Differential inhibition of brain specific [3H]flunitrazepam binding by several types of dyes

Several dyes, representing different structural classes, inhibit [3H]flunitrazepam binding to brain specific receptors in the rat with 50% inhibition in the 1 to 100 microM range. Crystal Violet and Methyl Violet 2B inhibited more potently in the forebrain than in the cerebellum. Congo Red yielded a Hill number near 2.3, probably reflecting positive cooperativity between interacting binding sites in benzodiazepine receptor complexes. Toluidine Blue 0 was the most potent of the dyes tested (IC50 = 1 microM in cerebellum) and inhibited more potently in cerebellum than in forebrain.