Visual function of transcriptomically defined glutamatergic neurons

Project Summary / Abstract Primary visual cortex (V1) processes visual information along parallel pathways and distributes the results to high level cortical areas and subcortical targets. In mice, a species that lacks a strong, columnar organization, neurons carrying information from different streams are spatially intermixed, but nevertheless connect with specificity, both within and across areas. How are connections between neurons established on such a fine scale despite the spatial intermixing of neurons? We hypothesize that the visual properties of receptive fields of V1 neurons correlate with transcriptomic cell types, which further guide their projection patterns and orchestrate the wiring of local connections. We will establish if there is a correlation between cell type and visual function in V1. Our strategy consists of the following steps. Step 1) Express GCaMP8 in a sparse set of L2/3 neurons under the control of tamoxifen. Step 2) Use volumetric, in-vivo 2-photon calcium imaging to extensively characterize the visual properties of the labeled neurons. Step 3) Process the tissue using expansion-assisted iterative FISH (EASI-FISH) to yield the transcriptomic signatures of cells within the volume. Importantly, we will determine which cells express GCaMP8 that will provide the landmarks for alignment. Step 4) Alignment between in-vivo recordings and transcriptomic data using GCaMP6 expression. Step 5) Clustering of neurons according to visual properties and transcriptomic signature. The project addresses one of NEI’s priorities: to improve the understanding of neural activity and molecular events in the formation of central visual circuits. Success in this project will deliver the first database of excitatory cells in L2/3 of the mouse containing a characterization of their visual properties, cortical location, and transcriptomic signatures. We will test if basic properties of visual neurons, such as their receptive field linearity, correlate with cell types. The work will pave the way to study critical questions about how early visual experience interacts with genetic programs that lead to cell differentiation and their connectivity in a future R01.