Biology subjects

Kasai, A.

Publications and source records attributed to Kasai, A..

6 recordsLinked to original sources

bioRxiv2025

Noradrenergic efferent subsystems that gate traumatic social learning

Individuals experience varying magnitudes of stress in their daily lives. Although stress responses facilitate adaptive processes to cope with changing environments, severe stress can lead to traumatic learning and anxiety disorders. However, the neuronal mechanisms underlying the influence of stress severity on these processes remain unclear. Here, we show that traumatic social stress engages anatomically distinct locus coeruleus noradrenergic (LCNA) subpopulations that exhibit dynamic responses scaled to aversive salience. Using whole-brain activity and axonal projection mappings, we identified projectome subtypes of LCNA neurons, which are differentially recruited by single versus consecutive aversive social experiences. While hippocampus-projecting LCNA neurons responded to general social contacts, thalamus-projecting LCNA neurons tracked the aversive salience of social stimuli. Functional manipulations revealed a bidirectional role of thalamus-projecting LCNA neurons in social avoidance learning. These findings reveal the functional architecture of LCNA subsystems that regulate traumatic social learning via dynamic scaling to aversive salience.

neuroscience↗

bioRxiv2021

Optical and computational dissection of emergent prefrontal rewiring to encode fear memory

Associative learning is crucial for adapting to environmental changes. The encoding of associative learning involves the dorso-medial prefrontal cortex (dmPFC), and is underpinned by interactions within the resident neuronal population. However, the nature of this population coding is poorly understood. Here we developed a pipeline for computational dissection and longitudinal two-photon imaging of neural population activities in the mouse dmPFC during fear-conditioning procedures, enabling us to detect learning-dependent changes in the dmPFC topology. Through regularized regression methods and graphical modeling, we found fear conditioning organized neuronal ensembles encoding conditioned responses (CR), with enhancing their coactivity, functional connectivity, and association with conditioned stimuli (CS). This suggests that fear conditioning drives dmPFC reorganization to generate novel associative circuits for CS-to-CR transformation. Importantly, neurons strongly responding to unconditioned stimuli (US) during conditioning anterogradely became a hub of the CR ensemble. Altogether, we demonstrate learning-dependent dynamic modulation of population coding structured on an activity-dependent hub-network formation within the dmPFC. TeaserOptical and computational dissection uncovered how prefrontal cortical networks are rewired to encode new associative memory Significance statementAnimals learn to adapt to changing environments. Associative learning is one of the simplest types of learning that has been intensively studied over the past century. Recent development in molecular, genetic, and optogenetic methods has enabled the identification of a neural population encoding the associative memory in the brain. However, it remains unclear how information is stored and processed by the neural population to encode and retrieve the associative memory. To investigate the nature of this population coding, we developed an optical and computational dissection method, demonstrating how associative learning drives reorganization of the neural network in the dorso-medial prefrontal cortex and generates novel circuits for associative memory and signal transformation.

neuroscience↗

bioRxiv2020

Comprehensive characterization of migration profiles of murine cerebral cortical neurons during development using FlashTag labeling

In mammalian cerebral neocortex, different regions have different cytoarchitecture, neuronal birthdates and functions. In most regions, neuronal migratory profiles have been speculated similar to each other based on observations using thymidine analogues. Few reports investigated regional migratory differences from mitosis at the ventricular surface. Here, in mice, we applied FlashTag technology, in which dyes are injected intraventricularly, to describe migratory profiles. We revealed a mediolateral regional difference in migratory profiles of neurons that is dependent on the developmental stages, e.g., neurons labeled at E12.5-15.5 reached their destination earlier dorsomedially than dorsolaterally even where there were underlying ventricular surfaces, reflecting sojourning below the subplate. This difference was hardly recapitulated by thymidine analogues, which visualize neurogenic gradient, suggesting biological significance different from neurogenic gradient. These observations advance understanding of cortical development, portraying strength of FlashTag in studying migration, and are thus a resource for studies of normal and abnormal neurodevelopment.

neuroscience↗

bioRxiv2020

Trans-scale-scope to find rare cellular activity in sub-million cells

In many phenomena of biological systems, not a majority, but a minority of cells act on the entire multicellular system causing drastic changes in the system properties. To understand the mechanisms underlying such phenomena, it is essential to observe the spatiotemporal dynamics of a huge population of cells at sub-cellular resolution, which is difficult with conventional tools such as microscopy and flow cytometry. Here, we describe an imaging system named AMATERAS that enables optical imaging with an over-one-centimeter field-of-view and a-few-micrometer spatial resolution. This trans-scale-scope has a simple configuration, composed of a low-power lens for machine vision and a hundred-megapixel image sensor. We demonstrated its high cell-throughput, capable of simultaneously observing more than one million cells. We applied it to dynamic imaging of calcium ions in HeLa cells and cyclic-adenosine-monophosphate in Dictyostelium discoideum, and successfully detected less than 0.01% of rare cells and observed multicellular events induced by these cells.

cell biology↗

bioRxiv2020

Evaluation of biodiversity in estuaries using environmental DNA metabarcoding

Biodiversity is an important parameter for the evaluation of the extant environmental conditions. Here, we used environmental DNA (eDNA) metabarcoding to investigate fish biodiversity in five different estuaries in Japan. Water samples for eDNA were collected from river mouths and adjacent coastal areas of two estuaries with high degrees of development (the Tama and Miya Rivers) and three estuaries with relatively low degrees of development (the Aka, Takatsu, and Sendai Rivers). A total of 182 fish species across 67 families were detected. Among them, 11 species occurred in all the rivers studied. Rare fishes including endangered species were successfully detected in rich natural rivers. Biodiversity was the highest in the Sendai River and lowest in the Tama River, reflecting the degree of human development along each river. Even though nutrient concentration was low in both the Aka and Sendai Rivers, the latter exhibited greater diversity, including many tropical or subtropical species, owing to its more southern location. Species composition detected by eDNA varied among rivers, reflecting the distribution and migration of fishes. Our results are in accordance with the ecology of each fish species and environmental conditions of each river, suggesting the potential of eDNA for non-invasive assessment of aquatic biodiversity.

ecology↗

bioRxiv2018

Estimating fish population abundance by integrating quantitative data on environmental DNA and hydrodynamic modelling

We propose a general framework of abundance estimation based on spatially replicated quantitative measurements of environmental DNA in which production, transport, and degradation of DNA are explicitly accounted for. Application to a Japanese jack mackerel (Trachurus japonicus) population in Maizuru Bay revealed that the method gives an estimate of population abundance comparable to that of a quantitative echo sounder method. These findings indicate the ability of environmental DNA to reliably reflect population abundance of aquatic macroorganisms and may o[ff]er a new avenue for population monitoring based on the fast, cost-e[ff]ective, and non-invasive sampling of genetic information.

ecology↗