Multiple types of navigational information are independently encoded in the population activities of the dentate gyrus neurons

Gene Expression Signatures of Immaturity, Decreased pH, and Neural Hyperexcitation in the Hippocampus of Alzheimer's Disease Model Mice

AIMS

Alzheimer's disease (AD) is a leading cause of dementia, with increasing prevalence. Mutations in genes like MAPT, PSEN1, and PSEN2 are risk factors, leading to the development of several AD model mice. Recent hypotheses suggest AD brain pathology involves abnormal neurodevelopment, decreased pH, and neural hyperexcitation. However, it remains unclear to what extent these pathologies are reflected in the gene expression changes of AD models. This study aims to compare gene expression patterns in the brains of multiple AD model mice with those related to these three factors, evaluating the extent of overlap.

METHODS

We conducted a comprehensive search of public databases, collecting 20 gene expression datasets from the hippocampus of AD model mice. These datasets were compared with gene sets related to hippocampal maturation, brain pH, and neural hyperexcitation to statistically assess overlap. Pathway enrichment analysis explored the biological relevance of these gene expression changes.

RESULTS

The extent of overlap with maturity-, pH-, and hyperexcitation-associated genes varied across AD models, showing significant correlations between lower maturity, lower pH, and increased neural hyperexcitation. In MAPT mutant and APP+PSEN1 homozygous transgenic mice, these signatures became more pronounced with age. Pathway meta-analysis revealed that genes associated with maturity, pH, and hyperexcitation in AD models are involved in synaptic and channel functions, as well as inflammatory responses, consistent with previous studies.

CONCLUSION

These findings suggest that pathophysiological changes related to maturity, pH, and neural hyperexcitation play varying roles across individual AD model mice. Our recent study found a negative correlation between disease progression and actual pH levels in human AD patients. Considering the results presented in this study, maturity and neural hyperexcitation, which are correlated with pH, may also be linked to disease progression. Thus, gene expression changes in these factors could be useful markers for assessing the pathology in AD models.

Calcium Signalling in Neurological Disorders, with Insights from Miniature Fluorescence Microscopy

Neurological disorders (NDs), such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and schizophrenia, represent a complex and multifaceted health challenge that affects millions of people around the world. Growing evidence suggests that disrupted neuronal calcium signalling contributes to the pathophysiology of NDs. Additionally, calcium functions as a ubiquitous second messenger involved in diverse cellular processes, from synaptic activity to intercellular communication, making it a potential therapeutic target. Recently, the development of the miniature fluorescence microscope (miniscope) enabled simultaneous recording of the spatiotemporal calcium activity from large neuronal ensembles in unrestrained animals, providing a novel method for studying NDs. In this review, we discuss the abnormalities observed in calcium signalling and its potential as a therapeutic target for NDs. Additionally, we highlight recent studies that utilise miniscope technology to investigate the alterations in calcium dynamics associated with NDs.

Transformation of spatial representations along hippocampal circuits

The hippocampus is thought to provide the brain with a cognitive map of the external world by processing various types of spatial information. To understand how essential spatial variables such as direction, position, and distance are transformed along its circuits to construct this global map, we perform single-photon widefield microendoscope calcium imaging in the dentate gyrus and CA3 of mice freely navigating along a narrow corridor. We find that spatial activity maps in the dentate gyrus, but not in CA3, are correlated after aligning them to the running directions, suggesting that they represent the distance traveled along the track in egocentric coordinates. Together with population activity decoding, our data suggest that while spatial representations in the dentate gyrus and CA3 are anchored in both egocentric and allocentric coordinates, egocentric distance coding is more prevalent in the dentate gyrus than in CA3, providing insights into the assembly of the cognitive map.

Glial-restricted precursors stimulate endogenous cytogenesis and effectively recover emotional deficits in a model of cytogenesis ablation

Adult cytogenesis, the continuous generation of newly-born neurons (neurogenesis) and glial cells (gliogenesis) throughout life, is highly impaired in several neuropsychiatric disorders, such as Major Depressive Disorder (MDD), impacting negatively on cognitive and emotional domains. Despite playing a critical role in brain homeostasis, the importance of gliogenesis has been overlooked, both in healthy and diseased states. To examine the role of newly formed glia, we transplanted Glial Restricted Precursors (GRPs) into the adult hippocampal dentate gyrus (DG), or injected their secreted factors (secretome), into a previously validated transgenic GFAP-tk rat line, in which cytogenesis is transiently compromised. We explored the long-term effects of both treatments on physiological and behavioral outcomes. Grafted GRPs reversed anxiety-like deficits and demonstrated an antidepressant-like effect, while the secretome promoted recovery of only anxiety-like behavior. Furthermore, GRPs elicited a recovery of neurogenic and gliogenic levels in the ventral DG, highlighting the unique involvement of these cells in the regulation of brain cytogenesis. Both GRPs and their secretome induced significant alterations in the DG proteome, directly influencing proteins and pathways related to cytogenesis, regulation of neural plasticity and neuronal development. With this work, we demonstrate a valuable and specific contribution of glial progenitors to normalizing gliogenic levels, rescuing neurogenesis and, importantly, promoting recovery of emotional deficits characteristic of disorders such as MDD.

End-to-end deep learning approach to mouse behavior classification from cortex-wide calcium imaging

Deep learning is a powerful tool for neural decoding, broadly applied to systems neuroscience and clinical studies. Interpretable and transparent models that can explain neural decoding for intended behaviors are crucial to identifying essential features of deep learning decoders in brain activity. In this study, we examine the performance of deep learning to classify mouse behavioral states from mesoscopic cortex-wide calcium imaging data. Our convolutional neural network (CNN)-based end-to-end decoder combined with recurrent neural network (RNN) classifies the behavioral states with high accuracy and robustness to individual differences on temporal scales of sub-seconds. Using the CNN-RNN decoder, we identify that the forelimb and hindlimb areas in the somatosensory cortex significantly contribute to behavioral classification. Our findings imply that the end-to-end approach has the potential to be an interpretable deep learning method with unbiased visualization of critical brain regions.

Behavioral phenotype, intestinal microbiome, and brain neuronal activity of male serotonin transporter knockout mice

The serotonin transporter (5-HTT) plays a critical role in the regulation of serotonin neurotransmission. Mice genetically deficient in 5-HTT expression have been used to study the physiological functions of 5-HTT in the brain and have been proposed as a potential animal model for neuropsychiatric and neurodevelopmental disorders. Recent studies have provided evidence for a link between the gut-brain axis and mood disorders. However, the effects of 5-HTT deficiency on gut microbiota, brain function, and behavior remain to be fully characterized. Here we investigated the effects of 5-HTT deficiency on different types of behavior, the gut microbiome, and brain c-Fos expression as a marker of neuronal activation in response to the forced swim test for assessing depression-related behavior in male 5-HTT knockout mice. Behavioral analysis using a battery of 16 different tests showed that 5-HTT-/- mice exhibited markedly reduced locomotor activity, decreased pain sensitivity, reduced motor function, increased anxiety-like and depression-related behavior, altered social behavior in novel and familiar environments, normal working memory, enhanced spatial reference memory, and impaired fear memory compared to 5-HTT+/+ mice. 5-HTT+/- mice showed slightly reduced locomotor activity and impaired social behavior compared to 5-HTT+/+ mice. Analysis of 16S rRNA gene amplicons showed that 5-HTT-/- mice had altered gut microbiota abundances, such as a decrease in Allobaculum, Bifidobacterium, Clostridium sensu stricto, and Turicibacter, compared to 5-HTT+/+ mice. This study also showed that after exposure to the forced swim test, the number of c-Fos-positive cells was higher in the paraventricular thalamus and lateral hypothalamus and was lower in the prefrontal cortical regions, nucleus accumbens shell, dorsolateral septal nucleus, hippocampal regions, and ventromedial hypothalamus in 5-HTT-/- mice than in 5-HTT+/+ mice. These phenotypes of 5-HTT-/- mice partially recapitulate clinical observations in humans with major depressive disorder. The present findings indicate that 5-HTT-deficient mice serve as a good and valid animal model to study anxiety and depression with altered gut microbial composition and abnormal neuronal activity in the brain, highlighting the importance of 5-HTT in brain function and the mechanisms underlying the regulation of anxiety and depression.