Blocking Ca2+ mobilization with thapsigargin reduces neurite initiation in cultured adult rat DRG neurons

Adult rat DRG neurons rapidly extend extensive neuritic arbors after a 1-2-day delay in culture and generate large depolarization-induced calcium signals during this time period that are derived primarily from intracellular calcium release. To assess whether intracellular calcium mobilization is required for neurite initiation, calcium stores were depleted by brief exposure to the irreversible endoplasmic reticulum calcium ATPase inhibitor thapsigargin; cultures were then maintained for 3 days, immunostained for neurofilament and scored for percentage of neurons with neurites at least twice as long as the cell body. Brief thapsigargin treatment (20 min) during the first 24 h in culture resulted in a substantial decrease in neurite initiation frequency without affecting neuronal or nonneuronal cell survival, suggesting that intracellular calcium mobilization is necessary for triggering neurite initiation in these neurons.