Laminar Organization and Projections of the Motor Cortex of the Sheep

Abstract

The organization of the motor cortex of the sheep is a gateway to understand quadrupedal locomotion, and a possible point of reference for comparison with other terrestrial Cetartiodactyla and hoofed mammals in general. The cortical structure, its laminar subdivision and projections, received scarce attention in the past.Since recent data using modern technics are lacking, we analyzed the lamination of the motor cortical columns using conventional histology, digital imaging and alternative statistical inference. We also traced the motor cortex projections using MR and Diffusion Tensor Imaging (DTI). Sampling topography was based on the available literature and physiological evidence.Our data suggest that the thickness of motor cortex of the sheep is comparable to that of other terrestrial Cetartiodactyla, but thicker than that of marine members of the same Order of equivalent body size. Analyses of the cortical columns showed a five‐layered agranular cortex only partially similar to that of rodents and primates. Layer I contained more round and sparse cells, while layer V had the most heterogeneous cell population profile, including gigantocellular pyramidal neurons.MR results and DTI revealed that the a) a robust bundle of fibers reaches the central pattern generators in the brainstem (Figure 1), thus indirectly emphasizing the existence of several extrapyramidal tracts; and b) the corticospinal tracts, presumed to be minor and limited in Cetartiodactyls given their limited dexterity in respect to primates and carnivores, forms a pathway comparable in size (if not superior) to the extrapyramidal tracts.Our data contrast the generally accepted idea that the extrapyramidal tracts are overwhelmingly dominant in ruminants, and that pyramidal projections to the spinal cord are minimal.Support or Funding InformationThis study was supported by Grant # 2015Y5W9YP from the Italian Ministry of Education, University and Research to Bruno Cozzi, including also all the other Authors.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.