Imaging mitral/tufted glomeruli in the mouse olfactory bulb using the genetically encoded voltage indicator ArcLight

In the mammalian olfactory bulb, each olfactory receptor neuron type corresponds to specific channels known as glomeruli. These input axons connect with the apical dendrites of mitral/tufted cells, which serve as projection neurons sending axons to the olfactory cortex. Consequently, each glomerulus embodies the input-output relationship for a unique olfactory receptor type, undergoing transformation through a complex synaptic network.

Although previous 2-photon Ca2+ imaging experiments have demonstrated the heterogeneous nature of glomerular output in processing odor concentration information, the specifics of voltage dynamics have remained elusive. To address this, researchers employed the genetically encoded voltage indicator (GEVI) ArcLight to directly observe glomerular output in living mice.

Their findings revealed that ArcLight could detect both excitatory and inhibitory odor-evoked signals from mitral/tufted glomeruli. Notably, ArcLight expression maintained stability throughout multi-week imaging sessions, successfully capturing odor- and concentration-specific patterns of activation across a broad range of concentrations.

A key advantage of this technique was its ability to resolve heterogeneous concentration-response sensitivities and respiratory-coupled dynamics. Additionally, the study showed that several newer GEVIs could also measure odor-evoked signals via epifluorescence imaging. Overall, this research establishes ArcLight and other emerging GEVIs as invaluable tools for understanding how sensory information is encoded and transformed within the mouse olfactory bulb.