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Abstract:
Measurement of population activity with single−action−potential, single−neuron resolution is pivotal for understanding information representation and processing in the brain and how the brain's responses are altered by experience. Genetically encoded indicators of neuronal activity allow long−term, cell type−specific expression. Fluorescent Ca2+ indicator proteins (FCIPs), a main class of reporters of neural activity, initially suffered, in particular, from an inability to report single action potentials in vivo. Although suboptimal Ca2+−binding dynamics and Ca2+−induced fluorescence changes in FCIPs are important factors, low levels of expression also seem to play a role. Here we report that delivering D3cpv, an improved fluorescent resonance energy transfer−based FCIP, using a recombinant adeno−associated virus results in expression sufficient to detect the Ca2+ transients that accompany single action potentials. In upper−layer cortical neurons, we were able to detect transients associated with single action potentials firing at rates of <1 Hz, with high reliability, from in vivo recordings in living mice
