Important nutrients or effector molecules, e.g., hormones, growth factors, toxins, enxymes or pathogens, are taken in by the neuronal plasma membrane and must be sorted to specific sites in the cell. Uptake and sorting of membrane compartments by epithelial cells is a research field of intense current investigation. However, relatively little attention is being focused on neurons, despite their highly elongated shape and vital interdependence on one another. In this grant the identity of the membrane compartments that transport macromolecules from the surface of the perikaryon to the axon terminal will be examined. We hypothesize that this path will involve perikaryal membrane that is fated for exocytosis by nerve terminals, i.e., neurons are capable of transcellular transport. Wheat germ agglutinin (WGA) will be used as a selective probe for the glycoproteins of neuronal membranes, due to its ability to bind selectively to N-acetyglucosamine and sialic acid residues. Iodiated WGA and EM autoradiography as well as immunocytochemical techniques will be the prime methods of procedure used to localize the WGA in various cellular compartments in the neuron cell body or axon. Evidence will also be sought for the intercellular transfer of WGA from nerve to muscle at the neuromuscular junction. Understanding the intracellular path followed by WGA through the neuron will provide us with new insight about the circulation of membrane within neurons. The information will also increase our understanding not only of axonal transport mechanisms, in general, but also of the cellular basis for many pathological conditions, including pathological intoxications with environmental toxins. We need to know the normal patterns of organelle and membrane sorting if we are to understand fully abnormal situations, either peripherally (e.g., peripheral neuropathies) or centrally (e.g., optic nerve compression in glaucoma). Moreover, information gained about the transfer of macromolecules between neurons should clarify the mechanisms by which trophic factors from neurons influence muscle cell development or neurons influence other neurons during development. Lastly, understanding the cellular basis for the transport of probes is expected to lead to the improved application of these probes in neuroanatomical tracing studies.
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