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PubMed2006

Vision of the hand prior to movement onset allows full motor adaptation to a multi-force environment.

In everyday life, because of unexpected mechanical perturbation applied to the hand or to the whole body, hand movements may become suddenly inaccurate. With prolonged exposure to the perturbation, trajectories slowly recover their normal accuracy, which is the mark of motor adaptation. However, full development of this adaptive process in complete darkness has been recently challenged in a multi-force environment. Here, we report on the effectiveness of static hand position information as specified through vision prior to movement onset on the adaptative changes, over trials, of pointing movements performed in a gravitoinertial force field. For this, subjects seated off-center on a platform rotating at constant velocity, were either confined to complete darkness (No Vision Session, NV) or provided with vision of the hand resting on the starting position prior to movement onset (Hand Vision Prior to Movement Session, HVPM). Overall, our results showed that adaptation to the centrifugal force was very rapid, and allowed subjects to demonstrate appropriate motor control as early as of the very first trials performed during the rotation period, even in the NV condition. They also showed that the integration by the Central Nervous System (CNS) of visual and proprioceptive information prior to the execution of a reaching movement allows subjects to reach full motor adaptation in a multi-force environment. Furthermore, our data confirm the existence of differentiated motor adaptive mechanisms for centrifugal and Coriolis forces. Adaptation to the former may fully develop on the basis of an a priori coding of the characteristics of the background force level even without visual information, while the latter needs visual cues about hand position prior to movement onset to take place.

Adaptation, Physiological↗
PubMed2005

Flowable materials as an intermediate layer could improve the marginal and internal adaptation of composite restorations in Class-V-cavities.

OBJECTIVES: The purpose of this in vitro study was to evaluate the marginal and internal adaptation of restorative systems in combination with flowable materials as an intermediate layer in Class-V-cavities. METHODS: Thirty Class-V-cavities with occlusal margins in enamel and gingival margins in dentin/cementum were prepared and randomly assigned to five groups. The following five restorative systems were used: compomer, composite E, flowable compomer/composite E, composite RF and flowable composite/composite RF. The flowable materials were added between the restorative composites and the cervical margins of the cavities. Marginal and internal adaptation were quantitatively evaluated before and after thermal (2,500 times between 5 and 55 degrees C) and mechanical load cycling (25,000 times 100 N) using standard SEM procedures. Statistical analysis was performed using the Kruskal-Wallis and Mann-Whitney U-Test. The morphology of the internal restorative interfaces was also evaluated. RESULTS: The present study revealed that the best marginal adaptation in dentin was attained with the compomer restoration (95.8% perfect margin). The marginal adaptation of composite restorative systems was improved by the use of a flowable compomer (45.5% vs. 68.2% perfect margin in dentin) or a flowable composite (46.7% vs. 80.7% perfect margin in dentin, p<0.05) as an intermediate layer. No differences were observed between the used materials for the parameter internal adaptation. SIGNIFICANCE: In Class-V-cavities compomers showed the best marginal adaptation and the marginal adaptation of composite fillings could be improved by the use of flowable materials as an intermediate layer.

Compomers↗
PubMed2005

Human efferent adaptation of DPOAEs in the L1,L2 space.

The adaptive properties of distortion product otoacoustic emissions (DPOAEs) at 2f(1)-f2 were investigated in 12 ears of normally hearing adults aged 18-30 years using long-lasting 1-s primary-tone on-times. In this manner, DPOAE adaptation at a single f2 of 1.55 kHz (f2/f1=1.21) was evaluated as a function of the levels of the primary tones in a matrix of L1, L2 settings, which varied from 45 to 80 dB SPL, in 5-dB steps. DPOAEs were elicited under both monaural and binaural stimulus-presentation conditions. Adaptation was defined as the difference in DPOAE levels between the initial 92-ms baseline measure using a standard protocol and one obtained during the final 92 ms of the prolonged 1-s primary-tones. These differences were averaged across subjects to create contour plots of mean adaptation in the L1,L2 space. The 2f(1)-f2 DPOAE revealed consistent regions of suppression (-0.5 dB difference) or enhancement (+0.5 dB difference) with respect to baseline measures within the L(1),L(2) matrix for both acoustic-stimulation conditions. Specifically, 2f(1)-f2 DPOAE suppressions of 1-2 dB occurred for both monaural and binaural presentations, typically at level combinations in which L1>L2. In contrast, larger 2f(1)-f2 DPOAE enhancements of 3-4 dB occurred for only the binaural condition, at primary-tone level combinations where L1<L2. Although adaptation activity was also evaluated for the DPOAEs at f(2)-f1, 2f(2)-f1, and 3f(1)-2f2, these emissions were either immeasurable (e.g., f(2)-f1) or only present in a subset of subjects over a narrow range of primary-tone frequencies and levels that did not support a systematic analysis. In summary, the 2f(1)-f2 results suggest that a potentially important area for adaptation measures exists in the L1,L2 space, when L1 is lower than L2. This combination of primary-tone levels can lead to large DPOAE adaptation effects that may be related to a notch in the DPOAE response/growth or input/output (I/O) function.

Acoustic Stimulation↗
PubMed2007

Exploring efferent-mediated DPOAE adaptation in three different guinea pig strains.

The aims of this study were to explore the correlation between DPOAE adaptation magnitude in three different guinea pig strains to examine if the genetic component affects the DPOAE adaptation magnitude. It was also to investigate the correlation between strains with certain characteristics i.e. reduced susceptibility to noise, and early onset of age-dependent hearing loss and the DPOAE adaptation magnitude. The animals were anaesthetized and the 2f1-f2 DPOAE (f1=8k Hz, and f2/f1=1.2) adaptation was established with a minimum of 144 combinations of f1; f2 where f1 was held fixed and f2 was varied in 1 dB or 0.4 dB steps. The DPOAE adaptation magnitude was defined as the difference between maximum positive level and the maximum negative level. ABRs were conducted at different age-groups (at 4, 6.3, and 12.5k Hz) to evaluate the progress of hearing thresholds by age. There was a significant difference between strains regarding the hearing loss at one year of age. There was no significant difference in DPOAE adaptation magnitude between strains included in this study and from this we conclude that the DPOAE adaptation magnitude is not a predictor for the susceptibility to noise trauma, or early onset of age-dependent hearing loss, using the methods described in this paper.

Adaptation, Physiological↗
PubMed2006

Maximum motor fusion combined with one-hour preoperative prism adaptation test in patients with acquired esotropia.

PURPOSE: Preoperative prism adaptation and the maximum motor fusion test reduce the risk of postoperative undercorrection, overcorrection, and bifocal requirements in acquired esotropia. The purpose of our study is to determine the efficacy of the maximum motor fusion test followed by a short prism adaptation test in patients with acquired esotropia undergoing bilateral medial rectus muscle recession. METHODS: We undertook a retrospective review of 29 subjects with acquired esotropia without history of amblyopia, previous strabismus surgery, use of bifocals, pattern anisotropia, dissociated vertical deviation, or oblique muscle dysfunction. All subjects underwent bilateral medial rectus muscle recessions based on the distance angle of deviation measured with the maximum motor fusion test followed by prism adaptation test. Alternate prism and cover testing was performed after 1 hour of prism adaptation to determine the angle of deviation for surgical correction. RESULTS: The age at surgery was 4.5 +/- 1 years. The preoperative angle of deviation at distance was 20.4 +/- 4.2(delta). It increased to 36.2 +/- 4.2(delta) after the maximum motor fusion test followed by 1 hour of prism adaptation testing. The final preoperative angle of deviation post motor fusion test-prism adaptation test was significantly larger than the initial angle of deviation (p < 0.0001). The final postoperative deviation at distance was 1.3 +/- 3.3(delta), and 5.2 +/- 1.5(delta) at near. Postoperative follow up was 18 +/- 2.6 months (range, 13-24 months). CONCLUSIONS: The combination of maximum motor fusion and preoperative prism adaptation allowed increased amounts of medial rectus muscle muscle recession, decreasing the risk of postoperative undercorrection without increasing the risk of overcorrection.

Adaptation, Ocular↗
PubMed2005

The incremental benefit of rate-adaptive pacing on exercise performance during cardiac resynchronization therapy.

OBJECTIVES: The purpose of this research was to investigate the effect of using rate-adaptive pacing and atrioventricular interval (AVI) adaptation on exercise performance during cardiac resynchronization therapy (CRT). BACKGROUND: The potential incremental benefits of using rate-adaptive pacing and AVI adaptation with CRT during exercise have not been studied. METHODS: We studied 20 patients with heart failure, chronotropic incompetence (<85% age-predicted heart rate [AP-HR] and <80% HR reserve), and implanted with CRT. All patients underwent a cardiopulmonary exercise treadmill test using DDD mode with fixed AVI (DDD-OFF), DDD mode with adaptive AVI on (DDD-ON), and DDDR mode with adaptive AVI on (DDDR-ON) to measure metabolic equivalents (METs) and peak oxygen consumption (VO2max). RESULTS: During DDD-OFF mode, not all patients reached 85% AP-HR during exercise, and 55% of patients had <70% AP-HR. Compared to patients with >70% AP-HR, patients with <70% AP-HR had significantly lower baseline HR (66 +/- 3 beats/min vs. 80 +/- 5 beats/min, p = 0.015) and percentage HR reserve (27 +/- 5% vs. 48 +/- 6%, p = 0.006). In patients with <70% AP-HR, DDDR-ON mode increased peak exercise HR, exercise time, METs, and VO2max compared with DDD-OFF and DDD-ON modes (p < 0.05), without a significant difference between DDD-OFF and DDD-ON modes. In contrast, there were no significant differences in peak exercise HR, exercise time, METs, and VO2max among the three pacing modes in patients with >70% AP-HR. The percentage HR changes during exercise positively correlated with exercise time (r = 0.67, p < 0.001), METs (r = 0.56, p < 0.001), and VO2max (r = 0.55, p < 0.001). CONCLUSIONS: In heart failure patients with severe chronotropic incompetence as defined by failure to achieve >70% AP-HR, appropriate use of rate-adaptive pacing with CRT provides incremental benefit on exercise capacity during exercise.

Adaptation, Physiological↗
PubMed2026

Temporal proteomic analysis reveals a three-phase adaptation strategy in Phytophthora cinnamomi during salinity stress.

Phytophthora cinnamomi, a highly invasive hemibiotrophic oomycete, threatens global agriculture, forestry, and native ecosystems. Although drought and temperature effects on P. cinnamomi-host interactions are well studied, current knowledge of abiotic stress responses in P. cinnamomi remains largely centered on infection and phytopathology, with limited molecular insight into the pathogen's direct response to salinity independent of its host. To address this gap, we combined growth assays, time-resolved proteomics, and network analysis to define how P. cinnamomi responds and adapts to salinity exposure. Growth assays showed that NaCl-modified agar enhanced mycelial expansion in a concentration-dependent manner, with 100&#xa0;mM NaCl significantly increasing growth at 48, 72, and 96&#xa0;h compared with controls, while 50&#xa0;mM NaCl remained comparable to control conditions. Temporal proteomic analysis of 100&#xa0;mM NaCl treatment at 0, 1, 6, 12, and 24&#xa0;h post treatment revealed dynamic shifts in protein abundance. Early induction of ROS (Reactive Oxygen Species)-detoxifying enzymes, including glutathione S-transferases and peroxidases, was consistent with ROS-specific staining assays. Network analysis identified modules enriched for redox regulation, ATP generation, ion transport, and translational control, highlighting multi-layered adaptation to elevated NaCl levels. Notably, clusters of conserved hypothetical proteins were strongly upregulated, indicating unexplored stress tolerance components in Phytophthora species. Here, we propose that P. cinnamomi rapidly activates a three-phase strategy involving metabolism readjustments, redox defenses, and cellular structure alterations under salinity conditions. With increasing soil salinization due to climate change, our study provides first mechanistic insights into P. cinnamomi's adaptive plasticity and ecological resilience to abiotic stress. SIGNIFICANCE: This study represents the first temporal proteomic analysis of salinity stress adaptation in Phytophthora cinnamomi, revealing a sophisticated three-phase adaptation strategy. This research fundamentally advances our understanding of how this globally destructive plant pathogen, P. cinnamomi, maintains environmental resilience. Our findings reveal proteome remodelling as a mechanistic framework for understanding stress tolerance in oomycetes, a group of microorganisms responsible for some of the world's most destructive agricultural and forest diseases. Our results show proteins involved in emergency damage control through metabolic recalibration to sustained adaptation. These findings have relevance for predicting pathogen behavior under climate change scenarios, where increasing soil salinity threatens agricultural productivity while simultaneously enhancing pathogen survival and virulence. Understanding how P. cinnamomi responds to prolonged salinity exposure may inform targeted biocontrol strategies and improve predictive models of disease pressure in salt-affected agricultural regions. The temporal analysis framework we present offers a broadly applicable approach for understanding microbial stress adaptation, with implications extending beyond plant pathology to environmental microbiology and biotechnology applications where stress tolerance is paramount.

Phytophthora↗
PubMed2005

Strain rate influences periosteal adaptation in mature bone.

Mechanical forces influence bone form and function. Although the adaptive capabilities of bone are well known, the nuances of the mechanical stimuli regulating adaptation remain elusive. Recently, it was suggested that strain rate influences bone adaptation, and impact exercises with high strain rates during growth may be more osteogenic than low impact aerobic exercises. Building on those findings, we hypothesized that higher rates of mechanical loading would evoke greater adaptive responses than lower rates of loading in mature bone. To test that hypothesis, skeletally mature (16 weeks) female C57BL/6 mice underwent non-invasive exogenous cantilever bending of the right tibia with a 1 Hz trapezoidal waveform for 60 s, 5 days per week, for 4 weeks. Loading was calibrated (strain gauge) to induce peak magnitudes of 1000 microepsilon on the lateral tibial middiaphysis. Mice were randomly assigned to three groups based on strain rate of the applied load: low (0.004 s(-1); n = 14), medium (0.020 s(-1); n = 15), and high (0.100 s(-1); n = 14). Calcein injections (i.p., 10 mg kg(-1)) permitted histomorphometric analyses of bone formation. Loading significantly enhanced periosteal mineral apposition rate (MAR), mineralizing surface (MS), and bone formation rate (BFR BS(-1)) in all three strain rate groups, relative to control tibiae. Furthermore, a graded dose-response relation was observed between the applied strain rate and periosteal BFR BS(-1). These increases in MAR, MS, and BFR BS(-1) were not seen on the endosteal surface. Endosteal adaptation was not statistically different between loaded and control tibiae in most endosteal indices of bone adaptation. Moreover, endosteal adaptation did not increase with strain rate. Understanding the nature of the stimuli to which bone cells respond to may underpin the development of non-pharmacological treatments devised to enhance bone mass.

Adaptation, Physiological↗
PubMed2005

Fast adaptation in vestibular hair cells requires myosin-1c activity.

In sensory hair cells of the inner ear, mechanical amplification of small stimuli requires fast adaptation, the rapid closing of mechanically activated transduction channels. In frog and mouse vestibular hair cells, we found that the rate of fast adaptation depends on both channel opening and stimulus size and that it is modeled well as a release of a mechanical element in series with the transduction apparatus. To determine whether myosin-1c molecules of the adaptation motor are responsible for the release, we introduced the Y61G mutation into the Myo1c locus and generated mice homozygous for this sensitized allele. Measuring transduction and adaptation in the presence of NMB-ADP, an allele-specific inhibitor, we found that the inhibitor not only blocked slow adaptation, as demonstrated previously in transgenic mice, but also inhibited fast adaptation. These results suggest that mechanical activity of myosin-1c is required for fast adaptation in vestibular hair cells.

Adaptation, Physiological↗
PubMed2004

A cell biologist's perspective on physiological adaptation to opiate drugs.

Opiate drugs such as morphine and heroin are among the most effective analgesics known but are also highly addictive. The clinical utility of opiates is limited by adaptive changes in the nervous system occurring after prolonged or repeated drug administration. These adaptations are believed to play an important role in the development of physiological tolerance and dependence to opiates, and to contribute to additional changes underlying the complex neurobehavioral syndrome of drug addiction. All of these adaptive changes are initiated by the binding of opiate drugs to a subfamily of G protein-coupled receptors that are also activated by endogenously produced opioid neuropeptides. It is increasingly evident that opiate-induced adaptations occur at multiple levels in the nervous system, beginning with regulation of opioid receptors themselves and extending to a complex network of direct and indirect modifications of "downstream" signaling machinery. Efforts in my laboratory are directed at understanding the biochemical and cell biological basis of opiate adaptations. So far, we have focused primarily on adaptations occurring at the level of opioid receptors themselves. These studies have contributed to defining a set of membrane trafficking mechanisms by which the number and functional activity of opioid receptors are controlled. The role of these mechanisms in affecting adaptation of "downstream" neurobiological substrates, and in mediating opiate-induced changes in whole-animal physiology and behavior, are exciting questions that are only beginning to be explored.

Adaptation, Physiological↗
PubMed2006

LTP and adaptation to inactivity: overlapping mechanisms and implications for metaplasticity.

LTP and other rapidly induced forms of synaptic modification tune individual synaptic weights, whereas slower forms of plasticity such as adaptation to inactivity are thought to keep neurons within their firing limits and preserve their capability for information processing. Here we describe progress in understanding the relationship between LTP and adaptation to inactivity. A prevailing view is that adaptation to inactivity is purely postsynaptic, scales synaptic strength uniformly across all synapses, and thus preserves relative synaptic weights without interfering with signatures of prior LTP or the relative capacity for future LTP. However, recent evidence in hippocampal neurons indicates that, like LTP, adaptation to AMPA receptor blockade can draw upon a repertoire of synaptic expression mechanisms including enhancement of presynaptic vesicular turnover and increased quantal amplitude mediated by recruitment of homomeric GluR1 AMPA receptors. These pre- and postsynaptic changes appeared coordinated and preferentially expressed at subset of synapses, thereby increasing the variability of miniature EPSCs. In contrast to the NMDA receptor-, Ca2+ entry-dependent induction of LTP, adaptation to inactivity may be mediated by attenuation of voltage-sensitive L-type Ca2+ channel function. The associated intracellular signaling involves elevation of betaCaMKII, which in turn downregulates alphaCaMKII, a key player in LTP. Thus, adaptation to inactivity and LTP are not strictly independent with regard to mechanisms of signaling and expression. Indeed, we and others have found that responses to LTP-inducing stimuli can be sharply altered by prior inactivity, suggesting that the slow adaptation changes the rules of plasticity-an interesting example of "metaplasticity".

Adaptation, Biological↗
PubMed2005

Direction-specific adaptation of magnetic responses to motion onset.

We investigated the direction-specificity of motion adaptation, by recording magnetic responses evoked by motion onsets under both adapted and control conditions. The inter-stimulus interval was equated between the conditions to precisely evaluate the effect of motion adaptation itself. The onset stimuli at 1.5, 3.0 or 6.0 deg/s moved in the same direction or in the opposite direction to an adaptation stimulus at 3.0 deg/s. The perceived velocity of each test stimulus was measured in separate sessions. The most prominent peak (M2) of evoked responses appeared around 200-300 ms after motion onsets, and the dipoles were mainly estimated in the temporo-occipital area. Adaptation largely affected both perceived velocities and the M2 amplitudes. The M2 amplitudes were decreased by adaptation for both directions of test stimuli, and the decreases were significantly larger for the test stimuli in the adapted direction (49-63% of control condition) than for the test stimuli in the opposite direction (17-27% of control condition). The present study, for the first time, found that magnetic responses evoked by motion onsets reflect the activities of neurons that have direction-specificity.

Adaptation, Physiological↗
PubMed2026

The genome of Thesium ramosoides (Santalales) reveals evolutionary dynamics associated with parasitism and alpine adaptation.

Plant species adapting to complex environments experience contrasting selection pressures that drive the expansion and contraction of different gene families. However, few studies have investigated simultaneous genomic responses to such diverse selective forces. Here, we generate a high-quality genome assembly for the hemiparasitic plant Thesium ramosoides, the first for the largest genus in the Santalales, and explore the genomic basis underlying the evolution of parasitism and alpine adaptation. Unlike many other parasitic plants, the Thesium genome has not undergone additional rounds of whole-genome duplication, making it particularly tractable for studying gene family evolution. Our analyses reveal substantial loss of photosynthesis-related genes and contraction of biotic defense gene families, likely reflecting adaptation to a hemiparasitic lifestyle and reduced pathogen pressure at high altitudes. The absence of key root hair development genes correlates with the degenerate root hair phenotype observed in this species. Furthermore, hallmarks of high-altitude adaptation include the expansion of gene families involved in responses to hypoxia. Notably, expansion of gene families associated with meristem development is consistent with the presence of below-ground crown buds that enable rapid regeneration after mountain fires. Unexpectedly, we detected tandem duplication and diversification of the strigolactone receptor gene D14, which regulates secondary shoot formation, but not of its ancestral paralog KAI2, which mediates seed germination in response to the smoke-derived compound karrikin. This finding suggests divergent signaling mechanisms underlying fire adaptation across different parasitic plant lineages. By integrating time-series transcriptomic data, we propose a post-fire "defense first, repair later, recovery last" model, in which resources are reallocated from immediate defense to rapid repair and ultimately to long-term recovery, to explain the adaptation of T. ramosoides to fire-prone habitats. Our study provides critical insights into the complex and contrasting genomic dynamics that drive adaptation to multiple co-occurring selection pressures.

Genome, Plant↗
PubMed2001

fMR-adaptation: a tool for studying the functional properties of human cortical neurons.

The invariant properties of human cortical neurons cannot be studied directly by fMRI due to its limited spatial resolution. One voxel obtained from a fMRI scan contains several hundred thousands neurons. Therefore, the fMRI signal may average out a heterogeneous group of highly selective neurons. Here, we present a novel experimental paradigm for fMRI, functional magnetic resonance-adaptation (fMR-A), that enables to tag specific neuronal populations within an area and investigate their functional properties. This approach contrasts with conventional mapping methods that measure the averaged activity of a region. The application of fMR-A to study the functional properties of cortical neurons proceeds in two stages: First, the neuronal population is adapted by repeated presentation of a single stimulus. Second, some property of the stimulus is varied and the recovery from adaptation is assessed. If the signal remains adapted, it will indicate that the neurons are invariant to that attribute. However, if the fMRI signal will recover from the adapted state it would imply that the neurons are sensitive to the property that was varied. Here, an application of fMR-A for studying the invariant properties of high-order object areas (lateral occipital complex--LOC) to changes in object size, position, illumination and rotation is presented. The results show that LOC is less sensitive to changes in object size and position compared to changes of illumination and viewpoint. fMR-A can be extended to other neuronal systems in which adaptation is manifested and can be used with event-related paradigms as well. By manipulating experimental parameters and testing recovery from adaptation it should be possible to gain insight into the functional properties of cortical neurons which are beyond the spatial resolution limits imposed by conventional fMRI.

Adaptation, Physiological↗
PubMed2002

Non-visual information does not drive saccade gain adaptation in monkeys.

Recent experiments have characterized the dependence of saccade gain adaptation on the characteristics of the visual error following inaccurate saccades. We currently know little about the potential role of non-visual information in driving saccade adaptation. The brain could use non-visual signals from the saccade burst generator or extraocular muscle (EOM) proprioceptors to determine if the eye had rotated the appropriate distance to aim at a target. Both saccade-related burst signals and EOM proprioceptive information reach the posterior vermis of the cerebellum, a brain area strongly implicated in saccade adaptation. In the experiment described here we determined if non-visual information has a significant affect on saccade adaptation. We made monkey saccades hypometric with intra-saccade target movements and then tested the recovery of saccade gain toward normal under three conditions: (1) when the target was continuously visible, (2) when the target extinguished for 1000 ms beginning during the saccade, and (3) when the monkey remained in the dark. In the first condition both visual and non-visual indications of hypometria were available. In the second, only non-visual information was available. In the third, the monkey made no visually guided saccades and very few spontaneous saccades in the dark so neither visual nor non-visual information could drive adaptation. We found that, though it was hypometric, saccade size during recovery changed the same small amount when monkeys made saccades to extinguishing targets or remained in the dark. Saccade size changed significantly (approximately 5x) more during recovery when the monkey tracked continuously visible targets. Thus non-visual information has no influence on adaptation and visual post-saccade error is the only known driver of saccade adaptation.

Adaptation, Physiological↗
PubMed1996

Aspects of the adaptive response to very low doses of radiation and other agents.

When human lymphocytes and other cells are pre-exposed to very low doses of ionizing radiation and subsequently exposed to a high dose, less genetic damage, i.e., fewer chromosome aberrations, is found than is observed in cells that had not been pre-exposed. This has been termed the adaptive response and has been attributed to the induction of a repair mechanism by the low dose exposure. Several experiments have now been carried out on this adaptive response to better characterize the phenomenon. (A) Experiments with differential display of mRNAs indicate that human lymphocytes exposed to 2 cGy of X-rays have somewhat different mRNAs expressed than do unexposed cells. This is providing access to DNA that might be involved in adaptation. (B) Other experiments with embryonic cells from transgenic mice that are deficient in superoxide dismutase (SOD) have shown that the adaptive response is unrelated to the amount of SOD in the cells, and thus is independent of superoxide radicals. (C) Experiments in which very low doses of various restriction enzymes were electroporated into human lymphocytes have shown that low levels of double-strand DNA breaks alone are able to induce the adaptive response. (D) Experiments in which human male lymphocytes (XY chromosome constitution) and human female lymphocytes (XX chromosome constitution) were cocultivated have shown that adaptation is not caused by a change in the rate of cell progression to mitosis after a challenge dose, and is a further indication that cell stage sensitivity is not a factor in the adaptive response.

Adaptation, Physiological↗
PubMed2000

A model of the Parkinsonian visual system: support for the dark adaptation hypothesis.

Considerable evidence suggests that some visual abnormalities in Parkinson's disease are mediated by disruption of dopaminergic processes in the retina. Since dopamine is thought to be involved in the process of dark adaptation, and some of these abnormalities are similar to the changes which accompany dark adaptation in normal subjects, it has been proposed that the parkinsonian retina behaves as though inappropriately dark-adapted. In Parkinson's disease, the apparent contrast of peripherally viewed medium and high spatial frequency gratings is reduced. In our first experiment, normal subjects were dark-adapted, and were required to match the apparent contrast of a peripherally viewed grating to that of a foveally viewed grating. The results showed an interaction between spatial frequency and dark adaptation, reflecting a greater reduction in the apparent contrast of peripheral high spatial frequency gratings. In a second experiment, no effect of dark adaptation was found on the apparent spatial frequency of a peripherally viewed grating required to match that of a foveally viewed grating. The first experiment supports the dark adaptation hypothesis of parkinsonian vision, and the second suggests that the changes in apparent contrast are mediated by different amounts of change in contrast gain in central and peripheral vision, rather than by differential changes in receptive field size.

Adaptation, Ocular↗
PubMed2001

Increased sensitivity to speed changes during adaptation to first-order, but not to second-order motion.

Observers adapted to drifting patterns varying either in luminance (first-order pattern), or in contrast (second-order pattern). Sensitivity to increases or decreases in the speed of the first-order pattern increased sharply as adaptation time increased, but sensitivity to speed changes of the second-order pattern remained unchanged throughout the adaptation time. Adaptation of first-order motion mechanisms seems thus to mediate increased sensitivity to variations in speed around the adapting speed. No evidence was found for such effects of adaptation to second-order motion. The observed differences in the effects of adaptation accord well with reports of fundamental differences between after-effects to drifting first- and second-order patterns and are in harmony with models of motion perception emphasizing different mechanisms for the detection of first- and second-order motion.

Adaptation, Physiological↗