[Dopamine sensitivity of brain-induced behavior after repeated administration of dopamine agonists and antagonists]

Comparative investigations were carried out on dopamine sensitivity, as judged by the rotational behavior of rats, of different nuclear areas of the central nervous system following repeated application of dopaminergic agonists, or the dopamine antagonist, haloperidol. In the mesolimbic area and in the Nucleus caudatoputamen, repeated pretreatment with amphetamine alone or in combination with another agonist did not result in a change of sensitivity to dopamine. In contrast, dopamine sensitivity of these target areas increased strongly by repeated pretreatment with haloperidol. Pretreatment with dopaminergic agonists distinctly increased the rotation intensity following dopamine injection into the Globus pallidus and Substantia nigra, whereas haloperidole pretreatment reversed the rotational direction after pallidally injected dopamine, and left unaffected the sensitivity of the Substantia nigra. Thus, repeated treatment with dopaminergic agonists produces different patterns of sensibilization. This does lend support to the hypothesis that behavioral facilitation and dopaminergic supersensitivity are mediated differently.