Quantitative study of the distribution of lithium in the mouse brain for various doses of lithium given to the animal.

Lithium is detected in the mouse brain with the aid of a (n,alpha) nuclear reaction. The resolving power is of a few micron. The detection efficiency is estimated in a first series of experiments with brain sections of progressively increasing thickness. This allows us to make the microlocation of lithium in the brain sections quantitative. Lithium accumulation in the different brain substructures is then measured for increasing lithium doses given to the animals (1--15 meq/kg animal). For measurements made 6 h after the last injection of lithium, it is corroborated that the accumulation of Li is much larger in the areas with cellular bodies of neurons than in those with nerve trunks only, especially for the smaller doses of lithium given as treatment. Whereas the accumulation curve as a function of the Li concentration of the blood is linear for areas with nerve trunks only, it is negatively bent for the areas with cellular bodies. This and previous data allow us to attempt an estimate of the Li content of the cellular bodies only. A saturation effect seems to appear as soon as the Li concentration in the blood is greater than 1 mM.