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PubMed1998

Vestibular adaptation: how models can affect data interpretations.

Vestibular adaptation can be induced optically or by chemical or physical injury to the vestibular apparatus or the brain stem. In searching for the sites or mechanisms of vestibular adaptation, neurophysiologists often rely on comparing central resting (background) activities and central modulations (sensitivity) during vestibular stimulation, before and after motor learning or vestibular compensation. It is assumed that adapted central sites must exhibit modulation changes that parallel vestibulo-ocular reflex changes. Using model simulations and analysis, we will show that such presumptions may be misleading. First, using a simple schematic of interconnected cells or nuclei, one can show that modulation depth and background "tone" can be modified (or fixed) independently, using weightings on direct or indirect afferent projections. That is, if synaptic weights along all stimulus pathways are altered, one may fix or strongly modify central premotor characteristics in a manner apparently unrelated to global reflex changes. In the vestibulo-ocular reflex, the dominant premotor pathways contain position-vestibular-pause cells and eye-head-velocity cells (which are behaviorally similar to floccular-target neurons). Several experiments have reported negligible changes in the velocity sensitivity of position-vestibular-pause cells, despite large gain changes in the vestibulo-ocular reflex induced by training with visual-vestibular conflict. On the other hand, the modulation changes on floccular-target neurons (position-vestibular-pause) can be much larger than the changes in reflex gain. Using a bilateral vestibulo-ocular reflex model, we show that overall increases or decreases in reflex gain can be expressed (even overexpressed) in one particular subgroup of premotor neurons. Nevertheless, such observations are theoretically compatible with synaptic changes on all primary projections in a widely interconnected central network. Hence, stable neural responses during reflex adaptation are not sufficient to exclude a potential site of sensory-motor adaptation. Similarly, modified neural responses (as in cerebellum) need not necessarily imply a direct role in supporting the adapted state. Model predictions should help to design additional experimental protocols, to test hypotheses, and to refine diagnostic measures of recovery after vestibular lesions.

Adaptation, Physiological↗
PubMed2002

The role of adaptation to disability and disease in health state valuation: a preliminary normative analysis.

Chronically ill and disabled patients generally rate the value of their lives in a given health state more highly than do hypothetical patients imagining themselves to be in such states. Much of this difference may be due to actual patients' adaptation to their health states, a phenomenon that would not typically affect the ratings of persons who only hypothetically imagine themselves to be patients. This article pursues a non-empirical, normative question: does such adaptation render actual patients' ratings of quality of life morally questionable for purposes of resource allocation? Distinguishing the different basic elements in patient adaptation reveals why, and in what respects, people are pulled strongly in opposite directions in responding to this question. Several more explicit moral arguments against using adapted patients' ratings have been articulated by economists and philosophers, and others are developed by the authors. While most of these arguments do not survive careful analysis, several do. Given the subsequent complexity of the matter, it is argued that: (1) Neither solely actual nor solely hypothetical patient perspectives should be used for rating quality of life. (2) Even if representatives of the general public acting as hypothetical patients provide ultimately the best perspective from which to discern societal values about health states, patients' values that are often influenced by adaptation must still be conveyed to and clearly understood by public representatives as a critically important fact about health-related quality of life. The article also points to the need for much additional work on adaptation, both empirical research and normative analysis.

Adaptation, Psychological↗
PubMed2000

Adaptation of dental plaque to metabolise maltitol compared with other sweeteners.

UNLABELLED: There is some evidence that plaque can adapt to regular exposure to some bulk sweeteners, leading to increased metabolism and acidogenic potential of the sweetener. This potential for adaptation varies between non-sugar sweeteners and has important implications for manufacturers of food, confectionery and medicines used long-term. Maltitol (99% purity crystalline D-maltitol) is a relatively newly approved non-sugar sweetener and appears to have potentially good dental properties. OBJECTIVES: To compare plaque adaptation to pure sucrose, sorbitol, xylitol or maltitol and the effect of their prolonged use on acid production by plaque from sucrose, in vivo. METHODS: Two series of plaque pH experiments were carried out. Each experiment involved a 14 day adaptive period when four 5 g lozenges of the sweetener were taken between meals each day. Each experiment was separated by a 14 day wash-out period. Acid production was quantified as: (a) minimum pH; and (b) cH area (difference between plaque pH curve and resting value, expressed as cH units). RESULTS: Thirteen adults, of mean age 41 years completed the study. When adaptation of dental plaque to the metabolism of sweeteners was compared, there was a statistically significant difference (p = 0.033) between xylitol and sorbitol, and between xylitol and sucrose but not between xylitol and maltitol. When the effect of prolonged use of sweeteners on acid production after sucrose rinsing was compared, there were no statistically significant differences between the sweeteners. CONCLUSION: Dental plaque does not adapt to metabolise xylitol or maltitol following prolonged exposure over 14 days.

Adaptation, Physiological↗
PubMed2002

A simulating cognitive system with adaptive capability.

Dedicated to the memory of Michael Conrad, this paper builds on his seminal ideas expressed in his famous book Adaptability, as well as in his later works. We investigate a recently published adaptive system for the instantaneous recognition of dynamics with respect to its adaptability to the Lorenz system. The system consists of a pool of internal dynamical elements. These elements are defined through a set of parameter values that encode for a specific dynamics behavior. If the system is now faced with an unknown external dynamics-unknown with respect to the parameter-it is capable not only to recognize the dynamics but also to adapt to the correct dynamics, which in turn leads to a simulation capability. The system impressively quickly follows the sudden qualitative changes of the external dynamics. The adaptation works even quicker when the correct dynamics are already represented within the internal pool. This leads to the idea of memorizing the represented dynamics within the pool, whereby the elements that correspond to rarely externally presented dynamics can be given free for the adaptation and memorization of more frequently presented dynamics.

Adaptation, Physiological↗
PubMed1996

Vascular thermal adaptation in tumors and normal tissue in rats.

PURPOSE: The vascular thermal adaptation in the R3230 adenocarcinoma, skin and muscle in the legs of Fischer rats was studied. METHODS AND MATERIALS: The legs of Fischer rats bearing the R3230 AC adenocarcinoma (subcutaneously) were heated once or twice with a water bath, and the blood flow in the tumor, skin and muscle of the legs was measured with the radioactive microsphere method. RESULTS: The blood flow in control R3230 AC tumors was 23.9 ml/100 g/min. The tumor blood flow increased about 1.5 times in 30 min and then markedly decreased upon heating at 44.5 degrees C for 90 min. In the tumors preheated 16 h earlier at 42.5 degrees C for 60 min, reheating at 44.5 degrees C increased the tumor blood flow by 2.5-fold in 30 min. Contrary to the decline in blood flow following an initial increase during the 44.5 degrees C heating without preheating, the tumor blood flow remained elevated throughout the 90 min reheating at 44.5 degrees C. These results indicated that thermal adaptation or thermotolerance developed in the tumor vasculatures after the preheating at 42.5 degrees C for 60 min. The magnitude of vascular thermal adaptation in the tumors 24 h and 48 h after the preheating, as judged from the changes in blood flow, were smaller than that 16 h after the preheating. Heating at 42.5 degrees C for 60 min induced vascular thermal adaptation also in the skin and muscle, which peaked in 48 h and 24 h, respectively, after the heating. CONCLUSION: Heating at 42.5 degrees C for 1 h induced vascular thermal adaptation in the R3230 AC tumor, skin, and muscle of rats that peaked 16-48 h after the heating. When the tumor blood vessels were thermally adapted, the tumor blood flow increased upon heating at temperatures that would otherwise reduce the tumor blood flow. Such an increase in tumor blood flow may hinder raising the tumor temperature while it may increase tumor oxygenation.

Adaptation, Physiological↗
PubMedDate not supplied

Adaptation in spiking neurons based on the noise shaping neural coding hypothesis.

Shin, Koch and Douglas [Shin, J., Koch, C., & Douglas, R. (1999). Adaptive neural coding dependent on the time-varying statistics of the somatic input current. Neural Computation, 11, 1983-2003] proposed an adaptive neural coding model that makes spiking neurons adapt its input/output relation to the stimulus statistics. In a surprisingly precise manner, the adaptive neural coding model has been supported by recent experiments. However, the previous report has two problems: (a) although the adaptive neural coding model was developed based on the noise shaping neural coding hypothesis, their connection was not explained clearly in the previous report; and (b) the previous model did not suggest a biologically plausible method to estimate the stimulus mean and variance from spike-evoked intracellular calcium concentration. In this paper, I present how the noise shaping neural coding hypothesis produced such a precise model without any available experimental data at that time. Moreover, I propose a computational model for a biologically plausible signal statistics extraction from spike-evoked intracellular calcium concentration. An asymmetry in contrast adaptation time between increasing and decreasing variance, observed in biological experiments, is explained using the signal statistics extraction method. In addition, a new perspective on the relationship between the spike train of spiking neurons and EEG (or local field potential (LFP)) is suggested based on the noise shaping neural coding hypothesis.

Action Potentials↗
PubMed2004

Profound contrast adaptation early in the visual pathway.

Prior exposure to a moving grating of high contrast led to a substantial and persistent reduction in the contrast sensitivity of neurons in the lateral geniculate nucleus (LGN) of macaque. This slow contrast adaptation was potent in all magnocellular (M) cells but essentially absent in parvocellular (P) cells and neurons that received input from S cones. Simultaneous recordings of M cells and the potentials of ganglion cells driving them showed that adaptation originated in ganglion cells. As expected from the spatiotemporal tuning of M cells, adaptation was broadly tuned for spatial frequency and lacked orientation selectivity. Adaptation could be induced by high temporal frequencies to which cortical neurons do not respond, but not by low temporal frequencies that can strongly adapt cortical neurons. Our observations confirm that contrast adaptation occurs at multiple levels in the visual system, and they provide a new way to reveal the function and perceptual significance of the M pathway.

Action Potentials↗
PubMed1992

The role of cytoplasmic calcium in photoreceptor light adaptation.

The process of light adaptation in vertebrate rod and cone photoreceptors is believed to involve a diffusible cytoplasmic messenger. Two lines of evidence indicate that photoreceptor light adaptation is mediated by a light-induced fall in cytoplasmic calcium concentration (Ca2+i). First, if changes in calcium concentration are slowed by the incorporation of calcium chelators into the photoreceptor cytoplasm then light adaptation is slowed also. Second, if the normal control of Ca2+i is prevented by simultaneously minimising calcium influx and efflux across the outer segment membrane by means of external solution changes, then all of the manifestations of light adaptation are abolished. Furthermore, recent results show that changes in Ca2+i imposed in the absence of light are sufficient to cause at least some of the manifestations of light adaptation. Together these results indicate that calcium acts as the messenger of light adaptation in the photoreceptors of both lower and higher vertebrates.

Adaptation, Physiological↗
PubMed1994

Humoral regulation of intestinal adaptation.

After the loss of small bowel through disease or surgery the residual bowel adapts by increasing its functional capacity. This process of adaptation involves dilatation, hypertrophy and mucosal hyperplasia, particularly distal to the area of bowel loss or disease. The response of the residual bowel is mediated by a complex interplay of factors including luminal nutrition, pancreaticobiliary secretions, luminal or local growth factors and also humoral or endocrine factors. The experimental model commonly used to characterize the adaptive response, massive small bowel resection (MSBR), involves 80% resection of the small bowel in the rat. Of the various putative humoral factors, most work has focused on the products of the ileal L cells: enteroglucagon and peptide YY. Plasma levels of both hormones are increased after MSBR and indeed their mRNA levels are also increased as a result of an increase in the amount of message per L cell. Whilst PYY probably serves as an 'ileal brake' to slow the movement of the luminal contents and hence increase their mucosal contact time, the role of the enteroglucagon is unresolved. The molecular cloning of the proglucagon gene has revealed, firstly, that there are a number of biologically active peptides which derive from the propeptide and, secondly, that tissue-specific differential processing occurs. Most studies do not clearly define which of these products of proglucagon is being measured and is termed as glucagon-like or enteroglucagon immunoreactivity. The insulin-like growth factors (IGF) have a potent mitogenic action on the bowel. Their role after MSBR is likely to be largely paracrine. Though IGF-I mRNA levels do not increase after MSBR, the precipitous and early fall in ileal IGF-binding protein-3 (IGFBP-3) mRNA levels suggests a fall in IGFBP-3 levels may increase local IGF-I bioactivity. Polyamine synthesis is a critical component of the adaptive response, although the stimulus to their dramatic increase in synthesis after MSBR remains to be elucidated. Other humoral factors such as cholecystokinin, neurotensin and bombesin probably have minor indirect roles in the adaptive response. Components of the epidermal growth factor/transforming growth factor alpha response pathway family of growth factors may be involved as paracrine regulators. There is thus strong evidence that humoral factors play an important role in intestinal adaptation; characterization of the nature of the humoral factors and their relationship with other influences such as luminal nutrition and pancreatic biliary secretions may facilitate the development of new therapeutic strategies for the short bowel syndromes.

Adaptation, Physiological↗
PubMed2000

The dynamics of velocity adaptation in human vision.

Since Barlow and Hill's classic study of the adaptation of the rabbit ganglion cell to movement [1], there have been several reports that motion adaptation is accompanied by an exponential reduction in spike rate, and similar estimates of the time course of velocity adaptation have been found across species [2-4]. Psychophysical studies in humans have shown that perceived velocity may reduce exponentially with adaptation [5,6]. It has been suggested that the reduction in firing of single cells may constitute the neural substrate of the reduction in perceived speed in humans [1,5-7]. Although a model of velocity coding in which the firing rate directly encodes speed may have the advantage of simplicity, it is not supported by psychophysical research. Furthermore, psychophysical estimates of the time course of perceived speed adaptation are not entirely consistent with physiological estimates. This discrepancy between psychophysical and physiological estimates may be due to the unrealistic assumption that speed is coded in the gross spike rate of neurons in the primary visual cortex. The psychophysical data on motion processing are, however, generally consistent with a model in which perceived velocity is derived from the ratio of two temporal channels [8-14]. We have examined the time course of speed adaptation and recovery to determine whether the observed rates can be better related to the established physiology if a ratio model of velocity processing is assumed. Our results indicate that such a model describes the data well and can accommodate the observed difference in the time courses of physiological and psychophysical processes.

Adaptation, Physiological↗
PubMed2002

Motion adaptation distorts perceived visual position.

After an observer adapts to a moving stimulus, texture within a stationary stimulus is perceived to drift in the opposite direction-the traditional motion aftereffect (MAE). It has recently been shown that the perceived position of objects can be markedly influenced by motion adaptation. In the present study, we examine the selectivity of positional shifts resulting from motion adaptation to stimulus attributes such as velocity, relative contrast, and relative spatial frequency. In addition, we ask whether spatial position can be modified in the absence of perceived motion. Results show that when adapting and test stimuli have collinear carrier gratings, the global position of the object shows a substantial shift in the direction of the illusory motion. When the carrier gratings of the adapting and test stimuli are orthogonal (a configuration in which no MAE is experienced), a global positional shift of similar magnitude is found. The illusory positional shift was found to be immune to changes in spatial frequency and to contrast between adapting and test stimuli-manipulations that dramatically reduce the magnitude of the traditional MAE. The lack of sensitivity for stimulus characteristics other than direction of motion suggests that a specialized population of cortical neurones, which are insensitive to changes in a number of rudimentary visual attributes, may modulate positional representation in lower cortical areas.

Adaptation, Ocular↗
PubMedDate not supplied

Effect of the distal remnant on ileal adaptation.

The ileum has a greater adaptive capacity than the jejunum after intestinal resection, which may be, in part, related to increased exposure to luminal contents and intrinsic properties of the ileum However, the intestinal remnant might contribute to this adaptive response as well. Our aim was to determine the effect of the distal intestinal remnant on ileal adaptation when the ileum is proximal in the intestinal tract. Twenty-one Lewis rats were included in the study. One group (n = 7) served as unoperated control subjects, the second group (n = 7) underwent transposition of the jejunum and ileum, and the third group (n = 7) underwent 50% proximal resection with syngeneic transplantation of the ileum Nutritional status and structural adaptation were studied at 14 days. Animals in both the transposition and transplant groups initially lost weight but weights returned to above preoperative levels at 14 days. Food intake, stool weight, and serum albumin levels were similar in these two groups. Intestinal weight and diameter were similar in the proximal end of the ileal segment in the two study groups and were significantly increased compared to control values (0.26 +/- 0.04 and 0.31 +/- 0.02 vs. 0.10 +/- 0.0 g/cm and 8.4 +/- 0.5 and 9.1 +/- 0.8 vs. 4.9 +/- 0.3 mm; P < 0.05) Intestinal weight and diameter of the distal end of the ileal segment were greater than those values in unoperated control animals but were greatest in the ileal transplant group (0.15 +/- 0.1 and 0.24 +/- 0.03 vs. 0.07 +/- 0.01 g/cm and 5.6 +/- 1.1 and 8.7 +/- 0.6 vs. 4.3 +/- 0.2 mm; P < 0.05). Villus height and crypt depth were similar in both the proximal and distal ends of the ileal segments in the two study groups and were significantly increased compared to control values (642 +/- 75 and 720 +/- 15 vs. 411 +/- 24 proximal and 443 +/- 49 and 500 +/- 46 vs. 343 +/- 22 microm distal, P < 0.05; 223 +/- 34 and 244 +/- 33 vs. 173 +/- 20 proximal and 192 +/- 28 and 209 +/- 18 vs. 144 +/- 26 microm distal, P < 0.05). Proximal placement of the ileum by either transposition or transplantation results in structural adaptation. This occurs to a similar extent whether the distal remnant is jejunum or ileum. Thus increased exposure to luminal contents and intrinsic properties appear to be the important factors in the adaptive capability of the ileum when the ileum is the proximal portion of the intestinal tract.

Adaptation, Physiological↗
PubMed2003

Effect of aging on the adaptive and proliferative capacity of the small bowel.

Our society is aging at a rapid rate; the effects of aging on physiologic functions (e.g., small bowel adaptation) are poorly understood. The purpose of this study was to determine the ability of the aged small bowel mucosa to adapt after resection. Young (2-month-old) and aged (24-month-old) F344 rats underwent massive (70%) proximal small bowel resection (SBR) or sham operation; rats were killed at 9 or 16 days after surgery. The remnant small bowel and corresponding sham segments were harvested, weighed, and analyzed for DNA content and villus height. To determine whether the adaptive response after SBR could be enhanced, aged rats underwent SBR or sham operation and were treated with either neurotensin or saline solution (control). SBR resulted in adaptive hyperplasia in the remaining small bowel remnant in both young and aged rats at 9 and 16 days compared with sham animals. At 9 days, significant increases were noted in weight, villus height, and DNA content of the distal remnant in young and aged rats after SBR; the increases were similar in both young and aged rats. At 16 days, both young and aged rats displayed significant increases in remnant weight after SBR. Administration of neurotensin increased the weight of the remnant intestine in aged rats after SBR compared with saline treatment. Our findings demonstrate that aged small bowel mucosa exhibits a proliferative and adaptive capacity in response to SBR that was similar to that of the young animals. In addition, neurotensin administration enhanced the normal adaptive response of the small bowel in aged rats, providing further evidence that neurotensin may be therapeutically useful to augment mucosal regeneration in the early periods after massive SBR.

Adaptation, Physiological↗
PubMed2001

Environmental adaptations as windows on molecular evolution.

Changes in gene regulation may play an important role in adaptive evolution, particularly during adaptation to a changing environment. However, little is known about the molecular mechanisms underlying adaptively significant variation in gene regulation. To address this question, we are using environmental adaptations in populations of a fish, Fundulus heteroclitus as a window into the molecular evolution of gene regulation. F. heteroclitus are found along the East Coast of North America, with populations distributed along a steep thermal gradient. At the extremes of the species range, populations have undergone local adaptation to their habitat temperatures. A variety of genes differ in their regulation between these populations. We have determined the mechanism responsible for changes in lactate dehydrogenase-B (Ldh-B) gene regulation. A limited number of mutations in the regulatory sequence of this gene result in changes in its expression. Both the phenotypic (increased LDH activity) and genotypic (changes in Ldh-B regulatory sequences) differences between populations have been shown to be affected by natural selection, rather than genetic drift. Therefore, even a small number of mutations within important regulatory sequences can provide evolutionarily significant variation and have an impact on environmental adaptation.

Adaptation, Physiological↗
PubMed2003

Asian medaka fishes offer new models for studying mechanisms of seawater adaptation.

Japanese medaka (Oryzias latipes) is a freshwater (FW) teleost that is popular throughout the world for laboratory use. In this paper, we discuss the utility of Japanese medaka and related species for studying mechanisms of seawater (SW) adaptation. In addition to general advantages as an experimental animal such as their daily spawning activity, transparency of embryos, short generation time and established transgenic techniques, Japanese medaka have some adaptability to SW unlike the strictly stenohaline zebrafish (Danio rerio). Since other species in the genus Oryzias exhibit different degrees of adaptability to SW, comparative studies between Japanese medaka, where molecular-biological and genetic information is abundant, and other Oryzias species are expected to present varying approaches to solving the problems of SW adaptation. We introduce some examples of interspecies comparison for SW adaptabilities both in adult fish and in embryos. Oryzias species are good models for evolutionary, ecological and zoogeographical studies and a relationship between SW adaptability and geographic distribution has been suggested. Medaka fishes may thus deliver new insights into our understanding of how fish have expanded their distribution to a wide variety of osmotic environments.

Adaptation, Physiological↗
PubMed2000

Aluminium triggers genotoxic adaptation to methyl mercuric chloride and ethyl methane sulfonate, but not to maleic hydrazide in plant cells in vivo.

Non-toxic, conditioning doses of aluminium chloride were tested for induction of adaptive response to the genotoxic challenge doses of methyl mercuric chloride (MMCl), maleic hydrazide (MH) and ethyl methane sulfonate (EMS). Embryonic shoot cells of Hordeum vulgare and root meristem cells of Allium cepa were employed as the assay systems. Plant tissues fixed at different recovery hours following the challenge treatments with or without prior Al-conditioning were analyzed for cells with genotoxicity markers that include spindle and/or chromosome aberrations and micronuclei (MNC). The results provided evidence that Al(3+) triggered adaptive response that protected the plant cells from the genotoxicity of MMCl and EMS. Al(3+), however, failed to induce adaptive response against the genotoxicity of MH. A comparison of Al-induced adaptive response with that induced by heavy metals: Cd(2+), Cu(2+), Hg(2+), Ni(2+), Pb(2+), Zn(2+) and oxidative agents: hydrogen peroxide (H(2)O(2)) and paraquat (PQ) pointed to the similarity of Al-adaptive response to that of PQ rather than to other heavy metals or H(2)O(2). Al-induced adaptive response demonstrated in the present study to MMCl and EMS possibly involved antioxidant defense and DNA repair systems, respectively.

Adaptation, Physiological↗
PubMed2003

Adaptation characteristics of steady-state motion visual evoked potentials.

OBJECTIVE: Motion visual evoked potentials (motion VEPs) are used in clinical diagnosis and basic research. Employing steady-state rather than the usual transient motion VEPs simplifies statistical evaluation and might drastically reduce examination durations. Protocols for recording transient motion-onset VEPs usually involve fairly long recovery intervals between trials to avoid neural adaptation. This is not feasible for steady-state VEPs. We investigated how adaptation affects the steady-state motion VEP. METHODS: Oscillatory (13.3rev/s) and continuous uni-directional random-dot motion served as adaptation stimuli. Steady-state motion VEPs and, for comparison, transient motion VEPs were recorded. RESULTS: In the first experiment, we investigated how adaptation affects the recordings. Contrary to our expectation, we did not find any sizable effect. However, there was a large inter-individual variability in steady-state amplitude and no correlation across subjects between transient and steady-state amplitude. In the second experiment, we confirmed that the steady-state VEP reflects veridical motion processing by assessing its susceptibility to uni-directional pre-adaptation. CONCLUSIONS: Taken together, the results suggest that steady-state motion VEPs provide a fast method of recording motion responses without suffering from adaptation, but at the expense of inter-individual reproducibility.

Adaptation, Physiological↗
PubMed1999

The evolutionary genetics of adaptation: a simulation study.

It is now clear that the genetic basis of adaptation does not resemble that assumed by the infinitesimal model. Instead, adaptation often involves a modest number of factors of large effect and a greater number of factors of smaller effect. After reviewing relevant experimental studies, I consider recent theoretical attempts to predict the genetic architecture of adaptation from first principles. In particular, I review the history of work on Fisher's geometric model of adaptation, including recent studies which suggest that adaptation should be characterized by exponential distributions of gene effects. I also present the results of new simulation studies that test the robustness of this finding. I explore the effects of changes in the distribution of mutational effects (absolute versus relative) as well as in the nature of the character studied (total phenotypic effect versus single characters). The results show that adaptation towards a fixed optimum is generally characterized by an exponential effects trend.

Adaptation, Physiological↗