Biology subjects

Yamada, K.

Publications and source records attributed to Yamada, K..

At least 37 records · Page 2Linked to original sources

bioRxiv2025

Cellular energy sensor SnRK1 suppresses salicylic acid-dependent and -independent defenses and bacterial resistance in Arabidopsis

In nature, plants cope with various pathogens that compete for cellular resources during infection. It has long been suggested that plant defense activity must be linked to cellular energy and metabolic states to optimize the balance between growth and defense. However, the molecular mechanisms that regulate immune activity in relation to cellular energy status remain unclear. Here, we demonstrate that the plant energy sensor SNF1-RELATED KINASE 1 (SnRK1) plays a critical role in modulating defense responses and bacterial resistance in Arabidopsis thaliana. Bacterial elicitor-induced expression of defense marker genes, such as PATHOGENESIS-RELATED 1 (PR1), is significantly repressed under sugar-limited conditions in wild-type seedlings, whereas this expression is markedly enhanced in the snrk1 knockdown mutants. SnRK1 restricts defense-related gene expression and resistance to the biotrophic bacterial pathogen Pseudomonas syringe pv. tomato DC3000, which are partly dependent on salicylic acid (SA). In addition, we found that the SnRK1 kinase activity is increased by high humidity. Consistently, SnRK1 is critical for the suppression of SA-mediated defense responses under high humidity conditions. SnRK1 physically associates with the SA-related transcription factors TGACG SEQUENCE-SPECIFIC BINDING PROTEIN 4 (TGA4) and TGA2 to attenuate PR1 expression. These findings provide valuable insight into the molecular mechanisms linking cellular energy status with immune regulation in plants.

plant biology↗

bioRxiv2025

Adapting a commercial anti-Aspergillus IgG ELISA kit for penguin sera: A novel approach using anti-chicken IgY antibody for the detection of anti-Aspergillus IgY titer

Penguins are susceptible to aspergillosis and are affected by the causative fungal pathogens Aspergillus spp., under immunocompromised conditions. Currently, there are limited serological tests available for diagnosing Aspergillus infections in penguins, highlighting the need for new diagnostic methods. While an anti-Aspergillus IgG detection kit using ELISA is commercially available and widely used in human medicine, it is not applicable for penguins because it incorporates anti-human antibodies as the secondary antibody for detection. To address this issue, an anti-chicken IgY antibody was incorporated into a commercial anti-Aspergillus IgG detection ELISA kit. First, anti-chicken IgY antibody was examined for cross-reactivity to penguin IgY, and the antibody recognized IgY from King, Gentoo, and African penguins in sera. Subsequently, serum samples from healthy penguins and penguins with aspergillosis were examined using anti-chicken IgY antibody incorporated into the anti-Aspergillus IgG ELISA kit. The results suggest that the combination method is applicable for the detection of anti-Aspergillus penguin IgY antibodies. However, because background titers can vary among individuals, we propose that routine monitoring could aid in the early detection of aspergillosis, even before the onset of symptoms.

microbiology↗

bioRxiv2025

Distinct effects of nonselective Rho-kinase inhibitor fasudil and selective Rho-kinase 2 inhibitor KD025 on serotonin and dopamine release in the nucleus accumbens of mice

Recent studies have indicated that the Rho GTPase family and Rho-kinases are associated with psychiatric diseases, such as schizophrenia. Rho-kinases have two subtypes, Rho-kinases 1 and 2 that regulate actin dynamics and mediate neurite outgrowth, spine morphology in neurons, and neurotransmitter release in vitro and ex vivo. However, the precise role of Rho-kinases in neurotransmitter release in vivo remains unclear. To clarify the role of Rho-kinases 1 and 2 in serotonin and dopamine release in the nucleus accumbens (NAc) of mice in vivo, we investigated the effect of a nonselective Rho-kinase inhibitor, fasudil, and a selective Rho-kinase 2 inhibitor, KD025, using an in vivo microdialysis technique. Fasudil perfusion (1-20 M) into the NAc increased the basal extracellular serotonin level but did not affect dopamine levels, whereas KD025 (10-20 M) had little effect on basal serotonin and dopamine levels. Notably, fasudil perfusion into the NAc suppressed depolarization-induced serotonin and dopamine release in a dose-dependent manner, whereas KD025 selectively suppressed depolarization-induced serotonin release. Our results suggested that Rho-kinases 1 and 2 are associated with dopamine and serotonin release, respectively, and that both may have significant but distinct roles in the regulation of serotonin and dopamine release in the NAc.

neuroscience↗

bioRxiv2025

Cortical excitatory and inhibitory neuron deficits may underlie the cognitive and social impairments in a mouse model of schizophrenia with exonic Reln deletion

Reelin is an essential extracellular matrix glycoprotein involved in the formation of cortical layers and has been associated with several neuropsychiatric conditions, such as schizophrenia (SCZ). To explore its role in brain function and its potential involvement in SCZ, we developed a Reln heterozygous deletion (Relndel/+) mouse model that mimics a genetic deletion observed in a Japanese patient with SCZ. In previous studies, we demonstrated that Relndel/+ mice exhibit cognitive impairments in a visual discrimination test. Here, we found that Relndel/+ mice displayed impairments in social novelty recognition, while social preference remained intact. Immunohistochemical analyses revealed a significant decrease in the numbers of calcium/calmodulin-dependent protein kinase II (CaMKII)-positive glutamatergic pyramidal neurons, gamma-aminobutyric acid (GABA)-ergic interneurons, and parvalbumin (PV)-positive interneurons in the medial prefrontal cortex (mPFC) of Relndel/+ mice. Furthermore, Relndel/+ mice exhibited significant deficits in excitatory spine density and morphology, as well as a decrease number of PV boutons in the mPFC compared to wild-type (WT) mice. Finally, we demonstrated that injection of AAV-R36-Myc virus into the mPFC can improve social novelty impairments in Relndel/+ mice, but no effects on WT control. These findings indicate that Relndel/+ mice could be a valuable model for exploring the neurobiological mechanisms underlying cognitive and social impairments in SCZ. Futhermore, our results with AAV-R36-Myc also suggest the therapeutic potential of Reelin replacement, warranting further investigation as a possible treatment strategy for SCZ. HighlightsO_LIReelin deficiency disrupts social novelty, but not social preference, in Relndel/+ mice C_LIO_LIRelndel/+ mice serve as a novel model to investigate impairments of neuronal mechanisms on schizophrenia C_LIO_LIAAV-R36-myc injection rescues social novelty deficits in Relndel/+ mice C_LIO_LIReelin replacement therapy is a potential treatment for schizophrenia C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=143 HEIGHT=200 SRC="FIGDIR/small/666057v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@1f4921aorg.highwire.dtl.DTLVardef@1a41b33org.highwire.dtl.DTLVardef@f5f2bcorg.highwire.dtl.DTLVardef@1134d8d_HPS_FORMAT_FIGEXP M_FIG C_FIG

animal behavior and cognition↗

bioRxiv2025

Japanese macaques (Macaca fuscata) adjust inter-individual distance based on aggressiveness rather than rank differences

Group-living animals form societies structured around linear dominance hierarchies. However, social relationships within groups range from relaxed to tense, with some subordinates staying proximity of dominants, while others fleeing at their mere sight. Despite this variation, the effects of personality in shaping these relationships remains unclear. In this study, we investigated whether subordinates adjust their flight initiation distance (FID) according to the dominants aggressiveness. We collected video recordings of supplanting behaviours between non-kin dyads in Japanese macaques (Macaca fuscata). For each dyad, we evaluated these supplantings whether the subordinates FID was greater or less than two meters. To assess aggressiveness, we conducted 20-min focal observations of 18 females, recording of threats and aggressions. We calculated repeatability of aggressiveness as a measure of dominants personality. Rank differences were determined based on supplantings and aggressive interactions. As a result, aggressiveness showed high repeatability, independent of rank and sex. Subordinates were more likely to flee at greater distances (FID > 60 cm) when paired with more aggressive dominants. Rank difference did not significantly influence FID. Whether the dyads exhibiting FIDs were regular grooming partners did not significantly predict their FID. Our findings suggest that Japanese macaques adjust inter-individual distance not based on rank differences but in response to aggressiveness. These results highlight the importance of incorporating personalities into studies of primate social relationships.

animal behavior and cognition↗

bioRxiv2025

Twinfilin-1 phosphorylation in reelin signaling regulates actin dynamics and spine development

Reelin is an extracellular glycoprotein essential for neuronal migration, spine development, and synaptic plasticity. Impaired reelin signaling is linked to neurological disorders, including schizophrenia and autism. While reelin mutant (reeler) mice exhibit behavioral deficits associated with impaired spine formation, the underlying molecular mechanisms remain unclear. We identified Twinfilin-1 (Twf1) as a downstream effector of reelin signaling via phosphoproteomic analysis, based on its reduced tyrosine phosphorylation in reeler mice. We found that Src regulated Twf1 phosphorylation at tyrosine 309, and reelin stimulation increased Twf1 phosphorylation in neurons, an effect blocked by the Src inhibitor PP2. A phospho-resistant Twf1 mutant (Twf1 Y309F) showed reduced capping protein binding and a lower F/G-actin ratio. Twf1Y309F mice exhibited cognitive deficits, reduced spine density, smaller spine head size, and a decreased F/G-actin ratio in synaptosomes. These findings highlight Twf1 phosphorylation as a key component of reelin signaling involved in actin remodeling and spine development.

neuroscience↗

bioRxiv2025

Deciphering the comprehensive relationship between 5'UTR and 3'UTR sequences with deep learning

MotivationRecent advances in mRNA therapeutics have driven further research on untranslated region (UTR) of mRNA. However, prior studies have mainly focused on either the 5' or 3' UTR individually. Increasing evidence suggests potential cooperative effects between these two regions, which remain largely unexplored in computational studies. ResultsWe present a deep learning-based approach to predicting relationships between 5' and 3' UTRs by leveraging latent representations from a pre-trained RNA language model and contrastive learning. Our method effectively identifies highly related UTR pairs, uncovering sequence and expression characteristics that suggest functional interplay. Our analysis revealed that Highly Related UTR pairs (HRUs) are significantly enriched in genes associated with neural development, exhibit distinctive UTR length and secondary structure characteristics, and are involved in cell type-specific regulation of translation efficiency. These findings provide new insights into UTR co-optimization for mRNA therapeutics. AvailabilityThe source code is available for free at https://github.com/hmdlab/utr_pairpred.git. The data and intermediate files used in our analysis are available at https://waseda.box.com/v/utr-pairpred-data.

bioinformatics↗

bioRxiv2025

Ultrasmall chemogenetic tags with group-transfer ligands

Chemogenetic tags are valuable tools for studying functions of a given protein-of-interest (POI) lacking small-molecule ligands, but most tags are too large for several POIs. Here, we report two ultrasmall chemogenetic tags (mgTag and cTag) of 36 and 50 amino acids (aa) that, to the best of our knowledge, are the smallest reported. These tags exhibit transferase-type reactivity with their ligands to append any moiety of interest to the tag. cTag utilizes an engineered C1 domain-bearing cysteine that undergoes group-transfer reaction with its ligand. Likewise, mgTag utilizes an engineered zinc-finger domain-bearing cysteine that undergoes group-transfer reaction with its molecular-glue ligand in the presence of cereblon (CRBN). We applied these tags in the context of cell signaling and proximity induction. While the fusion of HaloTag (297 aa) to the KRASG12D (188 aa) disrupted its ability to activate the growth-signaling pathway, fusion of mgTag or cTag did not. Group-transfer of BRD4 binder to tags appended to Abelson kinase (ABL) induced proximity between ABL and BRD4, resulting in the latters phosphorylation. Deletion of the transferase-type reactivity reduced phosphorylation levels, suggesting that proximity-inducing chimeras with group-transfer design may be more efficacious in certain scenarios. We envision these ultrasmall tags to have wide-ranging applications, including in basic science, biotechnology, and medicine. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=168 SRC="FIGDIR/small/653252v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@1f99888org.highwire.dtl.DTLVardef@18d3e0corg.highwire.dtl.DTLVardef@1e4a044org.highwire.dtl.DTLVardef@d610ee_HPS_FORMAT_FIGEXP M_FIG C_FIG

synthetic biology↗

bioRxiv2025

In-cell proximity target validation methods for heterobifunctional molecules with CRBN- or VHL-binder using AirID

Heterobifunctional molecules, such as proteolysis-targeting and autophagy-targeting chimera, represent new drug concepts. They are composed of two protein binders that can induce proximity interactions between two proteins and protein catalysis. Currently, cereblon (CRBN)- and von Hippel-Lindau (VHL)-binders with thalidomide- and VH032-backbones are widely used as E3 ligase binders. Here we developed a method to validate proteins that interact with heterobifunctional molecules in cells using AirID, a proximity biotinylation enzyme. Interactome of target proteins was validated for six heterobifunctional molecules. ThBD-AirID, a fusion of the thalidomide-binding domain (ThBD) of CRBN and AirID, effectively biotinylated the target proteins. AirID fused to full-length VHL also exhibited highly effective biotinylation. Heterobifunctional molecules with the same target binder but different E3 binders showed different proximity interactome profiles in cells. Analysis using ThBD-AirID revealed a nuclear interaction between androgen receptor and ARV-110. AirID-fused ThBD and VHL could be useful for validating the heterobifunctional molecular interactome in cells.

molecular biology↗

bioRxiv2025

Genetic evidence: zebrafish hoxba and hoxbb clusters are essential for the anterior-posterior positioning of pectoral fins

Vertebrate paired appendages, such as the pectoral fins in fish and the forelimbs in tetrapods, arise at specific regions along the anterior-posterior axis of the body. Hox genes have long been considered prime candidates for determining the anteroposterior positioning of these paired appendages during development. Evidence from various model organisms, including mouse and chick, supports a role for Hox genes in limb positioning. However, despite extensive phenotypic analyses of numerous single and compound Hox knockout mice, clear genetic evidence for substantial defects in limb positioning has been limited, leaving questions unresolved. In a previous study, we generated seven distinct hox cluster-deficient mutants in zebrafish. Here, we provide genetic evidence that zebrafish hoxba;hoxbb cluster-deleted mutants specifically exhibit a complete lack of pectoral fins, accompanied by the absence of tbx5a expression in pectoral fin buds. In these mutants, tbx5a expression in the pectoral fin field of the lateral plate mesoderm fails to be induced at an early stage, suggesting a loss of pectoral fin precursor cells. Furthermore, the competence to respond to retinoic acid is lost in hoxba;hoxbb cluster mutants, indicating that tbx5a expression cannot be induced in the pectoral fin buds. We further identify hoxb4a, hoxb5a, and hoxb5b as pivotal genes underlying this process. Although the frameshift mutations in these hox genes do not recapitulate the absence of pectoral fins, we demonstrate that deletion mutants at these genomic loci show the absence of pectoral fins with low penetrance. Our results suggest that, by establishing the expression domains along the anteroposterior axis, hoxb4a, hoxb5a, and hoxb5b within hoxba and hoxbb clusters cooperatively determine the positioning of zebrafish pectoral fins through the induction of tbx5a expression in the restricted pectoral fin field. Our findings also provide insights into the evolutionary origin of paired appendages in vertebrates.

developmental biology↗

bioRxiv2025

Involvement of orexin nerves in early stage of Alzheimer's disease model mice and preventive effect of orexin receptor antagonists

BackgroundMild cognitive impairment (MCI) is a condition between healthy cognition and dementia with a high probability of progression to Alzheimers disease (AD). Elevated levels of orexin (OX) have been reported in the cerebrospinal fluid of patients with MCI and AD. ObjectiveTo investigate the efficacy of dual OX receptor antagonists (suvorexant and lemborexant) in an early-stage AD mouse model (App-KI). MethodsThe expression of the OX receptor gene, the levels of suvorexant and lemborexant in the brain after a single oral dose, and their effects on locomotor activity were investigated in wild-type mice. In addition, the cognitive function of wild-type and App-KI mice was assessed using the Y-maze test after oral administration of suvorexant or lemborexant once a day for 60 d. After the behavioral test, amyloid-beta levels were quantified in the hippocampal CA1 region of App-KI mice. ResultsThe expression of the OX receptor gene was highest in the lateral hypothalamus and was also observed in other brain regions. Drug levels peaked at 20-40 min for suvorexant and 15 min for lemborexant and declined, still detectable 24 h later. Locomotor activity was reduced after suvorexant or lemborexant administration; however, 24 h after administration, locomotor activity did not differ from the control group. In particular, the Y-maze test showed that suvorexant and lemborexant prevented cognitive impairment in App-KI mice. Furthermore, suvorexant and lemborexant suppressed amyloid-beta accumulation in the hippocampal CA1 region of App-KI mice. ConclusionThe results suggest that suvorexant and lemborexant effectively suppress the early stages of AD.

animal behavior and cognition↗

bioRxiv2025

Detection of HTTex1p by western blot and immunostaining of HD human and mouse brain using neo-epitope antibody P90 highlights impact of CAG repeat expansion on its size, solubility, and response to MSH3 silencing

HTT1a was identified in human and mouse Huntingtons disease brain as the pathogenic exon 1 mRNA generated from aberrant splicing between exon 1 and 2 of HTT that contributes to aggregate formation and neuronal dysfunction.1 Detection of the huntingtin exon 1 protein (HTT1a) has been accomplished with fluorescence-based reporter assays (Meso Scale Discovery, Homogeneous Time Resolved Fluorescence) and immunoprecipitation assays in Huntingtons disease knock-in mice but direct detection in homogenates by gel electrophoresis and western blot assay has been lacking. Subcellular fractions prepared from mouse and human Huntingtons disease brain were separated by gel electrophoresis and probed by western blot with neo-epitope monoclonal antibodies 1B12 and 11G2 directed to the C-terminal eight residues of HTT1a. In caudate putamen of an allelic series of 6 month old Huntingtons disease knock-in mice (Q50, Q80, Q111, Q140 and Q175) HTT1a migration was inversely correlated with CAG repeat length and appeared as a SDS soluble high molecular mass smear in Q111, Q140 and Q175 mice but weakly in Q80 and not in WT mice or Q50 indicating a CAG repeat size threshold for detecting HTT1a. HTT1a immunoreactivity diminished if 1B12 and 11G2 antibodies were preincubated with an eight amino acid peptide containing the C-terminus of HTT1a but not with unrelated peptide sequence. Migration of HTT1a and its high molecular mass smear changed with age in caudate putamen of Q111, Q175 and YAC128 mice. Treating Q111 mice with siRNA to MSH3, a modifier of CAG repeat expansion, significantly reduced levels of the high molecular mass smear indicating that the effects of curbing CAG repeat expansion were quantifiable. A prominent 56-60 kDa doublet detected by 1B12 and 11G2 antibodies in lysates from human Huntingtons disease brain was not blocked by preincubation with C-terminal HTT1a blocking peptide and also appeared in brains of Parkinsons disease patients. 1B12 and 11G2 antibodies did not immunoprecipitate HTT proteins from either Huntingtons disease mouse or human brain lysates using conditions that pulled down full length HTT with anti-HTT antibody 2B7. Altogether these data show that 11G2 and 1B12 antibodies can be used in western blot assays to track and quantify immunoreactive HTT1a levels, solubility, and subcellular localization in Huntingtons disease mouse brain. Abbreviated SummarySapp et al., report that pathogenic exon 1 protein HTT1a is detected in brain of mouse models of Huntingtons disease by direct western blot assay using monoclonal antibodies 11G2 and 1B12. Lowering MSH3 mRNA in the caudate putamen to prevent CAG repeat expansion reduced levels of HTT1a.

neuroscience↗

bioRxiv2024

Divalent siRNA for prion disease

Prion protein (PrP) lowering is effective in animal models of prion disease and is being tested clinically in prion disease patients, but there remains a need for more potent PrP-lowering drug candidates. Inspired by the reported potency and duration of action of divalent short interfering RNA (siRNA), a new oligonucleotide drug modality for the central nervous system, we sought to discover and develop a new PrP-lowering drug candidate. Herein we identify a mouse Prnp-targeting divalent siRNA molecule, 1682-s4, that lowers PrP to 49% residual brain expression in wild-type mice, and, in the context of intracerebral infection with Rocky Mountain Laboratory (RML) prions, achieves a 2.7-fold increase in survival time with pre-symptomatic chronic treatment and 64% increase in survival time with a single dose after symptom onset. We describe the generation of two transgenic mouse lines, Tg25109 and Tg26372, expressing the full human PRNP gene and its non-coding sequence, and demonstrate their utility for in vivo discovery of potent human PRNP-targeting oligonucleotides. We discover siRNA sequence 2439 against human PRNP and compare its potency in different divalent siRNA chemical scaffolds. We determine that both the fixed UU tail and extended nucleic acid linkages of scaffold s4 contribute to superior potency compared to other scaffolds tested, offering 9.4 and 15.9 percentage points respectively of additional PrP knockdown. A single dose of 348 {micro}g of 2439-s4 lowered whole brain hemisphere human PrP in transgenic mice to 17% residual after 30 days, while 52 {micro}g lowered PrP to 49% residual. 1-2% of the dose of 2439-s4 delivered into cerebrospinal fluid is retained in the brain, and the median effective tissue concentration is estimated at 1.2 micrograms per gram of tissue. Good Laboratory Practices toxicology studies identified no significant liabilities, and the U.S. FDA has cleared an Investigational New Drug application to bring 2439-s4 into clinical trials.

neuroscience↗

bioRxiv2024

Multi-objective computational optimization of human 5' UTR sequences

The computational design of mRNA sequences is a critical technology for both scientific research and industrial applications. Recent advances in prediction and optimization models have enabled the automatic scoring and optimization of 5' UTR sequences, key upstream elements of mRNA. However, fully automated design of 5' UTR sequences with more than two objective scores has not yet been explored. In this study, we present a computational pipeline that optimizes human 5' UTR sequences in a multi-objective framework, addressing up to four distinct and conflicting objectives. Our work represents an important advancement in the multi-objective computational design of mRNA sequences, paving the way for more sophisticated mRNA engineering.

bioinformatics↗

bioRxiv2024

Potent and durable gene modulation in heart and muscle with chemically defined siRNAs

Small interfering RNA (siRNAs) hold immense promise for treating cardiac and muscular diseases, but robust and scalable delivery to these tissues remains a challenge. Recent advances in delivery strategies to muscle include conjugation of biologics (antibody/antibody fragments, peptides), which are currently in clinical development. However, the manufacturing of biologic-siRNA conjugates is a challenging and complex process. By contrast, lipophilic siRNAs are readily chemically synthesized at scale and support sufficient cardiac and skeletal muscle delivery. In this work, we refine siRNA design elements to enhance potency and durability and support clinically relevant silencing in muscle. Applying this strategy for siRNAs targeting myostatin (MSTN), a key target in muscle-wasting conditions, we show that a single subcutaneous dose in mice achieved robust and durable silencing ([~]80% inhibition up to 6 weeks, [~]30% at 14 weeks). Biweekly dosing resulted in >95% reduction of circulating MSTN for half a year, with no observed systemic or target-related toxicity. MSTN inhibition resulted in muscle growth and increased lean muscle mass, correlating with improved grip strength. Interestingly, the functional impact on muscle growth and strength significantly outlasts the target silencing, suggesting extended pharmacological effects. Systemic administration was equally efficacious in all muscle groups tested, including skeletal muscle, heart, tongue and diaphragm. The informational nature of the muscle-active chemically defined siRNA scaffold was confirmed by demonstrating muscle and heart efficacy with three additional targets. Our findings pave the way for potent and long-lasting gene modulation in muscle using chemically defined, lipophilic siRNAs, offering a new avenue for treating muscular diseases.

pharmacology and toxicology↗

bioRxiv2024

Antipsychotic-like effects of the selective Rho-kinase 2 inhibitor KD025 in genetic and pharmacological mouse models of schizophrenia

1Copy number variations in the ARHGAP10 gene encoding Rho GTPase-activating protein 10 are significantly associated with schizophrenia. ARHGAP10 negatively regulates RhoA/Rho-kinase (ROCK) signaling. We previously demonstrated that fasudil, a non-selective ROCK inhibitor, exhibited antipsychotic-like effects in several mouse models of schizophrenia. ROCK has two subtypes, ROCK1 and ROCK2. ROCK1 is mainly expressed in the thymus and blood, while ROCK2 is predominantly expressed in the brain. Therefore, it is expected that like fasudil, selective ROCK2 inhibitors will exhibit antipsychotic-like effects, accompanied by a lower incidence of adverse effects due to ROCK1 inhibition. Here, we used genetic and pharmacological models of schizophrenia to investigate whether the selective ROCK2 inhibitor KD025 would show antipsychotic-like effects with a favorable adverse effect profile. Oral administration of KD025 suppressed the abnormal increase in the phosphorylation level of myosin phosphatase-targeting subunit 1, a substrate of ROCK, and ameliorated the decreased spine density of layer 2/3 pyramidal neurons in the medial prefrontal cortex of Arhgap10 S490P/NHEJ mice. Furthermore, KD025 mitigated the methamphetamine-induced impairment of visual discrimination (VD) in Arhgap10 S490P/NHEJ and wild-type mice. KD025 also reduced MK-801-induced impairments of VD, novel object recognition, and hyperlocomotion. Regarding side effects that are commonly seen with typical antipsychotics, KD025 did not affect systolic blood pressure and did not induce extrapyramidal symptoms, hyperprolactinemia, or hyperglycemia at the effective dosage in naive wild-type mice. Taken together, KD025 shows antipsychotic-like effects with a favorable adverse effect profile in genetic and pharmacological mouse models of schizophrenia.

pharmacology and toxicology↗

bioRxiv2024

Systemic injection of scopolamine increased the variability of temporal prediction in head-fixed mice.

Several theories propose that interval timing and memory share common cognitive mechanisms. Pharmacological disruption of the cholinergic system using scopolamine, a muscarinic acetylcholine receptor antagonist, is widely used as a model of cognitive impairment. However, its effects on temporal prediction remain poorly understood. Previous timing studies in freely moving animals are difficult to interpret because motor activity may confound measures of interval timing. Here, we investigated the effects of systemic scopolamine administration on temporal prediction in mice using a head-fixed behavioral paradigm. Mice were trained on a fixed-time schedule task using a peak procedure, in which a 10% sucrose solution was delivered every 10 s through a spout positioned within licking distance. After training, mice developed anticipatory licking responses that peaked around the expected reward time, demonstrating temporal prediction of reward delivery. Systemic administration of scopolamine increased the variability of temporal prediction in a dose-dependent manner without altering the mean peak time. Trial-by-trial analysis further revealed that scopolamine reduced the duration of licking bouts while preserving the total number of licks during peak trials, suggesting impaired maintenance of reward-directed licking behavior rather than altered reward consumption. In a separate open-field assay, scopolamine increased spontaneous locomotor activity and reduced fecal output. These findings demonstrate that cholinergic blockade disrupts the precision of temporal prediction and alters behavioral organization in mice. The increased variability in timing behavior following scopolamine administration may reflect impaired regulation of transitions between behavioral states, providing new insights into the role of cholinergic signaling in temporal cognition.

neuroscience↗

bioRxiv2024

Extinction burst could be explained by curiosity-driven reinforcement learning

Curiosity encourages agents to explore their environment, leading to learning opportunities. Although psychology and neurobiology have tackled how external rewards control behavior, how intrinsic factors control behavior remains unclear. An extinction burst is a behavioral phenomenon in which a sudden increase in the frequency of a behavior immediately follows the omission of a reward. Although the extinction burst is textbook knowledge in psychology, there is little empirical evidence of it in experimental situations. In this study, we show that the extinction burst can be explained by curiosity by combining computational modeling of behavior and empirical demonstrations in mice. First, we built a reinforcement learning model incorporating curiosity, defined as expected reward prediction errors, and the model additively controlled the agents behavior to the primary reward. Simulations revealed that the curiosity-driven reinforcement learning model produced an extinction burst and burst intensity depended on the reward probability. Second, we established a behavioral procedure that captured extinction bursts in an experimental setup using mice. We conducted an operant conditioning task with head-fixed mice, in which the reward followed after pressing a lever at a given probability. After the training sessions, we occasionally withheld the reward delivery when the mice performed the task. We found that phasic bursts of responses occurred immediately after reward omission when responses were rewarded with a high probability, suggesting that the magnitude of reward prediction errors controlled the burst. These results provide theoretical and experimental evidence that intrinsic factors control behavior in adapting to an ever-changing environment. Significance statementIn theories of learning and behavior, primary rewards such as food, water, and sex occupy a dominant position as factors controlling behavior. However, primary rewards are scarce. Experimental investigations in psychology, neuroscience, ethology, and economics have revealed that novelty, uncertainty, and unpredictability drive behavior. How these intrinsic factors affect behavior is essential for a comprehensive understanding of the principles of learning and behavior. This study provides theoretical and experimental evidence that operant responses in mice are directly controlled by external rewards and intrinsic factors such as curiosity. Our study provides a robust example of curiosity-driven behavior and paves the way for understanding the mechanism of curiosity.

animal behavior and cognition↗