Fig. 2. The effects of intramuscular (IM) or subcutaneous (SQ) injection of H₂O₂ (100 mM, 0.6 ml) on conditioned place aversion (CPA) in rats.

Each column represents the time spent in the preferred and non-preferred chambers during the pre- and post-conditioning sessions (A), and the CPA scores (B). For the intramuscular co-injection of H₂O₂ and AP-18, sequential injections of AP-18 (50 mM, 0.3 ml) followed by H₂O₂ (200 mM, 0.3 ml), were made into the gastrocnemius muscle. Therefore, the total injection volume was 0.6 ml, and the final concentration of H₂O₂ was 100 mM. Each group contained six rats. All data are expressed as means ± SD. * P = 0.0075 by paired t-test. † = 0.0199 compared with the SIF group, ‡ P = 0.0194 compared with the subcutaneous injection of H₂O₂ group, # P = 0.0479 compared with the intramuscular co-injection of H₂O₂ and AP-18 group by one-way ANOVA (F_{3, 20} = 4.884, P = 0.0104) followed by post-hoc Tukey’s test.