| Abstrakt: |
Frog monocular optokinetic nystagmus (OKN) displays a directional asymmetry, reacting only to stimulations in the temporal-nasal (TN) direction. The nasal-temporal (NT) component is almost absent. The systemic or intrapretectal injection of Piribedil, a D2 dopamine agonist, provokes the appearance of a NT component suppressing the monocular OKN asymmetry. Conversely, dopamine or haloperidol (a dopamine antagonist, acting mainly on D2 receptors) have no effect upon the monocular OKN unidirectionality. The monocular OKN NT component still appears after administration of Piribedil even if this injection is preceded by administration of haloperidol which blocks the dopaminergic D2 receptors. Moreover administration of atropine (a cholinergic muscarinic antagonist) following that of Piribedil suppresses the NT component; when injected before Piribedil, atropine prevents the appearance of the NT component. These results suggest that in our experiments, Piribedil binds with muscarinic receptors. |
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