Evaluating the functional impact of synaptic nanoarchitecture

Summary Numerous brain disorders and diseases are caused by deficits in synapse function. Synaptic transmission is traditionally thought to be governed by the amount of neurotransmitter released and the number of neurotransmitter receptors localized to the postsynaptic membrane. However, accumulating evidence suggests synaptic function not only depends on the number of postsynaptic receptors, but also their precise nanoscale positioning within the postsynaptic membrane. For example, at excitatory synapses AMPA-type glutamate receptors (AMPARs) form one or more clustered sub-structures within the postsynaptic density that are precisely aligned with presynaptic neurotransmitter release sites. Modeling studies predict this pre/post alignment to be critical for efficient AMPAR activation, but this has been challenging to address experimentally. The degree to which receptor nano-positioning influences synaptic function remains unclear due to a lack of suitable approaches for 1. Rapid and reversible perturbations to synaptic nanostructure that allow simultaneous synaptic function measurements. 2. Probing glutamate concentrations directly within distinct synaptic nanodomains. 3. Testing the functional relationship between receptor activation and distance from neurotransmitter release sites. To address these issues, we have recently developed new approaches for rapidly manipulating postsynaptic scaffolds and receptors in real time. In parallel we have developed a new set of genetically encoded affinity reagents for labeling and manipulating endogenous AMPARs. We propose to combine these approaches to assess the functional relevance and regulation of nano-scale positioning within the PSD, a problem that has been challenging to assess using conventional approaches.