Chronic administration of lithium chloride increases immunodetectable glial fibrillary acidic protein in the rat hippocampus.

We studied the effect of treating rats with lithium salts on the content and in vitro phosphorylation rate of the astrocyte cell marker, glial fibrillary acidic protein (GFAP), in brain slices. Rats were fed a diet incorporating lithium chloride until the concentration of Li+ in serum reached 0.6-1.2 mM, a range similar to that achieved in clinical practice. Hippocampal tissue was analyzed for immunoreactive GFAP by a dot assay, and slices of hippocampus and caudate nucleus were labeled with [32P]phosphate to determine the in vitro rate of phosphorylation of GFAP. Compared with controls, the level of immunoreactive GFAP in the hippocampus from lithium-treated rats was increased 34%, and GFAP in hippocampal slices incorporated 39% more 32P. This effect of lithium was apparently not confined to the hippocampus because the in vitro rate of phosphorylation of GFAP in caudate slices was also increased in the treated rats.