The influence of unilateral 6-OH-dopamine lesions of the substantia nigra in the absence of the telencephalon.

Rats were injected unilaterally into the rostral substantia nigra pars compacta with 8 micron of 6-OHDA. Those animals that conformed to be behavioral criteria for an effective nigrostriatal dopamine lesion by turning ipsilaterally to the injected side upon IP amphetamine, and contralaterally upon apomorphine injection were bilaterally detelencephalized (neocrotex, hippocampus, striatum, septum, amygdaloid complex were removed). Most detelencephalized animals exhibited spontaneous turning to the contralateral side, i.e. no longer behaved like 6-OHDA-lesioned rats, but instead, acted like animals with nigral kainic acid or electrolytic lesions. Amphetamine (2-3 mg/kg) increased general activity but no longer influenced turning. Apomorphine in doses of 2-3 mg/kg completely suppressed all motility. In small doses (0.1-0.2 mg/kg) it reversed the spontaneous contraversive turning. This effect could be blocked by haloperidol (0.1 mg/kg) pretreatment. High doses of haloperidol (5.0-7.5 mg/kg) reversed the direction of circling from contraversive to ipsiversive. Arecoline (10-12 mg/kg) induced tremor as in normal animals. Atropine (50-100 mg/kg) did not affect turning, but increased activity level in the thalamic rats.