GABA conductance of chick spinal cord and dorsal root ganglion neurons in cell culture.

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Abstract
GABA chemosensitivity of embryonic chick spinal cord (SC) and of dorsal root ganglion (DRG) neurons in dissociated cell culture was studied using a pressure-ejection technique for rapid delivery of known drug concentrations. All SC cells and most DRG cells were sensitive to GABA. Pressure ejection of 0.1 mM GABA produced an increase in membrane conductance in all SC neurons tested (mean = 5.4 .times. 10-8 mho). DRG neurons examined during the 1st wk after plating were shunted by GABA, but the response to 0.1 mM GABA was < 5% of that observed in SC neurons. The DRG GABA conductance declined with time in culture. The GABA conductance of both SC and DRG cells was due primarily to an increase in Cl- permeability. When SC neurons were penetrated with a K acetate recording electrode, the GABA reversal potential was -53.9 mV; DRG responses reversed at -62.8 mV. The SC GABA dose-response function exhibited an ED50 of 17 .mu.M and a Hill coefficient of 1.83. SC cells responded to GABA applied as a cation by focal iontophoresis. The distribution of sensitivity was not uniform: foci of high sensitivity were detected on cell bodies and proximal dendrites. Positive pulses applied to pipettes filled with GABA at pH 4.0 also depolarized sensory neurons, but the DRG responses were caused primarily by H+ ions ejected along with GABA. Other amino acids (glycine, .beta.-alanine and taurine) mimicked the effect of GABA on SC neurons but are without effect on DRG neurons. GABA responses on both SC and DRG cells were blocked by picrotoxin and bicuculline, but not by low concentrations of strychnine. Glycine, .beta.-alanine and taurine responses of SC cells were all blocked by low concentrations of strychnine, but not by bicuculline or picrotoxin. At high concentration, these antagonists were not selective.