title: Chronic exposure of developing cortical neurons to GABA down-regulates GABA/benzodiazepine receptors and GABA-gated chloride currents.
abstract: Cultures of cerebral neurons were prepared from chick embryos, 8.5 days in ovo, and maintained in vitro. Following chronic exposure of these cells to GABA, the levels of [3H]flunitrazepam binding in situ and electrophysiological responsiveness to gamma-aminobutyric acid (GABA) was examined. Treatment with 100 microM GABA for 7 days reduced [3H]flunitrazepam binding in situ by 70 +/- 8% compared to untreated controls. The binding of [3H]N-methylscopolamine was unaffected by this treatment. The reduction in [3H]flunitrazepam binding was prevented by concomitant exposure of developing neurons to the GABA antagonist R 5135, suggesting that GABAA receptor occupancy is required. The loss of bezodiazepine receptors was dependent on the GABA concentration in the culture medium and a half-saturation (IC50) value of 11.2 +/- 3.7 microM was estimated. Whole-cell patch-clamp recordings were obtained to assess the functional properties of the labile receptor pool observed in the binding studies. Neurons cultured with 100 microM GABA for 7 days showed a 60-70% reduction in the peak current amplitudes observed in response to application of 10-100 microM GABA. However, the rate of rapid desensitization, quantified by measuring changes in input conductance, was unchanged by chronic GABA exposure, yielding decay time constants of 27.1 +/- 2.1 and 34.7 +/- 4.7 s for control and treated cells, respectively. The results are consistent with a GABA modulation of the GABAA/benzodiazepine receptor complex by means of down-regulation.
authors.affiliation: Department of Neurology, Baylor College of Medicine, Houston, TX 77030.
authors.forename: J J
authors.initials: JJ
authors.lastname: Hablitz
authors.forename: M H
authors.initials: MH
authors.lastname: Tehrani
authors.forename: E M
authors.initials: EM
authors.lastname: Barnes
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D002642:Chick Embryo; D002712:Chlorides / Q000493:pharmacokinetics / Q000502:physiology*; D005445:Flunitrazepam / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam