Postnatal rat neurons form apparent presynaptic elements on polylysine-coated beads in vivo

Polylysine-coated sepharose beads implanted in the cerebellum of 3-4-day-old rats resulted in the formation of neuronal swellings on the surface of the beads. These neuronal swellings resembled presynaptic elements and contained numerous 40 nm vesicles that accumulated at the site of contact with the bead. Uncoated beads did not show apparent presynaptic elements on the surface of the beads. The in vivo finding of apparent presynaptic elements on polylysine-coated beads suggests that polybasic surfaces may be involved in recognition leading to the formation of presynaptic elements. This system offers an excellent model to test developing or regenerating axons to determine their ability to form presynaptic elements.