摘要：

γ-Hydroxybutyric acid (GHB) is a metabolite of γ-aminobutyric acid (GABA) and a proposed neurotransmitter in the mammalian brain. We recently identified α4βδ \{GABAA\} receptors as possible high-affinity \{GHB\} targets. \{GABAA\} receptors are highly sensitive to allosteric modulation. Thus to investigate whether \{GHB\} high-affinity binding sites are also sensitive to allosteric modulation, we screened both known \{GABAA\} receptor ligands and a library of natural compounds in the rat cortical membrane \{GHB\} specific high-affinity [3H]NCS-382 binding assay. Two hits were identified: Monastrol, a positive allosteric modulator of \{GABA\} function at δ-containing \{GABAA\} receptors, and the naturally occurring flavonoid catechin. These compounds increased [3H]NCS-382 binding to 185–272% in high micromolar concentrations. Monastrol and (+)-catechin significantly reduced [3H]NCS-382 dissociation rates and induced conformational changes in the binding site, demonstrating a positive allosteric modulation of radioligand binding. Surprisingly, binding of [3H]GHB and the \{GHB\} high-affinity site-specific radioligands [125I]BnOPh-GHB and [3H]HOCPCA was either decreased or only weakly increased, indicating that the observed modulation was critically probe-dependent. Both monastrol and (+)-catechin were agonists at recombinant α4β3δ receptors expressed in Xenopus laevis oocytes. When monastrol and \{GHB\} were co-applied no changes were seen compared to the individual responses. In summary, we have identified the compounds monastrol and catechin as the first allosteric modulators of \{GHB\} high-affinity binding sites. Despite their relatively weak affinity, these compounds may aid in further characterization of the \{GHB\} high-affinity sites that are likely to represent certain \{GABAA\} receptors.

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