ARE RETINAL OR MESENCEPHALIC DOPAMINERGIC SYSTEMS INVOLVED IN MONOCULAR OPTOKINETIC NYSTAGMUS ASYMMETRY IN FROG

Tn monocular vision, frogs display a unidirectional optokinetic horizo ntal nystagmus (H-OKN) reacting only to temporal-nasal (T-N) stimulati on. The N-T component is almost absent. The analysis of search coil re cordings after administration of dopamine into the viewing eye, the oc cluded eye or directly into the pretectum, hardly modifies the H-OKN t riggered by the viewing eye irrespective of the concentration used. Co nversely, administration of Piribedil, a strong D2 dopamine agonist, p rovokes the appearance of a N-T component, suppressing the monocular H -OKN asymmetry, whether the drug is injected by intravitreal or intrap retectal route. It is suggested that Piribedil could also bind with re ceptors other than dopamine's.