Ionic behaviors and neuronal survival in developing ganglia. III. Studies with embryonic chick sympathetic neurons

We have shown in the past that (1) Nerve Growth Factor (NGF) controls the Na⁺,K⁺-pump in its ganglionic neuronal targets and (2) the NGF requirement for pump control is developmentally regulated in the chick embryo dorsal root ganglion. We report here that NGF is fully competent to insure the control of intracellular Na⁺ concentrations (as expression of pump control) in intact chick sympathetic ganglia and enriched suspensions of sympathetic neurons from embryonic day 8 (E8) through 13. At later stages (E13–E18), NGF becomes less and less required for that control as the neurons gain a self-sustained ionic pump competence. In monolayer cultures of enriched sympathetic neurons, an increasing neuronal survival in the absence of NGF occurs. These data demonstrate that the ability of developing sympathetic neurons to survive without NGF increases with the same temporal pattern as does their independence from NGF for ionic pump control, stressing the importance of ionic events for neuronal survival.