Effects of acute nicotine on thermal antinociception, locomotor activity, and body temperature in the B6J and B6N substrains. Thermal antinociception is expressed as the percentage of the maximal possible effect in (a) tail flick and (b) hot plate test. (c) Locomotion response to acute nicotine in male B6J and B6N mice. (d) Body temperature in response to acute nicotine in male B6J and B6N mice. Nicotine (0.1, 0.5, 1, and 2 mg/kg) or the vehicle (0.9% saline) was administered subcutaneously. Each data point for thermal antinociception is represented by the mean %MPE + SEM. Significant difference is based on Holm-Sidak post-hoc test following the two-way ANOVA between both substrains (* p < 0.05, *** p < 0.001, **** p < 0.0001), n = 8/group.