Analysis of pain related to movement in monoarthritis

K. Hygge Blakeman¹, S. Eriksson², K. Ängeby Möller¹ and O.-G. Berge¹

¹AstraZeneca, Bioscience, Södertälje, Sweden
²Trial Form Support AB, Stockholm, Sweden

Behavioral response to pain in monoarthritic rats can be measured by gait and stance analysis. We have investigated the effect of movement on pain behavior and pharmacological treatment by comparing two analysis paradigms; the box recording and the Paw Print walkway.

In the box recording, rats are placed in a 30x14 cm chamber, allowing only limited locomotion. Under the chambers glass floor a video camera is placed to record the rat’s movements. The Paw Print walkway consists of a 100x10 cm path on which the rats are trained to make a swift, continuous passage. Light is projected into the long margin of the walkway’s glass floor and internally reflected within the glass floor. When the rat’s paw touches the floor, it lights up at the point of contact and a wide-angle camera placed under the walkway records the resulting footprint. In both analysis paradigms, the rat’s behavior is manually given a pain score between one and three. In the Paw Print setup, there is also a computer-assisted analysis of the rat’s gait pattern and weight-bearing.

Subjects were male Sprague-Dawley rats. Monoarthritis was induced by a tibio-tarsal injection of Freund’s complete adjuvant and all animals were then sequentially scored in both setups for up to 8 days after induction. Morphine, dexamethasone and naproxen were administered at different time-points.

There was a strong positive correlation between the scores from the Paw Print walkway and box recording (tau=0.68). Linear regression showed a logarithmic relationship (R2=0.98) where the walkway tended to yield higher scores than box recording. Morphine and dexamethasone were less efficacious in reducing pain-scores in the walkway paradigm and this was also the case with naproxen.

There is a difference between the two analysis setups in both the behavioral endpoint and pharmacological sensitivity. The data suggest a higher level of pain in the Paw Print walkway, which may be a useful paradigm for studying pain related to movement.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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