Further work will be done with a purified post-synaptic density fraction isolated from dog cerebral cortex. whose structure has been characterized by electron microscopy, by gel electrophoresis, and by immunology. The major proteins have been fairly well identified as one similar to muscle actin and the other similar to neurofilament protein; while myosin is absent several other myofibrillar-like proteins may be present, and their identification is being attempted. Antibodies to some of these proteins will be coupled with ferritin or labeled with (125I) to try to localize their proteins witin the structure of the density. There seems to be similarity bettween some density proteins and some plasma membrane proteins, as indicated by gel electrophoresis and ommunology, and furhter work will be attempted to see what proteins anchor the density to the post-synaptic membrane. The function of the density, as possible modulator of nerve impulse conduction, will be examined by depolarizing synaptic membranes and then examining the density morphologically and biochemically for any changes. The role of CA ions in density structure and functton will be examined by looking for Ca ions-binding to or release from the density, under normal and depolarizing conditions. Antibodies to density proteins will also be used for their possible effects on electrophysiological behavior of cultured neurones or on the behavior of animals after various stimuli. A continuation of the studies on the mechanism of release of neurotransmitter form synaptic vesicles, using the protein toxin from black widow spider as a probe, will be undertaken.