Abstract
BackgroundThere are some previous reports of gait analysis using a rodent pain model. Applying the CatWalk method, objective measurements of pain-related behavior could be evaluated, but this method has not been investigated using the nucleus pulposus (NP) applied model, which was developed as a model of lumber disc herniation. We aimed to measure mechanical withdrawal thresholds and analyze gait patterns using the CatWalk method for the evaluation of the pain-related behavior caused by NP application.MethodsTwenty-four nine-week-old female Sprague-Dawley rats were randomly divided into two experimental groups, the NP group (n = 12), in which autologous NP from the tail was applied to the left L5 dorsal root ganglion, and the sham-operated group (n = 12). Measurements of mechanical withdrawal thresholds were performed using von Frey filaments touching the left footpads, and gait analysis was performed using the CatWalk method. These experiments were conducted 1 day before surgery and 7, 14, 21, and 28 days after surgery. Data were statistically analyzed using the Wilcoxon rank-sum test.ResultsThe NP group showed significantly lower withdrawal thresholds than the sham group at days 14 and 21. Stand (duration of contact of a paw with the glass plate) was significantly higher in the NP group at days 7 and 14, whereas step cycle (duration between two consecutive initial contacts of the same paw) and duty cycle (stand as a percentage of step cycle) were the same at day 7. Long initial dual stance (duration of ground contact for both hind paws simultaneously, but the first one in a step cycle of a target hind paw) of the right hind paw was measured at days 7 and 14. The left hind paw per right hind paw ratio of the stand index (speed at which the paw loses contact with the glass plate) and mean intensity (mean intensity of the complete paw) changed at day 7 or 14. Phase dispersion (parameter describing the temporal relationship between placement of two paws) of the hind paws decreased at day 7.ConclusionsRats with applied NP showed a decreased withdrawal threshold and abnormal gait. The differences in gait parameters between the NP and sham groups were observed at an earlier time point than the withdrawal thresholds. Gait analysis could be an effective method for understanding pain caused by applied NP.
Highlights
There are some previous reports of gait analysis using a rodent pain model
The aim of this study was to investigate pain-related behavior initiated by nucleus pulposus (NP) application using measurement of mechanical withdrawal thresholds and gait pattern analysis using the CatWalk method
Measurement of mechanical withdrawal threshold There was no significant difference in the withdrawal threshold between the two groups at baseline
Summary
There are some previous reports of gait analysis using a rodent pain model. Applying the CatWalk method, objective measurements of pain-related behavior could be evaluated, but this method has not been investigated using the nucleus pulposus (NP) applied model, which was developed as a model of lumber disc herniation. To evaluate the effects of various proinflammatory cytokines (Kawakami et al 1996; Olmarker and Larsson 1998; Igarashi et al 2000; Sasaki et al 2007) and other factors (Brisby et al 2000; Hashizume et al 2007; Otoshi et al 2010; Uesugi et al 2011), pain-related behavior in a nucleus pulposus (NP) rat model has previously been evaluated using the von Frey method (Igarashi et al 2000; Hashizume et al 2007; Kato et al 2008; Otoshi et al 2011; Uesugi et al 2011) This autologous NP applied rat model was developed to determine the pathological changes associated with lumber disc herniation (Yabuki et al 1998). In rodents, a low withdrawal threshold has been observed, and it reflects mechanical allodynia, not hypoalgesia
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