Memory retrieval-induced changes in the expression of memory-related signaling molecules in hippocampal tissues. (a) Photographs of immunohistochemical results showing memory retrieval-induced changes in the immunoreactivity of anti-phosphorylated CREB (pCREB), anti-phosphorylated ERK (pERK), or anti-phosphorylated CaMKII (pCaMKII) in the hippocampus. (b–d) Western blot analysis of pCREB (b), pERK (c), and pCaMKII (d). Mice were killed immediately after the retention trial of a one-trial passive avoidance task. Data are presented as the means±SEM (n=4). *p<0.05, compared with the control group. The control group was not subjected to a retention trial. The retrieval group was subjected to a retention trial. Magnification: × 50. Bar=200 μm.