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Nature Methods 5, 797–804 (1 September 2008) | doi:10.1038/nmeth.1242

Single-spike detection in vitro and in vivo with a genetic Ca2+ sensor

Damian J Wallace , Stephan Meyer zum Alten Borgloh , Simone Astori , Ying Yang , Melanie Bausen , Sebastian K|[uuml]|gler , Amy E Palmer , Roger Y Tsien , Rolf Sprengel , Jason N D Kerr , Winfried Denk & Mazahir T Hasan

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 in vivo recordings in living mice.