Animal Use in Neurobiological Research

Single-cell chromatin accessibility profiling reveals regulatory mechanisms and evolution in pig brains

BACKGROUND

Pig brains serve as a valuable biomedical model for studying brain-related diseases due to their significant structural similarities to the human brain. Furthermore, the long-term domestication and artificial selection of domestic pigs have profoundly shaped their brains, making them an interesting subject for research. However, a comprehensive understanding of the regulatory mechanisms governing pig brain function and their impact on various phenotypes remains elusive due to the high degree of cellular heterogeneity present in the brain.

RESULTS

In this study, we profiled 71,798 cells from domestic pig and wild boar cerebral cortex and cerebellum, identifying nine cell types, and integrated single-cell RNA sequencing data to explore cell type-specific regulatory landscapes and oligodendrocyte developmental trajectory. Furthermore, comparative analysis of each cell type between domestic pigs and wild boars indicated that oligodendrocyte progenitor cells may potentially exhibit a faster evolutionary rate. Finally, cross-species analysis suggested that, compared to humans, the proportion of sequence-conserved and functionally conserved regulatory elements in each cell type appears to be higher in pigs than in mice. Studies on the enrichment of genetic variants associated with 15 human diseases and complex traits in conserved regulatory elements across cell types indicated that immune-related diseases were more enriched in pigs, whereas neurological diseases were somewhat more enriched in mice. However, the enrichment of Alzheimer's disease-associated variants in pigs but not in mice suggests that pigs could be a more suitable model for this condition.

CONCLUSIONS

Our research offers preliminary insights into the heterogeneity of pig brains and suggests the potential underlying regulatory mechanisms. Additionally, we explore the possible impact of nervous system differences on phenotypic changes, which could lay the groundwork for further biomedical studies.

Maternal dietary folate imbalance alters cerebellar astrocyte morphology and density in offspring

Background

Maternal folate usage is essential for neurodevelopment, but its effects on cerebellar structure are unclear. Cerebellum undergoes a protracted period of development, making it sensitive to maternal nutritional imbalances. Astrocytes are necessary for cerebellar cortex structure and function. This study examined the impact of varying maternal dietary folate levels on the morphology and density of cerebellar astrocytes in rat offspring.

Materials and methods

Twelve adult female rats (Rattus norvegicus) were randomly allocated to one of four premixed food groups: standard (2 mg/kg), folate-deficient (0 mg/kg), folate-supplemented (8 mg/kg), or folate supra-supplemented (40 mg/kg). The rats began their diets 14 days before mating and continued throughout pregnancy and lactation. On postnatal day 35, five pups from each group were sacrificed and their cerebellums were processed for immunohistochemical examination. The cerebellar astrocytes were labelled with an antibody against Glial Fibrillary Acid Protein (GFAP).

Results

The offspring of the folate-deficient diet group exhibited few Bergmann and granule layer astrocytes. The Bergmann radial glial processes in this group were thinner, discontinuous, poorly organised, and had unclear end feet compared to controls. Conversely, the folate-supplemented group showed a predominance of well-organized Bergmann glia astrocytes with distinct, thicker, and densely packed processes, ending in clear conical pial foot processes. In the supra-supplemented group, there was evidence of astrogliosis in the form of large granule layer astrocytes with extended cytoplasmic projections. The Bergmann glia in this group were fewer and more varied in distribution and morphology. Some locations had many astrocytic processes, whereas others had none. Some processes were discontinuous and tortuous. The proportion of cerebellar cortical GFAP immunoreactive cells in folate-deficient diet, controls, folate-supplemented, and folate supra-supplemented groups were 2.09 ± 0.06 %, 4.69 ± 0.12 %, 10.14 ± 0.67 %, and 23.12 ± 3.48 %, respectively (p < 0.001).

Conclusions

These findings imply that both folate deficiency and excess supplementation in pregnancy can impair normal cerebellar astrocyte development, highlighting the importance of balanced folate levels during pregnancy for optimal neurodevelopmental outcomes.

Optimal Production of 3D Neuronal Lineage Population by Morphological Classification

BACKGROUND

The increasing prevalence of neurodegenerative diseases and toxic substance exposure highlights the need for neuronal cell models that closely mimic human neurons in vivo. Compared to traditional models, human pluripotent stem cell (hPSC)-derived three-dimensional models mimic human physiological characteristics and complex nervous system interactions. These models enable patient-specific treatments and improve the predictive accuracy of drug toxicity evaluations. However, differentiation efficiency varies based on organoid size, structure, and cell line characteristics, necessitating standardized protocols for consistent outcome.

METHODS

The morphological characteristics of hPSC-derived embryonic bodies (EBs) formed by concave microwells were analyzed at the early stage of neuronal differentiation. Criteria were established to identify cells with high differentiation efficiency, enabling the optimization of differentiation methods applicable across various cell lines. Neuronal organoids were generated using a microfluidic-concave chip, and their suitability for drug toxicity testing was assessed.

RESULTS

EBs, formed in 500 µm concave microwells, exhibited the highest efficiency for neuronal cell differentiation. Cavity-like EBs were more suitable for neuronal differentiation and maturation than cystic-like forms. The optimal neuronal lineage differentiation method was established, and the drug toxicity sensitivity of organoids generated from this method was validated.

CONCLUSIONS

This study identified EB structures suitable for neuronal lineage differentiation based on morphological classification. Furthermore, this study suggested an optimal method for generating neuronal organoids. This method can be applied to various cell lines, enabling its precise use in patient-specific treatments and drug toxicity tests.

Maternal brain plasticity, physiology and exercise science: A scoping narrative review

INTRODUCTION

The perinatal period is characterized by extreme shifts in hormones, neurochemistry, and life experiences that drive significant changes in the brain, known as maternal plasticity. Due to rising maternal health conditions, such as postpartum depression, there is a critical need to investigate factors, such as engagement in physical activity and exercise, that may mitigate susceptibility to maladaptive maternal plasticity. This scoping review aims to analyze exercise interventions and maternal brain outcomes during reproduction.

METHODS

A systematic search was completed in Medline, Embase, CINAHL, PsycINFO, SportDiscuss. The key concepts of the search were (i) brain plasticity, (ii) maternal reproductive period including pre-conception, pregnancy, and postpartum, and (iii) exercise interventions. Due to the limited amount of evidence available on this topic, the review findings were discussed using a combined scoping and narrative review approach.

RESULTS

The search produced 2,167 unique articles after removing 2588 duplicates. Covidence software was used for the screening procedure. Following title and abstract screening, 2160 articles were deemed irrelevant and removed. Seven articles moved forward to full-text screening. One article was excluded during full-text screening for wrong outcomes, leaving six papers for extraction. Extraction revealed that four out of six studies were conducted in the rodent alone, one was conducted in humans alone and one was conducted in both a human and a rodent model.

DISCUSSION

The methodological inconsistencies in the limited number of studies within this field highlight the need for standardization, which motivated the development of the Consensus on Exercise Reporting Template for animal research. Moreover, the present review highlights future directions and knowledge gaps, emphasizing the critical need for high-quality research to address the many unanswered questions regarding the impact of exercise on the maternal brain.

A quantitative weight-of-evidence review of preclinical studies examining the potential developmental neurotoxicity of acetaminophen

Acetaminophen [paracetamol; N-acetyl-para-aminophenol (APAP)] is an antipyretic/analgesic commonly used in the treatment of fever and mild to moderate pain, headache, myalgia, and dysmenorrhea. Recent literature has questioned the safety of acetaminophen use during pregnancy, with an emphasis on whether exposure to the developing nervous system results in behavioral changes consistent with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and/or other cognitive deficits in the offspring. No previous review has used a fully detailed, quantitative weight-of-evidence (QWoE) approach to critically examine the preclinical acetaminophen data with regards to potential developmental neurotoxicity (DNT). Following regulatory guidance, a QWoE framework using prespecified scoring criteria was developed consistent with previous approaches to characterize potential adverse DNT outcomes with considerations for biological relevance of the response to adverse outcomes (outcome score) and the strength of methods and study design (methods score). Considerations for the methods score included (1) experimental design, (2) details/reliability of measurement(s), (3) data transparency, and (4) translational/methodological relevance. Considerations for the outcome score included response-related (1) statistical significance, (2) dose-response, (3) relevance/reliability/magnitude, (4) plausibility, and (5) translational relevance, including consideration of systemic toxicity/hepatotoxicity and therapeutic and/or non-systemically toxic doses and durations of use. Application of this QWoE framework to the 34 in vivo studies identified that assess the potential DNT of acetaminophen resulted in 188 QWoE entries documented across 11 DNT endpoints: social behavior, stereotypic behavior, behavioral rigidity, attention/impulsivity, hyperactivity, anxiety-like behavior, sensorimotor function, spatial learning/memory, nonspatial learning/memory, neuroanatomy, and neurotransmission. For each endpoint, the mean outcome score and methods score were calculated for total entries and for entries segregated by sex to assist in determining data quality and potential adversity. Informed by all 188 entries, the QWoE analysis demonstrated data of moderate quality showing no consistent evidence of DNT in male and female rodents following exposure to acetaminophen at therapeutic and/or nonsystemically toxic doses. Although some of the DNT endpoints (behavioral rigidity, attention/impulsivity, spatial learning/memory, neuroanatomy, and neurotransmission) generally displayed a more limited dataset and/or relatively lower data quality, similar conclusions were drawn based on results indicating a lack of biological relevance and reliability of reported adverse effects. Overall, this QWoE analysis on the preclinical in vivo data demonstrates no consistent evidence of adverse effects following developmental exposure to acetaminophen at therapeutic and/or non-systemically toxic doses on the structure and function of the nervous system, including neuroanatomical, neurotransmission, and behavioral endpoints.

Animal models in neuroscience with alternative approaches: Evolutionary, biomedical, and ethical perspectives

Animal models have been a crucial tool in neuroscience research for decades, providing insights into the biomedical and evolutionary mechanisms of the nervous system, disease, and behavior. However, their use has raised concerns on several ethical, clinical, and scientific considerations. The welfare of animals and the 3R principles (replacement, reduction, refinement) are the focus of the ethical concerns, targeting the importance of reducing the stress and suffering of these models. Several laws and guidelines are applied and developed to protect animal rights during experimenting. Concurrently, in the clinic and biomedical fields, discussions on the relevance of animal model findings on human organisms have increased. Latest data suggest that in a considerable amount of time the animal model results are not translatable in humans, costing time and money. Alternative methods, such as in vitro (cell culture, microscopy, organoids, and micro physiological systems) techniques and in silico (computational) modeling, have emerged as potential replacements for animal models, providing more accurate data in a minimized cost. By adopting alternative methods and promoting ethical considerations in research practices, we can achieve the 3R goals while upholding our responsibility to both humans and other animals. Our goal is to present a thorough review of animal models used in neuroscience from the biomedical, evolutionary, and ethical perspectives. The novelty of this research lies in integrating diverse points of views to provide an understanding of the advantages and disadvantages of animal models in neuroscience and in discussing potential alternative methods.

A new Down syndrome rat model races forward

Animal models of Down syndrome (DS) provide an essential resource for understanding genetic, cellular, and molecular contributions to traits associated with trisomy 21 (Ts21). Recent genetic enhancements in the development of DS models, including the new TcHSA21rat model (Kazuki et al.), have potential to transform our understanding of and potential therapies for Ts21.

Neurogranin-like immunoreactivity in the zebrafish brain during development

Neurogranin (Nrgn) is a neural protein that is enriched in the cerebral cortex and is involved in synaptic plasticity via its interaction with calmodulin. Recently we reported its expression in the brain of the adult zebrafish (Alba-González et al. J Comp Neurol 530:1569–1587, 2022). In this study we analyze the development of Nrgn-like immunoreactivity (Nrgn-like-ir) in the brain and sensory structures of zebrafish embryos and larvae, using whole mounts and sections. First Nrgn-like positive neurons appeared by 2 day post-fertilization (dpf) in restricted areas of the brain, mostly in the pallium, epiphysis and hindbrain. Nrgn-like populations increased noticeably by 3 dpf, reaching an adult-like pattern in 6 dpf. Most Nrgn-like positive neurons were observed in the olfactory organ, retina (most ganglion cells, some amacrine and bipolar cells), pallium, lateral hypothalamus, thalamus, optic tectum, torus semicircularis, octavolateralis area, and viscerosensory column. Immunoreactivity was also observed in axonal tracts originating in Nrgn-like neuronal populations, namely, the projection of Nrgn-like immunopositive primary olfactory fibers to olfactory glomeruli, that of Nrgn-like positive pallial cells to the hypothalamus, the Nrgn-like-ir optic nerve to the pretectum and optic tectum, the Nrgn-like immunolabeled lateral hypothalamus to the contralateral region via the horizontal commissure, the octavolateralis area to the midbrain via the lateral lemniscus, and the viscerosensory column to the dorsal isthmus via the secondary gustatory tract. The late expression of Nrgn in zebrafish neurons is probably related to functional maturation of higher brain centers, as reported in the mammalian telencephalon. The analysis of Nrgn expression in the zebrafish brain suggests that it may be a useful marker for specific neuronal circuitries.

A Model of Discovery: The Role of Imaging Established and Emerging Non-mammalian Models in Neuroscience

Rodents have been the dominant animal models in neurobiology and neurological disease research over the past 60 years. The prevalent use of rats and mice in neuroscience research has been driven by several key attributes including their organ physiology being more similar to humans, the availability of a broad variety of behavioral tests and genetic tools, and widely accessible reagents. However, despite the many advances in understanding neurobiology that have been achieved using rodent models, there remain key limitations in the questions that can be addressed in these and other mammalian models. In particular, in vivo imaging in mammals at the cell-resolution level remains technically difficult and demands large investments in time and cost. The simpler nervous systems of many non-mammalian models allow for precise mapping of circuits and even the whole brain with impressive subcellular resolution. The types of non-mammalian neuroscience models available spans vertebrates and non-vertebrates, so that an appropriate model for most cell biological questions in neurodegenerative disease likely exists. A push to diversify the models used in neuroscience research could help address current gaps in knowledge, complement existing rodent-based bodies of work, and bring new insight into our understanding of human disease. Moreover, there are inherent aspects of many non-mammalian models such as lifespan and tissue transparency that can make them specifically advantageous for neuroscience studies. Crispr/Cas9 gene editing and decreased cost of genome sequencing combined with advances in optical microscopy enhances the utility of new animal models to address specific questions. This review seeks to synthesize current knowledge of established and emerging non-mammalian model organisms with advances in cellular-resolution in vivo imaging techniques to suggest new approaches to understand neurodegeneration and neurobiological processes. We will summarize current tools and in vivo imaging approaches at the single cell scale that could help lead to increased consideration of non-mammalian models in neuroscience research.

Comparative transcriptomic analysis of rat versus mouse cerebral cortex after traumatic brain injury

The heterogeneity of traumatic brain injury (TBI)-induced secondary injury has greatly hampered the development of effective treatments for TBI patients. Targeting common processes across species may be an innovative strategy to combat debilitating TBI. In the present study, a cross-species transcriptome comparison was performed for the first time to determine the fundamental processes of secondary brain injury in Sprague-Dawley rat and C57/BL6 mouse models of TBI, caused by acute controlled cortical impact. The RNA sequencing data from the mouse model of TBI were downloaded from the Gene Expression Omnibus (ID: GSE79441) at the National Center for Biotechnology Information. For the rat data, peri-injury cerebral cortex samples were collected for transcriptomic analysis 24 hours after TBI. Differentially expressed gene-based functional analysis revealed that common features between the two species were mainly involved in the regulation and activation of the innate immune response, including complement cascades as well as Toll-like and nucleotide oligomerization domain-like receptor pathways. These findings were further corroborated by gene set enrichment analysis. Moreover, transcription factor analysis revealed that the families of signal transducers and activators of transcription (STAT), basic leucine zipper (BZIP), Rel homology domain (RHD), and interferon regulatory factor (IRF) transcription factors play vital regulatory roles in the pathophysiological processes of TBI, and are also largely associated with inflammation. These findings suggest that targeting the common innate immune response might be a promising therapeutic approach for TBI. The animal experimental procedures were approved by the Beijing Neurosurgical Institute Animal Care and Use Committee (approval No. 201802001) on June 6, 2018.