Figure 2. Prolonged blockade of MAGL and FAAH causes differential analgesic tolerance.
(a) Acute treatment with JZL184 caused elevated withdrawal latencies in the tail immersion test for thermal nociception, while this hypoalgesic response was not observed following chronic treatment with JZL184 (p = 0.33). A similar magnitude hypoalgesic effect was observed in mice treated acutely with PF-3845, and this effect was maintained following chronic treatment with PF-3845. (b, c) Acute treatment with JZL184 or PF-3845 reduced mechanical (b) and cold (c) allodynia in nerve-injured mice. The anti-allodynic effects of PF-3845, but not JZL184, were maintained following chronic administration. (d) MAGL+/+, MAGL+/−, and MAGL−/− mice display similar tail withdrawal latencies. (e, f) Chronic JZL184 treatment causes cross-tolerance to the anti-allodynic effects of WIN55,212-2 and PF-3845. Data are presented as means ± s.e.m., with n = 6–8 per group in all studies. *p < 0.05, **p < 0.01, ***p < 0.001 versus vehicle-treated or wild-type littermate control mice (Dunnett’s post-hoc test). ##p < 0.01, ###p < 0.001 versus respective acute drug treatment group (Bonferroni test).