FIG. 2.

Time course of the whisker nuisance response in diffuse brain-injured rats. (A) The whisker nuisance task can detect injury-induced sensitivity to whisker stimulation up to 8 weeks after moderate, midline fluid percussion injury (FPI). Uninjured sham control animals were soothed by the stimulation (low scores). At 1 week after brain injury, the behavioral responses are not significantly different from sham animals. By 4 weeks and through 8 weeks post-injury, brain-injured rats responded to whisker stimulation by freezing, guarding mystacial pads, or acting aggressive (higher scores). At 4 weeks after injury, behavioral performance is significantly different from the sham and 1-week post-injury groups. The sensory sensitivity to whisker stimulation is maintained through 8 weeks post-injury (mean ± standard error of the mean [SEM]; *p < 0.05 compared to sham animals; ⁺p < 0.05 compared to 1 week post-FPI by Kruskal-Wallis analysis of variance [ANOVA] and Mann-Whitney U test). (B) Behavioral responses to whisker stimulation do not habituate over the three consecutive testing periods (P1–P3; mean ± SEM). The observation of behaviors in additional scoring categories contribute to the significant increase in the whisker nuisance score between P1 and P2 (*p < 0.05 by Friedman ANOVA). (C) Whisker nuisance persists once morbidity manifests. A subset of brain-injured animals was evaluated twice by the whisker nuisance task (the lines represent individual animals). Whisker nuisance scores are generally maintained over time. All animals shown here were brain-injured.