Expression and pharmacological modulation of visceral pain-induced conditioned place aversion in mice

Abstract

Pain encompasses both a sensory as well as an affective dimension and these are differentially processed in the brain and periphery. It is therefore important to develop animal models to reflect the non-reflexive assays in pain. In this study, we compared effects of the mu opioid receptor agonist morphine, the nonsteroidal anti-inflammatory drug ketoprofen and the kappa receptor opioid agonist U50,488H and antagonist JDTic on acetic acid-induced stretching and acetic acid-induced aversion in the condition place aversion (CPA) test in male ICR mice. Intraperitoneal administration of acetic acid (0.32-1%) was equipotent in stimulating stretching and CPA. Ketoprofen, morphine and U50,488H all inhibited the acid-induced stretching. Ketoprofen and morphine also blocked the acid-induced CPA but U50,488H failed to do so. The reversal ability of ketoprofen and morphine on acid-induced CPA is unique to pain-stimulated place aversion since these drugs failed to reduce non-noxious LiCl-induced CPA. Overall, this study characterized and validated a preclinical mouse model of pain-related aversive behavior that can be used to assess genetic and biological mechanisms of pain as well as improving the predictive validity of preclinical studies on candidate analgesics.

Keywords: Acetic acid; Analgesics; Conditioned place aversion; Mice; Pain.

Figure 1. Effects of acetic acid (AA) concentration and treatment interval on acid-stimulated stretching and acid-induced conditioned place aversion (CPA) in mice

Figure 1A shows the concentration-effect curve for intraperitoneal acetic acid (AA)-stimulated stretching, with AA concentration (log scale) on the x-axis and the number of stretches on the y-axis. Figure 1B shows the time course of 1% AA-stimulated stretching, with treatment time in min between AA injection and initiation of the observation period on the x-axis and the number of stretches on the y-axis. Figure 1C shows the concentration-effect curve for intraperitoneal AA-induced CPA with AA concentration (log scale) on the x-axis and the aversion score (in sec) on the y-axis. Figure 1D shows the time course of AA-induced CPA, with the treatment time in min between AA injection and initiation of the treatment conditioning session on the x-axis and the aversion score (in sec) on the y-axis. Data points above “V” represent effects of sterile water (vehicle of AA) control treatment on stretching (A,B) or aversion score (C,D), and filled symbols indicate significantly different from water as determined by one-way ANOVA followed by Tukey’s post hoc test (p<0.05). Data are expressed as means ± S.E.M. from 6–10 mice.

Figure 2. The effects of ketoprofen, morphine and U50,488H on AA-induced stretching

Subcutaneous pretreatment of saline, ketoprofen (1, 2, 4 mg/kg), morphine (0.32, 1 3.2 mg/kg), and U50,488H (0.1, 0.32, 1, 3.2, 10 mg/kg) on intraperitoneal 1% acetic acid (AA)-induced stretching. Data point “saline” represents number of stretches following acid administration after saline pretreatment. Data are expressed as means ± S.E.M. from 6–8 mice. Filled symbols indicate significantly different from saline pretreatment as determined by one-way ANOVA followed by Tukey’s post hoc test (p<0.05).

Figure 3. The effects of ketoprofen, morphine and U50,488H on AA-induced CPA

Subcutaneous pretreatment of (A) ketoprofen (1, 2, 4 mg/kg), (B) morphine (0.32, 1 3.2 mg/kg), and (C) U50,488H (0.1, 0.32, 1, 3.2, 10 mg/kg) on intraperitoneal 1% acetic acid (AA)-induced conditioned place aversion (CPA). For each panel, the abscissa shows drug dose in mg/kg (log scale, V=vehicle), and the ordinate shows preference score expressed as the time spent in drug-paired side of the box. Vehicle was saline for test drugs and sterile water for AA. “AA” represents time spent acid-induced aversion score (in sec) on test day. Data are expressed as means ± S.E.M. from 6–10 mice. Filled circles points indicate that the AA treatment is significantly different than the V treatment. Filled triangles points indicate significant difference from the V treatment and filled squares points indicate significant difference from the AA treatment by one-way ANOVA followed by Tukey’s post hoc test (p<0.05).

Figure 4. The effects of JDTic on AA-induced stretching and CPA

The effects of subcutaneous JDTic (10 mg/kg) pretreatment to vehicle, acetic acid (AA, 1%, intraperitoneal) and U,50488H (10 mg/kg) administrations on (A) AA-induced stretching and (B) conditioned place aversion (CPA). Vehicle was saline for test drugs and sterile water for AA. Data are expressed as means ± S.E.M. from 5–9 mice. * indicates a significant effect compared to correspondent vehicle by one-way ANOVA followed by Tukey’s post hoc test (*p<0.05). #indicates a significant effect compared to U50,488H by one-way ANOVA followed by Tukey’s post hoc test (^#p<0.05).

Figure 5. The effect of ketoprofen, morphine on non-noxious LiCl-induced CPA

Subcutaneous pretreatment of ketoprofen (4 mg/kg) and morphine (0.32 mg/kg) on intraperitoneal lithium chloride (LiCl, 150 mg/kg)-induced conditioned place aversion (CPA). Vehicle was saline for test drugs and LiCl. Data are expressed as means ± S.E.M. from 6–10 mice. * indicates a significant effect compared to correspondent vehicle by one-way ANOVA followed by Tukey’s post hoc test (*p<0.05).