Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Feedback regulation from the higher association areas is thought to control the primary sensory cortex, contribute to the cortical processing of sensory information, and work for higher cognitive functions such as multimodal integration and attentional control. However, little is known about the underlying neural mechanisms. Here, we show that the posterior parietal cortex (PPC) persistently inhibits the activity of the primary visual cortex (V1) in mice. Activation of the PPC causes the suppression of visual responses in V1 and induces the short-term depression, which is specific to visual stimuli. In contrast, pharmacological inactivation of the PPC or disconnection of cortical pathways from the PPC to V1 results in an effect of transient enhancement of visual responses in V1. Two-photon calcium imaging demonstrated that the cortical disconnection caused V1 excitatory neurons an enhancement of visual responses and a reduction of orientation selectivity index (OSI). These results show that the PPC regulates the response properties of V1 excitatory neurons. Our findings reveal one of the functions of the PPC, which may contribute to higher brain functions in mice.

DOI： 10.1111/ejn.14424

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DOI： 10.1093/cercor/bhy234

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The visual cortex of mice is a useful model for investigating the mammalian visual system. In primates, higher visual areas are classified into two parts, the dorsal stream ("where" pathway) and ventral stream ("what" pathway). The ventral stream is known to include a part of the temporal cortex. In mice, however, some cortical areas adjacent to the primary visual area (V1) in the occipital cortex are thought to be comparable to the ventral stream in primates, although the whole picture of the mouse ventral stream has never been elucidated. We performed wide-field Ca2+ imaging in awake mice to investigate visual responses in the mouse temporal cortex, and found that the postrhinal cortex (POR), posterior to the auditory cortex (AC), and the ectorhinal and temporal association cortices (ECT), ventral to the AC, showed clear visual responses to moving visual objects. The retinotopic maps in the POR and ECT were not clearly observed, and the amplitudes of the visual responses in the POR and ECT were less sensitive to the size of the objects, compared to visual responses in the V1. In the ECT, objects of different sizes activated different subareas. These findings strongly suggest that the mouse ventral stream extends to the ECT ventral to the AC, and that it has characteristic response properties that are markedly different from the response properties in the V1.

DOI： 10.1038/s41598-018-29530-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41598-018-28034-4

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Other Link： http://www.nature.com/articles/s41598-018-28034-4

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DOI： 10.1371/journal.pone.0193017

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Language：English   Publisher：FRONTIERS MEDIA SA  

The auditory thalamus and auditory cortex (AC) are pivotal structures in the central auditory system. However, the thalamocortical mechanisms of processing sounds are largely unknown. Investigation of this process benefits greatly from the use of mice because the mouse is a powerful animal model in which various experimental techniques, especially genetic tools, can be applied. However, the use of mice has been limited in auditory research, and thus even basic anatomical knowledge of the mouse central auditory system has not been sufficiently collected. Recently, optical imaging combined with morphological analyses has enabled the elucidation of detailed anatomical properties of the mouse auditory system. These techniques have uncovered fine AC maps with multiple frequency-organized regions, each of which receives pointto- point thalamocortical projections from different origins inside the lemniscal auditory thalamus, the ventral division of the medial geniculate body (MGv). This precise anatomy now provides a platform for physiological research. In this mini review article, we summarize these recent achievements that will facilitate physiological investigations in the mouse auditory system.

DOI： 10.3389/fncir.2017.00014

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Amid recent amendment of delineation of a mouse auditory cortical map, a caudal auditory field, originally defined as the primary auditory cortex (AI), was divided into the AI and dorsomedial field (DM), based on distinct high frequency areas. A low frequency area was not previously established in the DM because responses to low frequency tones were weak in this area. This may lead to the misconception that the DM is an atypical region that lacks a low frequency band. In the current study, we confirmed that the DM has a low frequency area that is completely independent from the AI. First, we conducted flavoprotein fluorescence imaging with improved signal to noise ratio and revealed the presence of two separated low frequency areas in the AI and DM. Next, we injected a retrograde neural tracer along the tonotopic axis of the AI or DM to reveal the thalamic origins in the ventral division of the medial geniculate body (MGv). We found that neurons projecting to low frequency areas of the AI and DM occupied different locations within the MGv and mutually independent topographic organizations consisting of thalamic neurons projecting to the AI or DM. These results indicate that the AI and DM have distinct low frequency areas with distinct thalamic projections from the MGv. Our findings reaffirm that the AI and DM should be regarded as independent regions in the mouse auditory cortex. (C) 2016 The Authors. Published by Elsevier Ireland Ltd.

DOI： 10.1016/j.neulet.2016.11.062

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/srep34421

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Other Link： http://www.nature.com/articles/srep34421.pdf

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DOI： 10.1038/srep22315

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Transient ischemia produces postischemic tingling sensation. Ischemia also produces nerve conduction block that may modulate spinal neural circuits. In the present study, reduced mechanical thresholds for hindpaw-withdrawal reflex were found in mice after transient hindpaw ischemia, which was produced by a high pressure applied around the hindpaw for 30 min. The reduction in the threshold was blocked by spinal application of LY354740, a specific agonist of group II metabotropic glutamate receptors. Neural activities in the spinal cord and the primary somatosensory cortex (S1) were investigated using activity-dependent changes in endogenous fluorescence derived from mitochondrial flavoproteins. Ischemic treatment induced potentiation of the ipsilateral spinal and contralateral S1 responses to hindpaw stimulation. Both types of potentiation were blocked by spinal application of LY354740. The contralateral S1 responses, abolished by lesioning the ipsilateral dorsal column, reappeared after ischemic treatment, indicating that postischemic tingling sensation reflects a sensory modality shift from tactile sensation to nociception in the spinal cord. Changes in neural responses were investigated during ischemic treatment in the contralateral spinal cord and the ipsilateral S1. Potentiation already appeared during ischemic treatment for 30 min. The present findings suggest that the postischemic potentiation shares spinal mechanisms, at least in part, with neuropathic pain.

DOI： 10.1038/srep11191

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DOI： 10.1152/jn.00932.2014

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Clustered protocadherins (cPcdhs) comprising cPcdh-α, -β, and -γ, encode a large family of cadherin-like cell-adhesion molecules specific to neurons. Impairment of cPcdh-α results in abnormal neuronal projection patterns in specific brain areas. To elucidate the role of cPcdh-α in retinogeniculate projections, we investigated the morphological patterns of retinogeniculate terminals in the lateral geniculate (LG) nucleus of mice with impaired cPcdh-α. We found huge aggregated retinogeniculate terminals in the dorsal LG nucleus, whereas no such aggregated terminals derived from the retina were observed in the olivary pretectal nucleus and the ventral LG nucleus. These aggregated terminals appeared between P10 and P14, just before eye opening and at the beginning of the refinement stage of the retinogeniculate projections. Reduced visual acuity was observed in adult mice with impaired cPcdh-α, whereas the orientation selectivity and direction selectivity of neurons in the primary visual cortex were apparently normal. These findings suggest that cPcdh-α is required for adequate spacing of retinogeniculate projections, which may be essential for normal development of visual acuity.

DOI： 10.1111/jnc.13053

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.neures.2014.07.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

Background: Visual information conveyed through the extra-geniculate visual pathway, which runs from the retina via the superior colliculus (SC) and the lateral posterior nucleus (LPN) of the thalamus to the higher visual cortex, plays a critical role in the visual capabilities of many mammalian species. However, its functional role in the higher visual cortex remains unclear. Here, we observed visual cortical area activity in anesthetized mice to evaluate the role of the extrageniculate pathway on their specialized visual properties.
Results: The preferred stimulus velocities of neurons in the higher visual areas (lateromedial [LM], anterolateral [AL], anteromedial [AM], and rostrolateral [RL] areas) were measured using flavoprotein fluorescence imaging and two-photon calcium imaging and were higher than those in the primary visual cortex (V1). Further, the velocity-tuning properties of the higher visual areas were different from each other. The response activities in these areas decreased after V1 ablation; however, the visual properties' differences were preserved. After SC destruction, these preferences for high velocities disappeared, and their tuning profiles became similar to that of the V1, whereas the tuning profile of the V1 remained relatively normal. Neural tracer experiments revealed that each of these higher visual areas connected with specific subregions of the LPN.
Conclusions: The preservation of visual property differences among the higher visual areas following V1 lesions and their loss following SC lesions indicate that pathways from the SC through the thalamus to higher cortical areas are sufficient to support these differences.

DOI： 10.1016/j.cub.2014.01.061

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Mice navigate nearby space using their vision and whiskers, and young mice learn to integrate these heterogeneous inputs in perceptual space. We found that cortical responses were depressed in the primary visual cortex of young mice after wearing a monocular prism. This depression was uniformly observed in the primary visual cortex and was eliminated by whisker trimming or lesions in the posterior parietal cortex. Compensatory visual map shifts of responses elicited via the eye that had worn the prism were also observed. As a result, cortical responses elicited via each eye were clearly separated when a visual stimulus was placed in front of the mice. A comparison of response areas before and after prism wearing indicated that the map shifts were produced by depression with spatial eccentricity. Visual map shifts based on whisker-guided cues may serve as a model for investigating the cellular and molecular mechanisms underlying higher sensory integration in the mammalian brain.

DOI： 10.1016/j.celrep.2013.11.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER IRELAND LTD  

To compare age-related deterioration of neural responses in each subfield of the auditory cortex in C57BL/6 mice, we evaluated amplitudes of tonal responses in young (5-11 weeks old) and adult (16-23 weeks old) groups using transcranial flavoprotein fluorescence imaging. Cortical responses to 20-kHz amplitude-modulated (AM) sounds, which were mainly found in the anterior auditory field (AAF) and the primary auditory cortex (AI) of the core region, were not markedly different between the two groups. In contrast, cortical responses to direction reversal of slow frequency-modulated (FM) sounds, which were mainly found in the ultrasonic field (UF), were significantly disrupted in the adult group compared with those in the young group. To investigate the mechanisms underlying such age-related deterioration, biotinylated dextran amine (BDA) was injected into UF. The number of retrograde labeled neurons in the dorsal division of the medial geniculate body (MGd) was markedly reduced in the adult group compared with that in the young group. These results strongly suggest that cortical responses to FM direction reversal in UF of adult C57BL/6 mice are mainly deteriorated by loss of non-lemniscal thalamic inputs from MGd to UF due to aging. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

DOI： 10.1016/j.neulet.2013.10.015

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We investigated precise projection patterns from the ventral division of the medial geniculate body (MGv) projecting to the core region of the auditory cortex in C57BL/6 mice. The core region in mice comprises two different tonotopically organized areas, the anterior auditory field (AAF) and the primary auditory cortex (AI). In the present study, AAF and AI were functionally identified using flavoprotein fluorescence imaging. Biotinylated dextran amine (BDA) was injected iontophoretically into the tonotopic bands to 5 kHz and 20 kHz in AAF, and those to 5 kHz, 10 kHz, and 20 kHz in AI for staining MGv neurons projecting to the injected sites. MGv neurons projecting to AAF were found in the medial part of MGv, while MGv neurons projecting to AI were found in the lateral part. In the medial part of MGv, areas projecting to 5-20 kHz bands in AAF were aligned along the medio lateral axis. In the lateral part of MGv, areas projecting to 5-20 kHz bands in AI were aligned along the dorso ventral axis. These results indicate that AAF and AI receive auditory information via two different MGv compartments with independent tonotopic axes, respectively. (C) 2013 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/j.neures.2013.05.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PUBLIC LIBRARY SCIENCE  

Species-specific vocalizations in mice have frequency-modulated (FM) components slower than the lower limit of FM direction selectivity in the core region of the mouse auditory cortex. To identify cortical areas selective to slow frequency modulation, we investigated tonal responses in the mouse auditory cortex using transcranial flavoprotein fluorescence imaging. For differentiating responses to frequency modulation from those to stimuli at constant frequencies, we focused on transient fluorescence changes after direction reversal of temporally repeated and superimposed FM sweeps. We found that the ultrasonic field (UF) in the belt cortical region selectively responded to the direction reversal. The dorsoposterior field (DP) also responded weakly to the reversal. Regarding the responses in UF, no apparent tonotopic map was found, and the right UF responses were significantly larger in amplitude than the left UF responses. The half-max latency in responses to FM sweeps was shorter in UF compared with that in the primary auditory cortex (A1) or anterior auditory field (AAF). Tracer injection experiments in the functionally identified UF and DP confirmed that these two areas receive afferent inputs from the dorsal part of the medial geniculate nucleus (MG). Calcium imaging of UF neurons stained with fura-2 were performed using a two-photon microscope, and the presence of UF neurons that were selective to both direction and direction reversal of slow frequency modulation was demonstrated. These results strongly suggest a role for UF, and possibly DP, as cortical areas specialized for processing slow frequency modulation in mice.

DOI： 10.1371/journal.pone.0068113

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Avulsion of spinal nerve roots in the brachial plexus (BP) can be repaired by crossing nerve transfer via a nerve graft to connect injured nerve ends to the BP contralateral to the lesioned side. Sensory recovery in these patients suggests that the contralateral primary somatosensory cortex (S1) is activated by afferent inputs that bypassed to the contralateral BP. To confirm this hypothesis, the present study visualized cortical activity after crossing nerve transfer in mice through the use of transcranial flavoprotein fluorescence imaging. In naive mice, vibratory stimuli applied to the forepaw elicited localized fluorescence responses in the S1 contralateral to the stimulated side, with almost no activity in the ipsilateral S1. Four weeks after crossing nerve transfer, forepaw stimulation in the injured and repaired side resulted in cortical responses only in the S1 ipsilateral to the stimulated side. At eight weeks after crossing nerve transfer, forepaw stimulation resulted in S1 cortical responses of both hemispheres. These cortical responses were abolished by cutting the nerve graft used for repair. Exposure of the ipsilateral S1 to blue laser light suppressed cortical responses in the ipsilateral S1, as well as in the contralateral S1, suggesting that ipsilateral responses propagated to the contralateral S1 via cortico-cortical pathways. Direct high-frequency stimulation of the ipsilateral S1 in combination with forepaw stimulation acutely induced S1 bilateral cortical representation of the forepaw area in naive mice. Cortical responses in the contralateral S1 after crossing nerve transfer were reduced in cortex-restricted heterotypic GluN1 (NMDAR1) knockout mice. Functional bilateral cortical representation was not clearly observed in genetically manipulated mice with impaired cortico-cortical pathways between S1 of both hemispheres. Taken together, these findings strongly suggest that activity-dependent potentiation of cortico-cortical pathways has a critical role for sensory recovery in patients after crossing nerve transfer.

DOI： 10.1371/journal.pone.0035676

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Natural sounds consist of a component at the fundamental frequency (f0) and its overtones. Pitch is perceived at f0, even when spectral energy at f0 is missing. This missing f0, or 'virtual pitch', is thought to be detected in the auditory cortex and related cortical areas, but the precise neural mechanisms are unknown. One possibility is that virtual pitch can be retrieved from the periodicity of sound waveforms. However, this mechanism requires the temporal accuracy in periodicity detection, and so far the detection of virtual pitch has only been demonstrated at frequencies lower than 1 kHz. We investigated the ability of mice to detect virtual pitch up to 5 kHz using a two-step sound discrimination test. In the first step of this test, mice were trained to discriminate between tone bursts at 2.5 and 5 kHz. In the second step, we tested the ability of mice to discriminate between virtual pitches at 2.5 kHz and at 5 kHz. It was demonstrated that the performance of mice to discriminate between virtual pitches at 2.5 and 5 kHz was significantly affected by previous discrimination learning between tone bursts, indicating that mice can detect virtual pitch up to 5 kHz. (C) 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/j.neures.2011.06.005

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We developed a technique of transcranial electrical stimulation (TES) to investigate cortico-cortical connections in mice. After the skull was shaved with the blade of a dental bar, a blunt tip of a needle was gently pushed onto the thinned skull. The skull was deformed by the force, and the subarachnoid space between the skull and the cortex was minimized around the needle tip. Under these conditions, stimulus currents applied to the needle directly flowed into the cortex through the thinned skull. Cortico-cortical functional connections stimulated by this method were visualized by transcranial flavoprotein fluorescence imaging. The cortical responses evoked by TES exhibited spatial and temporal activity patterns comparable to those elicited by a conventional method, in which an electrode is directly inserted into superficial cortical layers. A comparison of the two methods revealed that TES required a slightly stronger stimulus intensity and preferentially activated superficial layers of the cortex compared with the conventional method. Using the new method, we revealed the presence of reciprocal cortico-cortical functional connections between lateral and medial parts of higher visual cortices in mice. This new method combined with transcranial flavoprotein fluorescence imaging allowed us to activate cortico-cortical pathways arising from the primary sensory areas and investigate sensory information flow in the mouse cerebral cortex. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jneumeth.2011.08.007

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We investigated nociceptive cortical responses using transcranial flavoprotein fluorescence imaging in anesthetized mice with capsaicin-induced allodynia. Tactile stimuli applied to the hindpaw produced fluorescence increases in the contralateral somatosensory cortex of naive mice. Lesioning of the ipsilateral dorsal column in the spinal cord abolished most of the cortical responses. However, the responses to the same tactile stimuli appeared again after capsaicin was injected into the hindpaw.The capsaicin treatment reduced the thresholds of the hindpaw withdrawal responses. These findings strongly suggest that the responses to tactile stimuli in the lesioned mice after capsaicin injection represented nociceptive cortical responses. (c) 2011 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/j.neures.2011.01.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SOC NEUROSCIENCE  

We tested a hypothesis that the spinal plasticity induced within a few hours after nerve injury may produce changes in cortical activities and an initial phase of neuropathic pain. Somatosensory cortical responses elicited by vibratory stimulation were visualized by transcranial flavoprotein fluorescence imaging in mice. These responses were reduced immediately after cutting the sensory nerves. However, the remaining cortical responses mediated by nearby nerves were potentiated within a few hours after nerve cutting. Nerve injury induces neuropathic pain. In the present study, mice exhibited tactile allodynia 1-2 weeks after nerve injury. Lesioning of the ipsilateral dorsal column, mediating tactile cortical responses, abolished somatic cortical responses to tactile stimuli. However, nontactile cortical responses appeared in response to the same tactile stimuli within a few hours after nerve injury, indicating that tactile allodynia was acutely initiated. We investigated the trigger mechanisms underlying the cortical changes. Endogenous glial cell line-derived neurotrophic factor (GDNF), found in the Meissner corpuscles, induced basal firing approximately 0.1 Hz or less in its

DOI： 10.1523/JNEUROSCI.6753-10.2011

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DOI： 10.1016/j.brainres.2011.02.026

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Cortical responses after sound discrimination learning were investigated using transcranial flavoprotein fluorescence imaging in mice. Water-deprived mice were trained to discriminate between rewarded (S+) and unrewarded (S-) sound stimuli. After the learning, they were anesthetized, and cortical responses to S+ and S- were recorded in the right auditory cortex. When a pure tone (PT) at 10 kHz and a 10 kHz amplitude-modulated (AM) sound were used as S+ and S-, the cortical responses to S using AM were significantly depressed but those to S- using PT were not. The cortical responses to S+ showed no significant change. Upward frequency-modulated sounds from 5 kHz to 40 kHz (FM up arrow) and downward frequency-modulated sounds from 40 kHz to 5 kHz (FM down arrow) were also used as S+ and S. Cortical responses to S- using FM up arrow and FM down arrow were significantly depressed after learning, while those to S+ were unchanged. No significant change of cortical responses to S using FMs was observed in the left auditory cortex after learning. The learning-induced depression of S using FMs was most clearly observed in the medial part of the tonotopic band to 40 kHz in the right primary auditory cortex, which might be involved in processing FM sounds. (C) 2010 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/j.neures.2010.01.005

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Peripheral afferent denervation induces reorganization of somatotopic maps in the primary somatosensory cortex (S1). In the present study, we investigated somatotopic map plasticity after tail cut. Neonatal mice at postnatal days (P) 2-3 and adult mice at eight weeks of age were anesthetized with ether, and approximately two thirds of the tail was cut from the tip. Both groups of mice were anesthetized with urethane (1.7 g/kg, i.p.) at 10 weeks of age, and transcranial flavoprotein fluorescence imaging was performed in the Si. Neural activities in the Si were elicited by vibratory stimulation applied to the contralateral hindpaw or the tail in control mice. The cortical areas activated by hindpaw, tail base, and tail tip stimuli were placed in this order according to the medial and posterior direction. In mice with tail cut, the tail base area moved to the more medial and posterior area corresponding to the tail tip in control mice. The shift of the tail base area was observed in both neonatal and adult tail cut mice, indicating the absence of a critical period before eight weeks. Medial and posterior shift of the tail base area with regard to the bregma was confirmed in tail cut mice. These data suggest that transcranial flavoprotein fluorescence imaging is a useful technique for investigating somatosensory map plasticity in mice. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.brainres.2010.01.020

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DOI： 10.1016/j.neures.2010.07.2264

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DOI： 10.1016/j.neures.2010.07.371

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL PUBLISHING, INC  

Endogenous fluorescence signals derived from mitochondria reflect activity-dependent changes in brain metabolism and may be exploited in functional brain imaging. Endogenous flavoprotein fluorescence imaging in mice is especially important because many genetically manipulated strains of mice are available and the transparent skull of mice allows transcranial fluorescence imaging of cortical activities. In the primary sensory areas of mice, cortical activities and experience-dependent plasticity have been investigated using transcranial fluorescence imaging. Furthermore, differential imaging, based on stimulus specificity of cortical areas, distinguished activities in higher visual areas around the primary visual cortex from those in primary visual cortex. The combination of transcranial fluorescence imaging with the suppression of cortical activities using photobleaching of flavoproteins is expected to aid in elucidating the roles of sensory cortices including higher areas in mice.

DOI： 10.1111/j.1471-4159.2009.05926.x

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Flavoprotein fluorescence in the brain is intimately coupled with neuronal aerobic energy metabolism. If flavoproteins are photobleached, neural activities may be affected owing to dysfunction in aerobic energy metabolism in mitochondria. We tested this possibility in cortical slices from mice, and found that exposure to blue light (lambda = 475 nm) derived from a 20 mW diode laser for 50 min suppresses trans-synaptic components of field potentials. This finding formed the basis of a transcranial photo-inactivation technique, that was used to investigate auditory signal transmission between the anterior auditory field (AAF) and the primary auditory cortex (AI) in anesthetized mice. Cortical responses in AAF and AI, elicited by 5 kHz tonal stimuli, were visualized using transcranial flavoprotein fluorescence imaging. After determining responsive areas in AAF and AI, the auditory cortex was exposed to the blue diode laser via the intact skull, while either AAF or AI was protected with a piece of carbon paper. Although the photo-inactivation of AI had no significant effect on the fluorescence responses in AAF, the photo-inactivation of AAF significantly reduced the fluorescence responses in AI, indicating the presence of auditory signal transmission from AAF to AI. (C) 2008 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/j.neures.2007.12.013

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In sensory cortices, synaptic plasticities such as long-term potentiation (LTP) and long-term depression (LTD) have important roles in the development of neural circuits and sensory information processing. However, the differential roles and mechanisms of the various types of LTP and LTD are not clear. In the present study, we investigated LTP and two types of LTD in slices obtained from the rat auditory cortex. Supragranular field potentials elicited by layer VI stimulation were recorded through a metal electrode. Transsynaptic field potentials exhibited marked LTP after tetanic stimulation (TS, 100 Hz for 1 s) was applied to layer VI. The same field potential components exhibited LTD after low-frequency stimulation (LFS, 1 Hz for 900 s) was applied to layer VI. LTD of supragranular field potentials was also induced by local TS applied to supragranular layers 0.3 mm from the recording site. Neither LTP nor LTD of either type was induced in the presence of 50 mu M D-(-)-2 -amino-5-phosphonovalerate (APV), an NMDA receptor antagonist. However, 500 mu M (+)-alpha-methyl-4-carboxyphenylglycine (MCPG), an antagonist of metabotropic glutamate receptors, had no effect. LTD induced by LFS and that induced by local TS were suppressed in the presence of 3 mu M bicuculline, an antagonist of GABA(A) receptors. Each of these forms of LTD occluded the other. These results and intracellular recordings in supragranular pyramidal neurons during LFS and local TS strongly suggest that the two types of LTD share common neural circuits for their induction. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.brainres.2007.06.049

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Somatosensory information is serially processed by the primary (S1) and secondary (S2) cortices, which can be identified in fresh cortical slices. We visualized activity propagation between S1 and S2 in rat cortical slices using flavoprotein fluorescence imaging. When S1 was stimulated, fluorescence responses extended into S2, while responses hardly propagated to S1 following S2 stimulation. The dominant activity propagation pattern from S1 to S2 was not affected by antagonists of glutamate or GABA(A) receptors. Ca2+ imaging and electrophysiological recordings confirmed the anisotropic activity propagation pattern. This pattern could be formed as a result of serial information processing in SI and S2. To test this hypothesis, activity propagation was investigated in cortical slices prepared 2 weeks or 3 days after trimming contralateral whiskers that provide massive inputs to SI. Supragranular activities in the barrel cortex were clearly suppressed. Furthermore, activities elicited in the rostral small vibrissae/mouth area of S1 near the border between S I and S2 spread into the adjacent barrel cortex rather than into S2. Behavioral effects of whisker trimming were evaluated using a test, in which rats chose one of two bridges that had a wall on the right or left side only. Immediately after hemilateral whisker trimming, rats preferred to use the bridge with a wall close to the intact side. However, this preference disappeared 3 days after trimming. Modified activities observed in cortical slices after whisker trimming might be mechanisms for this behavioral compensation. These findings suggest experience-dependent formation of activity propagation patterns in the somatosensory cortex. (c) 2006 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.neuroimage.2006.08.049

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Sensory information is processed in neural networks connecting the primary sensory cortices with surrounding higher areas. Here, we investigated the properties of local connections between the primary auditory cortex (area 41) and surrounding areas (areas 20, 36, 18a and 39) in rat cerebral slices. Neural activities elicited by repetitive electrical stimulation were visualized using the activity-dependent changes in endogenous fluorescence derived from mitochondrial flavoproteins, which mostly reflect activities produced by polysynaptic glutamatergic transmission. Polysynaptic feedforward propagation was dominant compared with the corresponding polysynaptic feedback propagation between the primary (area 41) and secondary (areas 20 and 36) auditory cortices, while such a tendency was less clear in other pathways. Long inter-areal (> 1 mm) propagation with the same dominancy was observed after laver V stimulation between areas 41 and 20, and was not affected by cutting the underlying white matter. Activity-dependent changes in neural activities induced by low-frequency stimulation in the presence of I mu M bicuculline were investigated using Ca2+ imaging. Significant potentiation of the polysynaptic Ca2+ activities was only observed in polysynaptic feedforward pathways from the primary to secondary auditory cortices. Experience-dependence of the connections between areas 41 and 20 was investigated using flavoprotein fluorescence imaging. The activities from areas 41 to 20 were reduced by cochlear lesions produced at P12 but not at P28, while the activities from areas 20 to 41 were reduced by the lesions at P28, suggesting the critical period for the polysynaptic feedforward connection was before P28, while for the polysynaptic feedback connection was after P28. (c) 2006 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.neuroimage.2006.09.030

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Language：English   Publishing type：Part of collection (book)   Publisher：Springer US  

The close coupling of neuronal activities to glucose and oxygen metabolism is well established. The imaging of activity-dependent changes in the endogenous fluorescence of NADH and mitochondrial flavoproteins provides the basis for many experimental approaches to visualize brain activities based on local changes in cellular energy metabolism. This chapter summarizes the results of the novel experimental applications of flavoprotein fluorescence for imaging local dynamic coupling of the functional activities of brain cells and temporal linkage to different events (such as electrical activity, calcium flux, and redox changes). These points are discussed in comparison with other methods using endogenous signals (such as deoxygenation of hemoglobin or blood flow changes) and with those using exogenous probes that are sensitive to voltage, calcium, or pH. The technical merits of flavoprotein fluorescence imaging for investigating plastic changes in neural activities and visualizing mouse cortical activities through the intact skull are discussed. Flavoprotein fluorescence imaging is an excellent tool for investigating neural plasticity, and may be a complementary method of functional brain imaging that can be used to understand brain functions. © 2007 Springer Science+Business Media, LLC.

DOI： 10.1007/978-0-387-30411-3_13

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：LIPPINCOTT WILLIAMS & WILKINS  

We investigated the roles of the auditory cortex in discrimination learning of vowel-like sounds consisting of multiple formants. Rats were trained to discriminate between synthetic sounds with four formants. Bilateral electrolytic lesions including the primary auditory cortex and the dorsal auditory association cortex impaired multiformant discrimination, whereas they did not significantly affect discrimination between sounds with a single formant or between pure tones. Local lesions restricted to the dorsal/rostral auditory association cortex were sufficient to attenuate multiformant discrimination learning, and lesions restricted to the primary auditory cortex had no significant effects. These findings indicate that the dorsal/rostral auditory association cortex but not the primary auditory cortex is required for discrimination learning of vowel-like sounds with multiple formants in rats.

DOI： 10.1097/WNR.0b013e32800fef9d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Aerobic energy metabolism in the brain is reflected as changes in the green fluorescence of mitochondrial flavoproteins, and the activity-dependent changes in endogenous fluorescence are applicable for functional brain imaging. To understand the roles of cortical plasticity in discrimination learning, we used flavoprotein fluorescence imaging to visualize changes of neural activities in the rat primary somatosensory cortex (SI) after learning. Rats were trained to discriminate floor vibration at rewarded and unrewarded frequencies. After this discrimination learning was accomplished in 3-5 days, the rats were anesthetized with urethane (1.5 g/kg, i.p.), and neural responses were recorded in SI during flutter stimuli applied to the contralateral hindpaw. The fluorescence responses to the stimuli at unrewarded frequencies were selectively depressed in the trained rats, which had behaviorally neglected unrewarded stimuli. The depression of cortical responses was not observed in the rats trained with rewarded stimuli only. Therefore, the stimulus-specific depression in SI might explain a part of neural mechanisms underlying discrimination behavior. To reproduce the stimulus-specific depression of cortical responses in anesthetized rats, tetanic cortical stimulation was paired with flutter stimulation applied to the hindpaw. Selective depression of fluorescence responses or field potentials in SI was induced by the paired stimulation. Our findings suggest that some intracortical circuits in SI are specifically tuned to and modulated by unrewarded stimuli of a particular frequency while SI neurons are responsive to both of rewarded and unrewarded stimuli. The present results indicate the usefulness of flavoprotein fluorescence imaging for investigating somatosensory cortical plasticity after learning. (c) 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.neuroimage.2005.10.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING  

Functional brain imaging using endogenous fluorescence of mitochondrial flavoprotein is useful for investigating mouse cortical activities via the intact skull, which is thin and sufficiently transparent in mice. We applied this method to investigate auditory cortical plasticity regulated by acoustic environments. Normal mice of the C57BL/6 strain, reared in various acoustic environments for at least 4 weeks after birth, were anaesthetized with urethane (1.7 g/kg, i.p.). Auditory cortical images of endogenous green fluorescence in blue light were recorded by a cooled CCD camera via the intact skull. Cortical responses elicited by tonal stimuli (5, 10 and 20 kHz) exhibited mirror-symmetrical tonotopic maps in the primary auditory cortex (AI) and anterior auditory field (AAF). Depression of auditory cortical responses regarding response duration was observed in sound-deprived mice compared with naive mice reared in a normal acoustic environment. When mice were exposed to an environmental tonal stimulus at 10 kHz for more than 4 weeks after birth, the cortical responses were potentiated in a frequency-specific manner in respect to peak amplitude of the responses in AI, but not for the size of the responsive areas. Changes in AAF were less clear than those in AI. To determine the modified synapses by acoustic environments, neural responses in cortical slices were investigated with endogenous fluorescence imaging. The vertical thickness of responsive areas after supragranular electrical stimulation was significantly reduced in the slices obtained from sound-deprived mice. These results suggest that acoustic environments regulate the development of vertical intracortical circuits in the mouse auditory cortex.

DOI： 10.1111/j.1460-9568.2006.04662.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING LTD  

In the present study, short-term plasticity of somatosensory neural responses was investigated using flavoprotein autofluorescence imaging in rats anaesthetized with urethane (1.5 g/kg, i.p.) Somatosensory neural activity was elicited by vibratory skin stimulation (50 Hz for 1 s) applied on the surface of the left plantar hindpaw. Changes in green autofluorescence (lambda = 500-550 nm) in blue light (lambda = 450-490 nm) were elicited in the right somatosensory cortex. The normalised maximal fluorescence responses (DeltaF/F) was 2.0 +/- 0.1% (n = 40). After tetanic cortical stimulation (TS), applied at a depth of 1.5-2.0 mm from the cortical surface, the responses elicited by peripheral stimulation were significantly potentiated in both peak amplitude and size of the responsive area (both P < 0.02; Wilcoxon signed rank test). This potentiation was clearly observed in the recording session started 5 min after the cessation of TS, and returned to the control level within 30 min. However, depression of the responses was observed after TS applied at a depth of 0.5 mm. TS-induced changes in supragranular field potentials in cortical slices showed a similar dependence on the depth of the stimulated sites. When TS was applied on the ipsilateral somatosensory cortex, marked potentiation of the ipsilateral responses and slight potentiation of the contralateral responses to peripheral stimulation were observed after TS, suggesting the involvement of commissural fibers in the changes in the somatosensory brain maps. The present study clearly demonstrates that functional brain imaging using flavoprotein autofluorescence is a useful technique for investigating neural plasticity in vivo.

DOI： 10.1111/j.1460-9568.2004.03237.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING LTD  

Synaptic plasticity in polysynaptic neural circuits permits modulation of the dynamic properties of these circuits. We investigated the properties of polysynaptic potentiation in pyramidal neurons in layer V of rat auditory cortex (AC) slices using the perforated patch clamp technique. The GABA(A) receptor inhibitor bicuculline was used to facilitate polysynaptic activity. The amplitude and duration of the polysynaptic activity were both gradually potentiated with repetitive stimulation (RS) at 12 s intervals. Potentiation was saturated within 10 min of the onset of RS. After the cessation of RS, the polysynaptic responses returned to control levels within 30 min. RS-induced potentiation was confirmed by fluorescence imaging of slices loaded with the Ca2+ indicator rhod-2. Such potentiation was not induced by stimulation at 60 s intervals. The magnitude of the RS-induced potentiation in layer V pyramidal neurons in the AC was greater than that in either layer II/III pyramidal neurons in the AC or layer V pyramidal neurons in the visual cortex. The NMDA receptor antagonist APV (100 mum), inhibited RS-induced potentiation. When stimulated at 1 Hz, the potentiated response appeared rapidly. In the absence of bicuculline, RS consisting of five pulses at 30 ms intervals, repeated at 12 s intervals for 10 min, elicited potentiation of firing activity, suggesting that the potentiation is independent of bicuculline. The present study demonstrates the dynamic properties of polysynaptic circuits involving layer V pyramidal neurons in the AC are strongly affected by activity-dependent synaptic potentiation.

DOI： 10.1111/j.1460-9568.2003.03136.x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CAMBRIDGE UNIV PRESS  

We used autofluorescence of mitochondrial flavoproteins to image cortical neural activity in the rat. Green autofluorescence in blue light was examined in slices obtained from rat cerebral cortex. About half of the basal autofluorescence was modulated by the presence or absence of 0, or glucose in the medium. Repetitive electrical stimulation at 20 Hz for 1 s produced a localized fluorescence increase in the slices. The amplitude of the increase was 27 +/- 2 % (mean +/- S.D., n = 35). Tetrodotoxin or diphenyleneiodonium, an inhibitor of flavoproteins, blocked the autofluorescence responses. The autofluorescence responses were not observed in slices perfused with calcium-, glucose- or O-2-free medium. In the primary somatosensory cortex of rats anaesthetized with urethane (1.5 g kg(-1), i.p.), an activity-dependent increase in autofluorescence of 20 +/- 4 % (n = 6) was observed after electrical cortical stimulation at 100 Hz for 1 s, and an increase of 2.6 +/- 0.5 % (n = 33) after vibratory skin stimulation at 50 Hz for 1 s applied to the plantar hindpaw. These responses were large enough to allow visualization of the neural activity without having to average a number of trials. The distribution of the fluorescence responses after electrical or vibratory skin stimulation was comparable to that of the cortical field potentials in the same rats. The fluorescence responses were followed by an increase in arterial blood flow. The former were resistant to an inhibitor of nitric oxide synthase, while the latter was inhibited. Thus, activity-dependent changes in the autofluorescence of flavoproteins are useful for functional brain imaging in vivo.

DOI： 10.1113/jphysiol.2003.040709

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI IRELAND LTD  

We developed a new method to visualize the myeloarchitecture in fresh slices, and investigated the properties of the functional neural connections around the boundary between the primary auditory cortex (area 41) and area 18a in rat cerebral slices. A fresh slice illuminated by near-vertical light was observed with a CCD camera. The translucent images of the slice showed contrast patterns very similar to mycloarchitecture. The boundary between these areas was identified by the well-developed layer IV/V in area 41 but not in area 18a. Antidromic/presynaptic components of the field potentials stimulated and recorded across the areal boundary showed symmetric distribution, while the postsynaptic field potentials in the direction from area 41 to 18a were more prominent than those in the opposite direction in layer II/III. In contrast, the dominant direction of propagation of postsynaptic potentials was from area 18a to 41 in layer V. In the presence of 1 muM bicuculline, an inhibitor of GABA(A) receptors, the polysynaptic activities propagating from area 18a into 41 via layer V were elicited by stimulation of area 18a. The propagation measured by Ca2+ imaging or field potential recordings was potentiated after both areas 18a and 41 were alternately stimulated several times. (C) 2003 Elsevier Science Ireland Ltd and Japan Neuroscience Society. All rights reserved.

DOI： 10.1016/S0168-0102(03)00059-2

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS UNITED KINGDOM  

Proteins of the tolloid/bone morphogenetic protein (BMP)-1 family play important roles in the differentiation of cell fates, Among those proteins are BMP-1, which plays a role in cartilage and bone formation in mammals, the TOLLOID protein, which is required for the establishment of the dorsoventral axis of Drosophila embryos and BP10/SpAN, which are thought to act in the morphogenesis of sea urchins, These proteins have some properties in common, First, they contain the astacin metalloprotease domain, the CUB domain and the epidermal growth factor-like domain, Second, they are expressed in embryos at stages expected for their role in cell differentiation. Third, at least BMP-1 and TOLLOID are thought to interact with proteins of the transforming growth factor-beta family. We report that the hch-1 gene of the nematode Caenorhabditis elegans encodes a tolloid/BMP-1 family protein, The protein has the characteristic domains common to the tolloid/BMP-1 family, Like other members of the family, it is expressed in embryos, However, the phenotype of hch-1 mutants shows that it is required for normal hatching and normal migration of a post-embryonic neuroblast. Furthermore, in spite of its expression in embryogenesis, it is not required for the viability of embryos, These results show new functions of the tolloid/BMP-1 family proteins and give insight into their evolution.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG WIEN  

To clarify the role of acidic amino acid residues in the ''fusion segment'' of hemagglutinin (HA) of influenza A virus (H1N1) in pH-dependent membrane fusion, we have constructed and expressed five mutant HA cDNAs in CV-1 cells by SV40-HA virus vectors (SVHA). Fusion activities of the five mutant HAs were examined by lipid mixing and polykaryon formation assays. In spite of the substitution of Gly and Lys for the acidic residues, all the mutants were found to retain their low-pH-dependent fusion activity by lipid mixing assay. Although SVHA-G19(HA(2)19D-->G), -K11(HA(2)11E-->K) and -K19(HA(2)19D-->K) induced polykaryon formation at low pH as wild type HA did, SVHA-G11(HA(2)11E-->G) induced limited polykaryon formation and SVHA-G11,19 (HA(2)11E-->G, 19D-->G) did not. The substitution of Gly for Glu at position 11 inhibited widening of the initial fusion pore. However, Lys mutants induced the formation of an initial fusion pore and widened it at low pH where Lys residues might have positive charges. These results suggest that the neutralization of the charges on acidic residues in the ''fusion segment'' at low pH is not important for interaction of the ''fusion segment'' with the target lipid bilayer or for triggering the membrane fusion.

DOI： 10.1007/BF01314963

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BIOPHYSICAL SOCIETY  

We have synthesized five amphiphilic anionic peptides derived from E5 peptide [Murata, M., Takahashi, S., Kagiwada, S., Suzuki, A., Ohnishi, S. 1992. Biochemistry 31:1986-1992. E5NN and E5CC are duplications of the N-terminal and the C-terminal halves of E5, respectively, and E5CN is an inversion of the N- and the C-terminal halves. E5P contains a Pro residue in the center of E5 and E8 has 8 Glu residues and 9 Leu residues, We studied fusion of dioleoylphosphatidylcholine (DOPC) large unilamellar vesicles assayed by fluorescent probes. The peptides formed alpha-helical structure with different degrees; E5NN, E5CN, and E8 with high helical content and E5CC and E5P with low helical content. These peptides bound to DOPC vesicles at acidic pH in proportion to the helical content of peptide. The peptides caused leakage of DOPC vesicles which increased with decreasing pH. The leakage was also proportional to the helicity of peptide. Highly helical peptides E5NN, E5CN, and E8 caused hemolysis at acidic pH but not at neutral pH. The fusion activity was also dependent on the helicity of peptides. In fusion induced by an equimolar mixture of E5 analogues and K5 at neutral pH, E8, E5NN, and E5CN were most active but E5CC did not cause fusion. In fusion induced by E5-analogue peptides alone, E5CN was active at acidic pH but not at neutral pH. Other peptides did not cause fusion. Amphiphilic peptides also appear to require other factors to cause fusion.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Fusion of Golgi membranes isolated from rabbit liver with liposomes was studied by lipid mixing of fluorescent lipid analogues and internal content mixing and by electron microscopic observation of transfer of horseradish peroxidase from liposomes into Golgi membranes. A monoclonal antibody was used to confirm fusion of Golgi membranes but not other contaminating vesicles. Fusion was rapid and efficient, reaching about 20% of the maximum after a 5-min incubation using small or large unilamellar dioleoylphosphatidylcholine vesicles. The fusion was dependent on temperature, decreasing at lower temperatures, and becoming nearly zero below 10-degrees-C. The addition of ATP, GTP, cytosolic factors, or N-ethylmaleimide did not affect fusion. Treatments of Golgi membranes with 0.1 M Na2CO3 or 1 M KCl did not cause any changes in fusion. However, treatment with proteases inhibited fusion. These results suggest that Golgi integral membrane protein(s) are involved in fusion. Changing the medium to an isoosmotic substance, sucrose, in place of KCl or NaCl inhibited fusion. The binding assay of fluorescent liposomes to Golgi membranes showed that lowering the temperature or replacing salts with sucrose did not affect binding. However, treatment of Golgi membranes with proteases inhibited binding. Addition of phosphatidylserine or phosphatidylethanolamine to dioleoylphosphatidylcholine liposomes caused a 2-fold increase in binding and fusion. Fusion between Golgi membranes by themselves did not occur. These results provide some information on the mechanism of intracellular vesicular transport.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDITIONS SCIENTIFIQUES ELSEVIER  

We have developed a reconstituted model system to study the interaction of the Golgi membranes isolated from rabbit liver with taxol-stabilized bovine-brain microtubules without microtubule-associated proteins (MAPs). The Golgi membranes are associated with microtubules. The sheets of vesicles and the membranous tubules are observed along microtubules by direct visualization using differential-interference-contrast, dark field, or fluorescence microscopy. The monoclonal antibody against Golgi membranes suggests that the Golgi membranes, but not the contaminating vesicles, are interacting with microtubules. The degree of association is assayed quantitatively using rhodamine-labeled microtubules after separation of the complex from unbound microtubules by centrifugation upon sucrose gradient, The association is inhibited by crude MAPs, purified MAP2, or 1.0 mM ATP. However, the association neither requires the cytosol from rat liver or bovine brain nor N-ethylmaleimide, brefeldin A, or GTP-gamma-S. The association is mediated by trypsin-sensitive peripheral protein(s) on the Golgi membranes.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

DOI： 10.1016/0006-291X(91)91925-3

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Language：Japanese  

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Language：Japanese  

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Authorship：Lead author   Language：Japanese  

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