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221.
In vivo extracellular single-unit recording techniques revealed that chronic cold stress significantly alters both the basal and the evoked electrophysiological activity of noradrenergic neurons in the locus coeruleus of the anaesthetized rat. Following 17-21 days of chronic cold exposure (5 degrees C), the single-unit activity of histologically-identified locus coeruleus neurons in chloral hydrate-anaesthetized rats was recorded and analysed in terms of their basal firing rate and pattern of spike activity, as well as their response to footshock stimulation. There was no significant difference in the incidence of spontaneously active cells/electrode track between cold-stressed rats and control rats. However, the basal spike activity of locus coeruleus cells recorded from cold-stressed rats differed significantly from that of control rats along two dimensions: i) they displayed significantly higher basal firing rates (mean = 1.88 Hz vs 1.20 Hz, respectively); and ii) they frequently exhibited spontaneous burst-firing activity that was not observed in control rats (observed in 15/17 cold-stressed rats vs 1/26 control rats). The evoked spike activity of locus coeruleus cells in cold-stressed rats also differed significantly from that of control rats along two dimensions: i) they were more likely to respond to footshock stimulation (mean = 90.3% vs 74.4%, respectively); and ii) these responses were more likely to consist of multispike bursts of action potentials (mean = 8 bursts/50 stimulations vs 1 burst/50 stimulations, respectively). These results indicate that alterations in the electrophysiological activity of noradrenergic locus coeruleus neurons may contribute to the phenomenon of stress-induced sensitization of norepinephrine release that is thought to underlie some of the neuropathological changes that accompany long-term stress. 相似文献
222.
The nutritional effects on operant visual learning behavior were investigated in a flight simulator. Operant visual learning and memory formation were normal in Drosophila (S-flies) reared on standard medium, but absent in flies (P-flies) raised on Peking medium. S- and P-flies were transferred to the alternative medium soon after hatching and their progeny was also raised on corresponding medium for several generations. respectively. S-flies transferred showed significantly reduced learning acquisition and 20 min memory retention, and operant visual learning along with memory formation was abolished in their progeny within three generations. Transferred P-flies recovered slowly their learning acquisition and memory formation to normal levels within five generations. Further studies suggested that low protein and minerals or high carbohydrate contents in Peking medium might be related to abnormal performance of P-flies. These results confirm the feasibility of affecting learning behavior by dietary regimens and developing an insect model of maternal malnutrition for pre- or post-natal malnutrition in Drosophila. 相似文献
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Feil IK; Platas AA; van den Akker F; Reddy R; Merritt EA; Storm DR; Hol WG 《Protein engineering, design & selection : PEDS》1998,11(11):1103-1109
Members of the cholera toxin family, including Escherichia coli heat-
labile enterotoxins LT-I and LT-II, catalyze the covalent modification of
intracellular proteins by transfer of ADP-ribose from NAD to a specific
arginine of the target protein. The ADP-ribosylating activity of these
toxins is located in the A-subunit, for which LT-I and LT-II share a 63%
sequence identity. The flexible loop in LT-I, ranging from residue 47 to
56, closes over the active site cleft. Previous studies have shown that
point mutations in this loop have dramatic effects on the activity of LT-I.
Yet, in LT-II the sequence of the equivalent loop differs at four positions
from LT-I. Therefore five mutants of the active site loop were created by a
stepwise replacement of the loop sequence in LT-I with virtually all the
corresponding residues in LT- II. Since we discovered that LT-II had no
activity versus the artificial substrate
diethylamino-benzylidine-aminoguanidine (DEABAG) while LT-I does, our
active site mutants most likely probe the NAD binding, not the arginine
binding region of the active site. The five hybrid toxins obtained (Q49A,
F52N, V53T, Q49V/F52N and Q49V/F52N/V53T) show (i) great differences in
holotoxin assembly efficiency; (ii) decreased cytotoxicity in Chinese
hamster ovary cells; and (iii) increased in vitro enzymatic activity
compared with wild type LT-I. Specifically, the three mutants containing
the F52N substitution display a greater Vmax for NAD than wild type LT-I.
The enzymatic activity of the V53T mutant is significantly higher than that
of wild type LT-I. Apparently this subtle variation at position 53 is
beneficial, in contrast to several other substitutions at position 53 which
previously had been shown to be deleterious for activity. The most striking
result of this study is that the active site loop of LT- I, despite great
sensitivity for point mutations, can essentially be replaced by the active
site loop of LT-II, yielding an active 'hybrid enzyme' as well as 'hybrid
toxin'.
相似文献
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226.
The connections between two research areas, intelligent control systems and multi-dimensional systems, are established. Two-dimensional (2-D) system theory is used to analyze a class of learning control system. The 2-D state-space model of a learning control system is given. A class of learning control laws is proposed and the convergence of the learning process can be checked based on a 2-D model of the learning control system. The theory and methods proposed in this paper not only provide the learning control system with powerful tools for analysis and design, but also offer a multi-dimensional system theory with a new field of application as well as some new problems for further exploration.The original version of this paper was presented at the 2nd International Symposium on Robotics and Manufacturing (ISRAM), Albuquerque, New Mexico, 16–18 November 1988. The published proceedings of this meeting may be ordered from: CAD Laboratory for Systems/Robotics, EECE Dept., UNM, Albuquerque, NM 87131, U.S.A. 相似文献
227.
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230.
Kourosh Kabiri Sara Hesarian Mohammad-Jalal Zohuriaan-Mehr Ahmad Jamshidi Hossein Bouhendi Mohammad-Reza Pourheravi Seyd-Ali Hashemi Hossein Omidian Soheila Fatollahi 《Journal of Polymer Research》2011,18(6):1863-1870
Residual monomer is an important factor, particularly in hygienic materials such as superabsorbent polymer (SAP) hydrogels.
Recently, we reported different approaches to minimizing residual monomer content in SAPs. In this paper, the effect of a
long-chain monomer, poly(ethylene glycol) methylether methacrylate (PEG.MEMA), on the residual monomer content of SAP networks
of partially neutralized acrylic acid–PEG.MEMA is investigated. The aim of using PEG.MEMA in SAP synthesis was to reduce the
glass transition temperature (T
g) of SAP. As the temperature that is conventionally used to dry SAP (70–110 °C) is lower than the T
g of ordinary SAPs, the polymer is in the glassy state during the heating stage. It was assumed that converting SAP from the
glassy state to the rubbery state during drying would facilitate the removal of acrylic acid monomer (AA) from the gel, thus
reducing the residual monomer content. The results showed that the use of PEG.MEMA led to a reduction in residual AA when
the drying temperature was 100 °C. The residual AA was decreased from 169 to 95 ppm when the drying time was increased from
3 to 15 hours at 100 °C. This positive effect of PEG.MEMA on the level of unwanted residual AA became insignificant at a higher
drying temperature (140 °C). The effects of PEG.MEMA content on the thermal and mechanical properties (in the dried state)
and the rheological properties (in the water-swollen state) of the SAP hydrogels were also investigated. The swelling capacity
and rate was studied in relation to the PEG.MEMA content. It was found that a high level of PEG.MEMA restricted both the absorption
capacity and the rate of water absorption. 相似文献