The Wobbler mouse is an autosomal recessive animal model for the study of motor neuron disease (MND). About 25% of these animals develop MND related to pathology of cervical spinal cord cells. The mechanisms that might lead to cervical cord motor neuron dysfunction and death, as in amyotrophic lateral sclerosis (ALS), are yet to be completely understood. The goal of this study is the identification of abnormalities of neurotransmitter- receptor function in populations of viable spinal cord cells. The working hypothesis of this project is that genetic abnormalities in the Wobbler mouse may be phenotypically expressed by alterations in excitatory amino acid-receptor function of cervical spinal cord cells. The defects might be reflected by membrane potential abnormalities in response to excitatory amino acids. The rationale for this hypothesis is based on the role that excitatory amino acids and related substances, such as P-N-methyl amino-L- alanine (BMAA), play in motor neuron cytotoxicity. Electrical and chemical excitability will be studied in viable spinal cord cells from the Wobbler mouse using flow cytometry and voltage-sensitive dyes. Relative membrane potential changes to excitatory amino acids, voltage-dependent neurotoxins, inhibitory amino acids and neuropeptides will be analyzed in the first two, third, fourth and fifth years, respectively. Wobbler (NFR/wr) and control (NFR) spinal cords will be dissected in 6 regions and cells will be isolated using a papain dissociation protocol. After examination of viability, relative membrane potential changes to the treatments will be recorded using the anionic voltage-sensitive dye oxonol and a Coulter 753 dual laser flow cytometer. Data will be analyzed using the computers of the University of New Mexico and The Los Alamos National Laboratory. The strategy will permit a longitudinal assessment of excitability at various regions and at various pre and postnatal ages, including those that precede the development of clinical symptoms. The study of excitability in the normal congenic strain (NFR) will control for the experimental results. Single-cell quantitative fluorescence microscopy using voltage-sensitive dyes will complement the flow cytometer-population data. The characterization of possible membrane potential abnormality in response to amino acid neurotransmitters in Wobbler mouse spinal cord cells may contribute to the understanding of the pathogenesis of Werdnig-Hoffman disease and of ALS.
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