The form and physiology of the dendrites of nerve cells determine many aspects of neuronal function. The intradendritic transport of materials synthesized in the cell body must play a prominent role in controlling the formation of dendrites during development, in regulating their potential for modification in response to neuronal activity, and in determining their capacity for reinnervation following neural injury. The lack of direct information concerning the transport of materials from cell body to dendrites represents a major gap in our understanding of these crucial events. In the present proposal dendritic transport will be studied in hippocampal nerve cells maintained in culture by administering 3H uridine, which is incorporated exclusively in the cell body, and monitoring the transport of radioactive RNA into the dendrites by light microscopic autoradiography. In order to determine the rate of migration and to establish whether transport is an active process, the distance of transport will be assessed at varying times after labeling and the effects of inhibitors of axonal transport will be assessed. In order to address the mechanism of RNA transport in dendrites, several studies will investigate the relationship between RNA and the dendritic cytoskeleton. The association of dendritic mRNA and rRNA with detergent-extracted cytoskeletal preparations will be assessed using in situ hybridization, both in normal cells and after treatment with agents that dissociate polyribosomes. Binding between the cytoskeleton and RNA which is in transit within the dendrites will be assessed following labeling with 3H uridine, and the effects of dissociation of polyribosomes on transport of mRNA and rRNA will be assessed. To determine whether other molecules are transported within dendrites at similar rates, the transport of glycoproteins will be studied following labeling with precursor sugars. Finally, since innervation regulates many dendritic properties, the influence of innervation will be assessed by measuring transport rates in cultures established at both high and low plating densitites, conditions which either permit extensive synaptogenesis or greatly limit the possibilities for synaptic interaction.
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