TRAINED AND AMPHETAMINE-INDUCED CIRCLING BEHAVIOR IN LESIONED, TRANSPLANTED RATS

Rats were trained to turn for water reinforcement and then were given unilateral 6-hydroxydopamine lesions. After lesion, rats showed defici ts in trained turning both contra- and ipsilateral to the side of the lesion, with contralateral turning more severely impaired. The lesione d rats were then transplanted with fetal mesencephalic dopamine tissue into striatum. A control group of lesioned rats were sham transplante d. Four weeks after transplant, 1.5 mg/kg D-amphetamine challenge inje ctions were used to test the functioning of the transplants. In the co ntrol rats, D-amphetamine induced ipsilateral turning; in transplanted rats, D-amphetamine slowed the rate of ipsilateral turning or reverse d the direction of amphetamine-induced rotation. Only rats which rever sed their . amphetamine-induced turn direction after transplant were u sed for the rest of the experiment. Trained turning was assessed at 4, 8, 12 and 16 weeks post transplant. Transplants did not improve learn ed performance at any time post transplant. When D-amphetamine was adm inistered in conjunction with the trained turning sessions, a low dose (0.12 mg/kg) enhanced contralateral trained turn rates, without affec ting ipsilateral turn rates. Higher doses of amphetamine reduced ipsil ateral turn rate in the transplanted animals. The results of this stud y suggest that transplants alone do not reinstate performance of condi tioned rotation.