γ-Hydroxybutyric acid (GHB) and γ-aminobutyric acid B receptor (GABA BR) binding sites are distinctive from one another: molecular evidence

Abstract

γ-Hydroxybutyric Acid (GHB) is thought to be a weak partial agonist at the γ-aminobutyric acid B Receptor (GABA BR), but the precise relationship of the GHB receptor (GHBR) to the GABA BR remains unclear. In order to test the hypothesis that the GHBR is not identical to the GABA BR, we conducted two groups of experiments. First, GABA BR subtype 1 (R1) and/or subtype 2 (R2) were over expressed in HEK 293 cells and membrane binding studies on the transfected cells done using [ 3H]GHB and [ 3H] (2 E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene) ethanoic acid ([ 3H]NCS-382). The latter is a specific antagonist at the GHB binding site. Second, [ 3H]GHB and [ 3H]NCS-382 autoradiographic binding studies were done on the brains of mice in which the gene for GABA BR1a was deleted. Such mice do not have a functioning GABA BR. There was no detectable specific [ 3H]GHB or [ 3H]NCS-382 binding in HEK 293 cells transfected with GABA BR1, R2, or R1/R2. Binding to [ 3H]CGP54626A, a high affinity GABA BR antagonist, was absent in GABA BR1a −/− mice. There was no difference in [ 3H]NCS-382 binding observed in the brains of GABA BR1a −/−, GABA BR1a +/− or GABA BR1a +/+ mice. Specific [ 3H]GHB binding was observed in the brain of GABA BR1a −/− mice but was significantly lower than in wild type mice. These data support the hypothesis that the GHB binding site is separate and distinct from the GABA BR.