Brain Behavior and Evolution最新文献

Introduction: The study of non-laboratory species has been part of a broader effort to establish the basic organization of the mammalian neocortex, as these species may provide unique insights relevant to cortical organization, function, and evolution.

Methods: In the present study, the organization of three somatosensory cortical areas of the medium-sized (5-11 kg body mass) Amazonian rodent, the paca (Cuniculus paca), was determined using a combination of electrophysiological microelectrode mapping and histochemical techniques (cytochrome oxidase and NADPH diaphorase) in tangential sections.

Results: Electrophysiological mapping revealed a somatotopically organized primary somatosensory cortical area (S1) located in the rostral parietal cortex with a characteristic foot-medial/head-lateral contralateral body surface representation similar to that found in other species. S1 was bordered laterally by two regions housing neurons responsive to tactile stimuli, presumably the secondary somatosensory (S2) and parietal ventral (PV) cortical areas that evinced a mirror-reversal representation (relative to S1) of the contralateral body surface. The limits of the putative primary visual (V1) and primary auditory (A1) cortical areas, as well as the complete representation of the contralateral body surface in S1, were determined indirectly by the histochemical stains. Like the barrel field described in small rodents, we identified a modular arrangement located in the face representation of S1.

Conclusions: The relative location, somatotopic organization, and pattern of neuropil histochemical reactivity in the three paca somatosensory cortical areas investigated are similar to those described in other mammalian species, providing additional evidence of a common plan of organization for the somatosensory cortex in the rostral parietal cortex of mammals.

Uncovering relationships between neuroanatomy, behavior, and evolution are important for understanding the factors that control brain function. Voluntary exercise is one key behavior that both affects, and may be affected by, neuroanatomical variation. Moreover, recent studies suggest an important role for physical activity in brain evolution. We used a unique and ongoing artificial selection model in which mice are bred for high voluntary wheel-running behavior, yielding four replicate lines of high runner (HR) mice that run ∼3-fold more revolutions per day than four replicate nonselected control (C) lines. Previous studies reported that, with body mass as a covariate, HR mice had heavier whole brains, non-cerebellar brains, and larger midbrains than C mice. We sampled mice from generation 66 and used high-resolution microscopy to test the hypothesis that HR mice have greater volumes and/or cell densities in nine key regions from either the midbrain or limbic system. In addition, half of the mice were given 10 weeks of wheel access from weaning, and we predicted that chronic exercise would increase the volumes of the examined brain regions via phenotypic plasticity. We replicated findings that both selective breeding and wheel access increased total brain mass, with no significant interaction between the two factors. In HR compared to C mice, adjusting for body mass, both the red nucleus (RN) of the midbrain and the hippocampus (HPC) were significantly larger, and the whole midbrain tended to be larger, with no effect of wheel access nor any interactions. Linetype and wheel access had an interactive effect on the volume of the periaqueductal gray (PAG), such that wheel access increased PAG volume in C mice but decreased volume in HR mice. Neither linetype nor wheel access affected volumes of the substantia nigra, ventral tegmental area, nucleus accumbens, ventral pallidum (VP), or basolateral amygdala. We found no main effect of either linetype or wheel access on neuronal densities (numbers of cells per unit area) for any of the regions examined. Taken together, our results suggest that the increased exercise phenotype of HR mice is related to increased RN and hippocampal volumes, but that chronic exercise alone does not produce such phenotypes.

Crocodilians (alligators, crocodiles, and gharials) are the closet living relatives to birds and, as such, represent a key clade to understand the evolution of the avian brain. However, many aspects of crocodilian neurobiology remain unknown. In this paper, we address an important knowledge gap as there are no published studies of cerebellar connections in any crocodilian species. We used injections of retrograde tracers into the cerebellum of the American alligator (Alligator mississippiensis) to describe for the first time the origin of climbing and mossy fiber inputs. We found that inputs to the cerebellum in the American alligator are similar to those of other nonavian reptiles and birds. Retrograde labeled cells were found in the spinal cord, inferior olive, reticular formation, vestibular and cerebellar nuclei, as well as in nucleus ruber and surrounding tegmentum. Additionally, we found no retrogradely labeled cells in the anterior rhombencephalon which suggest that, like other nonavian reptiles, crocodilians may lack pontine nuclei. Similar to birds and other nonavian reptiles, we found inputs to the cerebellum from the pretectal nucleus lentiformis mesencephali. Additionally, we found retrogradely labeled neurons in two nuclei in the pretectum: the nucleus circularis and the interstitial nucleus of the posterior commissure. These pretectal projections have not been described in any other nonavian reptile to date, but they do resemble projections from the nucleus spiriformis medialis of birds. Our results show that many inputs to the cerebellum are highly conserved among sauropsids and that extensive pretectal inputs to the cerebellum are not exclusive to the avian brain. Finally, we suggest that the pontine nuclei of birds are an evolutionary novelty that may have evolved after the last common ancestor between birds and crocodilians, and may represent an intriguing case of convergent evolution with mammals.

Endocranial casts are capable of capturing the general brain form in extinct mammals due to the high fidelity of the endocranial cavity and the brain in this clade. Camelids, the clade including extant camels, llamas, and alpacas, today display high levels of gyrification and brain complexity. The evolutionary history of the camelid brain has been described as involving unique neocortical growth dynamics which may have led to its current state. However, these inferences are based on their fossil endocast record from approximately ∼40 Mya (Eocene) to ∼11 Mya (Miocene), with a gap in this record for the last ∼10 million years. Here, we present the first descriptions of two camelid endocrania that document the recent history of the camelid brain: a new specimen of Palaeolama sp. from ∼1.2 Mya, and the plaster endocast of Camelops hesternus, a giant camelid from ∼44 to 11 Kya which possessed the largest brain (∼990 g) of all known camelids. We find that neocortical complexity evolved significantly between the Miocene and Pleistocene Epochs. Already ∼1.2 Mya the camelid brain presented morphologies previously known only in extant taxa, especially in the frontal and parietal regions, which may also be phylogenetic informative. The new fossil data indicate that during the Pleistocene, camelid brain dynamics experienced neocortical invagination into the sagittal sinus rather than evagination out of it, as observed in Eocene to Miocene taxa.

The amygdala is a central node in functional networks regulating emotions, social behavior, and social cognition. It develops in the telencephalon and includes pallial and subpallial parts, but these are extremely complex with multiple subdivisions, cell types, and connections. The homology of the amygdala in nonmammals is highly controversial, especially for the pallial part, and we are still far from understanding general principles on its organization that are common to different groups. Here, we review data on the adult functional architecture and developmental genoarchitecture of the amygdala in different amniotes (mammals and sauropsids), which are helping to disentangle and to better understand this complex structure. The use of an evolutionary developmental biology (evo-devo) approach has helped distinguish three major divisions in the amygdala, derived from the pallium, the subpallium, and from a newly identified division called telencephalon-opto-hypothalamic domain (TOH). This approach has also helped identify homologous cell populations with identical embryonic origins and molecular profiles in the amygdala of different amniotes. While subpallial cells produce different subtypes of GABAergic neurons, the pallium and TOH are major sources of glutamatergic cells. Available data point to a development-based molecular code that contributes to shape distinct functional subsystems in the amygdala, and comparative genoarchitecture is helping to delineate the cells involved in same subsystems in non-mammals. Thus, the evodevo approach can provide crucial information to understand common organizing principles of the amygdala cells and networks that control behavior, emotions, and cognition in amniotes.

Here, we present the first evidence for brain adaptation in pigs tolerant to the human presence, as a behavioral trait favoring domestication. The study was carried out on minipiglets from population bred at the Institute of Cytology and Genetics (Novosibirsk, Russia). We compared the behavior, metabolism of monoaminergic neurotransmitter systems, and functional activity of the hypothalamic-pituitary-adrenal system, as well as neurotrophic markers in the brain of minipigs differing by tolerance to human presence (HT and LT - high and low tolerance). The piglets did not differ in the levels of activity in the open field test. However, the concentration of cortisol plasma was significantly higher in minipigs with a low tolerance to the presence of humans. Moreover, LT minipigs demonstrated a decreased level of serotonin in the hypothalamus and augmented levels of serotonin and its metabolite 5-HIAA in the substantia nigra as compared to HT animals. In addition, LT minipigs showed increased content of dopamine and its metabolite DOPAC in the substantia nigra and decreased dopamine level in the striatum as well as reduced content of noradrenaline in the hippocampus. Increased mRNA levels of two markers of the serotonin system - TPH2 and HTR7 genes - in the raphe nuclei and in the prefrontal cortex, respectively, were associated in minipigs with a low tolerance to human presence. However, the expression of genes regulating a dopaminergic system (COMT, DRD1, and DRD2) in HT and LT animal groups varied depending on brain structure. In addition, a decrease in the expression of genes encoding BDNF (brain-derived neurotrophic factor) and GDNF (glial cell line-derived neurotrophic factor) was revealed in LT minipigs. The results may contribute to our understanding of the initial stage of domestication in pigs.

The amygdala is a complex brain structure in the vertebrate telencephalon, essential for regulating social behaviors, emotions, and (social) cognition. In contrast to the vast majority of neuron types described in the many nuclei of the mammalian amygdala, little is known about the neuronal diversity in non-mammals, making reconstruction of its evolution particularly difficult. Here, we characterize glutamatergic neuron types in the amygdala of the urodele amphibian Pleurodeles waltl. Our single-cell RNA sequencing data indicate the existence of at least ten distinct types and subtypes of glutamatergic neurons in the salamander amygdala. These neuron types are molecularly distinct from neurons in the ventral pallium (VP), suggesting that the pallial amygdala and the VP are two separate areas in the telencephalon. In situ hybridization for marker genes indicates that amygdalar glutamatergic neuron types are located in three major subdivisions: the lateral amygdala, the medial amygdala, and a newly defined area demarcated by high expression of the transcription factor Sim1. The gene expression profiles of these neuron types suggest similarities with specific neurons in the sauropsid and mammalian amygdala. In particular, we identify Sim1+ and Sim1+ Otp+ expressing neuron types, potentially homologous to the mammalian nucleus of the lateral olfactory tract (NLOT) and to hypothalamic-derived neurons of the medial amygdala, respectively. Taken together, our results reveal a surprising diversity of glutamatergic neuron types in the amygdala of salamanders, despite the anatomical simplicity of their brain. These results offer new insights on the cellular and anatomical complexity of the amygdala in tetrapod ancestors.

The subgenual organ complex in the leg of Polyneoptera (Insecta) consists of several chordotonal organs specialized to detect mechanical stimuli from substrate vibrations and airborne sound. In stick insects (Phasmatodea), the subgenual organ complex contains the subgenual organ and the distal organ located distally to the subgenual organ. The subgenual organ is a highly sensitive detector for substrate vibrations. The distal organ has a characteristic linear organization of sensilla and likely also responds to substrate vibrations. Despite its unique combination of sensory organs, the neuroanatomy of the subgenual organ complex of stick insects has been investigated for only very few species so far. Phylogenomic analysis has established for Phasmatodea the early branching of the sister groups Oriophasmata, the Old World phasmids, and Occidophasmata, the New World phasmids. The species studied for the sensory neuroanatomy, including the Indian stick insect Carausius morosus, belong to the Old World stick insects. Here, the neuroanatomy of the subgenual organ complex is presented for a first species of the New World stick insects, the Peruvian stick insect Oreophoetes peruana. To document the sensory organs in the subgenual organ complex and their innervation pattern, and to compare these between females and males of this species and also to the Old World stick insects, axonal tracing is used. This study documents the same sensory organs for O. peruana, subgenual organ and distal organ, as in other stick insects. Between the sexes of this species, there are no notable differences in the neuroanatomy of their sensory organs. The innervation pattern of tibial nerve branches in O. peruana is identical to other stick insect species, although the innervation pattern of the subgenual organ by a single tibial nerve branch is simpler. The shared organization of the organs in the subgenual organ complex in both groups of Neophasmatodea (Old World and New World stick insects) indicates the sensory importance of the subgenual organ but also of the distal organ. Some variation exists in the innervation of the chordotonal organs in O. peruana though a common innervation pattern can be identified. The findings raise the question for the ancestral neuroanatomical organization and innervation in stick insects.

The human brain is composed of a complex web of pathways. Diffusion magnetic resonance (MR) tractography is a neuroimaging technique that relies on the principle of diffusion to reconstruct brain pathways. Its tractography is broadly applicable to a range of problems as it is amenable for study in individuals of any age and from any species. However, it is well known that this technique can generate biologically implausible pathways, especially in regions of the brain where multiple fibers cross. This review highlights potential misconnections in two cortico-cortical association pathways with a focus on the aslant tract and inferior frontal occipital fasciculus. The lack of alternative methods to validate observations from diffusion MR tractography means there is a need to develop new integrative approaches to trace human brain pathways. This review discusses integrative approaches in neuroimaging, anatomical, and transcriptional variation as having much potential to trace the evolution of human brain pathways.