Reversible physiological alterations in sympathetic neurons deprived of NGF but protected from apoptosis by caspase inhibition or Bax deletion

Abstract

Cell death in nervous system development and in many neurodegenerative diseases appears to be apoptotic or programmed. Withdrawal of nerve growth factor (NGF) from cultures of superior cervical ganglia neurons (SCG) is an excellent model of programmed cell death (PCD), producing apoptosis within 24-48 h. This death can be prevented by treatment with caspase inhibitors or deletion of the proapoptotic Bax gene. Since inhibition of apoptosis is an attractive strategy for the therapy of many neurological diseases and little is known about the function of neurons when apoptosis has been aborted, we examined the electrophysiological properties of NGF-deprived SCG neurons from rats and mice, saved by the caspase inhibitor boc-aspartyl(OMe)fluoromethyl ketone (BAF) or by Bax deletion. Compared to NGF-maintained controls, the resting membrane potentials of BAF-saved neurons were depolarized by 9 mV and the action potentials were prolonged by over 50%. Nicotinic cholinergic current density was depressed by about 50%. Electrophysiological parameters returned to normal within 4 days after NGF restoration. Neurons from Bax-deficient mice were altered differently by NGF withdrawal. There were no detectable changes in resting or action potentials. However, nicotinic current density was reduced just as in BAF-saved rat neurons. There were no observable changes in the processes of individual neurons after 6 days of NGF deprivation in the presence of BAF. Our results indicate that neurons are physiologically altered during pharmacological inhibition of PCD, but fully recover after trophic support is returned.