This study is focused on study of the function of neurotrophic factors (NTF) in the brain and their potential for use as therapeutic agents in treatment of human neurodegenerative disease. Among these neurodegenerative diseases are Alzheimer's disease, Parkinson's disease, ALS and developmental disorders including Rett syndrome. Two animal models of neurodegeneration are being used to study the potential therapeutic value of neurotrophic factors in treatment of neurodegenerative disease. These models are: axotomy of the facial nerve for study of motor neuron degeneration and chemical lesion of the nigrostriatal pathway for study of degeneration of the neurons in the substantia nigra (SN). Characterizing the mechanisms and time course of neuron death is an important step in evaluating potential therapeutic interventions which may be useful in treatment of neurodegenerative disease. We are using complementary molecular and neuroanatomical approaches to determine the precise time course and magnitude of neuronal cell death in each model. These techniques include: terminal deoxynucleotidyl transferase (TDT)-mediated dUTP-biotin nick end labeling (TUNEL), to identify regions of dying cells in brain tissue, immunocytochemistry in situ hybridization, Northern and Western blotting. Six days after axotomy of the facial nerve of the newborn rat, we have identified TUNEL-labeled profiles in the facial motor nucleus suggesting that axotomy induces apoptosis in these neurons. No such labeling is found in the adult facial nucleus after axotomy. Biochemical studies to support the TUNEL labeling were inconclusive. Continuing studies are underway to determine the time course of naturally occurring developmental cell death in the facial nucleus and to determine developmental changes in neurotrophic factor expression in the facial nucleus and target tissues. To enhance understanding of the potential for NTF use in treatment of diseases that involve degeneration of the SN (Parkinson's disease and Rett syndrome), studies have been initiated to determine the usefulness of neurotrophic factors in treatment of animal models of SN degeneration. Adult rats are given unilateral lesions of the SN by stereotaxic injection of 6-hydroxydopamine (6OHDA). The lesions are confirmed by quanitfication of dopamine agonist induced rotational behavior. We are currently in the process of characterizing the 6OHDA lesion to determine the precise time course and magnitude of cell death in this model. Future studies will be performed to evaluate the potential for neurotrophic factors to prevent or attenuate the chemically induced cell death in the SN. The lesioned animals will be treated with selected neurotrophic factors including GDNF, fibroblast growth factor or transforming growth factor-b and the potential for rescue of the SN neurons will be evaluated using anatomical and biochemical techniques.
