LITHIUM STIMULATES GLUTAMATE RELEASE AND INOSITOL 1,4,5-TRISPHOSPHATE ACCUMULATION VIA ACTIVATION OF THE N-METHYL-D-ASPARTATE RECEPTOR IN MONKEY AND MOUSE CEREBRAL-CORTEX SLICES

Beginning at therapeutic concentrations (1-1.5 mM), the anti-manic-depressive drug lithium stimulated the release of glutamate, a major excitatory neurotransmitter in the brain, in monkey cerebral cortex slices in a time- and concentration-dependent manner, and this was associated with increased inositol 1,4,5-trisphosphate [Ins(1,4,5)P-3] accumulation. (+/-)-3-(2-Carboxypiperazin-4-yl)propyl-1-phosphoric acid (CPP), dizocilpine (MK-801), ketamine, and Mg2+-antagonists to the N-methyl-D-aspartate (NMDA) receptor/channel complex selectively inhibited lithium-stimulated Ins(1,4,5)P-3 accumulation. Antagonists to cholinergic-muscarinic, alpha(1)-adrenergic, 5-hydroxytryptamine(2) (serotoninergic), and H-1 histaminergic receptors had no effect. Antagonists to non-NMDA glutamate receptors had no effect on lithium-stimulated Ins(1,4,5)P-3 accumulation. Possible reasons for this are discussed. Similar results were obtained in mouse cerebral cortex slices. Carbetapentane, which inhibits glutamate release, inhibited lithium-induced Ins(1,4,5)P-3 accumulation in this model. It is concluded that the primary effect of lithium in the cerebral cortex slice model is stimulation of glutamate release, which, presumably via activation of the NMDA receptor, leads to Ca2+ entry. Ins(1,4,5)P-3 accumulation increases due to the presumed increased influx of intracellular Ca2+, which activates phospholipase C. These effects may have relevance to the therapeutic action of lithium in the treatment of manic depression as well as its toxic effects, especially at lithium blood levels above 1.5 mM.