Lack of effect of mood stabilizers or neuroleptics on GSK-3β protein levels and GSK-3 activity

Glycogen synthase kinase (GSK)-3beta protein levels and GSK-3 activity were previously found to be over 40% reduced in the post-mortem prefrontal cortex of schizophrenic patients. Lithium and valproate have been reported to selectively inhibit GSK-3. We hypothesized that in-vivo administration of lithium and valproate would result in up-regulation of GSK-3beta protein levels and GSK-3 activity. The present study aimed to evaluate the possible involvement of neuroleptic treatment in the decrease of GSK-3 in schizophrenia. Rat frontal cortex GSK-3beta protein levels and GSK-3 activity were measured following administration of therapeutic doses of lithium or valproate for 11 d, or of haloperidol, chlorpromazine or clozapine for 21 d. None of the drugs induced a change in GSK-3beta protein levels. All the drugs except chlorpromazine (which was not tested) did not affect GSK-3 activity. This suggests that GSK-3 inhibition by lithium or valproate does not induce regulation of protein levels or activity and that the reduction in GSK-3beta protein levels and GSK-3 activity in the post-mortem prefrontal cortex of schizophrenic patients is not neuroleptic-treatment related.