Work is continuing on the identification of the major proteins in the post synaptic density (PSD) isolated from cerebral cortex. In addition to the previously identified actin, evidence is accumulating that neurofilament protein, the Ca ions-dependent regulator protein, a Mn ions or Mg ions-cAMP phosphodiesterase, and two specific protein substrates for a cAMP-dependent protein kinase are also present. Identification of these latter proteins will be completed. Work is ongoing as to whether a tropomyosin-like protein is present, whether there is some actomyosin activity, and whether the neuronal-specific 14-3-2, or alpha-antigen or enolase are also present. Previous work has indicated that treatment of isolated PSD's respond to various reagents, such as DTT and EGTA, by the extraction of some proteins and the consequent "opening up" of the dense, compact PSD structure. These experiments will be repeated by using a synaptic membrane fraction, in which the PSD is still attached to the post synaptic membrane. The idea is to start looking for the function of the PSD. In that vein, synaptosomes will be treated under depolarizing conditions, or with transmitter antagonists, and the PSD subsequently isolated, to look for possible differences in fine structure and protein components between "normal" and these PSD's. In another part of the project, work is continuing on the use of a purified protein (alpha-Latrotoxin) from black widow spider venom to probe the mechanism of release of neurotransmitters and concomitant depletion of synaptic vesicles. Radioactive alpha-latrotoxin is bound specifically to a preparation of synaptic membranes, and certain agents will be used to try to interfere with this binding, thus giving indications of the nature of the binding site. Also to be done are experiments whether the binding of the toxin results in modification of some membrane proteins such as by phosphorylation or methylation.