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At least 289 records · Page 16Linked to original sources
PubMed1998

20-Hz flicker stimulus can isolate the cone function in rat retina.

Cone electroretinograms (ERGs) are typically isolated in humans by flicker stimuli against rod-desensitizing adapting fields. To investigate the manner in which adapting-field luminance affects the cone ERGs, we recorded ERGs in normal albino Sprague-Dawley rats with flicker stimuli presented against adapting fields that ranged in luminance from to 1.75 log cd/m2. A flicker rate of 20 Hz was used to isolate the cone ERGs under all adaptation conditions. We found the amplitudes of cone ERGs to increase with increasing adapting-field luminance. These response characteristics are similar to human ERGs using 30-Hz flicker stimuli, which suggests that flicker stimuli are a useful technique to isolate the cone function in rats.

Adaptation, Ocular↗
PubMed2002

Perceived contrast following adaptation: the role of adapting stimulus visibility.

The issue of whether contrast adaptation can reduce the perceived contrast of gratings oriented orthogonal to the adapting stimulus to a greater extent than parallel gratings has been the subject of considerable debate (Snowden and Hammett, 1992; Ross and Speed, 1996). We compared the reductions in perceived contrast of various test gratings oriented parallel and orthogonal to the adapting stimulus across a range of spatial frequencies (2.25-9 c/deg) and adaptation contrasts (0.19-1.0). Our results show that when the adapting stimulus is low in contrast, parallel adaptation effects are always greater than the effects of orthogonal adaptation. When the adapting contrast is increased, however, the difference between parallel and orthogonal effects is reduced. Further increases in adapting contrast can produce a situation where cross-orientation adaptation effects exceed iso-orientation effects. This was observed at low spatial frequencies (2.25 and 4.5 c/deg) only. The difference in the pattern of results obtained at low and high spatial frequencies can be explained in terms of the adapting stimulus visibility. We conclude that cross-orientation adaptation effects can be greater than iso-orientation effects, but only when the adapting stimulus is highly suprathreshold.

Adaptation, Ocular↗
PubMedDate not supplied

[The nature of the dependence of the rate of development on temperature determines the greatest efficiency of metabolism at optimal temperatures].

Metabolism intensity and development rate have different pattern of dependence on temperature. Oxygen intake and several other metabolic processes bear an exponential relationship to temperature. The pattern of this relationship is similar in different poikilothermal species. On the contrary, the relationship between the rate of development and temperature is species-specific and more complex. Hence, the curves obtained by plotting oxygen intake per developmental stage against temperature resemble parabola and the minimum values of oxygen intake correspond to optimal temperatures. Such a correspondence is almost solely determined by parameters of the relationship between the rate of development and temperature. Therefore, the efficiency of metabolism does not determine the range of optimal temperatures. It is suggested that adaptive alterations of this range during evolution proceed via changes of the parameters of relationship between the rate of development and temperature dependence. Relatively small number of mutations is required to produce such changes.

Animals↗
PubMed2001

Creating an adaptable anterior margin for an implant-retained auricular prosthesis.

Achieving complete adaptation of the anterior margin of an auricular prosthesis often presents a challenge. Conventional solutions to this problem address soft tissue movements at static positions and do not necessarily reflect how the margin will adapt throughout a complete range of motion of the mandible and head. A technique is presented for creating an adaptable margin for an auricular prosthesis throughout a complete range of motion. This technique can be applied once adaptation of the diagnostic wax margin to the master cast is successful.

Acrylic Resins↗
PubMed2025

Combined Evidence Reveals the Origin of a Rapid Range Expansion Despite Retained Genetic Diversity and a Weak Founder Effect.

Many species are currently experiencing range shifts in response to changing environmental conditions with potentially serious genetic consequences. Repeated founder events and strong genetic drift are expected to erode genetic variation at the range front, reducing adaptive potential and slowing or even halting the expansion. However, the severity of these consequences for common and highly mobile species undergoing environment-driven range shifts (c.f. invasions) is less clear. Here, we combined historical observations and contemporary movement data of the common reed warbler (Acrocephalus scirpaceus) with genomic evidence from across its European breeding range to (1) infer the origin and (2) quantify the genetic consequences of a recent and rapid northward range expansion. Although there were no reductions in levels of nucleotide diversity or allelic richness, nor a signal of founder effect in the directionality index (ψ), our combined dataset approach was able to infer an expansion origin from the southwest. Furthermore, we found that private allelic richness retained a slight but significant linear decline along the colonisation route. These results suggest that high dispersal capabilities can allow even philopatric species to avoid the loss of genetic diversity during rapid range expansions. Nevertheless, if multiple lines of evidence enable identification of an expansion pathway, we may still detect genetic signals of expansion.

Founder Effect↗
PubMed2005

The evolution of species' distributions: reciprocal transplants across the elevation ranges of Mimulus cardinalis and M. lewisii.

Every species occupies a limited geographic area, but it remains unclear why traits that limit distribution do not evolve to allow range expansion. Hypotheses for the evolutionary stability of geographic ranges assume that species are maladapted at the range boundary and unfit beyond the current range, but this assumption has rarely been tested. To examine how fitness varies across species' ranges, we reciprocally transplanted two species of monkeyflowers, Mimulus cardinalis and M. lewisii, within and beyond their present elevation ranges. We used individuals of known parentage from populations collected across the elevation ranges of both species to examine whether populations are adapted to position within the range. For both species we found the greatest average fitness at elevations central within the range, reduced fitness at the range margin, and zero or near-zero fitness when transplanted beyond their present elevation range limits. However, the underlying causes of fitness variation differed between the species. At high elevations beyond its range, M. cardinalis displayed reduced growth and fecundity, whereas at low elevations M. lewisii experienced high mortality. Weak differences in performance were observed among populations within each species and these were not related to elevation of origin. Low fitness of both species at their range margin and weak differentiation among populations within each species suggest that adaptation to the environment at and beyond the range margin is hindered, illustrating that range margins provide an interesting system in which to study limits to adaptation.

Adaptation, Biological↗
PubMed1992

Niche breadth in parasites: an evolutionarily stable strategy model, with special reference to the protozoan parasite Leishmania.

A parasite's host range essentially defines its niche breadth, which, as foraging theory predicts, is influenced by resource availability. For parasites, the interaction of infection and transmission characteristics with host population dynamics determines host availability. An epidemiological model, involving two host types and describing competition between a "generalist" parasite strain and a related "specialist" strain, is used to examine the interplay among host range, relative host availabilities, and adaptational compromises engendered by increased host range. Results show that the generalist can predominate even when it cannot maintain itself in either host alone, but that the specialist can persist if its reproductive rate attains some threshold relative to either of the generalist's respective rates in its two hosts. The model is in rough, qualitative agreement with observed dynamics of two Leishmania parasite-host systems, and overall results suggest that infection of two species with a common parasite can lead to complex, indirect coevolutionary dynamics.

Adaptation, Biological↗
PubMed2006

Visual recalibration and selective adaptation in auditory-visual speech perception: Contrasting build-up courses.

Exposure to incongruent auditory and visual speech produces both visual recalibration and selective adaptation of auditory speech identification. In an earlier study, exposure to an ambiguous auditory utterance (intermediate between /aba/ and /ada/) dubbed onto the video of a face articulating either /aba/ or /ada/, recalibrated the perceived identity of auditory targets in the direction of the visual component, while exposure to congruent non-ambiguous /aba/ or /ada/ pairs created selective adaptation, i.e. a shift of perceived identity in the opposite direction [Bertelson, P., Vroomen, J., & de Gelder, B. (2003). Visual recalibration of auditory speech identification: a McGurk aftereffect. Psychological Science, 14, 592-597]. Here, we examined the build-up course of the after-effects produced by the same two types of bimodal adapters, over a 1-256 range of presentations. The (negative) after-effects of non-ambiguous congruent adapters increased monotonically across that range, while those of ambiguous incongruent adapters followed a curvilinear course, going up and then down with increasing exposure. This pattern is discussed in terms of an asynchronous interaction between recalibration and selective adaptation processes.

Adaptation, Physiological↗
PubMed1974

A Method for Characterizing the Relation between Nutrient Concentration and Flux into Roots of Intact Plants.

A method based on the rate of depletion of a nutrient from solution was developed to characterize nutrient flux of plant roots. Nutrient concentration of the solution was measured at a series of time intervals to describe the complete depletion curve. An integrated rate equation, based on a Michaelis-Menten model, was developed and fit to the data of the depletion curve using a least-square procedure. The equation contained values for V(max), the maximum rate of influx; Km, the Michaelis constant; and E, efflux, which were used to describe the relation between solution concentration and net influx rate. Models other than Michaelis-Menten could also be used. The method uses only one plant or group of plants to obtain data over a range of nutrient concentrations, is adapted particularly to the low concentration range, and measures the concentration below which net influx ceases. With this method the plant is in steady state absorption prior to the experiment and continues at this steady state until near the end of the experiment.A procedure was also developed to measure uptake rate at constant concentration by adding nutrients to the pot at a constant rate that matched net influx into the root. This method also provides a means of measuring diurnal fluctuations in net influx rates.

Journal Article↗
PubMed2005

Variation in stomatopod (Gonodactylus smithii) color signal design associated with organismal condition and depth.

In interactions, many tropical stomatopod species display conspicuous colored body spots that can communicate information about the sender's state (e.g., sex, aggressiveness, etc.). Species inhabiting a variety of depths experience large differences in illumination spectrum and intensity due to filtering of light by water and its constituents. Stomatopod spectral sensitivity is known to vary phenotypically with changes in light environment (associated with depth) that potentially affects the detection of color signals. Animals collected at different depths also have different body coloration. This study examines how spectral differences in colored body spots vary with organismal condition and models the effects of changing body coloration, light environment, and spectral sensitivity on the detection of color signals in a gonodactyloid species, Gonodactylus smithii. Of the seven conspicuous color spots that were measured in G. smithii, three had spectral differences that correlated with sex, aggression, and female reproductive state. A model of color detection in G. smithii indicates that longer-wavelength spectral content was affected most by varying body coloration and light conditions. Most color signals were perceived similarly both by shallow- and by deep-adapted photoreceptor sets over a range of depths (1-13 m). Eye spot ('meral spot') color detection also was invariant over the same depth range in shallow- and deep-adapted, long-wavelength receptors, but deep-adapted receptors continued to maintain a consistent detection of these spots down to 18 meters. These results suggest that meral spot coloration may have evolved as a constant signal when viewed by conspecifics from various depths.

Adaptation, Physiological↗
PubMed2006

Effects of increasing temperatures on population dynamics of the zebra mussel Dreissena polymorpha: implications from an individual-based model.

Zebra mussels (Dreissena polymorpha, Pallas, 1771) have had unprecedented success in colonizing European and North American waters under strongly differing temperature regimes. Thus, the mussel is an excellent model of a species which is able to cope with increasing water temperatures expected under global change. We study three principle scenarios for successful survival of the mussel under rising temperatures: (1) no adaptation to future thermal conditions is needed, existing performance is great enough; (2) a shift (adaptation) towards higher temperatures is required; or (3) a broadening of the range of tolerated temperatures (adaptation) is needed. We developed a stochastic individual-based model which describes the demographic growth of D. polymorpha to determine which of the alternative scenarios might enable future survival. It is a day-degree model which is determined by ambient water temperature. Daily temperatures are generated based on long-term data of the River Rhine. Predictions under temperature conditions as recently observed for this river that are made for the phenology of reproduction, the age distribution and the shell length distribution conform with field observations. Our simulations show that temporal patterns in the life cycle of the mussel will be altered under rising temperatures. In all scenarios spawning started earlier in the year and the total reproductive output of a population was dominated by the events later in the spawning period. For maximum temperatures between 20 and 26 degrees C no thermal adaptation of the mussel is required. No extinctions and stable age distributions over generations were observed in scenario 2 for all maximum temperatures studied. In contrast, no population with a fixed range of tolerated temperatures survived in scenario 3 with high maximum temperatures (28, 30, 32 degrees C). Age distributions showed an excess of 0+ individuals which resulted in an extinction of the population for several thermal ranges investigated.

Adaptation, Biological↗
PubMed2004

On the possible adaptive value of coprophagy in free-ranging chimpanzees.

Coprophagy occurred during major periods of feeding on fruits of Dialium spp. (Caesalpiniaceae) in a group of orphaned chimpanzees released in Conkouati Douli National Park, Republic of Congo. Since stress, boredom or food scarcity could not explain coprophagy according to our daily behavioral and veterinary control observations, we suggest that Dialium seeds were the item of interest in the feces. Two types of Dialium seeds were commonly found in the feces after chimpanzees swallowed the mesocarp and whole seeds together. These seeds were either whole and hard or whole/broken and soft imbibed. A mechanical and/or chemical effect of the gut passage may enable the chimpanzees to chew and ingest the seeds, thus providing nutritional intake.

Adaptation, Physiological↗
PubMed1979

Dark-adaptation of the aspartate-isolated rod receptor potential of the frog retina: threshold measurements.

1. The dark-adaptation of the aspartate-isolated rod receptor potential of the isolated and perfused frog retina has been measured after bleaching about 5-10% of the rhodopsin. The fraction bleached (DeltaR) and the decay of rhodopsin photoproducts were determined using alternating measurements with a photometric technique (Donner & Hemilä, 1975).2. The dark-adaptation time course of the log threshold elevation is exponential, log I(t)/I(0) = W exp (-t/tau)+P, where W is the extrapolated value for log I(t)/I(0)-P at t = 0 and P is log I(t)/I(0) for t = infinity. When DeltaR increases from 2 to 10% W increases from ca. 2.6 to ca. 5. The time constant tau is about 13 min at 9 degrees C and 7 min at 14 degrees C (DeltaR = 5-10%).3. When the bleaching period is extended, keeping the amount bleached (Ixt) constant, dark-adaptation is completed earlier.4. The time course of dark-adaptation and the decay of the photoproduct ;retinal' are similar, as is also their dependence on temperature (Q(10) approximately 3).5. The permanent log threshold rise P is approximately proportional to DeltaR after small bleaches; when more than about 10% is bleached the slope of the curve P(DeltaR) decreases. P is considerably larger (about 2.5-fold) for the same fraction bleached in experiments at 14 degrees C as compared to experiments at 9 degrees C.6. A comparison with previously obtained corresponding values for dark-adaptation after small bleaches at the ganglion cell level shows a close agreement between the time constants for the dark-adaptation curve, its range and the dependence of threshold on the fraction of rhodopsin bleached.

Animals↗
PubMed1990

[Electrophysiological properties of fast- and slow-adapting units and their generator potentials of the frog tongue].

The purpose of this study was to determine the stimulus response properties of fast and slow adapting units in the fungiform papillae of the frog tongue. Secondly, fast- and slow- adapting generator potentials were recorded from fast and slow-adapting mechanoreceptors in the single fungiform papilla glossopharyngeal nerve preparations, respectively. Results I. Impulse response properties of fast- and slow-adapting units 1) Most of the fungiform papillae were innervated by both fast- and slow-adapting units. Fast-adapting units evoked 1-4 impulses to each stimulus and the adaptation time was less than 17.5 msec. Slow-adapting units evoked 27.8 +/- 8.0 impulses (range: 11-49 impulses n = 18) during a pressure stimulation of 3 sec, and the adaptation time was 1.64 +/- 0.73 sec (range: 0.53-2.86 sec, n = 18). 2) Threshold, latency and absolute refractory period for fast-adapting units were 7.0 +/- 1.9 microns (range: 3.0-11.8 microns, n = 189), 2.31 +/- 1.29 msec (range: 0.85-6.80 msec, n = 31) and 2.9 +/- 1.0 msec (range: 1.8-5.6 msec, n = 33), respectively. Those for slow-adapting units were 4.6 +/- 1.8 microns (range: 2.0-11.8 microns, n = 152), 13.54 +/- 11.29 msec (range: 2.00-54.00 msec, n = 35) and 6.5 +/- 3.6 msec (range: 1.9-19.6 msec, n = 35), respectively. 3) A fast-adapting unit innervated 5.1 +/- 2.5 fungiform papillae (range: 1-13 fungiform papillae, n = 58) and the receptive area was 0.342 +/- 0.312 mm2 (range: 0.005-1.548 mm2, n = 55). A slow-adapting unit innervated 3.3 +/- 2.0 fungiform papillae (range: 1-12 fungiform papillae, n = 50) and the receptive area was 0.158 +/- 0.144 mm2 (range: 0.006-0.616 mm2, n = 29). 4) Conduction velocity of the fast-adapting unit was 23.0 +/- 3.1 m/sec (range: 15.0-30.6 m/sec, n = 528) and that of the slow-adapting unit was 12.8 +/- 2.2 m/sec (range: 4.4-21.1 m/sec, n = 495). The conduction velocity was calculated from the time necessary to conduct at two different points of the nerve fiber. 5) The upper limits of fast- and slow-adapting units for vibratory stimulation were 62.7 +/- 10.5 Hz (range: 50-80 Hz, n = 15) and 34.5 +/- 9.6 Hz (range: 15-45 Hz, n = 10), respectively. II.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Measures of hearing aid gain for real speech.

OBJECTIVE: Non-speech stimuli typically are used to estimate the electroacoustic characteristics of a hearing aid. At present, there is no consensus as to what type of input stimulus will best represent the gain for real speech. The purpose of this study was to measure hearing aid gain using continuous discourse and to compare these values with gain measured with five different types of simpler stimuli. DESIGN: Hearing aid gain as a function of frequency was measured in a 2 cm3 coupler for 20 commercially available hearing aids. Circuitry included features such as linear peak clipping, compression limiting, 1-, 2-, and 3-channel full dynamic range compression, and adaptive compression. Input stimuli were a) 15 sec of continuous discourse, b) swept pure tones (SPTs), c) speech weighted composite noise (SWCN), d) simulated speech, e) speech weighted warble tones, and f) speech modulated noise. Input levels ranged from 50 to 80 dB SPL. RESULTS: In general, both SPTs and SWCN tended to underestimate the high-frequency gain for real speech. These discrepancies increased as a function of input intensity. On average, the SPT produced the greatest departure from the gain for real speech, producing differences for individual hearing aids as large as 10 to 14 dB. An analysis by circuit type revealed that discrepancies most likely occurred when a hearing aid was operating in a nonlinear mode. Of the five non-speech stimuli used, speech modulated noise and simulated speech seemed to provide the closest approximation to the gain measured with continuous discourse. CONCLUSIONS: When a hearing aid is operating in a nonlinear mode, non-speech stimuli will tend to underestimate the gain for real speech, particularly in the high frequencies. Under some conditions, these discrepancies may impact clinical decisions during the hearing aid fitting process. Additional studies are needed to elucidate the factors that contribute to the gain discrepancies observed in this study and to explore the use of additional stimuli (including short speech samples), which may result in better predictions of the gain for speech.

Correction of Hearing Impairment↗
PubMed1988

Life, evolution, and the pursuit of single photon sensitivity.

Evolutionary forces have designed a large family of rod and cone photoreceptors, each member of which suits the lifestyle requirements and circadian patterns of a particular species. The three-segment architecture of signal transduction is conspicuous in the biochemistry of photoreceptors and supports their demonstrated properties of extreme sensitivity, low noise levels, extended dynamic range, and light adaptation. The designs elaborated by evolution reflect a gradual process of modification, with the sequential elaboration of layers of control and refinements in control. The end results of this long evolutionary labor are the functional efficiency and dynamic range that give the rod its utility. Our conceptual problems in deriving observed rod properties from the collective features of known rod gene products may well give way when we have learned more about the true composition and topology of the outer segment gene set and both bound and free nucleotide concentrations. The invertebrates have developed alternative solutions to the problems of photoreceptor sensitivity and wide dynamic range. The vertebrate rod represents a truly optimized way to capture and interpret low-intensity photon signals. One may anticipate, with some enthusiasm, those molecular and kinetic data that will permit an understanding of how cones differ from rods and how release from the requirement for single photon detection has shaped the design of this wavelength-specific companion photoreceptor. The utilization by evolution of the three-segment architecture of GTP-dependent signal transduction for other modalities of sensory perception, such as olfaction (Lancet et al., this volume) and gustation (Jones et al., this volume), is certainly a reasonable and successful choice.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1976

The inflation-catheter technique of ventilation during laryngoscopy.

Over the past three years the inflation-catheter technique (ICT) of controlled ventilation during general anaesthesia has proved a safe and useful method for use with laryngoscopy and other trans-oral endoscopies (most notably flexible fiberoptic bronchoscopy). The ICT allows full control of the patient's airway for the anaesthetist and exceptionally good exposure for the surgeon. In this technique ventilation of the patient is accomplished by intermittent high flow (10 ml/kg/sec) inflation of the lungs through a small (2 to 6 mm diameter) plastic orotracheal catheter. The inflation-catheter is stiffened by fixation of an intralumenal wire. Exhalation is passive around the catheter through the open airway. The Inflation Catheter Technique is readily adaptable for patients ranging from large adults to small babies by variation of catheter sizes. It can be used safely with nitrous oxide-oxygen as the ventilating gas(i.e., Bird N2O/O2 Blender) since air entrainment is not a feature. It is also readily adaptable for use with mechanical ventilation (i.e., Wolf Injectomat).

Adult↗
PubMed2006

An overview of Cistus ectomycorrhizal fungi.

The genus Cistus comprises a group of about 20 shrub species found in wide areas throughout the whole Mediterranean region to the Caucasus. Being one of the main constituents of the Mediterranean-type maquis, this plant genus is peculiar in that it has developed a range of specific adaptations to resist summer drought and frequent disturbance events, such as fire and grazing. In addition, it can form both ectomycorrhizas and arbuscular mycorrhizas. In this paper, we review the information available on the ectomycorrhizal fungi of Cistus across its entire geographic range, as gathered and critically sifted from both published literature sources and personal observations. Although the resulting data matrix was based primarily on accounts of sporocarp inventories in the field, existing knowledge on the features of Cistus natural and synthesized ectomycorrhizas was also included and discussed. In total, more than 200 fungal species belonging to 40 genera have been reported so far to be associated with Cistus. An analysis of the pattern of ectomycorrhizal diversity and host specificity revealed that members of the Cortinariaceae and Russulaceae make the most of both Cistus-aspecific and Cistus-specific mycobionts. Further studies are needed to expand our preliminary knowledge of the mycorrhizal ecology and biology of Cistus and its fungal associates, focusing on topics such as mycobiont diversity, host specificity, fungal succession, mycorrhizal influence on stress tolerance, and impact of disturbances, while comparing the findings with those from other ecosystems.

Ascomycota↗