Effects of chronic pentobarbital treatment on the GABA(A) receptor complex in mammalian cortical neurons

In this study we examined the binding characteristics of the γ- aminobutyric acid (GABA(A)) receptor complex after chronic pentobarbital sodium treatment in cultured mammalian cortical neurons. Chronic pentobarbital sodium treatment (200 μM, 5 days) did not alter the basal binding of ligands like [³H]flunitrazepam, [³H]ethyl-8-fluoro-5,6-dihydro- 5-methyl-6-oxo-4H-imidazo [1,5α][1,4]-BZ-3-carboxylate and [³H]ethyl-8- azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5α][1,4]BZ-3-carboxylate that bind to the benzodiazepine (BZ) recognition site of the GABA(A) receptor complex. Similarly, chronic pentobarbital sodium treatment did not alter the basal binding of [³H]GABA and t-butylbicyclophosphoro[³⁵S]thionate. However, chronic pentobarbital sodium treatment produced uncoupling between GABA, barbiturate and neurosteroid sites with the BZ site. The efficacy (E(max)) values of GABA, pentobarbital and neurosteroid, 5α-pregnan-3α-ol- 20-one, on [³H]flunitrazepam binding were significantly decreased, whereas their potency (EC₅₀) values were not altered after chronic pentobarbital sodium treatment. Taken together, these results suggest that chronic pentobarbital sodium treatment produces heterologous uncoupling of the GABA- BZ receptor ionophore complex.