Benzodiazepine receptors on cultured neurons: Binding with different [(3)H]ligands on homogenized and intact cells

Benzodiazepine receptors have been studied on primary neuronal culture of foetal rat brain using different labelled ligands. The agonists [(3)H]flunitrazepam and [(3)H]diazepam, the inverse agonist [(3)H]methyl-?-carboline-3-carboxylate and the antagonist [(3)H]Ro 15-1788 were used. The binding properties of these ligands to homogenate from cultured neurons are very similar to those determined on receptors mediating the pharmacological effects of benzodiazepines in the brain. The [(3)H]ligands behaved differently when the binding was performed with intact cells. Among them, [(3)H]Ro 15-1788 offers two advantages making it fitted for binding to intact cells: it shows a low non-specific binding and a specificity for "central type" of benzodiazepine receptors. On the contrary, [(3)H]diazepam is useless because of its high non-specific binding. In cultured neurons the benzodiazepine receptors are coupled to GABA receptors: this is shown by the enhancement of [(3)H]flunitrazepam binding by GABA and its reduction by bicuculline.