Age-Related Differences in Neuropathic Pain Behavior and Spinal Microglial Activity after L5 Spinal Nerve Ligation in Male Rats.

Abstract

Introduction:Several studies have reported the involvement of age-related changes in the development of neuropathic pain behaviors. However, limited data are available on the role of age in establishing and maintaining chronic neuropathic pain after peripheral nerve injury.Methods:In the present study, we examined age-related neuropathic behavior among rats in 4 age groups: pups (4 weeks old; weight, 60–80 g), juvenile rats (6 weeks old; weight, 120–140 g), and mature rats (10–12 weeks old; weight, 200–250 g). Because the exact contribution of spinal microglia and its association with the development of neuropathic pain remains unknown, we also evaluated the expression of spinal Iba1, a microglial marker, by using western blotting before and 5 days after spinal nerve ligation (SNL) as well as after the daily IP administration of minocycline (30 mg/kg).Results:Our results showed that SNL-induced mechanical allodynia but not thermal hyperalgesia in mature rats but not in pups (P<0.05 and P<0.01, respectively). The expression of spinal Iba1 in the juvenile rats was significantly lower than that in pups and mature rats (P<0.01). Moreover, administration of minocycline decreased the expression of spinal Iba1 in the pup rats more than in juvenile rats (P<0.001) and in the juvenile rats more than in the mature rats (P<0.05).Conclusion:These data suggest that the development of neuropathic behaviors and microglial activation after SNL could be age dependent.