Aversive reinforcement improves visual discrimination learning in free-flying honeybees

Background

Learning and perception of visual stimuli by free-flying honeybees has been shown to vary dramatically depending on the way insects are trained. Fine color discrimination is achieved when both a target and a distractor are present during training (differential conditioning), whilst if the same target is learnt in isolation (absolute conditioning), discrimination is coarse and limited to perceptually dissimilar alternatives. Another way to potentially enhance discrimination is to increase the penalty associated with the distractor. Here we studied whether coupling the distractor with a highly concentrated quinine solution improves color discrimination of both similar and dissimilar colors by free-flying honeybees. As we assumed that quinine acts as an aversive stimulus, we analyzed whether aversion, if any, is based on an aversive sensory input at the gustatory level or on a post-ingestional malaise following quinine feeding.

Methodology/Principal Findings

We show that the presence of a highly concentrated quinine solution (60 mM) acts as an aversive reinforcer promoting rejection of the target associated with it, and improving discrimination of perceptually similar stimuli but not of dissimilar stimuli. Free-flying bees did not use remote cues to detect the presence of quinine solution; the aversive effect exerted by this substance was mediated via a gustatory input, i.e. via a distasteful sensory experience, rather than via a post-ingestional malaise.

Conclusion

The present study supports the hypothesis that aversion conditioning is important for understanding how and what animals perceive and learn. By using this form of conditioning coupled with appetitive conditioning in the framework of a differential conditioning procedure, it is possible to uncover discrimination capabilities that may remain otherwise unsuspected. We show, therefore, that visual discrimination is not an absolute phenomenon but can be modulated by experience.     

Looking for trouble: a search for developmental defects of the hypothalamus

The hypothalamus is a critical integrator of several homeostatic processes that are required for the survival of vertebrates. Disruption of the development of the hypothalamus thus has the potential of perturbing important physiological processes with lifelong consequences. We review current knowledge about how cell types are specified and circuits are formed within the developing hypothalamus. We emphasize the potential clinical impact of the perturbations of these pathways using the regulation of energy balance as a model. We predict that disruption of hypothalamic development is a common, previously unsuspected cause of disorders of homeostatic processes such as obesity and high blood pressure.     

Perception of Affordance during Short-Term Exposure to Weightlessness in Parabolic Flight

We investigated the role of the visual eye-height (VEH) in the perception of affordance during short-term exposure to weightlessness. Sixteen participants were tested during parabolic flight (0g) and on the ground (1g). Participants looked at a laptop showing a room in which a doorway-like aperture was presented. They were asked to adjust the opening of the virtual doorway until it was perceived to be just wide enough to pass through (i.e., the critical aperture). We manipulated VEH by raising the level of the floor in the visual room by 25 cm. The results showed effects of VEH and of gravity on the perceived critical aperture. When VEH was reduced (i.e., when the floor was raised), the critical aperture diminished, suggesting that widths relative to the body were perceived to be larger. The critical aperture was also lower in 0g, for a given VEH, suggesting that participants perceived apertures to be wider or themselves to be smaller in weightlessness, as compared to normal gravity. However, weightlessness also had an effect on the subjective level of the eyes projected into the visual scene. Thus, setting the critical aperture as a fixed percentage of the subjective visual eye-height remains a viable hypothesis to explain how human observers judge visual scenes in terms of potential for action or “affordances”.     

The immune status of Schwann cells: what is the role of the P2X7 receptor?

The peripheral nervous system (PNS) displays structural barriers and a lack of lymphatic drainage which strongly limit the access of molecules and cells from the immune system. In addition, the PNS has the ability to set up some specific mechanisms of immune protection to limit the pathogenicity of inflammation processes following insults by pathogens or inflammatory autoimmune diseases like the Guillain-Barré syndrome. Schwann cells are among the most prominent cells which can display immune capabilities in the PNS. Numerous in vitro studies have shown that Schwann cells were indeed able to display a large repertoire of properties, ranging from the participation to antigen presentation, to secretion of pro- and anti-inflammatory cytokines, chemokines and neurotrophic factors. In vivo studies have confirmed the immune capabilities of Schwann cells. The aim of this review is to present how Schwann cells can participate to the initiation, the regulation and the termination of the immune response in the light of the recent discovery of the Schwann cell expression of purinergic P2X7 receptors.     

Two promising alkaline β-glucosidases isolated by functional metagenomics from agricultural soil,including one showing high tolerance towards harsh detergents,oxidants and glucose

New β-glucosidase activities were identified by screening metagenomic libraries constructed with DNA isolated from the topsoil of a winter wheat field. Two of the corresponding proteins, displaying an unusual preference for alkaline conditions, were selected for purification by Ni-NTA chromatography. AS-Esc6, a 762-amino-acid enzyme belonging to glycoside hydrolase family 3, proved to be a mesophilic aryl-β-glucosidase with maximal activity around pH 8 and 40 °C. A similar pH optimum was found for AS-Esc10, a 475-amino-acid GH1-family enzyme, but this enzyme remained significantly active across a wider pH range and was also markedly more stable than AS-Esc6 at pH greater than 10. AS-Esc10 was found to degrade cellobiose and diverse aryl glycosides, with an optimal temperature of 60 °C and good stability up to 50 °C. Unlike AS-Esc6, which showed a classically low inhibitory constant for glucose (14 mM), AS-Esc10 showed enhanced activity in the presence of molar concentrations of glucose. AS-Esc10 was highly tolerant to hydrogen peroxide and also to sodium dodecyl sulfate, this being indicative of kinetic stability. This unique combination of properties makes AS-Esc10 a particularly promising candidate whose potential in biotechnological applications is worth exploring further.     

Effect of breeding performance on the distribution and activity budgets of a predominantly resident population of black‐browed albatrosses

Pelagic seabirds breeding at high latitudes generally split their annual cycle between reproduction, migration, and wintering. During the breeding season, they are constrained in their foraging range due to reproduction while during winter months, and they often undertake long‐distance migrations. Black‐browed albatrosses (Thalassarche melanophris) nesting in the Falkland archipelago remain within 700 km from their breeding colonies all year‐round and can therefore be considered as resident. Accordingly, at‐sea activity patterns are expected to be adjusted to the absence of migration. Likewise, breeding performance is expected to affect foraging, flying, and floating activities, as failed individuals are relieved from reproduction earlier than successful ones. Using geolocators coupled with a saltwater immersion sensor, we detailed the spatial distribution and temporal dynamics of at‐sea activity budgets of successful and failed breeding black‐browed albatrosses nesting in New Island, Falklands archipelago, over the breeding and subsequent nonbreeding season. The 90% monthly kernel distribution of failed and successful breeders suggested no spatial segregation. Both groups followed the same dynamics of foraging effort both during daylight and darkness all year, except during chick‐rearing, when successful breeders foraged more intensively. Failed and successful breeders started decreasing flying activities during daylight at the same time, 2–3 weeks after hatching period, but failed breeders reached their maximum floating activity during late chick‐rearing, 2 months before successful breeders. Moon cycle had a significant effect on activity budgets during darkness, with individuals generally more active during full moon. Our results highlight that successful breeders buffer potential reproductive costs during the nonbreeding season, and this provides a better understanding of how individuals adjust their spatial distribution and activity budgets according to their breeding performance in absence of migration.     

Overlapping enhancer/promoter and transcriptional termination signals in the lentiviral long terminal repeat

We have studied the effects associated with two single amino acid substitution mutations in HIV-1 capsid (CA), the E98A and E187G. Both amino acids are well conserved among all major HIV-1 subtypes. HIV-1 infectivity is critically dependent on proper CA cone formation and mutations in CA are lethal when they inhibit CA assembly by destabilizing the intra and/or inter molecular CA contacts, which ultimately abrogate viral replication. Glu98, which is located on a surface of a flexible cyclophilin A binding loop is not involved in any intra-molecular contacts with other CA residues. In contrast, Glu187 has extensive intra-molecular contacts with eight other CA residues. Additionally, Glu187 has been shown to form a salt-bridge with Arg18 of another N -terminal CA monomer in a N-C dimer. However, despite proper virus release, glycoprotein incorporation and Gag processing, electron microscopy analysis revealed that, in contrast to the E187G mutant, only the E98A particles had aberrant core morphology that resulted in loss of infectivity.