FIGURE 1.

Repeated morphine treatment induced mechanical hypersensitivity in NK1R-GFP and GAD67-GFP transgenic mice. (A) Temporal diagram of drug administration and experiments. Morphine (blue arrow, 20 mg/kg) were administrated by intraperitoneal injection. At day 4, the mice were euthanized for electrophysiological recordings (red arrow). Pain behavioral test was performed 2 h post-morphine injection. Paw withdrawal threshold (PWT) was measured by von Frey tests (black arrow) using (B) NK1R-GFP mice for sNK1Rn (N = 6 for each group) and (C) GAD67-GFP mice for sGABAn (N = 6 for each group). (D) No gender effect on the repeated morphine induced mechanical hypersensitivity (Male,Vehicle (N = 3); Male, Morphine (N = 3); Female, Vehicle (N = 3); Female, Morphine (N = 3). ns: not significant, ^∗∗p < 0.01 vs. vehicle by Sidak’s multiple comparison test following multilevel analysis.