Presynaptic elements on artificial surfaces. A model for the study of development and regeneration of synapses.

Recently a model has been developed to study the synapse formation in which the components of a synapse can be isolated and examined independently. The observation of neurites forming presynaptic elements on polylysine-coated surfaces is a model for which the formation of presynaptic elements can be studied independently of a cellular postsynaptic element. Studies with neurons from both cell cultures and the intact cerebellum have shown that beads coated with poly-basic proteins can serve as a "postsynaptic element." With use of this system, observation have shown that the presynaptic element can form quickly, within 3 h, and contain many of the characteristics of a mature presynaptic element, such as synaptic vesicle antigens. Additional studies have shown that astrocytes appear to be involved in the loss or removal of the presynaptic elements on beads. Thus, synaptogenesis may involve the development of inappropriate synaptic contacts, which are eliminated by astrocytes. The lack of regeneration in the central nervous system (CNS) also may involve the astrocyte's ability to remove immature and/or inappropriate presynaptic elements and growth cones as they attempt to cross the lesion site.