Characterization of the Influence of Unsaturated Free Fatty Acids on Brain GABA/Benzodiazepine Receptor Binding In Vitro

Abstract: We have investigated the effect of unsaturated free fatty acids (FFAs) on the brain GABA/benzodiazepine receptor chloride channel complex from mammalian, avian, amphibian, and fish species in vitro. Unsaturated FFAs with a carbon chain length between 16 and 22 carbon atoms enhanced ³H]diazepam binding in rat brain membrane preparations, whereas the saturated analogues had no effect. The enhancement of ³H]diazepam binding by oleic acid was independent of the incubation temperature (0-30°C) of the binding assay and not additive to the enhancement by high concentrations of C1. In rat brain preparations, the stimulation of ³H]diazepam binding by oleic acid (10^?4M) was independent of the ontogenetic development. Phylogenetically, large differences were found in the effect of unsaturated FFAs on ³H]diazepam and ³H]muscimol binding: In mammals and amphibians, unsaturated FFAs enhanced both ³H]-muscimol and ³H]diazepam binding to 150-250% of control binding. In 17 fish species studied, oleic acid (10^?4M) stimulation of ³H]diazepam binding was weak (11 species), absent (four species), or reversed to inhibition (two species), whereas stimulation of ³H]muscimol binding was of the same magnitude as in mammals and amphibians. In 10 bird species studied, only weak enhancement of ³H]muscimol binding (110–130% of control) by oleic acid (10^?4M) was found, whereas ³H]diazepam binding enhancement was similar to values in mammal species. Radiation inactivation of the receptor complex in situ from frozen rat cortex showed that the functional target size for oleic acid to stimulate ³H]flunitrazepam binding has a molecular mass of ～200,000 daltons. Our data show that unsaturated FFAs have distinct effects on membranebound GABA/benzodiazepine receptors in vitro.