An Optical Neuron-Astrocyte Proximity Assay at Synaptic Distance Scales

Highlights

• An imaging method was developed to assess astrocyte-synapse proximity

• The method was used to determine the wiring diagram of striatal astrocytes

• Dynamics of striatal astrocyte interactions with excitatory inputs were evaluated

• Resources to track static and dynamic astrocyte-synapse interactions are provided

Summary

Astrocytes are complex bushy cells that serve important functions through close contacts between their processes and synapses. However, the spatial interactions and dynamics of astrocyte processes relative to synapses have proven problematic to study in adult living brain tissue. Here, we report a genetically targeted neuron-astrocyte proximity assay (NAPA) to measure astrocyte-synapse spatial interactions within intact brain preparations and at synaptic distance scales. The method exploits resonance energy transfer between extracellularly displayed fluorescent proteins targeted to synapses and astrocyte processes. We validated the method in the striatal microcircuitry following in vivo expression. We determined the proximity of striatal astrocyte processes to distinct neuronal input pathways, to D1 and D2 medium spiny neuron synapses, and we evaluated how astrocyte-to-excitatory synapse proximity changed following cortical afferent stimulation, during ischemia and in a model of Huntington’s disease. NAPA provides a simple approach to measure astrocyte-synapse spatial interactions in a variety of experimental scenarios.

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