Quantitative Behavioral Analysis of Neuropathic Pain After Chronic Nerve Constriction in the Rat

Abstract

Two types of animal models extrapolating neuropathic pain had been evaluated by artificially induced pain stimuli. Behavioral evaluation for grading pain would be a better quantitative measurement of neuropathic pain, since neuropathic pain represents an entity of inhibition of behavior rather than single response to the pain stimulus.
Left sciatic nerve was lightly ligated to induce neuropathic pain (Group L, n=7) (Group S; Sham n=5). Behavior of rats was continuously monitored by video recording system on 5, 12, 30 postoperative days. Specific behavior of rats was examined and counted.
Result: Frequency of standing in a day significantly decreased on days 5 (p < 0.01), 12 and 30 (p < 0.05) in Group L. Frequency of left leg lifting significantly increased on days 5 and 12 (p < 0.001) , and then decreased slightly on day 30 (p < 0.01).
Frequency of favoring behavior increased by day 30 (p < 0.01). Leg deformity was confirmed in all rats on days 5 and 12, then, decreased to 43% of rats on day 30 in Group L.
Conclusions: Total activity of CCI rat decreases during acute to chronic phase of CCI, then specific activity, favoring leg after standing, such as flinching, biting, licking becomes obvious during chronic phase. This behavior could be a reliable parameter to quantitate neuropathic pain in chronic phase.