Circumferential Alignment of Muscle Cells in the Tunica media of the Human Brain Artery

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Abstract
Our purpose was to measure how structurally coordinated is the network of muscle cells in the brain artery. Vessels from 7 autopsies were fixed with glutaraldehyde and formalin at physiologic pressure. We embedded each artery alongside a block of liver, formed into a rectangular prism, prepared it for light microscopy and stained the sections with haematoxylin and eosin (HE). The angle of cutting the arterial segments was determined with the aid of the block of liver tissue as a Cartesian reference. We measured the directional alignment of vascular smooth muscle using the centrally located nucleus as a vector of orientation. The end coordinates of the profiles of the nuclei (appearing dark with the HE stain) were recorded on a digitizer tablet, and analysis was done as suggested by a previous modelling study. The method provides an average alignment from the collective measurements on the hundreds of nuclei in each histological section. Data from 10 arteries (approximately 22,000 nuclei) from 17 sections showed that brain arteries have highly oriented medial muscle cells aligned circumferentially (average magnitude of 1.3 ± [SD] 1.5 ° from true cross section), with a helical variation (along the artery) of ± 7.9 ° and a variation in the spiral direction of ± 5.4 °, i.e. a three-dimensional variation from nucleus to nucleus of ± 10 °.