Contribution of PSD-95 protein to reward location memory

The molecular mechanisms involved in formation of memory are still poorly understood. We focus here on the function of post-synaptic density protein 95 (PSD-95) and its phosphorylation by CaMKII in spontaneous learning about reward location in female mice. We show that formation of reward location memory leads to downregulation of PSD-95 protein in dendritic spines of the stratum radiatum, area CA1, and selective shrinkage of dendritic spines that contain PSD-95. ShRNA-driven, long-term downregulation of PSD-95 in the area CA1 decreases precision of memory. Autophosphorylation deficient CaMKII mutant mice (CaMKII:T286A) need more time than wild-type animals to learn the location of reward. The same impairment is observed after CA1-targeted overexpression of CaMKII phosphorylation-deficient form of PSD-95 (PSD-95:S73A). In contrast to young adult mice, in aged animals reward location learning affects only spines that lack PSD-95. The frequency and size of the spines without PSD-95 are increased, while shRNA targeted to PSD-95 affects neither speed of learning nor precision of memory indicating alternative mechanisms to support successful memory formation in old mice. Altogether, our data suggest that dynamic regulation of PSD-95 expression is a mechanism that accelerates learning and improves precision of reward location memory in young mice. The function of PSD-95 in memory processes changes in aged animals.