SPECIFICITY OF SYNAPSE FORMATION

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This proposal is a continuation of studies aimed at understanding how appropriate synaptic connections between pre- and postganglionic neurons in the sympathetic nervous system are established during embryonic development. Using histological and electrophysiological techniques, I will examine, in the chick, the developmental events that result in ordered synaptic relations between pre- and postganglionic neurons. These experiments will delineate the time of formation of sympathetic ganglia from the neural crest, the outgrowth of pre- and postganglionic axons and the temporal relationships between these events. In a second group of studies, I will test the ability of growing embryonic axons to find their appropriate targets after experimental manipulations of the environment. These studies will test three hypotheses: 1) Are the projection patterns of preganglionic neurons determined by their segmental origin in the spinal cord or by the tissue environment outside of the spinal cord? 2) are target cues required for the guidance of preganglionic axons? 3) Is segmentally selective innervation of ganglion cells by preganglionic axons based on the segmental origins of pre- and postganglionic neurons in the neuraxis? The proposed experiments will exploit the accessibility of the chick embryo where it is possible to: 1) transplant preganglionic neurons to a novel environment without disrupting their target cells, 2) remove the neural crest cells that give rise to specific sympathetic ganglia prior to their migration and without damage to preganglionic neurons, 3) label both pre- and postganglionic neurons arising from particular segments of the neuraxis and examine the synaptic interactions between labelled cells using a combination of anatomical and intracellular recording methods. These studies will provide new data on the embryonic development of specific synaptic connection in sympathetic ganglia. At the same time, results from these studies are likely to represent general principles that are applicable to the development of the central nervous system.