Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “range adaptation”

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 757 records · Page 42Linked to original sources
PubMed1997

The effects of neonatal median nerve injury on the responsiveness of tactile neurones within the cuneate nucleus of the cat.

1. The capacity of cuneate neurones to attain normal functional properties following neonatal median nerve injury was investigated with single neurone recording in anaesthetized cats, 12-24 months subsequent to a controlled crush injury. Effectiveness of the peripheral nerve injury was confirmed by the abolition of the median nerve compound action potential following the crush. 2. Cuneate recording was carried out after denervation of the forearm, apart from the median nerve, to ensure that neurones studied had receptive fields within the distribution zone of the regenerated median nerve. Controlled and reproducible tactile stimuli were used to evaluate the functional capacities of neurones to determine whether they were consistent with those reported earlier for cuneate neurones in cats that had normal peripheral nerve development. 3. Twenty-two cuneate neurones with well-defined tactile receptive fields within the distribution zone of the regenerated median nerve were classified according to their adaptation characteristics and functional properties. Slowly adapting neurones responded throughout static skin indentations and had graded and approximately linear stimulus-response relations over indentation ranges up to 1.5 mm. Rapidly adapting neurones responded to the dynamic phases of skin indentations and could be divided into two broad classes, one most sensitive to vibrotactile stimuli at 200-400 Hz which appeared to receive a predominant input from Pacinian corpuscle receptors, and a non-Pacinian group that included neurones most sensitive to skin vibration at 5-50 Hz which appeared to receive glabrous skin input from the rapidly adapting class of afferent fibres. 4. Based on the stimulus-response relations and on measures of phase locking in the responses to vibrotactile stimuli, it appears that the functional properties of cuneate neurones activated from the field of a regenerated median nerve subsequent to a neonatal nerve crush injury were consistent with those reported previously for 'control' cuneate neurones. The results indicate that cuneate neurones can acquire normal tactile coding capacities despite the disruption caused by prior crush injury to their peripheral nerve source.

Animals↗
PubMed2006

Virulence of broad- and narrow-host-range Salmonella enterica serovars in the streptomycin-pretreated mouse model.

Salmonella enterica subspecies I serovars are common bacterial pathogens causing diseases ranging from enterocolitis to systemic infections. Some serovars are adapted to specific hosts, whereas others have a broad host range. The molecular mechanisms defining the virulence characteristics and the host range of a given S. enterica serovar are unknown. Streptomycin pretreated mice provide a surrogate host model for studying molecular aspects of the intestinal inflammation (colitis) caused by serovar Typhimurium (S. Hapfelmeier and W. D. Hardt, Trends Microbiol. 13:497-503, 2005). Here, we studied whether this animal model is also useful for studying other S. enterica subspecies I serovars. All three tested strains of the broad-host-range serovar Enteritidis (125109, 5496/98, and 832/99) caused pronounced colitis and systemic infection in streptomycin pretreated mice. Different levels of virulence were observed among three tested strains of the host-adapted serovar Dublin (SARB13, SD2229, and SD3246). Several strains of host restricted serovars were also studied. Two serovar Pullorum strains (X3543 and 449/87) caused intermediate levels of colitis. No intestinal inflammation was observed upon infection with three different serovar Paratyphi A strains (SARB42, 2804/96, and 5314/98) and one serovar Gallinarum strain (X3796). A second serovar Gallinarum strain (287/91) was highly virulent and caused severe colitis. This strain awaits future analysis. In conclusion, the streptomycin pretreated mouse model can provide an additional tool to study virulence factors (i.e., those involved in enteropathogenesis) of various S. enterica subspecies I serovars. Five of these strains (125109, 2229, 287/91, 449/87, and SARB42) are subject of Salmonella genome sequencing projects. The streptomycin pretreated mouse model may be useful for testing hypotheses derived from this genomic data.

Animals↗
PubMedDate not supplied

Movement direction analysers: independence and bandwidth.

Opponent, or ratio, models of movement direction perception propose that pairs of analysers, sensitive to opposite directions, are linked in an opponent fashion. Alternatively, distribution models posit independence of movement direction analysers. To investigate analyser independence, a direction-selective adaptation experiment was conducted in which motion coherence thresholds for random-dot apparent motion stimuli were measured for upward, downward, leftward and rightward motion with and without prior adaptation to rightward motion. Coherence thresholds for rightward motion were elevated on average by 0.64 log units after adaptation. Thresholds for motion in the other directions remained unchanged. Since opponent models predict enhanced sensitivity after adaptation for the direction opposite that of adaptation, these results suggest that movement direction analysers operate independently. In a second experiment subjects adapted to a bidirectional stimulus containing an equal number of leftward and rightward moving dots. Leftward and rightward coherence thresholds were elevated even though no motion aftereffects were produced. A third experiment in which coherence thresholds for test directions within a narrow range were measured with and without prior adaptation to motion in the direction of the range's mean showed that threshold elevation was maximal when test and adaptation direction were matched and fell off as the difference in adaptation and test direction increased. The resulting functions indicate that the bandwidth of movement direction analysers is between +/- 35 and +/- 40 deg, a value consistent with reported mean directional tuning functions of movement sensitive units in the middle temporal area but smaller than previously reported psychophysical values.

Adaptation, Ocular↗
PubMed2004

Tolerance to stress and environmental adaptability of Chromobacterium violaceum.

Chromobacterium violaceum is a Gram-negative bacterium, abundant in a variety of ecosystems in tropical and subtropical regions, including the water and borders of the Negro River, a major component of the Amazon Basin. As a free-living microorganism, C. violaceum is exposed to a series of variable conditions, such as different sources and abundance of nutrients, changes in temperature and pH, toxic compounds and UV rays. These variations, and the wide range of environments, require great adaptability and strong protective systems. The complete genome sequencing of this bacterium has revealed an enormous number and variety of ORFs associated with alternative pathways for energy generation, transport-related proteins, signal transduction, cell motility, secretion, and secondary metabolism. Additionally, the limited availability of iron in most environments can be overcome by iron-chelating compounds, iron-storage proteins, and by several proteins related to iron metabolism in the C. violaceum genome. Osmotically inducible proteins, transmembrane water-channel, and other membrane porins may be regulating the movement of water and maintaining the cell turgor, activities which play an important role in the adaptation to variations in osmotic pressure. Several proteins related to tolerance against antimicrobial compounds, heavy metals, temperature, acid and UV light stresses, others that promote survival under starvation conditions, and enzymes capable of detoxifying reactive oxygen species were also detected in C. violaceum. All these features together help explain its remarkable competitiveness and ability to survive under different types of environmental stress.

Adaptation, Physiological↗
PubMed2000

Caenorhabditis elegans is a model host for Salmonella typhimurium.

The idea of using simple, genetically tractable host organisms to study the virulence mechanisms of pathogens dates back at least to the work of Darmon and Depraitère [1]. They proposed using the predatory amoeba Dictyostelium discoideum as a model host, an approach that has proved to be valid in the case of the intracellular pathogen Legionella pneumophila [2]. Research from the Ausubel laboratory has clearly established the nematode Caenorhabditis elegans as an attractive model host for the study of Pseudomonas aeruginosa pathogenesis [3]. P. aeruginosa is a bacterium that is capable of infecting plants, insects and mammals. Other pathogens with a similarly broad host range have also been shown to infect C. elegans [3,4]. Nevertheless, the need to determine the universality of C. elegans as a model host, especially with regards pathogens that have a naturally restricted host specificity, has rightly been expressed [5]. We report here that the enterobacterium Salmonella typhimurium, generally considered to be a highly adapted pathogen with a narrow range of target hosts [6], is capable of infecting and killing C. elegans. Furthermore, mutant strains that exhibit a reduced virulence in mammals were also attenuated for their virulence in C. elegans, showing that the nematode may constitute a useful model system for the study of this important human pathogen.

Animals↗
PubMed2001

Adaptation as a mediator of intimate abuse and traumatic stress in battered women.

The purpose of this research was to test one aspect of a proposed middle-range theory synthesized from the Roy adaptation model and linked with the framework of post-traumatic stress. A predictive-correlational design was used to examine adaptation as a mediator of traumatic stress in battered women. Analysis included regression and path analytic procedures. Results indicated (a) direct relationships between the focal stimuli of abuse and the response of post-traumatic stress disorder and (b) adaptation in the physiologic, self-concept, and interdependence modes partially mediated the relationship between the focal stimuli of abuse and the response of post-traumatic stress disorder in battered women.

Adaptation, Psychological↗
PubMed2000

The adaptation of perimuscular connective tissue during distraction osteogenesis.

It is not known whether the decreased range of motion observed during distraction osteogenesis results from the lack of adaptation of muscle or from fibrosis in the perimysium. The adaptation of the perimysium in the tibialis anterior muscle in skeletally immature rabbits using two distraction regimens (0.7 and 1.4 mm/day with 15% lengthening) was characterized. The resulting data indicate that during distraction osteogenesis, the muscle adapts by reorganization of its connective tissue. At a lengthening rate of 1.4 mm/day, there is perimysial fibrosis without major cellular pathologic abnormalities in the muscle fibers. The increase in perimysial thickness is characterized by an increase of collagen Type I. In addition, collagen Type I is deposited around the endomysium. The increase in total collagen and its cross-linking are dependent on the lengthening rate. The faster lengthening rate also leads to a significant decreased passive plantar flexion. Supplemental growth of the tibia was not observed, and a lack of adaptation in the muscle (based on resting length) was not seen. Together, the data suggest that decreased range of motion during distraction osteogenesis may be a function of the adaptation of the perimysium rather than of the muscle fibers.

Adaptation, Physiological↗
PubMed1996

Light-dependent control of calcium in intact rods of the bullfrog Rana catesbeiana.

1. Using Fura-2, we measured cytosolic free calcium concentrations in rod outer segments of the bullfrog (Rana catesbeiana) under a wide range of steady-state, adapting light intensities. We also measured rod circulating currents under the same adapting conditions. 2. Both the steady-state cytosolic free calcium concentration and the steady-state circulating current were halved by background lights that isomerized approximately 100 rhodopsin molecules per rod per second. A just-measurable reduction in calcium was evoked by a background 1/10 as bright. The steady-state calcium concentration and the steady-state circulating current were proportional to each other over the full range of intensities tested, the brightest of which suppresses the circulating current by 75% and reduces flash sensitivity by about two orders of magnitude relative to the rods' sensitivity in darkness. 3. Additional experiments, in which the Na+:Ca2+,K+ exchanger in the rod outer segment was inactivated while maintaining intracellular calcium at physiological levels, demonstrated that steady-state calcium concentrations in the outer segment are set only by the influx of calcium through the light-sensitive channels and its efflux via the Na+:Ca2+,K+ exchanger. We found no measurable light-induced release of calcium from internal stores and no evidence of any other calcium flux between the cytosol and intracellular compartments. 4. Taken together, these findings lead us to conclude that over the normal operating range of the rod, the selectivity of the cGMP-gated channels for calcium does not change as a result of background illumination. 5. Our data also suggest that a major role of calcium-dependent cGMP synthesis by guanylyl cyclase is to stabilize both the circulating current and the cytosolic free calcium concentration in darkness. This would minimize the dark noise of the rod and thereby increase the reliability with which dim stimuli can be detected in the dark-adapted state.

Animals↗
PubMed2003

Natural patterns of neural activity: how physiological mechanisms are orchestrated to cope with real life.

Physiological mechanisms of neuronal information processing have been shaped during evolution by a continual interplay between organisms and their sensory surroundings. Thus, when asking for the functional significance of such mechanisms, the natural conditions under which they operate must be considered. This has been done successfully in several studies that employ sensory stimulation under in vivo conditions. These studies address the question of how physiological mechanisms within neurons are properly adjusted to the characteristics of natural stimuli and to the demands imposed on the system being studied. Results from diverse animal models show how neurons exploit natural stimulus statistics efficiently by utilizing specific filtering capacities. Mechanisms that allow neurons to adapt to the currently relevant range from an often immense stimulus spectrum are outlined, and examples are provided that suggest that information transfer between neurons is shaped by the system-specific computational tasks in the behavioral context.

Action Potentials↗
PubMed2003

Ecological characterization of Steinernema scarabaei, a scarab-adapted entomopathogenic nematode from New Jersey.

This study describes the basic ecological characteristics of the entomopathogenic nematode Steinernema scarabaei (Rhabditida: Steinernematidae) that was originally isolated from epizootics in scarab populations in New Jersey turfgrass areas. Under laboratory conditions, S. scarabaei infected a limited range of insect species and appeared best adapted to scarab larvae as hosts. It uses a widely ranging foraging strategy with a low attachment rate to mobile hosts on the soil surface but with excellent infection of sedentary host placed at >or=2 cm soil depth. It has a wide thermal activity range with optimum infectivity from 17.5 to 25 degrees C. Because of its foraging strategy and adaptation to scarab larvae as hosts, S. scarabaei has outstanding potential for the control of scarab pests.

Animals↗
PubMed1987

Morphologic criteria of progression and regression of cardiac hypertrophy.

The heart is able to adapt itself to a demanded load by increasing (hypertrophy) or decreasing (regression of hypertrophy) its muscular mass within a wide range. Overstressing of the ability of adaptation is accompanied by degenerative changes of myocytes. Semiquantitative investigations of endomyocardial biopsies (EMCBs) of patients with dilative cardiomyopathy (DCM) and hypertrophic nonobstructive cardiomyopathy (HNCM) show a fibrosis of the interstitial space, as well as almost similar changes of myofibrils and mitochondria. A reduced number of myocytes in hearts with DCM could explain the decreased functional capacity. Quantitative investigations of endomyocardial biopsies and myectomy specimens in patients with hypertrophic obstructive cardiomyopathy have revealed that hypertrophy and, to a certain extent, hyperplasia of muscle fibers cause asymmetrical thickening of the septum. Experimental investigations of the regression of training-induced hypertrophy in rats have shown that nearly all parameters (cardiac weight, thickness of muscle fibers, myofibrillar mass, interstitial space, and capillary width) returned to the values of controls 14 days after termination of a swimming training regimen. A significantly higher density of capillaries after regression of muscle fiber hypertrophy compared to controls points to a temporal dissociation in the regression of myocyte size and capillary network. Decrease in RNA concentration and an increased number of autophagic vacuoles give evidence for decreased anabolism and increased catabolism may occur during regression. In humans, fibrosis of the myocardium and scar formation explain the irreversibility of cardiac hypertrophy, as observed in some patients with valvular heart disease, despite valve replacement.

Adult↗
PubMed2002

Archaeology and cognitive evolution.

Archaeology can provide two bodies of information relevant to the understanding of the evolution of human cognition--the timing of developments, and the evolutionary context of these developments. The challenge is methodological. Archaeology must document attributes that have direct implications for underlying cognitive mechanisms. One example of such a cognitive archaeology is found in spatial cognition. The archaeological record documents an evolutionary sequence that begins with ape-equivalent spatial abilities 2.5 million years ago and ends with the appearance of modern abilities in the still remote past of 400,000 years ago. The timing of these developments reveals two major episodes in the evolution in spatial ability, one, 1.5 million years ago and the other, one million years later. The two episodes of development in spatial cognition had very different evolutionary contexts. The first was associated with the shift to an open country adaptive niche that occurred early in the time range of Homo erectus. The second was associated with no clear adaptive shift, though it does appear to have coincided with the invasion of more hostile environments and the appearance of systematic hunting of large mammals. Neither, however, occurred in a context of modern hunting and gathering.

Animals↗
PubMed1996

Temporal resolution in olfaction II: time course of recovery from adaptation in lobster chemoreceptor cells.

1. Adaptation and disadaptation rates determine the temporal response properties of sensory receptor cells. In chemoreception, temporal filter properties of receptor cells are poorly understood. We studied the time course of disadaptation in lobster antennular chemoreceptor cells by using in situ high-resolution stimulus measurement and extracellularly recorded spike responses. Fifteen receptor cells were each tested with two series (one at 10 microM, one at 100 microM) of three odor (hydroxyproline) pulses: a 200-ms test pulse, a 5-s adapting pulse, and a 200-ms probe pulse after time intervals ranging from 1 to 60 s. After complete adaptation by the adapting pulse, individual cells recovered at different rates. After 1 s, a third of the cells responded with a mean response of 3 spikes/cell, representing approximately 20% recovery. All cells fully recovered between 10 and 30 s. Mean full recovery was within 25 s, with a time constant of 14 s, independent of stimulus concentration.

Adaptation, Physiological↗
PubMed1994

The tactile movement aftereffect.

The existence of a tactile movement aftereffect was established in a series of experiments on the palmar surface of the hand and fingers of psychophysical observers. During adaptation, observers cupped their hand around a moving drum for up to 3 min; following this period of stimulation, they typically reported an aftereffect consisting of movement sensations located on and deep to the skin, and lasting for up to 1 min. Preliminary experiments comparing a number of stimulus materials mounted on the drum demonstrated that a surface approximating a low-spatial-frequency square wave, with a smooth microtexture, was especially effective at inducing the aftereffect; this adapting stimulus was therefore used throughout the two main experiments. In Experiment 1, the vividness of the aftereffect produced by 2 min of adaptation was determined under three test conditions: with the hand (1) remaining on the now stationary drum; (2) in contact with a soft, textured surface; or (3) suspended in air. Subjects' free magnitude estimates of the peak vividness of the aftereffect were not significantly different across conditions; each subject experienced the aftereffect at least once under each condition. Thus the tactile movement aftereffect does not seem to depend critically on the ponditions of stimulation that obtain while it is being experienced. In Experiment 2, the vividness and duration of the aftereffect were measured as a function of the duration of the adapting stimulus. Both measures increased steadily over the range of durations explored (30-180 sec). In its dependence on adapting duration, the aftereffect resembles the waterfall illusion in vision. An explanation for the tactile movement aftereffect is proposed, based on the model of cortical dynamics of Whitsel et al. (1989, 1991). With assumed modest variation of one parameter across individuals, this application of the model is able to account both for the data of the majority of subjects, who experienced the aftereffect as opposite in direction to the adapting stimulus, and for those of an anomalous subject, who consistently experienced the aftereffect as being in the same direction as the adapting stimulus.

Adult↗
PubMed1984

Helping parents understand the diagnosis of autism.

This paper offers guidelines to pediatricians and other developmental specialists who might be involved in counseling parents of autistic children. Although the paper focuses on the initial informing session, much of the material also applies to followup counseling of parents and other family members. The need for careful diagnosis is discussed as well as recent changes in thinking about autism that bear upon parental counseling. Suggestions are offered to facilitate the parents' understanding of their child's autistic condition, degree of cognitive and adaptive impairment, and long-range prognosis. Information is also provided to help in dealing with parents' questions about etiology and reactions to the diagnosis. The final section reviews material that should be considered by the clinician in making recommendations for treatment and education.

Adaptation, Psychological↗
PubMed1998

Measurement of circulating immunoreactive alpha-atrial natriuretic peptide in human plasma: validation and clinical application.

Recent evidence suggests that plasma alpha-atrial natriuretic peptide (alpha-ANP) may serve as a useful biochemical marker of severe heart failure, as circulating levels become ighly elevated. In the present study, a specific radioimmunoassay (RIA) protocol was adapted and optimised for rapid quantitative measurement of circulating alpha-ANP levels in plasma taken from clinically normal subjects and heart transplant recipients with no evidence of heart failure or heart transplant rejection. The plasma concentration of immunoreactive alpha-ANP in heart transplant recipients (115 +/- 10 pg/ml, n = 14) was significantly higher (p < 0.01) than in normal subjects (14 +/- 5 pg/ml, n = 20). Comparison of circulating plasma immunoreactive alpha-ANP levels obtained by the adapted assay to levels obtained by a standard RIA protocol revealed a significant correlation (r = 0.998, y = 1.004 x -2.94, n = 40). The adapted assay is simple, precise, and with a shorter incubation time that would enable results to be available within one working day. These results show that circulating biological active a-ANP levels are elevated in healthy heart transplant recipients with no evidence of heart failure; thus extending previous reports concerning the elevation in circulating alpha-ANP levels from patients with a wide range of heart disorders. The adapted RIA protocol would facilitate rapid detection and quantification of alpha-ANP in experimental research and routine clinical investigations.

Atrial Natriuretic Factor↗
PubMed2005

Crossing species' range borders: interspecies gene exchange mediated by hybridogenesis.

The distribution of species is limited by their ability to adapt to local environments. For adaptation by selection, genetic variability is crucial. As founder effects reduce genetic variability, extension of species' range borders is usually slow due to the reduced probability of successful colonization. However, the range limit might be extended by incorporating locally adapted genes. In western Palaearctic waterfrogs, interspecies hybrids show hemiclonal gametogenesis, are fertile and reproductively mimic one parental species. Genetic analysis, using allozyme loci, shows that they mediate gene exchange between the two parental species. Selection analysis provides evidence for local adaptation of single locus genotypes. This suggests that hybridogenesis presents a process which increases the number of neoform parental genotypes, exposing these to selection, and thereby revealing locally adapted genotypes which are essential for species range expansion.

Adaptation, Physiological↗
PubMed1981

A portable ERG system with an automatic driven LED Ganzfeld stimulation contact lens.

A portable ERG system with a Ganzfeld stimulation and adaptation light source is described. The stimulus flash energy can be selected from a range of 3.9 log units and the adapting background can be 0,10 or 100 lux at the cornea. The whole system has the dimensions of a standard ECG recorder, can operate independently of the main voltage and can be used in electrically unshielded rooms. It has a programmed measuring cycle that controls the paper transport, the changeover of the registration channel from one eye to the other, the stimulus presentation and the registration of a standard calibration pulse (100 microV/100 ms).

Adult↗