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At least 433 records · Page 24Linked to original sources
PubMed1997

[Induction of increased cardiac tolerance against damage--a new therapeutic principle?].

In animal experiments, brief periods of myocardial ischemia have shown to improve cardiac tolerance against a subsequent ischemic exposure. We argue that ischemic preconditioning may be only one example of a general protective biological adaption to harmful stimuli. We refer to several studies indicating that ischemic preconditioning may occur in patients, e.g. during episodes of angina pectoris, or during percutaneous transluminal coronary angioplasty or cardiac surgery. The phenomenon has also been demonstrated in cultured human myocytes after anoxic periods. In the future, therefore, it may be possible to use suitable drugs to induce higher ischemic tolerance in patients with cardiac disorders. It may also be possible to induce protection against other harmful stimuli. Extensive research is necessary, however, to reveal the underlying mechanisms and choose the most suitable procedures.

Angina Pectoris↗
PubMed1997

The muscles in chronic ligamentous instability of the knee: an experimental study.

Several authors have formulated the idea that insufficiency of the anterior cruciate ligament (ACL) might lead to a biological adaptation, consisting of atrophy of the quadriceps and other extensors (antagonists of the ACL) and relative preservation of the hamstrings and other flexors (agonists of the ACL). We studied the modifications in hindlimb muscles that spontaneously occurred in 36 rabbits with surgically-induced chronic ligamentous instability of the right knee. The unoperated left hindlimb served as a control. Three months after surgery the rabbits were sacrificed and the muscles dissected for macroscopic and microscopic evaluation. In the anterior cruciate ligament-deficient limbs the extensors (quadriceps, glutei and extensor digitorum longus) showed significantly greater atrophy than the other muscles (p < 0.05). Six hundred twenty-two fibers from atrophic muscles, 373 from hypertrophic muscles and 879 from control muscles were evaluated by microscopy. The atrophic muscles showed a significantly lower percentage of type I fibers (responsible for maintenance of posture) and a reduction in the diameter of both type I and II (responsible for rapid movement) fibers with respect to the controls (p < 0.05). The hypertrophic muscles showed a significantly greater proportion of type I fibers and an increase in the diameter of type II fibers with respect to the controls (p < 0.05). Our results support the idea that there is spontaneous adaptation of the muscles to compensate for ligamentous instability.

Adaptation, Physiological↗
PubMed1997

The full coverage restoration in relation to the gingival sulcus.

The full coverage restoration (FCR) and its effect on the periodontium have been the subject of much controversy over the last half century. The conflict relates to whether the margin of the FCR should be placed at or above the gingival crest, or into the gingival crevice. Clinicians and researchers alike have focused their attention primarily on the mechanistic aspects of fixed prosthetic design (i.e., marginal configuration and fit). Although marginal quality and form are factors in the fabrication of the FCR, they alone will not determine periodontal health and restorative success. What determines the success of the FCR is its ability to restore form and function to the masticatory system without adversely affecting its biology. Each technical phase of treatment (i.e., tooth preparation, impression-taking, the provisional restoration, and the final restoration) must be performed within the limits of biologic adaptation. This literature review discusses the scientific evidence regarding FCR margin placement and periodontal health.

Animals↗
PubMed1997

Design of a closed system water tunnel for lamprey swimming analysis.

This work presents a swim mill design that can be used to study locomotor behavior in intact awake lamprey. The design is constrained by the swimming characteristics and anatomy of young adult lamprey and allows for electrophysiological monitoring of muscle activity and imaging of motor behavior. The design has a test section for animal containment and monitoring of motor behavior, a water reservoir, a water pump, and equipment for biological adaptations (water purification, chilling, & aeration systems). The 36 sq. inch acrylic test section is preceded by a turbulence-reducing converging nozzle, while a 1400 gallon reservoir maintains the system's hydrostatic head and acts as a settling chamber. This swim mill design will be used to examine lamprey swimming behavior under different environmental conditions (e.g., water velocity, turbulence, external perturbations).

Animals↗
PubMed1989

Molecular biology of enzyme adaptations in higher eukaryotes.

Multicellular eukaryotes have evolved complex homeostatic mechanisms that buffer the majority of their cells from direct interaction with the external environment. Thus, in these organisms long-term adaptations are generally achieved by modulating the developmental profile and tissue specificity of gene expression. Nevertheless, a subset of eukaryotic genes are still involved in direct responses to environmental fluctuations. It is the adaptative responses in the expression of these genes that buffers many other genes from direct environmental effects. Both microevolutionary and macroevolutionary patterns of change in the structure and regulation of such genes are illustrated by the sequences encoding alpha-amylases. The molecular biology and evolution of alpha-amylases in Drosophila and other higher eukaryotes are presented. The amylase system illustrates the effects of both long-term and short-term natural selection, acting on both the structural and regulatory components of a gene--enzyme system. This system offers an opportunity for linking evolutionary genetics to molecular biology, and it allows us to explore the relationship between short-term microevolutionary changes and long-term adaptations.

Adaptation, Biological↗
PubMed1990

Adaptive filtering in biological signal processing.

The high dependence of conventional optimal filtering methods on the a priori knowledge of the signal and noise statistics render them ineffective in dealing with signals whose statistics cannot be predetermined accurately. Adaptive filtering methods offer a better alternative, since the a priori knowledge of statistics is less critical, real time processing is possible, and the computations are less expensive for this approach. Adaptive filtering methods compute the filter coefficients "on-line", converging to the optimal values in the least-mean square (LMS) error sense. Adaptive filtering is therefore apt for dealing with the "unknown" statistics situation and has been applied extensively in areas like communication, speech, radar, sonar, seismology, and biological signal processing and analysis for channel equalization, interference and echo canceling, line enhancement, signal detection, system identification, spectral analysis, beamforming, modeling, control, etc. In this review article adaptive filtering in the context of biological signals is reviewed. An intuitive approach to the underlying theory of adaptive filters and its applicability are presented. Applications of the principles in biological signal processing are discussed in a manner that brings out the key ideas involved. Current and potential future directions in adaptive biological signal processing are also discussed.

Animals↗
PubMed2003

The co-evolution of people, plants, and parasites: biological and cultural adaptations to malaria.

The urgency generated by drug-resistant strains of malaria has accelerated anti-malarial drug research over the last two decades. While synthetic pharmaceutical agents continue to dominate research, attention increasingly has been directed to natural products. The present paper explores the larger context in which plant use occurs and considers how the selection of medicinal plants has evolved over millennia as part of the larger human effort to mediate illness. First attention is directed to indigenous medicinal plants whose anti-malarial activity is based on an oxidant mode of action, by which intracellular constituents lose electrons (become more electropositive). Next, parallels are drawn between these plant substances and a suite of malaria-protective genetic traits: glucose-6-phosphate dehydrogenase deficiency; haemoglobins S, C and E; alpha- and beta-thalassemias. These erythrocyte anomalies are classic examples of Darwinian evolution, occurring in high frequency in populations who have experienced considerable selective pressure from malaria. Characterized by discrete loci and pathophysiologies, they are united through the phenomenon of increased erythrocyte oxidation. In this model, then, oxidant anti-malarial plants are culturally constructed analogues, and molecular mimics, of these genetic adaptations. To further reinforce the scheme, it is noted that the anti-malarial action of pharmaceutical agents such as chloroquine and mefloquine duplicates both the genetic anomalies and the folk therapeutic models based in oxidant plants. This discussion coheres around a theoretical foundation that relates plant secondary metabolites (oxidants) to plasmodial biochemistry and human biological and cultural adaptations to malaria. Co-evolution provides a theoretical link that illuminates how medical cultures manage the relationships among humans, plants, herbivores and their respective pathogens.

Adaptation, Physiological↗
PubMed2002

Digital and biological computing in organizations.

Michael Conrad unveiled many of the fundamental characteristics of biological computing. Underlying the behavioral variability and the adaptability of biological systems are these characteristics, including the ability of biological information processing to exploit quantum features at the atomic level, the powerful 3-D pattern recognition capabilities of macromolecules, the computational efficiency, and the ability to support biological function. Among many other things, Conrad formalized and explicated the underlying principles of biological adaptability, characterized the differences between biological and digital computing in terms of a fundamental tradeoff between adaptability and programmability of information processing, and discussed the challenges of interfacing digital computers and human society. This paper is about the encounter of biological and digital computing. The focus is on the nature of the biological information processing infrastructure of organizations and how it can be extended effectively with digital computing. In order to achieve this goal effectively, however, we need to embed properly digital computing into the information processing aspects of human and social behavior and intelligence, which are fundamentally biological. Conrad's legacy provides a firm, strong, and inspiring foundation for this endeavor.

Adaptation, Physiological↗
PubMed2006

Adaptation of gender derived from biological motion.

Human observers adapted to complex biological motions that distinguish males from females: viewing the gait of one gender biased judgments of subsequent gaits toward the opposite gender. This adaptation was not simply due to local features of the stimuli but instead relied upon the global motion of the figures. These results suggest the existence of neurons selective for gender and demonstrate that gender-from-motion judgments are not fixed but depend upon recent viewing history.

Adaptation, Physiological↗
PubMed1990

The biological limits of cardiac adaptation to chronic overload.

Cardiac hypertrophy, which occurs during chronic mechanical overload, is one of the numerous examples of biological adaptation to environmental requirements. As such, it is achieved at random by trial and error, and adaptation represents the sum of various modifications in gene expression, including the shift in isomyosin or in iso Na+/K+ ATPase; the decrease in beta-adrenergic and muscarinic receptors or in SR Ca2+ ATPase densities and the unchanged density in Ca2+ current. Some of these changes are beneficial at the cellular level but finally detrimental for the organism as a whole, as is the slowing of Vmax. There are also detrimental modifications, such as hypertensive macroangiopathy, the slowing of relaxation and changes in stiffness. These various modifications may provide a new key for future pharmaceutical research.

Adaptation, Physiological↗
PubMed1996

Recognition and tracking of impulse patterns with delay adaptation in biology-inspired pulse processing neural net (BPN) hardware.

The application of an electronic real time emulator for biology-inspired pulse processing neural networks (BPN) to recognition and temporal tracking of discrete impulse patterns via delay adaptation is demonstrated. The electronic emulation includes biologically plausible features, such as asynchronous impulses, membrane potentials and adaptive weights, as well as a mechanism to modify signal delays. The rule for the adaptation of impulse propagation delays is as follows: 'error neurons' detect temporal differences between single impulses of other neurons and adjust corresponding signal delay parameters. In the application presented BPN adapts its time delays in order to form a finely tuned match with a given sequence of three discrete impulses. After learning, BPN is capable not only of highly selective recognition of the learned impulse pattern but also of tracking a gradually changing impulse pattern. Tracking is achieved by continuously re-adjusting the delay profile. Delay adaptation (rather than weight adaptation) appears to be the more effective mechanism for such application.

Computers↗
PubMed2005

Chromatic adaptation of photosynthetic membranes.

Many biological membranes adapt in response to environmental conditions. We investigated how the composition and architecture of photosynthetic membranes of a bacterium change in response to light, using atomic force microscopy. Despite large modifications in the membrane composition, the local environment of core complexes remained unaltered, whereas specialized paracrystalline light-harvesting antenna domains grew under low-light conditions. Thus, the protein mixture in the membrane shows eutectic behavior and can be mimicked by a simple model. Such structural adaptation ensures efficient photon capture under low-light conditions and prevents photodamage under high-light conditions.

Adaptation, Biological↗
PubMed1994

Distinct rhythmic locomotor patterns can be generated by a simple adaptive neural circuit: biology, simulation, and VLSI implementation.

Rhythmic motor patterns can be induced in leg motor neurons of isolated locust thoracic ganglia by bath application of pilocarpine. We observed that the relative phases of levators and depressors differed in the three thoracic ganglia. Assuming that the central pattern generating circuits underlying these three segmental rhythms are probably very similar, we developed a simple model circuit that can produce any one of the three activity patterns and characteristic phase relationships by modifying a single synaptic weight. We show results of a computer simulation of this circuit using the neuronal simulator NeuraLOG/Spike. We built and tested an analog VLSI circuit implementation of this model circuit that exhibits the same range of "behaviors" as the computer simulation. This multidisciplinary strategy will be useful to explore the dynamics of central pattern generating networks coupled to physical actuators, and ultimately should allow the design of biologically realistic walking robots.

Adaptation, Physiological↗