Effects of Ketoprofen and Morphine on Pain-Related Depression of Nestlet Shredding in Male and Female Mice

Abstract

A primary goal in pain treatment is restoration of behaviors that are disrupted by pain. Measures of pain interference indicate the degree to which pain interferes with activities in pain patients, and these measures are used to evaluate the effects of analgesic drugs. As a result of the emphasis on the expression and treatment of functional impairment in clinical settings, preclinical pain researchers have attempted to develop procedures for evaluation of pain-related functional impairment in laboratory animals. The goal of the present study was to develop and validate a low cost procedure for the objective evaluation of pain-related depression of home cage behavior in mice. On test days, a 5 × 5 cm Nestlet was weighed prior to being suspended from the wire lid of the home cage of individually housed male and female ICR mice. Over the course of experimental sessions, mice removed pieces of the suspended Nestlet, and began to build a nest with the material they removed. Thus, the weight of the pieces of Nestlet that remained suspended at various time points in the session provided an indicator of the rate of this behavior. The results indicate that Nestlet shredding was stable with repeated testing, and shredding was depressed by intra-peritoneal injection of 0.32% lactic acid. The non-steroidal anti-inflammatory drug ketoprofen blocked 0.32% lactic acid-induced depression of shredding, but did not block depression of shredding by a pharmacological stimulus, the kappa opioid receptor agonist U69,593. The μ-opioid receptor agonist morphine did not block 0.32% lactic acid-induced depression of shredding when tested up to doses that depressed shredding in the absence of lactic acid. When noxious stimulus intensity was reduced by decreasing the lactic acid concentration to 0.18%, morphine was effective at blocking pain-related depression of behavior. In summary, the data from the present study support consideration of the Nestlet shredding procedure for use in studies examining mechanisms, expression, and treatment of pain-related functional impairment.

Keywords: behavior; depression; impairment; ketoprofen; morphine; nesting; pain.

Figure 1

Suspended Nestlet shredding under baseline and control conditions. The abscissa shows session time, and the ordinate shows mean % Removed. “No Manipulation” (squares) indicates mice received no treatment prior to the session. “Lactic Acid Vehicle” (circles) indicates mice received an intraperitoneal injection of sterile water immediately prior to the session. Symbols show mean ± SEM, and represent data from 12 mice (seven males and five females). Filled symbols indicate a significant difference compared to the no manipulation condition at that time point.

Figure 2

Effects of intraperitoneal lactic acid on Nestlet shredding. The abscissa shows lactic acid concentration, and the ordinate shows mean % Removed. Symbols show mean ± SEM, and represent data from 12 mice (seven males and five females). The same mice used for experiments associated with Figure 1 were used in experiments associated with this figure. Filled symbols indicate a significant difference compared to lactic acid vehicle.

Figure 3

Effects of ketoprofen on IP acid-induced depression of Nestlet shredding. The abscissa shows ketoprofen dose, and the ordinate shows mean % Removed. Circles indicate data for ketoprofen alone, and squares indicate data for ketoprofen administered prior to IP acid. Symbols show mean ± SEM, and represent data from 12 mice (five males and five females). Filled points indicate a significant difference compared to lactic acid in the absence of ketoprofen.

Figure 4

(A) Effects of U69,593 on Nestlet shredding. The abscissa shows U69,593 dose, and the ordinate shows mean % Removed. (B) Effects of ketoprofen on 1.0 mg/kg U69,593-induced depression of Nestlet shredding. The abscissa shows ketoprofen dose, and the ordinate shows mean % Removed. Symbols show mean ± SEM, and represent data from 12 mice (six males and five females). Filled points indicate a significant difference compared to vehicle.

Figure 5

(A) Effects of morphine on 0.32% IP acid-induced depression of Nestlet shredding. (B) Effects of morphine on 0.18% IP acid-induced depression of Nestlet shredding. The abscissa shows morphine dose, and the ordinate shows mean % Removed. Circles indicate data for morphine alone, and squares indicate data for morphine administered prior to IP acid. Symbols show mean ± SEM, and represent data from 12 mice (six males and five females). Separate groups of mice were used for the experiments associated with each panel. Filled points indicate a significant difference compared to morphine vehicle.