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PubMed2004

Does thyroid function in developing birds adapt to sustained ammonium perchlorate exposure?

The effects of a wide range of ammonium perchlorate (AP) concentrations in drinking water on thyroid function in bobwhite quail chicks was investigated at 2, 4, and 8 weeks of exposure. We measured plasma thyroid hormones (THs) to evaluate organismal thyroid status, thyroid weights to evaluate hypothalamic-pituitary-thyroid (HPT) axis activation, and thyroidal TH content to assess TH stores. At the highest AP exposures plasma THs were decreased, thyroid glands were hypertrophied, and thyroidal TH content was decreased. As in our previous studies, thyroidal thyroxine (T(4)) content was the most sensitive indicator of decreased thyroid function; plasma T(4) and thyroid weight were much less sensitive. The lack of sensitivity of these variables appears to result from cyclic patterns of thyroid responses involving the HPT axis and intermittent release of stored THs from the thyroid gland. With sustained AP exposure (8 weeks), at the lowest range of AP concentrations used, chicks showed adaptation in thyroid function that fully compensated for the initial (2 week) effects of AP. At the intermediate AP concentrations there was partial compensation for the initial AP effects. At the highest AP exposures used, thyroid function was very low throughout the study, with no indication of compensatory responses. The capability of chicks to increase some aspects of their thyroid function adaptively in response to some levels of sustained AP exposure is contrary to the common generalization that developing animals are most vulnerable to environmental contaminants.

Adaptation, Physiological↗
PubMed1983

Light and dark adaptation in Phycomyces light-growth response.

Sporangiophores of the fungus Phycomyces exhibit adaptation to light stimuli over a dynamic range of 10(10). This range applies to both phototropism and the closely related light-growth response; in the latter response, the elongation rate is modulated transiently by changes in the light intensity. We have performed light- and dark-adaptation experiments on growing sporangiophores using an automated tracking machine that allows a continuous measurement of growth velocity under controlled conditions. The results are examined in terms of the adaptation model of Delbrück and Reichardt (1956, Cellular Mechanisms in Differentiation and Growth, 3-44). The "level of adaptation," A, was inferred from responses to test pulses of light by means of a series of intensity-response curves. For dark adaptation to steps down in the normal intensity range (10(-6)-10(-2) W/m2), A decays exponentially with a time constant b = 6.1 +/- 0.3 min. This result is in agreement with the model. Higher-order kinetics are indicated, however, for dark adaptation in the high-intensity range (10(-2)-1 W/m2). Adaptation in this range is compared with predictions of a model relating changes in A to the inactivation and recovery of a receptor pigment. In response to steps up in intensity in the normal range, A was found to increase rapidly, overshoot the applied intensity level, and then relax to that level within 40 min. These results are incompatible with the Delbrück-Reichardt model or any simple generalizations of it. The asymmetry and overshoot are similar to adaptation phenomena observed in systems as diverse as bacterial chemotaxis and human vision. It appears likely that light and dark adaptation in Phycomyces are mediated by altogether different processes.

Adaptation, Biological↗
PubMed1993

An optical fiber transducer for single myofibril force measurement.

A force transducer has been developed for use in force measurement of skeletal muscle myofibrils. The transducer is suitable for measurement of passive and contractile forces in a range up to 200 micrograms, with 1 microgram resolution. It is based upon the operating principle of the deflection of an optical fiber of known compliance, sensed by the differential illumination of two phototransistors. Attractive features include ease of operation and specimen mounting, high bandwidth, adaptability for different force ranges, and simple and inexpensive construction.

Biomechanical Phenomena↗
PubMed1998

Environmental hypotheses of hominin evolution.

The study of human evolution has long sought to explain major adaptations and trends that led to the origin of Homo sapiens. Environmental scenarios have played a pivotal role in this endeavor. They represent statements or, more commonly, assumptions concerning the adaptive context in which key hominin traits emerged. In many cases, however, these scenarios are based on very little if any data about the past settings in which early hominins lived. Several environmental hypotheses of human evolution are presented in this paper. Explicit test expectations are laid out, and a preliminary assessment of the hypotheses is made by examining the environmental records of Olduvai, Turkana, Olorgesailie, Zhoukoudian, Combe Grenal, and other hominin localities. Habitat-specific hypotheses have prevailed in almost all previous accounts of human adaptive history. The rise of African dry savanna is often cited as the critical event behind the development of terrestrial bipedality, stone toolmaking, and encephalized brains, among other traits. This savanna hypothesis has been countered recently by the woodland/forest hypothesis, which claims that Pliocene hominins had evolved in and were primarily attracted to closed habitats. The ideas that human evolution was fostered by cold habitats in higher latitudes or by seasonal variations in tropical and temperate zones also have their proponents. An alternative view, the variability selection hypothesis, states that large disparities in environmental conditions were responsible for important episodes of adaptive evolution. The resulting adaptations enhanced behavioral versatility and ultimately ecological diversity in the human lineage. Global environmental records for the late Cenozoic and specific records at hominin sites show the following: 1) early human habitats were subject to large-scale remodeling over time; 2) the evidence for environmental instability does not support habitat-specific explanations of key adaptive changes; 3) the range of environmental change over time was more extensive and the tempo far more prolonged than allowed by the seasonality hypothesis; and 4) the variability selection hypothesis is strongly supported by the persistence of hominins through long sequences of environmental remodeling and the origin of important adaptations in periods of wide habitat diversity. Early bipedality, stone transport, diversification of artifact contexts, encephalization, and enhanced cognitive and social functioning all may reflect adaptations to environmental novelty and highly varying selective contexts.

Adaptation, Physiological↗
PubMed2004

Emergency services: a bird's eye perspective on the many different functions of stress proteins.

Life on our planet has adapted to a wide range of physical conditions, including extremely high and low temperatures, high pressures, extremes of pH and chemically aggressive conditions. To cope with these stress factors, organisms have evolved a variety of strategies operating on very different levels, from the small molecule response to physiological and behavioural adaptation. The only kind of stress response that is found universally in all species is the stress-induced expression or overexpression of specific proteins. Among these, the heat shock proteins are the best studied group. They have been shown to serve in a variety of specific functions, including those of molecular chaperones, proteases, and "capacitors of evolution." An overview of these different functions and also of the other kinds of stress proteins is given, with a perspective on how they serve the survival of the cell and the species in the presence of environmental stress factors, and how they can be used in medical applications.

Animals↗
PubMed1999

[Therapeutic monitoring: analytic, pharmacokinetic and clinical aspects].

This paper gives an overview of present aspects and future prospects of therapeutic drug monitoring (TDM). The main aims of TDM are to avoid therapeutic failures due to bad compliance or too low dose of a given drug, as well as adverse or toxic effects due to an excessive dose. The therapeutic drugs frequently monitored depend on the country, but are generally few. For some of these drugs or for others, only patients at risk or belonging to particular sub-populations for a given drug, need TDM. A pre-analytical management is necessary, comprising a correct information of the physician, concerning the nature of the sample to collect and the clinical data necessary to the interpretation, as well as their recording; the control of the sample routing and storing conditions. Nowadays, drug analyses are essentially performed using immunochemical techniques, rapid and easy to operate but limited to a small number of drugs, and chromatographic methods, more specific and adaptable to almost any therapeutic drug and financially and technically more and more accessible. The interpretation of analytical results is a most important part of TDM, which requires knowledge of clinical data, precise collection time, co-administered treatments, and to dispose of a previously defined therapeutic range or target concentration, adapted to the population to which the patient belongs; the limitations of the analytical technique used must also be considered. Clinical pharmacokinetics is a further step in the use of analytical results, allowing the prediction of an efficient dose and administration schedule in one step, using a limited number of blood samples and generally a Bayesian estimation algorithm, readily available through commercial software dedicated to a few drugs in different reference populations. The pharmacokinetic characteristics of different populations and the validation of bayesian estimation have also been published for a number of drugs, sometimes by pharmaceutical companies following phase I and II clinical trials, even taking into account various physiopathological co-variables, but mostly by independent researchers using smaller populations. The efficiency and cost of routine TDM are questionable when it is prescribed with no clinical information or even no indication of administration and sampling times. On the contrary, several studies reported that clinical pharmacokinetics significantly improved patient outcome and were cost-saving, particularly in terms of duration of hospitalisation. The author's opinion is that TDM, in the near future, will be mainly dedicated to drugs used to treat life-threatening diseases, such as anti-HIV, anticancer and immunosuppressive drugs, and maybe also biotechnological peptides or proteins, because of cost considerations. TDM will probably also be used preferentially in target populations, characterised by higher risk or pharmacokinetic variability. Very sensitive, specific and partly automated separative techniques, such as liquid chromatography-tandem mass spectrometry, might become more common than immunochemical methods, owing to a higher flexibility and improved sample throughout. Clinical pharmacokinetics may spread to a larger number of drugs and patients, due to larger reference populations available, taking into account a number of co-variables, computerised data collection and simplified modelisation. Therefore, TDM will mainly be performed in hospitals, with an essentially clinical role for the pharmacists or pharmacologists involved and routine use of recent and efficient technologies for the TDM laboratory technical staff.

Algorithms↗
PubMed2003

Tissue infection and site-specific gene expression in Candida albicans.

C. albicans is able to survive and proliferate in and on a range of different tissues, either as a commensal or as a pathogen. During the different stages and types of infection, the fungal cells need a broad flexibility since each anatomic site has its own set of environmental pressures (Calderone and Fonzi, 2001). The fact that C. albicans possesses gene families encoding known virulence factors may reflect an adaptation to the wide range of environmental pressures that a C. albicans cell is likely to encounter during growth in vivo. In fact, specific members of each family are likely to be differentially expressed in different tissues and at different stages of infection, suggesting that these features have evolved as a consequence of these pressures. It remains to be investigated whether the members of the families have different functions or if they are just proteins with the same function but adapted to the specific demands of each anatomical site. Furthermore, with a few exceptions, the regulatory mechanisms responsible for the differential expression of individual members within gene families are not clear. However, the use of microarrays and other high-throughput technologies will certainly accelerate our knowledge of tissue-specific gene expression in microorganisms and will therefore help to understand why C. albicans is such a successful fungal commensal and pathogen.

Candida albicans↗
PubMed2001

Cognitive-behavioral therapy with gay, lesbian, and bisexual clients.

Cognitive-behavioral therapy (CBT) can be adapted to a wide range of clinical difficulties and presenting problems that face lesbians, gay men, and bisexual persons. The following article presents general guidelines for and two case examples of the use of CBT. The first case is a gay male struggling with social phobia. This case is an example of how to adapt a structured, empirically supported cognitive-behavioral treatment focusing on social phobia to situations that are associated with his sexual orientation. The second is a woman struggling with multiple issues including coming out. This case provides an example of how to add specific cognitive-behavioral techniques to coming-out issues within the context of a more eclectic, longer-term therapy.

Adult↗
PubMed1992

Factors influencing accommodative adaptation.

Previous studies have ascertained that a broad range of parameters have the facility to induce or modify accommodative adaptation, i.e., the post-task shift in dark accommodation (DA) which may be observed after a period of sustained fixation. This paper reviews the optical (i.e., related to a change in the form of the retinal image) and nonoptical (i.e., independent of the composition of the retinal image) stimuli which can influence the degree of adaptation. It is concluded that DA probably represents an aggregate response resulting from multiple inputs whose interactions may be too complex to allow the isolation and measurement of any single nonoptical component. Accordingly, the exact mechanism of accommodative adaptation remains unclear at the present time.

Accommodation, Ocular↗
PubMed1993

Characteristics of periodontal mechanoreceptors supplying cat canine teeth which have sustained orthodontic forces.

The characteristics of these mechanoreceptors were investigated after orthodontic forces had been applied for either 3 days or 12 weeks, and also 8 weeks after the tooth had been moved into a new position and the tissues allowed to recover. Electrophysiological recordings were made from single mechanosensitive units dissected from the inferior alveolar nerve and each was characterized by applying forces to the tooth crown. The characteristics were compared with those of receptors innervating normal teeth. Three days after the onset of tooth movement, the periodontal mechanoreceptors had higher thresholds to forces applied at slow rates and lower discharge frequencies. Twelve weeks after the onset of tooth movement, the mechanoreceptors again had higher force thresholds and lower discharge frequencies but also responded to applied forces over a narrower range of directions and adapted more rapidly than the controls. After the tooth had been moved into a new position and the tissues allowed to recover, the mechanoreceptor characteristics were nearer to normal but they still had raised thresholds to forces applied at slow rates, lower discharge frequencies, and responded to applied forces over a narrower range of directions. It seems likely that the altered receptor characteristics would have resulted from a combination of disorganization of the collagen matrix and direct injury to the nerve terminals.

Action Potentials↗
PubMed2005

Local adaptation to winter conditions in a passerine spreading north: a common-garden approach.

Sedentary passerine birds living in temperate and boreal regions need a high metabolic capacity for thermogenesis to survive winter conditions. As a consequence of the increased thermogenic capacity, basal energetic demands rise at a time when resources and time to acquire them decrease. In a previous study, great tits (Parus major) from two localities in Fennoscandia with contrasting winter conditions differed in their metabolic response to ambient temperature. To investigate the physiological basis underlying interpopulation differences we performed a common-garden experiment to test whether these differences were genetically based. We found basal metabolic rate to be higher in birds originating from transferred eggs from the southern population compared to the ones from the northern population, contrary to the relationship among birds living in their region of origin. Despite previous evidence suggesting that gene flow prevents local adaptation at the northern range limits of a species expanding northward, we found that great tits differ in their reaction norm to winter conditions according to the population of origin.

Adaptation, Physiological↗
PubMed2000

Otolith regularities.

The masses and the area sizes of the otoliths for the utriculus, sacculus and lagena of 15 species of the Black Sea fish are analyzed. Morphometrical otolith regularities are derived and their functional and ecomorphological explanations are suggested. The otolith regularities are summarized in four otolith rules: (1) the masses of the otoliths gradually increase with the fish growth. (2) The mass ratio of the sacculus and utriculus or the sacculus and lagena otoliths does not change with the fish growth. (3) The ratio between the otolith area s and the otolith mass m is described by the exponential equation s=alpham(2/3). (4) The ratio between the otolith and macula sizes does not change with fish growth. Mathematical modeling of the otolith displacement responses to the acoustic and the instant force stimuli is performed. Based on the modeling the functional and ecomorphological explanations of the otolith regularities are suggested: (1) the greater the otolith mass, the higher the acoustic sensitivity at low frequencies and the sharper the frequency-response curve at its maximum. (2) The separation between maxima of the frequency-response curves for the saccular and lagenar otoliths remains virtually constant with the fish growth. (3) The bottom and littoral fish have better auditory capabilities than the pelagic fish. (4) The sensitivity to vestibular stimuli for greater otoliths is higher but the response is slower. The corresponding acceleration resolution for greater otoliths is higher and the range of accelerations in which the otolith organ can operate is narrower. (5) The relative vestibular sensitivities of the utriculus, sacculus and lagena otolith organs remain constant with fish growth. (6) The otolith organs of the bottom and littoral fish are tuned to different accelerations and possess different functional properties. The otolith organs of pelagic fish are adapted to a limited range of accelerations and are less sensitive to low accelerations as compared to the bottom and littoral fish.

Acoustic Stimulation↗
PubMed2006

SGCEdb: a flexible database and web interface integrating experimental results and analysis for structural genomics focusing on Caenorhabditis elegans.

The SGCEdb (http://sgce.cbse.uab.edu) database/interface serves the primary purpose of reporting progress of the Structural Genomics of Caenorhabditis elegans project at the University of Alabama at Birmingham. It stores and analyzes results of experiments ranging from solubility screening arrays to individual protein purification and structure solution. External databases and algorithms are referenced and evaluated for target selection in the human, C.elegans and Pneumocystis carinii genomes. The flexible and reusable design permits tracking of standard and custom experiment types in a scientist-defined sequence. The database coordinates efforts between collaborators and is adaptable to a wide range of biological applications.

Animals↗
PubMed1994

Transfer of short-term adaptation in human saccadic eye movements.

Controversy exists as to the extent to which the saccadic system, adapted in the so-called 'gain-shortening paradigm' for a particular target configuration, transfers the resulting change in saccade metrics to saccades elicited under different circumstances. In order to further assess this problem, we investigated the properties of human saccadic eye movements after visually induced short-term adaptation under a variety of conditions. We observed that saccades both during and after the adaptation did not significantly change their main sequence properties with respect to the pre-adaptation baseline. Saccade velocity profiles remained normal throughout the experiment, and we obtained no evidence that correction saccades were gradually absorbed in the primary saccade. We found that the effect of the short-term adaptation on saccade metrics is not confined to the particular combination of initial eye position and spatial position of the visual target used to induce the adaptation response. Saccades elicited from different initial positions towards targets with the same retinotopic coordinates as in the adaptation phase yield the same level of adaptation. However, our findings indicate that adaptation is confined to a limited range of saccade vectors around the oculocentric coordinates of the adaptation target ('restricted adaptation field'). Smaller and larger saccades are endowed with significantly lower adaptation values. Moreover, two further experiments showed that a retinal stimulus is not a prerequisite for adaptation to express itself: First, in a double-step experiment, we dissociated the retinal stimulus vector from the required oculomotor response. Second, we also investigated the effect of visually induced adaptation on auditory evoked saccades. In both tasks the adaptation was transferred to the required motor response. Based on our findings, we conclude that short-term adaptation is expressed at a multisensory stage, where saccadic eye movements are represented as desired eye displacement vectors (motor error). Possible neurophysiological implications are discussed.

Acoustic Stimulation↗
PubMed2005

Electrokinetic generation of temporally and spatially stable concentration gradients in microchannels.

Generating stable microscale concentration gradients is key to numerous biological and chemical analyses. Microfluidic systems offer the ability to maintain laminar fluid diffusion interfaces ideal for the production of temporally stable concentration gradients. Previous efforts have focused on pressure driven flows and have relied on networks of branching channels to create streams of varying concentrations which can subsequently be combined to form the desired gradients. In this study, we numerically and experimentally demonstrate a novel electrokinetic technique which utilizes applied voltages and surface charge heterogeneity in simpler channel geometries to control and manipulate microscale concentration gradients without the need for parallel lamination. Flow rates ranged from 30 to 460 nl min(-1) for Peclet numbers between 70 and 1100. Spatial stability of 0.6 mm or greater was obtained for a wide range of gradient shapes and magnitudes over lateral dimensions of 400-450 microm. Sensitivity analysis determined that this technique is largely independent of channel depth and species electrophoretic mobility, however channel width and the diffusion coefficient of the analyte are critical. It was concluded that by adjusting applied voltages and/or channel width, this approach to concentration gradient generation can be adapted to a wide range of applications.

Journal Article↗
PubMed2004

Molecular detection of genes responsible for cyanobacterial toxin production in the genera Microcystis, Nodularia, and Cylindrospermopsis.

Cyanobacteria are ubiquitous in the freshwater environment. Their success as a group in a wide range of aquatic habitats has been attributed to their unique physiological characteristics and their high adaptive ability over a wide range of environmental conditions. They are capable of reaching very high biomass levels, often dominating the other aquatic biota, and under some circumstances can accumulate near the water surface, producing scums. Such cyanobacterial "blooms" are of particular concern in reservoirs used to supply potable water. Dense aggregations of cyanobacterial cells may block water filters, and many species produce compounds that affect the taste and odor of water supplies. Of greatest concern, however, is the potential of many bloom-forming cyanobacteria to produce a wide range of toxic substances. These natural compounds, known as cyanotoxins, are chemically diverse and are usually either neuro- or hepatotoxic in pathology.

Alkaloids↗
PubMed1995

Virus and host-specific adaptations in the BL1 and BR1 genes of bipartite geminiviruses.

The host range of individual geminiviruses may be quite narrow, and closely related viruses can exhibit distinct host adaptations. Two such bipartite geminiviruses are bean golden mosaic virus (GBMV) and tomato golden mosaic virus (TGMV). In both, the BL1 and BR1 genes are required for the spread of virus infection in plants. We have investigated the contributions of BL1 and BR1 to host-specific phenotypes of BGMV and TGMV by constructing hybrid viruses in which these coding regions were exchanged. Hybrids were assayed on bean, a good host for BGMV, and Nicotiana benthamiana, a good host for TGMV. A BGMV hybrid having TGMV BL1 and BR1 efficiently infected beans, but elicited attenuated symptoms. In N. benthamiana, this hybrid had slightly increased virulence and DNA accumulation relative to wild-type BGMV. A TGMV hybrid having BGMV BL1 and BR1 was virulent in N. benthamiana, but elicited attenuated symptoms. However, this hybrid exhibited no gain of function in beans relative to wild-type TGMV. Hybrid viruses with TGMV BL1 and BGMV BR1 had severely defective phenotypes in either viral or host background. Although exchanging BL1 and BR1 between BGMV and TGMV did not change host range, some host adaptation of these genes is suggested. However, virus-specific compatibility between BL1 and BR1 is of more importance for viability. Thus, these gene products may act in concert to potentiate virus movement.

Adaptation, Physiological↗
PubMed2000

The development of scotopic sensitivity.

UNLABELLED: PURPOSE. Test the hypothesis that the developmental increases in rod photoreceptor sensitivity and rod-mediated visual sensitivity at 10 degrees, 20 degrees , and 30 degrees eccentric are concurrent. It is known that maturation of the parafoveal (10 degrees eccentric) rod outer segments and visual sensitivity is delayed compared to that at 30 degrees eccentric. METHODS: Rod isolated electroretinographic (ERG) responses to full-field stimuli were obtained from dark-adapted subjects (n = 71), ranging in age from early infancy through middle age. Rod photoreceptor sensitivity was calculated by fitting a model of the activation of phototransduction to the a-wave response. Rod driven b-wave sensitivity was calculated from stimulus-response functions. A logistic growth model was used to summarize the developmental increases in sensitivity of the rod photoreceptors and the b-wave. Previously reported dark-adapted, rod-mediated visual sensitivities at 10 degrees , 20 degrees, and 30 degrees eccentric, obtained using preferential looking procedures, were reanalyzed using the logistic growth model. RESULTS: The logistic growth model accounted for 57% to 85% of the variance of each sensitivity parameter with age in normal subjects. The shape of the growth curve and the age at which sensitivity reaches 50% of the adult value is similar (10.0-13.5 weeks) for the rods, the b-wave, and peripheral visual sensitivity, but is significantly older, 19.5 weeks, for rod-mediated parafoveal visual sensitivity. CONCLUSIONS: Rod photoreceptor sensitivity and peripheral, rod-mediated visual sensitivity develop concurrently. A parsimonious explanation is that rod photoreceptor sensitivity determines dark-adapted, rod-mediated visual sensitivity during development.

Adolescent↗