Storace, D. | bioRxiv Science

bioRxiv2026

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 maps to receptor-specific channels called glomeruli. These input axons interact with the apical dendrites of mitral/tufted cells, which are projection neurons that send axons to the olfactory cortex. Therefore, each glomerulus reflects the input-output relationship for a different olfactory receptor type, which is transformed by a complex synaptic network. While prior 2-photon Ca2+ imaging experiments have shown that the glomerular output is heterogeneous with respect to how odor concentration information is processed, the nature of voltage dynamics remains unclear. Therefore, we used the genetically encoded voltage indicator (GEVI) ArcLight to image the glomerular output in vivo in anesthetized mice. We found that ArcLight could resolve both excitatory and suppressive odor-evoked signals from mitral/tufted glomeruli. ArcLight expression remained stable over multi-week imaging sessions and successfully captured odor- and concentration-specific patterns of activation across a large concentration range. Importantly, this approach allowed us to resolve heterogeneous concentration-response sensitivities and respiratory-coupled dynamics. We also demonstrate that several newer GEVIs can similarly measure odor-evoked signals using epifluorescence imaging. Our study establishes ArcLight and other emerging GEVIs as powerful tools for dissecting how sensory information is encoded and transformed through the mouse olfactory bulb.

neuroscience↗

bioRxiv2026

Enhanced multisensory integration in the olfactory bulb of the Mexican cavefish

Astyanax mexicanus consists of eyed, river-dwelling "surface" fish, and multiple, independently evolved cave populations, which have converged on troglobitic traits such as eye loss and reduced metabolism. However, considerably less is known about constructive adaptations, which include a larger olfactory epithelium in cavefish. It is unknown how this relates to the olfactory bulb (OB), which is the first stage of olfactory sensory processing in the brain. The goal of the present study is to begin to define the structure and functional organization of the OB in A. mexicanus, and to begin to understand how it was transformed via cave adaptation. We addressed these questions using whole-mount immunohistochemistry and in vivo Ca2+ imaging from the OB of developmentally matched surface and Pachon cavefish. The cavefish OB was significantly larger than surface fish by 14 days post fertilization (dpf), which was accompanied by a broad and proportional increase in synaptic input to most glomerular regions. Increases in the size of the OB were accompanied by increases in the number of neurons expressing tyrosine hydroxylase and calretinin, the latter of which occurred primarily in the medial OB and could not be explained as a compensatory response to a larger OB. In vivo Ca2+ imaging from the dorsal OB of surface and cavefish in response to a panel of chemical stimuli revealed odor-evoked responses that were spatially organized and highly conserved across the two populations. Surprisingly, the medial OB was consistently activated by any change in water flow in both populations, although the number of water-responsive neurons was significantly greater in cavefish when measurements were performed using either in vivo imaging or the neuronal activity marker phospho-ERK. Water-responding neurons were similarly present in the olfactory epithelium in both populations, along with neurons expressing the mechanosensitive ion channel Piezo2, with significantly more Piezo2-expressing neurons present in cavefish. Therefore, cavefish exhibit enhanced multisensory integration of olfactory and mechanosensory input in the earliest stage of olfactory sensory processing in the brain.

neuroscience↗