Cerebellar interneurons control fear memory consolidation via learning-induced HCN plasticity

1. Download : Download high-res image (160KB)
2. Download : Download full-size image

     

Resource regulation of an invasive tree by a classical biological control agent

The invasive tree Melaleuca quinquenervia experienced substantial declines in growth and reproduction in response to chronic herbivory by the defoliating weevil Oxyops vitiosa. Plants subjected to unrestricted defoliation replaced leaves that were more suitable for feeding by the next generation, a process envisioned by the Resource Regulation Hypothesis which posits that attack by one generation increases the amount of the preferred host resources for the next, resulting in a positive feedback loop for the herbivore. The production of juvenile replacement leaves stimulated additional bouts of oviposition and feeding by O. vitiosa, which ultimately produced positive effects for the herbivore with negative consequences for the plant. The addition of water resources to the plant prolonged the positive feedback loop such that more than twice as many insects were produced on irrigated versus non-irrigated trees. In a more simple, reassembled food web on M. quinquenervia, the lack of biotic constraints like parasitoids may have prevented the earlier termination of the feedback loop and thus increased the impact of the biological control agent on the target. The overall effectiveness of this classical biological control program can be attributed, in part, to the phenomenon of the target plant’s induced susceptible response to a herbivore.     

Perception,regulation, and fitness effects of pollen phytosterols in the bumble bee,Bombus terrestris

Premise

Many flowering plants depend on insects for pollination and thus attract pollinators by offering rewards, mostly nectar and pollen. Bee pollinators rely on pollen as their main nutrient source. Pollen provides all essential micro- and macronutrients including substances that cannot be synthesized by bees themselves, such as sterols, which bees need for processes such as hormone production. Variations in sterol concentrations may consequently affect bee health and reproductive fitness. We therefore hypothesized that (1) these variations in pollen sterols affect longevity and reproduction in bumble bees and (2) can thus be perceived via the bees' antennae before consumption.

Methods

We studied the effect of sterols on longevity and reproduction of Bombus terrestris workers in feeding experiments and investigated sterol perception using chemotactile proboscis extension response (PER) conditioning.

Results

Workers could perceive several sterols (cholesterol, cholestenone, desmosterol, stigmasterol, β-sitosterol) via their antennae but not differentiate between them. However, when sterols were presented in pollen, and not as a single compound, the bees were unable to differentiate between pollen differing in sterol content. Additionally, different sterol concentrations in pollen neither affected pollen consumption nor brood development or worker longevity.

Conclusions

Since we used both natural concentrations and concentrations higher than those found in pollen, our results indicate that bumble bees may not need to pay specific attention to pollen sterol content beyond a specific threshold. Naturally encountered concentrations might fully support their sterol requirements and higher concentrations do not seem to have negative effects.

     

A Quantitative Study of the Ca2+/Calmodulin Sensitivity of Adenylyl Cyclase in Aplysia, Drosophila, and Rat

Studies in Aplysia and Drosophila have suggested that Ca2+/calmodulin-sensitive adenylyl cyclase may act as a site of convergence for the cellular representations of the conditioned stimulus (Ca2+ influx) and unconditioned stimulus (facilitatory transmitter) during elementary associative learning. This hypothesis predicts that the rise in intracellular free Ca2+ concentration produced by spike activity during the conditioned stimulus will cause an increase in the activity of adenylyl cyclase. However, published values for the Ca2+ sensitivity of Ca2+/calmodulin-sensitive adenylyl cyclase in mammals and in Drosophila vary widely. The difficulty in evaluating whether adenylyl cyclase would be activated by physiological elevations in intracellular Ca2+ levels is in part a consequence of the use of Ca2+/EGTA buffers, which are prone to several types of errors. Using a procedure that minimizes these errors, we have quantified the Ca2+ sensitivity of adenylyl cyclase in membranes from Aplysia, Drosophila, and rat brain with purified species-specific calmodulins. In all three species, adenylyl cyclase was activated by an increase in free Ca2+ concentration in the range caused by spike activity. Ca2+ sensitivity was dependent on both calmodulin concentration and Mg2+ concentration. Mg2+ raised the threshold for adenylyl cyclase activation by Ca2+ but also acted synergistically with Ca2+ to activate maximally adenylyl cyclase.     

Sex chromosome complement influences operant responding for a palatable food in mice

The procurement and consumption of palatable, calorie‐dense foods is influenced by the nutritional and hedonic value of foods. Although many factors can influence the control over behavior by foods rich in sugar and fat, emerging evidence indicates that biological sex may play a particularly crucial role in the types of foods individuals seek out, as well as the level of motivation individuals will exert to obtain those foods. However, a systematic investigation of food‐seeking and consumption that disentangles the effects of the major sex‐biasing factors, including sex chromosome complement and organizational and activational effects of sex hormones, has yet to be conducted. Using the four core genotypes mouse model system, we separated and quantified the effects of sex chromosome complement and gonadal sex on consumption of and motivation to obtain a highly palatable solution [sweetened condensed milk (SCM)]. Gonadectomized mice with an XY sex chromosome complement, compared with those with two X chromosomes, independent of gonadal sex, appeared to be more sensitive to the reward value of the SCM solution and were more motivated to expend effort to obtain it, as evidenced by their dramatically greater expended effort in an instrumental task with progressively larger response‐to‐reward ratios. Gonadal sex independently affected free consumption of the solution but not motivation to obtain it. These data indicate that gonadal and chromosomal sex effects independently influence reward‐related behaviors, contributing to sexually dimorphic patterns of behavior related to the pursuit and consumption of rewards.     

Flavour preference acquired via a beverage-induced conditioning and its transposition to solid food: Sucrose but not maltodextrin or saccharin induced significant flavour preferences in pigs

When exposed to novel food during food transitions, growing pigs often elicit a neophobic response that is responsible for decreased food consumption. Flavour preference conditioning may represent an interesting way to reduce neophobia and improve food intake in growing pigs. The present series of experiments investigated the pig's conditioned preference for a flavoured beverage added with different carbohydrates and sweeteners and the possible transition of those beverage-induced preferences to flavoured solid food. In Experiment 1A, nine juvenile pigs were given three two-day conditioning sessions: they received a flavoured beverage added with 1.125% sucrose (F + S_1.125) and a second flavoured beverage with no additive (F−). In Experiment 1B, nine juvenile pigs were given six two-day conditioning sessions: they received a flavoured beverage added with 10% sucrose (F + S₁₀) and a second flavoured beverage with no additive (F−). In subsequent two-choice drinking tests, the pigs exhibited no clear-cut preference for F + S_1.125, whereas F + S₁₀ was preferred compared to F− (P < 0.05) but only during the first subsequent two-choice drinking tests, suggesting that pigs developed a short-term preference for the flavour previously paired with 10% but not 1.125% sucrose. The Experiment 2 was conducted to assess the independent effects of visceral (caloric intake) and gustative (sweet taste) reinforcement in flavour preference conditioning. Nine juvenile pigs were subjected to four three-day conditioning sessions: they received flavoured beverages added with 2.25% maltodextrin (F + m, caloric intake), 0.37% saccharin (F + s, sweet taste), or no additive (F−). During further two-choice drinking tests, no clear-cut preference emerged, but the consumption of F + m was 107% and 35% higher than that of F− and F + s, respectively. Despite pigs exhibited some conditioned flavour preferences during two-choice drinking tests in Experiments 1B and 2, no clear-cut preference was observed during two-choice feeding tests with flavoured solid food. Overall, these findings highlight the importance of the combination and/or synergy between gustative and visceral reinforcements for conditioned flavour preference and suggest that a visceral reinforcement via maltodextrin might be sufficient to condition such a preference. Moreover, the absence of clear-cut preference during two-choice feeding test illustrates the difficulty to transpose a flavour preference acquired via a sweet beverage to solid food. Further studies are needed to investigate the failure of saccharin-conditioned preference in pigs.     

Genetic and environmental influences on one-trial conditioned context aversion in mice

Anticipatory nausea (AN) is caused by an association between contextual cues and the experience of nausea (the side effects of chemotherapy or radiation treatment) and it develops predominantly in female patients undergoing chemotherapy. Preclinical studies in rodents show that the administration of an illness-inducing agent in the presence of novel contextual cues can cause conditioned context aversion (CCA) and this has been proposed to model AN. The literature also suggests that brief pre-exposure to a novel context prior to shock delivery is critical in the development of contextual fear conditioning in rodents (a phenomenon known as Immediate Shock Deficit), but this has not been assessed in CCA. The aim of present study was to develop a CCA paradigm to assess this in outbred (CD1) and inbred (C57BL/6J) mice and evaluate potential sex differences. The results revealed that a single conditioning trial in which a distinctive context was paired with LiCl-induced illness was sufficient to elicit a conditioned response in both female and male CD1 outbred mice, but not in C57BL/6J inbred mice. In addition, CCA was facilitated when animals had prior experience with the context. Finally, outbred female mice showed longer and more robust retention of CCA than male mice, which parallels clinical findings. The results indicate the importance of using CD1 outbred mice as an animal model of AN as well as examining sex differences in the CCA paradigm. Similar findings in humans encourage the future use of this novel CCA preclinical mouse model.     

Conditioning of a glass surface for the outgrowth of insect epidermis (Leucophaea maderae,blattaria)

Summary A method has been developed by which the surface of cover slips can be conditioned for rapid outgrowth of the epidermis of cockroach legs. The method permits in vitro observation of wound-healing processes. The conditioning is brought about by materials given off by the hemocytes, possibly materials from the granules of plasmatocytes which are extruded during the flattening of the cells. Coating of the glass surface with other proteins (including cockroach hemolymph serum) and carbohydrates was completely ineffective. Dedicated to my teacher, Dr. Gerhard Krause, from whom I received the decisive stimulation to start tissue culture work, on the occasion of his 70th birthday. The work has been supported by the Deutsche Forschungsgemeinschaft (Grant Bo 453)