Hippocampal Cortactin Levels are Reduced Following Spatial Working Memory Formation, an Effect Blocked by Chronic Calpain Inhibition

Abstract

The mechanism by which the hippocampus facilitates declarative memory formation appears to involve, among other things, restructuring of the actin cytoskeleton within neuronal dendrites. One protein involved in this process is cortactin, which is an important link between extracellular signaling and cytoskeletal reorganization. In this paper, we demonstrate that total hippocampal cortactin, as well as Y421-phosphorylated cortactin are transiently reduced following spatial working memory formation in the radial arm maze (RAM). Because cortactin is a substrate of the cysteine protease calpain, we also assessed the effect of chronic calpain inhibition on RAM performance and cortactin expression. Calpain inhibition impaired spatial working memory and blocked the reduction in hippocampal cortactin levels following RAM training. These findings add to a growing body of research implicating cortactin and calpain in hippocampus-dependent memory formation.

Keywords: calpain; cortactin; hippocampus; radial arm maze; spatial working memory.

Figure 1

Mean latencies to complete the training phase of the SWSh RAM task during acquisition. Each data point represents the group mean (±SEM) of each experimental group for training block 1–8.

Figure 2

Cortactin is transiently reduced 30 min after RAM training. Representative immunoblots and group means for hippocampal cortactin (±SEM; expressed as percent of untrained controls) at 5 min, 30 min, and 4 h following RAM training. * p < 0.05 compared to untrained controls.

Figure 2

Cortactin is transiently reduced 30 min after RAM training. Representative immunoblots and group means for hippocampal cortactin (±SEM; expressed as percent of untrained controls) at 5 min, 30 min, and 4 h following RAM training. * p < 0.05 compared to untrained controls.

Figure 3

Y421-phosphorylated cortactin is reduced 30 min after RAM training. Representative samples and graphical depictions of group means for hippocampal Y421-phosphorylated cortactin (±SEM; expressed as percent of untrained controls) at 5 min, 30 min, and 4 h following RAM training. * p < 0.05 compared to controls.

Figure 3

Y421-phosphorylated cortactin is reduced 30 min after RAM training. Representative samples and graphical depictions of group means for hippocampal Y421-phosphorylated cortactin (±SEM; expressed as percent of untrained controls) at 5 min, 30 min, and 4 h following RAM training. * p < 0.05 compared to controls.

Figure 4

Chronic calpain inhibition impairs spatial working memory formation in the RAM. Animals in both groups acquired the task (A) with both groups showing pre-surgery latencies that were not significantly different overall or on block 7 or block 8. Post-surgery, there were no differences between Veh and Cal-I groups for within phase errors (B); but a significant increase in across-phase errors for the Cal-I group was seen (C) compared to Veh controls. * p < 0.05.

Figure 5

Chronic calpain inhibition blocks the reduction in total, but not Y421-phosphorylated cortactin following spatial working memory formation in the RAM. Representative samples and graphical depictions of group means for hippocampal total, and Y421-phosphorylated, cortactin (±SEM; expressed as percent of untrained controls) at 30 min following RAM training for Veh and Cal-I groups. * p < 0.05 compared to untrained controls, ** p < 0.05 compared to both untrained control and Cal-I groups.