Water deprivation upregulates the three calmodulin genes in exclusively the supraoptic nucleus of the rat brain

Calmodulin (CaM), the ubiquitous intracellular calcium-binding protein, is coded by three bona fide CaM genes (CaM I, CaM II and CaM III) in mammals. They code for the same protein and are transcribed at particularly high lev els in the brain, where CaM plays an essential role in basic neuronal funct ions. In this study, the expression of the three CaM genes in response to o smotic stimuli by water deprivation was investigated in the rat brain, with particular interest as concerns the hypothalamic magnocellular nuclei. CaM mRNA levels were determined by quantitative in situ hybridization autoradi ography with gene specific [S-35]cRNA probes. In response to osmotic challe nge, it was found that upregulation of the three CaM genes participates in the activation of the hypothalamo-hypophyseal system in the supraoptic nucl eus (SON) (126% to 169%), but not in the magnocellular part of the paravent ricular hypothalamic nucleus (PVN) (-10%). CaM mRNA levels decreased by 10% -15% in the suprachiasmatic nucleus (SCh) and many other extrahypothalamic brain areas. The opposite responses of the CaM gene expression in the SON a nd the magnocellular part of the PVN suggest a functional difference betwee n them. Moreover, the significantly different magnitudes of the changes in the CaM mRNA levels in the SON nucleus (138%, 126% and 169% for CaM I, CaM II and CaM III, respectively) exemplify the precise differential control of the CaM gene expression in the brain. (C) 1999 Elsevier Science B.V. All r ights reserved.