Autonomic neuropathy occurring in sympathetic nerves of the spontaneously diabetic BB rat has been characterized using ultrastructural and morphometric techniques. Paravertebral thoracic ganglion cells, preganglionic myelinated fibers of the white ramus, and postganglionic unmyelinated fibers of the gray ramus communicans were examined in a longitudinal fashion. The main structural abnormality consisted of expanded axons containing a variety of normal and abnormal subcellular structures, so-called dystrophic axonal changes. These increased with duration of diabetes and were found in close proximity to the somata of ganglion cells, suggesting a preganglionic origin. The ganglion cells showed no alteration in perikaryal or nuclear volume but exhibited decreased number of synapses, which correlated with the progressive increase of dystrophic changes. While no qualitative or quantitative abnormalities could be demonstrated in preganglionic myelinated fibers of the white ramus, postganglionic fibers in the gray ramus showed an increased numberof glycogenosomes, axonal sequestration, and reduction in axonal size. The present findings suggest an axonopathy in sympathetic nerves of the diabetic BB rat.

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