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PubMed1994

Optimization by trees on simple adaptive landscapes.

We evaluate the optimizing ability (rate of adaptation) of trees on simple adaptive landscapes. At points away from a peak, there is a strong negative relationship between rate of adaptation and tree precision P, a relationship that is independent of the size of the tree. P measures the variability among trial solutions generated by the tree: high precision trees have low variability, low precision trees have high variability. Near a peak, the situation reverses, with high precision trees showing higher rates of adaptation than low precision trees; however, for all trees, the absolute rate of adaptation is uniformly low. On multiple-peak landscapes, the probability of crossing an adaptive valley from a lower peak to a higher peak is also negatively correlated with tree precision. These results suggest that under a wide range of conditions, trees with low precision are, on average, the best optimizers.

Adaptation, Biological↗
PubMed1993

Properties of the mouse cone-mediated electroretinogram during light adaptation.

Cone-mediated electroretinograms (ERGs) were obtained from normal mice during the course of light adaptation to a rod-desensitizing adapting field. Responses obtained during the early minutes of light adaptation were smaller in amplitude, and delayed in implicit time in comparison to responses obtained to the same stimulus presented later during light adaptation. These changes resemble those observed in the human cone ERG obtained under similar stimulus conditions, and indicate that the underlying mechanism may be similar. While the use of an adapting field appears to isolate the mouse cone ERG, these adaptation-induced changes should be considered when evaluating this response.

Adaptation, Ocular↗
PubMed1990

Pattern adaptation in cat visual cortex is a co-operative phenomenon.

The effects of microiontophoretic application of glutamate, GABA and the GABA antagonist, bicuculline methiodide were tested on the degree of adaptation exhibited by striate cortical cells to moving sin wave grating patterns. Application of GABA, which prevents firing of the cell and thereby any fatigue of the cell, did not reduce the degree of adaptation. Administration of either glutamate or GABA, without simultaneous exposure to the adapting high-contrast gratings did not reduce the sensitivity of the cell to subsequent exposure of a low-contrast grating, showing that adaptation is not caused by the excitatory or inhibitory activity of the cell itself. Application of the GABA antagonist, bicuculline did not prevent pattern adaptation, indicating that the lowered sensitivity of the cell is not mediated by a GABAergic inhibition acting on the cell. Thus adaptation of a striate neuron is not due to altered sensitivity of the cell to a constant input but depends upon changes in the input itself. It is most likely that these changes occur in a co-operative cortical network, whose effect on individual cortical cells is mediated by intracortical excitatory connections.

Adaptation, Physiological↗
PubMed1994

Noradrenergic agents in the cerebellar vermis affect adaptation of the vestibulospinal reflex gain.

In precollicular decerebrate cats, the vestibulospinal reflex (VSR) was intermittently recorded from the triceps brachii during sinusoidal roll tilt of the whole animal (at 0.15 Hz, +/- 10 degrees), leading to selective stimulation of labyrinth receptors. This reflex, tested during and after a 3-h period of sustained animal tilt at the same parameters indicated above, showed an adaptive increase in gain in some experiments but not in others. In a second group of experiments, however, rotation of the head (at 0.15 Hz, +/- 10 degrees) was associated with a synchronous body rotation (at 0.15 Hz, +/- 12.5 degrees) which led to an additional neck input, due to 2.5 degrees of out-phase body-to-head displacement. In these experiments, the VSR, tested every 10-15 min, consistently showed an adaptive increase in gain during and after a 3-h period of sustained vestibular and neck stimulation. Microinjection into the cerebellar anterior vermis of beta-adrenergic agents (0.25 microliters at 8 micrograms/microliters saline) produced slight and short-lasting changes in the basic amplitude of the VSR, due to the neuromodulatory influence of these agents on the Purkinje cells activity. In addition, the beta-adrenergic agonist isoproterenol brought to the light an adaptive process in those experiments in which no adaptation occurred during a sustained roll tilt of the whole animal. On the other hand, the beta-adrenergic antagonists propranolol or sotalol either suppressed the increase in gain of the VSR which occurred in other experiments during sustained animal rotation, or prevented the occurrence of an adaptive increase in gain during a continuous out-phase head and body rotation. We conclude that the adaptive changes in gain of the VSR are facilitated by the noradrenergic system acting within the cerebellar cortex through beta-adrenoceptors.

Adaptation, Physiological↗
PubMed1987

Adaptation of the suprahyoid muscle complex to mandibular advancement surgery.

The suprahyoid musculature has been implicated as one of the major factors responsible for relapse after mandibular advancement surgery. Previous studies have also indicated that the muscle and connective tissues comprising the suprahyoid complex must adapt to increased length brought about by mandibular advancement for skeletal stability to be achieved. The purpose of this study was to provide quantitative data concerning the immediate changes and long-term adaptations that take place within the suprahyoid complex over a 2-year period after mandibular advancement. Mandibular advancement was performed on ten adult Macaca mulatta monkeys with and without suprahyoid myotomy (n = 5/group). Six animals were used as controls. Mandibular length and changes in the length of the various anatomic regions of the suprahyoid complex were evaluated radiographically with the aid of radiopaque bone, muscle, and tendon markers implanted preoperatively. The results for the nonmyotomy group showed that the suprahyoid complex was elongated approximately two thirds the amount of mandibular lengthening, the major immediate adaptations within the suprahyoid complex after the surgical procedure occurred at the muscle-bone interface and the muscle-tendon interface, the change in length at the muscle-tendon junction was maintained throughout the 2-year follow-up period, indicating that significant long-term adaptations took place primarily at that location, and no significant short-term changes or long-term adaptations were seen within the anterior digastric muscle or the intermediate digastric tendon. Within the myotomy group, it was found that the suprahyoid complex recoiled immediately after myotomy such that the anterior belly of the digastric muscle became separated from the advanced distal mandibular segment by more than twice the amount of mandibular lengthening, the anterior digastric muscle remained essentially at this posterior position throughout the 2-year follow-up period, and though not significant, there was a trend for a decrease in the length of the anterior digastric muscle belly. On the basis of these results, it was concluded that both short-term changes and long-term adaptations to lengthening of the suprahyoid complex as a result of mandibular lengthening occur primarily within the connective tissues comprising the muscle-tendon and muscle-bone interfaces, not within the muscle fibers themselves.

Adaptation, Physiological↗
PubMed1996

Biochemical adaptations in the mesolimbic dopamine system in response to repeated stress.

We have demonstrated previously that chronic administration of morphine, cocaine, or ethanol produces some common biochemical adaptations in the ventral tegmental area (VTA) and nucleus accumbens (NAc), components of the mesolimbic dopamine system implicated in the reinforcing and locomotor activating properties of these drugs of abuse. Because this neural pathway is also regulated by stress, and because stress has been shown to influence an animal's behavioral responses to drugs of abuse, it was of interest to determine whether repeated exposure to stress results in similar biochemical adaptations. By use of immunoblot analysis, we show here that a course of chronic "unpredictable" stress, like chronic drug exposure, increased levels of immunoreactivity of tyrosine hydroxylase and glial fibrillary acidic protein and decreased levels of immunoreactivity of neurofilament proteins in the VTA. Chronic unpredictable stress also increased levels of cyclic AMP-dependent protein kinase activity and decreased levels of immunoreactivity of the G protein subunit, Gi alpha, in the NAc. These effects required long-term exposure to stress and were in most cases not seen in the substantia nigra and caudate-putamen, components of the nigrostriatal dopamine system studied for comparison. The biochemical effects of chronic stress in the VTA and NAc differed among three strains of rat studied. Fischer 344 rats were the most responsive in that they exhibited all of the aforementioned adaptations, whereas Lewis rats were the least responsive in that they exhibited none of these adaptations; Sprague-Dawley rats exhibited an intermediate number of responses. Taken together, the results of the present study demonstrate that chronic exposure to stress results in biochemical adaptations in the mesolimbic dopamine system that resemble the chronic actions of several drugs of abuse. These adaptations could contribute to the convergent behavioral effects induced by treatments that are mediated via the VTA-NAc pathway.

Adaptation, Physiological↗
PubMed2007

Culturally specific adaptation of a prevention intervention: an international collaborative research project.

This study adapted a U.S. drug use prevention program for use with Russian at-risk adolescents, and explored directions for further development of programs addressing prevention of substance abuse and other health risk behaviors including risk of HIV infection. The adaptation process was conducted in phases, initially carried out in Seattle with 23 bilingual (English-Russian) youth and then further adapted in two Moscow schools with 44 "typical" youth. In the final phase, program adaptation for the Russian at-risk adolescents was achieved by conducting a pilot test of the adapted program lessons with Moscow at-risk adolescents (n=10), who met criteria of poor school performance and/or truancy. Observations and experience were used throughout to adapt and refine the program for at-risk youth. Modifications were made to represent more accurately colloquial Russian and to capture teen experiences common to Russian culture. Both U.S. and Russian youth characterized the lessons as engaging and valuable. They also expressed a need to learn about sexuality, drug use, and health; peer and romantic relationships; and problem-solving strategies.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Prism adaptation in schizophrenia.

The prism adaptation test examines procedural learning (PL) in which performance facilitation occurs with practice on tasks without the need for conscious awareness. Dynamic interactions between frontostriatal cortices, basal ganglia, and the cerebellum have been shown to play key roles in PL. Disruptions within these neural networks have also been implicated in schizophrenia, and such disruptions may manifest as impairment in prism adaptation test performance in schizophrenia patients. This study examined prism adaptation in a sample of patients diagnosed with schizophrenia (N=91) and healthy normal controls (N=58). Quantitative indices of performance during prism adaptation conditions with and without visual feedback were studied. Schizophrenia patients were significantly more impaired in adapting to prism distortion and demonstrated poorer quality of PL. Patients did not differ from healthy controls on aftereffects when the prisms were removed, but they had significantly greater difficulties in reorientation. Deficits in prism adaptation among schizophrenia patients may be due to abnormalities in motor programming arising from the disruptions within the neural networks that subserve PL.

Adaptation, Psychological↗
PubMed2005

Total lactate dehydrogenase activity of tail muscle is not cold-adapted in nocturnal lizards from cool-temperate habitats.

The dependence of metabolic processes on temperature constrains the behavior, physiology and ecology of many ectothermic animals. The evolution of nocturnality in lizards, especially in temperate regions, requires adaptations for activity at low temperatures when optimal body temperatures are unlikely to be obtained. We examined whether nocturnal lizards have cold-adapted lactate dehydrogenase (LDH). LDH was chosen as a representative metabolic enzyme. We measured LDH activity of tail muscle in six lizard species (n=123: three nocturnal, two diurnal and one crepuscular) between 5 and 35 degrees C and found no differences in LDH-specific activity or thermal sensitivity among the species. Similarly, the specific activity and thermal sensitivity of LDH were similar between skinks and geckos. Similar enzyme activities among nocturnal and diurnal lizards indicate that there is no selection of temperature specific LDH enzyme activity at any temperature. As many nocturnal lizards actively thermoregulate during the day, LDH may be adapted for a broad range of temperatures rather than adapted specifically for the low temperatures encountered when the animals are active. The total activity of LDH in tropical and temperate lizards is not cold-adapted. More data are required on biochemical adaptations and whole animal thermal preferences before trends can be established.

Adaptation, Physiological↗
PubMed2024

Stochastic modeling of single-cell gene expression adaptation reveals non-genomic contribution to evolution of tumor subclones.

Cancer progression is an evolutionary process driven by the selection of cells adapted to gain growth advantage. We present a formal study on the adaptation of gene expression in subclonal evolution. We model evolutionary changes in gene expression as stochastic Ornstein-Uhlenbeck processes, jointly leveraging the evolutionary history of subclones and single-cell expression data. Applying our model to sublines derived from single cells of a mouse melanoma revealed that sublines with distinct phenotypes are underlined by different patterns of gene expression adaptation, indicating non-genetic mechanisms of cancer evolution. Sublines previously observed to be resistant to anti-CTLA4 treatment showed adaptive expression of genes related to invasion and non-canonical Wnt signaling, whereas sublines that responded to treatment showed adaptive expression of genes related to proliferation and canonical Wnt signaling. Our results suggest that clonal phenotypes emerge as the result of specific adaptivity patterns of gene expression. A record of this paper's transparent peer review process is included in the supplemental information.

Animals↗
PubMed2005

Mechanisms of light adaptation in Drosophila photoreceptors.

Phototransduction in Drosophila is mediated by a phospholipase C (PLC) cascade culminating in activation of transient receptor potential (TRP) channels. Ca(2+) influx via these channels is required for light adaptation, but although several molecular targets of Ca(2+)-dependent feedback have been identified, their contribution to adaptation is unclear. By manipulating cytosolic Ca(2+) via the Na(+)/Ca(2+) exchange equilibrium, we found that Ca(2+) inhibited the light-induced current (LIC) over a range corresponding to steady-state light-adapted Ca(2+) levels (0.1-10 microM Ca(2+)) and accurately mimicked light adaptation. However, PLC activity monitored with genetically targeted PIP(2)-sensitive ion channels (Kir2.1) was first inhibited by much higher (>/= approximately 50 microM) Ca(2+) levels, which occur only transiently in vivo. Ca(2+)-dependent inhibition of PLC, but not the LIC, was impaired in mutants (inaC) of protein kinase C (PKC). The results indicate that light adaptation is primarily mediated downstream of PLC and independently of PKC by Ca(2+)-dependent inhibition of TRP channels. This is interpreted as a strategy to prevent inhibition of PLC by global steady-state light-adapted Ca(2+) levels, whereas rapid inhibition of PLC by local Ca(2+) transients is required to terminate the response and ensures that PIP(2) reserves are not depleted during stimulation.

Adaptation, Ocular↗
PubMed2006

Response adaptation to broadband sounds in primary auditory cortex of the awake ferret.

Driven by previous reports of adaptation to persistent stimuli in other brain regions, we investigated adaptive effects in the Primary Auditory Cortex of awake non-behaving ferrets (Mustela putorius furo). Electrophysiological data was obtained in response to the presentation of auditory gratings with a structured spectro-temporal envelope of varying bandwidth which had repeated transitions between low and high modulation depths. The responses were analyzed in terms of the evoked spike rates and in terms of the degree of phase locking to the modulation. We found two populations of cells, both of which showed adaptation in the traditional sense. For one population, we also found a second order of adaptation--i.e., adaptation of the adaptation. This suggests the existence of at least two coding strategies which differ in the weight placed on sensory context.

Acoustic Stimulation↗
PubMed2005

Effect of trisodium phosphate adaptation on changes in membrane lipid composition, verotoxin secretion, and acid resistance of Escherichia coli O157:H7 in simulated gastric fluid.

Escherichia coli O157:H7 (HEC), E. coli O157:H7 rpoS mutant (HEC-RM), and nonpathogenic E. coli (NPEC) were step-wise adapted to trisodium phosphate (TSP) by incubation in broths of increasing concentration, from 0% to 0.6%, at 37 degrees C for 24 h. After incubation at each concentration, each population was examined for acid resistance (D value) in simulated gastric fluid of pH 1.5, cell envelope membrane lipid composition, and intracellular and extracellular verotoxin concentrations. The ratio of cis-vaccenic acid (18:1omega7c) to palmitic acid (16:0) increased, indicating increased membrane fluidity with increasing TSP concentration up to 0.4%, but decreased at 0.6%. HEC and HEC-RM adapted at 0.4% TSP had the highest verotoxin concentrations of 1805 and 1879 ng/ml, respectively. In addition, with HEC the ratio of extracellular to intracellular verotoxin concentration decreased at higher TSP concentrations. In contrast, the ratio for HEC-RM increased at 0.4% TSP. HEC adapted to 0.4% TSP had the greatest survival in gastric fluid (58 min D value) among all treatments. For HEC, the increase in membrane fluidity was associated with increased acid resistance and extracellular verotoxin concentration for cells adapted to 0.4% TSP. In contrast, the increase in membrane fluidity was associated with decreased acid resistance of TSP adapted HEC-RM although the extracellular verotoxin concentration increased. Therefore, the deletion of the rpoS gene appeared to affect the changes in verotoxin concentration and acid resistance of TSP adapted E. coli O157:H7.

Adaptation, Physiological↗
PubMed2005

Six-month variability of the dark-adapted pupil diameter.

PURPOSE: To determine the individual variability of the dark-adapted pupil diameter over 6 months using a standardized dark-adaptation protocol. SETTING: Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: This prospective observational cohort study comprised volunteers with no history of ocular disease, surgery, or injury other than requirement for refractive correction. The right eye was tested. A standardized dark-adaptation protocol was used that controlled for accommodation and patient alertness. Infrared, still digital photographs were taken after 10 minutes of dark adaptation at 1 lux and were analyzed using digital image software. Testing was performed at baseline in the afternoon, at 3 months in the afternoon, and at 6 months in the morning. Lifestyle factors such as diet and exercise were not controlled. RESULTS: Mean intersession differences were 0.04 mm (95% confidence interval [CI]: -0.68-0.146), 0.15 mm (95% CI: -0.001-0.297), and 0.09 mm (95% CI: -0.048-0.236) for baseline-3 month, baseline-6 month, and 3 month-6 month comparisons, respectively. None of these differences was significantly different from zero (P>.05, 2-tailed Student t tests). The likelihood that the mean intersession difference was >.25 mm was negligible for all comparisons (P=.9996, .9099, and .9829 respectively, 1-tailed Student t tests). CONCLUSION: When a consistent dark-adaptation protocol that controls for alertness and accommodation is used, normal young individuals showed no significant variation in the dark-adapted pupil diameter over a 6-month period.

Accommodation, Ocular↗
PubMed2004

Preventing enterocyte apoptosis after massive small bowel resection does not enhance adaptation of the intestinal mucosa.

BACKGROUND: After massive small bowel resection (SBR), increased rates of enterocyte apoptosis are observed in the remnant bowel via a mechanism requiring bax gene expression. This study tested the hypothesis that adaptive mucosal growth could be enhanced by the novel strategy of preventing postresection enterocyte apoptosis. METHODS: Male bax-null and corresponding wild-type (WT) mice underwent a 50% proximal SBR or sham operation (bowel transaction with reanastomosis alone). Mice were killed after a full adaptation interval of 1 month. Adaptation was measured in the remnant ileum as alterations in villus height, crypt depth, and wet weight. Rates of enterocyte proliferation were derived by immunostaining of crypt enterocytes for Ki-67 and apoptosis by the presence of apoptosis bodies. RESULTS: The expected increase in enterocyte apoptosis after SBR occurred in the WT mice but was unchanged in the bax-null mice. Despite the prevention of postresection apoptosis in the bax-null mice, all parameters of adaptation and proliferation increased equally after SBR in both groups of mice. CONCLUSIONS: Bax deficiency prevents the increase in enterocyte apoptosis that occurs after massive SBR throughout the entire adaptation period. Attenuation of postresection enterocyte apoptosis does not augment mucosal adaptation to massive intestinal loss.

Adaptation, Physiological↗
PubMed2005

Effect of sex and sex hormones on structural intestinal adaptation after massive small bowel resection in rats.

PURPOSE: The gonadal steroids play a major role in the regulation of many functions. The purpose of the current study was to evaluate the effect of sex and sex hormones on intestinal adaptation in a rat model of short bowel syndrome (SBS). METHODS: In the first experiment, male and female Sprague-Dawley rats underwent bowel transection and re-anastomosis (sham group) or 75% small bowel resection and anastomosis (SBS group). Relative changes in parameters of intestinal adaptation (overall bowel and mucosal weight, mucosal DNA and protein, villus height, and crypt depth) were measured on day 15 and were compared with respect to sex. In the second experiment, male rats were divided into 4 experimental groups: SBS rats, SBS castrated rats, SBS castrated rats treated with testosterone, and SBS castrated rats treated with estradiol. Parameters of intestinal adaptation were compared with respect to hormonal treatment. Statistical significance was determined by Student's t test and analysis of variance with P < .05 considered significant. RESULTS: Sex had minimal effects on intestinal adaptation. Both male and female rats showed a comparable increase in all parameters of intestinal adaptation. In the second experiment, castration led to significant decrease in bowel and mucosal weight, mucosal DNA and protein in both jejunum and ileum compared with SBS animals. Castrated rats also had lower jejunal villus height and crypt depth compared with SBS animals. Testosterone attenuated this negative effect of castration on bowel regrowth. Rats treated with testosterone showed a significant increase in bowel and mucosal weight, mucosal protein in both jejunum and ileum, mucosal DNA, villus height, and crypt depth in jejunum compared with castrated nontreated animals. Treatment with estradiol after resection and castration had minimal effect on bowel regrowth. CONCLUSIONS: Bowel regrowth after massive small bowel resection is not sex-related. Depletion of androgens by castration inhibited intestinal adaptation. Testosterone has shown a strong stimulating effect on bowel regrowth.

Adaptation, Physiological↗
PubMed2006

Resilience, misfortune, and mortality: evidence that sense of coherence is a marker of social stress adaptive capacity.

OBJECTIVE: The purpose of this study is to test the hypothesis that sense of coherence (SOC) distinguishes adaptive capacity to adverse event experience. METHODS: A population-based cohort of 20,921 men and women completed a postal assessment of their lifetime experience of specific adverse events and a measure of their SOC. Reports of 111,857 events allowed construction of measures of event impact and adaptation. RESULTS: Those with a weak SOC reported significantly slower adaptation to the adverse effects of their event experiences than those with a strong SOC (P<.0001). During mean follow-up of 6.7 years, 1617 deaths were recorded. A one standard deviation increase in mean adaptation score (representing slower adaptation) was associated with a 6% increase in mortality rate (P=.03) after adjusting for age and sex. Measures of event occurrence and impact were less strongly associated with SOC and were not significantly associated with mortality. CONCLUSION: These results suggest that SOC is a potential marker of an individual's social stress adaptive capacity, which is predictive of mortality.

Adaptation, Psychological↗
PubMed2005

Possible constraints on adaptive variation in sex ratio at birth in humans and other primates.

There is general agreement that adaptive variation of sex ratio at birth has not been decisively demonstrated in primates (including human beings). So some workers have questioned whether it actually exists. Others have conjectured that it exists but is subject to as yet unidentified 'constraints' (factors opposing the modifying influences of selection in the phenotype). Meanwhile though most workers have called for research to reveal the proximate causes of sex ratio variation, few (if any) have directed studies toward that end. Here it is argued that hormonal action is responsible both for much adaptive and non-adaptive sex ratio variation, and for constraints on the adaptive variation. My hypothesis proposes that levels of steroid hormones (testosterone and oestrogen) of both parents around the time of conception are positively associated with offspring sex ratio (proportion male at birth) of mammals including man. Testosterone in men and oestrogen in women are also known to be positively associated with the health, attractiveness and fertility of individual human beings. However, high levels of testosterone in women are frequently associated with adverse medical conditions. It is suggested that for these reasons (and contrary to some adaptive theory) some classes of people (particularly women) in suboptimal health ("condition") produce excesses of sons. It seems that gonadal hormones are responsible for adaptive variation; and that maternal adrenal hormones are responsible for maladaptive variation. In evolutionary terms, gonadal hormones precede adrenal hormones.

Adaptation, Physiological↗