Adult rat DRG neurons rapidly extend extensive neuritic arbors after a
1-2-day delay in culture and generate large depolarization-induced ca
lcium 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 c
alcium ATPase inhibitor thapsigargin; cultures were then maintained fo
r 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 resul
ted in a substantial decrease in neurite initiation frequency without
affecting neuronal or nonneuronal cell survival, suggesting that intra
cellular calcium mobilization is necessary for triggering neurite init
iation in these neurons.