The Brain Anatomy of the Brown Bear (Carnivora, Ursus arctos L., 1758) Compared to That of Other Carnivorans: A Cross-Sectional Study Using MRI

Abstract

In this study, we aimed to provide a neuroanatomy atlas derived from cross-sectional and magnetic resonance imaging (MRI) of the encephalon of the brown bear ( Ursus arctos ). A postmortem brain analysis using magnetic resonance imaging (MRI – 1,5T; a high-resolution submillimeter three-dimensional T1-3D FFE) and cross-sectional macroscopic anatomy methods revealed major embryological and anatomical subdivisions of the encephalon, including the ventricular system. Most of the internal structures were comparably identifiable in both methods. The tractus olfactorius medialis, corpus subthalamicum, brachium colliculi rostralis, fasciculus longitudinalis medialis, nuclei vestibulares, velum medullare rostrale, nucleus fastigii, fasciculi cuneatus et gracilis were identified entirely by cross-sectional macroscopic analysis. However, the glandula pinealis, lemniscus lateralis and nuclei rhaphe were visualized only with MRI. Gross neuroanatomic analysis provided information about sulci and gyri of the cerebral hemispheres, components of the vermis and cerebellar hemispheres, and relative size and morphology of constituents of the rhinencephalon and cerebellum constituents. Similarities and discrepancies in identification of structures provided by both methods, as well as hallmarks of the structures facilitating identification using these methods are discussed. Finally, we compare the brown bear encephalon with other carnivores and discuss most of the identified structures compared to those of the domestic dog, the domestic cat, Ursidae and Mustelidae families and Pinnipedia clade.

Surface models and true-color sectioned images of hypothalamic nuclei and its neighboring structures

“…In CTs and MRIs, the appearances of the nuclei and white bundles of the hypothalamus were very vague and illegible [5][6][7]. For the purpose of segmenting based on color, density, and position, high resolution and real color of the sectioned images were more suitable.…”

“…The second is the use of computed tomographs (CTs) and magnetic resonance images (MRIs), which are in almost all current studies and clinics [5][6][7]. However, using radiation and magnetic resonance to target the hypothalamus and, in particular, specific nuclei and white bundles are very vague approaches and does not provide useful information because the hypothalamus is small compared to the other brain structures and is located deep in the brain.…”

Comparative anatomy of the middle cerebral artery, rhinal and endorhinal sulci, piriform lobe, entorhinal cortex, olfactory tubercule, anterior perforate substance, and hippocampus: A dissection study

“…The endorhinal sulcus is rarely mentioned in the recent literature (Duvernoy, 1988; Duvernoy, 1999; Gillilan, 1967; Gloor, 1997; van Staalduinen & Zeineh, 2022). The outlined medial rhinal sulcus (Sienkiewicz et al, 2019) may describe the endorhinal sulcus. Duvernoy demonstrates the endorhinal sulcus in the adult human brain between the anterior perforate substance and the uncus of the temporal lobe (Duvernoy, 1988), The endorhinal sulcus is not listed in any search engine.…”

“…The olfactory tubercule is an important olfactory sensory center and part of the ventral striatum (Allison, 1954; Gloor, 1997). In many vertebrates the olfactory tubercules are prominent bulges on the ventral surface of the central frontal brain (Allison, 1953; Meyer & Allison, 1949; Nachman & Topol, 2002; Papez, 1929; Sienkiewicz et al, 2019). This can be seen in the dissections of the rabbit and cat (Figure 7a,b).…”

Lead and Other Trace Element Levels in Brains of Croatian Large Terrestrial Carnivores: Influence of Biological and Ecological Factors

“…Lower portions of the brain stem ( medulla oblongata [ 52 ]) were obtained from 114 brown bears (period 2015–2018), 8 grey wolves (2016–2017), 3 Eurasian lynx (2017–2022) and 2 golden jackals (2017) from Croatia (app. 43.5°–46° N, 14.5°–16.5° E).…”