Transient improvement of amphetamine-induced rotational behavior by PC12 cell grafts: studies with microdialysis

The effects of striatal transplantation of PC12 cells on amphetamine-induced rotational behavior and monoamine levels were examined in rats with unilateral 6-hydroxydopamine (6-OHDA) lesions in the nigrostriatal pathway. A total of 9 × 104 or 9 × 105 cells of PC12 was implanted into 3 sites in the striatum and changes in amphetamine (3 mg/kg, i.p.)-induced rotational behavior were observed for 8 weeks. Two weeks after transplantation, a significant reduction in rotation was observed. However, this improvement disappeared after 3 weeks. Three of 7 rats implanted with 9 × 104 cells and 6 of 7 rats with 9 × 105 cells died between 3 and 4 weeks after transplantation. In 6-OHDA-injected control rats, the levels of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in brain dialysates were profoundly reduced to between 0 and 11% of normal rats, while the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) level remained unchanged. These reductions in DA and its metabolites did not recover at 2 or 8 weeks after the transplantation of 9 × 104 PC12 cells. 5-HIAA was reduced at 2 weeks and recovered to nearly control levels at 8 weeks. Histologically, PC12 cells proliferated to form a large tumor mass at 2 weeks. There were almost no processes growing from the aggregated PC12 cells into the host tissue. These results indicate that PC12 grafts do not release detectable quantities of DA into the deafferented striatum, and suggest that the transient improvements in rotational behavior may be due to a non-specific suppression in neuronal function induced by the growing tumor mass.