Takeshi Suzuki

Keio University, Edo, Tōkyō, Japan

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Publications (19)35 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Adenosine deaminase acting on RNA 2 (ADAR2) catalyzes RNA editing at the glutamine/arginine (Q/R) site of GluA2, and an ADAR2 deficiency may play a role in the death of motor neurons in ALS patients. The expression level of ADAR2 mRNA is a determinant of the editing activity at the GluA2 Q/R site in human brain but not in cultured cells. Therefore, we investigated the extent of Q/R site-editing in the GluA2 mRNA and pre-mRNA as well as the ADAR2 mRNA and GluA2 mRNA and pre-mRNA levels in various cultured cell lines. The extent of the GluA2 mRNA editing was 100% except in SH-SY5Y cells, which have a much lower level of ADAR2 than the other cell lines examined. The ADAR2 activity at the GluA2 pre-mRNA Q/R site correlated with the ADAR2 mRNA level relative to the GluA2 pre-mRNA. SH-SY5Y cells expressed higher level of the GluA2 mRNA in the cytoplasm compared with other cell lines. These results suggest that the ADAR2 expression level reflects editing activity at the GluA2 Q/R site and that although the edited GluA2 pre-mRNA is readily spliced, the unedited GluA2 pre-mRNA is also spliced and transported to the cytoplasm when ADAR2 expression is low.
    Neuroscience Research 02/2012; 73(1):42-8. · 2.20 Impact Factor
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    ABSTRACT: GluR2 is a subunit of the AMPA receptor, and the adenosine for the Q/R site of its pre-mRNA is converted to inosine (A-to-I conversion) by the enzyme called adenosine deaminase acting on RNA 2 (ADAR2). Failure of A-to-I conversion at this site affects multiple AMPA receptor properties, including the Ca(2+) permeability of the receptor-coupled ion channel, thereby inducing fatal epilepsy in mice (Brusa et al., 1995; Feldmeyer et al., 1999). In addition, inefficient GluR2 Q/R site editing is a disease-specific molecular dysfunction found in the motor neurons of sporadic amyotrophic lateral sclerosis (ALS) patients (Kawahara et al., 2004). Here, we generated genetically modified mice (designated as AR2) in which the ADAR2 gene was conditionally targeted in motor neurons using the Cre/loxP system. These AR2 mice showed a decline in motor function commensurate with the slow death of ADAR2-deficient motor neurons in the spinal cord and cranial motor nerve nuclei. Notably, neurons in nuclei of oculomotor nerves, which often escape degeneration in ALS, were not decreased in number despite a significant decrease in GluR2 Q/R site editing. All cellular and phenotypic changes in AR2 mice were prevented when the mice carried endogenous GluR2 alleles engineered to express edited GluR2 without ADAR2 activity (Higuchi et al., 2000). Thus, loss of ADAR2 activity causes AMPA receptor-mediated death of motor neurons.
    Journal of Neuroscience 09/2010; 30(36):11917-25. · 6.91 Impact Factor
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    ABSTRACT: The motor neurons of patients with sporadic amyotrophic lateral sclerosis (ALS) express abundant Q/R site-unedited GluR2 mRNA, whereas those of patients with other motor neuron diseases including familial ALS associated with mutated SOD1 (ALS1) and those of normal subjects express only Q/R site-edited GluR2 mRNA. Because adenosine deaminase acting on RNA type 2 (ADAR2) specifically catalyzes GluR2 Q/R site-editing, it is likely that ADAR2 activity is not sufficient to edit this site completely in motor neurons of patients with sporadic ALS. Because these molecular abnormalities occur in disease- and motor neuron-specific fashion and induce fatal epilepsy in mice, we have hypothesized that GluR2 Q/R site-underediting due to ADAR2 underactivity is a cause of neuronal death in sporadic ALS. We found that cytoplasmic fragile X mental retardation protein interacting protein 2 (CYFIP2) mRNA had an ADAR2-mediated editing position using RNA interference knockdown. Our review will include a discussion of new ADAR2 substrates that may be useful for research on sporadic ALS.
    Journal of Pharmacological Sciences 01/2010; 113(1):9-13. · 2.15 Impact Factor
  • Neuroscience Research - NEUROSCI RES. 01/2007; 58.
  • Article: P3-350
    Takeshi Suzuki, James R. Brorson, Kwak Shin
    Alzheimers & Dementia - ALZHEIMERS DEMENT. 01/2006; 2(3).
  • Source
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    ABSTRACT: For pathophysiological studies, it is advantageous to label specific neuronal populations in living animals. This study aimed to establish a method for stable and long-lasting fluorescent labeling of corticospinal neurons in the living animal. The two fluorescent dyes Fluoro-Red and Fluoro-Green were injected in the cervical spinal cord of anesthetized newborn rats. After a recovery period, treated rats were returned to the mother. After 24 h and 14 days, fixed brain sections revealed wide-spread fluorescence in elongated or pyramidal-shaped cell profiles in a discrete internal cortical layer, consistent with layer V pyramidal cells. Labeled neurons displayed spontaneous synaptic activity using the slice patch clamp method. These results suggest that these dyes are effective tools for pathophysiological and slice patch clamp studies focused on specific neuron groups.
    Brain Research Protocols 09/2004; 13(3):183-8. · 1.82 Impact Factor
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    James R Brorson, Dongdong Li, Takeshi Suzuki
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    ABSTRACT: Initial models of AMPA receptor assembly postulated the unrestricted stochastic association of individual subunits. The low Ca(2+) permeability and nonrectified current-voltage relationship of most native AMPA receptors were ascribed to dominant effects of the glutamate receptor 2 (GluR2) subunit. A recent model, however, proposes instead the preferred assembly of GluR1 and GluR2 subunits into tetrameric complexes as pairs of identical heteromeric dimers. To compare unrestricted versus selective models of GluR1 and GluR2 assembly, these subunits, in both flip and flop isoforms, were expressed in varying ratios in human embryonic kidney 293 cells. Coexpression of pairs of wild-type subunits produced expression of a predominance of heteromeric over homomeric receptors. Only a single functional type of heteromeric receptor was observed, indicating a pattern of apparent dominance not only of GluR2 for ion selectivity, but also of the flip isoform for receptor desensitization. Expression of wild-type GluR1 flip, however, with a mutant form of the same subunit carrying an arginine residue at the glutamine/arginine site (GluR1(R) flip) demonstrated a lack of dominance of GluR1(R) in determination of ion selectivity, whereas expression of GluR1(R) flip with GluR1 flop reproduced the pattern of apparent complete dominance. Together, the data support the selective expression of heteromeric receptors and are compatible with an equilibrium model of assembly of tetramers as pairs of identical heteromeric dimers. Expression of co-assemblies of the flip and flop isoforms, like that of the GluR1 and GluR2 subunits, is strongly favored over that of homomeric assemblies.
    Journal of Neuroscience 05/2004; 24(14):3461-70. · 6.91 Impact Factor
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    ABSTRACT: GABA is a major inhibitory neurotransmitter in the mature mammalian brain. In the early stages of brain development, it has been reported that GABA(A) receptor stimulation and the associated increase in Cl(-) conductance lead to membrane depolarization. In this study, we tested the effects of picrotoxin, a GABA(A) receptor Cl(-) channel blocker, on spontaneously released acetylcholine (ACh) from cultured rat embryonic septal cells. Picrotoxin increased spontaneously released ACh. These results indicate that blockade of GABA-activated Cl(-) channel increases neuronal excitability even in an early stage of the development.
    Neuroscience Letters 03/2004; 356(1):57-60. · 2.03 Impact Factor
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    ABSTRACT: As glutamate is a dominant excitatory neurotransmitter in the central nervous system, glutamate receptors, and especially AMPA receptors, are located ubiquitously in all brain areas. In this paper, we reviewed recent advances of studies on AMPA receptor functions. AMPA receptors are cation-conducting complexes composed of various combinations of four subunits (GluR1 to GluR4). The glutamine residue located in the pore-forming segment of GluR2 subunit (Q/R site) is changed to arginine by RNA editing at the pre mRNA stage in normal adult mammalian animal. The edited GluR2 subunit is a major determination of Ca(2+) permeability of the AMPA receptor; only edited GluR2-lacking receptor shows high-Ca(2+) permeability. The assembly of glutamate AMPA receptor subunit is not completely according to the stochastic theory. The heteromeric subunits assembly is more rapid than the homomeric assembly is. The transfer of AMPA receptor subunit to the plasma membrane is conducted in multiple ways. Many molecules that interact with the intracellular domain of AMPA receptor subunits are reported as the modulators of AMPA receptor subunit transfer. In the motoneuron of sporadic amyotrophic lateral sclerosis (ALS) patients, the efficiency of RNA editing at the GluR2 Q/R site is significantly decreased. Relative low level of edited GluR2 subunit expression is likely responsible for motoneuronal death in ALS. Recently, AMPA receptors in glial cells have been studied. Bergmann glial cells in cerebellum express Ca(2+)-permeable AMPA receptors. Conversion of these AMPA receptors to Ca(2+)-impermeable type receptors induces morphological and functional changes. Glioblastoma cells also express Ca(2+)-permeable AMPA receptors, and their conversion to Ca(2+)-impermeable receptors inhibits cell locomotion and induces apoptosis.
    Folia Pharmacologica Japonica 01/2004; 122(6):515-26.
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    ABSTRACT: We tested the characteristics of acetylcholine (ACh) release from cultured rat septal cells. The spontaneous release was inhibited by treatment with tetrodotoxin (TTX) and omega-conotoxin (GVIA), indicating that the release was elicited by synaptic activity. The release was also inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor blocker, in both the absence and presence of nerve growth factor (NGF), suggesting that endogenously released glutamate produced the ACh release by stimulating AMPA receptors. This is the first report of detection of the release of ACh by endogenous spontaneous synaptic activity conducted by glutamate AMPA receptor activation in cultured septal cells. This in vitro experimental system is useful for the study of cholinergic functions.
    Neuroscience Research 11/2003; 47(3):341-7. · 2.20 Impact Factor
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    ABSTRACT: The mechanisms involved in the enhancement of acetylcholine (ACh) release in the rat hippocampus by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a serotonin (5-HT)1A receptor agonist, were investigated using in vivo microdialysis. Administration of p-chlorophenylalanine (PCPA, 300 mg/kg, i.p.), a tryptophan hydroxylase inhibitor, 3 days before the dialysis experiments reduced the hippocampal 5-HT content to 30% of that in saline-treated rats, but did not affect basal ACh release in the hippocampus. 8-OH-DPAT administered systemically (0.5 mg/kg, s.c.) or applied locally (30 μM) into the hippocampus through the dialysis probe significantly enhanced the release of ACh in the hippocampus of PCPA-treated rats to the same degree as that in saline-treated rats. Pretreatment with (+)WAY-100135 (5 mg/kg, i.p.), a selective 5-HT1A receptor antagonist, completely eliminated the enhancement of ACh release induced by locally applied 8-OH-DPAT, but only partially reduced the effects induced by systemically administered 8-OH-DPAT, in both groups of rats. Systemically administered 8-OH-DPAT induced hyperlocomotion in the both saline- and PCPA-treated rats, but this was not eliminated by (+)WAY-100135. 8-OH-DPAT applied locally into the hippocampus did not elicit hyperlocomotion in either group of rats. These results suggest that the modification of endogenous 5-HT release via the 5-HT1A autoreceptor is not involved in the 8-OH-DPAT-induced increase of hippocampal ACh release, and that the increase of ACh release induced by locally applied 8-OH-DPAT involves mainly hippocampal postsynaptic 5-HT1A receptor stimulation. In addition, a possibility that subtypes of 5-HT receptors other than the 5-HT1A receptor, probably 5-HT7 receptor in the septum as well as postsynaptic 5-HT1A receptor in the hippocampus, are involved in the increased hippocampal ACh release induced by systemically administered 8-OH-DPAT is discussed.
    Neuroscience Research 06/1998; · 2.20 Impact Factor
  • Neuroscience Research 01/1997; 28. · 2.20 Impact Factor
  • Japanese Journal of Pharmacology - JPN J PHARMACOL. 01/1997; 73(1):83-91.
  • Neuroscience Research 01/1997; 28. · 2.20 Impact Factor
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    ABSTRACT: Various concentrations of acetylcholine (ACh) were detected in samples of bovine, goat, horse, porcine, rat and sheep blood and plasma using a specific, sensitive radioimmunoassay. The ACh levels in whole blood in bovine and horse samples were about 40- and ten-fold higher, respectively, than in humans, but levels comparable to those in humans were measured in porcine samples. Goat, rat and sheep samples had lower whole blood ACh concentrations than those of humans. When plasma samples were assayed, the ACh contents of bovine and porcine plasma were found to be about two- to five-fold those of human. On the other hand, levels in horse, goat, rat and sheep samples were much lower than in humans. The ratio of the ACh contents of plasma to whole blood was high in porcine and rat samples, indicating that porcine and rat blood ACh is distributed mostly in the plasma, while in the other species tested most of the ACh is present in the blood cells. These results demonstrate that variable levels of ACh are present in the blood of different species, and that the distribution of ACh in the blood constituents varies according to species.
    Neuroscience Letters 01/1996; · 2.03 Impact Factor
  • Takeshi Suzuki, Koichiro Kawashima
    Neuroscience Research - NEUROSCI RES. 01/1996; 25.
  • Proceedings of The Japan Academy Series B-physical and Biological Sciences - PROC JPN ACAD B. 01/1995; 71(7):231-235.
  • Japanese Journal of Pharmacology - JPN J PHARMACOL. 01/1995; 69(3):215-222.
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    ABSTRACT: The effects of the centrally acting cholinesterase (ChE) inhibitors, tetrahydroaminoacridine (THA) and E2020 (1-benzyl-4-[(5,6-dimethoxy-l-indanon)-2-yl] methylpiperidine hydrochloride), potential drugs for the treatment of senile dementia, on the basal extracellular acetylcholine (ACh) concentration in the hippocampus of freely moving rats, were determined using a microdialysis technique without the use of a ChE inhibitor in the perfusion fluid and a sensitive RIA. The mean (SEM) basal ACh content in the perfusate was 103.1 3.6 fmol/sample collected over 30 min when microdialysis probes with a length of 3 mm dialysis membrane were used. The content of ACh decreased to an almost undetectable level upon perfusion of magnesium, suggesting that, in the present study, most of the ACh detected in the perfusates was due to cholinergic neuronal activity. THA (1.65 mg/kg, i.p.) produced an insignificant increase in the extracellular ACh concentration, but a dose of 5 mg/kg, i.p. caused a prolonged and significant 5.5-fold increase from the control value. E2020 (0.65 and 2 mg/kg, i.p.) produced significant, prolonged and dose-dependent increases (4 and 12 times the control value, respectively), the peak effect occurring within 1 h. Perfusion with 10 mol/l physostigmine produced an about 30-fold increase of ACh output, suggesting that the basal extracellular ACh concentration is highly dependent on ChE activity. When ChE was inhibited locally by perfusion with physostigmine, THA (5 mg/kg) produced a transient and, at its maximum, a 1.42-fold increase in extracellular ACh concentration. These results demonstrate that the basal, physiological, extracellular ACh concentration in the hippocampus of freely moving rats can be determined using a microdialysis technique and a sensitive RIA, and suggest that THA and E 2020 increase ACh concentration in the synaptic cleft of the hippocampus in a dose-dependent manner mostly through ChE inhibition.
    Archiv für Experimentelle Pathologie und Pharmakologie 10/1994; 350(5):523-528. · 2.15 Impact Factor

Publication Stats

179 Citations
35.00 Total Impact Points

Institutions

  • 2012
    • Keio University
      • Faculty of Pharmacy
      Edo, Tōkyō, Japan
  • 2010–2012
    • The University of Tokyo
      • Department of Neuroscience
      Tokyo, Tokyo-to, Japan
  • 2004
    • University of Chicago
      • Department of Neurology
      Chicago, IL, United States
  • 1994–2004
    • Kyoritsu College of Pharmacy
      • Department of Pharmacology
      Tōkyō, Japan