Thallium distribution in organs and brain regions of developing rats.

The concentration of thallium in body organs and brain regions was studied in rats as a function of the animals age from newborn to 20-days old. Thallium was analyzed at different times after a single sublethal i.p. injection of the metal (16 mg/kg). The results indicate that the brain is less permeable to thallium in the older animals, suggesting that reduced thallium transport into the brain is related to the establishment of the blood-brain barrier in the rats. Differences between weanling and newborn rats were also found in regard to regional distribution of thallium in the brain as the older animals showed a region-dependent distribution while newborn rats presented an homogeneous content of thallium among all regions.