Many years ago, my lab used immunocytochemical methods to provide an important piece of evidence leading to the recognition that glutamate is the main excitatory neurotransmitter. Since then, my attention has focused mainly on postsynaptic mechanisms. We have employed light microscopic immunocytochemistry and immunogold EM to examine the relationship of AMPA and NMDA-type glutamate receptors to the synaptic active zone. We continue this basic line of research: Proteomics studies have identified over 100 proteins associated with the postsynaptic density (PSD). We are using quantitative immunogold methods and high-resolution electron tomography to examine the organization of a variety of these proteins, to elucidate the supramolecular architecture of the PSD.
We want to use this information to explore how the organization of molecules within the synapse may help to regulate postsynaptic signaling pathways. For example, calcium ions entering through NMDA receptor channels may modify synaptic activity. Might the targets of this calcium entry (e.g., CaMKII, nNOS, or calcium-dependent adenylyl cyclase) be situated close to the NMDA pore, suitably positioned to respond selectively to calcium entry through that pore? Likewise, might specific enzymes (e.g., PKA) that can modulate AMPA receptors be held close to these receptors?
This leads to a second theme in my research, to study the anatomical basis of synaptic plasticity. Of particular interest to us is the trafficking of AMPA receptors (implicated in the control of postsynaptic efficacy), and the organization of second messengers likely to regulate receptor expression. The issue of trafficking has led us to study motor and endocytic proteins, in relation to the actin cytoskeleton.
A synapse -processed by freeze substitution for electron microscopy