9728003 BENSON The long term goal of this research is to understand how the axons of neurons are guided to particular parts of their target cells, and once there, how they assemble synaptic contacts. Several classes of adhesion molecules, such as cadherins, integrins and members of the immunoglobulin superfamily are known to generate junctions between cells, and recent research has shown that these same molecules are also localized at synaptic junctions in the central nervous system (CNS). These new data strongly suggest that the mechanisms by which pre- and postsynaptic membranes adhere to one another in the CNS may be substantially similar to those that generate intercellular adhesion in other, non-neural tissues. Consistent with this hypothesis is the following evidence: Immunolocalization of N- and E-cadherin at synaptic junctions; the tight adhesive nature of cadherins and their resultant intermembrane distances correlate well with biochemical properties and calculated intermembrane distances described for synapses; and both synapse formation and targeting to the appropriate cellular domain (somata, dendritic shafts, spines) occur in the absence of neural activity. Synapse development and organization are well-characterized in the rat hippocampus and in hippocampal neurons grown in culture. Together they make an excellent model system in which to examine interneuronal synapse formation and targeting. The first aim of Dr. Benson's research is to test the hypothesis that cadherin incorporation is critical for synapse formation. This will be accomplished by examining the deposition of cadherins at synapses in cultured hippocampal neurons in relation to other well- characterized synaptic markers, in the presence and absence of inhibitors and antisense oligonucleotides that block the production of cadherins. The second aim is to examine the relationship between different cadherins and functionally distinct synapses. Co-localization of cadherins or ca tenins and transmitter-specific synaptic markers will be assessed in vivo and in vitro. Together, data from these aims will be used to describe the dynamics of cadherin localization during synapse development and will have broad implications for the mechanisms underlying synapse assembly in CNS.
