This is a revised application to continue our research on the development of cholinergic neurons in mammalian spinal cord. The primary focus of the proposed research is to obtain a better understanding of the determinants of neuronal form, especially those associated with dendritic development and the formation of dendritic patterns. We will study the development of the sympathetic and parasympathetic preganglionic cholinergic neurons of the thoracolumbar and lumbosacral spinal cord. These neurons offer several advantages for our studies. For example, they can be identified by immunocytochemical localization of choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme. Moreover, their dendrites form distinctive patterns that allow critical comparisons of dendritic development between different subsets of cholinergic neurons within the spinal cord. We intend to take advantage of these characteristics to determine the role of the following factors in the development of dendritic organization: 1) the neuronal birthdays of sympathetic and parasympathetic cells; 2) the development of synaptic afferents associated with preganglionic neuronal dendrites; and 3) the relationships of preganglionic cell dendrites with radial glial fibers. These studies constitute the specific objectives of our proposed research on the development of dendritic organization. Dendrites are integrally involved in synaptic networks, but their development and organization into functional arrangements have received less attention than the axonal components of developing synaptic circuits. Therefore, studies of dendritic development are needed to obtain a comprehensive understanding of a central problem of developmental neurobiology; namely the formation of synaptic connections.
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