Figure 4.

The dorsal hippocampus Arc mRNA upregulation by spatial memory recall at 24 h and 1 month retention intervals. A, Spectrum images of autoradiograms show the elevated Arc mRNA expression in DG (dorsal blade), CA3, CA1, and subiculum after a recent memory test in a WMT rat compared with its SW and naive matched controls. Images of the ¹⁴C microscales that were exposed in parallel with the samples illustrate the conversion of mean gray level into nanocuries per gram of tissue equivalents. The mean values in WMT, SW, and naive rats (experimental group 1), respectively, of Arc mRNA signal measured over the entire CA1 (644.5, 415.5, and 254.3 nCi/g), CA3 (247.1, 197.4, and 103 nCi/g), subiculum (843.95, 475.24, and 227.45 nCi/g), and dorsal blade of DG (199.91, 143.94, and 113.63 nCi/g) are shown. Scale bar, 1 mm. B, Autoradiograms show characteristic for long-term memory recall elevated Arc mRNA expression in CA3 and subiculum of a WMT rat compared with its SW and naive controls. The mean values in WMT, SW, and naive rats, respectively (experimental group 10), of Arc mRNA signal measured over CA1 (1154, 1123, and 446.2 nCi/g), CA3 (589.1, 346.7, and 124.7 nCi/g), subiculum (1339, 1142, and 339.3 nCi/g), and DG (360.6, 321, and 113.2 nCi/g) are shown. The small and inconsistent difference between WMT and SW controls was characteristic for CA1. The DG-specific signal was smaller but consistent. Displayed images represent different in situ hybridization experiments and therefore cannot be compared directly over the memory retention period.