Quantitation and localization of 204thallium in the central and peripheral nervous system of adult and young rats.

A single dose of 204Tl, representing about 2-3 ng 204Tl per gm/wt was injected into young and adult rats. Rats were killed daily over a period of 10 days and the levels of Tl were estimated in nervous and other tissues. The greatest concentrations of Tl (peak concentration time - PCT) in all tissues in the adult rat occurred 24 hours after injection. In the young rat PCT in the sciatic nerve and spinal cord were 48 hours after injection whereas it occurred 24 hours after injection in the brain and somatic organs. There were differences in biological half-lives of the organs in the young as compared to the adult rats. Tl level in all organs except the kidney, were about 2 pg/mg of tissue. It was concentrated in the cytoplasm of most cells examined. Tl levels then fell rapidly during the few days following the injection, and slowly afterwards. Thirty days after the injection, tracts of 204Tl were present in the cytoplasm of nervous and somatic cells.