Modification of the pigment screening of the frog retina following administration of neuroactive drugs

Frog retinal pigment screening and lithium

The effect of the intraperitoneal injection of lithium on the pattern of the pigment screening (PS) of the frog retina has been studied in various illumination conditions. Lithium enhances the PS pattern induced by dark and it substantially modifies the PS pattern induced by the other light conditions. The dark-induced PS pattern is very stable and might be regulated by a single factor. The PS of light-adapted frogs is easily modified by drug administration and probably depends on a variety of factors which may be affected differently by the various injected substances. The possibility that lithium, melatonin and darkness might act in the same way or on the same system which regulates the PS in dark-adaptation must not be disregarded.

Drugs and the frog retina. Effect of dopaminergic agents on the pigment screening of light- and dark-adapted frogs

This is a study, using the light and electron microscope, of the action of a dopamine agonist (apomorphine) and of a dopamine antagonist (haloperidol) on the retinal pigment screening (PS) of light- and dark-adapted frogs. Pigment screening is a phenomenon which consists of the migration of melanin granules into processes of the pigment epithelium that extend between photoreceptors, in response to changes in the conditions of illumination. In the light the pigment migrates vitreally , in the dark it aggregates sclerally . A single intravenous injection of apomorphine (0.15 mg/kg) and of haloperidol (1 mg/kg) did not induce substantial modifications in the pattern of pigment screening which was similar to that of controls both in light- and dark-adapted frogs. This suggests that dopamine is probably not directly involved in the phenomenon of pigment screening in the retina of the frog.