Myelin Area and Axon Diameter Relation in Renal Nerve Myelinated Fibers of Acute and Chronic Diabetic Rats

The positive relation between the axon size and its respective myelin sheath has long been known. We tested the hypothesis that the expected correlation between myelin sheath area (Mya ) and the axonal diameter (Dax) of myelinated fibers in the renal nerves is altered by diabetes, using a regression analysis study. Male Wistar rats were used after 15 days or 12 weeks of diabetes induction by a single injection of streptozotocin (STZ i.v.). Control rats received vehicle. Insulin-treated animals received a single subcutaneous injection of insulin on a daily basis. Then, the left renal nerves were dissected, removed and prepared for light microscopy. Morphometry of the myelinated fibers was carried out with computer software. The Mya and the Dax of all myelinated fibers in each nerve were automatically measured. Regression lines were calculated for all nerves in each group. Differences between the regression lines were tested for slope and intercept as well as differences between the correlation coefficients. The regression lines were coincident between the three acute groups. Also, there was a coincidence between the regression lines from control and insulin-treated chronic groups. The chronic diabetic group showed a significant slope reduction on the regression lines, as well as a reduced correlation coefficient when compared to all other experimental groups. These results show that there are morphological alterations on the renal nerve myelinated fibers in STZ induced diabetes consisting of axonal atrophy and/or demyelinating-remyelinating processes. These results may be useful in the understanding of the renal dysfunctions found in diabetic nephropathy.