Supravital Staining of Mammalian Brain with Intraarterial Methylene Blue Followed by Pressurized Oxygen

In 25-day-old rats, injected intraperitoneally with 0.2 ml aliquots of 6% methylene blue in saline over 1 hr followed by a single 4–6 ml intra-arterial injection; O2 pressurized to 45 lb/in2 was used to improve reblueing of 1.5–2 mm slices of cerebellum, thus increasing staining selectivity. Factors believed to influence this selectivity for axonal elements and fine dendrites are the rapidity and pressure (about 300 mm Hg) of the terminal intra-arterial injection, the hyperbaric O2 treatment of tissue slabs for 1 hr as a substiute for room air, and immersion in 6% ammonium molybdate for 1 hr before return to atmospheric conditions.