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At least 55 records · Page 3Linked to original sources
PubMed2006

Transcriptional regulation of neuropeptide and peptide hormone expression by the Drosophila dimmed and cryptocephal genes.

The regulation of neuropeptide and peptide hormone gene expression is essential for the development and function of neuroendocrine cells in integrated physiological networks. In insects, a decline in circulating ecdysteroids triggers the activation of a neuroendocrine system to stimulate ecdysis, the behaviors used to shed the old cuticle at the culmination of each molt. Here we show that two evolutionarily conserved transcription factor genes, the basic helix-loop-helix (bHLH) gene dimmed (dimm) and the basic-leucine zipper (bZIP) gene cryptocephal (crc), control expression of diverse neuropeptides and peptide hormones in Drosophila. Central nervous system expression of three neuropeptide genes, Dromyosuppressin, FMRFamide-related and Leucokinin, is activated by dimm. Expression of Ecdysis triggering hormone (ETH) in the endocrine Inka cells requires crc; homozygous crc mutant larvae display markedly reduced ETH levels and corresponding defects in ecdysis. crc activates ETH expression though a 382 bp enhancer, which completely recapitulates the ETH expression pattern. The enhancer contains two evolutionarily conserved regions, and both are imperfect matches to recognition elements for activating transcription factor-4 (ATF-4), the vertebrate ortholog of the CRC protein and an important intermediate in cellular responses to endoplasmic reticulum stress. These regions also contain a putative ecdysteroid response element and a predicted binding site for the products of the E74 ecdysone response gene. These results suggest that convergence between ATF-related signaling and an important intracellular steroid response pathway may contribute to the neuroendocrine regulation of insect molting.

Animals↗
PubMed1985

Sequential recruitment in the discrimination of velocity.

Human observers can discriminate a 5% difference in velocity for a wide range of velocities. Using an apparent-motion stimulus, we demonstrated that velocity discrimination depends on the detection of small changes in asynchrony, changes of the order of 1 msec or less. The simplest component of an apparent-motion stimulus is a pair of spatially separate lines presented asynchronously. Generally the incremental asynchrony threshold for a single pair of lines is much too large to account for velocity discrimination. A sequence of five to eight asynchronously presented targets, equivalent to continuous motion viewed for a duration of 80-100 msec is required to reach asymptotic velocity discrimination. Our experiments rule out probability summation as the explanation for the enhanced temporal sensitivity observed with the sequential presentation of multiple asynchronous targets. Sequential recruitment, a descriptive term for this enhanced temporal sensitivity, depends on the summation of a velocity-specific signal within the physiological network responding to motion.

Adolescent↗
PubMed2003

Plant-centered biosystems in space environments: technological concepts for developing a plant genetic assessment and control system.

Plants will play an essential role in providing life support for any long-term space exploration or habitation. We are evaluating the feasibility of an adaptable system for measuring the response of plants to any unique space condition and optimizing plant performance under those conditions. The proposed system is based on a unique combination of systems including the rapid advances in the field of plant genomics, microarray technology for measuring gene expression, bioinformatics, gene pathways and networks, physiological measurements in controlled environments, and advances in automation and robotics. The resulting flexible module for monitoring and optimizing plant responses will be able to be inserted as a cassette into a variety of platforms and missions for either experimental or life support purposes. The results from future plant functional genomics projects have great potential to be applied to those plant species most likely to be used in space environments. Eventually, it will be possible to use the plant genetic assessment and control system to optimize the performance of any plant in any space environment. In addition to allowing the effective control of environmental parameters for enhanced plant productivity and other life support functions, the proposed module will also allow the selection or engineering of plants to thrive in specific space environments. The proposed project will advance human exploration of space in the near- and mid-term future on the International Space Station and free-flying satellites and in the far-term for longer duration missions and eventual space habitation.

Agriculture↗
PubMed2004

Alarm-enhancement systems for ventilators.

Ventilator alarms can be crucial for safeguarding the health and even the lives of patients. Therefore, it's vital that they--like other critical alarms--be readily detected in even the busiest, noisiest hospital departments. One way to make sure that this happens is to use alarm-enhancement systems, which communicate ventilator alarms to locations where they are more likely to be detected by caregivers. There are four basic categories of ventilator alarm enhancements: (1) interfacing ventilators with networked physiologic monitors, (2) incorporating commercially available systems for centralized remote monitoring of ventilator alarms, (3) interfacing ventilators with nurse call systems, and (4) utilizing remote annunciators for ventilator alarms. These options range widely in complexity, cost, and the types of care settings for which they're likely to be suitable. In this article, we describe the ventilator alarm-enhancement systems that are currently on the market. We highlight their pluses and minuses based on information we have gained from product literature, through conversations with suppliers, and, where possible, through discussions with users. We also provide guidance to facilities on how to choose among the various options and products available.

Decision Making, Organizational↗
PubMed1993

Molecular mechanisms of thyroid hormone action. A physiologic perspective.

At present, it appears abundantly clear that thyroid hormone exerts its major action at the nuclear level by regulating the level of mRNAs of specific genes. There are at least three TR isoforms that mediate hormonal effects at the tissue level. Characterization of the functional domains of these receptor isoforms is as yet incomplete, and the possibility that these receptors could have ligand-independent functions is a matter under current investigation. TRs are now recognized as members of a large superfamily of transactivating proteins involved in the regulation of gene expression. Recent studies have shown an unexpected degree of complexity in the nature of the association of the T3 receptors and the DNA of target genes. They have vividly pointed out the multiple interactions possible between the T3-receptor complex and other proteins participating in the process of gene regulation. These insights have provided a solid base for understanding differences in the gradation of thyroid hormone effect from one tissue to another. The microdissection of the molecular process that has occurred in the past 20 years has proceeded in part through the application of relatively artificial in vitro systems and assays. Whereas such approaches have undoubtedly reaped rich rewards in pointing out potential or possible mechanisms, they do not define the actual workings in the animal. Additional studies designed to examine at the molecular level the operation in vivo of physiologic networks influenced by thyroid hormones appear as an essential next step in understanding the biology of the hormone system. The application of transgenic models should materially assist such efforts.

Animals↗
PubMed1998

Optical monitoring of living brain tissue.

Optical methods can usefully augment classical techniques such as electrical recording for investigating cellular and network physiology. Here, recent developments in optical methods--including confocal and nonlinear fluorescence imaging, semiconductor array imaging, and improved fluorescent indicators of ion concentration and transmembrane electrical potential--are briefly reviewed, and examples are offered that may suggest potential applications to experimental studies in alcoholism research.

Alcoholism↗
PubMed2006

Modeling gravity-dependent plasticity of the angular vestibuloocular reflex with a physiologically based neural network.

A neural network model was developed to explain the gravity-dependent properties of gain adaptation of the angular vestibuloocular reflex (aVOR). Gain changes are maximal at the head orientation where the gain is adapted and decrease as the head is tilted away from that position and can be described by the sum of gravity-independent and gravity-dependent components. The adaptation process was modeled by modifying the weights and bias values of a three-dimensional physiologically based neural network of canal-otolith-convergent neurons that drive the aVOR. Model parameters were trained using experimental vertical aVOR gain values. The learning rule aimed to reduce the error between eye velocities obtained from experimental gain values and model output in the position of adaptation. Although the model was trained only at specific head positions, the model predicted the experimental data at all head positions in three dimensions. Altering the relative learning rates of the weights and bias improved the model-data fits. Model predictions in three dimensions compared favorably with those of a double-sinusoid function, which is a fit that minimized the mean square error at every head position and served as the standard by which we compared the model predictions. The model supports the hypothesis that gravity-dependent adaptation of the aVOR is realized in three dimensions by a direct otolith input to canal-otolith neurons, whose canal sensitivities are adapted by the visual-vestibular mismatch. The adaptation is tuned by how the weights from otolith input to the canal-otolith-convergent neurons are adapted for a given head orientation.

Adaptation, Physiological↗
PubMed2006

Readdressing the issue of thermally significant blood vessels using a countercurrent vessel network.

A physiologically realistic arterio-venous countercurrent vessel network model consisting of ten branching vessel generations, where the diameter of each generation of vessels is smaller than the previous ones, has been created and used to determine the thermal significance of different vessel generations by investigating their ability to exchange thermal energy with the tissue. The temperature distribution in the 3D network (8178 vessels; diameters from 10 to 1000 microm) is obtained by solving the conduction equation in the tissue and the convective energy equation with a specified Nusselt number in the vessels. The sensitivity of the exchange of energy between the vessels and the tissue to changes in the network parameters is studied for two cases; a high temperature thermal therapy case when tissue is heated by a uniformly distributed source term and the network cools the tissue, and a hypothermia related case, when tissue is cooled from the surface and the blood heats the tissue. Results show that first, the relative roles of vessels of different diameters are strongly determined by the inlet temperatures to those vessels (e.g., as affected by changing mass flow rates), and the surrounding tissue temperature, but not by their diameter. Second, changes in the following do not significantly affect the heat transfer rates between tissue and vessels; (a) the ratio of arterial to venous vessel diameter, (b) the diameter reduction coefficient (the ratio of diameters of successive vessel generations), and (c) the Nusselt number. Third, both arteries and veins play significant roles in the exchange of energy between tissue and vessels, with arteries playing a more significant role. These results suggest that the determination of which diameter vessels are thermally important should be performed on a case-by-case, problem dependent basis. And, that in the development of site-specific vessel network models, reasonable predictions of the relative roles of different vessel diameters can be obtained by using any physiologically realistic values of Nusselt number and the diameter reduction coefficient.

Animals↗
PubMed2005

Physiological and pathological oscillatory networks in the human motor system.

Human brain functions are heavily contingent on neural interactions both at the single neuron and the neural population or system level. Accumulating evidence from neurophysiological studies strongly suggests that coupling of oscillatory neural activity provides an important mechanism to establish neural interactions. With the availability of whole-head magnetoencephalography (MEG) macroscopic oscillatory activity can be measured non-invasively from the human brain with high temporal and spatial resolution. To localise, quantify and map oscillatory activity and interactions onto individual brain anatomy we have developed the 'dynamic imaging of coherent sources' (DICS) method which allows to identify and analyse cerebral oscillatory networks from MEG recordings. Using this approach we have characterized physiological and pathological oscillatory networks in the human sensorimotor system. Coherent 8 Hz oscillations emerge from a cerebello-thalamo-premotor-motor cortical network and exert an 8 Hz oscillatory drive on the spinal motor neurons which can be observed as a physiological tremulousness of the movement termed movement discontinuities. This network represents the neurophysiological substrate of a discrete mode of motor control. In parkinsonian resting tremor we have identified an extensive cerebral network consisting of primary motor and lateral premotor cortex, supplementary motor cortex, thalamus/basal ganglia, posterior parietal cortex and secondary somatosensory cortex, which are entrained in the tremor or twice the tremor rhythm. This low frequency entrapment of motor areas likely plays an important role in the pathophysiology of parkinsonian motor symptoms. Finally, studies on patients with postural tremor in hepatic encephalopathy revealed that this type of tremor results from a pathologically slow thalamocortical and cortico-muscular coupling during isometric hold tasks. In conclusion, the analysis of oscillatory cerebral networks provides new insights into physiological mechanisms of motor control and pathophysiological mechanisms of tremor disorders.

Efferent Pathways↗
PubMed1992

Neuronal multipotentiality: evidence for network representation of physiological function.

Extracellular action potentials of single neurons in motor cortex and rectified and integrated electromyographic activity (EMG) of gastrocnemius and anterior tibialis were recorded while a monkey performed isometric ankle plantar and dorsal flexion tasks. This study determined the consistency of neuronal behaviors across different tasks. Methods characterized neuronal behaviors by determining which behavioral event within a single task, such as the appearance of the 'go' signal, force onset, or agonist and antagonist EMG onset, was best related to changes in neuronal activity. Another method compared the temporal profiles of discharge modulation across different tasks. Of 220 neurons recorded, 44 were selected because they were consistently active in the tasks. Of these, 37 were in the precentral cortex and the remaining seven were in the postcentral cortex. Only 14 of the 33 in motor cortex were consistent in their behavioral correlations. Several had multiple changes in activity within a single task that were related to different behavioral events. Half were consistent for direction of force and a third were consistent for magnitude of force. Furthermore, there was little consistency in the temporal profiles of discharge activity for all 44 neurons across tasks. Similar modulations of discharge activity among neurons in one task were different in another task. Such inconsistencies are evidence against the cardinal cell hypothesis of physiological representation. We offer a new hypothesis analogous to connectionism in parallel distributed processing.

Action Potentials↗
PubMed1996

Mathematical modeling of AVM physiology using compartmental network analysis: theoretical considerations and preliminary in vivo validation using a previously developed animal model.

The development of computer modeling technique of cerebral arteriovenous malformations using circuit network analysis, validated with a previously developed animal model is presented. Such a malformation and its vascular connections are rendered into a complex system of interconnecting tubes, which is then simulated by an analogous electrical circuit using commercially available computer software. This methodology was tested using a swine model, of which a detailed computer model was constructed from anatomic and angiographic measurements of the cranial vessels. Flow conditions, before and after creation of the in vivo model, were predicted from the computer model and compared with previously reported in vivo measurements. Detailed analysis of flow within the CAVM nidus was also performed. There was a good correlation between the computer and in vivo models regarding changes in flow and pressure drop across the rete. Flow mapping within the nidus showed localized directional flow that was determined by global inputs, consistent with functional compartmentalization. This method of computer modeling appears promising for studying clinically relevant aspects of cerebral arteriovenous malformation pathophysiology. To our knowledge it is the first computer model to demonstrate functional compartmentalization.

Animals↗
PubMed2004

Fibrillin microfibrils: multipurpose extracellular networks in organismal physiology.

Organismal physiology depends significantly on the proper assembly of extracellular matrix (ECM) macroaggregates that impart structural integrity to the connective tissue. Recent genetic studies in mice have unraveled unsuspected new functions of architectural matrix components in regulating signaling events that modulate patterning, morphogenesis, and growth of several organ systems. As a result, a new paradigm has emerged whereby tissue-specific organization of the ECM dictates not only the physical properties of the connective tissue, but also the ability of the matrix to direct a broad spectrum of cellular activities through the regulation of growth factor signaling. These observations pave the way to novel therapeutic approaches aimed at counteracting the deleterious consequences of perturbations of connective tissue homeostasis.

Animals↗
PubMed2003

Effect of steroids on intestinal lipid uptake in rats is enhanced by a saturated fatty acid diet. Cell and molecular biology collaborative network in gastrointestinal physiology.

Glucocorticosteroids enhance sugar digestive and absorptive functions of the intestine, but their effect on lipid uptake is unknown. Modifications in dietary lipids alter the nutrient transport properties of the intestine. The influence of 4 weeks' treatment with budesonide (BUD), prednisone (PRED), or control vehicle in weanling rats fed either an isocaloric semisynthetic saturated fatty acid diet (SFA) or a polyunsaturated fatty acid diet (PUFA), on the uptake of lipids was assessed using everted gut rings. PRED and BUD increased the uptake of several fatty acids, and this was higher when the animals were fed SFA rather than PUFA. Changes in expression of the mRNAs for L-FABP (liver fatty acid binding protein) and ILBP (ileal lipid binding protein) did not explain these alterations in lipid uptake. Dietary lipid signalling of this adaptive response may involve proglucagon, c-jun, TNF-alpha and IL-10, whereas steroid signalling may involve proglucagon. In summary, steroids increase the absorption of lipids by a process which can be enhanced by the substitution of saturated for polyunsaturated lipids in the diet, and which is not explained by alterations in the expression of the mRNAs of L-FABP or ILBP.

Adaptation, Biological↗
PubMed1999

Testable predictions from realistic neural network simulations of vestibular compensation: integrating the behavioural and physiological data.

Neural network simulations have been used previously in the investigation of the horizontal vestibulo-ocular reflex (HVOR) and vestibular compensation. The simulations involved in the present research were based on known anatomy and physiology of the vestibular pathway. This enabled the straightforward comparison of the network response, both in terms of behavioural (eye movement) and physiological (neural activity) data to empirical data obtained from guinea pig. The network simulations matched the empirical data closely both in terms of the static symptoms (spontaneous nystagmus) of unilateral vestibular deafferentation (UVD) as well as in terms of the dynamic symptoms (decrease in VOR gain). The use of multiple versions of the basic network, trained to simulate individual guinea pigs, highlighted the importance of the particular connections: the vestibular ganglion to the type I medial vestibular nucleus (MVN) cells on the contralesional side. It also indicated the significance of the relative firing rate in type I MVN cells which make excitatory connections with abducens cells as contributors to the variability seen in the level of compensated response following UVD. There was an absence of any difference (both in terms of behavioural and neural response) between labyrinthectomised and neurectomised simulations. The fact that a dynamic VOR gain asymmetry remained following the elimination of the spontaneous nystagmus in the network suggested that the amelioration of both the static and dynamic symptoms of UVD may be mediated by a single network. The networks were trained on high acceleration impulse stimuli but displayed the ability to generalise to low frequency, low acceleration sinusoids and closely approximated the behavioural responses to those stimuli.

Models, Biological↗
PubMed1991

Anti-stress role of the melatonin-immuno-opioid network: evidence for a physiological mechanism involving T cell-derived, immunoreactive beta-endorphin and MET-enkephalin binding to thymic opioid receptors.

Our previous work showed that the pineal neurohormone melatonin induces activated T lymphocytes to release opioid peptides with immunoenhancing and anti-stress properties. Here we present evidence that these peptides crossreact with anti-beta-endorphin and anti-met-enkephalin antisera, and bind specifically to thymic opioid receptors. Furthermore, the same antisera injected in prednisolone treated mice prevented the normal recovery of thymus cellularity and of the capacity to mount a primary antibody response against T-dependent antigens. Surgical pinealectomy, i.e. inhibition of endogenous melatonin and absence of antigen activation negated the effect of such antisera demonstrating the physiological relevance of this melatonin-immuno-opioids network. It is proposed that function of this network may be that of driving a correct immune recovery after the depression caused by the elevated corticosteroids level associated with immune responses and/or stressful situations.

Animals↗