The antibipolar drug valproate mimics lithium in stimulating glutamate release and inositol 1,4,5-trisphosphate accumulation in brain cortex slices but not accumulation of inositol monophosphates and bisphosphates

A piece in the puzzle: an ion channel candidate gene for schizophrenia

Mutations in ion channels have been found to cause a variety of mendelian genetic diseases, and polyglutamine repeat expansion is a newly recognized pathogenic mechanism that causes several rare, genetic, late-onset neurological syndromes. Polymorphic polyglutamine tracts are present in a recently described human, calcium-activated potassium channel, KCNN3 (also known as hKCa3), and alleles of this gene that contain longer repeats have been associated with schizophrenia. The physiological function of the channel is consistent with an etiological role in this disease; drugs designed to target this channel might therefore provide novel psychotherapeutics.

Lithium acutely inhibits and chronically up-regulates and stabilizes glutamate uptake by presynaptic nerve endings in mouse cerebral cortex

We previously reported that lithium stimulated extracellular glutamate accumulation in monkey and mouse cerebrocortical slices. We report here that this is caused by lithium-induced inhibition of glutamate uptake into the slice. Glutamate release was amplified 5-fold over inhibition of uptake. When the effects of lithium and the specific glutamate transporter inhibitors, L-trans-pyrrolidine-2, 4-dicarboxylic acid and dihydrokainic acid, were plotted as glutamate accumulation vs. inhibition of glutamate uptake, the plots were superimposable. This finding strongly indicates that lithium-induced glutamate accumulation is caused entirely by inhibition of uptake. With cerebrocortical synaptosomes, inhibition of glutamate uptake was greater than in slices, suggesting that presynaptic nerve endings are the primary site of inhibition of uptake by lithium. Inhibition of uptake was caused by a progressive lowering of Vmax, as the lithium concentration was increased, whereas the Km remained constant, indicating that lithium inhibited the capacity of the transporter but not its affinity. Chronic treatment of mice with lithium, achieving a blood level of 0.7 mM, which is on the low side of therapeutic, up-regulated synaptosomal uptake of glutamate. This would be expected to exert an antimanic effect. Lithium is a mood stabilizer, dampening both the manic and depressive phases of bipolar disorder. Interestingly, although the uptake of glutamate varied widely in individual control mice, uptake in lithium-treated mice was stabilized over a narrow range (variance in controls, 0.423; in lithium treated, 0.184).