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An increasing flow of evidences collected on elementary forms of learning processes in selected animal models evidentiates some mechanisms which can represent the basic cellular principles underlying plastic changes: 1. 5HT and second messengers of nucleotide type (like cAMP) have a pivotal role in the learning process. 2. In almost all short-term learning processes the modifications are subserved by a mechanism of protein phosphorylation. 3. In various animal models the modulation of K+ and Ca2+ channels is the molecular mechanism for learning. Experiments performed in sensory T neuron of the leech indicate that the modulation of Na+/K+ electrogenic pump is one of the fundamental mechanism for learning. 4. In long-term plastic changes, the most important finding is that newly synthesized proteins are formed. 5. In addition to what has been observed in the Aplysia model, where changes in synaptic efficacy represent the basic principles of memory storage, in the leech it has been demonstrated that a molecular machinery present in a single neuron can adapt the activity of the cell to environmental stimuli.  相似文献   
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A linear, apparent zero-order, in vitro release profile may be approximated from triple-pressed tablets using synthetic gum systems in the first and second press coats. This is coupled with varying concentrations of the actives (Melperone HCl. Diethylpropion HCl, and Dyphylline) in the core and press coats. The approximately linear release function obtained from these tablet systems is in stark contrast to a supposedly prolonged release tablet (comparative formulation) from the literature, which actually releases by the square root of time function characteristic of diffusion control. Addition of a placebo press coat to the outside of the synthetic gum systems simply increases the lag times for release (while the placebo coat is undergoing hydration, etc.). The linearity following the lag is reminiscent of saturation kinetics. Results suggest that the almost linear release profile is a function of the concentration of the various layers (core first and second press coats) coupled with the gelation characteristics of the synthetic gums. This zero order release does not hold for the systems of the comparative formulation taken from the patent literature.  相似文献   
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Whenever metal electrodes are used for chronic exposure of biological material to ELF electric fields in a liquid medium, there is a possibility that observed effects are caused directly by ions from the electrodes rather than by the electric field. The problem can be avoided by using insulated electrodes, but ordinarily this severely limnits the fields which can be obtained in the medium. We show here that by using high dielectric constant ceramic electrodes, current densities greater than 10 A/M2 are achievable at frequencies above 50 Hz.  相似文献   
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Sensitivity of the Human Eye to Power Frequency Electric Fields   总被引:1,自引:0,他引:1  
Reports spanning more than a century have shown that tissues associated with the eye are able to respond to local electric fields with impressions of light called electrophosphenes. A finite element analysis of the field distributions in the head near the receptors shows that the 60 Hz threshold for perception of electrophosphenes is approximately 1 V/m. Thus, tissues associated with the eye appear to be among the most sensitive to power frequency electric fields in the human body.  相似文献   
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The addition of live and heat-shocked Lactobacillus casei-casei L2A and Neutrase© was tested for its ability to accelerate the maturation of Cheddar cheese. An evaluation of physicochemical and rheological properties showed that cheese pH was decreased by bacterial and enzymatic additives, while fracturability and cohesiveness were influenced principally by Neutrase. The integrated process recommended is composed of three parts: first, the addition of live L. casei-casei L2A to control the undesirable microflora, second, heat-shocked cells of the same species at a concentration of 1.0%, and third, Neutrase at a concentration not higher than 1.0 × 10-5 AU/g of cheese. This process led to a good-quality sharp Cheddar cheese with 60% increase in flavor intensity compared to control cheese.  相似文献   
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Serine proteases inhibitor with pl-7.3, isolated from potatoe tubers by isoelectric focusing procedure as described previously (V.V. Mosolov et al., Bioorganic Chem., 1, 1449, 1975), was homogeneous under ultracentrifugation, having sedimentation coefficient S20,w 2.8S. Its molecular weight, investigated by sedimentation equilibrium and gel filtration through Sephadex G-100, was found to be 32500 and 31500 respectively. The Stokes radius R and frictional ratio f/fo were found to be 24 A and 1.14. The molecular weight of the inhibitor as determined by sodium dodecylsulfate polyacrylamide electrophoresis was twice as low as determined in ultracentrifuge and by gel filtration procedure. It is suggested that the inhibitor is dimer and consists of two protomers of equal molecular weight.  相似文献   
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When patient records are to be auditied in a program designed to assess the quality of medical care rendered, careful consideration must be given to the cost of the system implemented. Structured data collection and a defined treatment plan are advantageous in facilitating the use of nonphysicians for the majority of the audit. A system using checklists to ensure adequate recording of subjective and objective data and a defined treatment plan for a common symptom complex were implemented by physicians and physician's assistants with a patient load averaging more than 1,000 patient contacts per week in a general medical clinic at Duke University Medical Center. Audit was subsequently accomplished at a cost of 96 cents per record. To reduce this cost, more efficient methods of selecting records for audit should be developed.  相似文献   
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