(A and B) Intranasally applied 125I-St-KKYL-NH2 reaches the body and the brain. Each rat (300 g) received 2 μl containing 1,723,373 ± 33,315 cpm, (i.e., 5,744 cpm/g). Animals were sacrificed at indicated times after administration, and tissue samples were weighed and assayed (in duplicate) for radioactivity in a γ-counter. (C) Intact 125I-St-KKYL-NH2 reached the brain after intranasal administration. Radioactive tissue samples (cerebral cortex) were homogenized and subjected to low-speed centrifugation. Supernatants were analyzed by using HPLC fractionation against St-KKYL-NH2. Samples were monitored for radioactivity in a γ-counter.