Fig. 3.

κ-Opioid receptor antagonist norBNI does not alter mechanical sensitivity in saline-treated rats. (A) Male and female Wistar rats were handled and habituated to subcutaneous (SC) saline injections for 1 week before the baseline (BL) paw withdrawal threshold measure. All of the rats then received subcutaneous saline injections once per day, five times per week. After 2 weeks of saline treatment, they were re-tested in the electronic von Frey test. On the following week, all of the rats received vehicle and were tested after 30 min (Table S1) and 24 h (Veh). Next, all of the rats received a single injection of norBNI (30 mg/kg, SC) and were tested at 30 min (Table S1) and 1, 4, 7, and 14 days post-norBNI. Importantly, after their single norBNI injection, the rats continued to receive their daily saline treatment five times per week throughout the experiment. We tested hyperalgesia 4–6 h after the saline injection. (B) Female rats received vehicle, which did not alter their paw withdrawal thresholds, followed by norBNI treatment. nor-Binaltorphimine did not alter mechanical sensitivity on any of the test days. (C) Male rats received vehicle, which did not alter their paw withdrawal thresholds, followed by a single norBNI treatment. nor-Binaltorphimine did not alter paw withdrawal thresholds in males. The data are expressed as mean ± SEM and were analyzed using one-way repeated-measures ANOVA. gf, gram force.