Visualization of Cortical Modules in Flattened Mammalian Cortices

Abstract

The cortex of mammalian brains is parcellated into distinct substructures or modules. Cortical modules typically lie parallel to the cortical sheet, and can be delineated by certain histochemical and immunohistochemical methods. In this study, we highlight a method to isolate the cortex from mammalian brains and flatten them to obtain sections parallel to the cortical sheet. We further highlight selected histochemical and immunohistochemical methods to process these flattened tangential sections to visualize cortical modules. In the somatosensory cortex of various mammals, we perform cytochrome oxidase histochemistry to reveal body maps or cortical modules representing different parts of the body of the animal. In the medial entorhinal cortex, an area where grid cells are generated, we utilize immunohistochemical methods to highlight modules of genetically determined neurons which are arranged in a grid-pattern in the cortical sheet across several species. Overall, we provide a framework to isolate and prepare layer-wise flattened cortical sections, and visualize cortical modules using histochemical and immunohistochemical methods in a wide variety of mammalian brains.

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“…Tissue Processing : Brains were stored for 24–48 h in 4% PFA at 4 °C prior to transfer to PBS solution. Cortices were flattened after removal of the underlying midline structures as per previously described techniques at room temperature (RT) and kept in 4% PFA for 24 h. The slices were then incubated for 1 h at RT in a blocking solution composed of PBS (0.01 m ), 3% Normal Donkey Serum, and 0.3% Triton X‐100. The slices were then transferred to a solution containing anti‐Vesicular Glutamate Transporter 2 (VGlut2) polyclonal guinea‐pig antibody (AB2251‐I Sigma Millipore) in a 1:2000 dilution and kept overnight at 4 °C.…”

Improved post-stroke spontaneous recovery by astrocytic extracellular vesicles

“…On day 21, the animals were intracardially perfused as indicated above with 4% PFA. The cortical hemispheres were collected, and the ipsilateral hemicortex was flattened as previously described 69 . The flattened cortices were clarified in a sucrose gradient (15,30,45,60, and 75 %) with Triton X-100 (0.4, 0.6, 0.8, and 1 %) for 15 d per stage.…”

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“…Fig. 3b) we first removed subcortical tissue and flattened the cortical sheet of each hemisphere between glass slides by applying pressure overnight before sectioning 100 µm slices with the vibratome (as described previously 80 ). For coronal sections, area borders were drawn by aligning and overlaying the reference section from the atlas 81 .…”