Force of limb withdrawals elicited by graded noxious heat compared with other behavioral measures of carrageenan-induced hyperalgesia and allodynia.
We investigated if carrageenan-induced thermal hyperalgesia and mechanical allodynia are associated with a reduction in threshold and-or enhancement of suprathreshold nocifensive responses, using a method to measure the force of a hind limb wilhdrawal reflex elicited by graded noxious heat stimuli (36-52 degrees C, 5s) delivered by Peltier thermode tethered to the ventral hind paw of conscious rats. Withdrawal reflexes were recorded 2.5 h after intraplantar injection of carrageenan (1 or 0.1%) or saline vehicle in sessions >2 weeks apart: baseline reflexes were assessed the day before. Withdrawal reflex force increased linearly from 42-52 degrees C. Carrageenan 1% significantly enhanced withdrawal reflexes at 40-46 degrees C, reducing the slope and threshold of the stimulus-response function. This was associated with significant reductions in thermal paw withdrawal latency (Hargreaves test: by 50%), mechanical withdrawal threshold (by 82%) and weight bearing on the injected side (by 81%) measured with independent force plates. Smaller reductions in thermal paw withdrawal latency and mechanical withdrawal threshold, and smaller enhancement of withdrawal reflex force, were observed following 0.1% carrageenan. Intraplantar saline was ineffective. This method allows assessment of hyperalgesic changes in stimulus-response coding over a broad range of noxious stimulus intensities.
Department of Anesthesiology and Resuscitology, Ehime University Japan.
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D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology*; D002351:Carrageenan / Q000008:administration & dosage / Q000494:pharmacology*; D004195:Disease Models, Animal; D004334:Drug Administration Schedule; D006614:Hindlimb / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D006930:Hyperalgesia / Q000139:chemically induced*; D007279:Injections, Subcutaneous; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D010146:Pain / Q000139:chemically induced*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D012879:Skin Physiological Phenomena / Q000187:drug effects; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology
D002351:Carrageenan