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. 2013 Nov 15;8(11):e79239. doi: 10.1371/journal.pone.0079239

Figure 2. Fentanyl self-administration in CFA-induced inflammation.

Figure 2

Complete Freund’s Adjuvant was injected intraplantarly (i.pl.) the day before the first self-administration session. (A) Mechanical hyperalgesia was assessed through day 19 of the study. CFA-treated hindpaws (inverted closed triangles) demonstrated significantly reduced (p < 0.05) thresholds to paw withdrawal relative to contralateral hindpaws (open triangles) or saline-treated controls (circles). Saline (B) or CFA (C) was injected i.pl. in the left hindpaw and establishment of fentanyl self-administration assessed by bar pressing on the active lever compared to the control lever. Responses represent lever presses on one of two bars. The first bar (active lever) delivers 70 µL of fentanyl (10 µg/ml) (triangles). Pressing the control lever results in no reward and is indicative of non-specific activity (circles). (D) The magnitude of discrimination between the active and control levers are displayed for the duration of the testing period for CFA (closed circles) and saline-treated (open triangles) mice. (E) Analysis of the AUC for the groups in B and C show that mice that had CFA-induced hyperalgesia did not lever press for fentanyl. (F) Analysis of the AUC for the groups in E show that while saline-treated mice discriminated between the active and control levers, mice with CFA-induced hyperalgesia did not. (*significance was determined by ANOVA; p < 0.05; n=8 per group).