Abstracts of the 11th Annual Meeting of the Israel Society for Neuroscience

Directed convergence of dendrites causes synaptic clusterin and strengthenin Abi-Jaoue E. 1, Blinder P.2’3.’Lafrenirre-Roula M. 1, Cove j.2,3, Devroye L. andD. JDept. ofAnatomv and Cell Bioloer; McGill Universit); Montreal, Canada; 2Dept. ofLife’8iences, Ben Gurion University ofthe Negev, Beer heva; 3Zlowtovski Centerfor Neuroscience, Be ’er Sheva; 4Dept. ofComputer Science, McGill University, Montreal, Canada Synaptic clustering influences synaptic efficacy by increasing cooperative interactions among neighboring synaptic inputs, however, the mechanism of synaptm clustrring is unknown. We found that in hippocampal neurons in culture synaptic clustering as well as synaptic strength increase at the point of intersection between dendrites compared to other areas along the dendrites. The clustering in the intersection increases linearly and the strengthening exponentially with an increase in the number of dendrites crossing the intersection. Intersections containing multiple dendrites are frequent (4 times more than in computer simulations ofrandomly distributed dendrites) and are formed by direct growth of dendrites toward pre-existing dendritic intersections. This process is disrupted by inhibitors of synaptic activity and of glutamate receptors. Thus, an activity-dependent mechanism exists that causes dendrites to converge to a single intersection, resulting in an increase in synaptm clustering and synaptie activity at the intersection. This may se.rve as a mechanism for activity-dependent pre-.synaptie plasticity. In addition to converging, dendrites in the culture tend to grow in parallel, even when separated over large distances, leiding to formation of areas where specific dendritic orientations are dominant. This order restricts the location of the dendritic intersections and their synaptie dusters. Thus, directed convergence combined with parallel growth of dendrites shapes the synaptie map in cultured neuronal networks.