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. Author manuscript; available in PMC: 2016 Sep 2.
Published in final edited form as: Neuropharmacology. 2012 May 2;63(3):427–433. doi: 10.1016/j.neuropharm.2012.04.028

Fig. 1.

Fig. 1

Differential development of antinociceptive tolerance to chronic morphine in male and female rats. Escalating doses of morphine were given for five consecutive days to groups of male (n = 14) and female (n = 15) rats. Control rats received an equivalent volume of saline (male, n = 14; female, n = 15). Tolerance was verified by measuring TFL before (A) and after (B) a challenge dose of morphine administered on the 6th day. Both male and female rats in the chronic morphine-treated groups showed less responsiveness to 10 mg/kg morphine than rats that received saline, but the degree of antinociceptive tolerance was greater in male rats. Asterisks (**) indicate decreased TFL compared to controls of the same sex (p < 0.01) and triangles (ΔΔ) indicate significantly less TFL compared to female rats (p < 0.01). Data were analyzed by two-way ANOVA with Bonferroni post-tests.