Published papers

Spike-and-wave discharges (SWDs) and sleep spindles are characteristic electroencephalographic (EEG) hallmarks of absence seizures and nonrapid eye movement sleep, respectively. They are commonly generated by the cortico–thalamo–cortical network including the thalamic reticular nucleus (TRN). It has been reported that SWD development is accompanied by a decrease in sleep spindle density in absence seizure patients and animal models. However, whether the decrease in sleep spindle density precedes, coincides with, or follows, the SWD development remains unknown. To clarify this, we exploited Pvalb-tetracycline transactivator (tTA)::tetO-ArchT (PV-ArchT) double-transgenic mouse, which can induce an absence seizure phenotype in a time-controllable manner by expressing ArchT in PV neurons of the TRN. In these mice, EEG recordings demonstrated that a decrease in sleep spindle density occurred 1 week before the onset of typical SWDs, with the expression of ArchT. To confirm such temporal relationship observed in these genetic model mice, we used a gamma-butyrolactone (GBL) pharmacological model of SWDs. Prior to GBL administration, we administered caffeine to wild-type mice for 3 consecutive days to induce a decrease in sleep spindle density. We then administered low-dose GBL, which cannot induce SWDs in normally conditioned mice but led to the occurrence of SWDs in caffeine-conditioned mice. These findings indicate a temporal relationship in which the decrease in sleep spindle density consistently precedes SWD development. Furthermore, the decrease in sleep spindle activity may have a role in facilitating the development of SWDs. Our findings suggest that sleep spindle reductions could serve as early indicators of seizure susceptibility.

Serotonin is an essential neuromodulator that affects behavioral and cognitive functions. Previous studies have shown that activation of serotonergic neurons in the dorsal raphe nucleus (DRN) promotes patience to wait for future rewards. However, it is still unclear whether serotonergic neurons also regulate persistence to act for future rewards. Here we used optogenetic activation and inhibition of DRN serotonergic neurons to examine their effects on sustained motor actions for future rewards. We trained mice to perform waiting and repeated lever-pressing tasks with variable reward delays and tested effects of optogenetic activation and inhibition of DRN serotonergic neurons on task performance. Interestingly, in the lever-pressing task, mice tolerated longer delays as they repeatedly pressed a lever than in the waiting task, suggesting that lever-pressing actions may not simply be costly, but may also be subjectively rewarding. Optogenetic activation of DRN serotonergic neurons prolonged waiting duration in the waiting task, consistent with previous studies. However, its effect on lever presses was nuanced, and was detected only by focusing on the period before premature reward check and by subtracting the trends within and across sessions using generalized linear model. While optogenetic inhibition decreased waiting, it did not affect lever pressing time or numbers. These results revealed that the necessity of motor actions may increase motivation for delayed rewards and that DRN serotonergic neurons more significantly promote waiting rather than persistent motor actions for future rewards.

Oligodendrocyte (OL) differentiation from oligodendrocyte precursor cells (OPCs) is considered to result in two populations: premyelinating and myelinating OLs. Recent single-cell RNA sequence data subdivided these populations into newly formed (NFOLs), myelin-forming (MFOLs), and mature (MOLs) oligodendrocytes. However, which newly proposed population corresponds to premyelinating or myelinating OLs is unknown. We focused on the NFOL-specific long non-coding oligodendrocyte 1 gene (LncOL1) and sought to label NFOLs under the control of the LncOL1 promoter using a tetracycline-controllable gene induction system. We demonstrated that LncOL1 was expressed by premyelinating OLs and that the MFOL-specific gene, Ctps, was not, indicating that NFOLs correspond to premyelinating OLs and that MFOLs and MOLs correspond to myelinating OLs. We then generated a LncOL1-tTA mouse in which a tetracycline transactivator (tTA) cassette was inserted downstream from the LncOL1 transcription initiation site. By crossing the LncOL1-tTA mice with tetO reporter mice, we generated LncOL1-tTA::tetO-yellow fluorescent protein (YFP) double-transgenic (LncOL1-YFP) mice. Although LncOL1 is non-coding, YFP was detected in LncOL1-YFP mice, indicating successful tTA translation. Unexpectedly, we found that the morphology of LncOL1-tTA-driven YFP+ cells was distinct from that of LncOL1+ premyelinating OLs and that the labeled cells instead appeared as myelinating OLs. We demonstrated from their RNA expression that YFP-labeled OLs were MFOLs, but not MOLs. Using the unique property of delayed YFP induction, we sought to determine whether MFOLs are constantly supplied from OPCs and differentiate into MOLs, or whether MFOLs pause their differentiation and sustain this stage in the adult brain. To achieve this objective, we irradiated adult LncOL1-YFP brains with X-rays to deplete dividing OPCs and their progeny. The irradiation extinguished YFP-labeled OLs, indicating that adult OPCs differentiated into MOLs during a single period. We established a new transgenic mouse line that genetically labels MFOLs, providing a reliable tool for investigating the dynamics of adult oligodendrogenesis. (Figure presented.).

＜文献概要＞筆者に与えられたテーマは「精神展開剤の作用機序」です。まさに今、筆者を含めた世界中の研究者もその機序解明に全力を捧げています。研究しているということはつまりわかっていないということです。じゃあ、わかっていないのに何を教えてくれるんですか?というもっともな指摘があろうかと思います。ここでは、精神看護に関わる方々に知ってもらって損のない豆知識を筆者の独断で選別して、読者の方々と共有したいと思います。

遺伝性小児神経疾患について,その原因遺伝子の同定が急速に進みつつある一方で,未だ根本的な治療法のない疾患も多い.皮質下嚢胞をもつ大頭型白質脳症(MLC)もまた,根治療法のない遺伝性小児神経疾患の1つである.MLC症例の大部分がアストロサイト特異的に発現するMLC1遺伝子の機能喪失変異によって引き起こされることから,われわれはアデノ随伴ウイルス(AAV)ベクターを用いてMLC患者に対しMLC1遺伝子補充療法を行うことを目指している.ここでは,病態モデルマウスを用いた前臨床遺伝子治療研究について報告する.(著者抄録)

＜文献概要＞レボドパ誘発性ジスキネジア(LID)と遅発性ジスキネジア(TD)は,それぞれ異なる薬剤の長期使用によって引き起こされる副作用であり,原因や治療対象は異なるにもかかわらず,共通して不随意運動という症状を示す.本研究では,この類似した病態の背景にある神経構造変化を明らかにするため,MRIによる全脳マクロ解析と,超解像顕微鏡および電子顕微鏡によるミクロ解析を組み合わせた階層的手法を用いた.その結果,両モデルマウスにおいて,淡蒼球(GPe)の線条体中型有棘ニューロン(MSN)の神経終末で小胞GABAトランスポーター(VGAT)の過剰発現と,MSN神経終末・標的細胞の肥大化が共通して認められた.さらに,VGATの発現量を操作する実験により,この構造変化がジスキネジアの原因であることが実証された.加えて,病態形成の背景には,ドパミンD2受容体シグナルの低下(1st hit)に加え,ドパミン濃度の周期的変動(2nd hit)が構造可塑性を誘導する"Two-Hit仮説"が提唱された.この成果は,構造解析技術によって病態の因果構造を明らかにし,基礎と臨床をつなぐ新たな視点を提供するものである.

男性船員の健診受診者2636例を対象に肝機能障害の実態と要因について検討した。その結果、肝機能障害は全体で63.4%(1670例)と高頻度に認められ、うち非アルコール性脂肪性肝疾患(NAFLD)が53.1%(887/1670例)、アルコール性肝障害(ALD)が43.5%(727/1670例)と大部分を占めていた。NAFLDとALDの要因は過体重・肥満、過剰飲酒であり、また、高血圧や耐糖能異常などの生活習慣病も高頻度に認めることが明らかになった。

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, social deficits, and cognitive impairments. Maternal use of valproic acid (VPA) during pregnancy is associated with an increased risk of ASD in offspring. The prevailing pathophysiological hypothesis for ASD involves excitation/inhibition (E/I) imbalances and serotonergic dysfunction. Here, we investigated the association between glutamatergic-serotonergic neuronal interactions and ASD-like behaviors in mice exposed to prenatal VPA. Prenatal VPA exposure induced excessive repetitive self-grooming behavior and impaired social behavior and object recognition memory in young adult period. Prenatal VPA mice showed hyper-glutamatergic function (increase in basal extracellular glutamate levels and CaMKII phosphorylation) and hypo-serotonergic function (decrease in 5-hydroxyindoleacetic acid and stimulation-induced serotonin [5-HT] release, but an increase in 5-HT transporter expression) in the prefrontal cortex. Treatment with a low-affinity NMDA receptor antagonist (memantine), a selective 5-HT reuptake inhibitor (fluoxetine), and a 5-HT1A receptor agonist (tandospirone) attenuated both the increase in CaMKII phosphorylation and ASD-like behavior of prenatal VPA mice. Opto-genetic activation of the serotonergic neuronal system attenuated impairments in social behavior and object recognition memory in prenatal VPA mice. WAY-100635—a 5-HT1A receptor antagonist—antagonized the effect of fluoxetine on impaired social behavior and object recognition memory. These results suggest that E/I imbalance and ASD-like behavior are associated with hypo-serotonergic receptor signaling through 5-HT1A receptors in prenatal VPA mice.

Duplication of chromosome 15q11–13 has been reported to be one of the most frequent cytogenetic copy number variations in autism spectrum disorder (ASD), and a mouse model of paternal 15q11–13 duplication was generated, termed 15q dup mice. While previous studies have replicated some of the behavioral and brain structural phenotypes of ASD separately, the relationship between brain structure and behavior has rarely been examined. In this study, we performed behavioral experiments related to anxiety and social behaviors and magnetic resonance imaging (MRI) using the same set of 15q dup and wild-type mice. 15q dup mice showed increased anxiety and a tendency toward alterations in social behaviors, as reported previously, as well as variability in terms of sociability. MRI analysis revealed that a lower sociability index was correlated with a smaller gray matter volume in the right medial entorhinal cortex. These results may help to understand how variability in behavioral phenotypes of ASD arises even in individuals with the same genetic background and to determine the individual differences in neurodevelopmental trajectory correlated with specific brain structures that underlie these phenotypes.

Reactive astrocytes play a pivotal role in the pathogenesis of neurological diseases; however, their functional phenotype and the downstream molecules by which they modify disease pathogenesis remain unclear. Here, we genetically increase P2Y1 receptor (P2Y1R) expression, which is upregulated in reactive astrocytes in several neurological diseases, in astrocytes of male mice to explore its function and the downstream molecule. This astrocyte-specific P2Y1R overexpression causes neuronal hyperexcitability by increasing both astrocytic and neuronal Ca2+ signals. We identify insulin-like growth factor-binding protein 2 (IGFBP2) as a downstream molecule of P2Y1R in astrocytes; IGFBP2 acts as an excitatory signal to cause neuronal excitation. In neurological disease models of epilepsy and stroke, reactive astrocytes upregulate P2Y1R and increase IGFBP2. The present findings identify a mechanism underlying astrocyte-driven neuronal hyperexcitability, which is likely to be shared by several neurological disorders, providing insights that might be relevant for intervention in diverse neurological disorders.

Kenji F. Tanaka is a Professor in Brain Sciences at the Institute for Advanced Medical Research, Keio University School of Medicine in Japan. He has been conducting research on glial cells for more than 20 years and is an expert in cell-type-specific and time-controllable gene expression techniques. Kenji F. Tanaka has been a member of the JNC Editorial Board since 2019 and recently transitioned to the role of Senior Editor for the new JNC manuscript category: “Neurotools, Methods, and Neurochemistry Resources”. We interviewed him to learn about his goals as Senior Editor for this category, as well as key moments in his career and advice for young scientists. (Figure presented.)

Alexander disease (AxD) is an intractable neurodegenerative disease caused by mutations in glial fibrillary acidic protein (GFAP), which is predominantly expressed in astrocytes. Thus, AxD is a primary astrocyte disease. However, it remains unclear how GFAP mutations affect astrocytes and cause AxD pathology. Three features are characteristic of AxD astrocytes in vivo: (1) Rosenthal fibers (RFs), the hallmark of AxD; (2) aberrant Ca2+ signals (AxCa); and (3) upregulation of disease-associated genes (AxGen). We established a primary culture system for astrocytes from an AxD transgenic mouse model, and used it to analyze the above features of AxD pathogenesis in astrocytes in vitro. We observed the formation of RFs in AxD primary cultures. The abundance of RFs was greater in AxD-transgene-homozygous compared with -hemizygous astrocytes, indicating a gene dosage effect, and this abundance increased with time in culture, indicating a developmental process effect. However, cultured AxD astrocytes did not exhibit changes in either AxCa or AxGen. We therefore conclude that RFs in astrocytes form via a cell-autonomous mechanism, whereas AxCa and AxGen are likely to occur via a non-cell-autonomous mechanism through interactions with other cells, such as neurons, microglia, and vascular cells. Although primary cultured AxD astrocytes are suitable for elucidating the mechanisms of RFs formation and for intervention studies, it should be noted that they cannot reflect the pathophysiology of non-cell-autonomous events in astrocytes.

Objective: This study aimed to examine the spatiotemporal coherence of capillary lumen fluctuations in relation to spatial variations in the pericyte lining in the cortex of anesthetized mice. Methods: Two-photon microscopic angiography data (previously published) were reanalyzed, and spatial variations in capillary diameter fluctuations at rest and in capillary lining with vascular mural cells were measured along capillary centerlines. Results: Relatively large diameters of the capillaries (5.5 μm) coincided with a dense pericyte lining, while small capillaries (4.3 μm) had a sparse pericyte lining. Temporal variations had a frequency of about 0.1 Hz with an amplitude of 0.5 μm, which were negatively correlated with pericyte lining density. Spatial frequency analysis further revealed a common pattern of spatial variations in capillary diameter and pericyte lining, but temporal variations differed. The temporal variations in capillary lumens were locally distinct from those in neighboring locations, suggesting intrinsic fluctuations independent of the pericyte lining. Conclusions: Capillary lumens in the brain exhibit slow microfluctuations that are independent of pericyte lining. These microfluctuations could affect the distribution of flowing blood cells and may be important for homogenizing their distribution in capillary networks.