Retrograde Axonal Transport of ¹²⁵I-Nerve Growth Factor in Rat Heal Mesenteric Nerves: Effect of Streptozocin Diabetes

The retrograde axonal transport of intravenously (i.v.) administered ¹²⁵I-nerve growth factor (¹²⁵I-NGF) was examined in mesenteric nerves innervating the small bowel of rats with streptozocin (STZ) diabetes using methods described in detail in the companion article. The accumulation of ¹²⁵I-NGF distal to a ligature on the ileal mesenteric nerves of diabetic animals was 30–40% less than in control animals. The inhibition of accumulation of ¹²⁵I-NGF in diabetic animals was greater at a ligature tied 2 h after i.v. administration than at a ligature tied after 14 h, which suggests that the diabetic animals may have a lag in initiation of NGF transport in the terminal axon or retardation of transport at some site along the axon. The ¹²⁵I-NGF transport defect was observed as early as 3 days after the induction of diabetes, a time before the development of structural axonal lesions, and did not worsen at later times when dystrophic axonopathy is present. Both the ileal mesenteric nerves, which eventually develop dystrophic axonopathy in experimental diabetes, and the jejunal mesenteric nerves, which never develop comparable structural alterations, showed similar ¹²⁵I-NGF transport deficits, suggesting that the existence of the transport abnormality does not predict the eventual development of dystrophic axonal lesions. Autoradiographic localization of ¹²⁵I-NGF in the ileal mesenteric nerves of animals that had been diabetic for 11–13 mo demonstrated decreased amounts of ¹²⁵I-NGF in transit in unligated paravascular nerve fascicles. There was, however, no evidence for focal retardation of transported ¹²⁵I-NGF at the sites of dystrophic axonal lesions.