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91.
Kevin D. Reilly 《Bulletin of mathematical biology》1968,30(4):565-579
A mathematical model for learning of a conditioned avoidance behavior is presented. An identification of the net excitation
of a neural model (Rashevsky, N., 1960.Mathematical Biophysics. Vol. II. New York: Dover Publications, Inc.) with the instantaneous probability of response is introduced and its usefulness
in discussing block-trial learning performances in the conditioned avoidance situation is outlined for normal and brain-operated
animals, using experimental data collected by the author. Later, the model is applied to consecutive trial learning and connection
is made with the approach of H. D. Landahl (1964. “An Avoidance Learning Situation. A Neural Net Model.”Bull. Math. Biophysics,26, 83–89; and 1965, “A Neural Net Model for Escape Learning.”Bull. Math. Biophysics,27, Special Edition, 317–328) wherein lie further data with which the model can be compared. 相似文献
92.
93.
94.
A proteolytically modified form of the Escherichia coli single-stranded DNA-Binding protein (SSB) has been crystallized from 15% saturated sodium citrate. Crystals as large as 1.0 mm x 0.3 mm x 0.2 mm were obtained and these diffract beyond 3A resolution. X-ray photographic analysis demonstrated a rhombohedral unit cell of space group R3 with an equivalent triple centered hexagonal unit cell having dimensions of a = b = 62.9A and c = 264.3A. These crystals were judged to be adequate for a three dimensional structure determination. 相似文献
95.
96.
M H Kim R Nakayama P Manos J E Tomlinson E Choi J D Ng D Holten 《Journal of lipid research》1989,30(5):663-671
Rats were fasted or fasted and refed simple purified diets so the effects of individual carbohydrates or fats could be studied. Freshly isolated hepatocytes from these animals were used to measure both apoE synthesis and mRNA levels so any changes in apoE synthesis that might occur without changes in its mRNA could be detected. Some of these experiments were done with both sexes. Both fasting and fasting and refeeding a 60% glucose fat-free diet significantly increased spoE synthesis. However, cyclic AMP is not likely to rapidly mediate the effect of fasting since dibutyryl cAMP slightly lowered (rather than increased) apoE synthesis and mRNA when injected into rats for 4.5 h. Dietary fat had no effect either in the absence of carbohydrate or when consumption of carbohydrate was constant in pair-fed rats. ApoE mRNA levels remained normal for 4 days in primary hepatocytes cultured in medium that had only amino acids as an energy source. Added hormones or fructose had no significant effect. Thus, only fasting and fasting and refeeding glucose were able to significantly change apoE synthesis or mRNA levels. Synthesis of apoE may be regulated to increase when apoE is secreted with very low density lipoprotein or when apoE in secreted high density lipoprotein is needed to acquire cholesteryl esters for the synthesis of bile salts and acids by liver. 相似文献
97.
Summary Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated. ATP-sensitive K+ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pH
i
. (1) The time course of K+(ATP) channel activity during exposure to and washout of NH4Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH4Cl entry and inhibition of the Na
o
+
H
i
+
exchanger, resembles the time course of pH
i
measured in other cell types that have been similarly treated. (2) Increasing pH
o
over the range 6.25–7.9 increases K+(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H+ by the application of the K+/H+ exchanger nigericin. (3) Increasing pH
i
over a similar range produces similar effects on K+(ATP) channels in inside-out excised patches exposed to small concentrations of ATP
i
. The physiological role of pH
i
in the metabolic gating of this channel remains to be explored. 相似文献
98.
Summary The condensation reactions of activated nucleotides, ImpN or 2-MeImpN, with the selfcomplementary ribo-octanucleotide GCGCGCGC or with the partially self-complementary heptanucleotide GCGCGCG were studied. The templatedirected reaction of 2-meImpC with the heptamer yields the 3–5 octamer as the main product. All other reactions yield 2–5-linked octamers and pyrophosphates as major products. Surprisingly, 2-MeImpG facilitates the reaction of 2-MeImpC with the heptamer.Procedures for the analysis by gel electrophoresis of the oligomeric products obtained in reactions of this kind are described. 相似文献
99.
We have previously demonstrated that most isolates of C. albicans are hydrophobic when grown at room temperature (RT, ca. 22-24 degrees C) and hydrophilic when grown at 37 degrees C. Variants of our standard strain LGH1095 were isolated that are hydrophobic at 37 degrees C and hydrophilic at RT. After repeated phase partitioning with cyclohexane-water cell populations that were 6-16% hydrophobic at RT and 66-80% hydrophobic at 37 degrees C were obtained. Subsequent limiting dilution experiments provided clones which were more hydrophobic at RT or hydrophilic at 37 degrees C. These were then recloned until the resultant populations were consistently under 5% cell surface hydrophobicity (CSH) at RT or over 95% at 37 degrees C. Treatment with several detergents as well as sugars did not decrease the CSH of these cells. Lipase and several proteases also had no effect. When treated with trypsin at a concentration twice that used to lower CSH of normal cells to less than 5%, the hydrophobic variant only decreased in CSH by 50%. Both variants were capable of germinating, although at different levels depending on prior growth temperature. Sensitivity to the germination inhibitor morphogenic autoregulatory substance (MARS) was similar to that of the parent strain. 相似文献
100.