| Project/Area Number |
59490003
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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 | Asahikawa Medical College |
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Principal Investigator |
MIKAMO Kazuya Asahikawa Medical College, Department of Biological Sciences, Professor, 医学部, 教授 (10002221)
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| Co-Investigator(Kenkyū-buntansha) |
TATENO Hiroyuki Asahikawa Medical College, Department of Biological Sciences, Research Associate, 医学部, 教務職員 (80163492)
TANAKA Kunio Asahikawa Medical College, Central Laboratory for Research and Education, Assoc., 医学部, 助教授 (20041840)
KAMIGUCHI Yujiroh Asahikawa Medical College, Department of Biological Sciences, Assoc. Professor, 医学部, 助教授 (60091568)
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| Project Period (FY) |
1984 – 1986
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥8,800,000 (Direct Cost: ¥8,800,000)
Fiscal Year 1986: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1985: ¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1984: ¥6,300,000 (Direct Cost: ¥6,300,000)
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| Keywords | Chinese hamstar oocyte / Neonate / X-rays / Ultrasound / Oocyte killing / Reproductive life span / Chromosome aberration / Dominant lethality / チャイニーズハムスター / 晩発効果 / 発生能 |
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| Research Abstract |
We studied the effects of X-rays and ultrasound on ovarian oocytes of neonatal Chinese hamsters aged between 0 and 20 days with regard to (a) acute oocyte-killing and chromosome aberration in irradiated oocytes, (b) dominant lethality and congenital anomaly in the embryos developed from irradiated oocytes, and (c) reproductive life span of the irradiated females. The results are as follows :
(1) The immature oocytes dramatically changed their sensitivity to oocyte-killing effect of radiation, depending upon their meiotic stages of oogenesis. They were highly radioresistant at the pachytene stage, but became sharply sensitive during the phase between diplotene and early dictyate, suffering severe killing effect after 1 Gy of X-rays. However, the oocytes recovered radioresistance again at the following stage, i. e., the resting dictyate stage.
(2) Reproductive life span was markedly shortened in the females irradiated with 1 Gy at their neonatal stage (4 to 8 days of age) at which most ova
… More
rian occytes are in radiosensitive stages (diplotene to early dictyate). This indicates that the reduction of ovarian oocytes in number due to acute oocyte-killing is responsible for the shortening of reproductive life (premature menopause).
(3) There was no increase of chromosome aberrations in female pronuclei of one-cell embryos derived from the pachytene and resting dictyate oocytes which survived 1 Gy X-rays. No increase was also found in the incidences of pre- and postimplantation death and congenital malformations in the 18.5-day fetuses developed from survived oocytes. These findings suggest that pachytene and resting dictyate oocytes are highly capable of repairing DNA damage.
(4) Diplotene and early dictyate oocytes which survived low doses of X-rays (0.1-0.5 Gy) were free from late deleterious effects on genetic and developmental abilities.
(5) Exposure of ultrasound (3.25 W/cm^2) to radiosensitive oocytes (those in diplotene and early dictyate stages) induced neither acute oocyte-killing nor late effects due to genetic damage.
It has been generally believed that the late fetal and neonatal stages are relatively resistant to the teratogenic effects of mutagens such as radiation and chemicals. In this study, however, we demonstrated that premature menopause owing to oocyte-killing occurred after the irradiation during the radiosensitive periods. Considering that diplotene and early dictyate oocytes are also sensitive to some chemicals, the late fetal stages should be regarded as a critical period in determining fertility span of women. Fortunately, however, ultrasound seems to have a different nature from the radiations as far as the present study was concerned. Less
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