Brain Behavior and Evolution最新文献

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 evolve. 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. We further propose a framework for examining the evolution of brain morphology plasticity, including four hypothesized patterns of selection that may cause 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.

Introduction: The factors shaping vertebrate brain evolution and cognition are broadly categorized as being either social or environmental. Yet, their relative importance is debated, partly due to the limitations associated with standard interspecific evolutionary comparisons. Here, we adopt a complementary strategy leveraging within-population variation in fish brain size to ask how variation in social and environmental factors correlates with individual brain size.

Methods: We investigated how overall brain size and brain part sizes varied between demes of the same population in the coral reef-associated batu coris Coris batuensis. This species is ideal for our approach because its local population densities are dissociated from both interspecific densities and habitat complexity.

Results: We found that individuals from demes with higher population densities possess larger overall brain volumes than those from lower population density environments, caused by an enlargement of all five main brain regions. Brain anatomical measures show no correlation with interspecific density or habitat complexity.

Conclusion: Our results suggest that variation in intraspecific social challenges is selected on individual batu coris brain size, either through phenotypic plasticity, differential survival, or habitat choice. These results conform with a broader version of the social brain hypothesis, emphasizing the importance of the entire brain over specific regions like the neocortex in mammals or the telencephalon in fishes.

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.

The plainfin midshipman fish (Porichthys notatus) relies on the production and reception of social acoustic signals for reproductive success. During spawning, male midshipman 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 is 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 vs. non-reproductive male midshipman. 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. 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.

Introduction: Prairie voles (Microtus ochrogaster) are one of the few mammalian species that are monogamous and engage in the biparental rearing of their offspring. Biparental care impacts the quantity and quality of care the offspring receives. The increased attention by the father may translate to heightened tactile contact the offspring receives through licking and grooming.

Methods: In the current study, we used electrophysiological multiunit techniques to define the organization of the perioral representation in the primary somatosensory area (S1) of prairie voles. Functional representations were related to myeloarchitectonic boundaries.

Results: Our results show that most of S1 is occupied by the representation of the contralateral mystacial whiskers and the lower and upper lips. The mystacial vibrissae representation encompassed a large portion of the caudolateral S1, while the representation of the lower and upper lips occupied a large portion of the rostrolateral aspect of S1. We found that neuronal populations representing the perioral structures tended to have small receptive fields relative to other body part representations on the head and that the representation of the mystacial whiskers and perioral structures was coextensive with cytoarchitectonically defined barrel fields that extend from the caudolateral to a rostrolateral aspect of S1.

Conclusions: The relative magnification of the perioral representation in S1 reflects the importance of these regions for sensory-mediated behaviors such as tactile interactions in biparental care and social bonding. This highlights how environmental and behavioral factors shape S1 organization through brain-body synergy, suggesting that relatively small changes in experience can drive adaptive cortical plasticity that, over subsequent generations, drives the cortical phenotypic diversity across the rodent clade and mammals in general.

Introduction: Noise associated with human activities in aquatic environments can affect the physiology and behavior of aquatic species which may have consequences at the population and ecosystem levels. Low-frequency sound is particularly stressful for fish since it is an important factor in predator-prey interactions. Even though behavioral and physiological studies have been conducted to assess the effects of sound on fish species, neurobiological studies are still lacking.

Methods: In this study, we exposed farmed salmon to low-frequency sound for 5 min a day for 30 trials and conducted behavioral observations and tissue sampling before sound exposure (timepoint zero; T0) and after 1 (T1), 10 (T2), 20 (T3), and 30 (T4) exposures, to assess markers of stress. These included plasma cortisol, neuronal activity, monoaminergic signaling, and gene expression in 4 areas of the forebrain.

Results: We found that sound exposure induced an activation of the stress response by eliciting an initial startle behavioral response, together with increased plasma cortisol levels and a decrease in neuronal activity in the hypothalamic tubercular nuclei (TN). At T3 and T4 salmon showed a degree of habituation in their behavioral and cortisol response. However, at T4, salmon showed signs of chronic stress with increased serotonergic activity levels in the dorsolateral and dorsomedial pallium, the preoptic area, and the TN, as well as an inhibition of growth and reproduction transcripts in the TN.

Conclusions: Together, our results suggest that prolonged exposure to sound results in chronic stress that leads to neurological changes which suggest a reduction of life fitness traits.

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.

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.