Down-regulation of benzodiazepine receptors by ethyl beta-carboline-3-carboxylate in cerebrocortical neurons.

Effect of exposure of primary cultured cerebral cortical neurons to ethyl beta-carboline-3-carboxylate (beta-CCE) on the function of benzodiazepine receptors was studied. Exposure of neurons to beta-CCE (0.1-10 microM) decreased the binding of [3H]flunitrazepam to extensively washed membrane fractions in a dose- and time-dependent manner, whereas the binding of [3H]flunitrazepam to the cytosolic fractions increased (180%) under the same conditions as described above. Ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a] [1,4] benzodiazepine-3-carboxylate (Ro15-1788), an antagonist of the central type of benzodiazepine receptors, completely abolished the beta-CCE-induced decrease in [3H]flunitrazepam binding and the IC50 value for [3H]flunitrazepam binding to the extensively washed membrane fractions prepared from beta-CCE-treated neurons was similar to that from non-treated neurons. Scatchard analysis revealed that only the Bmax value for [3H]flunitrazepam binding decreased after the exposure to beta-CCE (1 microM) for 12 h, although the Kd value was not altered. These results indicate that beta-CCE induces the down-regulation of benzodiazepine receptors by an increase in benzodiazepine receptor internalization.