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Kouichi Hashimoto

Publications and source records attributed to Kouichi Hashimoto.

18 recordsLinked to original sources
PubMed2006

Depolarization-induced suppression of inhibition mediated by endocannabinoids at synapses from fast-spiking interneurons to medium spiny neurons in the striatum.

Endogenous cannabinoids (endocannabinoids) act as retrograde inhibitory messengers in various regions of the brain. We have recently reported that endocannabinoids mediate short-term retrograde suppression of excitatory synaptic transmission from the neocortex to medium spiny (MS) neurons, the major projection neurons from the striatum. However, it remains unclear whether endocannabinoids modulate inhibitory transmission in the striatum. Here we show that depolarization of MS neurons induces transient suppression of inhibition that is mediated by retrograde endocannabinoid signalling. By paired recording from a fast-spiking (FS) interneuron and an MS neuron, we demonstrated that FS-MS inhibitory synapses undergo endocannabinoid-mediated retrograde suppression. We verified that GABAergic inhibitory terminals immunopositive for parvalbumin (PV), a marker for FS interneurons, expressed CB1 receptors. These PV-CB1 double-positive terminals surrounded dopamine D1 receptor-positive and D2 receptor-positive MS neurons; these constitute direct and indirect pathways, respectively. These results suggest that endocannabinoid-mediated retrograde suppression of inhibition influences information flow along both direct and indirect pathways, depending on the activity of MS neurons.

Amino Acid Sequence↗
PubMed2006

Disturbance of cerebellar synaptic maturation in mutant mice lacking BSRPs, a novel brain-specific receptor-like protein family.

By DNA cloning, we have identified the BSRP (brain-specific receptor-like proteins) family of three members in mammalian genomes. BSRPs were predominantly expressed in the soma and dendrites of neurons and localized in the endoplasmic reticulum (ER). Expression levels of BSRPs seemed to fluctuate greatly during postnatal cerebellar maturation. Triple-knockout mice lacking BSRP members exhibited motor discoordination, and Purkinje cells (PCs) were often innervated by multiple climbing fibers with different neuronal origins in the mutant cerebellum. Moreover, the phosphorylation levels of protein kinase Calpha (PKCalpha) were significantly downregulated in the mutant cerebellum. Because cerebellar maturation and plasticity require metabotropic glutamate receptor signaling and resulting PKC activation, BSRPs are likely involved in ER functions supporting PKCalpha activation in PCs.

Animals↗
PubMed2006

Endocannabinoid-mediated short-term suppression of excitatory synaptic transmission to medium spiny neurons in the striatum.

Medium spiny neurons in the dorsal striatum receive glutamatergic excitatory synaptic inputs from the cerebral cortex. These synapses undergo long-term depression that requires release of endocannabinoids from medium spiny neurons and activation of cannabinoid CB1 receptors. However, it remains unclear how cortico-striatal synapses exhibit endocannabinoid-mediated short-term suppression, which has been found in various brain regions including the hippocampus and cerebellum. Endocannabinoids are released from postsynaptic neurons by strong depolarization and resultant Ca2+ elevation or activation of postsynaptic Gq/11-coupled receptors such as group I metabotropic glutamate receptors (mGluRs) and M1/M3 muscarinic acetylcholine receptors. Moreover, endocannabioids are effectively released when weak depolarization is combined with Gq/11-coupled receptor activation. We found that muscarinic activation induced transient suppression of excitatory synaptic transmission to medium spiny neurons, which was independent of retrograde endocannabinoid signaling but was mediated directly by presynaptic muscarinic receptors. Neither postsynaptic depolarization alone nor depolarization and muscarinic activation caused suppression of cortico-striatal synapses. In contrast, activation of group I mGluRs readily suppressed cortico-striatal excitatory synaptic transmission. Furthermore, postsynaptic depolarization induced clear suppression when combined with group I mGluR activation. These results indicate that group I mGluRs but not muscarinic receptors contribute to endocannabinoid-mediated short-term suppression of cortico-striatal excitatory synaptic transmission.

Animals↗
PubMed2006

Miniature synaptic events elicited by presynaptic Ca2+ rise are selectively suppressed by cannabinoid receptor activation in cerebellar Purkinje cells.

Activation of cannabinoid receptors suppresses neurotransmitter release in various brain regions. In cerebellar Purkinje cells (PCs), cannabinoid agonists suppress both EPSC and IPSC evoked by stimulating the corresponding inputs. However, cannabinoid agonists suppress miniature IPSC (mIPSC) but not miniature EPSC (mEPSC) at normal external Ca2+ concentration ([Ca2+]o). Therefore, cannabinoid agonists are thought to suppress release machinery for IPSCs but not that for EPSCs. Here we investigated the possible cause of this difference and found that cannabinoid agonists selectively suppressed Ca2+-enhanced miniature events. A cannabinoid agonist, WIN55,212-2 (5 microM), did not affect mEPSC frequency with 2 mM extracellular Ca2+ (Ca2+(o)). However, WIN55,212-2 became effective when mEPSC frequency was enhanced by elevation of presynaptic Ca2+ level by perfusion with 5 mM Ca2+(o) or bath application of A23187, a Ca2+ ionophore. In contrast, WIN55,212-2 suppressed mIPSC frequency with 2 mM Ca2+(o), but it became ineffective when the presynaptic Ca2+ level was lowered by perfusion with a Ca2+-free solution containing BAPTA-AM. Experiments with systematic [Ca2+]o changes revealed that mIPSC but not mEPSC regularly involved events elicited by presynaptic Ca2+ rise with 2 mM Ca2+(o). Importantly, Ca2+-enhancement of mEPSC and mIPSC was not attributable to activation of voltage-dependent Ca2+ channels. Activation of GABAB receptor or group III metabotropic glutamate receptor, which couple to G(i/o)-protein, also preferentially suppressed Ca2+-enhanced miniature events in PCs. These results suggest that the occurrence of Ca2+-enhanced miniature events at normal [Ca2+]o determines the sensitivity to the presynaptic depression mediated by cannabinoid receptors and other G(i/o)-coupled receptors in PCs.

Animals↗
PubMed2006

Mutational study on alphaGln90 of Fe-type nitrile hydratase from Rhodococcus sp. N771.

Nitrile hydratase (NHase) from Rhodococcus sp. N771 is a non-heme iron enzyme having post-translationally modified cysteine ligands, alphaCys112-SO2H and alphaCys114-SOH. We replaced alphaGln90, which is conserved in all known NHases and involved in the hydrogen-bond network around the catalytic center, with glutamic acid or asparagine. The kcat of alphaQ90E and alphaQ90N mutants decreased to 24% and 5% that of wild type respectively, but the effect of mutations on Km was not very significant. In both mutants, the alphaCys114-SOH modification appeared to be responsible for the catalysis as in native NHase. We crystallized the nitrosylated alphaQ90N mutant and determined its structure at a resolution of 1.43 A. The structure was basically identical to that of native nitrosylated NHase except for the mutated site and its vicinity. The structural difference between native and alphaQ90N mutant NHases suggested the importance of the hydrogen bond networks between alphaGln90 and the iron center for the catalytic activity.

Crystallography, X-Ray↗
PubMed2005

Postnatal development and synapse elimination of climbing fiber to Purkinje cell projection in the cerebellum.

Cerebellar climbing fiber (CF) to Purkinje cell (PC) synapses in rodents provides a good model to study mechanisms underlying postnatal development of synaptic functions and elimination of redundant synapses in the central nervous system. At birth, each PC is innervated by multiple CFs. Then, single CF input is selected, matured and strengthened, while surplus CFs are eliminated. By the end of the third postnatal week, most PCs become innervated by single CFs. This up-date article aims to provide an overview of recent studies on the mechanisms of this process.

Afferent Pathways↗
PubMed2004

Ca2+ activity at GABAB receptors constitutively promotes metabotropic glutamate signaling in the absence of GABA.

Type B gamma-aminobutyric acid receptor (GABABR) is a G protein-coupled receptor that regulates neurotransmitter release and neuronal excitability throughout the brain. In various neurons, GABABRs are concentrated at excitatory synapses. Although these receptors are assumed to respond to GABA spillover from neighboring inhibitory synapses, their function is not fully understood. Here we show a previously undescribed function of GABABR exerted independent of GABA. In cerebellar Purkinje cells, interaction of GABABR with extracellular Ca2+ (Ca(2+)o) leads to a constitutive increase in the glutamate sensitivity of metabotropic glutamate receptor 1 (mGluR1). mGluR1 sensitization is clearly mediated by GABABR because it is absent in GABABR1 subunit-knockout cells. However, the mGluR1 sensitization does not require G(i/o) proteins that mediate the GABABR's classical functions. Moreover, coimmunoprecipitation reveals complex formation between GABABR and mGluR1 in the cerebellum. These findings demonstrate that GABABR can act as Ca(2+)o-dependent cofactors to enhance neuronal metabotropic glutamate signaling.

Animals↗
PubMed2004

P/Q-type Ca2+ channel alpha1A regulates synaptic competition on developing cerebellar Purkinje cells.

Synapse formation depends critically on the competition among inputs of multiple sources to individual neurons. Cerebellar Purkinje cells have highly organized synaptic wiring from two distinct sources of excitatory afferents. Single climbing fibers innervate proximal dendrites of Purkinje cells, whereas numerous parallel fibers converge on their distal dendrites. Here, we demonstrate that the P/Q-type Ca2+ channel alpha1A, a major Ca2+ channel subtype in Purkinje cells, is crucial for this organized synapse formation. In the alpha1A knock-out mouse, many ectopic spines were protruded from proximal dendrites and somata of Purkinje cells. Innervation territory of parallel fibers was expanded proximally to innervate the ectopic spines, whereas that of climbing fibers was regressed to the basal portion of proximal dendrites and somata. Furthermore, multiple climbing fibers consisting of a strong climbing fiber and one or a few weaker climbing fibers, persisted in the majority of Purkinje cells and were cowired to the same somata, proximal dendrites, or both. Therefore, the lack of alpha1A results in the persistence of parallel fibers and surplus climbing fibers, which should normally be expelled from the compartment innervated by the main climbing fiber. These results suggest that a P/Q-type Ca2+ channel alpha1A fuels heterosynaptic competition between climbing fibers and parallel fibers and also fuels homosynaptic competition among multiple climbing fibers. This molecular function facilitates the distal extension of climbing fiber innervation along the dendritic tree of the Purkinje cell and also establishes climbing fiber monoinnervation of individual Purkinje cells.

Animals↗
PubMed2004

ORP150/HSP12A regulates Purkinje cell survival: a role for endoplasmic reticulum stress in cerebellar development.

The endoplasmic reticulum (ER) stress response contributes to neuronal survival in ischemia and neurodegenerative processes. ORP150 (oxygen-regulated protein 150)/HSP12A (heat shock protein 12A), a novel stress protein located in the ER, was markedly induced in Purkinje cells maximally at 4-8 d after birth, a developmental period corresponding to their vulnerability to cell death. Both terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end-labeling analysis and immunostaining using anti-activated caspase-3 antibody revealed that transgenic mice with targeted neuronal overexpression of ORP150 (Tg ORP150) displayed diminished cell death in the Purkinje cell layer and increased numbers of Purkinje cells up to 40 d after birth (p < 0.01), compared with those observed in heterozygous ORP150/HSP12A-deficient (ORP150+/-) mice and wild-type littermates (ORP150+/+). Cultured Purkinje cells from Tg ORP150 mice displayed resistance to both hypoxia- and AMPA-induced stress. Behavioral analysis, using rotor rod tasks, indicated impairment of cerebellar function in Tg ORP150 animals, consistent with the concept that enhanced survival of Purkinje cells results in dysfunction. These data suggest that ER chaperones have a pivotal role in Purkinje cell survival and death and thus may highlight the importance of ER stress in neuronal development.

Animals↗
PubMed2004

Successful use of zonisamide for central poststroke pain.

UNLABELLED: We present 2 patients with severe and intractable central poststroke pain (CPSP) after right posterolateral thalamic infarcts who were successfully treated with zonisamide. The mechanism of action was presumed to be the suppression of overacting thalamic relay neurons by blockade of low voltage-activated calcium channel or by increasing gamma-aminobutyric acid (GABA) release. Zonisamide can be one of the therapeutic options for severe CPSP and might provide an insight into the pathogenesis of CPSP. PERSPECTIVE: The blockade of T-type VGCC or the increase in GABA release caused by zonisamide presumably suppresses abnormal activities of thalamic sensory neurons.

Anticonvulsants↗
PubMed2004

Altered agonist sensitivity and desensitization of neuronal mGluR1 responses in knock-in mice by a single amino acid substitution at the PKC phosphorylation site.

mGluR1 and mGluR5 of the metabotropic glutamate receptor family are coupled to inositol trisphosphate-Ca2+ signal cascades and evoke distinct Ca2+ responses in neural cells and heterologously expressing cells. In heterologous cells, stimulation of recombinant mGluR1 evokes a single-peaked Ca2+ response whereas mGluR5 elicits an oscillatory Ca2+ response. The distinct Ca2+ responses are interchangeable by single amino substitution of aspartate for threonine at the corresponding position of the carboxy-terminal cytoplasmic regions of mGluR1 and mGluR5, respectively. In this investigation, we generated knock-in mice, termed mGluR1 D854T mice, in which aspartate of mGluR1 was replaced with threonine. We examined the effect of this D854T substitution on Ca2+ and current responses mediated by mGluR1 in cultured cerebellar Purkinje cells. Stimulation of mGluR1 D854T by a group 1 mGluR agonist, 3,5-dihydroxyphenylglycine (DHPG) evoked, as in wild-type mGluR1, only single-peaked Ca2+ responses as measured by Ca2+ fluorometric analysis. We then examined mGluR1-induced inward currents carried by nonselective cation channels during whole-cell recordings from cultured Purkinje cells. The mGluR1 D854T mutation abolished the responsiveness of mGluR1 to low concentrations of DHPG (0.5-500 nM) and reduced its desensitization during prolonged agonist application. mGluR1 D854T homozygous mutants showed no apparent behavioural abnormality as analysed by motor movement tests. These results indicate that, although additional modulatory mechanisms seem to be required to produce oscillatory Ca2+ responses of mGluR1, the single amino acid substitution at position 854 of mGluR1 is capable of influencing the kinetics of neuronal mGluR1 responses, most probably through PKC-mediated phosphorylation.

Amino Acid Sequence↗
PubMed2003

Impaired motor coordination in mice lacking neural recognition molecule NB-3 of the contactin/F3 subgroup.

The neural recognition molecule NB-3, which belongs to the contactin subgroup of the immunoglobulin superfamily, is expressed exclusively in the nervous system and mainly upregulated at the early postnatal stage during mouse brain development. The expression of NB-3 in the cerebellum increases until adulthood. In contrast, the expression in the cerebrum declines to a low level after postnatal day 7. To characterize the functional roles of NB-3 in vivo, we generated NB-3-deficient mice by substituting a part of the NB-3 gene with the beta-galactosidase (Lac Z) gene. Complete overlap of the Lac Z expression in the heterozygous mouse brain with the NB-3 immunostaining pattern in the rat cerebellum and with the previously reported pattern of in situ hybridization of NB-3 transcripts indicated that Lac Z expression reflects the expression of NB-3 in the mouse brain. NB-3-deficient mice were viable and fertile. The formation and organization of all nuclei and layers throughout the brains of mutant mice appeared normal. Behavioral tests to examine motor function showed that the mice deficient for NB-3 were slow to learn to stay on the rotating rod in the rotorod test during repeated trials, and that they displayed dysfunction of equilibrium and vestibular senses in the wire hang and horizontal rod-walking tests. In contrast, the mutant mice showed no difference of grasp force from the wild-type mice. Thus, NB-3-deficient mice are impaired in motor coordination.

Animals↗
PubMed2003

Functional differentiation of multiple climbing fiber inputs during synapse elimination in the developing cerebellum.

We studied how physiological properties of cerebellar climbing fiber (CF) to Purkinje cell (PC) synapses change during developmental transition from multiple to mono CF innervation onto each PC. From P3 to P6, differences in the strengths of multiple CFs became larger. Around P10, each PC was either monoinnervated by one strong CF (CF-mono) or multiply innervated by one strong CF (CF-multi-S) plus a few weaker CFs (CF-multi-W). We show that simultaneous release of multiple vesicles per site occurs normally from CF-multi-S, CF-mono, and mature CFs, but less frequently from CF-multi-W and neonatal CFs. We also present evidence suggesting that weaker CFs with lower probability of multivesicular release would be withdrawn preferentially. The results suggest that differentiation into strong and weak CFs with high and low probabilities of multivesicular release precedes developmental CF synapse elimination.

Afferent Pathways↗
PubMed2002

A long CAG repeat in the mouse Sca1 locus replicates SCA1 features and reveals the impact of protein solubility on selective neurodegeneration.

To faithfully recreate the features of the human neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) in the mouse, we targeted 154 CAG repeats into the endogenous mouse locus. Sca1(154Q/2Q) mice developed a progressive neurological disorder that resembles human SCA1, featuring motor incoordination, cognitive deficits, wasting, and premature death, accompanied by Purkinje cell loss and age-related hippocampal synaptic dysfunction. Mutant ataxin-1 solubility varied with brain region, being most soluble in the neurons most vulnerable to degeneration. Solubility decreased overall as the mice aged; Purkinje cells, the most affected in SCA1, did not form aggregates of mutant protein until an advanced stage of disease. It appears that those neurons that cannot sequester the mutant protein efficiently and thereby curb its toxicity suffer the worst damage from polyglutamine-induced toxicity.

Animals↗
PubMed2002

Motor discoordination in mutant mice lacking junctophilin type 3.

Junctional complexes between the plasma membrane and endoplasmic reticulum (ER), often called "subsurface cisternae" or "peripheral coupling," are shared by excitable cells. These junctional membranes probably provide structural foundation for functional crosstalk between cell-surface and intracellular ionic channels. Our current studies have indicated that junctophilins (JPs) take part in the formation of junctional membrane complexes by spanning the ER membrane and interacting with the plasma membrane. Of the JP subtypes defined, JP type 3 (JP-3) is specifically expressed in neurons in the brain. It has been currently reported that triplet repeat expansions in the JP-3 gene are associated with Huntington's disease-like symptoms including motor disorder in human. To survey the physiological role of JP-3, we generated the knockout mice. The JP-3-knockout mice grew and reproduced normally, and we did not observe any morphological abnormality in the mutant brain. In the behavioral study, the mutant mice showed impaired performance specifically in balance/motor coordination tasks. Although obvious defects could not be observed in excitatory transmission among cerebellar neurons from the mutant mice, the data indicate that JP-3 plays an active role in certain neurons involved in motor coordination.

Animals↗
PubMed2002

The cannabinoid CB1 receptor mediates retrograde signals for depolarization-induced suppression of inhibition in cerebellar Purkinje cells.

Action potential firing or depolarization of the postsynaptic neuron can induce a transient suppression of inhibitory synaptic inputs to the depolarized neuron in the cerebellum and hippocampus. This phenomenon, termed depolarization-induced suppression of inhibition (DSI), is initiated postsynaptically by an elevation of intracellular Ca2+ concentration ([Ca2+]i) and is expressed presynaptically as a suppression of the transmitter release. It is, therefore, thought that some retrograde signal must exist from the depolarized postsynaptic neurons to the presynaptic terminals. Recent studies on hippocampal neurons have revealed that endogenous cannabinoids (endocannabinoids) play a key role as a retrograde messenger. There are, however, conflicting reports that glutamate may be a candidate retrograde messenger for cerebellar DSI that acts on presynaptic group II metabotropic glutamate receptors (mGluRs). In this study, we examined whether endocannabinoids mediate retrograde signal for cerebellar DSI. We recorded IPSCs from Purkinje cells by stimulating putative basket cell axons in mouse cerebellar slices. DSI was readily induced in evoked IPSCs by a depolarizing pulse train. We found that DSI was completely occluded by a cannabinoid agonist, WIN55,212-2, was totally eliminated by a specific antagonist of the type 1 cannabinoid (CB1) receptor, SR141716A, and was deficient in the CB1 knock-out mouse. In contrast, a group II mGluR-specific agonist, (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine, did not completely occlude DSI, and an mGluR antagonist, (RS)-alpha-methyl-4-carboxyphenylglycine, had no depressant effect on DSI. These results clearly indicate that the CB1 receptor mediates retrograde signal for DSI in cerebellar Purkinje cells.

Animals↗
PubMed1998

Sulfur-Bridged Sandwich Cubane-Type Molybdenum-Antimony Cluster. Synthesis, X-ray Structure, and (121)Sb Mössbauer Spectra of [(H(2)O)(9)Mo(3)S(4)SbS(4)Mo(3)(H(2)O)(9)](CH(3)C(6)H(4)SO(3))(8).24H(2)O.

A sulfur-bridged sandwich cubane-type molybdenum-antimony cluster [(H(2)O)(9)Mo(3)S(4)SbS(4)Mo(3)(H(2)O)(9)](8+) (2) has been synthesized through the reaction of incomplete cubane-type molybdenum cluster [Mo(3)S(4)(H(2)O)(9)](4+) (1) with antimony metal, and has been isolated as 2(pts)(8).24H(2)O (2.pts) (Hpts = p-toluenesulfonic acid), whose structure has been characterized by X-ray crystallography. Crystal data of 2.pts: triclinic, space group P&onemacr;, a = 14.468(3) Å, b = 18.531(5) Å, c = 13.713(6) Å, alpha = 105.26(2) degrees, beta = 119.71(1) degrees, gamma = 72.48(3) degrees, V = 3016(1) Å(3), Z = 1, D(calcd) = 1.696 g cm(-)(3), D(obsd) = 1.72 g cm(-)(3), R (R(w)) = 4.7 (7.5) for 6593 reflections (I > 2.0sigma(I)). The Mo-Sb distances (3.68[2]) Å) are much longer than the Mo-Mo (2.717[7] Å) distances. Peak positions and epsilon values (lambda(max), nm (epsilon, M(-)(1) cm(-)(1))) of the electronic spectrum of 2.pts in 2 M HCl are 384 (13 220), 625 (10 440), and 700 (10 080). The (121)Sb Mössbauer parameters (delta = -2.64 mm s(-)(1), e(2)qQ = 18.1 mm s(-)(1), eta = 0.29), and the binding energies (eV) and full widths at half-maximum (in parentheses, eV) obtained from XPS spectrum (Sb(3d3/2), 540.3(2.3); Mo(3d3/2), 233.2(2.1); Mo(3d5/2), 230.2(1.9); (C(1s) = 285.0)) of 2.pts indicate that the oxidation number of antimony is III, and the mean oxidation number of molybdenum is +3.5.

Journal Article↗