TOXIC EFFECTS OF L-DOPA ON MESENCEPHALIC CELL-CULTURES - PROTECTION WITH ANTIOXIDANTS

The toxicity of L-3,4-dihydroxyphenylalanine (L-DOPA) was studied in n euronal cultures from rat mesencephalon. The survival and function of DA neurons were assessed by the number of tyrosine hydroxylase-positiv e (TH+) cells and H-3-DA uptake and those non-DA neurons by the exclus ion of Trypan blue and the high-affinity H-3-GABA uptake. L-DOPA was t oxic for both DA and non-DA neurons. DA neurons were more severely aff ected than non-DA neurons after short periods of treatment and with ex posure to a low dose of L-DOPA (25 vs. 100 mu M) and less selectively affected after 1 or 2 days of treatment. After incubation with L-DOPA, a disruption of the neuritic network and an overall deterioration wer e observed, more evident for TH+ cells in the whole culture. Auto-oxid ation to quinones is responsible in part for L-DOPA toxicity in non-DA neurons since the levels of quinones correlated well with the severit y of cell death in the cultures. The damage of DA neurons took place b efore the rising of quinones, suggesting that quinones are not essenti al in L-DOPA toxicity for DA neurons. Antioxidants, such as ascorbic a cid and sodium metabisulfite, completely prevented L-DOPA-induced quin one formation as well as the death of non-DA neurons. In contrast, the y could only partially prevent the damage produced by L-DOPA in DA neu rons. Mazindol, a selective inhibitor of DA uptake, protected TH+ cell s from L-DOPA.