Ionic behaviors and nerve growth factor dependence in developing embryonic chick ganglia. I. Studies with intact...

We have recently shown that intact and dissociated 8-day embryonic (E8) chick dorsal root ganglia (DRG) lose the ability to regulate their intracellular Na+, K+ levels when deprived of nerve growth factor (NGF) for 6 h; recovery occurs within minutes of NGF presentation. These ganglionic neurons are believed to depend on NGF for survival and neurite production over a defined period of embryonic life--between about E6 and E15 in the chick. Using intact DRG from E6-E16 chick embryos we determined developmental changes in: (i) 22Na+ accumulation in the presence and absence of NGF, or in the presence of ouabain; and (ii) intra- and extracellular fluid spaces. Sodium accumulation, in the presence of NGF, increases from E6 to E10. It parallels the total fluid space under ouabain but then decreases conspicuously between E10 and E16, despite little change in the latter. NGF thus prevents Na+ accumulation during the early period, and becomes increasingly irrelevant for this behavior in later (after E10) development. These data are interpreted as indicating that: (i) NGF is required for ionic control by DRG neurons up to E10; and (ii) indigenous behaviors for the control of ion pump mechanism(s) are progressively acquired by these cells from E10 to E16, in parallel with the decreasing ionic relevance of NGF. These findings are consistent with the view that the ionic responses to NGF correlate closely with the survival and neurite-promoting effects of this factor.