Classifying visual system cells and studying their microcircuitry is essential to understanding the neural networks which underlie visual processes. Our laboratory identifies specific cell classes and synapses and traces their curcuitry in the visual system in order to study the structural correlates of cell physiology. We use a variety of research techniques, including neurotransmitter labeling, filling of cells and axons with horseradish peroxidase conjugated wheat germ agglutinin, computerized morphometry, and 3-D serial section reconstruction. Using these approaches, we have recently identified four types of relay cell and two classes of gamma - aminobutyric acid accumulating cell in the superior colliculus. We have also found distinctive synaptic relationships of retinal synapses in different visual structures. During the proposed grant period, we want to study the relay cells and interneurons of the superior colliculus and lateral geniculate nucleus. Cells and processes will be marked by retrograde filling with HRP-conjugated wheat germ agglutinin (WGA). The density and spatial distribution of synapses on these cells from the retina, visual cortex, and tegmentum will be studied from serial section reconstructions. We will also examine the cell's size, cytology, and dendritic geometry using computerized morphometry. The putative neurotransmitters of these cells and synapses will also be studied. We will look for the accumulation of radiolabeled glutamate, glycine, gamma-aminobutyric acid, choline, b-alanine, and taurine using electron microscope autoradiography after in vivo injection or in vitro incubation. We will localize putative cholinergic receptor sites using radiolabeled alpha-bungarotoxin. Serotonin and two peptides will be localized using antibody immunohistochemistry. The results will allow us to classify cell types in the superior colliculus and lateral geniculate nucleus based upon a parametric analysis of their morphology, synaptic patterns, and accumulation of neurotransmitters and to determine the synaptic interconnections with underlie the functional circuits of these two visual structures.
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