of the putative norepinephrine-containing amacrine cells of the fish retina remains to be elucidated.
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