Transitional choice behavior in concurrent-chain schedules

The choice responses of four pigeons were examined in 20 periods of transition in a concurrent-chain procedure with variable-interval schedules as initial links and fixed delays to reinforcement as terminal links. In some conditions, the delays to reinforcement were different for the two terminal links, and changes in preference were recorded after the delays for the two response keys were switched. In other conditions, the reinforcer delays were equal for the two keys, but which key delivered 80% of the reinforcers was periodically switched. Choice proportions changed more quickly after a switch in reinforcement percentages than after a switch in the delays, thereby contradicting the hypothesis that faster changes would occur when the switch in conditions was easier to discriminate. Analyses of response sequences showed that the effects of individual reinforcers were larger and lasted longer in conditions with changing reinforcement percentages than in conditions with changing terminal-link delays. Rates of change in choice behavior do not appear to be limited by the unpredictability of variable reinforcement schedules, because the changes in behavior were slow and gradual even when there was a large and sudden change in reinforcer delays.     

Varying initial-link and terminal-link durations in concurrent-chains schedules: a comparison of three models

In Experiment 1, pigeons responded on concurrent-chains schedules with equal variable-interval schedules as initial links and fixed delays to food as terminal links. One terminal-link delay was always three times as long as the other. As terminal-link delays increased, response percentages on the key with the shorter terminal link increased according to a curvilinear function. This result supported the predictions of the hyperbolic value-added model and the contextual-choice theory but not delay-reduction theory. In Experiment 2, the terminal links were always delays of 2s and 12s, followed by food, and the durations of the initial links varied across conditions. As initial-link durations increased, pigeons' response percentages on the key with the shorter terminal link decreased, but toward an asymptote greater than 50%, indicating a continued preference for the shorter terminal link with very long initial links. This result was more consistent with the predictions of the hyperbolic-value added model than with those of the contextual-choice model or of delay-reduction theory.     

Parrotfish recruitment revisited: a key role for sea surface currents

Despite considerable attention to the role of parrotfish assemblages in maintaining coral reef ecosystem integrity, little is known about the factors affecting parrotfish settlement, which could play an important role in structuring parrotfish assemblages. Here, I expand on a previous study that sought to identify environmental correlates of the temporal patterns of recruitment of Sparisoma parrotfishes onto standardized settlement units sampled at 52 consecutive 10-day intervals over an uninterrupted 17-month period on the west coast of Barbados (W.I.). By (1) including previously unavailable satellite-derived island-wide current speed data in the analyses and (2) using a more flexible (non-linear) analytical framework, the re-analysis increased the variance explained from 24% to 74%. Furthermore, island-wide current speed had stronger predictive power than all of the previously identified environmental correlates of Sparisoma recruitment, i.e. sea surface temperature and chlorophyll a concentration, and lunar phase, underscoring a dominant role for large-scale, transport-related physical processes in driving parrotfish settlement. Relationships between Sparisoma recruitment and the environmental correlates were better explained as non-linear functions, with a hump-shaped relationship for current speed. Most variability in current speed reflected external forcing due to the passage through Barbados of a large, slow-moving, low-salinity intrusion of South American riverine origin. Considering the high recruitment variance explained and that satellite-derived data on key environmental correlates are publicly available, prediction of temporal patterns of parrotfish settlement in Barbados might be more feasible than previously expected.     

The mobile receptor hypothesis revisited: a mechanistic role for hormone receptor lateral mobility in signal transduction

Recent application of the technique of fluorescence photobleaching recovery to direct measurement of the lateral mobility of plasma membrane-localized hormone receptors has shed new light on the role of receptor lateral mobility in signal transduction. Receptor for insulin and EGF have been known for some time to be largely immobile at physiological temperatures. This presumably relates to their signal transduction mechanism, which appears to require intermolecular autophosphorylation (receptor aggregation) for activation. In contrast, G-protein coupled receptors must interact with other membrane components to bring about signal transduction and it is interesting in this regard that the adenylate cyclase (AC) activating vasopressiin V₂-receptor is highly laterally mobile at 37°C. It has recently been possible to reversibly modulate the V₂-receptor mobile fraction (F) to largely varuing extents and to demonstrate thereby a direct effect on the maximal rate of in vivo cAMP production at 37°C in response to vasopressin. A direct correlation between f and maximal cAMP production indicates that f may be a key parameter in hormone signal transduction in vivo, especially at sub-K_D (physiological) hormone concentrations, with mobile receptors being required to effect G-protein activation.     

The ecological role of chemical stimuli for the zooplankton: predator-induced morphology in Daphnia

Summary Numerous adaptive predator-induced responses occurred when eight clones representing seven Daphnia (Crustacea: Cladocera) species were tested against three common predators: fourth instar larval phantom midge Chaoborus americanus, adult backswimmer Notonecta undulata, and small sunfish Lepomis macrochirus. The predators were confined within small mesh bags, suggesting that the signal for induction is chemical. The induced responses included longer tail spines, longer heads, smaller bodies, increased egg clutches, and decreased lipid reserves. Each Daphnia species responded to each of the three predators in a unique manner. Induced responses in the above characters showed no significant association. The induced morphological changes are generally consistent with current theories of what is an adaptive response for the various sizes of Daphnia exposed to tactile and visual predators. The abundance of induced responses in these experiments suggests that predator-induced responses are a widespread and ecologically important phenomenon of the freshwater zooplankton.     

The role of Arginine 38 in horseradish peroxidase enzyme revisited: A computational investigation

Molecular dynamics simulations on hydrogen peroxide complex with wild-type (WT) and Arg38Leu mutated (R38L) Horseradish Peroxidase (HRP) were carried out over nanoseconds timescale in water solution at 300 K. Comparison of the results provides interesting insights about the role of highly conserved Arg38 and His42 residues in the chemical features of HRP, underlying its biological activity which initiates with Compound0 (Cpd0). In the WT-HRP enzyme current molecular dynamics simulations show, for the first time, that Arg38 residue: i) prevents the entrance of water inside the reaction cavity, hence providing a hydrophobic reactive scenario, ii) it maintains the distance between His42 and heme–H₂O₂ complex suitable for the occurrence of proton transfer reaction leading, thereafter, to heme–H₂O₂ disruption according to Poulos-Kraut mechanism. On the other hand, R38L mutant can be considered as a “wet enzyme” where the presence of water solvent molecules in the heme reaction pocket, unfavoring the initial heme–H₂O₂ complex formation, decreases the catalytic efficiency in agreement with experimental kinetics measurements. Furthermore, we note that Arg38Leu mutation pushes the His42 residue far from the heme–H₂O₂ complex, making unlikely a direct proton transfer and suggesting that, in the mutant, a solvent water molecule could be involved in the first step of the Poulos-Kraut mechanism.     

The Gomphidiaceae revisited: a worldwide perspective

Recent studies in the Gomphidiaceae have clearly delimited two genera, Gomphidius and Chroogomphus, both of which are mycorrhizal associates only with the Pinaceae. Ecological studies show Chroogomphus as a mycorrhizal associate of Pinus (Pinoideae), while Gomphidius is associated with the other three gymnosperm subfamilies Piceoideae, Lariceideae, and Abietoideae. The genus Brauniellula, which is based upon the secotioid habit and the presence of orthotropic, statismosporic basidia, falls within Chroogomphus in a clade with ballistosporic species. Brauniellula is, therefore, placed in synonymy with Chroogomphus. Molecular and morphological studies of new material from Nepal, Russia, Korea, and the United States have delimited two new species in each genus. The morphologically identical Chroogomphus rutilus clades are separate, one European and one North American. The relationship of the two genera in the Gomphidiaceae, with their mycorrhizal associates, is related to similar host relationships within other genera in the Suilloid Clade.     

Analysis of vaccine's schedules using models

We present a further, yet important, step in applying Catania Mouse Model & simulator (SimTriplex) of immune system response to vaccination. In particular we show that, as immune response can induce toxicity, one can calibrate the vaccine administrations in such a way to avoid toxicity effects, keeping immunoprevention from cancer. This result increases the model's potential applications.     

The mobile receptor hypothesis revisited: a mechanistic role for hormone receptor lateral mobility in signal transduction.

Recent application of the technique of fluorescence photobleaching recovery to direct measurement of the lateral mobility of plasma membrane-localized hormone receptors has shed new light on the role of receptor lateral mobility in signal transduction. Receptors for insulin and EGF have been known for some time to be largely immobile at physiological temperatures. This presumably relates to their signal transduction mechanism, which appears to require intermolecular autophosphorylation (receptor aggregation) for activation. In contrast, G-protein coupled receptors must interact with other membrane components to bring about signal transduction, and it is interesting in this regard that the adenylate cyclase (AC) activating vasopressin V2-receptor is highly laterally mobile at 37 degrees C. It has recently been possible to reversibly modulate the V2-receptor mobile fraction (f) to largely varying extents, and to demonstrate thereby a direct effect on the maximal rate of in vivo cAMP production at 37 degrees C in response to vasopressin. A direct correlation between f and maximal cAMP production indicates that f may be a key parameter in hormone signal transduction in vivo, especially at sub-KD (physiological) hormone concentrations, with mobile receptors being required to effect G-protein activation.     

The ins and outs of reticulocyte maturation revisited: The role of autophagy in sickle cell disease

Autophagy plays an important role in the removal of membrane bound organelles during the last stage of erythropoiesis as the enucleate reticulocyte matures into the erythrocyte. Autophagic vesicles are expelled from the reticulocyte as intact, inside-out, phosphatidylserine (PS) decorated vesicles and are subsequently removed during splenic passage. Failure to remove these vesicles causes the elevation in PS exposed red cells in Sickle Cell Disease.     

Glutathione revisited: a vital function in iron metabolism and ancillary role in thiol-redox control

Glutathione contributes to thiol-redox control and to extra-mitochondrial iron-sulphur cluster (ISC) maturation. To determine the physiological importance of these functions and sort out those that account for the GSH requirement for viability, we performed a comprehensive analysis of yeast cells depleted of or containing toxic levels of GSH. Both conditions triggered an intense iron starvation-like response and impaired the activity of extra-mitochondrial ISC enzymes but did not impact thiol-redox maintenance, except for high glutathione levels that altered oxidative protein folding in the endoplasmic reticulum. While iron partially rescued the ISC maturation and growth defects of GSH-depleted cells, genetic experiments indicated that unlike thioredoxin, glutathione could not support by itself the thiol-redox duties of the cell. We propose that glutathione is essential by its requirement in ISC assembly, but only serves as a thioredoxin backup in cytosolic thiol-redox maintenance. Glutathione-high physiological levels are thus meant to insulate its cytosolic function in iron metabolism from variations of its concentration during redox stresses, a model challenging the traditional view of it as prime actor in thiol-redox control.     

The role of chemotactile stimuli in the oviposition preferences of Colias butterflies

Summary The legume foodplants of Colias butterflies possess specific chemical components which stimulate oviposition in females of the genus. Different legumes provide different degrees of stimulation, as demonstrated by close correlation between field observations and laboratory experiments with a new behavioral assay. Several generalizations emerge from this study. 1) Chemical preferences for various foodplants are under genetic control in C. meadii, and are at least partly independent of an individual's previous exposure to different legumes. 2) In some cases, chemical cues alone do not allow females to discriminate between species. Long-range search cues may be used to enhance discrimination in such instances. 3) Lupinus, a legume which is not usually utilized by Colias, stimulates oviposition in the laboratory, indicating its chemical affinity with other Leguminosae. The behavioral assay described should prove useful for the future identification of specific oviposition stimulants and deterrents. It is stressed, however, that chemotactile cues are involved only in the final step of oviposition, and that understanding foodplant choice in nature will require in-depth investigation into the mechanics of individual search processes.     

The role of hallucinogenic drugs and sensory stimuli in Peruvian ritual healing

On Peru's north coast, curanderos perform night-long curing ceremonies in which the mescaline-bearing cactus San Pedro is used. The concept of autonomic nervous system tuning is presented as the best explanation for the overall physiological effect of the ritual. An assessment of the possible therapeutic impact of this condition is provided. Organic response and symbolic message are seen to resonate in the purificatory connotations of the ritual.     

Switching neuronal state: optimal stimuli revealed using a stochastically-seeded gradient algorithm

Inducing a switch in neuronal state using energy optimal stimuli is relevant to a variety of problems in neuroscience. Analytical techniques from optimal control theory can identify such stimuli; however, solutions to the optimization problem using indirect variational approaches can be elusive in models that describe neuronal behavior. Here we develop and apply a direct gradient-based optimization algorithm to find stimulus waveforms that elicit a change in neuronal state while minimizing energy usage. We analyze standard models of neuronal behavior, the Hodgkin-Huxley and FitzHugh-Nagumo models, to show that the gradient-based algorithm: 1) enables automated exploration of a wide solution space, using stochastically generated initial waveforms that converge to multiple locally optimal solutions; and 2) finds optimal stimulus waveforms that achieve a physiological outcome condition, without a priori knowledge of the optimal terminal condition of all state variables. Analysis of biological systems using stochastically-seeded gradient methods can reveal salient dynamical mechanisms underlying the optimal control of system behavior. The gradient algorithm may also have practical applications in future work, for example, finding energy optimal waveforms for therapeutic neural stimulation that minimizes power usage and diminishes off-target effects and damage to neighboring tissue.     

Ionic selectivity revisited: The role of kinetic and equilibrium processes in ion permeation through channels

The Journal of Membrane Biology -     

The role of auditory stimuli in the courtship of Drosophila melanogaster

Simulated courtship song of male Drosophila melanogaster was played to males or females of this species. Upon receiving the song males increase their locomotor activity and start courting each other, whereas females reduce their locomotor activity. In wingless males the locomotor activity difference between the silent control and the experimental sound situation is much larger than in winged males, due to the inactivity of wingless males in the control situation. Males which had been kept singly up to the time of the experiment exhibit higher locomotor and sexual activity than group housed males. A second component of the male courtship song ‘sine song’ is described, together with experiments which investigate the sensory basis of the effect male courtship song has on males.     

FREAD revisited: Accurate loop structure prediction using a database search algorithm

Loops are the most variable regions of protein structure and are, in general, the least accurately predicted. Their prediction has been approached in two ways, ab initio and database search. In recent years, it has been thought that ab initio methods are more powerful. In light of the continued rapid expansion in the number of known protein structures, we have re‐evaluated FREAD, a database search method and demonstrate that the power of database search methods may have been underestimated. We found that sequence similarity as quantified by environment specific substitution scores can be used to significantly improve prediction. In fact, FREAD performs appreciably better for an identifiable subset of loops (two thirds of shorter loops and half of the longer loops tested) than the ab initio methods of MODELLER, PLOP, and RAPPER. Within this subset, FREAD's predictive ability is length independent, in general, producing results within 2Å RMSD, compared to an average of over 10Å for loop length 20 for any of the other tested methods. We also benchmarked the prediction protocols on a set of 212 loops from the model structures in CASP 7 and 8. An extended version of FREAD is able to make predictions for 127 of these, it gives the best prediction of the methods tested in 61 of these cases. In examining FREAD's ability to predict in the model environment, we found that whole structure quality did not affect the quality of loop predictions. Proteins 2010. © 2009 Wiley‐Liss, Inc.