CHI-1, but not CHI-2 mice acquired an active place avoidance task.

<p>The sham-CHI, CHI- 1 or CHI-2 groups received four 10-minute trials with a 50-minute intertrial interval. Panel A, Representative tracks of the final trial of sham-CHI, CHI-1 and CHI-2 mice. The 60° stationary shock zone is shown in red. Black circles show the location of the mouse when being shocked. Panel B, Summary of total shock zone entrances during the 4 trials of active place avoidance. The number of shock zone entrances significantly differed on the basis of trial number for the Sham-CHI (F_3,12 = 12.88, p < 0.0005) and the CHI-1 groups (F_3,18 = 8.07, p = 0.001), but not for the CHI 2 group (F_3,21 = 0.32, p = 0.81). Furthermore, there was a statistically significant interaction between group and trial number (F_6,51 = 3.81, p < 0.003). The CHI-2 group had significantly more shock zone entrances than the sham-CHI or CHI-1 groups. In contrast, the sham-CHI and CHI-1 groups had a similar number of shock zone entrances (post hoc, p = 0.05) suggesting that the sham-CHI and CHI-1 groups, but not the CHI-2 group acquired the shock zone location.</p

A single impact produces a heterogeneous vertical g-force.

<p>Panel A, A video still image taken at 16.8msec after impact; a time when the head was no longer moving. A color overlay shows the movement of the ipsilateral (green), midline (red) and contralateral (blue) spots after the impact. Scale bar, 10 mm. The units of g-force are newtons per kg. Panel B, Summary of high-speed video analysis of movements of spots ipsilateral, midline and contralateral to the impact site. An arrow indicates the time of the impact. Panel C, Summary of vertical g-forces computed ipsilateral, midline and contralateral to the impact site. CHI-2 mice had a significantly larger acceleration and deceleration at all three sites than CHI-1 mice (post hoc, *p<0.05). CHI-2 mice had greater rebound acceleration than CHI-1 mice (post hoc, *p<0.05). Panel D, Scatter plot of vertical g-force of individual CHI-1 and CHI-2 mice with time to regain righting reflex. The CHI-2 (<b>ρ</b> = 0.724, p = 0.05), but not CHI-1 (<b>ρ</b> = -0.468, p > 0.2) group had a significant correlation with the time needed to regain righting reflex.</p

CHI-1 mice acquire, but do not retain, a new shock zone location in conflict active place avoidance.

<p>Panel A, Representative tracks from sham-CHI and CHI-1 mice in the final trial of conflict active place avoidance. The 60° stationary shock zone is shown in red. Black circles show the location of the mouse when receiving a shock. Panel B, Summary of conflict active place avoidance. On shock zone entrances during conflict active place avoidance, group and trial did not significantly interact (F_1630,30 = 14.0, p = 0.50). The number of entrances did not significantly differ. (F_1,10 = 0.006, p = 0.94).</p

Grey matter injury in the hippocampi of CHI-1 and CHI-2 mice.

<p>Panel A, Representative photomicrographs of sagittal sections of hippocampus one month after injury stained with antibodies against NeuN (Panel A1) or MAP2 (Panels A2, A3). Panel A3 provides a higher magnification of the CA3 region of the images in Panel A2. Dendrites are fewer and more disorganized in the CHI-1 and CHI-2 groups (arrows). Panel B, Summary of changes in number of NeuN+ cells (left) in the CA3 and CA1 pyramidal cell layers, the granule cell layer of the dentate gyrus or the hilus. The number of NeuN+ cells in the CHI-2 group was significantly lower than the CHI-1 group in the hilus and the CA1 pyramidal cell layer (post hoc, p > 0.05). The CHI-1 and CHI-2 groups had a similar number of NeuN+ cells in the CA3 pyramidal cell layer of CA3; this number was significantly lower than in the sham-CHI group (post hoc p < 0.005). The CHI- 1 and CHI-2 groups had similar loss of MAP2 immunoreactivity in the hilus and the pyramidal cell layers of CA1 and CA3. The amount of MAP2 immunoreactivity was significantly lower than in the sham-CHI group (post hoc p < 0.05). Panel A3 provides a higher magnification of the CA3 region of the images in Panel A2. Dendrites are fewer and more disorganized in the CHI-1 and CHI-2 groups (arrows). Scale bar, 200μm; panels A and B; 100μm, panel C.</p

Assessment of white matter injury in CHI-1 and CHI-2 mice.

<p>Panel A, Representative photomicrographs of sagittal sections of splenium stained with Bielschowsky's modified silver stain (top), or the luxol fast blue myelin stain (bottom). The scale bar is 200μm. Panel B, Summary of changes in silver stain intensity in CHI-1 and CHI-2 mice. Panel C, Summary of myelin loss in CHI-1 and CHI-2 mice. In some brain regions, silver stain or myelin stain intensity in the CHI-1 or CHI-2 groups was significantly lower than in sham-CHI mice (post hoc, *p < 0.05).</p

CHI-1 and CHI-2 mice have differing deficits in righting reflex and rotarod after closed head injury.

<p>Panel A, Assessment of righting reflex. Recovery of righting reflex differed among sham-CHI, CHI-1 and CHI-2 mice (ANOVA, F_2,30 = 18.4, p < 0.001). Sham-CHI mice recovered righting reflex most rapidly followed by CHI-1 and then by CHI-2 (post hoc p<0.01). Panel B, One, three and seven days after either sham-CHI or CHI, mice received four 5-minute trials on the rotarod. Performance on the rotarod had a significant interaction between group and time (F_4,14 = 5.03, p = 0.01). Rotarod performance also had a significant effect between-subjects across days F_2,7 = 5.45, p = 0.04). The three groups significantly differed on the time on the rotarod on Days 1 (F_2,17 = 10.25, p = 0.001), and 3 (F_2,17 = 10.63, p = 0.001), but not on Day 7 (F_2,10 = 0.42, p = 0.68). The performance of the sham-CHI group on Day 1 and 3 was significantly better than the CHI-1 and CHI-2 groups (post hocs, p = 0.001). There were no statistically significant differences in rotarod performance between conditions on Day 7 suggesting that the motor deficits at 1 and 3 days were transient.</p

CHI-1 and CHI-2 mice retain behavioral deficits one month after injury.

<p>Panel A, Summary of active place avoidance one month after injury. Active place avoidance at one month post-injury showed a significant interaction between group and trial (F_6,51 = 6.06, p < 0.0005). The sham-CHI and CHI-2 groups significantly differed between the sham-CHI and CHI 2 (post-hoc, p = 0.001). The CHI 1 group strongly trended toward differing from the CHI 2 group (p = 0.056). Panel B, Sham-CHI mice had a significantly longer time to 1st entrance than CHI-1 or CHI-2 mice (post hoc *p < 0.01). Panel C, At 1 month, number of entrances for conflict active place avoidance, group and trial did not statistically interact (F_1764,39) = 0.662, p = 0.51). The two groups had a similar number of entrances (F_1,13 = 0.136, p = 0.72). On the final trial of conflict active place avoidance, sham-CHI and CHI-1 mice had a similar number of total entrances (t₁₀ = 0.3, p > 0.5), but differed significantly on time to 1st entrance (t₁₀ = 2.98, *p < 0.02).</p

Measurements of mouse behavior during behavioral testing.

<p>Measurements of mouse behavior during behavioral testing.</p