1987 Fiscal Year Final Research Report Summary
Mechanisms of stress analgesis: vasopressin hypothesis
| Project/Area Number |
61490029
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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 |
広領域
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| Research Institution | Jichi Medical School |
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Principal Investigator |
HAMAMURA Mitsuko Department of Physiology, Jichi Medical School, 医学部, 講師 (90118456)
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| Co-Investigator(Kenkyū-buntansha) |
ONAKA Tatsushi Department of Physiology, Jichi Medical School, 医学部, 助手 (90177254)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Vasopressin / Stress / Stress analgesis / Posterior Pituitary / Noxious stimuli / Pain / Hypothalamus / 下垂体 |
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| Research Abstract |
Introduction: Footshocks (Fs) have been shown to induce 'analgesis' as determined by prolongation of latency of tail flick (TF) after noxious heat stimuli. Recently we have demonstrated that a variety of noxious stimuli excite putative vasopressin (VP)- secreting neurones in the supraoptic nucleus. VP unjected systemically was reported to prolong TF latency. It is therefore possible that noxious stimuli may release VP into the plasma and this VP may in turn produce an increase in threshold of TF after FS. Results: Effects of FS on plasma VP; FS (50 Hz, 60 s, 3mA) increased plasma VP in rats (about 30 pg/ml). The increase was related to the FS intensity. Quantification of thermal threshold; We measured tail surface temperature at which TF reflex occurred in the conscious rat using a fine thermocouple. Effects of FS on thermal threshold; Tail surface temperature at TF increased after application of the FS in a intensity-related manner. These data are consistent with the earlier reports t
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hat FS prolonged latency of TF. Effects of I.v.vp; I.V. injected VP at a dose of more than 0.5 ([TA.micrn.])g/kg increased thermal threshold of TF significantly. Plasma VP after an I.V.VP injection at this dose is calculated to be much higher than the level after the FS, assuming that the injected VP would be distributed immediately and evenly in the whole plasma. Effects of posterior pituitary stimulation; Stimulation of the posterior pituitary did not increase effectively thermal threshold of TF, whereas the stimulation increased plasma VP up to about 450 pg/ml. Effects of VP V1-receptor antagonist; VP V1-receptor antagonist injected I.V. decreased the increase after I.V. VP (1.6 <micrn>g/kg) in a dose-related manner (5 - 150 <micrn>g/kg. The antagonist (5 <micrn>g/kg) also blocked the threshold increase after FS. Conclusion: These data lead us to conclude that plasma VP increased after FS dose not mediate a footshock-induced increase in thermal threshold of TF. Since FS have been shown to decrease VP in the brain and the VP V1-receptor antagonist is known to cross the blood-brain barrier, the possibility remains to be tested that FS may release VP within the brain and the VP may in turn mediate the FS-induced increase in threshold temperature of TF. Less
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