Using Heterologous Synapse Systems to Study the Impact of Postsynaptic Molecules on Presynaptic Strengthening at Excitatory Synapses

The field of neurobiology focuses on the development, maintenance, and function of the nervous system. Of particular interest is the formation of synapses, the junctions which allow for transmission and control of information between neurons. Synapse formation can be broken into two general processes: structural formation and activity-dependent validation. Structural formation requires transmembrane adhesion proteins that connect the two sides of the synapse. This newly-formed connection is then validated through neurotransmitter-mediated activity, which is deciphered by receptors on the postsynaptic side.In order to compare the role of two adhesion molecules (NL1 and SynCAM) and two glutamate receptors (NMDAR and AMPAR) on synaptogenesis, heterologous synapse systems were created between neurons and HEK cells expressing various combinations of these proteins (NL1 alone; SynCAM alone; NL1/NMDAR; NL1/AMPAR; SynCAM/NMDAR; SynCAM/AMPAR). These heterologous synapses were then stained for synapsin, and the size of the presynaptic contact (determined by the area of synapsin staining) was compared between the experimental groups. Results show that receptor expression causes the formation of smaller contacts than when the adhesion molecule is expressed on its own. These results suggest a role for the glutamate receptors in refining synaptic contacts during the process of synaptic validation