Survival promotion of mesencephalic dopaminergic neurons by depolarizing concentrations of K+ requires concurrent inactivation of NMDA or AMPA/kainate receptors

The death of dopaminergic neurons that occurs spontaneously in mesencephali c cultures was prevented by depolarizing concentrations of K+ (20-50 mM). H owever, unlike that observed previously in other neuronal populations of th e PNS or CNS, promotion of survival required concurrent blockade of either NM DA or alpha -amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kaina te receptors by the specific antagonists, MK-801 and GYKI-52466, respective ly. Rescued neurons appeared to be healthy and functional because the same treatment also dramatically enhanced their capacity to accumulate dopamine. The effects on survival and uptake were rather specific to dopaminergic ne urons, rapidly reversible and still observed when treatment was delayed aft er plating. Glutamate release increased substantially in the presence of el evated concentrations of K+, and chronic treatment with glutamate induced a loss of dopaminergic neurons that was prevented by MK-801 or GYKI-52466 su ggesting that an excitotoxic process interfered with survival when only the depolarizing treatment was applied. The effects of the depolarizing stimul us in the presence of MK-801 were mimicked by BAY K-8644 and abolished by n ifedipine, suggesting that neuroprotection resulted from Ca2+ influx throug h L-type calcium channels. Measurement of intracellular calcium revealed th at MK-801 or GYKI-52466 were required to maintain Ca2+ levels within a trop hic range, thus preventing K+-induced excitotoxic stress and Ca2+ overload. Altogether, our results suggest that dopaminergic neurons may require a fi nely tuned interplay between glutamatergic receptors and calcium channels f or their development and maturation.