CORE H: Mouse Physiology

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The past decade has seen the definition of large families and super-families of neural genes whose related but different sequences provide great opportunity if we can understand their functions and exploit their diversity. There can be no doubt that a major challenge facing modern neurobiology is the understanding and manipulation of gene function, both known and unknown. Institutions concerned with the critical issues of mental health and cognitive disability must look beyond gene identification and into the structure and function of the proteins encoded by these newly discovered sequences and the roles these proteins play in the development and behavior of the individual. While the techniques for gene discovery have become less expensive and more accessible, the most powerful techniques for the study of function have become more expensive and more technically demanding. It is increasingly difficult for any single investigator to be able to fully explore the structure of a gene and its regulation, the structure of the protein it encodes, the localization of the protein in the animal, the role of the protein in the normal animal, and the consequences of the absence or alteration of that protein in disease. However, successful exploitation of the gene discovery requires at least portions of each of these activities in part simply to set priorities for further studies. It is the purpose of the BCM-IDDRC cores to provide access to techniques and assays that will allow the investigator to make maximum progress, without undue duplication of effort. The Mouse Physiology Core is designed to provide BCM-IDDRC investigators with a battery of functional assays that will provide initial insight into the neurophysiologic consequences of a specific mutation. This core is considered a significant component of the BCM-IDDRC because it will help address the most common question following the creation of a new mouse mutant; "What is wrong with my mouse?" The BCM-IDDRC proposes to offer its investigators access to a battery of electrophysiologic assays that will help answer this question and direct the investigator's attention to experiments that might more directly address the role of a particular gene in generating a mental retardation or developmental disability phenotype. The BCM-IDDRC at Baylor College of Medicine is well established in studying synaptic transmission and synaptic plasticity in the central nervous system. For many years Dr. Rosenmund's laboratory has been investigating basic function and dysfunction of excitatory and inhibitory synapses as well as hippocampal electrophysiology and plasticity. Dr. Jeff Noebels has been a pioneer in the use of EEG techniques to understand the genetic and molecular basis of epilepsy, and specifically in the use of mouse models to understand epilepsy. The Mouse Physiology Core will be divided into two components. The Synaptic Physiology component of the Core will allow investigators to determine the basic attributes of synaptic function from cultured neurons as well as from acute slices from hippocampus. These preparations will allow for detailed examination of synaptic properties, circuitry function and synaptic plasticity. This information is particulariy germane to the mission of the BCM-IDDRC, given the well-documented role of the hippocampus in learning and memory, and the newly arising notion that autism and related diseases have their etiology (at least in part) at dysfunctional synapses. The procedures established will allow the assessment of several parameters related to normal synaptic physiology. For the presynaptic site, this includes determination of quantal content, readily releasable vesicle pool size, vesicular release probability, synaptic release probability, and several forms of short time facilitation and depression. For the postsynaptic site, this includes mlPSC and mEPSC amplitude and kinetics, GABAA, AMPA and NMDA receptor function, as well as the determination of synaptic and extrasynaptic receptor population. These measurements will be based on patch clamp whole cell recording techniques. Morphological analysis of dendritic structure, synapse formation and synapse activity are provided using quantitative light microscopy analysis. In slices, additional analysis of input-output relationships for various intensities of presynaptic stimulation as well as several short- and long-term forms of synaptic plasticity will be assessed, including: paired-pulse facilitation, post-tetanic potentiation, long-term potentiation (LTP), and longterm depression (LTD). Latter procedures will utilize extracellular recording in the hippocampal slice preparation, using ongoing standard protocols already used here. The Electroencephalography component of the Core will enable BCM-IDDRC investigators to evaluate the development of cortical excitability and brain function over prolonged periods in behaving animal models of mental retardation produced by genetic engineering techniques. Depressed excitability or abnormal brain rhythms are among the eariiest objective phenotypes of genetic human mental retardation syndromes. A high incidence of epilepsy is also associated with mental retardation, and the facility specializes in state of the art seizure detection techniques and assessment of seizure threshold. The ability to correlate spontaneous EEG activity with behavioral analysis by use of synchronized video/EEG monitoring is critical to the interpretation of the mutant nervous system phenotypes studied by the BCM-IDDRC.