Figure 5.

Multiple rostro-caudal levels of the parietal association cortex show time-dependent changes in laminar profiles for Arc gene expression specific to water-maze memory recall. (A,C) Following a recent memory recall, stronger Arc mRNA expression occurs consistently in the upper layers when compared to the deep layers. The spectrum images of autoradiograms were obtained from brain sections of WMT, SW and naive control rats. For the illustrated sections, a task-specific Arc signal is 304.3 nCi/g for the deep (L5 and L6) layers and 472.1 nCi/g for the upper (L2/3 and L4) layers. A task-specific signal is the difference in absolute values of Arc mRNA expression between the WMT and SW sections. The scatter plots show that a stronger Arc expression was found in WMT rats relative to SW and naïve matched controls in all layers at the multiple rostro-caudal levels. The data points in the scatter plots are individual mean values of Arc mRNA levels obtained by between-subject normalizations for anatomical matches pooled from the five triads. (B,D) Following a remote memory recall, a stronger task-specific Arc expression was found in the upper layers compared to the deep layers but only in a few sections located around 5-mm level (100.5 and 275.3 nCi/g, respectively; see images on B). Overall, however, the difference between upper and deep layers diminished and was not consistent at this point. After a 1-month memory recall, the caudal part of the parietal cortex (Par-2, within a 5.19–2.5 mm segment, indicated by an arrow) displayed a smaller increase in Arc expression. In the rostral part (Par-1, within a 5.8–5.2 mm segment), the Arc signal in the WMT group became even smaller than the SW signal. Scale bar: 1 mm. The brain sections in (A,B) were obtained from experimental triads 1 and 9, respectively.