Patterns of nerve fiber impairments and neuronal activation in male diabetic rats with and without mechanical allodynia: a comparative study

Abstract Aim It is still clinically difficult to definitively distinguish between painful and nonpainful diabetic peripheral neuropathy (DPN). In this study, pain patterns were further categorized; diabetic rats were grouped according to the presence or absence of mechanical allodynia (MA), which is a hallmark of neuropathic pain; and comparisons were made between diabetic rats with and without MA. Methods and materials Diabetes was established in rats by a single intraperitoneal streptozotocin injection, and vehicle injection was administered in the control group. Pain behavioral tests for MA and thermal hyperalgesia were performed every week. At the 4th week, the diabetic group with thermal hyperalgesia was further grouped by the presence of MA. Morphometric analysis of sciatic nerves and myelin basic protein (MBP) quantification were conducted. The numbers of c-Fos-immunoreactive neurons in both the dorsal root ganglion (DRG) and spinal dorsal horn (SDH) were determined. Results Diabetic rats with MA had more severe impairment of myelinated nerve fibers than those without MA (P Conclusion The impairment of primary myelinated fibers and the pattern of neuronal activation in both the DRG and SDH are certain features that differentiate diabetic rats with MA from those without MA.