Figure 5.
Arc mRNA upregulation in the ventral hippocampus and entorhinal cortex by spatial memory recall at 24 h and 1 month retention intervals. A, Spectrum images of autoradiograms show characteristically elevated Arc mRNA expression in the DG, CA1, subiculum, and rostral LEA after a recent spatial memory test in a WMT rat compared with SW, and naive controls. Mean values of Arc mRNA signal were measured over the entire regions in WMT, SW, and naive rats, respectively, (experimental group 4) in CA1 (631.3, 394.2, and 313.5 nCi/g), DG (158.6, 78.7, and 115.3 nCi/g), upper subiculum (445.4, 251.7, and 193.3 nCi/g), lower subiculum (353.6, 205.4, and 131 nCi/g), and rostral LEA (123.4, 91, and 32.3 nCi/g). Scale bar, 1 mm. B, Autoradiograms show characteristically elevated Arc mRNA expression in subiculum but not in rostral LEA after the long-term spatial memory test. The Arc mRNA expression in CA1 of the WMT and SW control animals did not differ, and there was a moderate but consistent increase in DG. Mean values of Arc mRNA signal were measured over CA1 (485.1, 488.6, and 297.9 nCi/g; experimental group 10), upper subiculum (539.5, 438.6, and 179.2 nCi/g), lower subiculum (393.6, 321.1, and 152.8 nCi/g), DG (150.5, 128, and 135.5 nCi/g), and rostral LEA (130.6, 142.4, and 36.8 nCi/g). C, Elevated Arc mRNA expression in the MEA and caudal LEA after a recent spatial memory test compared with SW and naive controls (LEA: 194.05, 127.7, and 29.5 nCi/g; MEA: 130.5, 118, and 48.3 nCi/g; experimental group 3). Scale bar, 1 mm. D, Elevated Arc mRNA expression in the MEA and caudal LEA after a remote memory test compared with SW and naive controls (LEA: 475.4, 229, and 63.4 nCi/g; MEA: 264.3, 120, and 62.1 nCi/g; experimental group 7). Note the heightened Arc mRNA levels in the visual cortex, postsubiculum (Post), parasubiculum (PaS), and presubiculum (PrS) after both recent and remote memory activation. VI, Primary visual cortex; VII, secondary visual cortex; RS, retrosplenial cortex.