Multiple benzodiazepine receptors: autoradiographic localization in normal human amygdala

Because previous studies have emphasized the importance of the amygdala in the therapeutic actions of benzodiazepines and described differences in benzodiazepine receptor distribution between human and rat, this study examined the distribution of multiple benzodiazepine receptors in normal human amygdala by light microscopic autoradiography. Benzodiazepine receptors were labeled with [3H]flunitrazepam at 5 representative rostro-caudal levels. Type 1 and Type 2 receptors were differentiated by the addition of 200 nM CL218,872 to serial sections and subsequent analysis based on the differential occupancy at Type 1 and Type 2 receptors by this drug. Results demonstrated that like the rat amygdala, human amygdala contains a higher density of benzodiazepine receptors in the basolateral nuclear complex compared to the corticomedial complex, and more Type 2 than Type 1 receptors overall. However, while rat amygdala is enriched rostrally in Type 1 receptors, this subclass in humans is elevated caudally. Pathways including the amygdala and limbic and cortical targets of its efferents may be preferential loci of benzodiazepine anxiolytic activity.