Radioautographic localization of radioactivity in rat brain after intracarotid injection of 125I-alpha-melanocyte-stimulating hormone.

125I-alpha-melanocyte-stimulating hormone (MSH) was injected into the carotid artery of the rat and the radioactivity localized by radioautography. Radioactivity in the areas surrounding the ventricles and blood vessels after administration of 125I-alpha-MSH but not 125I-luteinizing hormone indicated passage of labeled material through the blood brain barrier. A specific concentration of radioactivity was found in the striatum and reticular nucleus of the thalamus. This localization, particularly in the thalamus, could be correlated with the previously reported effects of MSH on the brain of animals and man.