Overactive dopaminergic neurons in the brain are thought to play an important role in the etiology of schizophrenia. It has been hypothesized that prolonged exposure of catecholamine neurons to excessive levels of dopamine or the oxidative metabolites of dopamine may produce neuronal damage, cell death, and be partially responsible for some of the negative symptoms of schizophrenia. Catecholamines have been shown to be neurotoxic to norepinephrine and dopamine neurons in primary culture (J Neurosci Res 26:428, 1990; J Pharmacol Exp Ther 262:1274, 1992). We are evaluating the neurotoxic effects of dopamine by using a clonal cell line developed by Chikaraishi and co-workers (J Neurosci 13:1280, 1993). This cell line was derived from a tyrosine hydroxylase positive tumor obtained from the CNS of transgenic mice carrying the SV 40 T antigen oncogene under the transcriptional control of the rat tyrosine hydroxylase gene. We found that incubation of CATH.a cells with dopamine produced a time and dose dependent increase in cell death. Cell death also occurred after treatment with the catecholamines, l-dihydroxy- phenylalanine, norepinephrine, epinephrine, and isoparoterenol, as well as the neurotoxic compound, 6-hydroxydopamine. Cell death did not appear to be receptor mediated, since selective noradrenergic and dopaminergic receptor agonists had no effect on CATH.a cell viability. Dopamine induces apoptotic cell death as indicated by DNA fragmentation measured by gel electrophoresis and by flow cytometric analysis. Apoptosis appears to be produced by dopamine autoxidation, since intracellular peroxides increase after dopamine treatment and cell death can be inhibited by catalase and n-acetylcysteine. N-acetylcysteine produced a dose dependent (100-1250 mM) decrease in dopamine-induced cell death and this correlated with a decrease in peroxide formation. In addition, antisense to the antioxidant protein, Bcl-2, increases the sensitivity of CATH.a cells to dopamine induced cell death. These findings indicate that the oxidative products of dopamine cause neurotoxicity through apoptosis.
