Effect of strychnine and of bicuculline on dopamine synthesis in retinas of dark-maintained rats

The intravitreal administration of strychnine produced a significant elevation of dopamine (DA) synthesis in the retinas of dark-adapted rats. Strychnine had no antagonistic effect on the ability of muscimol to suppress the normal increase in retinal DA synthesis observed after exposure of rats to light. This latter observation suggests that strychnine is not merely acting in a non-selective fashion to suppress the inhibitory GABAergic tone exerted on the DA neurons in darkness. These results suggest that there may be a direct or indirect strychnine-sensitive input to the retinal DA neurons in the dark. This input may not be glycinergic, however, as even high dosages of glycine did not suppress the light-mediated enhancement of DA synthesis in the retina.