TOMOGRAPHIC RECONSTRUCTION OF CEREBELLAR GLOMERULUS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We believe that the structure of the cerebellar glomerulus,mainly the glial sheath that envelops the granule cell dendrites and the mossy fiber terminal, leads to the isolation of the extracellular space outsidethe glomerulus from the ec space inside the glomerulus. We believe that such geometry would limit access of ec Ca++into the glomerulus, thus allowing for conditions where the concentration of Ca++ inside the glomerulus is regulated mostly by the activity of the Ca++ channels and pumps localized within the glial ensheathment. Webelieve that in there may be a direct relation between the post-synaptic acticity of the granulecell dendrites and the ec concenatrionof Ca++ inside the glomerulus. Since many cellular processes depend on Ca++ and since their type and/or efficacy depend on the concentration of ec Ca++, we propose that the geometry of the cerebellar glomerulus would lend itself to a new ICA-like learning rule where each granule cell can measure the sum total of the activities of other granule cells whose dendrites are localized within the same glomerulus by gauging the concentration of ec Ca++ inside the glomerulus.In order to more fully appreciate the geometry of the cerebellar glomerulus, and in order to perform more quantitatively correct simulations, we propose to performEM tomograhpy on several glomeruli.