研究者詳細 - 田中　謙二

論文 - 田中　謙二

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Heparan Sulfate Organizes Neuronal Synapses through Neurexin Partnerships

Zhang P., Lu H., Peixoto R., Pines M., Ge Y., Oku S., Siddiqui T., Xie Y., Wu W., Archer-Hartmann S., Yoshida K., Tanaka K., Aricescu A., Azadi P., Gordon M., Sabatini B., Wong R., Craig A.

Cell （Cell） 174 （ 6 ） 1450 - 1464.e23 2018年09月

ISSN 00928674

© 2018 Elsevier Inc. Synapses are fundamental units of communication in the brain. The prototypical synapse-organizing complex neurexin-neuroligin mediates synapse development and function and is central to a shared genetic risk pathway in autism and schizophrenia. Neurexin's role in synapse development is thought to be mediated purely by its protein domains, but we reveal a requirement for a rare glycan modification. Mice lacking heparan sulfate (HS) on neurexin-1 show reduced survival, as well as structural and functional deficits at central synapses. HS directly binds postsynaptic partners neuroligins and LRRTMs, revealing a dual binding mode involving intrinsic glycan and protein domains for canonical synapse-organizing complexes. Neurexin HS chains also bind novel ligands, potentially expanding the neurexin interactome to hundreds of HS-binding proteins. Because HS structure is heterogeneous, our findings indicate an additional dimension to neurexin diversity, provide a molecular basis for fine-tuning synaptic function, and open therapeutic directions targeting glycan-binding motifs critical for brain development. Neurexins, major synaptic-organizing proteins, are heparan sulfate (HS) proteoglycans, and HS modification is required for neurexin functions in synaptic transmission, development, and behavior.

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5-HT<inf>3</inf> antagonists decrease discounting rate without affecting sensitivity to reward magnitude in the delay discounting task in mice

Mori M., Tsutsui-Kimura I., Mimura M., Tanaka K.

Psychopharmacology （Psychopharmacology） 235 （ 9 ） 2619 - 2629 2018年09月

ISSN 00333158

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Rationale: Impulsive choice has often been evaluated in rodents according to the proportion of choices for the delayed large magnitude reinforcer (%large choice) in a delay-discounting task (DDT). However, because %large choice is influenced by both sensitivity to reinforcer magnitude and sensitivity to delayed reinforcement (i.e., discounting rate), distinctively evaluating such discounting parameters represents a critical issue demanding methods to determine each parameter in rats. The serotonin (5-HT) system is well known to be involved in impulsive choice; nevertheless, only a few studies have distinguished discounting parameters and investigated how 5-HT modulators affect discounting rate. Objective: Here, we performed a discounting parameter analysis in mice and examined the effects of various 5-HT modulators on discounting rate. Methods: We set up DDTs with different delay schedules to determine which schedule could address delay-discounting rates in mice. We examined the effect of the following drugs on impulsive choice: a 5-HT reuptake inhibitor (paroxetine), a 5-HT1A receptor agonist (8-OH-DPAT), and two 5-HT3 receptor antagonists (granisetron and ondansetron). Results: Mice showed typical delay discounting at the shorter delay schedules (up to 4 s delay). The %large choice under shorter, but not longer, schedules followed an exponential function and allowed us to derive discounting rates. We selected a DDT with a 4-s delay schedule for further experiments. Granisetron and ondansetron, but not paroxetine or 8-OH-DPAT, decreased discounting rates without affecting sensitivity to reinforcer magnitude. Conclusion: We found that a method to calculate discounting rates in rats is also applicable to mouse models. We also provided evidence that 5-HT3 antagonism controls impulsive choice in mice.

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Optogenetic astrocyte activation evokes BOLD fMRI response with oxygen consumption without neuronal activity modulation

Takata N., Sugiura Y., Yoshida K., Koizumi M., Hiroshi N., Honda K., Yano R., Komaki Y., Matsui K., Suematsu M., Mimura M., Okano H., Tanaka K.

GLIA （GLIA） 66 （ 9 ） 2013 - 2023 2018年09月

ISSN 08941491

© 2018 Wiley Periodicals, Inc. Functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) signal has been used to infer sites of neuronal activation in the brain. A recent study demonstrated, however, unexpected BOLD signal generation without neuronal excitation, which led us to hypothesize the presence of another cellular source for BOLD signal generation. Collective assessment of optogenetic activation of astrocytes or neurons, fMRI in awake mice, electrophysiological measurements, and histochemical detection of neuronal activation, coherently suggested astrocytes as another cellular source. Unexpectedly, astrocyte-evoked BOLD signal accompanied oxygen consumption without modulation of neuronal activity. Imaging mass spectrometry of brain sections identified synthesis of acetyl-carnitine via oxidative glucose metabolism at the site of astrocyte-, but not neuron-evoked BOLD signal. Our data provide causal evidence that astrocytic activation alone is able to evoke BOLD signal response, which may lead to reconsideration of current interpretation of BOLD signal as a marker of neuronal activation.

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Calcium Transient Dynamics of Neural Ensembles in the Primary Motor Cortex of Naturally Behaving Monkeys

Kondo T., Saito R., Otaka M., Yoshino-Saito K., Yamanaka A., Yamamori T., Watakabe A., Mizukami H., Schnitzer M., Tanaka K., Ushiba J., Okano H.

Cell Reports （Cell Reports） 24 （ 8 ） 2191 - 2195.e4 2018年08月

© 2018 The Authors To understand brain circuits of cognitive behaviors under natural conditions, we developed techniques for imaging neuronal activities from large neuronal populations in the deep layer cortex of the naturally behaving common marmoset. Animals retrieved food pellets or climbed ladders as a miniature fluorescence microscope monitored hundreds of calcium indicator-expressing cortical neurons in the right primary motor cortex. This technique, which can be adapted to other brain regions, can deepen our understanding of brain circuits by facilitating longitudinal population analyses of neuronal representation associated with cognitive naturalistic behaviors and their pathophysiological processes. Kondo et al. demonstrate calcium imaging from neuronal populations using a miniature fluorescence microscope in naturally behaving non-human primates (NHPs), common marmosets. This technique marks an advance beyond methods that use fixed head positioning, which limits the study of complex, self-determined behaviors such as social interactions or fear and anxiety.

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Chemical Landscape for Tissue Clearing Based on Hydrophilic Reagents

Tainaka K., Murakami T., Susaki E., Shimizu C., Saito R., Takahashi K., Hayashi-Takagi A., Sekiya H., Arima Y., Nojima S., Ikemura M., Ushiku T., Shimizu Y., Murakami M., Tanaka K., Iino M., Kasai H., Sasaoka T., Kobayashi K., Miyazono K., Morii E., Isa T., Fukayama M., Kakita A., Ueda H.

Cell Reports （Cell Reports） 24 （ 8 ） 2196 - 2210.e9 2018年08月

© 2018 The Author(s) We describe a strategy for developing hydrophilic chemical cocktails for tissue delipidation, decoloring, refractive index (RI) matching, and decalcification, based on comprehensive chemical profiling. More than 1,600 chemicals were screened by a high-throughput evaluation system for each chemical process. The chemical profiling revealed important chemical factors: salt-free amine with high octanol/water partition-coefficient (logP) for delipidation, N-alkylimidazole for decoloring, aromatic amide for RI matching, and protonation of phosphate ion for decalcification. The strategic integration of optimal chemical cocktails provided a series of CUBIC (clear, unobstructed brain/body imaging cocktails and computational analysis) protocols, which efficiently clear mouse organs, mouse body including bone, and even large primate and human tissues. The updated CUBIC protocols are scalable and reproducible, and they enable three-dimensional imaging of the mammalian body and large primate and human tissues. This strategy represents a future paradigm for the rational design of hydrophilic clearing cocktails that can be used for large tissues. Tainaka et al. describe a strategy for developing hydrophilic tissue-clearing reagents based on comprehensive chemical profiling. The strategic integration of optimal chemical cocktails provided a series of CUBIC protocols, which enable the 3D imaging of the mammalian body and large primate and human tissues.

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Anti-Depressant Fluoxetine Reveals its Therapeutic Effect Via Astrocytes

Kinoshita M., Hirayama Y., Fujishita K., Shibata K., Shinozaki Y., Shigetomi E., Takeda A., Le H., Hayashi H., Hiasa M., Moriyama Y., Ikenaka K., Tanaka K., Koizumi S.

EBioMedicine （EBioMedicine） 32 72 - 83 2018年06月

© 2018 The Authors Although psychotropic drugs act on neurons and glial cells, how glia respond, and whether glial responses are involved in therapeutic effects are poorly understood. Here, we show that fluoxetine (FLX), an anti-depressant, mediates its anti-depressive effect by increasing the gliotransmission of ATP. FLX increased ATP exocytosis via vesicular nucleotide transporter (VNUT). FLX-induced anti-depressive behavior was decreased in astrocyte-selective VNUT-knockout mice or when VNUT was deleted in mice, but it was increased when astrocyte-selective VNUT was overexpressed in mice. This suggests that VNUT-dependent astrocytic ATP exocytosis has a critical role in the therapeutic effect of FLX. Released ATP and its metabolite adenosine act on P2Y 11 and adenosine A2b receptors expressed by astrocytes, causing an increase in brain-derived neurotrophic factor in astrocytes. These findings suggest that in addition to neurons, FLX acts on astrocytes and mediates its therapeutic effects by increasing ATP gliotransmission.

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Aberrant astrocyte Ca 2+ signals “AxCa signals” exacerbate pathological alterations in an Alexander disease model

Saito K., Shigetomi E., Yasuda R., Sato R., Nakano M., Tashiro K., Tanaka K., Ikenaka K., Mikoshiba K., Mizuta I., Yoshida T., Nakagawa M., Mizuno T., Koizumi S.

GLIA （GLIA） 66 （ 5 ） 1053 - 1067 2018年05月

ISSN 08941491

© 2018 Wiley Periodicals, Inc. Alexander disease (AxD) is a rare neurodegenerative disorder caused by gain of function mutations in the glial fibrillary acidic protein (GFAP) gene. Accumulation of GFAP proteins and formation of Rosenthal fibers (RFs) in astrocytes are hallmarks of AxD. However, malfunction of astrocytes in the AxD brain is poorly understood. Here, we show aberrant Ca 2+ responses in astrocytes as playing a causative role in AxD. Transcriptome analysis of astrocytes from a model of AxD showed age-dependent upregulation of GFAP, several markers for neurotoxic reactive astrocytes, and downregulation of Ca 2+ homeostasis molecules. In situ AxD model astrocytes produced aberrant extra-large Ca 2+ signals “AxCa signals”, which increased with age, correlated with GFAP upregulation, and were dependent on stored Ca 2+ . Inhibition of AxCa signals by deletion of inositol 1,4,5-trisphosphate type 2 receptors (IP3R2) ameliorated AxD pathogenesis. Taken together, AxCa signals in the model astrocytes would contribute to AxD pathogenesis.

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A three-dimensional single-cell-resolution whole-brain atlas using CUBIC-X expansion microscopy and tissue clearing

Murakami T., Mano T., Saikawa S., Horiguchi S., Shigeta D., Baba K., Sekiya H., Shimizu Y., Tanaka K., Kiyonari H., Iino M., Mochizuki H., Tainaka K., Ueda H.

Nature Neuroscience （Nature Neuroscience） 21 （ 4 ） 625 - 637 2018年04月

ISSN 10976256

© 2018 The Author(s). A three-dimensional single-cell-resolution mammalian brain atlas will accelerate systems-level identification and analysis of cellular circuits underlying various brain functions. However, its construction requires efficient subcellular-resolution imaging throughout the entire brain. To address this challenge, we developed a fluorescent-protein-compatible, whole-organ clearing and homogeneous expansion protocol based on an aqueous chemical solution (CUBIC-X). The expanded, well-cleared brain enabled us to construct a point-based mouse brain atlas with single-cell annotation (CUBIC-Atlas). CUBIC-Atlas reflects inhomogeneous whole-brain development, revealing a significant decrease in the cerebral visual and somatosensory cortical areas during postnatal development. Probabilistic activity mapping of pharmacologically stimulated Arc-dVenus reporter mouse brains onto CUBIC-Atlas revealed the existence of distinct functional structures in the hippocampal dentate gyrus. CUBIC-Atlas is shareable by an open-source web-based viewer, providing a new platform for whole-brain cell profiling.

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日中の運動によりもたらされる「良質な睡眠」の脳内機序の解明　脳内アストロサイトの細胞内エネルギー状態に着目して

夏堀晃世, 辛島彰洋, 山本正道, 小島崇, 児玉亨, 高田則雄, 田中謙二, 本多真

若手研究者のための健康科学研究助成成果報告書（(公財)明治安田厚生事業団）（ 33 ） 88 - 92 2018年04月

Near-infrared deep brain stimulation via upconversion nanoparticle–mediated optogenetics

Chen S., Weitemier A., Zeng X., He L., Wang X., Tao Y., Huang A., Hashimotodani Y., Kano M., Iwasaki H., Parajuli L., Okabe S., Loong Teh D., All A., Tsutsui-Kimura I., Tanaka K., Liu X., McHugh T.

Science （Science） 359 （ 6376 ） 679 - 684 2018年02月

ISSN 00368075

2017 © The Authors. Optogenetics has revolutionized the experimental interrogation of neural circuits and holds promise for the treatment of neurological disorders. It is limited, however, because visible light cannot penetrate deep inside brain tissue. Upconversion nanoparticles (UCNPs) absorb tissue-penetrating near-infrared (NIR) light and emit wavelength-specific visible light. Here, we demonstrate that molecularly tailored UCNPs can serve as optogenetic actuators of transcranial NIR light to stimulate deep brain neurons. Transcranial NIR UCNP-mediated optogenetics evoked dopamine release from genetically tagged neurons in the ventral tegmental area, induced brain oscillations through activation of inhibitory neurons in the medial septum, silenced seizure by inhibition of hippocampal excitatory cells, and triggered memory recall. UCNP technology will enable less-invasive optical neuronal activity manipulation with the potential for remote therapy.

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Role of purinergic receptor P2Y1 in spatiotemporal Ca2+ dynamics in astrocytes

Shigetomi E., Hirayama Y., Ikenaka K., Tanaka K., Koizumi S.

Journal of Neuroscience （Journal of Neuroscience） 38 （ 6 ） 1383 - 1395 2018年02月

ISSN 02706474

© 2018 the authors. Fine processes of astrocytes enwrap synapses and are well positioned to sense neuronal information via synaptic transmission. In rodents, astrocyte processes sense synaptic transmission via Gq-protein coupled receptors (GqPCR), including the P2Y1 receptor (P2Y1R), to generate Ca2+signals. Astrocytes display numerous spontaneous microdomain Ca2+signals; however, it is not clear whether such signals are due to local synaptic transmission and/or in what timeframe astrocytes sense local synaptic transmission. To ask whether GqPCRs mediate microdomain Ca2+ signals, we engineered mice (both sexes) to specifically overexpress P2Y1Rs in astrocytes, and we visualized Ca2+ signals via a genetically encoded Ca2+ indicator, GCaMP6f, in astrocytes from adult mice. Astrocytes overexpressing P2Y1Rs showed significantly larger Ca2+ signals in response to exogenously applied ligand and to repetitive electrical stimulation of axons compared with controls. However, we found no evidence of increased microdomain Ca2+signals. Instead, Ca2+waves appeared and propagated to occupy areas that were up to 80-fold larger than microdomain Ca2+ signals. These Ca2+ waves accounted for only 2% of total Ca2+ events, but they were 1.9-fold larger and 2.9-fold longer in duration than microdomain Ca2+ signals at processes. Ca2+ waves did not require action potentials for their generation and occurred in a probenecid-sensitive manner, indicating that the endogenous ligand for P2Y1R is elevated independently of synaptic transmission. Our data suggest that spontaneous microdomain Ca2+ signals occur independently of P2Y1R activation and that astrocytes may not encode neuronal information in response to synaptic transmission at a point source of neurotransmitter release.

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Amplitude and frequency feature extraction of neural activity in mouse ventrolateral striatum under different motivational states using fiber photometric system

Imai S., Mitsukura Y., Yoshida K., Tsutsui-Kimura I., Takata N., Tanaka K.

2017 IEEE Signal Processing in Medicine and Biology Symposium, SPMB 2017 - Proceedings （2017 IEEE Signal Processing in Medicine and Biology Symposium, SPMB 2017 - Proceedings） 2018-January 1 - 6 2018年01月

ISSN 9781538648735

© 2017 IEEE. In this paper, we focused on the motivation of mice and aimed to extract neural activity features of D2 medium spiny neurons (D2-MSNs) in the ventrolateral striatum of mice under different motivational states. Motivated behavior is defined as the activation of goal-directed behavior, and this enables actions such as ingestion, sleeping and reproduction, which are essential for living. In human society, motivation allows us to participate in society, improving our quality of life. Loss of motivation has been causing problems such as withdrawal from society. If the symptom is heavy, it can even threaten our lives, and treatment is necessary. The mechanisms which lead to loss of motivation are yet to be understood, and an effective treatment does not exist. To solve these problems, we decided to find features in the neural activity which affect motivation, because understanding the mechanism may contribute to the establishment of treatment. In the experiment, the neural activity was recorded using gene-encoded ratio metric calcium ion (Ca2+) indicator and by constructing a fiber photometric system, which enabled recording of neural activity at specific brain region for specific type of neurons. While the recording took place, mice performed food-incentive leverpressing tasks, which were used to define motivational states. The experimental results show that both the amplitude and frequency components of Ca2+ fluctuation have features which are good predictors of motivational states.

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Hippocampal activity during serotonergic neuronal activity manipulation using optogenetics

Kondo D., Mitsukura Y., Yoshida K., Tsutsui-Kimura I., Takata N., Tanaka K.

ISSN 9781538648735

© 2017 IEEE. In order to improve brain dysfunction such as mental disease, it is necessary to clarify the mechanism of activity in the brain. To clarify the relationship between the brain region and the neurotransmitter is important for elucidating the brain. Especially investigating the relationship between serotonin and hippocampus leads to elucidate of the mechanism of depression and sleep. The technique called optogenetics enabled only specific cells to be manipulated by light stimulation in recent years. This technique is a useful technique for clarifying the function of the brain. Because instead of stimulating multiple cells such as electrical stimulation, optogenetics can stimulate only specific cells, so that its function can be clarified. This study focused on neurotransmitter serotonin and the brain region called the hippocampus. For these purpose we can clarify the relationship between serotonin and hippocampus by manipulating serotonin neural activity using optogenetics while invasively measuring the ventral hippocampus of the mouse. In addition, identification of pyramidal cell layer is necessary to clarify hippocampal activity. Currently, visual estimation is performed based on the histology that dissected the brain, it still has a problem. Now this technique can't estimate ambiguous of the brain part and measure in an online manner. For this problem, we focus on the clarity of the brain part estimation when we used optogenetics. Therefore, we could estimate the pyramidal cell layer of the hippocampus by analyzing nerve activity and thought that the effect of serotonin activation or suppression on the hippocampus could be clarified. As a result, we showed that pyramidal cell layer can be identified by using principal component analysis, and could clarify the variation of nerve activity in the pyramidal cell layer of hippocampus during serotonin operation.

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Abrogated freud-1/Cc2d1a repression of 5-HT1A autoreceptors induces fluoxetine-resistant anxiety/ depression-like behavior

Vahid-Ansari Faranak, Daigle Mireille, Manzini M. Chiara, Tanaka Kenji F., Hen René, Geddes Sean D., Béïque Jean Claude, James Jonathan, Merali Zul, Albert Paul R.

Journal of Neuroscience 37 （ 49 ） 11967 - 11978 2017年12月

ISSN 0270-6474

Freud-1/Cc2d1a represses the gene transcription of serotonin-1A (5-HT1A) autoreceptors, which negatively regulate 5-HT tone. To test the role of Freud-1 in vivo, we generated mice with adulthood conditional knock-out of Freud-1 in 5-HT neurons (cF1ko). In cF1ko mice, 5-HT1A autoreceptor protein, binding and hypothermia response were increased, with reduced 5-HT content and neuronal activity in the dorsal raphe. The cF1ko mice displayed increased anxiety- and depression-like behavior that was resistant to chronic antidepressant (fluoxetine) treatment. Using conditional Freud-1/5-HT1A double knock-out (cF1/1A dko) to disrupt both Freud-1 and 5-HT1A genes in 5-HT neurons, no increase in anxiety- or depression-like behavior was seen upon knock-out of Freud-1 on the 5-HT1A autoreceptor-negative background; rather, a reduction in depression-like behavior emerged. These studies implicate transcriptional dysregulation of 5-HT1A autoreceptors by the repressor Freud-1 in anxiety and depression and provide a clinically relevant genetic model of antidepressant resistance. Targeting specific transcription factors, such as Freud-1, to restore transcriptional balance may augment response to antidepressant treatment.

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Time-controllable Nkcc1 knockdown replicates reversible hearing loss in postnatal mice

Watabe Takahisa, Xu Ming, Watanabe Miho, Nabekura Junichi, Higuchi Taiga, Hori Karin, Sato Mitsuo P., Nin Fumiaki, Hibino Hiroshi, Ogawa Kaoru, Masuda Masatsugu, Tanaka Kenji F.

Scientific Reports 7 （ 1 ） 2017年12月

ISSN 2045-2322

Identification of the causal effects of specific proteins on recurrent and partially reversible hearing loss has been difficult because of the lack of an animal model that provides reversible gene knockdown. We have developed the transgenic mouse line Actin-tTS::Nkcc1^tetO/tetO for manipulatable expression of the cochlear K⁺ circulation protein, NKCC1. Nkcc1 transcription was blocked by the binding of a tetracycline-dependent transcriptional silencer to the tetracycline operator sequences inserted upstream of the Nkcc1 translation initiation site. Administration of the tetracycline derivative doxycycline reversibly regulated Nkcc1 knockdown. Progeny from pregnant/lactating mothers fed doxycycline-free chow from embryonic day 0 showed strong suppression of Nkcc1 expression (∼90% downregulation) and Nkcc1 null phenotypes at postnatal day 35 (P35). P35 transgenic mice from mothers fed doxycycline-free chow starting at P0 (delivery) showed weaker suppression of Nkcc1 expression (∼70% downregulation) and less hearing loss with mild cochlear structural changes. Treatment of these mice at P35 with doxycycline for 2 weeks reactivated Nkcc1 transcription to control levels and improved hearing level at high frequency; i.e., these doxycycline-treated mice exhibited partially reversible hearing loss. Thus, development of the Actin-tTS::Nkcc1^tetO/tetO transgenic mouse line provides a mouse model for the study of variable hearing loss through reversible knockdown of Nkcc1.

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Serotonin hormonally regulates lacrimal gland secretory function via the serotonin type 3a receptor

Imada Toshihiro, Nakamura Shigeru, Hisamura Ryuji, Izuta Yusuke, Jin Kai, Ito Masataka, Kitamura Naoki, Tanaka Kenji F., Mimura Masaru, Shibuya Izumi, Tsubota Kazuo

Scientific Reports 7 （ 1 ） 2017年12月

ISSN 2045-2322

Tears are extracellular fluid secreted from the lacrimal gland (LG). Tears consist of a dynamic tri-layered film composed of secretions from the LG, Meibomian gland, and conjunctival goblet cells. The LG secretes the aqueous component of the tear, the Meibomian gland secretes the lipid component, and conjunctival goblet cells secrete mucin. The regulation of LG activity via the autonomic nervous system has been recognized as fundamental to maintaining aqueous tear flow. Here, we describe the role of a hormone, peripheral serotonin, in tear secretion. We found that blood serotonin concentration, changed by feeding a diet deprived of the serotonin precursor tryptophan, correlated with tear secretion, and that a sustained decrease in serotonin resulted in LG atrophy and autophagy. The combination of a decrease in serotonin with the interruption of autonomic neural stimuli to the LG preceded these alterations. Furthermore, we found that the serotonin type 3a receptor expressed in LG acinar cells is involved in tear secretion via intracellular calcium mobilization. Our findings demonstrate that hormonal regulation by serotonin, in cooperation with the autonomic nervous system, regulates tear secretion.

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Maturation of Cerebellar Purkinje Cell Population Activity during Postnatal Refinement of Climbing Fiber Network

Good Jean Marc, Mahoney Michael, Miyazaki Taisuke, Tanaka Kenji F., Sakimura Kenji, Watanabe Masahiko, Kitamura Kazuo, Kano Masanobu

Cell Reports 21 （ 8 ） 2066 - 2073 2017年11月

ISSN 2211-1247

Neural circuits undergo massive refinements during postnatal development. In the developing cerebellum, the climbing fiber (CF) to Purkinje cell (PC) network is drastically reshaped by eliminating early-formed redundant CF to PC synapses. To investigate the impact of CF network refinement on PC population activity during postnatal development, we monitored spontaneous CF responses in neighboring PCs and the activity of populations of nearby CF terminals using in vivo two-photon calcium imaging. Population activity is highly synchronized in newborn mice, and the degree of synchrony gradually declines during the first postnatal week in PCs and, to a lesser extent, in CF terminals. Knockout mice lacking P/Q-type voltage-gated calcium channel or glutamate receptor δ2, in which CF network refinement is severely impaired, exhibit an abnormally high level of synchrony in PC population activity. These results suggest that CF network refinement is a structural basis for developmental desynchronization and maturation of PC population activity. In the cerebellum, the climbing fiber to Purkinje cell network is extensively remodeled during postnatal development. Good et al. show that in vivo population activity of Purkinje cells in response to climbing fiber synaptic inputs is highly synchronized in newborn mice and massively desynchronized due to climbing fiber network refinement.

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Mitochondrial DNA double-strand breaks in oligodendrocytes cause demyelination, axonal injury, and CNS inflammation

Madsen Pernille M., Pinto Milena, Patel Shreyans, McCarthy Stephanie, Gao Han, Taherian Mehran, Karmally Shaffiat, Pereira Claudia V., Dvoriantchikova Galina, Ivanov Dmitry, Tanaka Kenji F., Moraes Carlos T., Brambilla Roberta

Journal of Neuroscience 37 （ 42 ） 10185 - 10199 2017年10月

ISSN 0270-6474

Mitochondrial dysfunction has been implicated in the pathophysiology of neurodegenerative disorders, including multiple sclerosis (MS). To date, the investigation of mitochondrial dysfunction in MS has focused exclusively on neurons, with no studies exploring whether dysregulation of mitochondrial bioenergetics and/or genetics in oligodendrocytes might be associated with the etiopathogenesis of MS and other demyelinating syndromes. To address this question, we established a mouse model where mitochondrial DNA (mtDNA) double-strand breaks (DSBs) were specifically induced in myelinating oligodendrocytes (PLP:mtPstI mice) by expressing a mitochondrial-targeted endonuclease, mtPstI, starting at 3 weeks of age. In both female and male mice, DSBs of oligodendroglial mtDNA caused impairment of locomotor function, chronic demyelination, glial activation, and axonal degeneration, which became more severe with time of induction. In addition, after short transient induction of mtDNA DSBs, PLP:mtPstI mice showed an exacerbated response to experimental autoimmune encephalomyelitis. Together, our data demonstrate that mtDNA damage can cause primary oligodendropathy, which in turn triggers demyelination, proving PLP:mtPstI mice to be a useful tool to study the pathological consequences of mitochondrial dysfunction in oligodendrocytes. In addition, the demyelination and axonal loss displayed by PLP:mtPstI mice recapitulate some of the key features of chronic demyelinating syndromes, including progressive MS forms, which are not accurately reproduced in the models currently available. For this reason, the PLP: mtPstI mouse represents a unique and much needed platform for testing remyelinating therapies.

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Distinct Roles of Ventromedial versus Ventrolateral Striatal Medium Spiny Neurons in Reward-Oriented Behavior

Tsutsui-Kimura Iku, Natsubori Akiyo, Mori Marina, Kobayashi Kenta, Drew Michael R., de Kerchove d'Exaerde Alban, Mimura Masaru, Tanaka Kenji F.

Current Biology 27 （ 19 ） 3042 - 3048.e4 2017年10月

ISSN 0960-9822

The ventral striatum (VS) is a key brain center regulating reward-oriented behavior [1–4]. The VS can be anatomically divided into medial (VMS) and lateral (VLS) portions based on cortical input patterns. The VMS receives inputs from medial pallium-originated limbic structures (e.g., the medial prefrontal cortex [mPFC]), and the VLS receives inputs from the lateral pallium-originated areas (e.g., the insula) [5, 6]. This anatomical feature led us to hypothesize a functional segregation within the VS in terms of the regulation of reward-oriented behavior. Here, we engineered a fiber photometry system [4] and monitored population-level Ca²⁺ activities of dopamine D2-receptor-expressing medium spiny neurons (D2-MSNs), one of the major cell types in the striatum, during a food-seeking discrimination task. We found that VLS D2-MSNs were activated at the time of cue presentation. In stark contrast, VMS D2-MSNs were inhibited at this time point. Optogenetic counteraction of those changes in the VLS and VMS impaired action initiation and increased responding toward non-rewarded cues, respectively. During lever-press reversal training, VMS inhibition at the time of cue presentation temporarily ceased and optogenetic activation of VMS D2-MSNs facilitated acquisition of the new contingency. These data indicate that the opposing inhibition and excitation in VMS and VLS are important for selecting and initiating a proper action in a reward-oriented behavior. We propose distinct subregional roles within the VS in the execution of successful reward-oriented behavior. Tsutsui-Kimura, Natsubori, et al. find opposing activity patterns of medium spiny neurons at the medial and lateral portions of the ventral striatum during reward-oriented behavior. Each activity mediates distinct function but cooperates with successful reward-oriented behavior, proposing a new functional dichotomy of the ventral striatum.

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Hearing loss controlled by optogenetic stimulation of nonexcitable nonglial cells in the cochlea of the inner ear

Sato Mitsuo P., Higuchi Taiga, Nin Fumiaki, Ogata Genki, Sawamura Seishiro, Yoshida Takamasa, Ota Takeru, Hori Karin, Komune Shizuo, Uetsuka Satoru, Choi Samuel, Masuda Masatsugu, Watabe Takahisa, Kanzaki Sho, Ogawa Kaoru, Inohara Hidenori, Sakamoto Shuichi, Takebayashi Hirohide, Doi Katsumi, Tanaka Kenji F., Hibino Hiroshi

Frontiers in Molecular Neuroscience 10 2017年09月

ISSN 1662-5099

Light-gated ion channels and transporters have been applied to a broad array of excitable cells including neurons, cardiac myocytes, skeletal muscle cells and pancreatic β-cells in an organism to clarify their physiological and pathological roles. Nonetheless, among nonexcitable cells, only glial cells have been studied in vivo by this approach. Here, by optogenetic stimulation of a different nonexcitable cell type in the cochlea of the inner ear, we induce and control hearing loss. To our knowledge, deafness animal models using optogenetics have not yet been established. Analysis of transgenic mice expressing channelrhodopsin-2 (ChR2) induced by an oligodendrocyte-specific promoter identified this channel in nonglial cells—melanocytes—of an epithelial-like tissue in the cochlea. The membrane potential of these cells underlies a highly positive potential in a K⁺-rich extracellular solution, endolymph; this electrical property is essential for hearing. Illumination of the cochlea to activate ChR2 and depolarize the melanocytes significantly impaired hearing within a few minutes, accompanied by a reduction in the endolymphatic potential. After cessation of the illumination, the hearing thresholds and potential returned to baseline during several minutes. These responses were replicable multiple times. ChR2 was also expressed in cochlear glial cells surrounding the neuronal components, but slight neural activation caused by the optical stimulation was unlikely to be involved in the hearing impairment. The acute-onset, reversible and repeatable phenotype, which is inaccessible to conventional gene-targeting and pharmacological approaches, seems to at least partially resemble the symptom in a population of patients with sensorineural hearing loss. Taken together, this mouse line may not only broaden applications of optogenetics but also contribute to the progress of translational research on deafness.

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