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S Hamaguchi

Publications and source records attributed to S Hamaguchi.

43 records · Page 3Linked to original sources
PubMed1988

Evidence for the sexual bipotentiality of spermatogonia in the fish, Oryzias latipes.

The origin of the oocyte-like cells (testis-ova) induced by the administration of estradiol in the testis of the fish, Oryzias latipes, was examined by light and electron microscopy. A small number of testis-ova at the zygotene stage was seen on the sixth day after the beginning of treatment with estradiol, and on the 12th day testis-ova at the pachytene and diplotene stages were observed. Ultrastructural observations revealed that the testis-ova at the zygotene stage were organized as cysts and that all testis-ova within a given cyst developed synchronously. The number of these testis-ova in each cyst varied but cysts containing 16-20 or 26-30 testis-ova were most frequently observed. Spermatogonia of O. latipes are classified morphologically into two types: the type A and the type B spermatogonia (Grier, '76 Cell Tissue Res., 168:419-431). Type A spermatogonia, which were separated from each other by Sertoli cells, were of the stem type and type B spermatogonia appeared to divide clonally 9-10 times in each cyst before entering meiosis. The present observations on zygotene testis-ova indicate that the testis-ova originate from type B spermatogonia which have divided clonally four or five times, suggesting that male germ cells remain sexually bipotent through the early stages of development of type B spermatogonia.

Animals↗
PubMed1985

Histochemistry of liver tumors induced by diethylnitrosamine and differential sex susceptibility to carcinogenesis in Oryzias latipes.

Liver tumor nodules were induced by the administration of diethylnitrosamine [(DENA) CAS: 55-18-5; N-nitrosodiethylamine] to the fish, Oryzias latipes. A histochemical study showed decreased ATPase and glucose 6-phosphatase (Glc-6-Pase) activities in most of the tumor nodules. Increased ATPase staining and, occasionally, Glc-6-Pase staining were also observed. In some nodules, the distribution of bile canaliculi was disordered, indicating positive ATPase activity. Basophilic and eosinophilic nodules could be discriminated by histologic examination. The observations on serial histochemical and histologic sections revealed extreme heterogeneity in the phenotypes of the nodules. Measurement of the enzyme-altered areas indicated that the development of nodules was more prominent in male than in female fish. Experiments with sex-reversed fish, XX males and XY females, suggested that the sex difference in the susceptibility to DENA does not result from the difference in sex chromosomes but from the difference in sexual phenotypes.

Adenosine Triphosphatases↗
PubMed1982

A light- and electron-microscopic study on the migration of primordial germ cells in the teleost, Oryzias latipes.

The primordial germ cells (PGCs) of Oryzias latipes in migration to the gonadal anlage have been investigated by light and electron microscopy. The ultrastructure of the PGCs, which occur in the subendodermal space on the syncytial periblast, differ conspicuously from that of the surrounding endodermal cells. After the PGCs move to the cavity between lateral plate and ectoderm, they are taken into the somatomesodermal layer and transferred to the dorsal mesentery where they form gonadal anlage with mesodermal cells. During their translocation to the formation of pseudopods, the PGCs are completely surrounded by mesodermal cells. Since these conditions seem unfavorable to the active translocation of the PGCs to the dorsal mesentery, it is more likely that the PGCs are transferred passively by the morphogenic activity of the lateral-plate mesoderm. Counts of the number of the PGCs revealed that they are mitotically dormant during the migratory period. After the completion of the migration, they regain their proliferative activity. The PGCs in the female proliferate more actively than those in the male, which provides the first morphological indication of sex differentiation in this species of fish.

Animals↗
PubMed1976

Change in the radiation responses of oogonia in the embryos and fry of the fish Oryzias latipes.

Embryos of the fish Oryzias latipes were irradiated with 1000 R of X-rays 1 day before hatching,and the post-irradiation change in the female germ-cell population was observed. Scarcely any reduction in the number of oogonia was observed, but their proliferation was inhibited. Repopulation occurred between 12 and 20 days after hatching. These responses were quite different from those of germ cells in the irradiated fry (Hamaguchi and Egami 1975). Embryos and/or fry were also exposed to 1000 R of X-rays 1 day before hatching and 0, 1, 2, and 3 days after hatching. A comparison of their responses suggested that the change in the radiation responses of oogonia is correlated with the initiation of meiosis.

Animals↗
PubMedDate not supplied

Acute cigarette smoking reduces vasodilative effect induced by sympathetic block in dogs.

BACKGROUND AND OBJECTIVES: The aim of this study is to clarify the influence of acute cigarette smoking on vasodilation induced by sympathetic block. METHODS: We measured mean arterial pressure, heart rate, left brachial artery blood flow (BABF), right femoral artery blood flow (FABF), and plasma catecholamines in dogs to examine the effect of acute cigarette smoking after stellate ganglion block (SGB). The experimental protocol was: (1) Left SGB using 1.0 mL 0.5% mepivacaine without smoking (sham smoking); and (2) left SGB using 1.0 mL 0.5% mepivacaine followed by a single cigarette smoking (nicotine 1 mg) 15 minutes after the block. RESULTS: SGB induced a significant increase of BABF during the study (baseline, 100%; peak at 10 minutes after SGB, 176% +/- 9%; P <.05) in sham smoking and a significant decrease of FABF from 10 minutes after the block to 20 minutes after sham smoking (baseline, 100%; bottom at 5 minutes after sham smoking, 82% +/- 8%; P <.05). Smoking after SGB induced a significant decrease of BABF 60 minutes after smoking (baseline, 100%; 69% +/- 11%; P <.05) and a significant decrease of FABF during the study (baseline, 100%; bottom at 20 minutes after smoking, 74% +/- 20%; P <.05). Smoking significantly increased plasma norepinephrine and epinephrine through the study. CONCLUSIONS: Sympathetic block induces a significant increase of peripheral blood flow, but smoking produces a significant decrease in the blood flow in the SGB-induced dilated vessels.

Anesthetics, Local↗
PubMedDate not supplied

Addition of clonidine increases duration and magnitude of vasodilative effect induced by sympathetic block with mepivacaine in dogs.

BACKGROUND AND OBJECTIVES: The aim of this study is to examine the duration and magnitude of vasodilative effect induced by sympathetic block with the addition of clonidine to mepivacaine. METHODS: We measured mean arterial pressure (MAP), heart rate (HR), and right and left brachial artery blood flow (BABF) before and after stellate ganglion block (SGB) in dogs. The experimental protocol was designed as follows: (1) left SGB using 1.0 mL 0.5% mepivacaine (n = 6) and (2) left SGB using the addition of clonidine 0.5 microg to 1.0 mL 0.5% mepivacaine (n = 6). RESULTS: MAP and HR did not change significantly throughout the study in either group. Left SGB with mepivacaine increased left BABF significantly from 10 minutes through 50 minutes after SGB (baseline, 100%; peak at 10 minutes after SGB, 176% +/- 28%; P <.01). Left SGB with the addition of clonidine to mepivacaine induced a significant increase of left BABF from 10 minutes through 70 minutes after SGB (baseline, 100%; peak at 10 minutes after SGB, 223% +/- 42%; P <.01). The values of left BABF after SGB with the addition of clonidine to mepivacaine were significantly higher than those of SGB with mepivacaine alone from 10 minutes through 80 minutes after SGB (P <.05). Right BABF decreased significantly after SGB throughout the study in both groups. CONCLUSIONS: The addition of clonidine increases both duration and magnitude of the vasodilative effect induced by sympathetic block over that caused by mepivacaine alone.

Adrenergic alpha-Agonists↗