Cerebral Lithium, Inositol and Inositol Monophosphates

: Cerebral regional inositol, inositol-1-phosphate (InslP), and inositol-4-phosphate (Ins4P), intermediates in phosphoinositide (PI) cycle, and brain lithium levels were studied in male HamWistar rats 24 hr after an intraperitoneal injection of a single dose (2, 5–1. mEq./kg) of LiCl. A dose of LiCl higher than 5 mEq/kg caused a remarkable accumulation of Li+ in the brain. Basal brain regional inositol levels (17–2. mmol/kg) were reduced by 6-8 mmol/kg dry brain tissue at doses exceeding 5 mEq/kg of LiCl in all brain regions except the piriform cortex. However, higher doses of LiCl did not cause any further decrease in brain inositol. LiCl increased basal brain regional InslP levels (170–24. μmol/kg) by 0.8 mmol/kg dry brain tissue at most, and there were no consistent additional increases of InslP at LiCl doses exceeding 5 mEq./kg. Moreover, lithium slightly decreased regional cerebral concentrations of Ins4P. Thus, lithium-induced accumulation of InslP or changes of Ins4P levels do not explain lithium-induced decrease in cerebral inositol. Effects of lithium on brain PI turnover are likely to be multifocal and to differ markedly at different concentrations of Li+ in the brain.