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PubMed2001

Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise.

We determined the effect of fat adaptation on metabolism and performance during 5 h of cycling in seven competitive athletes who consumed a standard carbohydrate (CHO) diet for 1 day and then either a high-CHO diet (11 g. kg(-1)x day(-1) CHO, 1 g x kg(-1) x day(-1) fat; HCHO) or an isoenergetic high-fat diet (2.6 g x kg(-1) x day(-1) CHO, 4.6 g x kg(-1) x day(-1) fat; fat-adapt) for 6 days. On day 8, subjects consumed a high-CHO diet and rested. On day 9, subjects consumed a preexercise meal and then cycled for 4 h at 65% peak O(2) uptake, followed by a 1-h time trial (TT). Compared with baseline, 6 days of fat-adapt reduced respiratory exchange ratio (RER) with cycling at 65% peak O(2) uptake [0.78 +/- 0.01 (SE) vs. 0.85 +/- 0.02; P < 0.05]. However, RER was restored by 1 day of high-CHO diet, preexercise meal, and CHO ingestion (0.88 +/- 0.01; P < 0.05). RER was higher after HCHO than fat-adapt (0.85 +/- 0.01, 0.89 +/- 0.01, and 0.93 +/- 0.01 for days 2, 8, and 9, respectively; P < 0.05). Fat oxidation during the 4-h ride was greater (171 +/- 32 vs. 119 +/- 38 g; P < 0.05) and CHO oxidation lower (597 +/- 41 vs. 719 +/- 46 g; P < 0.05) after fat-adapt. Power output was 11% higher during the TT after fat-adapt than after HCHO (312 +/- 15 vs. 279 +/- 20 W; P = 0.11). In conclusion, compared with a high-CHO diet, fat oxidation during exercise increased after fat-adapt and remained elevated above baseline even after 1 day of a high-CHO diet and increased CHO availability. However, this study failed to detect a significant benefit of fat adaptation to performance of a 1-h TT undertaken after 4 h of cycling.

Adaptation, Physiological↗
PubMed2004

Encoder adaptation modulates the visual responses of crayfish interneurons.

The responses of sustaining and dimming fibers were characterized by the time varying firing rates elicited by extrinsic current and flashes of light. These data were simulated by an adaptive integrate-and-fire model. A postimpulse shunt conductance simulated spike-frequency adaptation. The correlation between observed and model current-elicited impulse rates was 0.94-0.98. However, except for a difference in input resistance (both measured and simulated), the voltage to impulse encoders of the two cell groups was similar and exhibited comparable degrees of spike-frequency adaptation (40 to 45%). The encoder model derived from current-elicited responses (with fixed parameters) was used to simulate visual responses elicited by light flashes. These simulations included a synaptic current derived from the time course of the postsynaptic potential (PSP). The sustaining fiber visual response consisted of a large excitatory PSP and high-frequency transient burst that adapted (by approximately 80%) to a low-frequency plateau discharge. The simulations indicated that spike-frequency adaptation had no effect on the transient discharge but reduced the plateau firing rate by approximately 60%. Encoder adaptation enhances the sustaining fiber response to the time derivative of the stimulus. In dimming fibers, the light flash elicits an inhibitory PSP that interrupts the "dark discharge" and an off response following the end of the flash. The simulations indicated that spike-frequency adaptation reduces the firing rate of both the dark discharge and the off response. Thus the model suggests that different effects of encoder adaptation on the two cell types arise from the same encoder mechanisms, but different actions are determined by differences in impulse rate and the time course of the discharge.

Action Potentials↗
PubMed2002

Computational study on monkey VOR adaptation and smooth pursuit based on the parallel control-pathway theory.

Much controversy remains about the site of learning and memory for vestibuloocular reflex (VOR) adaptation in spite of numerous previous studies. One possible explanation for VOR adaptation is the flocculus hypothesis, which assumes that this adaptation is caused by synaptic plasticity in the cerebellar cortex. Another hypothesis is the model proposed by Lisberger that assumes that the learning that occurs in both the cerebellar cortex and the vestibular nucleus is necessary for VOR adaptation. Lisberger's model is characterized by a strong positive feedback loop carrying eye velocity information from the vestibular nucleus to the cerebellar cortex. This structure contributes to the maintenance of a smooth pursuit driving command with zero retinal slip during the steady-state phase of smooth pursuit with gain 1 or during the target blink condition. Here, we propose an alternative hypothesis that suggests that the pursuit driving command is maintained in the medial superior temporal (MST) area based on MST firing data during target blink and during ocular following blank, and as a consequence, we assume a much smaller gain for the positive feedback from the vestibular nucleus to the cerebellar cortex. This hypothesis is equivalent to assuming that there are two parallel neural pathways for controlling VOR and smooth pursuit: a main pathway of the semicircular canals to the vestibular nucleus for VOR, and a main pathway of the MST-dorsolateral pontine nuclei (DLPN)-flocculus/ventral paraflocculus to the vestibular nucleus for smooth pursuit. First, we theoretically demonstrate that this parallel control-pathway theory can reproduce the various firing patterns of horizontal gaze velocity Purkinje cells in the flocculus/ventral paraflocculus dependent on VOR in the dark, smooth pursuit, and VOR cancellation as reported in Miles et al. at least equally as well as the gaze velocity theory, which is the basic framework of Lisberger's model. Second, computer simulations based on our hypothesis can stably reproduce neural firing data as well as behavioral data obtained in smooth pursuit, VOR cancellation, and VOR adaptation, even if only plasticity in the cerebellar cortex is assumed. Furthermore, our computer simulation model can reproduce VOR adaptation automatically based on a heterosynaptic interaction model between parallel fiber inputs and climbing fiber inputs. Our results indicate that different assumptions about the site of pursuit driving command maintenance computationally lead to different conclusions about where the learning for VOR adaptation occurs. Finally, we propose behavioral and physiological experiments capable of discriminating between these two possibilities for the site of pursuit driving command maintenance and hence for the sites of learning and memory for VOR adaptation.

Adaptation, Physiological↗
PubMed2002

Differential adaptation of the linear and nonlinear components of the horizontal vestibuloocular reflex in squirrel monkeys.

Previous work in squirrel monkeys has demonstrated the presence of linear and nonlinear components to the horizontal vestibuloocular reflex (VOR) evoked by high-acceleration rotations. The nonlinear component is seen as a rise in gain with increasing velocity of rotation at frequencies more than 2 Hz (a velocity-dependent gain enhancement). We have shown that there are greater changes in the nonlinear than linear component of the response after spectacle-induced adaptation. The present study was conducted to determine if the two components of the response share a common adaptive process. The gain of the VOR, in the dark, to sinusoidal stimuli at 4 Hz (peak velocities: 20-150 degrees /s) and 10 Hz (peak velocities: 20 and 100 degrees /s) was measured pre- and postadaptation. Adaptation was induced over 4 h with x0.45 minimizing spectacles. Sum-of-sines stimuli were used to induce adaptation, and the parameters of the stimuli were adjusted to invoke only the linear or both linear and nonlinear components of the response. Preadaptation, there was a velocity-dependent gain enhancement at 4 and 10 Hz. In postadaptation with the paradigms that only recruited the linear component, there was a decrease in gain and a persistent velocity-dependent gain enhancement (indicating adaptation of only the linear component). After adaptation with the paradigm designed to recruit both the linear and nonlinear components, there was a decrease in gain and no velocity-dependent gain enhancement (indicating adaptation of both components). There were comparable changes in the response to steps of acceleration. We interpret these results to indicate that separate processes drive the adaptation of the linear and nonlinear components of the response.

Acceleration↗
PubMed2002

Learning and adaptation in a recurrent model of V1 orientation selectivity.

Learning and adaptation in the domain of orientation processing are among the most studied topics in the literature. However, little effort has been devoted to explaining the diverse array of experimental findings via a physiologically based model. We have started to address this issue in the framework of the recurrent model of V1 orientation selectivity and found that reported changes in V1 orientation tuning curves after learning and adaptation can both be explained with the model. Specifically, the sharpening of orientation tuning curves near the trained orientation after learning can be accounted for by slightly reducing net excitatory connections to cells around the trained orientation, while the broadening and peak shift of the tuning curves after adaptation can be reproduced by appropriately scaling down both excitation and inhibition around the adapted orientation. In addition, we investigated the perceptual consequences of the tuning curve changes induced by learning and adaptation using signal detection theory. We found that in the case of learning, the physiological changes can account for the psychophysical data well. In the case of adaptation, however, there is a clear discrepancy between the psychophysical data from alert human subjects and the physiological data from anesthetized animals. Instead, human adaptation studies can be better accounted for by the learning data from behaving animals. Our work suggests that adaptation in behaving subjects may be viewed as a short-term form of learning.

Adaptation, Physiological↗
PubMed1986

A new approach to understanding adaptive visual-vestibular interactions in the central nervous system.

Recent neurophysiological findings, cited in previous publications imply that some vestibular commissural pathways may form positive feedback loops across the midline. It has already been shown theoretically that such feedback coupling of the vestibular nuclei could play an important role in the realization of the central integrator in the vestibuloocular reflex (VOR). In addition, it was found that known commissural plasticity during vestibular compensation, if placed at the level of such cross-midline loops, could reconcile findings after labyrinthine lesions. This paper examines theoretically the role such commissural feedback loops could play in the adaptation of the dynamics of the VOR in normal behaving animals. A simple static example is used to illustrate that changes in synaptic efficacy along cross-midline feedback loops could serve to adjust both balance and gain in vestibular reflexes. A bilateral model of the VOR and its interactions with vision is used to explore analytically the consequences of parametric changes along cerebellar and/or commissural pathways in three protocols: VOR in the dark, visual pursuit, and visual VOR suppression. Model predictions are systematically related to published findings after short- and long-term adaptation of the VOR. Conclusions arising from the theoretical results point to specific strategies that can be used in experiments on intact alert animals, in the further study of vestibular adaptation, and in the diagnosis of possible sites of plasticity. This should be relevant to arguments on cerebellar versus brain stem sites for vestibular adaptation, currently a highly controversial issue. For example, it is found that observations of responses in the adapted VOR in the dark are not sufficient to distinguish between a brain stem or cerebellar site for VOR plasticity. Also, the analysis shows that, in the model, changes in the VOR gain would often be associated with parallel changes in VOR dynamics; this has often been reported, but previously left unexplained. Model predictions of response changes in the adapted VOR, during VOR suppression, do provide a means of distinguishing between brain stem or cerebellar sites of plasticity; only the brain stem site, postulated here in the commissural loops, would produce cerebellar response changes compatible with the observations of Miles and Lisberger, during long-term adaptation of the VOR. A cerebellar site for VOR adaptation in the model would produce changes in cerebellar responses that would only be compatible with observations to date during rapid, or short-term (hours), modification of the VOR, as reported by Ito and his group.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1988

Electrophysiology of mammalian tectal neurons in vitro. II. Long-term adaptation.

1. The long-term adaptation of repetitive firing in guinea pig superior colliculus neurons was studied in a mesencephalic slice preparation using intracellular recording techniques. 2. This long-term adaptation was characterized by a decrease in the number of action potentials generated by a depolarizing pulse of constant amplitude applied at frequencies of 0.5-2 Hz. Long-term adaptation appeared in all cells tested regardless of whether they showed short-term spike frequency adaptation during each pulse. 3. Long-term adaptation had a close-to-exponential time course with a time constant of 4.085 +/- 0.675 s (mean +/- SD, n = 8). This phenomenon developed more rapidly as the stimulus frequency increased and was paralleled by a progressive hyperpolarization of the membrane potential which, at the termination of the train of stimuli, remained 6-10 mV more negative than the resting value. 4. The hyperpolarization and the spike frequency adaptation recovered spontaneously in approximately 60 s. The time constant of recovery was 14.66 +/- 1.189 s (n = 4). 5. The afterhyperpolarization (AHP) was also paralleled by a decrease in the input resistance of the cells. This response and the adaptation disappeared after removal of Ca2+ or after addition of Cd2+ to the external solution. This suggests that Ca2+ entry during trains of action potentials activates a Ca2+-dependent K+ conductance with an unusually slow kinetics. 6. This conductance appears to differ from other Ca2+-dependent K+ conductances in that it was blocked by 4-aminopyridine. 7. The properties of this long-term adaptation are remarkably similar to those reported for visual habituation; thus this newly described K+ conductance may be pertinent to the understanding of this behavioral phenomenon.

Action Potentials↗
PubMed1992

Effects of OFF-BF tones on responses of chopper units in ventral cochlear nucleus. I. Regularity and temporal adaptation patterns.

1. We have recorded the responses of neurons in the anteroventral cochlear nucleus (AVCN) of barbiturate-anesthetized cats to pure tones [either at the unit's best frequency (BF) or at another frequency (OFF-BF)] and to two-tone combination stimuli. 2. The effects of OFF-BF input (either alone or presented simultaneously with a BF tone in a two-tone stimulus) on the response patterns of choppers may include not only rate inhibition but changes in the discharge regularity and the temporal adaptation properties of the spike trains. 3. In the majority of cases we studied (119 of 146 frequencies examined in 45 units), the discharge regularity of a response to an OFF-BF or two-tone stimulus is comparable with that of a "rate-matched" BF tone response. In a minority of cases (27 of 146 frequencies examined), however, OFF-BF input (either alone or in a two-tone stimulus format) changed the regularity compared with that of a rate-matched BF tone response. 4. In the majority of cases studied (139 of 171 frequencies examined in 53 units), the initial pattern of rate adaptation ["temporal adaptation pattern" (TAP)] was the same in response to a short tone burst at BF, to an OFF-BF tone burst, or to a pair of tones. The TAP can, however, be significantly altered by OFF-BF input, although this is a comparatively infrequent occurrence in our data sample (32 of 171 frequencies examined), from the response to BF tone to the response to the two-tone or OFF-BF stimulus, are as follows: sustained to slowly adapting; slowly adapting to transiently adapting, and transiently adapting to slowly adapting. Changes in the TAPs of chopper unit responses have been recorded from both regular and irregular choppers and cannot be accounted for on the basis of changes in sustained firing rate. These changes in the discharge regularity and TAP in the small minority of cases suggest that (at least in these cases) the inhibitory effect of OFF-BF input is not simply the result of two-tone suppression at the level of the auditory nerve fiber input. 5. We have observed that regular choppers may be transformed into irregular choppers by OFF-BF (rate inhibitory) input.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed2001

Phosphate depletion in opossum kidney cells: apical but not basolateral or transepithelial adaptions of Pi transport.

Monolayers of opossum kidney (OK) cells are widely used as models for the renal proximal tubule. OK cells adapt to phosphate (Pi) depletion by increasing their capacity for apical and basolateral Na+-dependent Pi uptake. Because NMR-visible cell Pi was found to be decreased in Pi-deprived kidney cells, we suggested that up-regulation of basolateral Pi efflux also occurs during adaptation to Pi deprivation [American Journal of Physiol 1994;267:C915-919]. In order to test this hypothesis, we measured the cell Pi pool, basolateral Pi efflux and transepithelial Pi fluxes in OK cells grown on permeable plastic filters, exposed overnight to solutions containing either 0.5 mM (deprived) or 2.0 mM (replete) Pi or 32Pi. Following steady state or acute loading with 32Pi, the specific activity (SA) of cell Pi, the cell Pi pool and the basolateral efflux of 32Pi were measured. In the steady state, a 2-fold increase in Pi uptake sustained the intracellular Pi pool at 85% of the control level (30 +/- 5 nmol/mg) in spite of a decrease in extracellular Pi from 2 to 0.5 mM. When the extracellular Pi was acutely (1 h) reduced to 0.1 mM, the cell Pi pool decreased (to 3 +/- 1 nmol/mg) both in cells previously adapted overnight to either 0.5 or to 2 mM Pi (p >0.3). The rates of absolute and fractional basolateral washout of cell 32Pi after 1 h loading with 0.1 mM 32Pi were similar in cells adapted to 0.5 compared to 2 mM Pi. This indicates that Pi depletion did not affect the effective permeability of the basolateral membranes to Pi. Adaptation for 16 h to 0.5 compared to 2 mM Pi did not alter the rate of net transepithelial transport of 0.1 mM Pi from the apical to the basal compartment but reduced (p < 0.05) the unidirectional fluxes of both 32Pi and 14C-mannitol. An insufficient driving force (unchanged or low Pi concentration in the transport pool, low electrical or coupled-anion gradients) and a constant effective basolateral Pi permeability must have limited basolateral Pi efflux in cells exposed to 0.1 mM Pi. Thus, in OK cells grown on plastic support there are no adaptive increases in either basolateral Pi efflux, or in transcellular and paracellular Pi transport, in response to Pi depletion. Adaptations are limited to increases in apical and basolateral sodium-dependent Pi uptakes that can maintain the cell Pi pool as long as apical Pi is not too low (> or =0.5 mM). The OK cells adapt to low Pi concentrations conserving cell Pi but not increasing basolateral Pi efflux nor transepithelial Pi transport.

Adaptation, Physiological↗
PubMed1976

The influence of interrrupted vitamin D metabolism on acute low calcium adaptation in the rat.

The small intestine of animals place on a low calcium diet adapts to the dietary restriction by transporting calcium more efficiently. Adaptation has been observed in most mammalian species; however, the mechanism of adaptation has not been well defined. Recent evidence indicates that 1,25-dihydroxycholecalciferol [1,25(OH)2-D3], the active metabolite of vitamin D, may be involved in the process of adaptation. The present study was designed to examine the inflluence of experimental interruption of vitamin D metabolism on acute low calcium adaptation. Partial hepatectomy, cortisone treatment and dietary strontium supplements were used to inhibit the production of 1,25(OH)2-D3. In separate experiments partial hepatectomy produced a 38% reduction in adaptation; cortisone treatment (5 mg/day, s.c.) caused a 88% reduction and dietary strontium abolished adaptation completely. The possible roles of parathyroid hormone and 1,25(OH)2-D3 and their relationships in the process of adaptation are discussed.

Adaptation, Physiological↗
PubMed1981

Adaptation to ozone: duration of effect.

Repeated ozone exposure induces an adaptative response whereby subsequent ozone exposure induces little or no pulmonary function change. The time course of the adaptation and the persistence of this adaptation was determined in 24 subjects. Subjects were studied for 125 min while they exercised intermittently. They were exposed to filtered air for 1 day and then in the next week for 5 consecutive days to 0.5 ppm ozone. After the fifth day, subjects were randomly assigned to return for one more ozone exposure at 1, 2, or 3 wk. The greatest decrement in FEV1 occurred on the second day of exposure. The number of consecutive ozone exposures required to produce adaptation varied from 2 to 5 days. Persistence of adaptation in ozone-sensitive subjects (initial decrease in FEV1 greater than 10%) showed marked individual variability, but the duration of adaptation was shortest for the more sensitive subjects. Adaptation, on the average, lasted for less than 2 wk, being as short as 7 days and as long as 20 days. We concluded that more sensitive subjects required more daily sequential exposures in order to adapt.

Adaptation, Physiological↗
PubMed2006

Adaptation aftereffects in the perception of gender from biological motion.

Human visual perception is highly adaptive. While this has been known and studied for a long time in domains such as color vision, motion perception, or the processing of spatial frequency, a number of more recent studies have shown that adaptation and adaptation aftereffects also occur in high-level visual domains like shape perception and face recognition. Here, we present data that demonstrate a pronounced aftereffect in response to adaptation to the perceived gender of biological motion point-light walkers. A walker that is perceived to be ambiguous in gender under neutral adaptation appears to be male after adaptation with an exaggerated female walker and female after adaptation with an exaggerated male walker. We discuss this adaptation aftereffect as a tool to characterize and probe the mechanisms underlying biological motion perception.

Adaptation, Physiological↗
PubMedDate not supplied

Effect of fiber and its fermentation on colonic adaptation after cecal resection in the rat.

BACKGROUND: The role of fiber in postresection adaptation is poorly understood. We examined the significance of short-chain fatty acids produced by intracolonic fiber fermentation during colonic adaptation. METHODS: Rats underwent one of three surgeries: control laparotomy, cecal resection, or cecal resection with placement of perfusion catheter. Rats of each surgical group were randomly assigned to receive treatment regimens of standard fiber diet (with or without fermentation-suppressing antibiotics), fiber-free diet, or diet plus intracolonic perfusion of short-chain fatty acids. Adaptation parameters of mucosal weight, mucosal DNA and protein content, water absorption, and butyrate absorption were measured. RESULTS: Compared with controls, postresection rats that were fed fiber had 65% greater basal and 112% greater butyrate-stimulated water absorption as well as 140% greater butyrate absorption. Fiber-fed rats exhibited significantly greater colonic weight and colonic mucosal protein after cecal resection. These changes were absent in postresection rats fed a fiber-free diet. Inhibition of fermentation by neomycin and metronidazole added to a standard fiber diet also prevented postresection adaptation. All adaptive changes were restored when the cecal-resection rats that were fed the fiber diet with antibiotics received an intracolonic infusion of short-chain fatty acids. Adaptation did not occur when short-chain fatty acids were infused into colons of postresection rats that were fed a fiber-free diet. CONCLUSIONS: Cecal resection leads to significant functional and structural changes in the adapting residual colon. Fermentation of dietary fiber by colonic flora to short-chain fatty acids is necessary, but it alone is not sufficient to mediate adaptation.

Adaptation, Physiological↗
PubMed1997

Adaptation: a concept analysis.

The concept of adaptation is historically evident in nursing practice. Florence Nightingale showed how the environment required adaptation to meet the needs of the patient. Following her lead, several nurse theorists developed models with examples of the concept of adaptation: the nurse either adapts to the patient's needs, works to help the patient adapt to the environment, or adapts the environment to the needs of the patient. Sr. Callista Roy's Adaptation Model of Nursing is one such nursing model. Although this model has been applied in many clinical and administrative areas, the use of the concept in a school setting with special-need's student requires additional definition and clarification. The goal of this concept analysis paper is to clarify and explore the definition of adaptation in the school setting with application to an Individualized Healthcare Plan (IHP).

Adaptation, Psychological↗
PubMed1997

I. Impaired dark adaptation in symptomatic carotid artery disease.

It has been known for more than a century that even slight hypoxemia reduces dark adaptation. We studied dark adaptation in symptomatic carotid artery disease. Twenty-one consecutive patients scheduled for first-time carotid endarterectomy and 31 age-matched control subjects with normal carotid arteries were examined by dark adaptometry monocularly and were tested repeatedly on consecutive days. The average degree of internal carotid stenosis on the symptomatic side was much greater than that on the contralateral side. Dark adaptation was markedly impaired in the patients as compared with the control subjects. In the patients there was no difference in dark adaptation between the symptomatic and nonsymptomatic sides. The existence of carotid stenosis correlated to the level of dark adaptation. Pupillary size and age correlated to the dark adaptational level but did not affect the effect of carotid stenosis on dark adaptation. The decreased dark adaptation may be due to insufficient blood supply or repeated subclinical microembolization to the retinae, the brain, or both.

Aged↗
PubMed1993

[The role of the central monoaminergic nervous system relative to mechanisms of stress adaptation].

The difference of amine dynamics in central noradrenergic, dopaminergic and serotonergic systems of adaptive or non-adaptive rats to repeated restraint stress was investigated neurochemically. A single immobilization induced stress responses, such as reductions in growth rate, food intake, water intake and locomotor activity, and an increase in pain threshold. These responses disappeared after repeated immobilization 1 or 2 hr daily for 7 days, but not after 4 hr daily for 7 days. These results suggest that stress adaptation models should include the parameter of repeated exposure to restraint stress 1 or 2 hr daily for 7 days. In the frontal cortex, midbrain-thalamus, striatum, hypothalamus, medulla-pons, cerebellum, cervical cord, thoracic cord and lumbar cord of models with adaptability to repeated restraint stress, a marked increase in serotonin (5-HT) turnover was observed. This neurochemical change was seen in the hypothalamus and lumbar cord of non-adaptive models, but not in the other brain and spinal cord regions. Also, an increase in norepinephrine (NE) turnover in spinal cord regions was observed in adaptive models, but NE turnover was decreased in the frontal cortex, striatum or cervical cord of non-adaptive models. These findings suggest that enhancement of central 5-HT turnover and NE turnover in the spinal cord contribute to the formation of adaptation to repeated restraint stress.

Adaptation, Physiological↗
PubMedDate not supplied

Effects of potassium adaptation on blood pressure and pressor responses in normotensive and renal hypertensive Wistar rats.

Potassium adaptation reduces blood pressure (BP) in hypertensive humans and animals but its effects on normotensive BP and the nature of pressor responses to vasoactive drugs are not known. We measured directly, the mean arterial pressure (MAP) of normotensive control, normotensive potassium-adapted (given 0.75% potassium chloride solution for 5 weeks), renal hypertensive (RHP), and renal hypertensive Wistar rats later adapted to potassium. The maximum percentage change, the ED25, and recovery times after bolus injections of noradrenaline (NA), angiotensin II (Ang. II), sodium nitroprusside (SNP), and acetylcholine (ACh) were compared. The MAP of normotensive potassium-adapted rats was significantly lower than that of the normotensive controls (95.6+/-5.0 vs. 110.8+/-2.8 mmHg, p<0.05). The potassium-adapted hypertensive rats (RHP-A) also had significantly lower MAP values than the non-adapted hypertensive ones (116.0+/-4.4 vs. 138.2+/-4.1 mmHg, p<0.01). Potassium adaptation significantly blunted responses to NA and augmented responses to SNP but while the duration of action of Ang. II was significantly shortened, that of SNP was significantly increased. We conclude that potassium adaptation reduces BP in the normotensive and hypertensive rats and may influence both the degree and duration of action of vasoactive drugs given as bolus injections.

Adaptation, Physiological↗
PubMed1995

Color appearance under chromatic adaptation varied along theoretically significant axes in color space.

Changes in color appearance caused by chromatic adaptation were measured with a wide range of adapting fields. Observers viewed a 39'-55' annular test field composed of an admixture of lights from the red phosphor and the green phosphor of a CRT. The annular mixture field was centered and superimposed upon a 4.7 degrees steady, circular background field. After the observer was completely adapted to the background, the luminance of the red phosphor in the test was held fixed while the observer adjusted the luminance of the green phosphor until the test appeared neither reddish nor greenish. Twenty-two equiluminant backgrounds (4.5 cd/m2, approximately 50 Td) were systematically selected along two axes in Judd chromaticity space. One axis was along tritanopic confusion lines, with middle-wavelength-sensitive- (M-) and long-wavelength-sensitive- (L-) cone stimulation held constant. The other axis maintained constant short-wavelength-sensitive- (S-) cone stimulation. The results show that adapting backgrounds that were varied along tritanopic confusion lines do not have a differential effect on color appearance at high test levels (well above the adapting level). At lower test levels there is a systematic change in color appearance of the test light, which is quantitatively described by additive redness. Along constant S-cone-stimulation lines, adapting backgrounds differentially affect color appearance in a systematic way, reflecting changes in receptoral gain and the additive contribution. The measurements taken with adapting fields throughout color space are described by the two-process model of chromatic adaptation.

Adaptation, Ocular↗