Peripheral Neuropathy in the Spontaneously Diabetic WBN/Kob Rat

We report that the morphological characteristics of the peripheral neuropathy in WBN/Kob rat, a diabetic animal model that develops persistent diabetes, were primary segmental demyelination and secondary axonal degeneration. These findings are similar to those in human patients with diabetes mellitus and unlike those in rodents with streptozotosin-induced diabetes. However, these changes were also indistinguishable from those of age-dependent neuropathy. In the spontaneous peripheral motor neuropathy of rats, pressure neuropathy from housing in wire-mesh cages has also been reported to be indistinguishable from the peripheral neuropathy in plantar nerve or tibial nerve. Therefore, we examined phrenic nerves that were free from the pressure of body weight in rats and described the changes with light and electron microscopy. The morphological changes of the nerve fibers consisted of myelin blebbing or distention, and early remyelination. The changes were seen with age. On morphometric analysis, a marked reduction of fiber occupancy was observed in WBN/Kob rats over 23 months old. The present study demonstrated that the peripheral neuropathy of WBN/Kob rats is myelinopathy. Since the phrenic nerve was not affected by pressure neuropathy anatomically, this study indicates that the peripheral neuropathy of WBN/Kob rats is not pressure neuropathy.