EFFECT OF SERUM ON INTRACELLULAR CALCIUM HOMEOSTASIS AND SURVIVAL OF PRIMARY CORTICAL AND HIPPOCAMPAL CA1 NEURONS FOLLOWING BRIEF GLUTAMATETREATMENT

Glutamate neurotoxicity was studied in primary neuronal cultures prepa red from rat cerebral cortex and hippocampal CAI sector. Neurons were cultivated with 5% native horse serum and then exposed to 0.1 or 1.0 m M glutamate for 5 min. Subsequently, neurons were allowed to recover f or 24 hours either in the presence or in the absence of 5% native hors e serum. In the absence of serum, neurons showed morphological signs o f degeneration and exhibited marked loss of vitality as tested by vita l staining and release of lactate dehydrogenase (LDH). In contrast, wh en neurons were cultivated in the presence of serum, no degenerative c hanges were seen and the neurons survived. Heat inactivated serum did not prevent neuronal death but addition of basic fibroblast growth fac tor (bFGF) or transforming growth factor-beta 1 (TGF-beta 1) had the s ame protective effect as native serum. Measurements of intracellular c alcium activity ([Ca2+](i)) with the indicator dye fura-2 revealed a s harp increase during glutamate exposure. In the absence of serum, [Ca2 +](i) returned to near control within 5 min but it secondarily increas ed after 1 hour to almost the same level as during glutamate exposure. This delayed increase was more pronounced in CA1 than in cortical neu rons, it correlated linearly with the initial rise during glutamate ex posure, and it was greatly reduced in the presence of serum. These obs ervations suggest that glutamate neurotoxicity in vitro is a function of the delayed and not of the primary rise of intracellular calcium ac tivity, and that trophic factors prevent neurotoxicity by attenuating this delayed response.