ENHANCEMENT OF APOMORPHINE-INDUCED ROTATIONAL BEHAVIOR IN RATS FOLLOWING THE COMBINATION OF 6-HYDROXYDOPAMINE AND ELECTROLYTIC LESIONS IN THE SUBSTANTIA NIGRA

Electrolytic lesion in combination with 6-hydroxydopamine (6-OHDA) microinjection was produced in rat substantia nigra (SN) and the animals were observed for drug-induced rotational behaviour. Apomorphine produced rotation toward the left (contralateral) while methamphetamine produced totation toward the right (ip silateral) in rats with 6-OHDA lesion of the right SN. Both apomorphine and methamphetamine produced rotations ipsilateral to the side of the lesion in rats with unilateral electrolytic lesion of the SN. When the electrolytic lesion was placed in the right SN in an animal that had been treated with 6-OHDA (group 3), apomorphine-induced rotation toward the left was markedly suppressed. Methamphetamine-induced rotation was not affected by this treatment. When the electrolytic lesion was placed in the left SN of rats with 6-OHDA lesion of the right SN (group 4), apomorphine-induced rotation toward the left was significantly enhanced. Methamphetamine induced rotation obviously decreased. The results in group 3 indicate that electrolytic lesion may induce a dysfunction of postsynaptic factors (i.e. efferent pathways and dopamine receptors) in addition to the degeneration of the nigrostriatal dopaminergic pathway, which may indicate a difference in the direction of apomorphine-induced rotation in groups 1 and 2. The enhancement of rotation produced by apomorphine in group 4 appears to be the result of a dysfunction of the postsynaptic factors in the left SN in combination with the denervation supersensitivity to apomorphine in the right striatum. © 1979, The Japanese Pharmacological Society. All rights reserved.