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. 2023 Mar 8;43(10):1692–1713. doi: 10.1523/JNEUROSCI.2049-22.2023

Figure 5.

Figure 5.

Morphine analgesia, tolerance, and pain-related suppression of operant responding in Oprm1-Cre rats and wildtype littermates. A, von Frey test and timeline of experiment for morphine analgesia and tolerance. Left, Baseline and von Frey thresholds (g) after ascending doses of morphine (0.625, 1.25, and 2.5 mg/kg, i.p.). Middle, von Frey thresholds (g) after vehicle, 2.5 mg/kg morphine, or 2.5 mg/kg morphine + naloxone (1.0 mg/kg, i.p.). Right, von Frey thresholds (g) after vehicle, 2.5 mg/kg morphine, or 2.5 mg/kg morphine after 21 d of chronic morphine (2.5 mg/kg/day, i.p.). Wildtype (7 males, 3 females), Oprm1-Cre (7 males, 3 females). Individual data points are depicted for males (blue) and females (red). B, Tail flick test and timeline of experiment for morphine analgesia and tolerance. Left, Latency (s) measured after ascending doses of vehicle and morphine (1.25, 2.5, 5, and 10 mg/kg, i.p.). Middle, Latency (s) after vehicle, 5 mg/kg morphine, or 5 mg/kg morphine + naloxone (1.0 mg/kg, i.p.). Right, Latency (s) after vehicle, 5 mg/kg morphine, or 5 mg/kg morphine after 21 d of chronic morphine (5 mg/kg/day, i.p.). Wildtype (5 males, 5 females), Oprm1-Cre (5 males, 4 females). Individual data points are depicted for males (blue) and females (red). C, Acute lactic acid-induced suppression of operant responding for food pellets. Left panels, Mean ± SEM pellet intake change score from baseline after injections of lactic acid (0%, 0.9%, 1.35%, and 1.8%, i.p.), morphine (0, 1, 3, and 10 mg/kg, s.c.), and lactic acid (1.8%) plus morphine (0, 1, and 3 mg/kg, s.c). Right panels, Mean ± SEM percent change from baseline of the data presented on the left panels. Wildtype (4 males, 4 females) and Oprm1-Cre (4 males, 3 females) rats.