It is interesting that, in the mammalian brain, MAPK activity regulates mRNA translation and memory (Kelleher et al., 2004b). Our data indicate that, in addition to SCOP, calpains control synaptic plasticity and memory, in part via activity-dependent degradation of PAIP2A. Despite the similarity in the mechanisms of activity-dependent regulation of SCOP and PAIP2A levels in the brain, their downstream effectors

PLX4032 mw are different; therefore, memory alterations in Paip2a−/− and SCOP-overexpressing mice are not similar. SCOP-overexpressing mice exhibit impaired novel object recognition LTM ( Shimizu et al., 2007), while PAIP2A deletion results in alterations in contextual fear and spatial LTM. We showed here that, in Paip2a−/− mice, the threshold for induction of the protein synthesis-dependent phase of LTP is lowered, and L-LTP was induced with just 1HFS. Remarkably, the threshold for the induction of CaMKIIα translation was similarly reduced in slices from Paip2a−/− mice. 1HFS in Paip2a−/− slices induced robust CaMKIIα expression, whereas no significant CaMKIIα expression was observed

in WT slices. This indicates that the threshold for induction of L-LTP is determined by the sensitivity of the translational machinery to stimulation, which is negatively controlled by PAIP2A. Long-term memory in Paip2a−/− mice was enhanced after weak training, paralleling the low threshold for induction of L-LTP and translation. In response to more intense stimulation (TBS or strong Ku-0059436 research buy contextual fear conditioning), L-LTP and Linifanib (ABT-869) LTM were impaired, akin to earlier reports using other suppressors of translation, such as 4E-BP2 and GCN2 ( Banko et al., 2005; Costa-Mattioli et al., 2005). Similar to Paip2a−/−, in 4E-BP2 and GCN2−/− hippocampal slices 1HFS elicited L-LTP, while stronger tetanic stimulation (4HFS) led to L-LTP impairment. Moreover, weak

training enhanced LTM in GCN2−/− mice, while more intense training caused LTM deficits. In Tsc2+/− mice, the mTOR pathway, an important regulator of translation, is hyperactivated resulting in impaired memory ( Ehninger et al., 2008). Treatment with the mTOR inhibitor, rapamycin, reversed the learning and memory deficits, indicating that enhanced mTOR activity—and probably translation—are responsible for memory deficits ( Ehninger et al., 2008). A conceivable explanation for the impairment is that strong stimulation in Paip2a−/− mice results in excessive translation leading to impairment of L-LTP and memory. One possibility is that synthesis of proteins detrimental to L-LTP and memory maintenance (negative regulators) after strong stimulation in Paip2a−/− mice leads to L-LTP and memory deficits. Physiologically, this mechanism can serve to protect the brain under conditions of excessive stimulation such as seizure activity.