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81.
David I. Dunstan Terry D. Bethune Cheryl A. Bock 《In vitro cellular & developmental biology. Plant》1993,29(3):109-112
Summary The production of cotyledonary somatic embryos of white spruce from cultures grown long-term as suspensions was investigated.
We report the effects of removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from the maintenance medium (ordinarily containing
both 2,4-D and benzyl adenine) before (±)-ABA-stimulated maturation. In particular the use of a 1-wk culture period
without 2,4-D was found to improve the production of normal-looking cotyledonary somatic embryos. Using high performance liquid
chromatography analyses of culture supernatants, it was determined that this affect was not related to altered ABA metabolism.
Germination of cotyledonary somatic embryos from cultures pretreated by the 1-wk culture period without 2,4-D was improved
compared with similar embryos from cultures that had not been pretreated. 相似文献
82.
Alfonso Gonzalez Terry D. Oberley Janice L. Schultz Jennifer Ostrom Jonathan J. Li 《In vitro cellular & developmental biology. Animal》1993,29(7):562-573
Summary Primary diethylstilbestrol-induced kidney tumors from Syrian hamsters were grown in vitro and maintained in culture for 6
mo. Combined immunohistochemical studies using antibodies to intermediate filaments and ultrastructural studies of tumor cells
in culture exhibited characteristics similar to tumor cells in vivo. Furthermore, the cells manifested transformed properties
in culture; they grew both as multilayered colonies attached to the tissue culture substrate and as floating multicellular
colonies (spheroids). When cultured cells were injected into diethylstilbestrol-treated recipient hamsters, tumors developed
at the injection sites. In contrast, renal tubules or whole kidney cortex from control hamsters cultured in the same medium
underwent only short-term growth, with senescence developing after approximately 1 mo. However, cell cultures of kidney cortex
from animals treated in vivo for 5 mo. with diethylstilbestrol formed a cell line. This diethylstilbestrol-induced cell line
has been maintained in culture for 1.5 yr and has the following characteristics: a) it is anchorage-dependent, b) it is negative
in in vivo tumorigenicity tests, and c) cultured cells are histochemically and ultrastructurally similar to cultured tumor
cells. This culture system should prove to be of use in studying hormonal carcinogenesis in vitro.
This study was supported by the Medical Research Service, Department of Veterans Affairs, Washington, DC, and by grant CA-22008
from the National Cancer Institute, NIH, DHHS, Bethesda, MD. 相似文献
83.
84.
Simple-sequence tandem repeat sequences in the 3 UTR of interleukin 5 (IL5)-receptor gene of human and mouse are polymorphic in their length among humans and different strains of mice. In 20 different human Epstein-Barr virus (EBV)-transformed cell lines, six alleles of IL5R could be distinguished. In the mouse, three different alleles are found. With the human-specific IL5R tandem repeat marker in human-rodent somatic cell hybrids, the IL5R gene was mapped to human Chromosome (Chr) 3 p25–p26. With the mouse-specific IL5R tandem repeat sequence in recombinant inbred strains of mice, the Il5r gene was mapped to the distal part of mouse Chr 6 close to the Raf-1 locus. 相似文献
85.
86.
Terry Harrison 《American journal of physical anthropology》1992,88(3):407-409
87.
In addition to assessing the impacts of CO2 doubling on environment and society, more consideration is needed to estimate extreme events or surprises. This is particularly important at the intersection of disciplines like climate and ecology because the potential for large discontinuities is high given all the possible climate/biota interactions. The vast disparities in scales encountered by those working in traditional ecology (typically 20 m) and climatology (typically 200 km) make diagnoses of such interactions difficult, but these can be addressed by an emerging research paradigm we call strategic cyclical scaling (SCS). The need to anticipate outlier events and assign them subjective probabilities suggests emphasis on interdisciplinary research associations. The desire to reduce societal vulnerability to such events suggests the need to build adaptive management and diverse economic activities into social organizations. The effectiveness of adaptation responses to anticipated climatic changes is complicated when consideration of transient changes, regional disturbances, large unforseeable natural fluctuations and surprises are considered. Slowing down the rate of disturbances and decreasing vulnerability are advocated as the most prudent responses to the prospect of human-induced climatic changes. 相似文献
88.
89.
Increased intracellular calcium concentration ([Ca2+]i) is required for smooth muscle contraction. In tracheal and other tonic smooth muscles, contraction and elevated [Ca2+]i are maintained as long as an agonist is present. To evaluate the physiological role of steady-state increases in Ca2+ on tension maintenance, [Ca2+]i was elevated using ionomycin, a Ca2+ ionophore or charybdotoxin, a large-conductance calcium-activated potassium channel (KCa) blocker prior to or during exposure of tracheal smooth muscle strips to Ach (10–9 to 10–4
M). Ionomycin (5 µM) in resting muscles induced increases in [Ca2+]i to 500±230 nM and small increases in force of 2.6±2.3 N/cm2. This tension is only 10% of the maximal tension induced by ACh. Charybdotoxin had no effect on [Ca2+]i or tension in resting muscle. After pretreatment of muscle with ionomycin, the concentration-response relationship for ACh-induced changes in tension shifted to the left (EC50=0.07±0.05 µM ionomycin; 0.17±0.07 µM, control, p<0.05). When applied to the muscles during steady-state responses to submaximal concentrations of ACh, both ionomycin and charybdotoxin induced further increases in tension. The same magnitude increase in tension occurs after ionomycin and charybdotoxin treatment, even though the increase in [Ca2+]i induced by charybdotoxin is much smaller than that induced by ionomycin. We conclude that the resting muscle is much less sensitive to elevation of [Ca2+]i when compared to muscles stimulated with ACh. Steady-state [Ca2+]i limits tension development induced by submaximal concentrations of ACh. The activity of KCa moderates the response of the muscle to ACh at concentrations less than 1 µM. 相似文献
90.
The present study was undertaken to further characterize the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata in the central processing of nociceptive and cardiovascular signals, and its modulation by metenkephalin. In Sprague-Dawley rats anesthetized with pentobarbital sodium, we found that all 125 spontaneously active NRGC neurons that responded to noxious stimuli (tail clamp) also exhibited arterial pressure-relatedness. Forty neurons additionally manifested cardiac periodicity that persisted even during nociceptive responses. While maintaining their cardiovascular responsive characteristics, the nociception-related NRGC neuronal activity was blocked, naloxone-reversibly (0.5 mg/kg, i.v.), by morphine (5 mg/kg, i.v.). Microiontophoretically applied met-enkephalin suppressed the responsiveness of NRGC neurons to individually delivered tail clamp or transient hypertension induced by phenylephrine (5 µg/kg, i.v.). Interestingly, in NRGC neurons that manifested both nociception and arterial pressure relatedness, the preferential reduction in the response to noxious stimuli upon simultaneous elevation in systemic arterial pressure was reversed to one that favored nociception in the presence of met-enkephalin. All actions of met-enkephalin were discernibly blocked by the opioid receptor antagonist, naloxone. Our results suggest that individual NRGC neurons may participate in the processing of both nociceptive and cardiovascular information, or in the coordination of the necessary circulatory supports during nociception. In addition, neuropeptides such as met-enkephalin may exert differential modulation on neuronal responsiveness according to the prevailing physiologic status of the animal. They also showed that NRGC may be a central integrator for pain and cardiovascular-related functions. 相似文献