Nerve cell degeneration and loss are pivotal events in most hereditary diseases of the central nervous system. Among these diseases are the heredo-degenerative ataxias, Parkinson's disease, and Alzheimer's disease. in the heredo-degenerative ataxias, the degeneration of Purkinje cells (PC), which are essential for normal motor functions, leads to incoordination. In Parkinson's disease, degeneration of midbrain dopamine (DA) neurons, that participate in a variety of motor functions and mental processes, leads to tremor, rigidity, bradykinesia and deficit of posture. Neuronal loss triggers a cascade of transsynaptic changes, whose mechanisms are poorly understood. Understanding the mechanisms of such degeneration is best achieved by studying a given neuronal population prior to or early in the degenerative process. An analysis of the cascade of transsynaptic changes can be best achieved in natural models of degenerative diseases in which nerve cell loss and the transneuronal sequelae occur in a well known and predictable time sequence. In the Purkinje cell degeneration (pcd) and weaver (wv) mutant mice, loss of PC and of midbrain (DA) neurons, respectively, are among the major phenotypic events and they occur in a fixed time frame. A long term goal of this project is to investigate the mechanisms leading to cell loss at the cellular and molecular level and to attempt to understand the primary defect. We will construct cDNA libraries from cerebella of pcd mutants at the onset of Purkinje cell degeneration and we will isolate clones that are differentially expressed. These cDNAs will be evaluated by sequencing and their cell of origin determined by in situ hybridization. We will begin molecular/biochemical characterization of the pcd-induced neurodegenerative cascade by following the expression of these clones, PC markers and cytoskeletal markers during the disease and we will attempt to clone the pcd cDNA. For the wv mutant, studies will be carried out in order to determine the effect of DA losses on the GABAergic striatal interneurons and efferents and on the striato-pallidal enkephalin and the striato-nigral dynorphin systems. In addition, we will determine the significance of the increased content of serotonin in the striatum of the wv mutant. Since the trophic interactions between DA neurons and their target cells in the establishment and maintenance of the nigrostriatal DA projection are not understood, we will utilize the three-dimensional reaggregate tissue culture system to investigate whether the loss of DA neurons observed in the wv mutant is due to a defect in the DA neurons themselves, or in their target cells. Embryonic brain cells from wv and normal (non-weaver) mice will be cocultured to test whether target cells from normal mice can promote the survival of the wv DA neuron. Conversely, target cells from wv mice will be assessed for their ability to produce a loss of DA cells from normal mice. In addition, we propose to use the wv mouse as a means of obtaining a selected population of medial DA neurons, cells which project to limbic and cortical areas and are relatively spared in wv mutants, for the purposes of generating an immortalized DA cell line by somatic cell hybridization. The availability of such a DA cell line will be an important model for examining DA neuronal target recognition and neurotoxicity.
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