The underlying hypothesis of the present study is that the survival of peripheral neurons is regulated by the neurotrophins nerve growth factor (NGF) and neurotrophin-3 (NT-3). The mechanisms regulating the expression of these neurotrophins are poorly understood. The processing of the NGF gene product results in preproneurotrophin which, following proteolytic cleavage, results in the mature form of NGF. Yet, using Western blot analysis, we observed very little mature NGF form in peripheral neurons or target tissues. In fact, the majority of neurotrophic protein expressed in these tissues (superior cervical ganglion, trigeminal ganglion and peripheral targets) was proNGF along with large molecular weight NGF precursors, with each tissue exhibiting a characteristic NGF expression pattern. NT-3 appears to undergo similar processing though it is not well studied. One goal of the current project is to use NGF and NT-3 Western analysis to correlate tissue-specific NGF and NT-3 expression patterns with protein detection obtained using ELISA and to determine any influences of a two week in vivo intracerebroventricular infusion of NGF. Also, using real time RT-PCR, we detect NGF and NT-3 transcripts in peripheral ganglia, both of which are influenced by exogenous NGF and neuronal activity. The primary objectives of this study are to: 1) Investigate NGF protein and mRNA expression in sympathetic and sensory ganglia and peripheral target tissues and determine any effects of in vivo exogenous NGF; 2) Determine the effects of exogenous NGF on NT-3 protein and mRNA expression in peripheral ganglia and targets; 3) Delineate the role of neuronal activity in NGF and NT-3 expression in peripheral tissues; and 4) Examine the regulatory influences of sympathetic innervation on neurotrophin expression in peripheral targets. The results of this project will contribute to our understanding of the complex mechanisms regulating neurotrophin expression, and thus neuronal survival, and will help to determine the factors responsible for the neuronal death that occurs in aging and disease.
