Effects of age and size on development of allodynia in a chronic pain model produced by sciatic nerve ligation in rats

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Abstract
F rat age and weight on the model has not been previously studied. We noted that a group of older rats failed to develop all the characteristics of the model and designed the present study to determine the effect of age and weight on the development of allodynia and hyperalgesia. Three groups of rats varying in age (54, 71, and 107 days) and weight (220–250 g, 270–350 g, and 370–470 g) with the experimental lesion were tested for hyperalgesia, cold allodynia, and tactile allodynia. We found that although the degree of hyperalgesia of all groups was the same, the oldest group had significantly longer response latencies to allodynia tests than the younger 2 groups. Responses to the cold test were no different than control in the oldest group. The results of the present study demonstrate that larger, older rats fail to develop allodynia after sciatic nerve ligation. ∗Correspondence to: Jeffrey S. Kroin, Ph.D., Department of Neurosurgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago, IL 60612, USA. Tel.: (312) 942-5000. (Received 21 April 1992; revised 3 June 1992; accepted 17 June 1992.) © Lippincott-Raven Publishers....