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Biomedical subjects

N Egami

Publications and source records attributed to N Egami.

At least 19 recordsLinked to original sources
PubMed1989

Life-span studies on spontaneous tumor development in the medaka (Oryzias latipes).

A total of 961 medaka, separated chronologically from the first to the fifth year of life, were examined for spontaneous tumor development. While no liver tumors were found in either male or female medaka under the age of 1 year and the incidence in 2-year-old fish was relatively low (males 1.9% and females 1.7%), they became more common with advancing age. The incidence was higher in females than in males from 3 to 5 years of age, reaching 7.1% in 5-year-old female stock. These liver tumors included a total of 12 adenomas and 9 hepatocellular carcinomas. The hepatocellular carcinomas were histologically well differentiated and were all observed in female medaka. Spontaneous tumors occurring in organs other than the liver were rare and sporadic. Four squamous cell carcinomas, 5 melanomas and 4 lymphosarcomas were observed with no sexual or pronounced age bias being evident. The squamous cell carcinomas developed in the surface epithelium with local invasion into the dermis. Melanomas occurred in the abdominal cavity and demonstrated systemic invasion into various parts of the body. Three out of the 4 lymphosarcomas arose from the inner part of the operculum suggesting that these tumors were of thymic origin. They also showed extensive invasion. The data indicate a particular susceptibility of older female medaka to liver but not other tumor development.

Adenoma↗
PubMed1986

Effect of corticosteroids on the thymus of the fish Oryzias latipes.

Morphology and development of the thymus in fish Oryzias latipes was studied in response to corticosteroids. Adult fish were subjected to different concentrations of two corticosteroids, deoxycorticosterone acetate (DOCA) and cortisone acetate (CA). Histology of the thymus and thymocyte counts in treated fish were compared to normal ones. There was no change in histology of thymus due to CA treatment even those subjected to 10 mg/l water which is a lethal dose of DOCA. In contrast, the effect of DOCA at low doses (0.01 and 0.1 mg/l water) was examined and resulted in reduction of thymus volume due to depopulation of thymocytes from the entire gland. Thymus subjected to DOCA at a high dose (1 mg/l water) caused destruction of all thymocytes and reticular cells resulting in complete disappearance of the thymus. There was dose dependent mortality associated with DOCA. The maximum lethal dose was 10 mg/l causing death of all treated fish within a few hours. This information is relevant to the use of CS in fish therapy in response to stress.

Aging↗
PubMed1985

The production of cloned fish in the medaka (Oryzias latipes).

The measurement of cellular DNA content by DNA microfluorometry revealed that medaka embryos that were fertilized with normal sperm and exposed to heat shock (41 degrees C for 3 min) or hydrostatic pressure (700 kg/cm2 for 10 min) at 85-95 min after insemination were tetraploid. Embryos fertilized with normal sperm and exposed to heat shock (41 degrees C for 2 min at 2-3 min after insemination) were triploid. These results suggest that heat shock or hydrostatic pressure at 85-95 min after insemination arrests the first cleavage, while heat shock at 2-3 min after insemination arrests the second meiotic division. Medaka clones have been produced by the following method: Eggs from orange-red or variegated variety were activated by UV-irradiated, genetically impotent sperm of wild-type fish (UV sperm). The haploid eggs obtained were diploidized by preventing the first cleavage with heat shock or hydrostatic pressure to produce homozygous females. Each of the two homozygous females was mated with vasectomized male in isotonic balanced salt solution to collect unfertilized eggs. The collected eggs were activated with UV sperm and converted from haploid to diploid by arrest of the second meiotic division with heat shock. Hatched fry of each homozygous diploid (all females) were fed with a methyltestosterone-containing diet (40 micrograms/gm diet) to produce sex-reversed males, which were mated with brood females, and thus two cloned lines were obtained.

Animals↗
PubMed1985

Whole-body X-irradiation of mice accelerates polyploidization of hepatocytes.

Male C57BL/6 mice were whole-body irradiated with 4.75 Gy of X-rays at the age of 2 months and killed at 2, 6, 12 and 19 months after irradiation. The percentage survival began to decline earlier and faster in the irradiated group than the controls up to 19 months after exposure when the study was terminated. The nuclear DNA content of individual hepatocytes was measured by a Feulgen-DNA microfluorometric method, and hepatocytes were classified into various ploidy classes. In the irradiated mice, the degree of polyploidization was significantly higher than the controls by 2 months after exposure and steadily increased up to 6 months after exposure. Thereafter, however, a slow return to the control level was found up to 19 months after irradiation. These results appear to support a hypothesis that radiation accelerates the ageing process as judged from hepatocyte polyploidization.

Aging↗
PubMed1985

Effect of heat on radiosensitivity at different developmental stages of embryos of the fish Oryzias latipes.

Embryos of the fish, Oryzias latipes, at various developmental stages were heated before or after gamma-irradiation. The lethal effects of heat and radiation treatments were determined by the hatchability of the irradiated embryos. The radiosensitivity suddenly decreased at 3-days after fertilization. Heat (41 degrees C), either preceding or following irradiation, decreased the shoulder region (Dq) of the dose-response curves of the embryos irradiated at the 1-3 day stages, and increased the slope (D0) only at the 3 day stage. The magnitude of enhancement of radiosensitivity by pre- and post-heating was found to depend on the time and temperature of the heat as well as the developmental stage of the embryos; in 1- and 2-day embryos the effectiveness of post-irradiation heating was larger than that of pre-irradiation heating whereas in 3-day embryos there was no difference between the effectiveness of pre- and post-treatment. The sequence of heat (41 degrees C) and radiation treatment, and the time interval between the two treatments, also influenced the effectiveness of heat on radiosensitivity, depending upon the developmental stage; recovery from heat effects was not observed within a time interval of up to 3 h before radiation exposure for either 1- or 3-day embryos, whereas recovery from the radiation lesion occurred, for only 1-day embryos, within 1 h of subsequent heat exposure.

Age Factors↗
PubMed1984

Dominant lethal mutations induced by MMS and mitomycin C in the fish Oryzias latipes.

Males of the fish Oryzias latipes were treated with various chemicals and then mated with normal females. The fertility and hatchability of the eggs laid by the parents were examined, and the dominant lethal effects were estimated. Mitomycin C induced dominant lethals in the fish spermatids and spermatocytes after the males had been treated with concentrations of 2.5 and 25 micrograms/ml. Methyl methanesulfonate (MMS) induced dominant lethals in spermatozoa and spermatozoa and spermatids after the injection of 200 and 400 mg/kg. These results are in good agreement with the results obtained with mice. However, the effects of ethyl methanesulfonate (EMS) were not clear on spermatogenic cells at any stage. We could not recognize any significant induction of dominant lethals by urethanes, bleomycin, caffeine, and two kinds of food-color additives, at least under the present experimental conditions.

Animals↗
PubMed1984

The unique responses of the primordial germ cells in the fish Oryzias latipes to gamma-rays.

The effects of gamma-radiation on the development of the primordial germ cells (PGCs) of medaka embryos (Oryzias latipes) during the early stages of development were quantitatively examined and compared to the effects on the intestinal cells. The PGCs develop in three stages: an extra-gonadal proliferative stage (1-2.5 days after fertilization), a mitotically inactive stage after the termination of the migration into the gonad (2.5-4.5 days), and an extensive proliferative stage (between 4.5 days and hatching). A dose-rate effect was absent in the PGCs, regardless of their mitotic activity, when dose rates were 2.5 and 0.14 Gy/min. The radiation effect on the PGCs was not reduced by hypoxia and was not enhanced by heat treatment during the proliferating stages. Conversely, radiation resistance was induced in the PCGs during the mitotocally inactive stage by hypoxia and, unexpectedly, by heat treatment. From the present data, we conclude that the PGCs have a small repair ability, and we discuss the radiation resistance induced in the PGCs by hypoxia and heat treatment.

Animals↗
PubMed1984

Effect of gamma irradiation on the reproductive system of the pond snail Physa acuta.

Changes in the survival rate in adults and embryos of the pond snail Physa acuta were studied after acute whole-body gamma irradiation. The LD50 value of the adult snails was about 40 kR. The LD50 values of the embryos irradiated 0 and 1 day after oviposition were about 0.9 and 2 kR, respectively. Histological changes in the ovotestis, the number of eggs laid, and their hatchability were examined in the irradiated adult snails. A fall and a subsequent recovery were observed for these characteristics after irradiation with 8 kR of gamma rays. The relative constitution of the germ-cell populations was greatly changed by the same dose of gamma rays. The proportion of immature germ cells was reduced, and the total number of germ cells also diminished 11 days after irradiation. After depletion, the ovotestis was first repopulated with gonia , and then with oocytes, spermatocytes, and spermatids.

Animals↗
PubMed1983

Dominant lethal mutation rate after gamma-irradiation of the fish, Oryzias latipes.

When laying females or males of the small fish Oryzias latipes were irradiated with gamma-rays and then mated with a non-irradiated partner, the fertility and hatchability of the embryos were reduced as the doses increased. In respect to hatchability (the induction of dominant lethality), the male was more sensitive than the female, and mature sperm were most sensitive among the various stages of spermatogenetic cells. The dose-rate effects on the production of the dominant lethality were observed in spermatogonia and spermatocytes. The inbred strain of the fish, HB-1, was sensitive to gamma-rays. Since the relationship between dose and the decrease in hatchability was almost linear, at least within a limited range, we think that this system would be useful for monitoring mutagenic factors in an aquatic environment.

Animals↗
PubMed1983

Effects of gamma-irradiation on the rejection of transplanted scale melanophores in the teleost, Oryzias latipes.

The effects of gamma-irradiation on allograft rejection in the teleost, Oryzias latipes, were examined at 25 degrees C. The survival of melanophores in the transplanted scale was observed as an index of rejection. Allografts were rejected in non-irradiated fish within 7 days. In the gamma-irradiated recipients (2kR), the grafts were rejected more slowly, but still within 20 days. The gamma-ray effects, however, disappeared almost completely within 25 days after the irradiation. If the same recipient again received transplants, the secondary response occurred clearly and the melanophores were rejected very rapidly. The secondary response was suppressed by gamma-rays if the fish was irradiated just before the second transplantation. Immunologic memory against the first transplants disappeared within 30 days, a period shorter than that of mammals.

Animals↗