Figure 3.

mTBI increases mechanical hypersensitivity to a low dose of NTG 4 and 12 weeks after closed head injury. Post-sham or injury, C57BL/6J mice received vehicle, low (0.1 mg/kg, ip), or high (10 mg/kg, ip) dose NTG every other day for 9 days (five test days total). (a) and (c) In both 4 and 12 week groups, assessment prior to vehicle or NTG administration revealed that mTBI animals treated with low dose NTG had significantly lower basal thresholds compared to corresponding shams. p < 0.01 treatment, time, and interaction; two-way RM ANOVA and Holm-Sidak post hoc analysis. **p < 0.01, ***p < 0.001, n = 11–18/group. (b) and (d) In the same animals tested 2 h post-NTG/vehicle, both low-and high-dose NTG evoked hyperalgesia that did not differ between sham and mTBI groups. Even after 12 weeks post-injury, mTBI animals are more susceptible to developing NTG-induced chronic pain.