This research is directed at an understanding of structure/function relationships and their development among single neurons of the mammalian visual system. The object is to gain insight into the neural basis of both normal visual perception as well as amblyopia that results from early visual deprivation. Focus is directed at cells of the lateral geniculate nucleus (LGN) of the cat, partly because of its basic importance to vision and visual attention, but also because our increasing knowledge of the cat's LGN makes it an attractive and unique in vivo model system to explore fundamental questions of mammalian neurobiology and neural development. The basic approach involves the extra- and intracellular recording of the two cell classes (called X and Y), often with micropipettes filled with HRP to permit morphological correlates from the same neuron as studied physiologically. Physiological data to be collected involve: 1) the measurement of the cell's passive cable properties (i.e., electrotonic length, membrane time constant, specific membrane resistance and capacitance, input resistance of the cell, etc.); 2) the description of certain voltage and time dependent conductances, especially the voltage dependent Ca++ conductance thought to control gating in geniculate cells; and 3) the description of synaptic interactions evoked via anatomically well-described circuits. The last group of studies are designed to test how a cell's cable properties and various conductances are used under physiological conditions of synaptic integration. We shall particularly focus on any differences in these integrative properties among various functional classes (e.g., X and Y). Finally, we have observed dramatic changes in retinogeniculate circuitry and geniculate neuronal morphology that develop during monocular deprivation or neonatal monocular enucleation. We shall explore how these developmental abnormalities affect the post-synaptic geniculate cells' integrative properties and central projections to visual cortex.
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