Cellular mechanisms and second messengers: relevance to the psychopharmacology of bipolar disorders

The discovery of lithium's efficacy as a mood-stabilizing agent revolutionized the treatment of patients with bipolar disorder and after five decades, lithium continues to be the mainstay of treatment for bipolar disorder. Recent research on the molecular mechanism underlying the therapeutic effect of lithium has focused on how it changes the activities of cellular signal transduction systems, especially the cyclic AMP and phosphomositide second-messenger systems. Considerable data suggest that carbamazepine and valproate (VPA) are an alternative or adjunctive treatment to lithium. VPA, despite being dissimilar structurally to lithium, shares most of the effects of lithium at the level of protein kinase C (PKC). Like lithium, VPA reduces the activity of PKC and reduces the protein levels of different PKC isoforms, however the effects of VPA appear to be largely independent of inositol. The ton-term efficacy of VPA and lithium in bipolar disorder suggested that modulation of gene expression might be an important target for these drugs. Both VPA and lithium altered the expression of the early inducible genes for c-fos and cjun thus promoting the expression of specific proteins. The genes known to be regulated by the AP-1 family of transcription factors include genes for various neuropeptides, neurotrophins, receptors, transcription factors, enzymes, proteins that bind to cytoskeletal elements, and cytoprotective proteins such as bcl-2. In conclusion chronic treatment with lithium and other mood stabilizers, by regulating transcriptional factors, may modulate the expression of a variety of genes that compensate for aberrant signalling associated with the pathophysiology of bipolar disorder.