Neuropathy is a common complication of diabetes, causing discomfort and disability in many patients with diabetes. In animal models of the disease. Specific defects in retrograde axonal transport and in slow anterograde axonal transport occur early after the induction of diabetes. The link between reduced retrograde transport and the known metabolic abnormalities of hyperglycemia, nerve sorbitol accumulation, or nerve myoinositol depletion is not known. Neither has the mechanism underlying slowed anterograde axonal transport of neurofilaments (and the associated structural alterations) been identified. We intend to investigate the mechanisms responsible for the alterations in order to define the alterations in axonal biology that cause neuropathy. We propose to study three specific questions. 1. Can the reductions in retrograde transport be reversed by aldose reductase inhibition or dietary myo-inositol supplementation? 2. Are alterations in the transport of neurofilaments caused by alterations in the post-transnational modification and/or in situ degradation of neurofilaments mediated by calcium activated neutral proteases? 3. Are there specific alterations in the intra-axonal distribution of calcium in the nerve in diabetes? We will use the 3H NSP method to measure retrograde axonal transport in rats with STZ diabetes, and determine whether treatment with sorbinil or dietary supplementation with myo- inositol reverses the defect in retrograde transport we have identified. We will use in-vitro assays to measure the post- transnational modification and degradation of neurofilaments by endogenous protease activated by micromolar Ca++ in normal and diabetic rats. We will measure the activity of that enzyme with an.exogenous substrate to determine whether reduced protease activity is due to reduced enzyme activity or increased inhibitor. We will use the oxalate pyroantimonate method to identify the ultrastructural distribution of calcium in the nerve of diabetic rats. The results of these studies should allow insight into the pathogenesis of diabetic neuropathy, as well as into the biochemical mechanisms involved in axonal transport in normal nerve.
