Elevated RalA activity in the hippocampus of PI3K gamma knock-out mice lacking NMDAR-dependent long-term depression

Abstract

Phosphoinositide 3-kinases (PI3Ks) play key roles in synaptic plasticity and cognitive functions in the brain. We recently found that genetic deletion of PI3K gamma, the only known member of class IB PI3Ks, results in impaired N-methyl-D-aspartate receptor-dependent long-term depression (NMDAR-LTD) in the hippocampus. The activity of RalA, a small GTP-binding protein, increases following NMDAR-LTD inducing stimuli, and this increase in RalA activity is essential for inducing NMDAR-LTD. We found that RalA activity increased significantly in PI3K gamma knockout mice. Furthermore, NMDAR-LTD-inducing stimuli did not increase RalA activity in PI3K gamma knockout mice. These results suggest that constitutively increased RalA activity occludes further increases in RalA activity during induction of LTD, causing impaired NMDAR-LTD. We propose that PI3K gamma regulates the activity of RalA, which is one of the molecular mechanisms inducing NMDAR-dependent LTD.