INTRODUCTION:Baird's beaked whale, a member of the family Ziphiidae, is one of the largest odontocetes, second only to the sperm whale in body mass. The species is known for its exceptional diving abilities, but this behavior makes it difficult to observe in its natural habitat and has contributed to major gaps in our understanding of its biology, including its neuroanatomy. This study provides a detailed anatomical and quantitative description of the Baird's beaked whale brain. METHODS:The brain was examined using magnetic resonance imaging. External and internal neuroanatomical features were described, including sulcal and gyral patterns. Quantitative measurements were obtained for the cerebral cortex, amygdala, hippocampus, ventricular system, superior and inferior colliculi, cerebellum, the midsagittal cross-sectional area of the corpus callosum, the gyrification index, and the encephalization quotient. RESULTS:The Baird's beaked whale brain shows an organization typical of odontocetes, including a large and highly gyrencephalic neocortex. The encephalization quotient and relative cerebellar volume are lower than those reported for delphinids, consistent with findings in other deep-diving cetaceans. CONCLUSION:These neuroanatomical differences may reflect energy allocation strategies related to diving behavior and body size. By placing these traits within a broader mammalian comparative framework, this study contributes to our understanding of how ecological pressures may shape brain evolution, particularly in rarely studied cetacean lineages such as the Ziphiidae.

Carnivorans are an important study object for comparative neuroscience, as they exhibit a wide range of behaviours, ecological adaptations, and social structures. Previous studies have mainly examined relative brain size, but a comprehensive understanding of brain diversity requires the investigation of other aspects of their neuroanatomy. Here, we obtained primarily post-mortem brain scans from 26 species of the order Carnivora, spanning across eight families with diverse representatives and including additional individuals for selected species, to create the largest carnivoran brain collection to date. We reconstructed their cortical surfaces and examined neocortical sulcal anatomy to establish a framework for systematic interspecies comparisons, revealing distinct regional variations in sulcal anatomy, potentially related to the species’ behaviour and ecology. Arctoidea species with pronounced forepaw dexterity exhibited complex sulcal configurations in the presumed somatosensory cortex but low sulcal complexity in the presumed visual and auditory occipitotemporal cortex. Canidae had the largest number of unique major sulci, including one in the occipital cortex and highly social canids featuring an additional frontal cortex sulcus. We also observed differentially complex occipitotemporal sulcal patterns in Felidae and Canidae, indicative of changes in auditory and visual areas that may be related to foraging strategies and social behaviour. In conclusion, this study presents an inventory of the sulcal anatomy of a number of rarely studied carnivoran brains including detailed digital atlases and establishes a framework and novel avenues for further investigations employing a variety of neuroimaging modalities to reveal more about carnivoran brain diversity.

As neuroscience techniques become increasingly sophisticatedand accessible, their application to marine mammal research remainsunderdeveloped and fragmented. Cetacean and pinniped brains exhibit remarkableevolutionary specializations; yet systematic, reproducible data across speciesare scarce. Ethical, logistical, and methodological constraints hinder samplingand analysis of central nervous system tissues, often limiting studies to smallcohorts and reducing diagnostic accuracy in neuropathological investigations.Gaps persist in understanding neuroanatomical organization, pathogeneticmechanisms of neurodegeneration, and the effects of acoustic and environmentalstressors on brain health. Noninvasive neuroimaging methods such as post-mortemmagnetic resonance imaging and diffusion-weighted imaging offer promise butsuffer from incompatible protocols and limited standardization. In-vitro andmolecular techniques including cellular reprogramming may provide new avenuesfor translational research if harmonized approaches are adopted. We identify a criticalneed for coordinated efforts to standardize best practice protocols for the sampling, storage and systematic analyses of marine mammal nervous tissues. To this end, we propose the formation of an inclusive, multidisciplinary network and invitecollaboration through our Open Science Framework project. By aligning methodologies and broadeninginternational partnerships, we aim to transform marine mammal neuroscience intoa robust contributor to comparative neurobiology and environmental healthmonitoring. This is a call to action to collectively grow this emerging field.

Background/Objectives: Although multiple magnetic resonance imaging (MRI) indices are known to be sensitive to the noninvasive assessment of myelin integrity, their relative sensitivities have not been directly compared. This study aimed to identify the most sensitive MRI index for characterizing myelin composition in the spinal cord’s gray matter (GM) and white matter (WM). Methods: MRI was performed on a deer’s ex vivo cervical spinal cord. Quantitative indices known to be sensitive to myelin, including the myelin water fraction (MWF), magnetization transfer ratio (MTR), the signal ratio between T1- and T2-weighted images (T1W/T2W), fractional anisotropy (FA), mean diffusivity (MD), electrical conductivity (σ), and T1, T2, and T1ρ relaxation times were calculated. Their mean values were compared using repeated measures analysis of variance (ANOVA) and post hoc Bonferroni tests or Friedman and post hoc Wilcoxon tests to identify differences across GM and WM columns possessing distinct myelin distributions, as revealed by histological analysis. Relationships among the indices were examined using Spearman’s rank-order correlation analysis. Corrected p < 0.05 was considered statistically significant. Results: All indices except σ differed significantly between GM and all WM columns. Two of the three WM columns had significantly different MWF, FA, MD, and T2, whereas one WM column had significantly different MTR, σ, T1, and T1ρ from the others. A significant moderate to very strong correlation was observed among most indices. Conclusions: The sensitivity of MRI indices in distinguishing spinal cord regions varied. A strategic combination of two or more indices may allow the accurate differentiation of spinal cord regions.

The largest mammalian brains belong to cetacean species among the cetartiodactyls. Stereological analyses have estimated cetacean numbers of cerebral cortical neurons to be more than the average 16 billion of humans, yet isotropic fractionator estimates in artiodactyls predict that even the largest cetacean brains should have no more than a few billion cortical neurons. Here, we used the isotropic fractionator to investigate these contrasting estimates of neuronal numbers by determining the numbers of neurons and non-neuronal cells forming the brain of a northern minke whale, previously estimated using stereology as containing 12.8 billion cortical neurons (Eriksen and Pakkenberg 2007), and comparing it to our dataset of several dozen mammalian species analyzed with the same method. We report that, with 3.2 billion neurons, the minke whale cerebral cortex conforms to the quantitative scaling rules that apply to other mammals, especially the closely related artiodactyls. The same brain contained a total of 57.4 billion neurons, of which 54.2 billion were cerebellar neurons, matching the expected numbers of a hypothetical artiodactyl brain of similar cerebellar mass. In addition, we found that the northern minke whale brain, with a mass of 2683.9 g, contained 173.4 billion non-neuronal cells, following the universal scaling rules that apply to the brain in all therian mammals examined to date. Thus, how non-neuronal cells are added to the mammalian brain is conserved across therian mammals and is not affected by the transition to an obligatory aquatic life history. Strikingly, we find that the minke whale is an outlier amongst mammals in having almost 18 cerebellar neurons for every neuron in the cerebral cortex, compared to the average ratio of 4, which might be related to infrasonic communication. In addition, with only approximately 88 million neurons, the remainder of the brain (brainstem/diencephalon/subcortical telencephalon) of the northern minke whale exhibited the lowest relative neuronal density of these regions reported in mammalian brains, which might be related to the absence of limbs compared to all other mammalian species. Our results indicate that the number of neurons in cetacean brains has been grossly overestimated by stereological accounts, and place whale brains on par with highly cognitively capable macaws, macaques, baboons, and elephants, but below great apes and humans, in terms of numbers of cortical neurons.

The Guiana dolphin (Sotalia guianensis) is a common species along Central and South American coastal waters. Although much effort has been made to understand its behavioral ecology and evolution, very little is known about its brain. The use of ultra-high field MRI in anatomical descriptions of cetacean brains is a very promising approach that is still uncommon. In this study, we present for the first time a full anatomical description of the Guiana dolphin’s brain based on high-resolution ultra-high-field magnetic resonance imaging, providing an exceptional level of brain anatomical details, and enriching our understanding of the species. Brain structures were labeled and volumetric measurements were delineated for many distinguishable structures, including the gray matter and white matter of the cerebral cortex, amygdala, hippocampus, superior and inferior colliculi, thalamus, corpus callosum, ventricles, brainstem and cerebellum. Additionally, we provide the surface anatomy of the Guiana dolphin brain, including the labeling of main sulci and gyri as well as the calculation of its gyrification index. These neuroanatomical data, absent from the literature to date, will help disentangle the history behind cetacean brain evolution and consequently, mammalian evolution, representing a significant new source for future comparative studies.

Brain reconstruction, specially of the cerebral cortex, is a challenging task and even more so when it comes to highly gyrified brained animals. Here, we present Stitcher, a novel tool capable of generating such surfaces utilizing MRI data and manual segmentation. Stitcher makes a triangulation between consecutive brain slice segmentations by recursively adding edges that minimize the total length and simultaneously avoid self-intersection. We applied this new method to build the cortical surfaces of two dolphins: Guiana dolphin (Sotalia guianensis), Franciscana dolphin (Pontoporia blainvillei); and one pinniped: Steller sea lion (Eumetopias jubatus). Specifically in the case of P. blainvillei, two reconstructions at two different resolutions were made. Additionally, we also performed reconstructions for sub and non-cortical structures of Guiana dolphin. All our cortical mesh results show remarkable resemblance with the real anatomy of the brains, except P. blainvillei with low-resolution data. Sub and non-cortical meshes were also properly reconstructed and the spatial positioning of structures was preserved with respect to S. guianensis cerebral cortex. In a comparative perspective between methods, Stitcher presents compatible results for volumetric measurements when contrasted with other anatomical standard tools. In this way, Stitcher seems to be a viable pipeline for new neuroanatomical analysis, enhancing visualization and descriptions of non-primates species, and broadening the scope of compared neuroanatomy.

The brain is a complex organ demonstrated by the occurrence of specific types of functional lipids. Despite some studies focusing on providing the animal brain lipid signature, there are limited studies focusing on the comprehensive and regiospecific characterization of multiple animal brain lipidome. Herein we characterized about 294 lipid molecular species from six different lipid classes in different portions of the brain after fixation from mammals of different habitats, fully-aquatic (n = 6), semi-aquatic (n = 6), and terrestrial (n = 4), using liquid chromatography-mass spectrometry. The untargeted brain lipid profiling revealed a significant difference in total lipid levels between fully-aquatic, semi-aquatic, and terrestrial mammals. The polyunsaturated fatty acids and cholesterol esters are abundant in brain tissue of semi-aquatic followed by fully-aquatic mammals whereas phosphatidylethanolamines are profoundly high in terrestrial species. The regiospecific analysis revealed a predominance of sphingolipids in all the groups but no significant differences were observed between the different portions of the brain such as the cerebellum, cortex, pons, spinal cord, and thalamus. Interestingly the multivariate analysis showed almost the same lipid compositions in the spinal cord and thalamus of terrestrial mammals. Overall, this is the first report to compare the comprehensive brain-lipidome among different mammalian groups inhabiting three distinct habitats. These results indicate that the brain lipid composition is specific to the animal habitat.

Abstract Several environmental chemicals are suspected risk factors for autism spectrum disorder (ASD), including valproic acid (VPA) and pesticides acting on nicotinic acetylcholine receptors (nAChRs), if administered during pregnancy. However, their target processes in fetal neuro-development are unknown. We report that the injection of VPA into the fetus impaired imprinting to an artificial object in neonatal chicks, while a predisposed preference for biological motion (BM) remained intact. Blockade of nAChRs acted oppositely, sparing imprinting and impairing BM preference. Beside ketamine and tubocurarine, significant effects of imidacloprid (a neonicotinoid insecticide) appeared at a dose ≤1 ppm. In accord with the behavioral dissociations, VPA enhanced histone acetylation in the primary cell culture of fetal telencephalon, whereas ketamine did not. VPA reduced the brain weight and the ratio of NeuN-positive cells (matured neurons) in the telencephalon of hatchlings, whereas ketamine/tubocurarine did not. Despite the distinct underlying mechanisms, both VPA and nAChR blockade similarly impaired imprinting to biological image composed of point-light animations. Furthermore, both impairments were abolished by postnatal bumetanide treatment, suggesting a common pathology underlying the social attachment malformation. Neurotransmission via nAChR is thus critical for the early social bond formation, which is hindered by ambient neonicotinoids through impaired visual predispositions for animate objects.

Several environmental chemicals are suspected as risk factors for autism spectrum disorder (ASD), including valproic acid (VPA) and pesticides acting on nicotinic acetylcholine receptor (nAChR) if exposed during pregnancy. However, their target processes in fetal neuro-development are unspecified. We report that fetal injection of VPA impaired the imprinting of an artifact object in hatchlings, while the predisposed preference to biological motion (BM) remained intact. Blockade of nAChR acted oppositely, namely, spared imprinting and impaired BM in chicks. Beside ketamine and tubocurarine, significant effects of imidacloprid (a neonicotinoid insecticide) appeared at dose ≤1ppm. Despite the distinct processes, both VPA and nAChR blockade similarly impaired imprinting of biological image composed of point-light animation. Furthermore, both impairments were rescued by post-natal bumetanide treatment, suggesting common pathology underlying the social attachment malformation. Ambient neonicotinoid could hinder adaptive socialization through impaired development of visual perception in early neonates.

To elucidate factors underlying the evolution of large brains in cetaceans, we examined 16 brains from 14 cetartiodactyl species, with immunohistochemical techniques, for evidence of non-shivering thermogenesis. We show that, in comparison to the 11 artiodactyl brains studied (from 11 species), the 5 cetacean brains (from 3 species), exhibit an expanded expression of uncoupling protein 1 (UCP1, UCPs being mitochondrial inner membrane proteins that dissipate the proton gradient to generate heat) in cortical neurons, immunolocalization of UCP4 within a substantial proportion of glia throughout the brain, and an increased density of noradrenergic axonal boutons (noradrenaline functioning to control concentrations of and activate UCPs). Thus, cetacean brains studied possess multiple characteristics indicative of intensified thermogenetic functionality that can be related to their current and historical obligatory aquatic niche. These findings necessitate reassessment of our concepts regarding the reasons for large brain evolution and associated functional capacities in cetaceans.

The current study provides an analysis of the cytoarchitecture, myeloarchitecture, and chemoarchitecture of the amygdaloid body of the banded mongoose (Mungos mungo) and domestic ferret (Mustela putorius furo). Using architectural and immunohistochemical stains, we observe that the organization of the nuclear and cortical portions of the amygdaloid complex is very similar in both species. The one major difference is the presence of a cortex‐amygdala transition zone observed in the domestic ferret that is absent in the banded mongoose. In addition, the chemoarchitecture is, for the most part, quite similar in the two species, but several variances, such as differing densities of neurons expressing the calcium‐binding proteins in specific nuclei are noted. Despite this, certain aspects of the chemoarchitecture, such as the cholinergic innervation of the magnocellular division of the basal nuclear cluster and the presence of doublecortin expressing neurons in the shell division of the accessory basal nuclear cluster, appear to be consistent features of the Eutherian mammal amygdala. The domestic ferret presented with an overall lower myelin density throughout the amygdaloid body than the banded mongoose, a feature that may reflect artificial selection in the process of domestication for increased juvenile‐like behavior in the adult domestic ferret, such as a muted fear response. The shared, but temporally distant, ancestry of the banded mongoose and domestic ferret allows us to generate observations relevant to understanding the relative influence that phylogenetic constraints, adaptive evolutionary plasticity, and the domestication process may play in the organization and chemoarchitecture of the amygdaloid body.

We quantified both proliferative (Ki-67 immunohistochemistry) and immature (doublecortin immunohistochemistry) cells within the dentate gyrus of adult Egyptian fruit bats from three distinct environments: (a) primary rainforest, (b) subtropical woodland, and (c) fifth-generation captive-bred. We used four different previously reported methods to assess the effect of the environment on proliferative and immature cells: (a) the comparison of raw totals of proliferative and immature cells; (b) these totals standardized to brain mass; (c) these totals expressed as a density using the volume of the granular cell layer (GCLv) for standardization; and (d) these totals expressed as a percentage of the total number of granule cells. For all methods, the numbers of proliferative cells did not differ statistically among the three groups, indicating that the rate of proliferation, while malleable to experimental manipulation or transiently in response to events of importance in the natural habitat, appears to occur, for the most part, at a predetermined rate within a species. For the immature cells, raw numbers and standardizations to brain mass and GCLv revealed no difference between the three groups studied; however, standardization to total granule cell numbers indicated that the two groups of wild-caught bats had significantly higher numbers of immature neurons than the captive-bred bats. These contrasting results indicate that the interpretation of the effect of the environment on the numbers of immature neurons appears method dependent. It is possible that current methods are not sensitive enough to reveal the effect of different environments on proliferative and immature cells.

This study provides an analysis of the cytoarchitecture, myeloarchitecture, and chemoarchitecture of the diencephalon (dorsal thalamus, ventral thalamus, and epithalamus) of the banded mongoose (Mungos mungo) and domestic ferret (Mustela putorius furo). Using architectural and immunohistochemical stains, we observe that the nuclear organization of the diencephalon is very similar in the two species, and similar to that reported in other carnivores, such as the domestic cat and dog. The same complement of putatively homologous nuclei were identified in both species, with only one variance, that being the presence of the perireticular nucleus in the domestic ferret, that was not observed in the banded mongoose. The chemoarchitecture was also mostly consistent between species, although there were a number of minor variations across a range of nuclei in the density of structures expressing the calcium-binding proteins parvalbumin, calbindin, and calretinin. Thus, despite almost 53 million years since these two species of carnivores shared a common ancestor, strong phylogenetic constraints appear to limit the potential for adaptive evolutionary plasticity within the carnivore order. Apart from the presence of the perireticular nucleus, the most notable difference between the species studied was the physical inversion of the dorsal lateral geniculate nucleus, as well as the lateral posterior and pulvinar nuclei in the domestic ferret compared to the banded mongoose and other carnivores, although this inversion appears to be a feature of the Mustelidae family. While no functional sequelae are suggested, this inversion is likely to result from the altricial birth of Mustelidae species.