Figure 4. Effect of intramuscular TTX on oxaliplatin-induced mechanical hyperalgesia.

After assessment of the mechanical nociceptive threshold (Base), rats received an i.v. dose of oxaliplatin (2 mg/kg) and their mechanical nociceptive thresholds were assessed 4 and 15 days later (OXP). At these time points sequentially increasing doses of TTX, each one-half log unit greater than the previous dose, were injected at 45 min inter-injection intervals. Prior to each higher dose of TTX, the mechanical nociceptive threshold was again assessed, to determine the effect of that dose on the oxaliplatin-induced mechanical hyperalgesia. (A) Four days after oxaliplatin injection TTX produced a small, albeit statistically significant, increase in mechanical nociceptive threshold compared to D-PBS vehicle (Veh). (B) Also four days after oxaliplatin injection, the higher dose of TTX (1 μg) was injected i.m., and the mechanical nociceptive threshold was measured at four different time points. TTX induced a small, albeit statistically significant, increase in mechanical nociceptive threshold after the local injection. (C) Fifteen days after oxaliplatin, only the highest dose of TTX (1 μg) produced a small, yet significant, increase in mechanical nociceptive threshold compared to vehicle. (B) Fifteen days after oxaliplatin injection, the dose of TTX (1 μg) was devoid of statistically significant effect on muscle mechanical hyperalgesia, as revealed by readings taken at 30 min to 2 hours. *P < 0.05; **P < 0.01.