Gamma-hydroxybutyric acid (GHB) and gamma-aminobutyric acidB receptor (GABABR) binding sites are distinctive from one another: molecular evidence

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] (2E)-(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.