The response of spermatogonia and spermatocytes of the Northern vole Microtus oeconomus to the induction of sex-chromosome nondisjunction, diploidy and chromosome breakage by X-rays and fast fission neutrons

Cytogenetic damage in preimplantation mouse embryos generated after paternal and parental gamma-irradiation and the influence of vitamin C

Cytogenetic damage expressed as micronuclei (MN) in 4-8-cell embryos generated after irradiation of male or male and female mice in the absence and presence of vitamin C was investigated. Male NMRI mice were whole body exposed to 4 Gy gamma-rays and mated with non-irradiated superovulated female mice in 6 successive weeks after irradiation in a weekly interval. In experiments involving irradiation of both male and female mice, irradiated male mice for 6 weeks post irradiation were mated with female mice irradiated after induction of superovulation. Effect of 100 mg/kg vitamin C (ascorbic acid) on the frequency of MN was also studied. Pregnant animals were euthanized and embryos flushed from the oviducts and fixed on slides. The rate of MN observed in embryos generated from irradiated male compared with control group dramatically increased (P<0.01). Frequency of MN in this group decreased dramatically after vitamin C treatment (P<0.01). Frequency of MN in embryos generated by mating both male and female irradiated mice was higher than that observed for those embryos generated by irradiated male mice alone. However, a considerable modifying effect of vitamin C was observed for this group too (P<0.05). Results indicate that irradiation of gonads during spermatogenesis and preovulatory stage oocytes may lead to unstable chromosomal aberrations and probably stable chromosomal abnormalities affecting pairing and disjunction of chromosomes in successive preimplantation embryos expressed as MN. The way vitamin C reduces clastogenic effects of radiation on germ cells leading to reduced frequency of MN in pre-embryos might be due to its antioxidation and radical scavenging properties.

Micronucleus response of human glioblastoma and neuroblastoma cells toward low-LET photon and high-LET p(66)/Be neutron irradiation

The identification of photon resistant tumors that are sensitive to neutrons is still an unresolved problem, and no radiobiological criteria have been developed that could help the selection of patients for neutron therapy. The micronucleus (MN) assay has been evaluated for this purpose in a panel of human glioblastoma and neuroblastoma cell lines spanning a wide range of photon sensitivities defined by mean inactivation doses ([Latin capital letter D with macron above][gamma]) of 1.25-3.21 Gy. We show that the relative biologic effectiveness (RBE) of the p(66)/Be neutrons is significantly correlated with inherent photon sensitivity (r = 0.89, p < 0.01), indicating that the panel of cell lines used is suitable to study the differential biologic response to neutrons and photons. We find that p(66)/Be neutrons are 1.43 to 5.29 times more effective per unit dose in inducing micronuclei than 60Co [gamma]-rays. Surprisingly, cells that are inherently photon resistant tend to show a higher yield of micronuclei following exposure to either photons or neutrons, but no significant correlation could be demonstrated. However, RBE values based on micronucleus yield were found to strongly correlate with RBE values derived from cell survival data (r = 0.91, p < 0.01). It is concluded that although micronucleus yield does not reflect intrinsic sensitivity to either photons or neutrons, the strong correlation between RBE calculated from micronucleus formation and RBE derived from cell survival demonstrates that the micronucleus endpoint has a potential for detecting photon resistant cells that show increased sensitivity to neutrons.

Kinetochore-staining of spermatid micronuclei: Studies of mice treated with X-radiation or acrylamide

The rodent spermatid micronucleus (MN) assay was used in conjunction with immunofluorescent techniques to distinguish kinetochores in MN following exposure of mice to X-radiation or acrylamide. After either treatment, modest increases in kinetochore-positive MN were observed. Spermatids which had been exposed during meiotic prophase to X-rays (400 cGy) had approximately 10-fold increases in MN compared to controls; up to 15% of the MN observed were kinetochore-positive. Following acrylamide treatment of meiotic prophase cells, there was a doubling of spermatid MN over baseline levels, approximately one-third of which were kinetochore-positive.