| Project/Area Number |
01480129
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Neurophysiology and muscle physiology
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| Research Institution | Kurume University |
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Principal Investigator |
AKASU Takashi Kurume University School of Medicine, Professor, 医学部, 教授 (60113213)
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| Co-Investigator(Kenkyū-buntansha) |
HASUO Hiroshi Kurume University School of Medicine, Asistant Professor, 医学部, 講師 (90172882)
TOKIMASA Takayuki Kurume University School of Medicine, Associate Professor, 医学部, 助教授 (50155511)
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| Project Period (FY) |
1989 – 1991
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| Project Status |
Completed (Fiscal Year 1991)
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| Budget Amount *help |
¥6,600,000 (Direct Cost: ¥6,600,000)
Fiscal Year 1991: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1990: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1989: ¥5,700,000 (Direct Cost: ¥5,700,000)
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| Keywords | Electrophysiology / Intracellular recordings / Suprachiasmatic nucleus / Spontaneous activity / Inward rectification / Low-threshold Ca-current / EPSP / IPSP / Rat / Central nervous system / Suprachiasmatic nucleus / Circadian rhythm / PIーturn over / Metabotropic receptors / 視交叉上核 / 静止・活動電位 / 細胞内微小電極法 / 脳スライス標本 / バゾプレッシン / ソマトスチタン |
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| Research Abstract |
Extracellular and intracellular recordings were made from neurons in brain slice containing suprachiasmatic nucleus(SCN)of the rat, in vitro. A majority of SCN neurons(85 %)displayed a spontaneous firing of action potential with frequency of 2-10 Hz. The action potential was preceded by a depolarizing prepotential and followed by a shallow and short spike after-hyperpolarization. Spontaneous action potentials were blocked by applying hyperpolarizing DC current or by tetrodotoxin. Injection of depolarizing current with duration of 400 msec to SCN neurons evoked a tonic discharge of action potentials which comprised of no obvious accommodation. A time and voltage-dependent decrease in the membrane resistance 'sag' on hyperpolarizing electrotonic potential was produced by injection of inward current pulses with duration of 200 msec. Voltage-current relationship showed an inward rectification at potentials more negative than -80 mV. The inward rectification was blocked by extracellular Cs(2 mM)but not by Ba(200 muM). SCN neurons also displayed a rebound slow depolarization in response to relaxation of hyperpolarizing current that was blocked in Ca-free solution and by application of Cd(500 muM)or Co(1 mM). 4-AP enhanced the slow depolarization. Cd and Cs depressed the depolarizing pre-potential, resulting in a decreased rate of firings in SCN neurons. These results suggest that the low-threshold Ca-spike, the inward rectification and the Acurrent are important factors for determining the rate of spontaneous firing activity in SCN neurons. Stimulation of optic chiasma elicited EPSP and IPSP in SCN neurons. The EPSP is blocked by application of both CNQX and APV, suggesting that the EPSP is mediated by both NMDA and non-NMDA receptors. Since the IPSP was blocked by bicuculline, GABA_A receptors may mediate the IPSP. These results suggest that these synaptic activities may modulate the rate of spontaneous activity of the SCN.
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