Differential response of calmodulin genes in the mouse brain after systemic kainate administration

In the central nervous system, many of the effects resulting from an increase in the intracellular levels of calcium are mediated by calmodulin, a major calcium-binding protein in the mammalian brain. Calmodulin is expressed by three different genes, namely CaM I, CaM II and CaM III, all of which encode an identical protein. We studied the expression of calmodulin in the mouse brain at different times after the administration of a convulsant dose of kainate, a potent neuroexcitotoxic agent. We detected the presence of the different calmodulin messenger RNAs and of the protein itself in brain sections by in situ hybridization histochemistry and immunocytochemistry respectively. In addition, we determined the calmodulin content in brain regions by radioimmunoassay. Kainate-treated animals did not show areas of neuronal death at the different times following administration considered. An increase in the hybridization signal for CaM I messenger RNAs was observed from 5 h after kainate administration in the different brain regions tested. In contrast, the CaM II messenger RNA signal decreased gradually to a minimum 24 h after treatment in the hippocampus, while the CaM III messenger RNA signal was mostly unaffected. Calmodulin immunoreactivity also increased in the hippocampus. Nevertheless, we did not detect any significant difference in calmodulin content between brain regions of control and treated animals by radioimmunoassay. Kainate treatment induced modifications in the expression of calmodulin at the level of both messenger RNAs and protein. The results suggest a differential regulation of the three calmodulin genes in the adult mouse brain and a post-transcriptional or a post-translational regulation of calmodulin expression.