MECHANICAL ALLODYNIA IS MORE STRONGLY MANIFESTED IN OLDER RATS IN AN EXPERIMENTAL-MODEL OF PERIPHERAL NEUROPATHY

Partial peripheral nerve injury often leads to chronic neuropathic pai n characterized by symptoms such as allodynia. In the present study, e mploying a rat model of experimental neuropathy produced by partial de nervation of the tail, we examined whether peripheral nerve injury-ind uced mechanical and thermal allodynia were affected by the animal's;ag e at the time of the injury. The motive of this study was the demonstr ation in other neuropathy models of the age effects on the manifestati on of neuropathic pain symptoms following partial peripheral nerve inj ury. We compared two groups of young (n = 23, 7-8 weeks old, 150-200 g ) and old rats (n = 14, 16-18 months old, 550-800 g). We found that th e older rats exhibited more vigorously the behavioral signs of mechani cal allodynia during the first week after the nerve injury. With respe ct to thermal (cold or warm) allodynia, however, we detected no signif icant difference between young and old rat groups. The results of the present study, as those of previous studies, support the idea that the age at the time of partial peripheral nerve injury affects the severi ty of certain neuropathic pain symptoms appearing after the injury. Ho wever, the present results argue against the suggestion from previous studies that younger subjects are more vulnerable to partial periphera l nerve injury-induced neuropathic pain symptoms.