The objectives of the Mouse Physiology Core are two-fold. The first objective is to provide the members of the BCM-IDDRC the ability to determine if their mutant mice display derangements in neuronal synaptic transmission and synaptic plasticity, using primary neuronal cultures as well as hippocampal slice in vitro preparation to obtain a detailed analysis of synaptic function. The second objective is to enable BCM-IDDRC investigators to evaluate and correlate the development of cortical excitability and brain function with behavioral activity using continuous video/EEG monitoring in behaving mutant mice. Thus the Physiology Core will assess neuronal physiology in mouse models of human intellectual and developmental disability (IDD) across a broad functional range – from baseline synaptic function, to short- and long-term forms of plasticity, to the behavior of the neuron when imbedded in its native circuit in vivo . Assessments of these types of function also specifically examine the basic cellular processes that are likely to be (or are known to be) prominently associated with cognition, including long-term alterations in synaptic function and epileptic seizures in vivo .
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 particularly 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 mIPSC 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 long-term 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 earliest 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.
John W Swann, Ph.D.
Jeffrey Noebels, M.D., Ph.D.