SPONTANEOUS FUNCTIONAL RECOVERY FROM PARKINSONISM IS NOT DUE TO REINNERVATION OF THE DORSAL STRIATUM BY RESIDUAL DOPAMINERGIC-NEURONS

Cats exposed to MPTP experience severe motor deficits that spontaneously recover after 4-6 weeks. This recovery occurs despite a persistent deficit (approximately 95%) in dorsal striatal DA levels. To determine whether residual DA neurons that previously did not innervate the dorsal caudate nucleus (CD) have innervated this area in recovered MPTP-treated animals, HRP was injected into the dorsal lateral and dorsal medial CD and the locations of retrogradely labeled neurons in Ventral mesencephalon were mapped in normal and recovered MPTP-treated cats. Tyrosine hydroxylase (TH) positive cells were also counted in ventral mesencephalic DA-containing cell groups in normal, symptomatic, and recovered MPTP-treated cats. Results showed no difference in the pattern of HRP labeling in normal and recovered cats except for the loss of labeled substantia-nigra pars compacta (SNc) cells in MPTP-treated cats. Cells counts revealed no significant difference in the degree of TH-positive cell loss in all ventral mesencephalic areas studied in both symptomatic and recovered cats. The results suggest that spontaneous recovered of gross motor function in MPTP-treated cats in most likely no dependent upon reinnervation of the dorsal striatum from residual DAergic neurons.