Development of a Stepping Force Analgesic Meter for a Rat Arthritic Model

Abstract

Behavioural assessment of experimental pain is an essential method for analysing and measuring pain levels. Rodent models, which are widely used in behavioural tests, are often subject to external forces and stressful manipulations that cause variability of the parameters measured during the experiment. Therefore, these parameters may be inappropriate as indicators of pain. In this article, a stepping-force analgesimeter was designed to investigate the variations in the stepping force of rats in response to pain induction. The proposed apparatus incorporates new features, namely an infrared charge-coupled device (CCD) camera and a data acquisition system. The camera was able to capture the locomotion of the rats and synchronise the stepping force concurrently so that each step could be identified. Inter-day and intra-day precision and accuracy of each channel (there were a total of eight channels in the analgesimeter and each channel was connected to one load cell and one amplifier) were studied using different standard load weights. The validation studies for each channel also showed convincing results whereby intra-day and inter-day precision were less than 1% and accuracy was 99.36–100.36%. Consequently, an in vivo test was carried out using 16 rats (eight females and eight males). The rats were allowed to randomly walk across the sensor tunnel (the area that contained eight channels) and the stepping force and locomotion were recorded. A non-expert, but from a related research domain, was asked to differentiate the peaks of the front and hind paw, respectively. The results showed that of the total movement generated by the rats, 50.27 ± 3.90% in the case of the male rats and 62.20 ± 6.12% in that of the female rats had more than two peaks, a finding which does not substantiate the assumptions made in previous studies. This study also showed that there was a need to use the video display frame to distinguish between the front and hind paws in the case of 48.80 ± 4.01% of the male rats and 66.76 ± 5.35% of the female rats. Evidently the assumption held by current researchers regarding stepping force measurement is not realistic in terms of application, and as this study has shown, the use of a video display frame is essential for the identification of the front and hind paws through the peak signals.

Overview of Neurological Mechanism of Pain Profile Used for Animal “Pain-Like” Behavioral Study with Proposed Analgesic Pathways

“…Eventually, the force exerted by each limb will be expressed as the percentage of either their body weight or the sum of the force exerted by both hind paws. The stepping force difference between each hind limb will further be calculated as a ratio for clearer comparison [ 167 ].…”

Screening of Stepping Forces in an Arthritic Rat Model Using a Novel Analgesic Meter and Data Acquisition System

“…A Bakelite box hosts a Huper H4MR type IR CCD camera (Huper, USA). A Picolo PCI card (Euresys, USA) is used to transfer the captured image from the CCD camera to the personal computer [ 10 ]. The computer is used to gather and process the data acquired by the analgesic meter.…”

“…The computer is used to gather and process the data acquired by the analgesic meter. The data acquisition software was programmed using Visual Basic 6 [ 10 ]. The data acquisition software allows researchers to customise their in vivo studies based on individual requirements.…”

“…Therefore, a weight distribution model that uses sensors to capture the weight load of an animal was proposed [ 9 ]. The state of arthritic pain can be determined by measuring the weight load while the rat is walking freely because weight bearing is reduced in arthritic animals when walking [ 10 ]. However, in this protocol the rat is not restrained nor forced to maintain its static position [ 10 ].…”

“…The state of arthritic pain can be determined by measuring the weight load while the rat is walking freely because weight bearing is reduced in arthritic animals when walking [ 10 ]. However, in this protocol the rat is not restrained nor forced to maintain its static position [ 10 ]. Therefore, it is difficult to identify the correct paw of the rat when using the device, especially given the lack of a camera to capture real-time movements, which might affect the peak signal captured.…”