Figure 9

Disruption in the hippocampus of the CA1 layer by excised lacunosum-moleculare tissue. Shown are diascopic bright/dark field images from a control (A) and a 3×−chronic exposure rat (B) analyzed at 10 months post blast (animal 590). A tear in the primary visual cortex is indicated by arrows in panels B and C. In panel C, an H&E stained section is shown in which a fragment from the hippocampal lacunosum-moleculare is visible (arrow in panel B) that has been excised and disrupts the hippocampal CA1 field. Panels D-F show the response of this rat which was tested in a previously published behavioral study [8] in a contextual and cued fear paradigm. Methods and original pooled group data were described in Elder et al. [8]. Panel D shows response during the training phase in which rats were exposed to an 80dB tone that was paired with a foot shock. Freezing behavior was measured at baseline, after the tone and after the shock. Panel D shows the test for contextual fear memory performed 24 h after the initial training. Freezing was measured during four minutes in the initial conditioning chamber. Panel F shows the cued fear response performed 24 h after the testing in E. Animals were placed in a novel context and freezing was measured at baseline and after exposure to the conditioned stimulus (80-dB tone). As compared to the control group (n = 13) and the pooled blast exposed group (n = 14), rat 590 failed to freeze following the pairing of the tone and the foot shock in the conditioning phase. It also showed no freezing in the contextual phase but normal freezing in response to the tone in the cued phase. Scale bars: 1 mm, A and B; 200 μm, C.