EFFECTS OF CHRONICALLY ADMINISTERED L-DOPA IN NORMAL AND LESIONED CATS

¹ Laboratoires de Neurobiologie et Département d'Anatomie, Faculté de Médecine, Université Laval, Québec, Canada

The administration of a single dose of L-dopa (100 mg/kg p.o.) to cats with a lesion of the dopaminergic nigrostriatal pathway and to normal cats results in a conspicuous increase of dopamine (DA) and homovanillic acid (HVA) in the thalamus, hypothalamus and neostriatum. The maximal DA and HVA increases are associated with a significant decrease of serotonin as determined in the thalamus and hypothalamus. The administration of L-dopa (100 mg/kg p.o.) during several consecutive days to similar groups of cats results in more conspicuous HVA increases in the same tissues, and, moreover, the maximal increase of DA is reached sooner than after a single dose of L-dopa. This treatment is also associated with a greater serotonin decrease than after a single dose of L-dopa. In both experimental conditions (single dose or chronic administration of L-dopa the DA and HVA values in the intact. striata are higher than those determined in the striatum of the lesioned side where the concentrations of DA are somewhat similar to those found in the thalamus and hypothalamus. These results suggest that the administration of large amounts of L-dopa leads to the formation of DA and HVA in nervous structures which, in the absence of dopa treatment, form small amounts of DA.