NEUROTROPHINS PROTECT CULTURED CEREBELLAR GRANULE NEURONS AGAINST THEEARLY PHASE OF CELL-DEATH BY A 2-COMPONENT MECHANISM

Cerebellar granule neurons cultured with serum develop a mature neuron al phenotype, including stimulus-coupled release of glutamate, and dep end on elevated potassium for survival. We find that cells cultured wi th serum undergo two phases of cell death. By 6 d in vitro, 30-50% of the cells present are dead; after this time the remaining cells die. E levated potassium prevents only this later phase of death, whereas neu rotrophins protect these cells against the early phase of death. Facto rs that bind p75(NTR) Or TNF-R, members of the same receptor family, e xhibit voltage-sensitive calcium channel-dependent protection, whereas ligands of expressed Trk receptors show additional calcium channel-in dependent protection. The cells express TrkB protein and show elevated c-Fos and c-Jun levels in response to BDNF. No TrkA is detected, alth ough p75(NTR) protein is expressed and NGF induces depolarization-depe ndent elevation of c-Jun levels. In the presence of the protein kinase C inhibitor bisindolylmaleimide, BDNF-induced survival promotion is r educed partially, whereas NGF-induced death is unmasked. Basal surviva l mechanisms are insensitive to inhibition of PK-C or PI-3 kinase. We conclude that BDNF promotes survival in part via its TrkB receptor, wh ereas there is an additional pathway promoting survival and elevating c-Jun evoked by both NGF and BDNF via a non-Trk receptor.