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At least 217 records · Page 12Linked to original sources
PubMed2007

Ion channels and their neural functions: contribution to general problems from studies of brains in non-mammalian species.

Ion channels and their neural functions have often been studied in the brains of mammals. However, the brains of some teleost fish species have special features that, at first glance, appear to be atypical and peculiar to that species alone. These teleost fish will contribute considerably to the understanding of general features of the ion channels and their neural functions. We have been interested in the neural mechanisms underlying the adaptive and flexible response of animals to changing environments and have been studying gonadotropin-releasing hormone (GnRH) peptidergic neuron systems, which we think are central for controlling such biologically adaptive responses. We have also been interested in a pretectal nucleus, corpus glomerulosum, which is tentatively regarded to play important roles in the organization of visually-guided feeding behaviors. In both systems, we found that certain types of apparently 'non-typical' Na(+) channels play important roles in neurobiological functions. Here we discuss how the study of functions of these apparently non-typical ion channels might contribute to our understanding of neural functions of vertebrate brains in general.

Animals↗
PubMed2003

Mobile genetic elements and bacterial toxinoses: the superantigen-encoding pathogenicity islands of Staphylococcus aureus.

It is a remarkable observation that virtually all bacterial toxins associated with specific clinical conditions (toxinoses) are encoded by mobile (and therefore variable) genetic elements. Remarkably, these rarely, if ever, carry determinants of antibiotic resistance. Examples are the toxins responsible for diphtheria, anthrax, tetanus, botulism, cholera, toxic shock, scarlet fever, exfoliative dermatitis, food poisoning, travelers' diarrhea, shigella dysentery, necrotizing pneumonia, and others. A recently discovered example of this phenomenon is the family of related staphylococcal pathogenicity islands encoding superantigens (SAgs). These are 15-20kb elements that occupy constant positions in the chromosomes of toxigenic strains, and are characterized by certain phage-related features, namely genes encoding integrases, helicases, and terminases, and the presence of flanking direct repeats. The prototype, SaPI1 of Staphylococcus aureus, encodes TSST-1 plus two newly described SAgs, SEK and SEL. Other members of the family encode enterotoxins B (SaPI3) and C (SaPI4), plus at least two other SAgs each. SaPI1 and SaPI2, also encoding TSST-1, are excised and induced to replicate by certain staphylococcal phages, and are then encapsidated at high efficiency into phage-like infectious particles with heads about 1/3 the size of the helper phage heads, commensurate with the sizes of the respective genomes. This results in transfer frequencies of the order of 10(8)/ml, and is presumably responsible for the spread of these elements as well as for their acquisition in the first place. In the absence of a helper phage, these two islands are highly stable; neither excision, loss, or transfer occurs at detectable frequency. Several general implications of this phenomenon will be discussed. One is that the determinants of these toxins have been imported from other species and therefore are not components of the basic genome of the extant producing organisms. This raises the question of the biological (adaptive?) roles of these toxins. Another is that the toxin-carrying units can spread among different (though probably related) species. An interesting question is that of the biological basis for the separation of toxin and resistance determinants.

Animals↗
PubMed1997

Unweighting accelerates tidemark advancement in articular cartilage at the knee joint of rats.

Morphologic development of articular cartilage is influenced by biologic adaptation to functional demands. It has been theorized that intermittent stresses generated by load bearing and motion determine cartilage thickness by controlling advancement of the subchondral mineralization front. The mineralization front is comprised of two interfaces, the tidemark and chondroosseus junction, each of which advances through a different biologic process. This study was designed to evaluate the influence of one month of hind limb unweighting, with and without concurrent restriction of joint motion, on mineral apposition at the tidemark and vascular invasion at the chondroosseus junction in the knee joints of young adult rats. In mobile joints, hind limb unweighting induced a 2-fold increase in the tidemark mineral apposition rate (p = 0.0001) at the primary weight bearing region, resulting in a thinning of the uncalcified cartilage layer and a concurrent thickening of the calcified layer. Cast immobilization negated the effect of unweighting at the tidemark while it activated subchondral vascular encroachment into the calcified cartilage (p = 0.001). These findings suggest that cartilage thinning associated with the elimination of weight bearing is mediated through a different biological mechanism than cartilage loss associated with restriction of joint motion.

Adaptation, Physiological↗
PubMed2006

Bioavailability of trace metals to aquatic microorganisms: importance of chemical, biological and physical processes on biouptake.

An important challenge in environmental biogeochemistry is the determination of the bioavailability of toxic and essential trace compounds in natural media. For trace metals, it is now clear that chemical speciation must be taken into account when predicting bioavailability. Over the past 20 years, equilibrium models (free ion activity model (FIAM), biotic ligand model (BLM)) have been increasingly developed to describe metal bioavailability in environmental systems, despite the fact that environmental systems are always dynamic and rarely at equilibrium. In these simple (relatively successful) models, any reduction in the available, reactive species of the metal due to competition, complexation or other reactions will reduce metal bioaccumulation and thus biological effects. Recently, it has become clear that biological, physical and chemical reactions occurring in the immediate proximity of the biological surface also play an important role in controlling trace metal bioavailability through shifts in the limiting biouptake fluxes. Indeed, for microorganisms, examples of biological (transport across membrane), chemical (dissociation kinetics of metal complexes) and physical (diffusion) limitation can be demonstrated. Furthermore, the organism can employ a number of biological internalization strategies to get around limitations that are imposed on it by the physicochemistry of the medium. The use of a single transport site by several metals or the use of several transport sites by a single metal further complicates the prediction of uptake or effects using the simple chemical models. Finally, once inside the microorganism the cell is able to employ a large number of strategies including complexation, compartmentalization, efflux or the production of extracellular ligands to minimize or optimize the reactivity of the metal. The prediction of trace metal bioavailability will thus require multidisciplinary advances in our understanding of the reactions occurring at and near the biological interface. By taking into account medium constraints and biological adaptability, future bioavailability modeling will certainly become more robust.

Bacteria↗
PubMed1992

Anhydrobiosis: a strategy for survival.

Many organisms from a wide variety of taxa have the ability to survive extreme dehydration, a phenomenon called "anhydrobiosis." Concomitantly with resistance to the adverse effects of drying, these organisms are also resistant to the effects of freezing to very low temperatures, elevated temperature for brief periods, and the effects of ionizing radiation. One result of their resistance to environmental extremes is a greatly prolonged life span. The anhydrobiotes that have been investigated share a common metabolic adaptation, the production of certain disaccharides as a large proportion of their dry weight. Using these disaccharides, we have investigated the sources of damage attendant upon drying and the mechanisms by which anhydrobiotes and model systems of isolated membranes and proteins avoid damage. This report summarizes aspects of this work.

Adaptation, Biological↗
PubMed2004

What are theories for? Concept use throughout the continuum of dinosaur expertise.

Although it is now well established that object concepts are situated within broader systems of theoretical knowledge, it is less clear how theories influence the use of object concepts at various points throughout the continuum of expertise. Two studies were conducted to investigate the impact of specific theories (concerning dinosaurs) and overarching framework theories (of biology) on children's and adults' performance on categorization tasks involving familiar and less familiar concepts. Although expertise increased the quantity of deep feature knowledge possessed by children and increased their understanding of biologically adaptive relations among features, few aspects of children's performance generalized beyond highly familiar dinosaurs. Children's specific theories related to dinosaurs were empirically constrained and relatively dissociated from other types of biological knowledge. The interaction of specific concept knowledge with broader framework theories of biology throughout the continuum of expertise is considered.

Animals↗
PubMed1999

In vitro cultured cells as probes for space radiation effects on biological systems.

Near future scenarios of long-term and far-reaching manned space missions, require more extensive knowledge of all possible biological consequences of space radiation, particularly in humans, on both a long-term and a short-term basis. In vitro cultured cells have significantly contributed to the tremendous advancement of biomedical research. It is therefore to be expected that simple biological systems such as cultured cells, will contribute to space biomedical sciences. Space represents a novel environment, to which life has not been previously exposed. Both microgravity and space radiation are the two relevant components of such an environment, but biological adaptive mechanisms and efficient countermeasures can significantly minimize microgravity effects. On the other hand, it is felt that space radiation risks may be more relevant and that defensive strategies can only stem from our deeper knowledge of biological effects and of cellular repair mechanisms. Cultured cells may play a key role in such studies. Particularly, thyroid cells may be relevant because of the exquisite sensitivity of the thyroid gland to radiation. In addition, a clone of differentiated, normal thyroid follicular cells (FRTL5 cells) is available in culture, which is well characterized and particularly fit for space research.

Animals↗
PubMed1994

Gene loss and gain in the evolution of the vertebrates.

Homeobox cluster genes (Hox genes) are highly conserved and can be usefully employed to study phyletic relationships and the process of evolution itself. A phylogenetic survey of Hox genes shows an increase in gene number in some more recently evolved forms, particularly in vertebrates. The gene increase has occurred through a two-step process involving first, gene expansion to form a cluster, and second, cluster duplication to form multiple clusters. We also describe data that suggests that non-Hox genes may be preferrentially associated with the Hox clusters and raise the possibility that this association may have an adaptive biological function. Hox gene loss may also play a role in evolution. Hox gene loss is well substantiated in the vertebrates, and we identify additional possible instances of gene loss in the echinoderms and urochordates based on PCR surveys. We point out the possible adaptive role of gene loss in evolution, and urge the extension of gene mapping studies to relevant species as a means of its substantiation.

Amino Acid Sequence↗
PubMed1989

[The artificial heart from the aspect of results thus far and from the aspect of further perspectives for research and clinical practice].

The author gives an account of the present position in the development of research of artificial hearts and mechanical support whereby special attention is paid to research in the CSSR which holds one of the foremost places in the world. When resolving some basic questions of long-term biological adaptation to the activity of the mechanical system, i.e. the artificial heart, this research becomes very important as a unique model for investigation of the isolated peripheral circulation the reactions of which are not affected by the action of the biological heart which has been eliminated. Moreover, specific conditions are created for the investigation of other general biologically important problems (hormonal regulation, metabolic factors, leading to calcification of biomaterials and its prevention, problems of dynamics of the coagulation system, thrombogenesis etc.) in the organism with an artificial heart. At present there are essentially two methods suitable for clinical application, i.e. mechanical support of the heart of the type of mono- or biventricular bypass with total replacement of the heart as a temporary operation before subsequent transplantation. Both these methods are promising. Further intensive research of the long-term survival of subjects with an artificial heart creates in addition to typical features of fundamental research the basis for permanent implantation of an artificial heart in clinical work which is another important stage of clinical applications.

Animals↗