Acute and repeated restraint differentially activate orexigenic pathways in the rat hypothalamus

Stress and obesity are highly prevalent conditions, and the mechanisms through which stress affects food intake are complex. In the present study, stress-induced activation in neuropeptide systems controlling ingestive behavior was determined. Adult male rats were exposed to acute (30 min/d × 1 d) or repeated (30 min/d × 14 d) restraint stress, followed by transcardial perfusion 2 h after the termination of the stress exposure. Brain tissues were harvested, and 30 μm sections through the hypothalamus were immunohistochemically stained for Fos protein, which was then co-localized within neurons staining positively for the type 4 melanocortin receptor (MC4R), the glucagon-like peptide-1 receptor (GLP1R), or agouti-related peptide (AgRP). Cell counts were performed in the paraventricular (PVH), arcuate (ARC) and ventromedial (VMH) hypothalamic nuclei and in the lateral hypothalamic area (LHA). Fos was significantly increased in all regions except the VMH in acutely stressed rats, and habituated with repeated stress exposure, consistent with previous studies. In the ARC, repeated stress reduced MC4R cell activation while acute restraint decreased activation in GLP1R neurons. Both patterns of stress exposure reduced the number of AgRP-expressing cells that also expressed Fos in the ARC. Acute stress decreased Fos-GLP1R expression in the LHA, while repeated restraint increased the number of Fos-AgRP neurons in this region. The overall profile of orexigenic signaling in the brain is thus enhanced by acute and repeated restraint stress, with repeated stress leading to further increases in signaling, in a region-specific manner. Stress-induced modifications to feeding behavior appear to depend on both the duration of stress exposure and regional activation in the brain. These results suggest that food intake may be increased as a consequence of stress, and may play a role in obesity and other stress-associated metabolic disorders.     

Song and Sperm in Crickets: A Trade‐off between Pre‐ and Post‐copulatory Traits or Phenotype‐Linked Fertility?

When females mate multiply (polyandry) both pre‐ and post‐copulatory sexual selection can occur. Sperm competition theory predicts there should be a trade‐off between investment in attracting mates and investment in ejaculate quality. In contrast, the phenotype‐linked fertility hypothesis predicts a positive relationship should exist between investment in attracting mates and investment in ejaculate quality. Given the need to understand how pre‐ and post‐copulatory sexual selection interacts, we investigated the relationship between secondary sexual traits and ejaculate quality using the European house cricket, Acheta domesticus. Although we found no direct relationship between cricket secondary sexual signals and ejaculate quality, variation in ejaculate quality was dependent on male body weight and mating latency: the lightest males produced twice as many sperm as the heaviest males but took longer to mate with females. Our findings are consistent with current theoretical models of sperm competition. Given light males may have lower mating success than heavy males because females take longer to mate with them in no‐choice tests, light males may be exhibiting an alternative reproductive tactic by providing females with more living sperm. Together, our findings suggest that the fitness of heavy males may depend on pre‐copulatory sexual selection, while the fitness of light males may depend on post‐copulatory fertilization success.     

Epithelial,dendritic, and CD4 T cell regulation of and by reactive oxygen and nitrogen species in allergic sensitization

Background

While many of the contributing cell types and mediators of allergic asthma are known, less well understood are the factors that induce allergy in the first place. Amongst the mediators speculated to affect initial allergen sensitization and the development of pathogenic allergic responses to innocuous inhaled antigens and allergens are exogenously or endogenously generated reactive oxygen species (ROS) and reactive nitrogen species (RNS).

Scope of review

The interactions between ROS/RNS, dendritic cells (DCs), and CD4⁺ T cells, as well as their modulation by lung epithelium, are of critical importance for the genesis of allergies that later manifest in allergic asthma. Therefore, this review will primarily focus on the initiation of pulmonary allergies and the role that ROS/RNS may play in the steps therein, using examples from our own work on the roles of NO₂ exposure and airway epithelial NF-κB activation.

Major conclusions

Endogenously generated ROS/RNS and those encountered from environmental sources interact with epithelium, DCs, and CD4⁺ T cells to orchestrate allergic sensitization through modulation of the activities of each of these cell types, which quantitiatively and qualitatively dictate the degree and type of the allergic asthma phenotype.

General significance

Knowledge of the effects of ROS/RNS at the molecular and cellular levels has the potential to provide powerful insight into the balance between inhalational tolerance (the typical immunologic response to an innocuous inhaled antigen) and allergy, as well as to potentially provide mechanistic targets for the prevention and treatment of asthma.     

The common hepatic branch of the vagus is not required to mediate the glycemic and food intake suppressive effects of glucagon-like-peptide-1

The incretin and food intake suppressive effects of intraperitoneally administered glucagon-like peptide-1 (GLP-1) involve activation of GLP-1 receptors (GLP-1R) expressed on vagal afferent fiber terminals. Central nervous system processing of GLP-1R-driven vagal afferents results in satiation signaling and enhanced insulin secretion from pancreatic-projecting vagal efferents. As the vast majority of endogenous GLP-1 is released from intestinal l-cells following ingestion, it stands to reason that paracrine GLP-1 signaling, activating adjacent GLP-1R expressed on vagal afferent fibers of gastrointestinal origin, contributes to glycemic and food intake control. However, systemic GLP-1R-mediated control of glycemia is currently attributed to endocrine action involving GLP-1R expressed in the hepatoportal bed on terminals of the common hepatic branch of the vagus (CHB). Here, we examine the hypothesis that activation of GLP-1R expressed on the CHB is not required for GLP-1's glycemic and intake suppressive effects, but rather paracrine signaling on non-CHB vagal afferents is required to mediate GLP-1's effects. Selective CHB ablation (CHBX), complete subdiaphragmatic vagal deafferentation (SDA), and surgical control rats received an oral glucose tolerance test (2.0 g glucose/kg) 10 min after an intraperitoneal injection of the GLP-1R antagonist, exendin-(9-39) (Ex-9; 0.5 mg/kg) or vehicle. CHBX and control rats showed comparable increases in blood glucose following blockade of GLP-1R by Ex-9, whereas SDA rats failed to show a GLP-1R-mediated incretin response. Furthermore, GLP-1(7-36) (0.5 mg/kg ip) produced a comparable suppression of 1-h 25% glucose intake in both CHBX and control rats, whereas intake suppression in SDA rats was blunted. These findings support the hypothesis that systemic GLP-1R mediation of glycemic control and food intake suppression involves paracrine-like signaling on GLP-1R expressed on vagal afferent fibers of gastrointestinal origin but does not require the CHB.     

The temporal structure of feeding behavior

Meals have long been considered relevant units of feeding behavior. Large data sets of feeding behavior of cattle, pigs, chickens, ducks, turkeys, dolphins, and rats were analyzed with the aims of 1) describing the temporal structure of feeding behavior and 2) developing appropriate methods for estimating meal criteria. Longer (between-meal) intervals were never distributed as the negative exponential assumed by traditional methods, such as log-survivorship analysis, but as a skewed Gaussian, which can be (almost) normalized by log-transformation of interval lengths. Log-transformation can also normalize frequency distributions of within-meal intervals. Meal criteria, i.e., the longest interval considered to occur within meals, can be estimated after fitting models consisting of Gaussian functions alone or of one Weibull and one or more Gaussian functions to the distribution of log-transformed interval lengths. Nonuniform data sets may require disaggregation before this can be achieved. Observations from all species were in conflict with assumptions of random behavior that underlie traditional methods for criteria estimation. Instead, the observed structure of feeding behavior is consistent with 1) a decrease in satiety associated with an increase in the probability of animals starting a meal with time since the last meal and 2) an increase in satiation associated with an increase in the probability of animals ending a meal with the amount of food already consumed. The novel methodology proposed here will avoid biased conclusions from analyses of feeding behavior associated with previous methods and, as demonstrated, can be applied across a range of species to address questions relevant to the control of food intake.     

Effect of substrate type on bacterial community composition in biofilms from the Great Barrier Reef

Natural and anthropogenic impacts such as terrestrial runoff, influence the water quality along the coast of the Great Barrier Reef (GBR) and may in turn affect coral reef communities. Associated bacterial biofilms respond rapidly to environmental conditions and are potential bioindicators for changes in water quality. As a prerequisite to study the effects of water quality on biofilm communities, appropriate biofilm substrates for deployment in the field must be developed and evaluated. This study investigates the effect of different settlement substrates (i.e. glass slides, ceramic tiles, coral skeletons and reef sediments) on bacterial biofilm communities grown in situ for 48 days at two locations in the Whitsunday Island Group (Central GBR) during two sampling times. Bacterial communities associated with the biofilms were analysed using terminal restriction fragment length polymorphism (T-RFLP) and clone library analyses of 16S rRNA genes. Findings revealed that substrate type had little influence on bacterial community composition. Of particular relevance, glass slides and coral skeletons exhibited very similar communities during both sampling times, suggesting the suitability of standardized glass slides for long-term biofilm indicator studies in tropical coral reef ecosystems.     

Immunohistological localization of serotonin in the CNS and feeding system of the stable fly Stomoxys calcitrans L. (Diptera: Muscidae)

Serotonin, or 5-hydroxytryptamine (5-HT), plays critical roles as a neurotransmitter and neuromodulator that control or modulate many behaviors in insects, such as feeding. Neurons immunoreactive (IR) to 5-HT were detected in the central nervous system (CNS) of the larval and adult stages of the stable fly, Stomoxys calcitrans, using an immunohistological technique. The location and pattern of the 5-HT IR neurons are described and compared for these two different developmental stages. Anatomical features of the fly feeding system were analyzed in third instar larvae and adult flies using a combination of histological and immunohistological techniques. In third instar larvae, the cibarial dilator muscles were observed within the cibarial pump skeleton and innervated by 5-HT IR neurons in nerves arising from the brain. There were four pairs of nerves arising from the frontal surface of the larval brain that innervate the cibarial pump muscles, pharynx, and muscles controlling the mouth hooks. A strong serotoninergic innervation of the anterior stomatogastric system was observed, which suggests 5-HT may play a role in the coordination of different phases of food ingestion by larvae. Similarly, many 5-HT IR neurons were found in both the brain and the thoracico-abdominal ganglia in the adult, some of which innervate the cibarial pump dilator muscles and the stomatogastric muscles. This is tnhe first report describing neuromuscular structures of the stable fly feeding system. The results reported here suggest 5-HT may play a critical role in feeding behaviors of stable fly larvae and adults.