Mapping sheep to human brain: The need for a sheep brain atlas

Abstract

A brain atlas is essential for understanding the anatomical relationship between neuroanatomical structures. Standard stereotaxic coordinates and reference systems have been developed for humans, non-human primates and small laboratory animals to contribute to translational neuroscience research. Despite similar neuroanatomical and neurofunctional features between the sheep and human brain, little is known of the sheep brain stereotaxy, and a detailed sheep atlas is scarce. Here, we briefly discuss the value of using sheep in neurological research and the paucity of literature concerning the coordinates system during neurosurgical approaches. Recent advancements such as computerized tomography, positron emission tomography, magnetic resonance imaging, functional magnetic resonance imaging and diffusion tensor imaging are used for targeting and localizing the coordinates and brain areas in humans. Still, their application in sheep is rare due to the lack of a 3D stereotaxic sheep atlas by which to map sheep brain structures to its human counterparts. More recently, a T1- and T2-weighted high-resolution MRI 3D stereotaxic atlas of the sheep brain has been generated, however, the journey to create a sheep brain atlas by which to map directly to the human brain is still uncharted. Therefore, developing a detailed sheep brain atlas is valuable for the future to facilitate the use of sheep as a large animal experimental non-primate model for translational neurological research.

Keywords: atlas; brain; sheep; stereotaxic coordinates; template; translational neuroscience.

Figure 1

Representative images of two-dimensional sections of the brain, coronal (right) and sagittal (left) sectons of brains of various species. (A) Human brain. Coronal sections show the fiber tracts in the left panel and schematic diagrams in the right panel. The sagittal section shows the plane of the 69 sections depicted in the atlas. The intercommisural line (ICL) and the vertical line (VCA) pass through the center of the anterior and posterior commissure, and the center of the anterior commissure, respectively. (B) Pig brain. Coronal and sagittal sections in this example show the coordinates 14.50 mm ahead of the posterior commissure and 4.00 mm laterally from the midsagittal plane, respectively. (C) Cat brain. Coronal and sagittal sections are examples of Nissl stained sections from the adult cat (Felis Catus). (D) Dog brain. Coronal and sagittal sections are shown in the maps of the whole brain from a 5 month old dog (Canis Lupus). The blue line shows the levels at the frontal lobe Images in (A) are reproduced from the human brain website https://www.thehumanbrain.info/brain/sections.php. Retrieved May 12, 2022. Images in (B) are reproduced from the Stereotaxic atlas of the pig brain by Felix et al. (1) with permission from Elsevier. Images (C,D) are reproduced from the brain maps website http://brainmaps.org/ajax-viewer.phpdatid=32&sname=p099-100, retrieved on May 13, 2022.