Presynaptic elements formed on polylysine-coated beads contain synaptic vesicle antigens

Summary Cell cultures of the rat cerebellum were immunostained with antibodies to synaptic vesicle antigens, Synapsin I and SV48. Light microscopic immunocytochemistry showed that the initial appearance of demonstrable SV48 and Synapsin I immunoreactivity occurred at different times. Synapsin I immunostaining, unlike SV48 immunostaining, was first seen at 3 daysin vitro as occasional punctate immunofluorescence in neurites, while SV48 immunostaining was first seen at 5 daysin vitro. Both SV48 and Synapsin I punctate immunostaining became frequent at 7 daysin vitro. Double labelling experiments showed coexistence of the above proteins in punctate swellings and growth cones. Using the electron microscope, either SV48 or Synapsin I immunostaining was demonstrated within presynaptic elements in the neuropil. When cultures were incubated with polylysine-coated beads, both types of immunostaining were found in the vesicle containing presynaptic elements formed on the bead surface. It is concluded that Synapsin I and SV48 are (1) co-localized in the same populations of presynaptic elements, (2) co-localized in some growth cones and (3) found in presynaptic elements on beads.