Peripheral neuropathy in selectively-inbred spontaneously diabetic rats: electrophysiological, morphometrical and freeze-replica studies.

Function and structure of peripheral nerves in selectively-inbred spontaneously diabetic rats (SDR) were quantitatively examined in order to clarify the relationship between these two changes. Electrophysiologically, SDR showed a significant decrease in motor nerve conduction velocity of the tail by 2 months of age. Thereafter, the conduction velocity was constantly lower in SDR than in age-matched control rats. Morphometrical analysis of peripheral nerves from light and electron micrographs could not yield any definite structural differences, except for a reduction in caliber of unmyelinated axons, between 2 month-old and age-matched controls, whereas an endoneurial space was widened in 3 month-old SDR as compared with those of controls. In contrast, loss of myelinated nerve fibers, a reduction in nerve fiber size and axonal size were apparent in 6 month-old SDR. By freeze-replica studies, neither any qualitative changes of intramembrane faces nor any quantitative differences in the density of intramembranous particles of internodal myelin and Schwann cell membranes were detected in 2 month-old SDR when compared with those in controls. The results suggested that the delayed nerve conduction velocity was most related to diabetic dysmetabolism and independent of the structural changes of peripheral nerves being in the course of distal axonopathy.