The long term objective is to study insulinlike growth factor (IGF) and insulin's neurophysiological role, mechanism for regulation of neurite growth, and involvement in neuronal disorders. In this Project period, the following will be studied. A) The mechanism of neurite formation is a fundamental neurobiological problem whose solution may permit manipulation of axon regeneration. We will determine whether tubulin mRNA levels are commonly regulated by neuritogenic polypeptides as a prelude to neurite formation in cultured sensory, sympathetic, and PC12 cells. B) We will study the developmental and tissue specific regulation of IGF-II gene expression, and the relationship between gene expression and innervation in the rat. The neuritogenic potential of insulin and IGF-I in spinal cord cultures will be examined. Following the intrathecal administration of insulin, anti-insulin- antiserum, and anti-IGF-I antiserum, spinal cord will be tested for changes in conduction velocity, microscopic anatomy, and levels of NGF, IGF-I, and tubulin mRNAs. C) Neuropathy is a common complication of diabetes, a disorder affecting millions of individuals. The National Diabetes Advisory Board recommend the need to better understand its fundamental pathophysiology, and sequence of pathophysiologic events, so that the hypotheses concerned with its causation may be both newly formulated and tested to the end that better modalities of treatment may ultimately be found. Despite the microscopic lesions found in human spinal cord in post-mortem studies, convincing evidence of functional pathology has been difficult to obtain because virtually all the signs and symptoms of spinal cord involvement are masked by the peripheral neuropathy. Following the induction of diabetes with streptozotocin in the rat, we shall correlate the temporal sequence for the emergence of microscopic lesions with alterations in spinal cord conduction velocity, and levels of IGF-I, NGF, and tubulins mRNAs. Whether these alterations can be ameliorated by intrathecal insulin administration will be evaluated. These studies will simultaneously test our novel hypothesis for the pathogenesis of diabetic neuropathy. Mice will be used to isolate NGF, rabbits to produce antisera, and fertile eggs for neurite studies.
