Quantitative autoradiography of [3H]prazosin binding sites in rat forebrain

We have used the LKB Ultrofilm method of autoradiography to localize and quantify in rat forebrain the binding sites for [3H]prazosin, a highly-selective antagonist for the alpha 1 adrenoreceptor subtype. Frozen 32 microns thick brain sections were labeled in vitro with 1 nM [3H]prazosin and applied against LKB Ultrofilm for 60 days to generate autoradiograms. Non-specific binding was defined as the labeling in the presence of 10 microM phentolamine. The highest levels of prazosin binding were found in layer V of the motor portion of the frontoparietal cortex and in all nuclei of the thalamus. Moderate levels of alpha 1 receptors were observed in the remaining layers of the cerebral cortex and in most regions of the limbic system. Low levels of prazosin binding occurred in the caudate-putamen and the accumbens nucleus. Our results indicate that alpha 1 adrenoceptors are distributed heterogeneously throughout the rat forebrain.