Biology subjects

Tanimura, A.

Publications and source records attributed to Tanimura, A..

5 recordsLinked to original sources

bioRxiv2026

Hippocampal CA2 modulates trace fear conditioning through circuit-specific control of CA1

Forming associations between temporally separated events depends on pathways linking the CA1, the subiculum (SUB), and the entorhinal cortex. The degree to which this process requires the CA2, which shares extensive connectivity with these regions, remains unknown. Using trace fear conditioning (TFC), where mice learn to associate a tone and shock separated by a temporal gap, we showed that the dCA2 contributes to TFC. Interestingly, whereas chronic dCA2 inhibition decreased cue-associated freezing, acute dCA2[->]dCA1 projection inhibition increased freezing. Combined with differential effects on cFos expression, this suggests that global and projection-specific perturbations of the dCA2 have distinct effects on TFC and hippocampal activity states. Fiber photometry revealed that dCA2[->]dCA1 activity shifted from tone responsiveness during conditioning to expected shock activation during recall, consistent with learning-associated activity remodeling. Together, these findings identify the dCA2 as a contributor to TFC and implicate dCA2[->]dCA1 signaling in shaping fear expression across learning and recall.

neuroscience↗

bioRxiv2025

Cholinergic disruption of state-dependent retrosplenial layer 1 activity causes temporal associative memory deficit under stress

Memory functions rely on discrete patterns of neuronal activity emerging from individual neurons, their interconnected circuits, and their alignment with global brain states. We show that such patterns are generated by layer 1 inhibitory neurons in the ventral retrosplenial cortex (vRSPL1), whose activity correlated with immobility and specifically contributed to the formation of temporal associative memories. This state-dependent activity was subject to stress-induced cholinergic modulation through muscarinic 1 receptor (M1R) signaling, leading to selective impairments in temporal but not contextual associative memory. Slice studies showed that these effects were likely due to M1R-mediated inhibition of vRSPL1 neurons, transiently disrupting their local connectivity as well as responsiveness to afferent input. Together, we demonstrate a mechanism by which vRSPL1 activity aligned to immobility coordinate the formation of temporal associations. Through its sensitivity to stress-related cholinergic modulation, this mechanism presents vulnerability to traumatic amnesia, especially for temporal details of episodic memories.

neuroscience↗

bioRxiv2024

Ca2+-dependent phosphodiesterase 1 regulates the plasticity of striatal spiny projection neuron glutamatergic synapses

Long-term synaptic plasticity at glutamatergic synapses on striatal spiny projection neurons (SPNs) is central to learning goal-directed behaviors and habits. Although considerable attention has been paid to the mechanisms underlying synaptic strengthening and new learning, little scrutiny has been given to those involved in the attenuation of synaptic strength that attends suppression of a previously learned association. Our studies revealed a novel, non-Hebbian, long-term, postsynaptic depression of glutamatergic SPN synapses induced by interneuronal nitric oxide (NO) signaling (NO-LTD) that was preferentially engaged at quiescent synapses. This form of plasticity was gated by local Ca2+ influx through CaV1.3 Ca2+ channels and stimulation of phosphodiesterase 1 (PDE1), which degraded cyclic guanosine monophosphate (cGMP) and blunted NO signaling. Consistent with this model, mice harboring a gain-of-function mutation in the gene coding for the pore-forming subunit of CaV1.3 channels had elevated depolarization-induced dendritic Ca2+ entry and impaired NO-LTD. Extracellular uncaging of glutamate and intracellular uncaging of cGMP suggested that this Ca2+-dependent regulation of PDE1 activity allowed for local regulation of dendritic NO signaling. This inference was supported by simulation of SPN dendritic integration, which revealed that dendritic spikes engaged PDE1 in a branch-specific manner. In a mouse model of Parkinsons disease (PD), NO-LTD was absent not because of a postsynaptic deficit in NO signaling machinery, but rather due to impaired interneuronal NO release. Re-balancing intrastriatal neuromodulatory signaling in the PD model restored NO release and NO-LTD. Taken together, these studies provide novel insights into the mechanisms governing NO-LTD in SPN and its role in psychomotor disorders, like PD.

neuroscience↗

bioRxiv2024

Endopiriform neurons projecting to ventral CA1 are a critical node for recognition memory

The claustrum complex is viewed as fundamental for higher order cognition; however, the circuit organization and function of its neuroanatomical subregions are not well understood. We demonstrated that some of the key roles of the CLA complex can be attributed to the connectivity and function of a small group of neurons in its ventral subregion, the endopiriform (EN). We identified a subpopulation of EN neurons by their projection to the ventral CA1 (ENvCA1-proj. neurons), embedded in recurrent circuits with other EN neurons and the piriform cortex. Although the ENvCA1-proj. neuron activity was biased toward novelty across stimulus categories, their chemogenetic inhibition selectively disrupted the memory-guided but not innate responses of mice to novelty. Based on our functional connectivity analysis, we suggest that ENvCA1-proj. neurons serve as an essential node for recognition memory through recurrent circuits mediating sustained attention to novelty, and through feed forward inhibition of distal vCA1 neurons shifting memory-guided behavior from familiarity to novelty.

neuroscience↗

bioRxiv2023

Isolation and genomic and physiological characterization of Parageobacillus sp. G301, the isolate capable of both hydrogenogenic and aerobic carbon monoxide oxidation

Prokaryotes, known as carbon monoxide (CO) oxidizers, use CO as the carbon or energy source with CO dehydrogenases (CODHs), which are divided into nickel-containing CODH (Ni-CODH) that are sensitive to O2 and molybdenum-containing CODH (Mo-CODH) that are capable of aerobic functioning. The oxygen conditions for CO oxidizers to oxidize CO may be limited because CO oxidizers isolated and characterized so far have either Ni- or Mo-CODH. Here, we report a novel CO oxidizer capable of CO oxidation with both types of CODH based on genomic and physiological characterization of the isolate Parageobacillus sp. G301. This thermophilic facultative anaerobic Bacillota bacterium was isolated from the sediment of a freshwater lake. Genomic analyses showed that G301 was the only isolate possessing both Ni-CODH and Mo-CODH. Genome-based reconstruction of the respiratory machinery and physiological investigation indicated that CO oxidation by Ni-CODH was coupled with H2 production (proton reduction), and CO oxidation by Mo-CODH was coupled with O2 reduction under aerobic conditions and nitrate reduction under anaerobic conditions. G301 would thus be able to thrive via CO oxidation under a wide range of conditions, from aerobic environments to anaerobic environments even without terminal electron acceptors other than protons. As comparative genome analyses revealed no significant differences in genome structures and encoded cellular functions, except for CO oxidation between CO oxidizers and non-CO oxidizers in the genus Parageobacillus, CO oxidation genes would be retained exclusively for CO metabolism and related respiration. ImportanceMicrobial CO oxidation has received a lot of attention because it contributes to global carbon cycling in addition to functioning as a remover of CO, which is toxic to many organisms. Microbial CO oxidizers have a punctate phylogenetic distribution throughout bacteria and archaea, even in genus-level monophyletic groups. In this study, we demonstrated that the new isolate Parageobacillus sp. G301 is capable of both anaerobic (hydrogenogenic) and aerobic CO oxidation, which had not been previously reported. The discovery of this new isolate, which is versatile in CO metabolism, would accelerate research into such CO oxidizers with diverse CO metabolisms, expanding our understanding of microbial diversity. Through comparative genomic analyses, we propose that CO oxidation genes are optional but not essential genetic elements in the genus Parageobacillus, providing insight into a factor that shapes the mosaic phylogenetic distribution of CO oxidizers, even in genus-level monophyletic groups.

microbiology↗