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1.
Janusz Uchmaski 《Oikos》2000,90(3):539-548
To study the influence of individual variability on population dynamics an individual-based model of the dynamics of a single population consisting of different individuals is constructed. The model is based on differences in individual assimilation rates due to intraspecific competition and variability of initial weights. The model exhibits "imperfect regulation", i.e., the number of individuals in the population oscillates and sooner or later the population becomes extinct. When individual variability is included, the model produces longer population extinction times than without individual variability. The average extinction time is not however a monotonic function of the degree of individual variability. 相似文献
2.
Stability of o-phthalaldehyde-derived isoindoles 总被引:1,自引:0,他引:1
The degradation of 1-alkylthio-2-alkylisoindoles, generated in situ by reaction of o-phthalaldehyde with primary alkylamines in the presence of selected thiols, was studied under conditions typical of those used in precolumn derivatization applications. In all cases, loss of isoindole followed pseudo first order kinetics and was strongly accelerated by excess o-phthalaldehyde in the reaction mixture. Reactivity toward o-phthalaldehyde was found to be influenced by a number of experimental parameters including thiol structure, thiol concentration, amine structure, solvent composition, and pH. In the absence of excess o-phthalaldehyde, the stability of all derivatives examined was excellent. These results provide a basis for optimization of reaction conditions for maximum derivative stability. 相似文献
3.
4.
Janusz Janiszewski Dietmar Otto 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1988,162(6):739-746
1. | Intracellular recordings of suboesophageal neurons were performed in the cricketGryllus bimaculatus during applied changes of head temperature in the range 8 to 32.5 °C. The temperature was controlled by perfusing the head with Ringer solution of appropriate temperature. Subsequent staining with Lucifer Yellow revealed descending, ascending or T-shaped cells with ventrally located somata (Fig. 1). |
2. | In 6 out of 7 neurons recorded (Fig. 1, neurons A, B, C, D, E, G) the firing rate was correlated with abdominal ventilatory pumping (Fig. 2a, b). These neurons also received input from cereal sensory hairs (Fig. 2c). Furthermore, one of them (Fig. 1, neuron A) showed responses to auditory (Fig. 2d) and another (Fig. 1, neuron E) to visual input (Fig. 2e). |
3. | Activity of every tested neuron was correlated with the temperature of the perfusing Ringer solution: the amplitude and duration of spikes and excitatory postsynaptic potentials increased with cooling (Fig. 3). Two types of temperature-dependent changes in firing rate were identified. In type I the spiking rate was higher at higher temperature (Figs. 4a, b; 5). In type II spiking rate was related to the direction of temperature change (Fig. 4c, d). |
4. | The possible involvement of one of the recorded cells (Fig. 1, neuron F) in thermoreception processes is discussed. Activity of this neuron was not related to the rhythm of abdominal ventilatory pumping, nor did the cell receive cereal, visual or auditory input. Its activity was related mainly to the direction of temperature changes i.e. with an increase in firing rate during cooling, independent of the temperature at which the cooling started and with a transient decrease in firing rate during warming from starting point of 10 °C. |
5.
A colostral protein that induces the growth and differentiation of resting B lymphocytes 总被引:5,自引:0,他引:5
We describe the first protein of mammalian origin that induces the growth and differentiation of resting B lymphocytes. A proline-rich protein has been isolated from sheep colostrum. A purified proline-rich protein preparation (PRPP) induced resting mouse B cells into and supported their progression through the cell cycle at frequencies comparable with those seen for LPS. Differentiation of resting B cells to plaque formation was also supported as efficiently by PRPP as it was by LPS. However, PRPP was distinct from LPS in that it supported the growth and differentiation of resting B cells derived from either C3H/Tif or C3H/HeJ mice. Splenocytes from neonatal mice responded robustly to PRPP with the growth and differentiation of contained B cells to plaque formation. Unlike LPS, PRPP did not induce detectable Ig isotype switching. 相似文献
6.
Janusz Dabrowski Michael Hauck Elzbieta Romanowska Andrzej Gamian 《Carbohydrate research》1988,180(2):163-174
The main features of the primary structure of the octasaccharide, -
-Glcp-(1→2)--
-Glcp-(1→2)-[-
-GalpNAc- (1→3)]--
-Galp-(1→3)--
-Glcp-(1→3)-[-
-Hepp-(1→7)]--
-Hepp-(1→3)--
-Hep, have been determined in the ab initio manner by 1H-n.m.r. spectroscopy without resorting to biochemical methods of analysis. Several nontypical interresidue n.O.e. values point to a preferred solution conformation of the molecule. 相似文献
7.
Isolation of soluble yeast beta-glucans that inhibit human monocyte phagocytosis mediated by beta-glucan receptors 总被引:2,自引:0,他引:2
M J Janusz K F Austen J K Czop 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(10):3270-3276
The trypsin-sensitive receptor that mediates phagocytosis of unopsonized zymosan particles by human monocytes has been designated as a beta-glucan receptor because of its functional inhibition by specific algal and plant beta-glucans. Soluble ligands that are chemically and structurally identical to beta-glucan constituents of zymosan were isolated from a carbohydrate-enriched fraction of yeast extract by sequential chromatography on DE-cellulose, SP-Sephadex, and Con A-Sepharose. Preincubation of adherent human monocytes with 278, 210, and 2.5 micrograms/ml hexose equivalents in pooled chromatographic fractions from DE-cellulose, SP-Sephadex, and Con A-Sepharose, respectively, effected 50% reductions in subsequent phagocytosis of zymosan particles without affecting Fc-mediated ingestion of IgG-coated sheep erythrocytes (ESIgG). The purified yeast extract-derived beta-glucans, which contained 92% glucose and 8% mannose by gas chromatographic analysis and eluted from a Sephacryl S-200 column as a broad peak with a Kav of 0.39 and estimated molecular sizes of from 20,000 to 70,000 m.w., required only 3.5 +/- 0.9 micrograms/ml (mean +/- SD, n = 6), as compared with 31.5 micrograms/ml of the algal beta-glucan laminarin to achieve 50% decreases in zymosan ingestion. Alternatively, soluble yeast beta-glucans with estimated molecular sizes of from 2 X 10(5) to 2 X 10(6) were prepared from yeast glucan particles, which contained 98% glucose and 0% mannose, by sonication and sequential centrifugation at 15,000 and 100,000 X G for 30 and 60 min, respectively. Monocyte ingestion of zymosan was reduced by 50% by pretreatment with 60 ng/ml of the soluble beta-glucans in 15,000 X G supernatants, whereas ingestion of ESIgG was unaffected by as much as 50 micrograms/ml of this material. Partial acid hydrolysis of soluble glucan-derived beta-glucans in 15,000 X G supernatants followed by gel filtration on Bio-Gel P-4 revealed two well-defined peaks within the inclusion volume of the column with phagocytosis-inhibiting activity. Oligoglucosides that eluted at a Kav of 0.46 had an estimated molecular size of 2,000 m.w. and effected a 48% reduction in zymosan ingestion at inputs of 2 to 5 micrograms/ml, and smaller oligoglucosides with a Kav of 0.82 and an estimated molecular size of 1,000 m.w. effected a 50% reduction at inputs of 25 micrograms/ml. Preincubation of monocytes for 2 min with 25 micrograms/ml of the oligoglucosides with estimated molecular size of 1,000 m.w. and with 50 ng/ml of soluble glucan-derived beta-glucans in 100,000 X G supernatants reduced zymosan ingestion by 41% +/- 4 and 44% +/- 3 (mean +/- SD, n = 3), respectively.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
8.
L1210 leukemic cells injected in vivo are eliminated from the blood and disintegrated in organs such as the lungs and liver. We present a compartmental model which reproduces one type of in vivo experiment, based on the so-called perfusion curves. Although the data are not complete and some are only approximated, modeling gives a consistent picture of the process. 相似文献
9.
Jacek Hennig Jocelyn Malamy Grzegorz Grynkiewicz Janusz Indulski Daniel F. Klessig 《The Plant journal : for cell and molecular biology》1993,4(4):593-600
Salicylic acid (SA) has been proposed to play a role in the induction of pathogenesis-related (PR) proteins and systemic acquired resistance (SAR) in tobacco. Since SA is rapidly converted to salicylic acid β-glucoside (SAG) in tobacco, we have attempted to assess the role of SAG in pathogenesis by application of chemically synthesized SAG to tobacco leaves. SAG was as active as SA in induction of PR-1 gene expression. This induction was preceded by a transient release of SA, which occurred in the extracellular spaces. The existence of a mechanism that releases SA from SAG suggests a possible role for SAG in SAR. 相似文献
10.
Daniel W. Armstrong Mary Gasper Sun Haing Lee Janusz Zukowski Nuran Ercal 《Chirality》1993,5(5):375-378
Plasma, urine, cerebrospinal fluid (CSF), and amniotic fluid were examined to determine whether free D-amino acids were present and if so at what levels. It was found that D-amino acids exist in all physiological fluids tested, but that their level varied, considerably. The lowest levels of D-amino acids were usually found in amniotic fluid or CSF (almost always <1% of the corresponding L-amino acid). The highest levels were found in urine (usually tenth percent to low percent levels). Pipecolic acid seemed to be different from the other amino acids tested in that it was excreted primarily as the D-enantiomer (often >90%). Correspondingly high levels of D-pipecolic acid were not found in plasma. Some of the trends found in this work seemed to be analogous to those found in a recent rodent study. © 1993 Wiley-Liss, Inc. 相似文献