To further investigate the mechanism of Mme KO memory impairment, we used brain extracts containing the cortex or hippocampus from WT and Mme KO mice to perform ELISA experiments on four neuropeptides (somatostatin, substance P, cholecystokinin and neuropeptide Y) that are considered to be substrates of NEP in the CNS at least in a test-tube paradigm (Turner et al., 2001; Saito et al., 2003; Fig. 2A). Here, CCK is linked to memory impairment.