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  • 1
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The rat median eminence contains at least three kinds of granules or vesicles: 1. large electron-dense granules (perhaps carriers of neurohypophysial hormones), 2. small electron-dense granules with or without haloes (perhaps carriers of catecholamines) and 3. synaptic vesicle-like structures (perhaps carriers of acetylcholine). The former two electrondense granules exist in separate axons but they coexist with the latter vesicles in the same axons. The pars nervosa shows basically a similar structure to the median eminence. However, the axons containing the small electron-dense granules are very few. In the pars tuberalis, there are at least two types of cells: the cells of one type contain much cytoplasm with large round nuclei and those of the other type contain a small amount of cytoplasm with polymorphic nuclei. The cells of the former include multivesicular bodies and secretory granules, but those of the latter do not. Some of capillaries of the primary plexus are surrounded by the cells of the pars tuberalis on one side and by neurosecretory axon endings on the other side. The median eminence contains high concentration of acetylcholine or an acetylcholine-like substance and shows neurohypophysial hormone activity.
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  • 2
    ISSN: 1432-136X
    Keywords: Prolactin ; Growth hormone ; Calcium ; Pituitary ; Eel, Anguilla japonica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Effects of changes in environmental Ca2+ on the secretion of prolactin, a possible hypercalcemic hormone, were examined both in vivo and in vitro in the Japanese ecl, Anguilla japonica. Transfer of seawater- or freshwater-adapted fish to fresh water, fresh water containing 10 mmol Ca2+ · 1-1 sea water, Ca2+-free sea water, or deionized water was accompanied by significant changes in plasma Ca2+ levels after 7 days, except for the fish transferred from fresh water to fresh water and from sea water to sea water. Changes in external Ca2+ concentrations did not affect plasma prolactin levels, although plasma prolactin levels as well as pituitary prolactin contents were significantly greater in fish in a hypotonic environment than those in a hypertonic environment, regardless of the external Ca2+ concentration. Hypercalcemia, induced by removal of the corpuscles of Stannius, did not alter plasma prolactin levles. Incubation of the pituitary in the medium with different Ca2+ concentrations (up to 2.9 mmol·l-1) did not affect the basal release of prolactin, except at an extremely low Ca2+ concentration (less than 0.1 mmol·l-1) where prolactin release was inhibited. Addition of Ca2+ ionophore (A23187) to the medium led to a marked and significant increase in prolactin release, indicating that an increase in intracellular Ca2+ stimulates prolactin release. However, the effect was not specific to prolactin cells; a similar increase was seen in growth hormone release. These results indicate that changes in environmental Ca2+ concentration may not be the primary factor influencing prolactin secretion in the eel; changes in environmental osmolality or Na+ levels seem to be more critical for the regulation of prolactin secretion.
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  • 3
    ISSN: 1434-6079
    Keywords: PACS. 32.80.Pj Optical cooling of atoms; trapping - 39.90.+d Other instrumentation and techniques for atomic and molecular physics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We utilized a blue-detuned Laguerre-Gaussian (doughnut) laser beam to trap cold rubidium atoms by optical dipole force. ”Pulsed” polarization gradient cooling was applied to the trapped atoms to suppress the trap loss due to heating caused by random photon scattering of the trapping light. In this trap about 108 atoms were initially captured and the trap lifetime was 1.5 s, which was consistent with losses due to background gas collisions. This trap can readily be applied to atom guiding, compression, and evaporative cooling.
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  • 4
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    ISSN: 1573-5168
    Keywords: chum salmon ; osmoregulation ; prolactin ; growth hormone ; cortisol ; thyroxine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The osmoregulatory ability of chum salmon (Oncorhynchus keta), reared in fresh water for a prolonged period, was examined by transferring them directly to seawater and then back to fresh water. When fry and juveniles weighing 0.3–125g, reared in fresh water for 1.5–13 months, were transferred directly to seawater, they adjusted their plasma Na+ concentration to the seawater-adapted level within 12–24h. When they were transferred back to fresh water after having been adapted to seawater for 2 weeks, the plasma Na+ level gradually decreased during the first 12–24h, and then increased to reattain the initial freshwater level after 5–7 days. No mortality was observed during the experiment except among the smallest fry weighing about 0.3g after transfer to seawater (2.1%). The maintenance of good osmoregulatory ability of the chum salmon for a prolonged period in fresh water seems to be unique among Pacific salmon, with the possible exception of the pink salmon. Changes in plasma levels of hormones during the transfer experiments were recorded in juveniles reared in fresh water for 13 months. Prolactin levels increased maximally 3 days after transfer from seawater to fresh water, as would be expected from its well-established role in freshwater adaptation in several euryhaline teleosts. In addition, an increase in plasma growth hormone was observed during the first 12h after seawater transfer, along with a tendency towards a decrease during freshwater transfer, suggesting an important role for this hormone in seawater adaptation. There were no consistent changes in plasma levels of thyroxine and cortisol during freshwater to seawater or seawater to freshwater transfer.
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  • 7
    ISSN: 1573-5168
    Keywords: thyroid hormones in maturing gonads ; ovary ; testis ; thyroxin ; triiodothyronine ; teleost
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T4) were less than 5 ng ml−1, and those of 3,5,3′-triiodo-L-thyroxine (T3) were less than 2 ng ml−1 I in both males and females, regardless of the degree of sexual maturity or the gonadosomatic index (GSI). There was no clear relationships between circulating thyroid hormone levels and tissue levels. The ovarian T4 concentrations were undetectable (less than 0.2 ng g−1) or less than 2 ng g−1 when GSI was lower than 1%, but increased thereafter and reached a plateau of 8–10 ng g−1 when GSI became 2%. The ovarian T3 concentrations were about 5 ng g−1 when GSI was 1%, increased to a maximum level (20 ng g−1) when GSI was about 2%, and decreased to a constant level of 10 ng g−1 thereafter. The T4 and T3 content in single oocyte increased proportionally to the oocyte volume, indicating a constant incorporation of the hormones into the oocyte. The T4 concentrations in the testis were 1 ng g−1 or less regardless of the GS1. On the other hand, the T3 concentrations were highest (15 ng g−1) when the GSI was less than 1%, decreased thereafter when spermatocytes appeared in the testis, and became about 5 ng g−1 I in testes containing spermatozoa, raising the possibility of a role for T3 during early gamete and/or gonad maturation of testes.
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  • 8
    ISSN: 1573-5168
    Keywords: tilapia ; Oreochromis mossambicus ; osmoregulation ; larva ; embryo ; water permeability ; chloride turnover ; drinking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Euryhaline tilapia (Oreochromis mossambicus) can breed either in fresh water (FW) or in seawater, and the developing embryos and larvae withstand direct transfer from FW to SW or vice versa, before the development of osmoregulatory organs. In the study, developmental changes in drinking rate and ion and water permeability were examined after transfer of the embryos from FW to SW. Drinking was measured by accumulation of fluorescent beads in the intestine and also by 14C-dextran accumulation he whole body. The drinking rate increased steadily from 2 to 10 days after hatching, and the larvae in SW consistently imbibed more water than those in FW. The diffusional water permeability remained low during embryonic stages but increased markedly after hatching in both FW and SW; the water permeability was consistently less in SW-adapted embryos and larvae than those in FW. In contrast, the turnover rates of chloride ion in SW were 50 to 100 times greater than those in FW, and increased markedly after hatching. The drinking rate as well as ion and water permeability of the tilapia embryos and larvae in FW and SW were comparable with those reported for stenohaline species. These results clearly indicate that different water and ion regulatory mechanisms are operating in the tilapia embryos and larvae in FW and those in SW to convey their strong euryhalinity.
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  • 9
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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