We investigated the effect of progesterone (P4) treatment on diabetes/hyperglycemia-induced pathological changes in brain, spinal cord and sciatic nerve tissue in male rats. Animals were rendered hyperglycemic by a single dose of streptozotocin (STZ). P4 treatment was started after hyperglycemia was confirmed and body weight and blood glucose levels were monitored once/week for 5 weeks. Rats underwent behavioral testing at week 5 and were then euthanized for histology. We assessed the expression of markers of angiogenesis (vascular endothelial growth factor (VEGF)), inflammation (interleukin-6 (IL-6)) and tissue injury (CD11b, NG2, COX2 and matrix metalloproteinase-2 (MMP2)) in the brain, spinal cord and sciatic nerve. We also examined the regenerative effect of P4 on pathological changes in intra-epidermal nerve fibers (IENF) of the footpads. Diabetes/hyperglycemia led to body weight loss over 5 weeks and P4 treatment reduced this loss. At week 5, blood glucose levels were significantly lower in the P4-treated diabetic group compared to vehicle. Compared to sham or P4-treated groups, the diabetic vehicle group showed hyperactivity on the spontaneous locomotor activity test. Western blot data revealed upregulation of VEGF, IL-6, CD11b, NG2, COX2 and MMP-2 levels in the vehicle group and P4 treatment normalized these expression levels. IENF densities were reduced in the vehicle group and normalized after P4 treatment. We conclude that P4 can reduce some of the chronic pathological responses to STZ-induced diabetes. (C) 2017 IBRO. Published by Elsevier Ltd. All rights reserved.