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921.
922.
Vasoactive intestinal peptide (VIP) and, to a lesser extent, glucagon were found to increase intracellular cyclic AMP rapidly in cultured glial (Müller) cells of the chick embryo retina. Although VIP elicited higher cyclic AMP accumulation than glucagon at each concentration tested, the half-maximal concentrations were similar, i.e., 6 X 10(-8) M for VIP and 8 X 10(-8) M for glucagon. Secretin had a minimal effect on cyclic AMP accumulation even at a very high (5 X 10(-6) M) concentration. Several other peptide and nonpeptide putative agonists also had little effect on cyclic AMP accumulation. The cultured Müller cell may thus be a useful model for examining VIP and glucagon effects on glial elements of the CNS. 相似文献
923.
Gerald Drews Kay Kohlhaw Daniel Palmes Petra Madaj-Sterba Thomas Hartwig Johann Hauss Hans-Ullrich Spiegel 《Journal of Experimental Animal Science》2000,41(3)
Sampling of rat hepatic tissue for histomorphological analysis is usually performed in two different ways: either by killing the animals or by minilaparotomy.In this study we describe a percutaneous core biopsy technique which has been used on day 7, 14 and 21 after allogeneic rat liver transplantation (DA → LEW) in order to examine grafts for rejection in different treatment groups. Fifty-two liver biopsies were performed in 24 animals using a 16-gauge intravenous cannula. Forty-five provided usable specimens which were sufficient for both light or electron microscopy and immunohistochemical analyses to determine the degree of graft rejection. In 7 cases (13.5%) sampling was unsuccessful, especially on day 21 after transplantation, as the plastic cannula could not penetrate the hardened tissue. In 3 animals (5.8%) puncture was immediately followed by death due to perforation of the diaphragm or ether intoxication.In conclusion, this technique is a reliable method for providing ample tissue samples from the rat liver with a low risk of complications. 相似文献
924.
Gerald A. Schwarting Gail Deutsch Devin M. Gattey James E. Crandall 《Developmental neurobiology》1992,23(2):120-129
Primary sensory neurons in the vomeronasal organ (VNO) project axons to the glomeruli of the accessory olfactory bulb (AOB) where they form connections with mitral cell dendrites. We demonstrate here that monoclonal antibodies to specific carbohydrate antigens define stage- and position-specific events during the development of the vomeronasal system (VN). CC1 monoclonal antibodies react with specific N-acetyl galactosamine containing glycolipids. In the embryo, CC1 antigens are expressed throughout the VNO and on vomeronasal nerves. Beginning approximately at birth and continuing into adults, CC1 expression is spatially restricted in the VNO to centrally located cell bodies. In the postnatal AOB, CC1 is expressed in the nerve layer and glomeruli, but only in the rostral half of the AOB. These data suggest that CC1 antigens may participate in the targeting of axons from centrally located VNO neurons to rostral glomeruli in the AOB. In contrast, CC2 monoclonal antibodies, which recognize complex α-galactosyl and α-fucosyl glycoproteins and glycolipids, react with all VNO cell bodies and VN nerves from embryonic (E) day 15 to adults. CC2 antibodies do not distinguish rostral from caudal regions of the AOB, nor are the CC2 glycoconjugates developmentally regulated. P-Path monoclonal antibodies, which recognize 9-O-acetyl sialic acid, react with cell bodies in the VNO and nerve fibers from E13 to postnatal (P) day 2. P-Path immunoreactivity disappears from the VNO system almost completely by P14, when only a few P-Path reactive nerve fibers can be seen. These studies suggest that specific cell surface glycoconjugates may participate in spatially and temporally selective cell–cell interactions during development and maintenance of vomeronasal connections. 相似文献
925.
926.
927.
David I. Friedman Gerald S. Wilgus Richard J. Mural 《Journal of molecular biology》1973,81(4):505-516
We report the isolation and characterization of a new mutation in the hybrid phage λimm21. Both genetic and physiological studies demonstrate that this new mutation, N21?1, is similar to N mutations of phage λ. As in the case of the N gene of λ (Niλ), the N21?1 mutation maps immediately to the left of the cI gene and has a pleiotropic effect on the expression of phage functions. Although these studies strongly suggest that phage 21 has an N function, they do not definitely locate the N21?1 mutation within the N21 structural gene.Reported here are studies demonstrating that N21 acts in trans, similar to Nλ, to stimulate the expression of phage functions. N products show an immunity specificity; N21 being only active on phage carrying the immunity region of phage 21, while the nλ is only active on phage carrying the immunity region of λ or phage 434. However, one site of action for Nλ can be rescued from phage 21. We propose that the specificity of an N function is determined by its sites of recognition and that these sites may be different from the sites of N action. 相似文献
928.
A field study was conducted to test the hypothesis that wheatdevelopment rate responds to the rate of change of photoperiod.Two wheat cultivars (Condor and Thatcher) were sown on 18 Aug.1992 at Melbourne (38° S). Photoperiod was extended artificiallyto give five treatments up to terminal spikelet initiation (TS)viz.: natural photoperiod (rate of change of photoperiod, 2·3mind d-1), two faster rates of change (9·8 and 13·1min d-1) and two constant photoperiods of 14·0 and 15·5h. After TS, the two constant photoperiods were extended to15·0 and 16·5 h, respectively and treatments wererandomly re-allocated, i.e. some plots received different photoperiodregimes before and after TS. There were no significant differences among treatments in thelength of the period from sowing (S) to seedling emergence (E)phase, ranging from 15 to 16·3 d. The rate of developmentfrom E to TS responded to increases in photoperiod in both cultivars,increasing with average photoperiod across all treatments butthere was no effect of rate of change of photoperiod independentof its average photoperiod. The rate of development from TSto anthesis (A) did not show any trend with average photoperiod.This lack of effect of photoperiod on the period from TS toA contrasts with other results from the literature and possiblereasons for this conflicting result are discussed. Rate of changeof photoperiod did not affect the duration of the phase fromTS to A either. Therefore, the effect of photoperiod on theduration of the S-A period was strongly and positively correlatedto that of the length of the E-TS phase.Copyright 1994, 1999Academic Press Triticum aestivum L., wheat, phasic development, photoperiod, rate of change 相似文献
929.
The coat protein of tobacco mosaic virus forms numerous aggregates, including the small A-protein, the disk, and two helical forms. The structures of the disk, the helical protein forms, and the virus are compared. Most of the differences are in the conformation of the chain between residues 89 and 113, which lies in the region of protein at the center of the virus, inside the RNA. It is disordered in the disk, but has a fixed conformation in the virus and the protein helices. The differences between the virus and the two helical protein forms are largely in the conformations of arginines and carboxylic acids in this region. 相似文献
930.
AbstractSilk sericin is a globular protein whose resistance against fouling is important for applications in biomaterials and water-purification membranes. Here it is shown how sericin generates a water-exclusion zone that may facilitate antifouling behavior. Negatively charged microspheres were used to mimic the surface charge and hydrophobic domains in bacteria. Immersed in water, regenerated silk sericin formed a 100-µm-sized exclusion zone (for micron-size foulants), along with a proton gradient with a decrease of >2?pH-units. Thus, when in contact with sericin, water molecules near the surface restructure to form a physical exclusionary barrier that might prevent biofouling. The decreased pH turns the aqueous medium unviable for neutrophilic bacteria. Therefore, resistance to biofouling seems explainable, among other factors, on the basis of water-exclusionary phenomena. Furthermore, sericin may play a role in triggering the fibroin assembly process by lowering the pH to the required value. 相似文献