Biology subjects

Tani, K.

Publications and source records attributed to Tani, K..

9 recordsLinked to original sources

bioRxiv2025

Cerebellum involvement in visuo-vestibular interaction for the perception of gravitational direction: a repetitive transcranial magnetic stimulation study

Accurate perception of the direction of gravity relies on the integration of multisensory information, particularly from the visual and vestibular systems, within the brain. Although a recent study of patients with cerebellar degeneration suggested a cerebellar role in visuo-vestibular interaction in the perception of gravitational direction, direct evidence remains limited. To address this gap, we conducted two experiments with 42 healthy participants to evaluate the impact of repetitive 1-Hz transcranial magnetic stimulation (rTMS) over the posterior cerebellum on visual dependency, quantified by the subjective visual vertical bias induced by rotating optokinetic stimulation (OKS). Electric field simulations in high-resolution head models were used to ensure focal stimulation of the cerebellum at the group level. The results demonstrated that repetitive transcranial magnetic stimulation (rTMS) applied to the cerebellar vermis significantly attenuated the OKS-induced shift in visual vertical (SVV) bias. This effect was not observed when stimulation was applied to the early visual cortex (V1-2) or the cerebellar hemisphere. Also, the vermis rTMS had no effect on the judgement precision in the absence of visual motion cues, suggesting that the rTMS may reduce visual weight in visuo-vestibular processing by increasing visual motion noise rather than affecting vestibular function. These findings suggest a direct involvement of the cerebellar vermis in the visuo-vestibular interaction underlying the perception of gravitational direction, providing new insights into cerebellar contributions in human spatial orientation. Significance StatementThe cerebellum has been implicated in multisensory integration for spatial orientation, but its direct role in visuo-vestibular interactions remains limited. Using 1-Hz rTMS, we demonstrated that stimulation of the cerebellar vermis significantly reduced visual dependency in the perception of gravitational direction, as measured by the subjective visual vertical bias induced by rotating optokinetic stimulation. This effect was absent when adjacent areas, such as early visual cortex and the cerebellar hemisphere, were stimulated. These results suggest that the cerebellar vermis is directly involved in visuo-vestibular interaction, providing new insights into the cerebellar contribution to spatial orientation in humans.

neuroscience↗

bioRxiv2024

Role of the right middle occipital gyrus in egocentric spatial orientation in reference to gravitational information: Evidence from a pre-registered rTMS study

Accurate perception of the orientation of external objects relative to the body, known as egocentric spatial orientation, is fundamental to action. Previously, we found via behavioral and magnetic resonance imaging voxel-based morphometry studies that egocentric spatial orientation is distorted when the whole body is tilted with respect to gravity, and that the magnitude of this perceptual distortion is correlated with grey matter volume in the right middle occipital gyrus (rMOG). In the present pre-registered study, we demonstrated that neural processing in the rMOG is indeed a cause of the perceptual distortion. We transiently suppressed neural activity in the rMOG by applying low-frequency repetitive transcranial magnetic stimulation (rTMS) and evaluated the consequent effect on perceptual distortion. Our results showed that while rTMS over the rMOG significantly reduced perceptual distortion when the body was tilted with respect to gravity, it did not affect egocentric spatial orientation when in the upright position. No changes in perceptual distortion were observed when rTMS was applied to a control site (right temporoparietal junction) or to air (sham TMS). These results indicate that neural processing in the rMOG during body tilt is an essential cause of perceptual distortion, suggesting that the rMOG is engaged in egocentric spatial orientation concerning gravitational information. Significance statementThe findings of this pre-registered study support a causal role of neural activity in the right middle occipital gyrus (rMOG) in the perceptual distortion of egocentric spatial orientation induced by whole-body tilt relative to gravity. We suppressed neural activity in the rMOG using low-frequency repetitive transcranial magnetic stimulation (rTMS) and measured perceptual distortion. We observed a significant reduction in perceptual distortion after rTMS over the rMOG, but not after control or sham rTMS. These results provide, for the first time, direct evidence of the engagement of the rMOG in egocentric spatial orientation in reference to gravitational information.

neuroscience↗

bioRxiv2021

Asymmetric Structure of the Native Rhodobacter sphaeroides Dimeric LH1-RC Complex

The light-harvesting-reaction center (LH1-RC) core complex of purple photosynthetic bacterium Rhodobacter (Rba.) sphaeroides is characterized by the presence of both a dimeric form and a monomeric form. Following structure determination of the monomeric LH1-RC including its previously unrecognized component designated protein-U (Nat. Commun. 12, 6300, 2021), here we present cryo-EM structures of the dimeric LH1-RC from native Rba. sphaeroides IL106 at 2.75 [A] resolution and from an LH1-RC monomer lacking protein-U ({Delta}U) at 2.64 [A] resolution. The native dimeric core complex reveals many asymmetric features in the arrangement of its two monomeric components including the structural integrity of protein-U, the overall LH1 organization, and the rigidities of the proteins and pigments that form the complex. PufX polypeptides play a critical role in connecting two monomers, with one PufX interacting at its N-terminus with another PufX and an LH1 {beta}-polypeptide in another monomer, in good agreement with biochemical analyses. One of the proteins-U was only partially identified in the dimeric structure, signaling significantly different degrees of disorder in the two monomers. The {Delta}U LH1-RC monomer revealed a half-moon-shaped structure containing 11 - and 10 {beta}-polypeptides (compared with 14 of each in the wild type), indicating a critical role for protein-U in controlling the number of {beta}-subunits required for correct assembly and stabilization of the LH1-RC dimer. The structural features are discussed in relation to the unusual topology of intracytoplasmic photosynthetic membranes and an assembly model proposed for the native Rba. sphaeroides dimeric LH1-RC complex in membranes of wild-type cells.

biochemistry↗

bioRxiv2021

A Novel Membrane Protein in the Rhodobacter sphaeroides LH1-RC Photocomplex

We present a cryo-EM structure of the monomeric light-harvesting-reaction center (LH1-RC) core complex from photosynthetic purple bacterium Rhodobacter (Rba.) sphaeroides at 2.9 [A] resolution. The LH1 complex forms a C-shaped structure composed of 14 {beta}-polypeptides around the RC with a large ring opening. From the cryo-EM density map, a previously unrecognized integral membrane protein, referred to as protein-U, was identified. Protein-U has a U-shaped conformation near the LH1-ring opening and was annotated as a hypothetical protein in the Rba. sphaeroides genome. Deletion of protein-U resulted in a mutant strain that expressed a much-reduced amount of the dimeric LH1-RC, indicating an important role for protein-U in dimerization of the LH1-RC complex. PufX was located opposite protein-U on the LH1-ring opening, and both its position and conformation differed from that of previous reports of dimeric LH1-RC structures obtained at low-resolution. Twenty-six molecules of the carotenoid spheroidene arranged in two distinct configurations were resolved in the Rba. sphaeroides LH1 and were positioned within the complex to block its pores. Our findings offer a new view of the core photocomplex of Rba. sphaeroides and the connections between structure and function in bacterial photocomplexes in general.

biochemistry↗

bioRxiv2021

Cryo-EM Structure of the Photosynthetic LH1-RC Complex from Rhodospirillum rubrum

We present a cryo-EM structure of the light-harvesting-reaction center (LH1-RC) core complex from purple phototrophic bacterium Rhodospirillum (Rsp.) rubrum at 2.76 [A] resolution. The LH1 complex forms a closed, slightly elliptical ring structure with 16 {beta}-polypeptides surrounding the RC. Our biochemical analysis detected rhodoquinone (RQ) molecules in the purified LH1-RC, and the cryo-EM density map specifically positions RQ at the QA site in the RC. The geranylgeraniol sidechains of bacteriochlorophyll (BChl) aG coordinated by LH1 {beta}-polypeptides exhibit a highly homologous tail-up conformation that allows for interactions with the bacteriochlorin rings of nearby LH1 -associated BChls aG. The structure also revealed key protein-protein interactions in both N- and C-terminal regions of the LH1 {beta}-polypeptides, mainly within a face-to-face structural subunit. Our findings enable to evaluate past experimental and computational results obtained with this widely used organism and provide crucial information for more detailed exploration of light-energy conversion, quinone transport, and structure-function relationships in pigment-protein complexes.

biochemistry↗

bioRxiv2020

Trk Agonist Drugs Rescue Noise-Induced Hidden Hearing Loss

TrkB agonist drugs are shown here to have a significant effect on the regeneration of afferent cochlear synapses after noise-induced synaptopathy. The effects were consistent with regeneration of cochlear synapses that we observed in vitro after synaptic loss due to kainic acid-induced glutamate toxicity and were elicited by administration of TrkB agonists, amitriptyline and 7,8-dihydroxyflavone, directly into the cochlea via the posterior semicircular canal 48 h after exposure to noise. Synaptic counts at the inner hair cell and wave 1 amplitudes in the ABR were partially restored 2 weeks after drug treatment. Effects of amitriptyline on wave 1 amplitude and afferent auditory synapse numbers in noise-exposed ears after systemic (as opposed to local) delivery were profound and long-lasting; synapses in the treated animals remained intact one year after the treatment. However, the effect of systemically delivered amitriptyline on synaptic rescue was dependent on dose and the time window of administration: it was only effective when given before noise exposure at the highest injected dose. The long-lasting effect and the efficacy of post-exposure treatment indicate a potential broad application for the treatment of synaptopathy, which often goes undetected until well after the original damaging exposure(s).

neuroscience↗

bioRxiv2020

An Antibody to RGMa Promotes Regeneration of Cochlear Synapses after Noise Exposure

Auditory neuropathy is caused by the loss of afferent input to the brainstem via the components of the neural pathway comprising inner hair cells and the first order neurons of the spiral ganglion. Recent work has identified the synapse between cochlear primary afferent neurons and sensory hair cells as a particularly vulnerable component of this pathway. Loss of these synapses due to noise exposure or aging results in the pathology identified as hidden hearing loss, an initial stage of cochlear dysfunction that goes undetected in standard hearing tests. We show here that repulsive axonal guidance molecule a (RGMa) acts to prevent regrowth and synaptogenesis of peripheral auditory nerve fibers with inner hair cells. Treatment of noise-exposed animals with an anti-RGMa blocking antibody regenerated inner hair cell synapses and resulted in recovery of wave-I amplitude of the auditory brainstem response, indicating effective reversal of synaptopathy.

neuroscience↗

bioRxiv2020

The effects of dynamic arm movements during prolonged whole-body tilt on the perception of gravitational direction

Additional gravitational cues generated by active body movements may play a role in the perception of gravitational space, but no experimental evidence has been shown on this. To investigate this possibility, we evaluated how arm movements made against gravity influenced the perceptual distortion of visual and postural vertical induced by prolonged whole-body tilt. In Experiment 1, participants were asked to perform static or dynamic arm movements during prolonged whole-body tilt and we assessed their effects on subjective visual vertical (SVV) at the tilt position (during-tilt session) and after tilting back to the upright position (post-tilt session). In Experiment 2, we evaluated how static or dynamic arm movements during prolonged tilt subsequently affected the subjective postural vertical (SPV). In Experiment 1, we observed that prolonged tilt induced the SVV shifts toward the side of body tilts in both sessions. The prolonged tilt-induced SVV shifts effectively decreased when performing dynamic arm movements in the during-tilt session, but not in the post-tilt session. In Experiment 2, the SPV shifted toward the side of prolonged body tilt, which was not significantly influenced by the performance of static or dynamic arm movements. Results of the during-tilt session suggest that the central nervous system utilizes additional cues generated by dynamic body movements for the perception of the visual vertical.

neuroscience↗

bioRxiv2020

Quantitative assessment of pain threshold induced by a single-pulse transcranial magnetic stimulation

ObjectiveTranscranial magnetic stimulation (TMS) is commonly used in basic research to evaluate human brain function. Although scalp pain is a side effect, no studies have quantitatively assessed the TMS intensity threshold for inducing pain and whether sensitivity to TMS-induced pain differs between sexes. MethodsWe measured pain thresholds when single-pulse TMS was applied over either Brocas area (BA) or left primary motor cortex (M1). We compared these thresholds with motor threshold for inducing motor evoked potential (MEP) through M1 stimulation. We also compared pain thresholds for BA and M1 between males and females. ResultsPain thresholds for both sites were significantly lower than motor threshold. Further, the pain threshold for BA was much lower than that for M1. No significant difference was observed between sexes. ConclusionThe results suggest that TMS at an intensity equivalent to motor thresholds, which is often used in experimental or clinical studies, causes slight scalp pain. SignificanceExperimental designs using TMS to evaluate functional relationships between brain and behaviors should consider scalp pain and reduce its likelihood as much as possible. HighlightsO_LIWe investigated pain thresholds induced by a single-pulse TMS over the head. C_LIO_LIPain thresholds for TMS over Brocas area (BA) and primary motor cortex (M1) were much lower than motor threshold. C_LIO_LINo significant differences in the pain thresholds were observed between sexes. C_LI

neuroscience↗