Selective alterations in presynaptic cytomatrix protein organization induced by calcium and other divalent cations that modulate exocytosis

Monoclonal antibody Br4 recognizes specific neuronal cell types

A monoclonal antibody termed as Br4 was prepared by a fusion of the myeloma P3 x 63-AG8-653 with spleen cells from BALB/c mice immunized with chick embryonic brain cells. Immunocytochemically, it reacts strongly with certain neurons in cerebral cortex, hippocampus, substantia nigra, and granular layer of cerebellum from rat brain but does not react with the white matter. A monoclonal antibody Br4 also reacts with primary cultured chick neurons, but not with cultured astrocytes. Western blots show that Br4 recognizes three proteins of 145,000, 108,000, and 97,000 molecular weight from the rat brain. The protein with molecular weight 145,000 (p145) and the protein with 97,000 molecular weight (p97) are essentially soluble; p145 is especially enriched in the synaptosomal soluble fraction. The protein with 108,000 molecular weight (p108) is found in both membrane-bound and soluble forms. Western blots show that among the tissues examined the three proteins are found most abundant in brain and especially enriched in the cerebral cortex and hippocampus. The Br4 antigens may be useful in identifying neuronal cell subpopulations in the central nervous system.

Cytoplasmic matrix proteins in central nervous system presynaptic terminals: turnover and effects of osmotic lysis

Cytomatrix proteins, of primary functional importance in central nervous system neuron terminals, are provided to their site of action in the terminal by axonal transport. Slow component b (SCb) of axonal transport has been proposed to be the biochemical counterpart of the moving cytoplasmic matrix, or cytomatrix, in axons. In the current study, axonally transported SCb proteins destined for neuron terminals were pulse-radiolabeled with [35S]methionine in guinea pig retinal ganglion cells. After SCb proteins reached the terminals in the superior colliculi, synaptosomes were prepared to distinguish between SCb proteins in the preterminal axons and those of the presynaptic terminals. Study of the initial entry and turnover of individual SCb proteins in presynaptic terminals revealed different residence times of certain SCb proteins in comparison with their cohorts. Preliminary information about the structural relationships of the proteins comprising the presynaptic cytomatrix was obtained by examining the solubility of individual SCb proteins relative to other SCb proteins, or membranes from osmotically lysed terminals. Last, treatment of those radiolabeled synaptosomes with varying concentrations of salts was performed to determine possible effects on observed structural relationships.