Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “network physiology”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources
PubMed1987

A hierarchical neural-network model for control and learning of voluntary movement.

In order to control voluntary movements, the central nervous system (CNS) must solve the following three computational problems at different levels: the determination of a desired trajectory in the visual coordinates, the transformation of its coordinates to the body coordinates and the generation of motor command. Based on physiological knowledge and previous models, we propose a hierarchical neural network model which accounts for the generation of motor command. In our model the association cortex provides the motor cortex with the desired trajectory in the body coordinates, where the motor command is then calculated by means of long-loop sensory feedback. Within the spinocerebellum--magnocellular red nucleus system, an internal neural model of the dynamics of the musculoskeletal system is acquired with practice, because of the heterosynaptic plasticity, while monitoring the motor command and the results of movement. Internal feedback control with this dynamical model updates the motor command by predicting a possible error of movement. Within the cerebrocerebellum--parvocellular red nucleus system, an internal neural model of the inverse-dynamics of the musculo-skeletal system is acquired while monitoring the desired trajectory and the motor command. The inverse-dynamics model substitutes for other brain regions in the complex computation of the motor command. The dynamics and the inverse-dynamics models are realized by a parallel distributed neural network, which comprises many sub-systems computing various nonlinear transformations of input signals and a neuron with heterosynaptic plasticity (that is, changes of synaptic weights are assumed proportional to a product of two kinds of synaptic inputs). Control and learning performance of the model was investigated by computer simulation, in which a robotic manipulator was used as a controlled system, with the following results: (1) Both the dynamics and the inverse-dynamics models were acquired during control of movements. (2) As motor learning proceeded, the inverse-dynamics model gradually took the place of external feedback as the main controller. Concomitantly, overall control performance became much better. (3) Once the neural network model learned to control some movement, it could control quite different and faster movements. (4) The neural network model worked well even when only very limited information about the fundamental dynamical structure of the controlled system was available.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

Systems conceptualization and treatment of anger.

Clinicians, researchers, and patients tend to view anger as attributable to immediate circumstances and current thoughts. In contrast, systems-oriented thinking approaches anger as a contextual and dynamic phenomenon. Personal dispositional systems of anger (cognitive, physiological, and behavioral) are embedded in an interdependent network of interpersonal and environmental systems. Anger coevolves with and is in equilibrium with these systems. The more adaptive and embedded it is within a system, the greater will be its inertia or resistance to change. The automaticity of anger further challenges its regulation, as does its transfer across domains. Other troublesome systems phenomena associated with anger and aggression are escalation and threshold effects. Anger arousal, as a deviation from homeostasis, is inhibited and counteracted by various negative feedback loops that are properties of internal, interpersonal, and environmental systems. Treatment augments anger-regulatory mechanisms. Interventions aimed at anger reduction should consider the systems in which anger is embedded and the adaptive functions anger serves within those systems. These and other systems concepts are explicated and are illustrated with material from two clinical cases.

Adaptation, Psychological↗
PubMed2001

Metabolic oscillations in an E. coli fermentation.

Recombinant E. coli fermentations were observed to undergo regular, reproducible oscillations in oxygen uptake for several hours during a controlled fermentation process. Culture growth slowed during the period of oscillations, delaying induction of recombinant protein production. The oscillations were similar in 10-L and 1,000-L fermentors and also occurred with different feed control algorithms. Both observations support the hypothesis that the oscillations are metabolic in nature. Analysis of amino acid, ATP, and GTP pools suggests that the oscillations result from aberrant regulation of isoleucine biosynthesis leading to repeated starvation events in which protein synthesis and growth are impaired. Both a nutritional solution, isoleucine feeding, and a genetic solution, repair of an ilvG frameshift mutation in E. coli K-12 strains, were found to eliminate the oscillations, further supporting the proposed mechanism for the behavior. These results illustrate the interesting and complicated physiological behavior which can be displayed in metabolic networks and provide another example of surprising problems that can arise in growing recombinant organisms in fermentors.

Adenosine Triphosphate↗
PubMed1990

Electrosensory systems in fish.

A close integration of behavioral, neurophysiological, and neuroanatomical approaches has guided research on the neural basis of electrosensation and the generation of behaviors associated with this modality. By postulating neuronal implementations of specific computations in sensory information processing, behavioral studies have been crucial in focusing studies at the neuronal level onto behaviorally relevant structural and functional aspects. Physiological and anatomical studies have analyzed a) neural networks underlying the distributed processing of sensory information, b) the role of descending recurrent pathways and efference copy mechanisms for the filtering of incoming information, c) the significance of multiple topographic representations for sensory information processing, and d) the modulation of sensory and motor structures through various transmitters and receptor subtypes. Developmental studies have explored the significance of steroid hormones for the tuning of electroreceptors to the frequency of an endogenous neuronal oscillator which drives the electric current pulses necessary for their stimulation. Embryological studies have revealed that the development of mechanoreceptors and electroreceptors in the fish's skin is induced by the innervation of primary afferent nerve fibers which are specific with regard to their central connections as well as with regard to the type of receptor induced in the periphery.

Animals↗
PubMed1995

Models of tumor-host interaction as competing populations: implications for tumor biology and treatment.

Population ecology mathematical models examine tumors not as an isolated collection of transformed individuals but as part of a dynamic society of interacting malignant and normal cells. This approach investigates the mechanisms by which a small clone of neoplastic cells is able to replace the much larger and previously stable population of normal cells, despite the numerical advantage of the latter and the inhibitory effects of the host response. The models define a sequence of different stable equilibria with critical mathematical parameters which control the outcome of different stages of the neoplasm-host competition--parameters which can be correlated with cellular physiologic properties. When neoplasm is viewed as a network of interacting tumor and normal populations, a unifying hypothesis can be developed that allows the diverse but inconsistent properties of transformed cells to be understood according to their specific contributions to tumorigenesis within this network. It predicts general sequences of genetic changes necessary for tumor survival and invasion and demonstrates that apparently disparate properties found in different tumor models can be functionally equivalent. The paper proposes novel modes of therapy requiring classification and treatment of tumors according to the strategies they employ, rather than the traditional criteria of cell type and organ of origin.

Cell Survival↗
PubMed2002

Native and cloned 5-HT(3A)(S) receptors are anchored to F-actin in clonal cells and neurons.

Using selective antibodies to visualize the short isoform of the 5-HT(3A) receptor, we report here that both native and cloned 5-HT(3A)(S) receptors formed clusters associated with F-actin in all cell types studied. NG 108-15 cells expressing native 5-HT(3A)(S) receptors, COS-7 cells transiently expressing 5-HT(3A)(S) subunits, and CHO cells stably transfected with a plasmid encoding the 5-HT(3A)(S) sequence all exhibited similar surface receptor topology with 5-HT(3A)(S) receptor cluster accumulation in F-actin-rich lamellipodia and microspikes. Colocalization and coclustering of 5-HT(3A)(S) subunits and F-actin were also observed in transfected hippocampal neurons. Treatment of the neurons with latrunculin-A, a compound altering F-actin polymerization, demonstrated that 5-HT(3A)(S) receptor cluster size and topology were dependent on F-actin integrity. These results suggest that the anchoring of 5-HT(3A)(S) receptor clusters to the cytoskeletal network probably plays a key role in the physiological regulation of the receptor topology and dynamics, as is the case for other members of the 4-TMD ion channel receptor family.

Actins↗
PubMed1996

Distributed processing on the basis of parallel and antagonistic pathways simulation of the femur-tibia control system in the stick insect.

In inactive stick insects, sensory information from the femoral chordotonal organ (fCO) about position and movement of the femur-tibia joint is transferred via local nonspiking interneurons onto extensor and flexor tibiae motoneurons. Information is processed by the interaction of antagonistic parallel pathways at two levels: (1) at the input side of the nonspiking interneurons and (2) at the input side of the motoneurons. We tested by a combination of physiological experiments and computer simulation whether the known network topology and the properties of its elements are sufficient to explain the generation of the motor output in response to passive joint movements, that is resistance reflexes. In reinvestigating the quantitative characteristics of interneuronal pathways we identified 10 distinct types of nonspiking interneurons. Synaptic inputs from fCO afferents onto these interneurons are direct excitatory and indirect inhibitory. These connections were investigated with respect to position and velocity signals from the fCO. The results were introduced in the network simulation. The motor output of the simulation has the same characteristics as the real system, even when particular types of interneurons were removed in the simulation and the real system.

Animals↗
PubMed1992

Rate coherence and event coherence in the visual cortex: a neuronal model of object recognition.

We propose a function-oriented model of the visual cortex. The model addresses an essential task of the visual system: to detect and represent objects. These are defined as sets, which reappear in the input with invariant inner relations. A network, incorporating an idealized description of anatomical and physiological data, is presented with a movie showing various moving objects. In the course of time, as a result of Hebbian plasticity, a connection scheme develops which embodies in its forward and lateral connections the information necessary to perform the operations involved in object recognition. We demonstrate that coherent neural activity can exploit this information. Two types of coherence have to be distinguished in this respect. Rate coherence performs invariance operations and association, while event coherence accomplishes segmentation tasks. The model reproduces and explains experimental findings made both in physiological recordings from the visual cortex and in psychophysical studies.

Animals↗
PubMed2000

Structural symmetry of the metabolic reaction network. I. Carboxylic acid metabolism.

A new approach to systematization of the information on metabolism, based on the symmetry observed in the pattern of the metabolic reaction network, is discussed. A theoretical substantiation of symmetry existence is given. A symmetrical metabolic scheme is developed for metabolism of carboxylic acids. The symmetry of the metabolic reaction network can be used for systematization of biochemical, physiological, medical and other data associated with metabolism as well as for prediction of the new information.

Carboxylic Acids↗
PubMed2026

Listening forward: emerging roles of bioacoustics in ecology, evolution, and conservation.

Bioacoustics is increasingly shifting from a mostly descriptive pursuit to one that can anticipate ecological change. Recent innovations-from autonomous recording units and edge-computing sensors to speech-inspired feature extraction and machine-learning techniques like transfer learning, unsupervised discovery, and explainable AI-are transforming the study of animal communication. These advances let us work at scales previously difficult to imagine. Automated species recognition, individual identification, and even tracking cultural evolution over decades are now within reach. Entire ecosystem soundscapes can be mapped with unprecedented resolution. Looking ahead, global listening networks, adaptive acoustic indices, and live biodiversity dashboards seem increasingly realistic. We may soon build digital models that simulate communication networks under future scenarios. Closer integration with genomics, physiology, and robotics could link vocal traits to their genetic, physiological, and ecological drivers. Challenges remain, including data governance, acoustic privacy, and equitable access to the planet's sonic heritage. Bioacoustics may be on the way to becoming a predictive, integrative science - one particularly well suited to monitoring, interpreting, and helping safeguard life's communication systems in a rapidly changing world.

Animals↗
PubMed1996

Intracellular, genetic or congenital immunisation--transgenic approaches to increase disease resistance of farm animals.

Novel approaches to modify disease resistance or susceptibility in livestock are justified not only by economical reasons and with respect to animal welfare but also by recent advancements in molecular genetics. The control or elimination of infectious pathogens in farm animals is historically achieved by the use of vaccines and drugs and by quarantine safeguards and eradication. Currently, research on the improvement of disease resistance based on nucleic acid technology focuses on two main issues: additive gene transfer and the development of nucleic acid vaccines. The strategies aim at the stable or transient expression of components known to influence non-specific or specific host defence mechanisms against infectious pathogens. Thus, candidates for gene transfer experiments include all genes inducing or conferring innate and acquired immunity as well as specific disease resistance genes. Referring to the site and mode of action and the source of the effective agent the strategies are termed 'intracellular', 'genetic' and 'congenital' immunisation. The targeted disruption (deletive gene transfer) of disease susceptibility genes awaits the establishment of totipotential embryonic cell lineages in farm animals. The cytokine network regulates cellular viability, growth and differentiation in physiological and pathophysiological states. The identification of the JAK-STAT pathway used by many cytokines for their intracellular signal propagation has provided not only new target molecules for modulating the immune response but will also permit the further elucidation of host-pathogen interactions and resistance mechanisms.

Animal Diseases↗
PubMed1992

Cellular organization of reciprocal patchy networks in layer III of cat visual cortex (area 17).

There is no direct information available concerning the exact spatial characteristics of long-range axons and their relationship with the patchy phenomena observed after extracellular injection of retrograde tracers. In the present study, using the recently introduced neuronal tracer biocytin, we demonstrate by detailed three-dimensional reconstruction of 10 pyramidal cells in layer III, that their clustered axonal terminals form a specific patchy network in layers II and III. The reconstructed network occupied an area of 6.5 x 3.5 mm parallel to the cortical surface elongated in an anteroposterior direction. The average centre-to-centre distance between patches within the network was 1.1 mm. On average, the axonal field of each of the 10 pyramidal cells contained a total of 417 boutons at four to eight distinct sites (patches), and in each patch, an average of 79 boutons was provided by the same cell. The identified connections between the patches were predominantly reciprocal. Detailed analyses have shown that many pyramidal cells of the network are directly interconnected so that each of them can receive one to four, chiefly axospinous, contacts onto the distal segment of its apical and basal dendrites from the axon of another pyramidal cell belonging to a different patch labelled from the same injection site. We hypothesize that the possible functional role of the network is to link remote sites with similar physiological characteristics, such as orientation preference, supporting the model of Mitchison and Crick [(1982) Proc. natn. Acad. Sci. U.S.A. 79, 3661-3665].

Animals↗
PubMed2006

Enhanced c-Fos expression in the rostral ventral respiratory complex and rostral parapyramidal region by inhibition of the Na+/H+ exchanger type 3.

Previous studies have shown that selective inhibition of Na+/H+ exchanger type 3 (NHE3) induces intracellular acidification and activates CO2/H+-sensitive medullary neurons, mimicking the responses evoked by hypercapnic stimuli. In addition, NHE3 blockers administration decreases the duration of apnoea induced by laryngeal stimulation, presumably by means of central chemoreceptor activation. To test the hypothesis that the central chemoreceptor network may be affected by NHE3 inhibition, brainstem c-Fos immunoreactive cell counting was performed after systemic administration of the NHE3 blocker AVE1599 (Aventis Pharma Deutschland GmbH) (2 mg/kg). The rostro-caudal quantitative c-Fos analysis showed a significant increase in the number of c-Fos positive cells in the rostral part of the ventral respiratory complex (VRC) as well as in the rostral part of the parapyramidal (Ppy) region. The VRC activated region (-4.2 to -3.2mm interaural) included the pre-Bötzinger complex, the rostral ventral respiratory group and the rostral ventrolateral medulla, all of them involved in cardiorespiratory control. The activated Ppy region corresponded with the rostral chemosensitive area, which elicits the strongest ventilatory response upon ventral medullary surface stimulation with H+/CO2. Most cells activated in Ppy after NHE3 inhibition were serotonergic. Hence, systemic application of NHE3 blockers may induce central chemoreceptors activation and an increase in the respiratory network activity in a similar way to known physiological stimuli such as hypercapnia. On the other hand, selective NHE3 blockers could be excellent tools for treatment of pathological states where central chemoreceptor function is diminished or absent, such as central hypoventilation syndrome or sudden infant death syndrome.

Animals↗
PubMed2003

Adhesively-tensed cell membranes: lysis kinetics and atomic force microscopy probing.

Membrane tension underlies a range of cell physiological processes. Strong adhesion of the simple red cell is used as a simple model of a spread cell with a finite membrane tension-a state which proves useful for studies of both membrane rupture kinetics and atomic force microscopy (AFM) probing of native structure. In agreement with theories of strong adhesion, the cell takes the form of a spherical cap on a substrate densely coated with poly-L-lysine. The spreading-induced tension, sigma, in the membrane is approximately 1 mN/m, which leads to rupture over many minutes; and sigma is estimated from comparable rupture times in separate micropipette aspiration experiments. Under the sharpened tip of an AFM probe, nano-Newton impingement forces (10-30 nN) are needed to penetrate the tensed erythrocyte membrane, and these forces increase exponentially with tip velocity ( approximately nm/ms). We use the results to clarify how tapping-mode AFM imaging works at high enough tip velocities to avoid rupturing the membrane while progressively compressing it to a approximately 20-nm steric core of lipid and protein. We also demonstrate novel, reproducible AFM imaging of tension-supported membranes in physiological buffer, and we describe a stable, distended network consistent with the spectrin cytoskeleton. Additionally, slow retraction of the AFM tip from the tensed membrane yields tether-extended, multipeak sawtooth patterns of average force approximately 200 pN. In sum we show how adhesive tensioning of the red cell can be used to gain novel insights into native membrane dynamics and structure.

Cell Count↗
PubMed2002

Numerical studies on the effect of lowering temperature on the oxygen transport during brain hypothermia resuscitation.

There have been arguments about the advantage and shortcoming of hypothermia on the brain resuscitation during circulation arrest. People usually accepted that hypothermia may decrease the cerebral oxygen demands, which is beneficial for the patient to sustain longer time when subjected to a hypoxia. However, there are also quite a few disputes claiming that the blood viscosity would increase with the reduction of temperature, which may lead to an increase of cerebral vascular resistance and thus worsen the hypoxia state. To resolve this critical issue, a heat transfer model was established to characterize the thermal response of brain tissue during hypothermia resuscitation. Combined with this model, a compartmental model taking account of the temperature effect was further developed to analyze the transient oxygen partial pressure (PO(2)) distribution over the successive branches of the vascular network during circulation arrest. Using the morphological and physiological data of a sheep brain, effects of lowering temperature on the oxygen consumption dynamics were studied. Calculations indicated that the lower the temperature, the slower the decreasing rate for the PO(2). Although immediately lowering the brain temperature may induce an evident increase in blood viscosity and subsequently a decrease in blood flow rate, which is responsible for oxygen delivery, it seems to always result in a monotonic increase of PO(2). The results show a good qualitative accord with the experimental data. They also present better understanding on the transient oxygen transport in brain hypothermia during circulation arrest.

Animals↗
PubMed2002

Empowering patients with point-of-care testing.

Point-of-care testing (POCT) is becoming a major force in the future evolution of healthcare. It has the potential to expand further by increasing the accessibility, speed and accuracy of results. New developments in POCT technology will predictably occur in four areas: scope, connectivity, non-invasiveness and miniaturization. POCT test menus will continue to grow, wireless connectivity with automatic data capture will become the norm and non-invasive POCT will evolve into a wide range of sizes, shapes and functionalities.

Clinical Laboratory Information Systems↗