Quantitative autoradiographic localization of alpha 2-antagonist binding sites in rat brain using [3H]idazoxan

The distribution of alpha 2-receptors was determined by quantitative autoradiography with the antagonist [3H]idazoxan. Apart from regions which are known to be enriched in alpha 2-receptors, the highest silver grain densities were located over the subfornical organ and the area postrema. However, binding in these regions was not displaced by yohimbine and therefore, according to the present understanding, cannot be considered to represent alpha 2-receptors. Within the cerebellum, alpha 2-receptors were found to be arranged in 3 sagitally oriented strips within the molecular layer of lobules 9 and 10, suggesting a co-incidence with dopamine and substance P receptors in this structure.