The effect of graded doses of fission neutrons or X rays on the lymphoid compartment of the thymus in mice

Young adult CBA/H mice were exposed to graded doses of whole-body irradiation with either fast fission neutrons or 300 kVp X rays at center-line dose rates of 0.1 and 0.3 Gy/min, respectively. Dose-response curves were determined at Days 2 and 5 after irradiation for the total thymic cell survival and for the survival of thymocytes defined by monoclonal anti-Thy-1, -Lyt-1, -Lyt-2, and -T-200 antibodies as measured by flow cytofluorometric analysis. Cell dose-response curves of thymocytes show, 2 days after irradiation, a two-component curve with a radiosensitive part and a part refractory to irradiation. The radiosensitive part of the dose survival curve of the Lyt-2+ cells, i.e., mainly cortical cells, has a D0 value of about 0.26 and 0.60 Gy for neutrons and X rays, respectively, whereas that of the other cell types has corresponding D0 values of about 0.30 and 0.70 Gy. The radiorefractory part of the dose-response curves cannot be detected beyond 5 days after irradiation. At that time, the Lyt-2+ cells are again most radiosensitive with a D0 value of 0.37 and 0.99 Gy for neutrons and X rays, respectively. The other measured cell types have corresponding D0 values of about 0.47 Gy. The fission neutron RBE values for the reduction in the thymocyte populations defined by either monoclonal anti-Thy-1, -Lyt-1, -Lyt-2, or -T-200 antibodies to 1.0% vary from 2.6 to 2.8. Furthermore, the estimated D0 values of the Thy-1-, T-200- intrathymic precursor cells which repopulate the thymus during the bone marrow independent phase of the biphasic thymus regeneration after whole-body irradiation are 0.64-0.79 Gy for fission neutrons and 1.32-1.55 Gy for X rays.     

Detection of genomic instability in offspring of male mice chronically exposed to gamma-radiation by the "adaptive response" test

The genomic instability (GI) in somatic cells of the progeny (F1 generation) of male mice chronically exposed to low-dose gamma-radiation was studied by comparative analysis of chromosome damage. BALB/C male mice exposed to 0.1 Gy (0.01 Gy/day) and 0.5 Gy (0.01 and 0.05 Gy/day) were mated with unirradiated females 15 days after irradiation. For comparison of radiosensitivity, two-month-old males, the descendants of irradiated and unirradiated animals, were subjected to irradiation with a dose of 1.5 Gy (0.47 Gy/min) from a 60Co source. GI was revealed by the standard scheme of adaptive response. The experiments indicated that, by using the test "adaptive response", it is possible to detect the transition of gamma-radiation-induced genomic instability in sex cells of male parent into somatic cells of mice (F1 generation) either from changes in radiosensitivity or by the absence of the adaptive response induced by a standard scheme.     

Postirradiation change in the radiosensitivity of rats in relation to the preliminary radiation dose in the cutaneous form of radiation injury

The experimental animals were exposed two times to soft 17kV X-radiation. Post-irradiation changes in radiosensitivity were shown to depend upon dose of preliminary irradiation (10, 18 and 25 Gy). The state of radiosensitive tissues was studied and a comparison was made of a residual damage curve with a change in the proliferative activity of dividing tissue elements during 30 days after irradiation.     

Effect of X irradiation on secondary palate development in mice

The mechanisms whereby X irradiation induces palatal clefting were investigated in vivo and in an in vitro organ culture system. When pregnant mice at day 12.5 of gestation were exposed to a 4-Gy dose of whole-body X radiation, the incidence of palatal clefting in their offspring was 91%. The volume of the irradiated palatal shelves was too low for them to make contact with each other. On gestational day 13.5 after labeling, bromodeoxyuridine-positive cells were sparse and apoptotic cells were abundant in the irradiated shelves. To prevent secondary effects of irradiation from the injured maternal body, fetal palatal explants were immediately transferred to an organ culture system after X irradiation in utero. The incidence of palatal clefting was 24%, much lower than the incidence in vivo. The addition of 10(-4) M of dexamethasone to the culture medium increased the incidence of palatal clefting to 56%. These findings indicated that X irradiation inhibited cell proliferation and induced apoptosis, resulting in small-volume palatal shelves that could not fuse with each other. The organ culture data also indicated that 4 Gy of irradiation appears to produce its effects both by a direct action on the fetus and indirectly by affecting the metabolism of the pregnant dam.     

Induction and rejoining of DNA double-strand breaks in human cervix carcinoma cell lines of differing radiosensitivity

Five recently established cell lines of human carcinoma of the cervix of varying radiosensitivity have been used to determine whether the induction or rejoining of DNA double-strand breaks (dsb) shows any correlation with radiosensitivity or radiation recovery capacity. Double-strand DNA breaks have been measured using neutral filter elution at pH 9.6. The number of breaks induced immediately after irradiation with doses of 10 to 40 Gy 60Co gamma rays appeared to show some correlation with radiosensitivity particularly after 10 Gy; the two more radiosensitive lines incurred more breaks than the more radioresistant lines. In addition, the shape of the induction curve with dose was linear for the two sensitive lines but curvilinear for the resistant lines. Despite the dose scales being different, this mirrored their respective cell survival curve shapes. After 30 or 50 Gy irradiation, rejoining of breaks appeared to be rapid and almost complete within 60 min at 37 degrees C for the three resistant lines. However, for the sensitive lines, one line (HX160c) in particular exhibited a reduced rate of dsb rejoining. In addition, a residual level of dsb was present in this line even after allowing rejoining for 3 h. While induction and rejoining of DNA dsb therefore appears to be a factor in determining radiosensitivity, at doses relevant to cellular survival (up to 10 Gy), the greater induction of DNA dsb in radiosensitive lines may play a significant role in determining the cellular response to ionizing radiation.     

Variation in the sensitivity of the mouse spermatogonial stem cell population to fission neutron irradiation during the cycle of the seminiferous epithelium

Dose-response studies of the radiosensitivity of spermatogonial stem cells in various epithelial stages after irradiation with graded doses of fission neutrons of 1 MeV mean energy were carried out in the Cpb-N mouse. These studies on the stem cell population in stages IX-XI yielded simple exponential lines characterized by an average D0 value of 0.76 +/- 0.02 Gy. In the subsequent epithelial stages XII-III, a significantly lower D0 value of 0.55 +/- 0.02 Gy was found. In contrast to the curves obtained for stem cells in stages IX-III, the curves obtained in stages IV-VIII indicated the presence of a mixture of radioresistant and radiosensitive stem cells. In stage VII, almost no radioresistant stem cells appeared to be present and a D0 value for the radiosensitive stem cells of 0.22 +/- 0.01 Gy was derived. Previously, data were obtained on the size of colonies (in number of spermatogonia) derived from surviving stem cells. Combining these data with data from the newly obtained dose-response curves yielded the number of stem cells, per stage and with the specific radiosensitivities, present in the control epithelium. In stages IX-XI, there are approximately 6 stem cells per 1000 Sertoli cells with a radiosensitivity characterized by a D0 of 0.76 Gy, which corresponds to one-third of the As population in these stages. (The As spermatogonia are presumed to be the stem cells of spermatogenesis.) IN stages XII-III, there are approximately 12 stem cells per 1000 Sertoli cells with a radiosensitivity characterized by a D0 of 0.55 Gy, which roughly equals the number of A single spermatogonia in these stages. These calculations could not be made for stages IV-VIII since no simple exponential lines were obtained for these stages. In view of the pattern of the proliferative activity of the spermatogonial stem cells during the epithelial cycle, it appears that the stem cell population is most radiosensitive during the period when the majority of these cells are in G0 phase, most resistant when the cells are stimulated again into proliferation, and of intermediate sensitivity during active proliferation.     

Peculiarities of the ovary structure in the rat offspring developing under conditions of the removed thyroid gland of female rat with the thyroxine replacement therapy and external radiation exposure in utero

The influence of a single external gamma-radiation at a dose of 1.0 Gy (dose rate 9.08 x 10(-4) Gy/sec) on the 15th day of gestation in case of the removed complex of thyroid and parathyroid glands (thyroidparathyroidectomy) on the first day of gestation, as well as introduction of thyroxin and CaC12 on the structure of offspring ovary in postnatal ontogenesis (30-day old animals) was studied. It has been shown that thyroidparathyroidectomy of a female mother rat with thyroxine replacement therapy and irradiation, as well as the combination of these factors disturb the structure of ovarian tissues of the offspring. A single external irradiation on the 15th day of embryogenesis causes death of a considerable part of primordial follicles in the offspring ovary and growth of follicular layers in the secondary follicles. Thyroidparathyroidectomy of female rat on the first day of gestation with thyroxine replacement therapy causes delay in the development of follicles in the ovary at the early stages of maturation of 30-day old animals. The radiosensitivity of the ovarian tissues of the offspring that has been developed under the combined effect of the factors studied increases and results in an almost full loss of pool cells in the ovary of infant rats.     

Characteristics of the development of interphase death of hematopoietic tissue in dogs in response to gamma irradiation

In experiments with 2-3 week dogs it was shown that whole-body gamma-irradiation with a dose of 3 Gy causes an insignificant absolute rise in the amount of degrading chromatin of the haemopoietic organs during the first 24 h following irradiation. After 48 h, this cell death parameter is normalized. A considerably lower radiosensitivity of lymphoid cells of dogs compared to small laboratory animals is indicated by a stable DNA content per 1 g of thymus, intactness of its structure after irradiation, and the absence of an increase in thymidine content of blood of young and adult dogs under the effect of 3-3.7 Gy radiation.     

The influence of chronic and of acute irradiation on the polymorphism of RAPD-markers in offspring for irradiated mice

On mice lines BALB/c and CBA/lac was performed the study of molecular-genetics effects in mice progeny after the chronic (dose rate -0.0017 Gy/day, total dose -0.36 Gy) and acute (dose range 1-3 Gy) exposure of y-radiation on the parents. For variability analysis was used technique of amplification DNA with series of random primers (RAPD-assay). Random primers were used as single primer and in mixture of ones. In this work were held the comparative analysis of the genetic radiosensitivity for stem spermatogonia and spermatides. After the acute exposure the dose dependence for levels of polymorphism of RAPD-markers were obtained. After the chronic irradiation, significant differences from control group were obtained only by use primers mixture M1. Comparative analysis of the genetic radiosensitivity of different stages of mice spermatogenesis are display is similar sensitivity of stem spermatogonia and spermatides after doses of irradiation 1 Gy and 3 Gy. Indicated that after irradiation by dose 2 Gy, spermatogonia are more sensitivity than spermatides.     

Polyploidization of rat hepatocytes induced by x-ray radiation at different periods of the cell cycle

As determined by the yield of polyploid hepatocytes after X-irradiation of rats with a dose of 6 Gy the S-stage of the cell cycle was most radiosensitive; as to the yield of cells with chromosome aberrations the middle of the G1-stage was the most radiosensitive period of the cell cycle. The differences in the radiosensitivity of the cell cycle stages indicated that although primary lesions were similar molecular mechanisms leading to tre final effect were essentially different.     

Early effects of low doses of ionizing radiation on the fetal cerebral cortex in rats

Pregnant rats were exposed to gamma radiation from a 137Cs irradiator on gestational Day 15. Fetuses that received 0.25, 0.5, 0.75, or 1.0 Gy were examined 24 h after irradiation for changes in the cells of the cerebral mantle of the developing brain. The extent of changes following 0.5 Gy was studied at 3, 6, 12, or 24 h after exposure. Cortical thickness of the cerebral mantle was not significantly altered. The number of pyknotic cells, number of macrophages, nuclear area, and number of mitotic cells were altered in a dose-related way. The number of pyknotic cells was significantly increased at all doses. A positive correlation between the number of pyknotic cells and the number of macrophages developed with time. At 3 h after irradiation about 60% of pyknotic cells were found in the subventricular zone and about 25% in the intermediate zone and cortical plate. The number of such cells in the upper layers of the cortex steadily increased up to 24 h, at which time about 70% of pyknotic cells were in these two layers. The relationship of the movement of pyknotic cells to migration of postmitotic neuroblasts is discussed.     

Radioemetic protection at 24 h after 60Co irradiation in both normal and postremectomized cats

The radioemetic dose-response relationships were established in 46 unanesthetized cats for each of two whole-body exposures, 24 h apart, to 60Co radiation at selected doses between 7.5 and 60 Gy. Individual episodes of vomiting were recorded for a period of 48 h as distinctive intrathoracic pressure deflections signaled through a catheter placed in the superior vena cava. Five cats with chronic lesions of the area postrema were included in the group exposed to 45 Gy. The lesioned animals were not detectably different in their radiation response behavior from the intact cats. Initial exposure in the entire cat series produced an increasing incidence of radioemesis from 25 to 80% over the specified dose range for the first observation period of 24 h. By contrast, the second exposure produced an inverse dose-related incidence of emesis varying from 63% to zero with an apparent crossover of radioemetic susceptibility for the two exposures at about 15 Gy. Complete protection during 12 h after the second exposure was obtained at 30, 45, and 60 Gy, and for all of 24 h at 45 and 60 Gy. In a separate group of 11 normal cats, the emetic drug xylazine invariably evoked vomiting when radioemetic protection was otherwise manifest after initial irradiation at 45 Gy. We conclude that the temporary recovery of well-being following acute lethal irradiation results selectively through increased radioemetic resistance, and it does not depend on the integrity of the area postrema.     

不同剂量的X-射线全身照射对小鼠健康状况及涎腺的影响

目的:通过直线加速器全身照射昆明小鼠建立辐射损伤模型,探索不同放射剂量对小鼠健康状况及涎腺功能和结构的影响。方法:选取八种不同剂量对昆明小鼠行体外全身照射,于照射后一个月内观察小鼠生长情况、体重变化;照射后一周、一个月检测各组小鼠血象的变化;测定放射半数致死剂量;照射后两个月,测定各组小鼠的唾液流量及唾液淀粉酶含量,并对下颌下腺组织切片行HE染色。结果:13Gy和15Gy照射组小鼠的体重逐渐下降,一周后死亡,其余组小鼠体重最终呈增加趋势。X-射线全身照射的半数致死量为10Gy。照射后一周,照射组小鼠的白细胞数目明显降低,与对照组比较有明显统计学差异(P0.01);在其他血象方面,除了7Gy组外,其他照射组与对照组比较也均有统计学差异(P0.05)。照射一个月后,各照射组小鼠的血象均恢复正常。照射后两个月,9Gy组和11Gy组小鼠的唾液流量及唾液淀粉酶含量均显著低于0Gy组,且11Gy组较9Gy组亦明显降低,差异均有统计学意义(P0.05)。随照射剂量的增加,小鼠的下颌下腺腺泡细胞数目逐步减少,结构排列紊乱,组织损伤逐渐加重。结论:X-射线全身照射引起小鼠健康状况受损,免疫功能减低,损伤程度与放射线强度呈剂量依赖性,小鼠半数致死量为10Gy,该剂量适合建立全身放射损伤模型。     

Effects of irradiation on the nonlymphoid thymus in vitro

Thymic explant cultures were used to study the radiosensitivity of nonlymphoid thymic components in dogs. Thymic fragments from fetal (50 days gestation), newborn, and juvenile (70 days old) dogs were irradiated in vitro at 0, 0.5, 1, 2, or 4 Gy prior to culture. Colonies were classified as epithelial, spindle, or mixed cell type, and colony numbers were counted and diameters measured. Radiation caused a significant dose-related decrease in the number of spindle cell colonies from all ages. There was a corresponding, but smaller, dose-related increase in the number of epithelial colonies. The diameter of spindle cell colonies also decreased with dose, and this was accompanied by a reduction in cell density. While epithelial colony diameters did not change consistently with dose, there was an overall reduction in cell density in these colonies. This was more severe in the fetal than in the juvenile cultures. These results indicate that the putative mesenchymal (spindle cell) components of the thymus are significantly more radiosensitive than the epithelium at all ages and that fetal epithelium is more sensitive than epithelium from postnatal animals. This suggests that radiation-induced thymic epithelial defects reported after prenatal irradiation could be due to a combination of direct epithelial injury and defective inductive interaction between epithelium and the more radiosensitive mesenchyme.     

Neutron irradiation of human melanoma cells

The biological characteristics and in vitro radiosensitivity of melanoma cells to thermal neutrons were investigated as a guide to the effectiveness of boron neutron capture therapy. Plateau phase cultures of three human malignant melanoma-established cell lines were examined for cell density at confluence, doubling time, cell cycle parameters, chromosome constitution, and melanin content. Cell survival dose-response curves, for cells preincubated in the presence or absence of p-boronophenylalanine. HCl (10B1-BPA), were measured over the dose range 0.6-8.0 Gy (N + gamma). The neutron fluence rate was 2.6 x 10(9) n/cm2/s and the total dose rate 3.7 Gy/h (31% gamma). Considerable differences were observed in the morphology and cellular properties of the cell lines. Two cell lines (96E and 96L) were amelanotic, and one was melanotic (418). An enhanced killing for neutron irradiation was found only for the melanotic cells after 20 h preincubation with 10 micrograms/ml 10B1-BPA. In view of the doubling times of the cell lines of about 23 h (96E and 96L) or of 36 h (418), it seems likely that an increased boron uptake, and hence increased radiosensitivity, might result if the preincubation period with 10B1-BPA is extended to several hours longer than the respective cell cycle times.     

Comparison of three inbred lines of mice by overall and genetic radiosensitivity

The radiosensitivities of three mouse strains (BALB/cLacY, C3H/SnY, and 101/HY) have been compared using the following parameters: survival after irradiation at a dose of 6-7 Gy, chromosome aberration frequency in bone marrow cells after irradiation at a dose of 1.5 Gy, and the change in testis weight and frequency of abnormal sperm heads (ASHs) after irradiation at doses from 0.5 to 4 Gy. Strain BALB/c is the most radiosensitive with respect to the survival and chromosome aberration frequency in the bone marrow but the most resistant with respect to the change in testis weight and the frequency of abnormal sperm heads. Strain 101/HY was the most resistant with respect to survival and chromosome aberration frequency in bone marrow after irradiation but the most radiosensitive with respect to testis damage.     

The cytogenetic damage, radiosensitivity and adaptive response in children living in the different districts of Moscow

The spontaneous level of blood lymphocytes with micronuclei (MN), the sensitivity to 1.0 Gy irradiation and adaptive response (AR) after adaptive irradiation with a dose of 0.05 Gy 5 hr later have been studied in children population living in different districts of Moscow. It was shown that spontaneous frequency of cells with MN, the sensitivity to 1.0 Gy acute irradiation and the AR manifestation have significant differences in samples taken from children living in different districts. The individual variability is significant also. In each group of children the individuals with the enhanced radiosensitivity after adaptive irradiation have been observed. In conformance with the data of radioecological inspection the radiation situation in different Moscow districts is quite safe on overage but in some districts the spontaneous level of lymphocytes with MN, and radiosensitivity after 0.05 Gy irradiation were enhanced, the AR was not found.     

The effects of graded doses of 1 MeV fission neutrons or X rays on the murine hematopoietic stroma.

The acute radiosensitivity in vivo of the murine hematopoietic stroma for 1 MeV fission neutrons or 300 kVp X rays was determined. Two different assays were used: (1) an in vitro clonogenic assay for fibroblast precursor cells (CFU-F) and (2) subcutaneous grafting of femora or spleens. The number of stem cells (CFU-S) or precursor cells (CFU-C), which repopulated the subcutaneous implants, was used to measure the ability of the stroma to support hemopoiesis. The CFU-F were the most radiosensitive, and the survival curves after neutron and X irradiation were characterized by D0 values of 0.75 and 2.45 Gy, respectively. For regeneration of CFU-S and CFU-C in subcutaneously implanted femora, D0 values of 0.92 and 0.84 Gy after neutron irradiation and 2.78 and 2.61 Gy after X irradiation were found. The regeneration of CFU-S and CFU-C in subcutaneously implanted spleens was highly radioresistant as evidenced by D0 values of 2.29 and 1.49 Gy for survival curves obtained after neutron irradiation, and D0 values of 6.34 and 4.85 Gy after X irradiation. The fission-neutron RBE for all the cell populations was close to 3 and varied from 2.77 to 3.28. The higher RBE values observed for stromal cells, compared to the RBE of 2.1 reported previously for hemopoietic stem cells, indicate that stromal cells are relatively more sensitive than hemopoietic cells to neutron irradiation.     

Proliferation kinetics and PCNA expression of HL-60 cells following ionizing irradiation and granulocytic differentiation

The human promyelocytic leukaemia cell line, HL-60, was investigated with regard to proliferation and terminal differentiation following irradiation. The cells were X-irradiated and induced with 1.25% dimethyl sulfoxide (DMSO) towards the granulocytic lineage. Proliferation was measured via cell growth, clonogenicity and the bromodeoxyuridine/DNA incorporation assay. Immunohistochemical detection of proliferating cell nuclear antigen (PCNA) expression was used to discriminate cycling from non-cycling cells. The differentiation obtained was proved by testing for the immune function of the respiratory burst (NBT reduction test). The HL-60 cells studied revealed a high radiosensitivity (D₀= 0.63 Gy). After induction with DMSO, declines in cell growth, clonogenicity and PCNA positivity of the cells indicated a decrease in proliferation and an increase in differentiation. Starting on day 2 in culture, irradiation after seeding with 1 Gy accelerated the loss of the PCNA expression in induced cells (46%v. 3% PCNA-negative control cells on day 3). Induced cells gained the capability of exerting the respiratory burst, which was found to be dose-dependent radiosensitive (42% and 12% NBT-positive cells after 1 and 2 Gy, respectively, v. 53% NBT-positive control cells on day 8). Subpopulations in the cell line were evident in all parameters investigated. We discuss the HL-60 cell, not only as a model comparable to human progenitor cells, but also as a suitable tool in radiobiological research with regard to proliferation and differentiation following ionizing irradiation.     

Comparison of Three Inbred Mouse Strains with Respect to General and Genetic Radiosensitivity

The radiosensitivities of three mouse strains (BALB/cLacY, C3H/SnY, and 101/HY) have been compared using the following parameters: survival after irradiation at a dose of 6–7 Gy, chromosome aberration frequency in bone marrow cells after irradiation at a dose of 1.5 Gy, and the change in testis weight and frequency of abnormal sperm heads (ASHs) after irradiation at doses from 0.5 to 4 Gy. Strain BALB/c is the most radiosensitive with respect to the survival and chromosome aberration frequency in the bone marrow but the most resistant with respect to the change in testis weight and the frequency of abnormal sperm heads. Strain 101/HY was the most resistant with respect to survival and chromosome aberration frequency in bone marrow after irradiation but the most radiosensitive with respect to testis damage.