||Diabetes mellitus is a common disease worldwide. Diabetic patients have an increased risk of limb amputation and more severe herpes zoster infections. Post-amputation pain and post-herpetic neuralgia are neuropathic pain, and both are difficult to treat and often affect quality of life. In the present study, we used the L5 spinal nerve ligation (SNL) model to induce neuropathic pain in diabetic rats to mimic the above situation. Heat shock protein 70 (HSP70) expression increased after a spinal nerve injury, providing an anti-inflammatory effect as well as a neuroprotective function. We hypothesized that this increased HSP70 expression after a spinal nerve injury may be associated with neuropathic pain. The aim of this study was to determine the different reactions of HSP70 expression and pain sensation after inducing L5 SNL in diabetic and non-diabetic rats. |
We randomly assigned adult male Sprague-Dawley (SD) rats into four groups: diabetic with L5 SNL, non-diabetic with L5 SNL, diabetic (sham), and non-diabetic (sham) groups. The sham groups underwent the same surgical procedure but without L5 SNL. Diabetic rats were prepared by intraperitoneal injection of streptozotocin. After 14 days of streptozotocin injection, SNL was performed. We used a dynamic plantar aesthesiometer to assess mechanical withdrawal threshold. The HSP70 protein contents were analyzed by Western blotting and immunohistochemistry.
We found that both diabetic and non-diabetic rats after L5 SNL showed significant mechanical hyperalgesia, which is more prominent in diabetic rats. After day 7 and day 14 of L5 SNL, the expression of HSP70 in dorsal root ganglions (DRGs) increased in both diabetic with SNL and non-diabetic with SNL groups, but the extent of increase was lower in the diabetic with SNL group. Additionally, within both diabetic with L5 SNL and non-diabetic with L5 SNL groups, HSP70 was predominantly present in unmyelinated C-fiber and thinly myelinated A-δ fiber neurons in DRGs, and the diabetic with L5 SNL group exhibited less HSP70 expression.
Our results indicated that after L5 SNL, the diabetic with L5 SNL group had less increased expression of HSP70, specifically in C-fiber and A-δ fiber neurons in DRGs combined with more mechanical hyperalgesia, as compared to the non-diabetic with L5 SNL group.