title: Chronic neurosteroid treatment produces functional heterologous uncoupling at the gamma-aminobutyric acid type A/benzodiazepine receptor complex in mammalian cortical neurons.
abstract: We have investigated the effects of chronic treatment with the neurosteroid 5 alpha-pregnan-3 alpha-ol-20-one (5 alpha 3 alpha) on the gamma-aminobutyric acid (GABA)A receptor complex in cultured mammalian cortical neurons. Chronic 5 alpha 3 alpha treatment (up to 2 microM, 5 days) did not produce any changes in the morphological appearance or the cell protein content of cortical neurons. The basal binding of [3H]flunitrazepam, [3H]Ro15-1788, and [3H]Ro15-4513 was not altered after the chronic treatment. Chronic 5 alpha 3 alpha treatment did not alter the Kd or Bmax values of [3H]flunitrazepam binding to intact cortical neurons. However, chronic 5 alpha 3 alpha treatment produced uncoupling between GABA, barbiturate, and neurosteroid sites and the benzodiazepine site. The EC50 values of these ligands were not significantly altered; however, their Emax values were decreased after chronic 5 alpha 3 alpha treatment. The 5 alpha 3 alpha-induced uncoupling was time and concentration dependent. The binding of [3H]GABA and t-[35S]butylbicyclophosphorothionate was also decreased after chronic 5 alpha 3 alpha treatment. Chronic 5 alpha 3 alpha treatment decreased the Bmax of the low affinity GABAA receptor sites, without affecting the high affinity sites, and decreased the Bmax of t-butylbicyclophosphorothionate binding sites. The EC50 value for GABA-induced 36Cl- influx was not altered, whereas the Emax value was decreased after chronic 5 alpha 3 alpha treatment. Furthermore, the 5 alpha 3 alpha-induced uncoupling was reversed by concomitant exposure of the cortical neurons to 5 alpha-pregnan-3 beta-ol-20-one or R5135, suggesting an involvement of the neurosteroid and GABA recognition sites in the observed uncoupling. Taken together, these results suggest that chronic 5 alpha 3 alpha treatment produces heterologous uncoupling at the GABAA receptor complex.
authors.affiliation: Department of Pharmacology, University of Texas Health Science Center at San Antonio 78284-7764.
authors.forename: R
authors.initials: R
authors.lastname: Yu
authors.forename: M K
authors.initials: MK
authors.lastname: Ticku
mesh_terms: D000731:Androstanes / Q000494:pharmacology; D000818:Animals; D001378:Azasteroids / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000378:metabolism / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure*; D002712:Chlorides / Q000493:pharmacokinetics; D002713:Chlorine; D003292:Convulsants / Q000378:metabolism / Q000494:pharmacology; D004347:Drug Interactions; D018756:GABA Antagonists / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure*; D011280:Pregnanolone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011868:Radioisotopes; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000378:metabolism* / Q000502:physiology; D013462:Sulfur Radioisotopes; D013997:Time Factors; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000731:Androstanes; D001378:Azasteroids; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002712:Chlorides; D003292:Convulsants; D018756:GABA Antagonists; D011868:Radioisotopes; D011963:Receptors, GABA-A; D013462:Sulfur Radioisotopes; D014316:Tritium; D002713:Chlorine; D005680:gamma-Aminobutyric Acid; C037476:tert-butylbicyclophosphorothionate; D011280:Pregnanolone; C032061:RU 5135