Effects of chronic ethanol treatment on gamma-aminobutyric acid(A) and glycine receptors in mouse glycinergic spinal neurons

Five-day-old cultures of mouse glycinergic spinal interneurons were chronic ally treated with 100 mM ethanol and the glycine and gamma-aminobutyric aci d (GABA)(A) receptors were assayed using whole-cell recordings and fluoresc ence-imaging techniques. Control neurons displayed a glycine(50) of 19 +/- 0.6 mu M and a Hill coefficient of 3.1 +/- 0.3. Chronic ethanol treatment d id not significantly change these parameters. The maximal responses were 31 0 +/- 80 pA/pF in control and 440 +/- 19 pA/pF in treated cells, and the fl uorescence intensity associated to a monoclonal glycine receptor antibody w as unchanged. Strychnine inhibited the glycine current with smaller potency (29%) in treated neurons, thus the IC50 increased from 14 +/- 2 nM in cont rol to 18 +/- 6 nM in treated neurons. Zn2+ (10 mu M) potentiated the glyci ne current by 43 +/- 33% in control, but only by 18 +/- 13% in treated neur ons. Interestingly, no change on the inhibition produced by a high concentr ation of Zn2+ was found in treated neurons. The inhibitory effect of picrot oxin on the glycine receptor, associated to a homomeric receptor, was elimi nated with chronic ethanol, suggesting a faster switch to beta-subunit-cont aining receptors. Unlike glycine receptors, the sensitivity of GABA(A) rece ptors to GABA, pentobarbital, diazepam, and Zn2+, as well as the fluorescen ce intensity associated to a high-affinity benzodiazepine analog was unchan ged by chronic ethanol. In conclusion, we found that glycine receptors in s pinal interneurons were altered by chronic ethanol treatment and this may r eflect the expression of different subunits in control and treated neurons. GABA(A) receptors were resistant to the treatment.