Takuro Suzuki

Publications (3)6.95 Total impact

• Article: Characteristics, day-night changes, subcellular distribution and localization of melatonin binding sites in the goldfish brain

  Masayuki Iigo, Makito Kobayashi, Ritsuko Ohtani-Kaneko, Masayuki Hara, Atsuhiko Hattori, Takuro Suzuki, Katsumi Aida
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  ABSTRACT: Melatonin binding sites in the goldfish brain were characterized by radioreceptor assay using 2-[125I]iodomelatonin as the radioligand. Specific binding of 2-[125I]iodomelatonin was rapid, stble, saturable and reversible. Saturation experiments demonstrated that 2-[125I]iodomelatonin binds to a single class of receptor site with an affinity constant (Krmd) of 29.8±0.7pM and a total binding capacity (Bmax)of11.47 ± 0.33fmol/mg protein at mid-dark, the Bmax value decreased significantly to 7.90±0.23fmol/mg protein (Pˇ0.01) with no significant variation in the Kd value (33.8±1.5pM). Competition experiments revealed the following order of pharmacological affinities: 2-iodomelatonin>melatonin> 6-hydroxymelatonin> N-acetyl-5-hydrxytryptamine> 5-methoxytryptamine> 5-methoxytryptophol> 5-methoxyindole-3-acetic acid. 5-Hydroxytryptamine, 5-hydroxytryptophol, 5-hydroxyindole-3-acetic acid, norepinephrine and acetylcholine exhibited no inhibition. Subcellular distribution of melatonin binding sites was demonstrated to be greatest in the P2 and P3 fractions as compared with the P1 fraction. Localization of melatonin binding sites in discrete brain areas was determined to be highest in the optic tectum-thalamus and hypothalamus, intermediate in the telencephalon, cerebellum and medulla oblongata, and lowest in the olfactory bulbs and pituitary gland. These results suggest that characteristics of melatonin receptors are highly conserved during evolution and that in this species melatonin plays neuromodulatory roles in the central nervous system through specific receptors.
  Brain Research 05/1994; · 2.73 Impact Factor
• Article: Regulation by Guanine Nucleotides and Cations of Melatonin Binding Sites in the Goldfish Brain

  Masayuki Iigo, Ritsuko Ohtani-Kaneko, Masayuki Hara, Atsuhiko Hattori, Hidehito Takahashi, Mitsuo Tabata, Takuro Suzuki, Katsumi Aida
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  ABSTRACT: Effects of nucleotides and cations on 2-[125I]iodomelatonin binding sites in the goldfish brain were examined. Nucleotides (10–6–10–3 M) dose-dependently inhibited the specific binding with the following order of potency: guanosine 5'-O-(3-thiotriphosphate) (GTPγS) >GTP = GDP >GMP = ATP >cyclic GMP. Cyclic AMP was ineffective. The treatment of membranes with GTPγS induced rapid dissociation of 2-[125I]iodomelatonin from membranes when added at the steady state, increased the Kd and decreased the Bmax values as revealed by saturation analysis, and increased the IC50 value of melatonin to inhibit the specific binding. The treatment decreased the specific binding to membrane preparations obtained from six brain regions as well. Inorganic salts (5–200 mM) dose-dependently inhibited the specific binding with the following order of potency: CaCl2 > MgCl2 > LiCl > NaCl > choline chloride > KCl, except for 5 mM MgCl2, which enhanced the specific binding. Saturation experiments demonstrated that 75 mM CaCl2,100 mM MgCl2 and 200 mM NaCl increased the Kd and decreased the Bmax while 5 mM MgCl2 increased the Bmax value. These results imply that G protein and physiological concentrations of cations are involved in the regulation of melatonin binding sites in the goldfish brain.
  Neurosignals 08/1970; 6(1):29-39. · 2.11 Impact Factor
• Article: Administration of Melatonin and Related Indoles Prevents Exercise-Induced Cellular Oxidative Changes in Rats

  Masayuki Hara, Masayuki Iigo, Ritsuko Ohtani-Kaneko, Naoko Nakamura, Takuro Suzuki, Russel J. Reiter, Kazuaki Hirata
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  ABSTRACT: In an attempt to define the role of the pineal hormone melatonin and two analogues (5-methoxytryptamine, 5MT, and 6-hydroxymelatonin, 6HM) in limiting oxidative stress, the present study investigated the changes in glutathione, lipid peroxidation, and the activity of the antioxidant enzyme glutathione peroxidase after exercise (swimming for 60 min) with or without treatment with the indolamines mentioned. Lipid peroxidation was measured by estimating tissue levels of malondialdehyde and 4-hydroxyalkenals; the experimental animals in these studies were male Sprague-Dawley rats. In the liver, swimming exercise increased the levels of reduced glutathione (GSH) and also significantly increasing oxidized glutathione (GSSG), while decreasing the GSH/GSSG ratio, an index directly related to oxidative stress. When the animals were treated with melatonin, the concentrations of GSH and GSSG were also increased after swimming; however, no reduction in the GSH/GSSG ratio appeared. In the animals treated with 6HM the changes were the same as in those treated with melatonin. In muscle as well, the concentration of GSH and the GSH/GSSG ratio were decreased following 60 min of swimming. Pretreatment of the rats with melatonin prevented these effects. Pretreatment of the rats with both 5MT and 6HM also prevented the changes. Brain GSH/GSSG ratio was not affected by either exercise or indolamine administration. Swimming enhanced lipid peroxidation in the liver, muscle and brain; however, this was prevented in animals treated with melatonin or 6HM before swimming. Glutathione peroxidase was significantly elevated after exercise in the brain but not in the liver and muscle. It is concluded that swimming imposes a severe oxidative stress and suggests that melatonin and, to a lesser degree, 5MT and 6HM confer protection against the oxidative damage associated with swimming for 60 min. This mechanism may be reasonably attributed to their indole structure, which possibly allows these molecules to act as free-radical scavengers.
  Neurosignals 08/1970; 6(2):90-100. · 2.11 Impact Factor