MECHANISMS OF DOPAMINE-INDUCED CELL-DEATH IN CULTURED RAT FOREBRAIN NEURONS - INTERACTIONS WITH AND DIFFERENCES FROM GLUTAMATE-INDUCED CELL-DEATH

Injury to the brain, whether by ischemia or trauma, results in the unc ontrolled release of many neurotransmitters, including glutamate and d opamine. Both of these neurotransmitters are neurotoxic in high concen trations, and the oxidative stress caused by reactive oxygen species g eneration has been implicated in the mechanism of neurotoxicity. In th is study, we used cultured rat forebrain neurons to characterize cell death caused by exposure to dopamine and/or glutamate and to investiga te potential acute mechanisms of toxicity. Dopamine exposure (250 mu M for 2 h) reduced cell viability to 34.3 +/- 5.5% of untreated control 20 h later and increased the number of neurons with apoptotic morphol ogy. The antioxidant N-acetylcysteine (100 mu M) inhibited dopamine-in duced toxicity and prevented the covalent binding of dopamine quinones to protein. In contrast, glutamate toxicity lacked the hallmark chara cteristics of apoptosis. When neurons were exposed successively to sub lethal concentrations of dopamine and glutamate, cell viability at 20 h was reduced to 62.3 +/- 5.2% of untreated control. Apoptosis was not evident, and N-acetylcysteine blocked the potentiating effect of dopa mine on glutamate-induced toxicity. We used single-cell fluorescence a ssays to measure changes in intraneuronal glutathione, intraneuronal C a2+, mitochondrial membrane potential, and DNA integrity as potential acute inducers of neuronal injury. While changes in these parameters c ould be demonstrated, none were identified as the sole acute inducer o f cell death caused by dopamine. In summary, we have characterized a n umber of neuronal responses to lethal dopamine injury. Also, we have d emonstrated that dopamine and glutamate can interact in vitro to poten tiate cell death and that the potentiation appears to be induced by ox idative stress. (C) 1997 Academic Press.