Hypothermia-dependent and -independent effects of forced swim on the phosphorylation states of signaling molecules in mouse hippocampus.

Abstract Forced swim (FS) stress induces diverse biochemical responses in the brain of rodents. Here, we examined the effect of hypothermia induced by FS in cold water on the phosphorylationof FS-sensitive signaling molecules in the mouse brain. As we have shown previously, FS in cold water induced a significant increase in the level of tyrosine phosphorylationof SIRPα, a neuronal membrane protein, in mouse hippocampus, while such effect of FS was markedly reduced in mice subjected to FS in warm water. FS in cold water also induced phosphorylationof mitogen-activated protein kinase kinase(MEK) as well as of cAMP response element-binding protein ( CREB), or dephosphorylationof α isoform of Ca 2+ /calmodulin-dependent protein kinase II (αCaMKII) in the hippocampus. These effects of FS on the phosphorylationof these molecules were also lost in mice subjected to FS in warm water. Genetic ablation of SIRPα did not change the phosphorylationstates of these molecules in the brain. Forced cooling of anesthetized mice, which induced a marked increase in the phosphorylationof SIRPα, induced dephosphorylationof αCaMKII in the brain, while the same treatment did not affect the phosphorylationlevel of MEK and CREB. Hibernationalso induced an increase and a decrease of the phosphorylationof SIRPα and αCaMKII, respectively, in the brain of chipmunk. These results suggest that hypothermia is a major element that determines the levels of phosphorylationof αCaMKII and SIRPα during the FS in cold water, while it is not for the phosphorylationlevels of MEK and CREB.