vivo 3D MRI staining of mouse brain after subcutaneous application of MnCl2. Magn Reson Med 2002;48:852–859

brain in vivo (N 5) at 120 m isotropic resolution revealed spatially distinct signal increases 6–48 hr after subcutaneous application of MnCl2 (20 mg/kg). The effects result from a short-ening of the water proton T1 relaxation time due to the presence of unchelated paramagnetic Mn2 ions, which access the brain by systemic circulation and crossing of the blood–brain barrier (BBB). A pronounced Mn2-induced signal enhancement was first seen in structures without a BBB, such as the choroid plexus, pituitary gland, and pineal gland. Within 24 hr after administration, Mn2 contrast highlighted the olfactory bulb, inferior colliculi, cerebellum, and the CA3 subfield of the hip-pocampus. The affinity of Mn2 to various brain systems sug-gests the neuronal uptake of Mn2 ions from the extracellular space and subsequent axonal transport. Thus, at least part of the Mn2 contrast reflects a functional brain response of be