Distribution and retention of exogenously administered alkali metal ions in the mouse brain.

A pharmacokinetic study of the distribution and retention profiles of Li+, Rb+ and Cs+ in the brain and blood was performed in male mice given single (acute) or repeated (semi-chronic) injections of the respective chloride salt solutions. The concentration of Li+ in whole brain and in cerebral cortex, striatum, hippocampus, diencephalon, brain stem and cerebellum were similar after acute and semichronic LiCl treatment. In contrast, semi-chronic RbCl and CsCl treatment resulted in greater accumulation of Rb+ and Cs+ in brain compared to the levels obtained after acute administration. The Li+ concentration in brain declined to negligible amounts at 48 hr after termination of acute or semi-chronic LiCl administration, while the Rb+ and Cs+ concentration in the brain remained elevated for up to 6 days after termination of semi-chronic treatment. Differences in the distribution and retention patterns of Li+, Rb+ and Cs+ also were observed in the brain regions examined. In the blood, the concentration of Li+ reached a peak soon after LiCl administration and then progressively declined while Rb+ and Cs+ concentrations showed a biphasic course with the highest levels obtained 48 hr after administration of the salt solutions. It is suggested that the differences observed in the pharmacokinetics of Li+ compared to Rb+ and Cs+ in the brain might be related to their duration of actions.