Effects of sodium and chloride on neuronal survival after neurite transection

An in vitro investigation was undertaken to study the roles of Na+ and Cl- in mammalian spinal cord (SC) neuron deterioration and death after injury i nvolving physical disruption of the plasma membrane. Individual SC neurons in monolayer cultures were subjected to UV laser microbeam transection of a primary dendrite. Neurons lesioned in modified ionic environments (MIEs) w here 50%-75% of the NaCl was replaced with sucrose had higher survival (65% -75%) than neurons lesioned in medium with normal (125 mM) NaCl (28%: p < 0 .001). Subsequent experiments found a comparable increase in lesioned neuro n survival in MIEs in which only Na+ was replaced with specific ionic subst itutes; however, replacement of Cl was not protective. Electron microscope examinations of neurons fixed <16 min after lesioning showed a dramatic dec rease in vesiculation of the smooth endoplasmic reticulum and Golgi apparat us in the low NaCl or low Na+ MIEs. It is hypothesized that Na+ entry after membrane disruption may stimulate elevation of [Ca+2]i leading to ultrastr uctural disruption and death of injured neurons. The results of these studi es suggest that a low NaCl MIE may be useful as an irrigant to limit damage spread and cell death within CNS tissues during surgery or after trauma.