Extended Data Fig. 16: Neural inputs to the MOp.
Related to Fig. 3. a, TRIO experiments reveal monosynaptic input to projection-defined MOp cell types. (Upper panel) Schematic diagram of TRIO approach. AAVretro-Cre is injected into a downstream target of a MOp projection neuron population (ex. CP) and Cre-dependent, TVA- and RG-expressing helper virus (AAV8-hSyn-FLEX-TVA-P2A-GFP-2A-oG) and mCherry-expressing G-deleted rabies virus are injected into the MOp to label the MOp projection neurons population (1st-order) and their brain-wide monosynaptic inputs (2nd-order). (Lower panel) Example images of three separate TRIO experiments identifying monosynaptic inputs to IT, PT, and CT cell classes within the MOp showing Cre injection sties (left), helper virus and rabies injection sites in MOp (middle), and monosynaptically labeled inputs in the SSp and thalamus (right). b, Axonal projections to the MOp-ul arising from different cortical areas and thalamic nuclei display diverse laminar specificities in the MOp-ul. For example, MOs axons are preferentially distributed in L1, L5 & L6; densest TEa axons are primarily distributed in L6b; while axons from SSs and contralateral MOp are distributed diffusely across all layers of MOp-ul. Thalamocortical projections to the MOp-ul more or less follow a rough core/matrix organization described previously for thalamic inputs to primary sensory cortices37. In particular, VAL axons generate dense terminals specifically in MOp-ul L4, L5b & L6—a typical “core” type thalamocortical inputs. But, axonal inputs from the PO and PF in the MOp-ul are densely distributed in both L1 (a typical “matrix” type inputs) and L4, thus, a mixture core and matrix pattern. PF axons are further distributed in L6. Inputs from other thalamic nuclei, such as VM, MD, and PCN are diffusely distributed across multiple layers. Based on these results, it is reasonable to anticipate that different PN neuron types (IT, PT, and CT) with their soma and dendritic arbor distributions in different layers may preferentially receive discrete cortical and thalamic inputs at single neuron resolution.
