Chronic Treatment with Anti-bipolar Drugs Causes Intracellular Alkalinization in Astrocytes, Altering Their Functions

Bipolar disorder I and II are affective disorders with mood changes between depressive and manic (bipolar I) or hypomanic (bipolar II) periods. Current therapy of these conditions is chronic treatment with one or more of the anti-bipolar drugs, Li+ ('lithium'), carbamazepine and valproic acid. The pathophysiology of bipolar disorder is multifactorial and far from clear. Recent data on the dependence of normal brain function on neuronal-astrocytic interactions raise the possibility of astrocytic involvement. We will discuss our previously published and new results on effects of chronic treatment of primary cultures of normal mouse astrocytes with any of three conventional anti-bipolar drugs. The focus will be on several drug-induced events in relation to therapeutic effects of the drugs, such as myo-inositol uptake, intracellular pH and alkalinization, drug-induced modulation of glutamatergic activity in astrocytes and release of astrocytic 'gliotransmitters'. Finally, we will discuss the importance of phospholipase A2 (PLA(2)) and arachidonic acid cascade in drug-treated astrocytes, partly based on Dr. Barneda Cuirana's published thesis. All three drugs cause gradual intracellular alkalinization through different mechanisms. Alkalinization inhibit myo-inositol uptake, resulting in reduced inositolphosphate/phospholipid signaling. Accordingly, transmitter-induced increase in free intracellular Ca2+ ([Ca2+](i)) becomes inhibited, aborting release of astrocytic 'gliotransmitters'. The reduction of gliotransmitter effects on neurons may have therapeutic effects in mania. Alkalinization also up-regulates expression of cPLA(2), an enzyme releasing arachidonic acid, and triggered arachidonic acid cascade and production, but perhaps not release, of prostaglandins. Whenever tested, identical effects were observed in freshly isolated astrocytes, but not neurons, from carbamazepine-treated healthy animals.