Maintenance by nerve growth factor of the intracellular sodium environment in spinal sensory and sympathetic ganglionic cells.

A promising advance in our understanding of the mode of action of nerve growth factor (NGF) has been provided by our recent finding that dissociated cells from 8-day embryonic chick dorsal root ganglia (DRG) lose their competence to maintain a low intracellular Na+ when incubated without NGF for 6 h, and promptly recover it on delayed presentation of NGF. To ascertain whether control of intracellular Na+ is a general feature of the NGF action on its target neurons, we have now tested several NGF-sensitive tissues, both as intact ganglia and dissociates, for their ability to (i) accumulate large amounts of 22Na+ over a period of hours in the absence of NGF, and (ii) rapidly extrude the accumulated radioactivity upon delayed presentation of NGF. Intact and dissociated chick embryo DRG and sympathetic ganglia, as well as dissociated mouse DRG, displayed the expected Na+ responses to the lack or the administration of NGF. No such responses were observed with intact mouse DRG, which do not require NGF in explant cultures for neuritic outgrowth, or with intact and dissociated chick embryo ciliary ganglia, which are not sensitive to NGF in either explant or dissociated cell cultures. Thus, in all ganglionic preparations examined, the occurrence of Na+ responses to exogenous NGF correlated with traditional responses to NGF in culture. This together with other recent data, reinforces the view that ionic control may be a critical element in the mechanism of action of NGF.