Distribution of incorporated [3H]uridine in mouse brain as a function of route of administration

The effect of injection by intracranial and systemic routes on the localization of [3H]uridine incorporated into RNA of mouse brain was quantitated autoradiographically. The pattern of labeled RNA 45 min after intraventricular or intracisternal injection was highly variable throughout the brain, and activity was localized in structures adjacent to the ventricles or subarachnoid space. The amount incorporated was inversely related to distance from these cerebrospinal fluid compartments with little incorporation observed at distances greater than 200 microns. In contrast to intracranial administration, intrapleural and subcutaneous routes yielded a more homogeneous distribution of incorporated uridine throughout the brain. Regional differences in the autoradiographic pattern following systemic administration were correlated with regional differences in cell density. The results clearly indicate that injection route is a potent factor affecting the localization of agents used to study brain.