Intracranial drug implants: an autoradiographic analysis of diffusion.

Labeled crystalline atropine, administered to the hypothlalamus of rats, remainted strictly localized in a sphere, 1.0 to 1.8 millimeters in diameter, ditring the first 3 minutes. A similar distribution obtained after 1 hour. At intermediate times, slightly elevated radioactivity, reflecting concentrations 2,000 to 10,000 times below behaviorally effective doses, was observed several millimeters from the implantation site.