ABSENCE OF NEUROTOXICITY OF CHRONIC L-DOPA IN 6-HYDROXYDOPAMINE-LESIONED RATS

WE investigated the effects of 6 months' oral treatment with L-dihydro xy-phenylalanine (L-DOPA)/carbidopa on the remaining dopaminergic neur ones of the substantia nigra pars compacta (SNC) and the ventral tegme ntal area (VTA) of rats with moderate or severe 6-hydroxydopamine (6-O HDA)-induced lesions and sham-operated animals. Using a radioimmunohis tochemical method we counted tyrosine hydroxylase (TH)-radioimmunoreac tive cells in the SNC and the VTA in emulsion-coated sections and meas ured the remaining surface area of both structures on autoradiograms. The sole difference observed was a significant increase of the remaini ng surface area of TH radioimmunolabelling in the SNC of moderately le sioned rats treated with L-DOPA/carbidopa compared with the untreated animals, while the rest of the parameters recorded, in both structures and groups of animals, were unchanged. This suggest that in vivo, thi s treatment is not toxic either to healthy dopaminergic neurones of th e ventral mesencephalon or to those surviving after a 6-OHDA lesion.