Tumor necrosis factor α increases cytosolic calcium responses to AMPA and KCl in primary cultures of rat hippocampal neurons

Acute behavioral effects of tumor necrosis factor α (TNFα) have been previously reported, however the cellular basis for these actions are unknown. To address this issue we examined the effects of TNFα on AMPA- and depolarization-induced changes in cytosolic Ca 2+ in cultured hippocampal neurons. Single cell Ca 2+ levels were determined with the fluorescent calcium indicator fura-2. TNFα caused an up-regulation of AMPA (10 μM)- and depolarization (55 mM KCl)-induced Ca 2+ responses. This effect occurred within a window of concentrations (1 and 10 ng/ml but not 0.1 or 100 ng/ml) and times (3 and 6 h but not 1 and 24 h). The effect was dependent upon protein synthesis (blocked by cycloheximide) and was prevented by the soluble TNF receptor and by a soluble TNF receptor fragment. Treatment with the soluble TNF receptor fragment also caused a decrease in the basal response. The TNFα treatment protocols did not appear to produce any toxicity to the neurons. Results are consistent with the hypothesis that TNFα regulates proteins known to be involved in neuronal communication (AMPA receptors) and cell regulation (voltage-dependent calcium channels) in a relatively rapid period of time (a few hours). These actions may be related to the behavioral effects produced by TNFα that occur within this time frame.