DIFFERENT EFFECTS OF DOPAMINE AND PIRIBEDIL (A DOPAMINE D-2 AGONIST) ON FROG MONOCULAR OPTOKINETIC NYSTAGMUS ASYMMETRY

Frog monocular optokinetic nystagmus (OKN) displays a directional asym metry, reacting only to stimulations in the temporal-nasal (T-N) direc tion, The nasal-temporal (N-T) component is almost absent, The systemi c or intrapretectal injection of Piribedil, a D-2, dopamine agonist, p rovokes the appearance of a N-T component suppressing the monocular OK N asymmetry. Conversely, dopamine or haloperidol (a dopamine antagonis t, acting mainly on D-2 receptors) have no effect upon the monocular O KN unidirectionality. The monocular OKN N-T component still appears af ter administration of Piribedil even if this injection is preceded by administration of haloperidol which blocks the dopaminergic D-2 recept ors, Moreover administration of atropine (a cholinergic muscarinic ant agonist) following that of Piribedil suppresses the N-T component; whe n injected before Piribedil, atropine prevents the appearance of the N -T component. These results suggest that in our experiments, Piribedil binds with muscarinic receptors.