Brain Behavior and Evolution最新文献

Introduction: Chondrichthyans represent some of the earliest diverging lineages of jawed vertebrates, making them key models for studying the evolution of vertebrate brains. Despite their evolutionary significance, Mediterranean species remain understudied. This research focuses on the speckled skate (Raja polystigma), an endemic Mediterranean benthic species with distinct life history traits, such as bathymetric segregation and postnatal shifts in diet. These traits provide a unique opportunity to explore how ecological factors influence postnatal brain development and neuroecological adaptation in cartilaginous fishes.

Methods: We examined the allometric relationship between brain mass and body mass in postnatal individuals of R. polystigma and assessed the relative growth of major brain regions, including the olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and medulla oblongata. Data were analyzed using log-transformed linear regressions to determine differential growth rates and patterns of regional specialization during development.

Results: Our analysis revealed that brain growth scales with negative allometry relative to body mass, indicating a slowdown in brain growth as individuals mature. Region-specific trends showed that the olfactory bulbs, cerebellum, and medulla oblongata grow at a faster rate than the rest of the brain, suggesting enhanced development of sensory and motor capacities. Conversely, the optic tectum exhibited slower growth, implying a reduced visual reliance in adults. The telencephalon and diencephalon scaled isometrically with brain mass, suggesting stable roles in cognitive and integrative functions throughout postnatal development.

Conclusion: These findings highlight how ecological and behavioral shifts during development shape brain organization in R. polystigma. Enhanced growth of non-visual sensory regions and motor centers may reflect adaptations to a benthic lifestyle and bathymetric niche. This study contributes to our understanding of neuroecological evolution in Mediterranean chondrichthyans and underscores the value of R. polystigma as a model for investigating brain development in relation to ecological specialization.

Introduction: The plainfin midshipman fish (Porichthys notatus) relies on the production and reception of social acoustic signals for reproductive success. During spawning, male midshipman fish produce long duration advertisement calls to attract females, which use their auditory sense to locate and access calling males. While seasonal changes based on reproductive state in inner-ear auditory sensitivity and frequency encoding in midshipman are well documented, little is known about reproductive-state-dependent changes in central auditory sensitivity and auditory neural responsiveness to conspecific advertisement calls. Previous research indicates that forebrain dopaminergic neurons are preferentially active in response to conspecific advertisement calls and during female auditory-driven behavior in the breeding season. These dopamine neurons project to both the inner ear and central auditory nuclei and contribute to regulation of inner-ear auditory sensitivity based on reproductive state. The present study tested the hypothesis that exposure to the male advertisement call would elicit differential activation in auditory brain nuclei and in the forebrain auditory-projecting dopaminergic nucleus in reproductive versus non-reproductive male midshipman.

Methods: Fish were collected during the spring reproductive and winter non-reproductive months and were exposed to a playback of the advertisement call or ambient noise (control). Immunohistochemistry identified activated neurons (pS6-ir; proxy for neural activation) in midbrain and forebrain auditory and dopaminergic nuclei.

Results and conclusions: Our results revealed that in key auditory and dopaminergic areas, the greatest activation (most pS6-ir cells) occurred in reproductive males exposed to the advertisement call.

Background: Glia represent a major cell population of the nervous system, and they take part in virtually any process sustaining the development, the functioning, and the pathology of the nervous system. Glial cells diversified significantly during evolution and distinct signals have been adopted to initiate glial development in mammals as compared to flies. In the invertebrate model Drosophila melanogaster, the transcription factor Gcm is necessary and sufficient to generate glial cells. Although Gcm orthologs have been found in protostomes and deuterostomes, they do not act in glial fate commitment as in flies, calling for further investigations of the evolutionarily conserved role of Gcm.

Summary: Here, we review the impact of the fly Gcm transcription factor in the differentiation of phagocytic competent cells inside and outside the nervous system, glia, and macrophages, respectively. Then, we discuss the evolutionary conservation of Gcm and the neural/nonneural functions of Gcm orthologs. Finally, we present a recent work from Pavlidaki et al. [Cell Rep. 2022;41(3):111506] showing that the Gcm cascade is conserved from fly macrophages to mammalian microglia to counteract acute and chronic inflammation.

Key messages: Gcm has an ancestral role in immunity, and its anti-inflammatory effect is evolutionarily conserved. This opens new avenues to assess Gcm function in other species/animal models, its potential involvement in inflammation-related processes, such as regeneration, and to expand the investigation on glia evolution.

Introduction: Different functional domains can be identified along the longitudinal axis of the mammalian hippocampus. We have recently hypothesized that a similar functional gradient may exist along the longitudinal axis of the avian hippocampal formation (HF) as well. If the 2 gradients are homologous, we would expect the caudal HF to be more responsive to acute stress than the rostral HF.

Methods: We restrained 8 adult Dekalb White hens in a bag for 30 min under red-light conditions and compared FOS-immunoreactive (FOS-ir) cell densities in different hippocampal subdivisions to control hens.

Results: Although we could find no evidence of an activated stress response in the hypothalamic-pituitary-adrenal axis of the restrained birds, we did find a significant increase in FOS-ir cell densities in the rostral HF of the restrained birds compared to controls.

Conclusion: We speculate that the HF response is not due to an acute stress response, but instead, it is related to the change in spatial context that was part of taking the birds and restraining them in a different room. We see no activation in the caudal HF. This would be consistent with our hypothesis that the longitudinal axis of the avian HF is homologous to the long axis of the mammalian hippocampus.

Background: Astrocytes are a subtype of glial cells, which are non-neuronal cells that do not produce action potentials. Rather, astrocytes are involved in various functions vital to a functioning brain including nutrient supply to neuronal cells, blood-brain barrier maintenance, regulation of synaptic transmission, and repair following CNS injury.

Summary: While astrocytes have been examined extensively in rodents, it is now clear that there is a large amount of astrocyte heterogeneity and increased complexity in mammals and primates. Astrocytes have expanded in the human lineage with respect to density, soma volume, and the ratio of astrocytes to total glial cells. The human prefrontal cortex also possesses an overall increased glia:neuron ratio relative to other primates, coinciding with allometric expectations based on overall brain size.

Key messages: What are the underlying changes in astrocytes in primate evolution? For this review, we will focus on the evolution of gene expression and gene regulation in astrocytes as a read out of the phenotypic changes seen in cellular morphology. This is an exciting time to understand this cell type in a more dynamic and complex way with new technologies such as induced pluripotent stem cells and single-cell RNA sequencing. Furthermore, understanding the evolution of astrocytes across primates will help explain their role in neurological disease as alterations in astrocyte function are implicated in many neurodegenerative states such as Alzheimer's disease and Parkinson's disease.

Introduction: Domestication and subsequent breed selection has significantly changed the phenotype of most domesticated animal species. Not only has their external appearance changed, in many species, the brain and individual brain regions often differ in size in domesticated strains compared with their wild ancestors. Although the majority of studies on mammals focus on cortical regions, the cerebellum often differs in relative and absolute size between domestic and wild strains, but more specific data on cell sizes and numbers are often lacking.

Methods: We quantified cerebellar anatomy in two domesticated strains (Long-Evans and Sprague-Dawley) and one wild type of brown rat (Rattus norvegicus). Using unbiased stereology, we measured the total cerebellum and its layers' volumes, as well as the number and size of Purkinje cells.

Results: Long-Evans rats had a larger total cerebellum volume, in both absolute and relative terms, than Sprague-Dawley and wild rats, but no other significant differences were detected. Significant differences in the absolute and relative sizes of the molecular, granule cell, and white matter layers were also found, but the differences were inconsistent among strains such that the largest values alternated between the two laboratory strains. The absolute number of Purkinje cells did not differ among strains, but one population of Sprague-Dawley rats and the wild rats had more Purkinje cells relative to cerebellar volume. Last, Long-Evans rats had significantly smaller Purkinje cells than the other strains in both absolute and relative terms.

Conclusion: Only one of the two domesticated strains differed from wild rats in cerebellar anatomy. Our results therefore demonstrate that changes in the brains of domesticated animals do not necessarily follow a universal rule; they can vary between different strains. This highlights the importance of including more than one strain in wild-domesticate comparisons in brain anatomy and avoiding the oversimplification of the effects of domestication on the brain.

Introduction: Songbirds, especially corvids, and parrots are remarkably intelligent. Their cognitive skills are on par with primates and their brains contain primate-like numbers of neurons concentrated in high densities in the telencephalon. Much less is known about cognition and neuron counts in more basal bird lineages. Here, we focus on brain cellular composition of galliform birds, which have small brains relative to body size and a proportionally small telencephalon and are often perceived as cognitively inferior to most other birds.

Methods: We use the isotropic fractionator to assess quantitatively the numbers and distributions of neurons and nonneuronal cells in 15 species of galliform birds and compare their cellular scaling rules with those of songbirds, parrots, marsupials, insectivores, rodents, and primates.

Results: On average, the brains of galliforms contain about half the number of neurons found in parrot and songbird brains of the same mass. Moreover, in contrast to these birds, galliforms resemble mammals in having small telencephalic and dominant cerebellar neuronal fractions. Consequently, galliforms have much smaller absolute numbers of neurons in their forebrains than equivalently sized songbirds and parrots, which may limit their cognitive abilities. However, galliforms have similar neuronal densities and neuron counts in the brain and forebrain as equally sized non-primate mammals. Therefore, it is not surprising that cognitive abilities of galliforms are on par with non-primate mammals in many domains.

Conclusion: Comparisons performed in this study demonstrate that birds representing distantly related clades markedly differ in neuronal densities, neuron numbers, and the allocation of brain neurons to major brain divisions. In analogy with the concept of volumetric composition of the brain, known as the cerebrotype, we conclude that distantly related birds have distinct neuronal cerebrotypes.

Background: Brain morphology is a critical trait influencing animal performance that has been shown to demonstrate phenotypic plasticity in response to a variety of environmental cues. Further, plasticity itself has consistently been recognized as a trait that can be selected upon and evolved.

Summary: There has been limited research examining how evolution and selection act on plasticity in brain morphology. Here, we review the environmental factors that have been shown to cause plasticity in brain morphology across animal taxa.

Key messages: We further propose a framework for examining the evolution of brain morphology plasticity, including four hypothesized patterns of selection that may cause the evolution of plasticity in this critical trait. Finally, we outline potential ways these hypotheses can be tested to build our understanding of the evolution of brain morphology plasticity.

Background: Most studies comparing forebrain organization between reptiles and mammals have focused on similarities. Equally important are the differences between their brains. While differences have been addressed infrequently, this approach can highlight the evolution of brains in relation to their respective environments.

Summary: This review focuses on three key differences between the dorsal and ventral thalamus of reptiles and mammals. One is the organization of thalamo-telencephalic interconnections. Reptiles have at least three circuits that transmit information between the dorsal thalamus and telencephalon, whereas mammals have just one. A second is the number and distribution of local circuit neurons in the dorsal thalamus. Most reptilian dorsal thalamic nuclei lack local circuit neurons, whereas these same nuclei in mammals contain varying numbers. The third is the organization of the thalamic reticular nucleus. In crocodiles, at least, the neurons in the thalamic reticular nucleus are heterogeneous with two separate nuclei each being associated with a different circuit. In mammals, the neurons in the thalamic reticular nucleus, which is a single structure, are homogeneous.

Key messages: Transcriptomics and development are suggested to be the most likely approaches to explain these differences between reptiles and mammals. Transcriptomics can reveal which neuron types are "new" or "old" and whether neurons and their respective circuits have been re-purposed to be used differently. Examination of the development and connections of the dorsal and ventral thalamus will determine whether their formation is similar or different from what has been described for mammals.