Sciatic nerve morphology and morphometry in mature rats with streptozocin-induced diabetes

Controversy exists as to the morphological and morphometric changes seen in experimental diabetic neuropathy (EDN). Most previous studies have utilized immature animals, with controversy as to whether the observed changes are due to maturational delays induced by hyperglycemia, or to diabetes per se. This study utilizes mature 9-month-old Sprague-Dawley rats. Six control and six hyperglycemic rats were examined 24 weeks after streptozocin injection. No morphological abnormalities were seen in the sciatic nerve at the light microscopy level. Total fascicular area and myelinated fiber density showed no significant differences (ANOVA, P > 0.05). No significant differences [ANOVA, P > 0.05 and Kolmogorov-Smirnoff (K-S), P > 0.05] between control and diabetic groups were shown for fiber, axon, and myelin areas, fiber and axon diameters, and myelin thickness. Fiber index of circularity, axon index of circularity, and g ratio were not significantly different with ANOVA (P > 0.05), but the diabetic group showed significantly lower values (P < 0.001) with K-S testing. Regression analyses of axonal area and log(n) axonal area plotted against myelin thickness showed no significant differences between the control and diabetic animals. This study in mature rats confirms the relative lack of morphological and morphometric changes in EDN which have previously been reported in studies involving immature rats. It highlights the difficulties in trying to extrapolate from EDN to human diabetic neuropathy where severe morphological and morphometric abnormalities may be present.