Circulating Corticosterone Research Articles

Adolescent social isolation increases binge-like alcohol drinking in male but not female high-alcohol-preferring mice.

This study examined how adolescent social isolation affects adult binge-like alcohol drinking and stress-axis function, via basal levels of circulating corticosterone (CORT), in male and female mice with a genetic predisposition toward high alcohol preference (HAP). Male and female HAP2 mice were randomly assigned to a group-housed or social isolation (ISO) group. Social isolation began at postnatal Days 40-42 and lasted for 21days prior to assessment of binge-like alcohol drinking using a 4-day drinking-in-the-dark (DID) procedure. Blood samples to assess basal CORT were taken 6days after social isolation ended and 24h before DID started, and again 60h after DID ended, during the light portion of the light cycle. Adolescent social isolation increased adult binge-like alcohol drinking in male but not female mice. All groups showed significantly lower CORT after DID compared to before DID. Pearson bivariate correlation coefficients between the first 2h of grams-per-kilogram alcohol intake on Day 4 and CORT levels indicated a significant positive correlation in ISO males only after DID and negative correlations in ISO females before and after DID. These findings demonstrate that adolescent social isolation increased binge-like alcohol drinking in male but not female adult HAP2 mice. Stress-axis adaptations in male HAP2 mice may be associated with the social-isolation-induced increase in binge-like alcohol drinking.

The persistent effects of corticosterone administration during lactation on the physiology of maternal and offspring mitochondria.

Reproduction and environmental stressors are generally thought to be associated with a cost to the individual experiencing them, but the physiological mechanisms mediating costs of reproduction and maternal effects remain poorly understood. Studies examining the effects of environmental stressors on a female's physiological state and body condition during reproduction, as well as the physiological condition of offspring, have yielded equivocal results. Mitochondrial physiology and oxidative stress have been implicated as important mediators of life-history trade-offs. The goal of this investigation was to uncover the physiological mechanisms responsible for the enhanced trade-off between self-maintenance and offspring investment when an animal is exposed to stressful conditions during reproduction. To that end, we manipulated circulating corticosterone (CORT) levels by orally supplementing lactating female mice with CORT and investigated mitochondrial physiology and oxidative stress of both the reproductive females and their young. We found that maternal CORT exposure resulted in lower litter mass at weaning, but mitochondrial performance and oxidative status of females were not impacted. We also found potential beneficial effects of maternal CORT on mitochondrial function (e.g. higher respiratory control ratio) and oxidative stress (e.g. lower reactive oxygen species production) of offspring in adulthood, suggesting that elevated maternal CORT may be a signal for early-life adversity and prepare the organism with a predictive, adaptive response to future stressors.

Neuroendocrine correlates of juvenile amphibian behaviors across a latitudinal cline

We assessed the macrogeographic and neuroendocrine correlates of behavioral variation exhibited by juveniles, an important life stage for dispersal, across the expansive range of the wood frog. By rearing animals from eggs in a common garden then using a novel environment test, we uniquely demonstrated differential expression of juvenile behaviors among 16 populations spanning 8° latitude. On the individual level, cluster analysis indicated three major behavior profiles and principal component analysis resolved four unique axes of behavior, including escape, foraging, food intake, feeding efficiency. We found that increased escape behavior was associated with lower adrenocorticotropic hormone (ACTH)-induced circulating corticosterone (CORT) levels, however, foraging and food intake behaviors were not associated with either resting or ACTH-induced CORT. At the population level, the expression of foraging behaviors increased with latitude while food intake behaviors declined with latitude, which raised several hypotheses of eco-evolutionary processes likely driving this variation. Given that these behaviors covary along the same ecological gradient as locally adapted developmental traits, genomic studies in this species could provide deep insights into how HPA/I activity is associated with the eco-evolutionary processes that structure intraspecific variation in morphology and behavior.

Unique brain endothelial profiles activated by social stress promote cell adhesion, prostaglandin E2 signaling, hypothalamic-pituitary-adrenal axis modulation, and anxiety.

Chronic stress may precipitate psychiatric disorders including anxiety. We reported that Repeated Social Defeat (RSD) in mice increased accumulation of inflammatory monocytes within the brain vasculature, which corresponded with increased interleukin (IL)-1 Receptor 1-mediated activation of endothelia, and augmented anxiety-like behavior. One unknown, however, is the role of immune-activated endothelia in regulating the physiological and behavioral responses to social stress. Thus, we sought to determine the RNA profile of activated endothelia and delineate the pathways by which these endothelia communicate within the brain to influence key responses to social stress. First, endothelial-specific RiboTag mice were exposed to RSD and brain endothelial mRNA profiles from the whole brain and prefrontal cortex were determined using RNAseq. RSD increased expression of cell adhesion molecules (Icam1), inflammatory genes (Lrg1, Lcn2, Ackr1, Il1r1), and cyclooxygenase-2 (Ptgs2/COX-2). In studies with IL-1R1KO mice, there was clear dependence on IL-1R1 on endothelia-associated transcripts including Lrg1, Icam1, Lcn2. Moreover, prostaglandin (PG)E2 was increased in the brain after RSD and Ptgs2 was localized to endothelia, especially within the hypothalamus. Next, a selective COX-2 inhibitor, Celecoxib (CCB), was used with social stress. RSD increased PGE2 in the brain and this was abrogated by CCB. Moreover, CCB reduced RSD-induced Hypothalamic-Pituitary-Adrenal (HPA) axis activation with attenuation of hypothalamic paraventricular neuron activation, hypothalamic Crh expression, and corticosterone in circulation. Production, release, and accumulation of inflammatory monocytes after RSD was COX-2 independent. Nonetheless, CCB blocked anxiety-like behavior in response to RSD. Collectively, social stress stimulated specific endothelia RNA profiles associated with increased cell adhesion, IL-1 and prostaglandin signaling, HPA axis activation, and anxiety.

(3α,5α)3-Hydroxypregnan-20-one (3α,5α-THP) Regulation of the HPA Axis in the Context of Different Stressors and Sex.

Corticotropin-releasing factor (CRF) regulates the stress response in the hypothalamus and modulates neurotransmission across the brain through CRF receptors. Acute stress increases hypothalamic CRF and the GABAergic neurosteroid (3α,5α)3-hydroxypregnan-20-one (3α,5α-THP). We previously showed that 3α,5α-THP regulation of CRF is sex and brain region dependent. In this study, we investigated 3α,5α-THP regulation of stress-induced hypothalamic CRF, CRF receptor type 1 (CRFR1), CRF binding protein (CRFBP), pro-opiomelanocortin (POMC), and glucocorticoid receptor (GR) by western blot and circulating corticosterone (CORT) by enzyme-linked immunosorbent assay (ELISA) in male and female Sprague Dawley rats. Tissue was collected after rats were injected with 3α,5α-THP (15 mg/kg, IP) or vehicle 15 min prior to 30 min of restraint stress (RS), or 10 min of forced swim stress (FSS) and 20 min recovery. The initial exposure to a stress stimulus increased circulating CORT levels in both males and females, but 3α,5α-THP attenuated the CORT response only in females after RS. 3α,5α-THP reduced GR levels in male and females, but differently between stressors. 3α,5α-THP decreased the CRF stress response after FSS in males and females, but after RS, only in female rats. 3α,5α-THP reduced the CRFR1, CRFBP, and POMC increases after RS and FSS in males, but in females only after FSS. Our results showed different stress responses following different types of stressors: 3α,5α-THP regulated the HPA axis at different levels, depending on sex.

Sex-specific stress and biobehavioral responses to human experimenters in rats.

Important factors influencing the outcome of animal experiments in preclinical research are often overlooked. In the current study, the reaction of female and male rats toward the biological sex of a human experimenter was investigated in terms of anxiety-like behaviors and physiological stress responses, as measured by infrared (IR) thermography, circulating corticosterone (CORT) and oxytocin levels. Female rats displayed consistently exacerbated anxiety-related behaviors along with elevated body surface temperature during repeated exposure to male experimenters. Experimental stress further intensified thermal responses to a male experimenter, especially in female rats. The behavioral responses to a male experimenter in females were associated with higher circulating CORT and lower oxytocin levels. Similar responses were induced by a T-shirt worn by a human male. The findings suggest that psychophysiological responses of female rats to a male experimenter are influenced by both visual and olfactory cues. The results emphasize the need to not only consider sex differences in experimental animals, but also standardize and report the experimenter’s biological sex to avoid ambiguity in the generation and interpretation of results.

Clutch Abandoning Parasitised Yellow Warblers Have Increased Circulating Corticosterone With No Effect of Past Corticosterone or Differences in Egg Maculation Characteristics

Parental care can be costly to parents’ fitness. As such, abandonment of the current reproductive attempt may benefit potential future opportunities, maximising lifetime reproductive success. Obligate brood parasitism, a reproductive strategy in which parasites lay their eggs in the nests of other species and rely solely on them to raise the parasitic young, is an ideal system to study brood abandonment. Some parasitised host species have evolved anti-parasitic defences, notably clutch abandonment (egg burial and nest desertion), that may mitigate negative consequences of parasitism. Abandonment of clutches due to parasitism is not unlike abandonment of reproduction in times of stress, suggesting that host responses to parasitism could be triggered at least partly by elevated stress hormones that mediate individual decisions. Yet, the mechanistic basis for clutch abandonment remains unclear. Here, we experimentally parasitised clutches of yellow warblers (Setophaga petechia), a common host of the brown-headed cowbird (Molothrus ater), with model cowbird eggs to examine whether host circulating corticosterone (CORT) differed among females that accepted parasitic eggs or rejected them through clutch abandonment. We also assessed whether feather CORT, a measure of past corticosterone exposure, differed between accepters and abandoners. Finally, we investigated whether egg visual signals, specifically differences in maculation characteristics between model cowbird and host eggs, predicted abandonment of experimentally parasitised clutches. Circulating CORT was higher in females who abandoned their parasitised clutches, but not in those who accepted, relative to controls with no egg addition. Past stress and differences in maculation characteristics did not predict whether individuals accepted or abandoned experimentally parasitised clutches. Moreover, differences in maculation characteristics between the host and model cowbird eggs did not predict CORT levels or nest abandonment. Thus, parasitism with subsequent clutch abandonment may be associated with elevated circulating CORT, but neither past stress nor differences in maculation characteristics influenced abandonment. The combination of these results contributes to our understanding of the roles of corticosterone and egg visual signals in the context of clutch abandonment in brood parasitism specifically, and of parental care more broadly.

High-fat diet-induced increases in glucocorticoids contribute to the development of non-alcoholic fatty liver disease in mice.

This study aimed to investigate the causal relationship between chronic ingestion of a high-fat diet (HFD)-induced secretion of glucocorticoids (GCs) and the development of non-alcoholic fatty liver disease (NAFLD). We have produced a strain of transgenic mice (termed L/L mice) that have normal levels of circulating corticosterone (CORT), the major type of GCs in rodents, but unlike wild-type (WT) mice, their circulating CORT was not affected by HFD. Compared to WT mice, 12-week HFD-induced fatty liver was less pronounced with higher plasma levels of triglycerides in L/L mice. These changes were reversed by CORT supplement to L/L mice. By analyzing a sort of lipid metabolism-related proteins, we found that expressions of the hepatic cluster of differentiation 36 (CD36) were upregulated by HFD-induced CORT and involved in CORT-mediated fatty liver. Dexamethasone, an agonist of the glucocorticoid receptor (GR), upregulated expressions of CD36 in HepG2hepatocytes and facilitated lipid accumulation in the cells. In conclusion, the fat ingestion-induced release of CORT contributes to NAFLD. This study highlights the pathogenic role of CORT-mediated upregulation of hepatic CD 36 in diet-induced NAFLD.

Differences in circulating corticosterone levels associated with elevation of breeding sites in Rufous-collared Sparrows Zonotrichia capensis

To facilitate breeding and any energetically costly activity, individuals of the same species can substantially vary their circulating corticosterone (CORT) levels to cope with local environmental conditions at different elevations. We compared baseline and the stress-induced plasma CORT levels during the parental care stage between free-living Rufous-collared Sparrows (Zonotrichia capensis) that breed at high (~ 2500 m) and low (~ 500 m) elevations in central Chile. We found that baseline CORT levels at different elevations were similar and that stress-induced levels were significantly lower in birds breeding at high elevation; however, we detected no sexual dimorphism in CORT levels related to elevation. We found that larger individuals had higher stress-induced CORT levels at low elevation regardless of sex. Our results show that environmental conditions at high elevation seem to be not severe enough to promote more elevated baseline CORT levels. However, breeding Rufous-collared Sparrow must still deal with both shorter breeding seasons and increased exposure to unpredictable events. Thus, a reduced stress response during the parental care stage would be more favorable for supporting breeding activities at high elevations. Future studies should focus on describing the life-history traits of these populations and the effects that other stressors, such as predation pressure and food availability, may have on the adrenocortical response in these environments to evaluate the consequences for survival and reproductive success. This information is important for enhancing our understanding of the ecological and evolutionary mechanisms that modulate variation in the adrenocortical response among populations of the same species.

Innate immunity of Florida cane toads: how dispersal has affected physiological responses to LPS.

Physiological tradeoffs occur in organisms coping with their environments, which are likely to increase as populations reach peripheries of established ranges. Invasive species offer opportunities to study tradeoffs that occur, with many hypotheses focusing on how immune responses vary during dispersal. The cane toad (Rhinella marina) is a well-known invasive species. Populations near the expanding edge of the Australian invasion have altered immune responses compared to toads from longer-established core populations, although this has not been well-documented for Florida populations. In this study, cane toads from a northern edge [New Port Richey (NPR)] and southern core (Miami) population in Florida were collected and injected with lipopolysaccharide (LPS) to compare immune responses. Core population individuals injected with LPS showed greater metabolic increases compared to their baseline rates that were higher compared to those from the edge population. In addition, LPS-injected core individuals had different circulating leukocyte profiles compared to saline-injected cane toads while edge individuals did not. There was a significant interaction between plasma bacteria-killing capability (BKA) and treatment, such that BKA decreased with time in saline compared to LPS-injected individuals, and saline-injected toads from the edge population had lower BKA compared to LPS-injected edge toads at 20h post-injection. There was also a significant interaction between location and time on circulating corticosterone (CORT) levels following injections with saline or LPS, with CORT decreasing more with time in core population toads. The differential CORT response indicates that differential stress responses contribute to the tradeoffs observed with immunity and dispersal.

Water amino acid-chelated trace mineral supplementation decreases circulating and intestinal HSP70 and proinflammatory cytokine gene expression in heat-stressed broiler chickens

Heat stress (HS) is a financial and physiological burden on the poultry industry and the mitigation of the adverse effects of HS is vital to poultry production sustainability. The purpose of this study was, therefore, to determine the effects of an amino acid-chelated trace mineral supplement on growth performance, stress and inflammatory markers, and meat quality in heat-stressed broilers. One day-old Cobb 500 male broilers (n = 480) were allocated into 12 environmental chambers (24 floor pens) and divided into two groups: one group supplemented with amino acid-chelated trace mineral in drinking water and one control group. On day 28, birds were subjected to chronic heat stress (HS, 2 wk, 35 °C and 20% to 30% RH) or maintained at thermoneutral condition (TN, 24 °C) in a 2 × 2 factorial design. Feed intake (FI), water consumption, and body weight were recorded. At day 42, serum fluorescein isothiocyanate dextran (FITC-D) levels, blood gas, electrolyte, and stress markers were measured. Jejunum samples were collected to measure gene expression of stress, inflammation, and tight junction proteins. The rest of the birds were processed to evaluate carcass traits. HS resulted in an increase in core body temperature, which increased water intake and decreased FI, body weight, and feed efficiency (P < 0.05). HS reduced carcass yield and the weight of all parts (P < 0.05). HS significantly increased levels of circulating corticosterone (CORT), heat shock protein 70 (HSP70), interleukin 18 (IL-18), tumor necrosis factor alpha, C-reactive protein, and nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing 3 expression. HS significantly increased serum FITC-D levels and the expression of HSP70 and IL-18 in the jejunum. Although it did not affect the growth performance, amino acid-chelated trace mineral supplementation reversed the effect of HS by reducing CORT and FITC-D levels and the expression of stress and proinflammatory cytokines in the circulation and the jejunum. However, it upregulated these parameters in birds maintained under TN conditions. Together, these data indicate that the amino acid-chelated trace mineral might alleviate stress and inflammation and improve gut integrity in heat-stressed but not thermoneutral broilers.

Food supplementation by an invasive fleshy-fruited shrub sustains body condition of a native frugivorous bird during winter.

Birds tend to adjust their behavior and physiology to changes in food availability in their environment. Seasonal fluctuation of food resources may act as an energetic challenge, augmenting hypothalamus-pituitary-adrenal axis (HPA axis) activity, leading to an increase in corticosterone concentrations and promoting the metabolism of energy stores. Plant invasions may alter seasonal food fluctuations by providing a food supply during scarce seasons. This could attenuate the energetic challenge, reducing HPA axis activity and the metabolism of reserves. Using a system with seasonal fluctuation in food availability, we tested if fruit supplementation by the invasive fleshy-fruited Pyracantha angustifolia during the season of native fruit scarcity decreases the consumption of energy stores through activity attenuation of the HPA axis. We measured changes in body condition and circulating corticosterone (CORT) concentration in Turdus chiguanco occurring at sites both invaded and not invaded by P. angustifolia over 3 time periods that correspond to the periods prior to, during and after highest fruit production of the plant. Fruit scarcity in the ecosystem appears as an energetic challenge for T. chiguanco, given that body mass, fat score and residuals of body mass/tarsus length decreased during winter in a site not invaded by the exotic shrub. Conversely, the presence of the invasive plant seemed to attenuate the metabolism of energetic reserves, as we did not record changes in body condition in birds inhabiting the invaded site. Unexpectedly, plasma CORT concentration did not vary between sites or periods. Further evaluation is required to elucidate how enhanced body condition, resulting from the consumption of a fleshy-fruited invasive plant, affects survivorship and reproductive performance in T. chiguanco.

SUN-476 Corticosterone-Mediated Suppression of the Reproductive Neuroendocrine Axis in Male Mice

It is well identified that psychosocial stress disturbs reproductive hormone secretion at multiple levels of the reproductive axis. The neural and hormonal mechanisms underlying this reproductive suppression and the role of reproductive brain neuropeptides in this process is not fully understood. We previously showed that in gonadectomized (GDX) male mice, a one-time acute restraint stress strongly suppressed in vivo luteinizing hormone (LH) pulsatility within 12-18 min of stress initiation. Furthermore, similarly stressed GDX mice showed a rise in circulating corticosterone (CORT) levels by 15 min. These correlative data suggest that CORT may be an important signaling factor involved in the stress-induced suppression of LH pulses. Thus, the objective of the current work is to identify the role of CORT in mediating stress inhibition of the reproductive neuroendocrine axis. First, we performed a dose-response and time course study to determine an effective exogenous CORT treatment paradigm to mimic endogenous CORT levels during psychosocial stress. Next, to assess CORT effects on LH pulses, GDX male mice were pulse bled every 6 min for 90 min, then injected with either an oil vehicle or 1 mg/kg CORT, and pulse bled every 6 min for another 90 min. CORT-injected mice showed a reduction in LH pulses, though not as robust or for as long as in restraint stressed mice. These data suggest that while CORT is sufficient to decrease LH pulsatile secretion, additional factors may also be involved to achieve maximal stress-induced suppression. To determine if upstream neuroendocrine signaling of stimulatory (kisspeptin) and inhibitory (RFRP-3) neurons to GnRH neurons are involved in this CORT-mediated suppression, in situ hybridization was conducted in brains of vehicle- and CORT-injected mice to determine changes in Kiss1 and Rfrp mRNA content and neuronal activation. These data are currently being analyzed. Our findings suggest that while acute CORT is capable of moderately suppressing reproductive hormone secretion, it is not the only mechanism involved during psychosocial stress exposure. Future studies will need to investigate additional factors that are important.

Effects of High-Fat Diet on Stress Response in Male and Female Wildtype and Prolactin Knockout Mice.

Prolactin (PRL) is well characterized for its roles in initiation and maintenance of lactation, and it also suppresses stress-induced responses. Feeding a high-fat diet (HFD) disrupts activity of the hypothalamic-pituitary-adrenal (HPA) axis. Whether PRL regulates HPA axis activation under HFD feeding is not clear. Male and female wildtype (WT) and PRL knockout (KO) mice were fed either a standard low-fat diet (LFD) or HFD for 12 weeks. Circulating corticosterone (CORT) levels were measured before, during, and after mice were subjected to an acute restraint stress or remained in their home cages as no stress controls. HFD feeding increased leptin levels, but the increase was lower in KO than in WT mice. All stressed female groups and only LFD-fed stressed males had elevated CORT levels compared to their no stress same-sex counterparts regardless of genotype. These results indicated that HFD consumption blunted the HPA axis response to acute stress in males but not females. Additionally, basal hypothalamic CRH content was lower in HFD than LFD males, but was similar among female groups. Furthermore, although basal CORT levels were similar among KO and WT groups, CORT levels were higher in KO mice than their WT counterparts during stress, suggesting that loss of PRL led to greater HPA axis activation. Basal PRL receptor mRNA levels in the choroid plexus were higher in HFD than LFD same-sex counterparts, suggesting activation of central PRL’s action by HFD feeding in both males and females. Current results confirmed PRL’s roles in suppression of the stress-induced HPA axis activation. Although HFD feeding activated central PRL’s action in both sexes, only the male HPA axis was dampened by HFD feeding.

Ovalbumin expression in the oviduct magnum of hens is related to the rate of egg laying and shows distinct stress-type-specific responses.

Three trials were performed to evaluate the association of ovalbumin (OVA) abundance in the oviduct magnum with egg production and the underlying regulatory mechanism by glucocorticoids. In trial 1, twenty Hy-Line Brown layers (56-60weeks of age) with different combinations (n=5/combination) of laying rate (high or low) and egg weight (high or low) were selected from an initial group of 300. An upregulated expression of magnum OVA was observed (p<0.05) in hens with higher laying rate, regardless of egg weight. In trial 2, eighty Hy-Line Brown layers (80-90weeks of age) were subjected to the forced moulting (n=8). The abundance of OVA transcript and protein in the magnum was significantly decreased during moulting (p<0.01), and the same was true for laying rate (p<0.01) and serum oestrogen (p<0.05). In trial 3, forty-five 56-week-old Hy-Line Brown layers were kept individually (n=15) in the following conditions for 10days: constant optimal ambient temperature at 23°C and adlibitum feeding, high ambient temperature at 32°C for 6h/day (10:00-16:00) and adlibitum feeding (32AL), and constant optimal ambient temperature at 23°C and pair-fed to the 32AL hens. In spite of elevated corticosterone in circulation, OVA synthesis, blood oestrogen and laying rate were not affected by heat exposure (p>0.05). These results allow concluding that OVA expression in the oviduct magnum of hens is related to the rate of egg laying and shows distinct stress-type-specific responses.

Chronic activation of NPFFR2 stimulates the stress-related depressive behaviors through HPA axis modulation

Neuropeptide FF (NPFF) is a morphine-modulating peptide that regulates the analgesic effect of opioids, and also controls food consumption and cardiovascular function through its interaction with two cognate receptors, NPFFR1 and NPFFR2. In the present study, we explore a novel modulatory role for NPFF-NPFFR2 in stress-related depressive behaviors. In a mouse model of chronic mild stress (CMS)-induced depression, the expression of NPFF significantly increased in the hypothalamus, hippocampus, medial prefrontal cortex (mPFC) and amygdala. In addition, transgenic (Tg) mice over-expressing NPFFR2 displayed clear depression and anxiety-like behaviors with hyperactivity in the hypothalamic-pituitary-adrenal (HPA) axis, reduced expression of glucocorticoid receptor (GR) and neurogenesis in the hippocampus. Furthermore, acute treatment of NPFFR2 agonists in wild-type (WT) mice enhanced the activity of the HPA axis, and chronic administration resulted in depressive and anxiety-like behaviors. Chronic stimulation of NPFFR2 also decreased the expression of hippocampal GR and led to persistent activation of the HPA axis. Strikingly, bilateral intra-paraventricular nucleus (PVN) injection of NPFFR2 shRNA predominately inhibits the depressive-like behavior in CMS-exposed mice. Antidepressants, fluoxetine and ketamine, effectively relieved the depressive behaviors of NPFFR2-Tg mice. We speculate that persistent NPFFR2 activation, in particular in the hypothalamus, up-regulates the HPA axis and results in long-lasting increases in circulating corticosterone (CORT), consequently damaging hippocampal function. This novel role of NPFFR2 in regulating the HPA axis and hippocampal function provides a new avenue for combating depression and anxiety-like disorder.

No evidence for an effect of traffic noise on the development of the corticosterone stress response in an urban exploiter

Anthropogenic noise can have important physiological and behavioral effects on wild animals. For example, urban noise could lead to a state of chronic stress and could alter the development of the hypothalamus–pituitary–adrenal (HPA) axis. Supporting this hypothesis, several studies have found that human disturbance is associated with increased circulating corticosterone (CORT) levels. However, it remains unclear whether increased CORT levels are the result of anthropogenic noise or other anthropogenic factors. Here, we experimentally tested the impact of urban noise on the CORT stress response in an urban exploiter (the house sparrow, Passer domesticus) by exposing chicks to a traffic noise (‘disturbed chicks’) or not (‘control chicks’). If noise exposure has a negative impact on developing chicks, we predicted that (1) disturbed chicks will grow slower, will be in poorer condition, and will have a lower fledging probability than controls; (2) disturbed chicks will have higher baseline CORT levels than control; (3) the CORT stress response will be affected by this noise exposure. Contrary to these predictions, we found no effect of our experiment on growth, body condition, and fledging success, suggesting that house sparrow chicks were not negatively affected by this noise exposure. Moreover, we did not find any effect of noise exposure on either baseline CORT levels or the CORT stress response of chicks. This suggests not only that house sparrow chicks did not perceive this noise as stressful, but also that the development of the HPA axis was not affected by such noise exposure. Our study suggests that, contrary to urban avoiders, urban exploiters might be relatively insensitive to urban noise during their development. Further comparative studies are now needed to understand whether such insensitivity to anthropogenic noise is a consistent phenomenon in urban exploiters and whether this is a major requirement of an urban way of life.

The effect of different degrees of feed restriction on heat shock protein 70, acute phase proteins, and other blood parameters in female broiler breeders

The aim of the current study was to determine the physiological response to feed restriction in female broiler breeders using a range of conventional and novel indicators. One hundred female breeders were subjected to one of five feeding regimens from d 28 to 42 as follows (i) ad libitum feeding (AL), (ii-v) 75, 60, 45, and 30% of ad libitum feed intake. Blood heterophil to lymphocyte ratio (HLR), and plasma circulating corticosterone (CORT), ghrelin (GHR), serotonin (5-HT), and dopamine (DA) and serum acute phase proteins (APP) concentrations together with brain heat shock protein (HSP) 70 level were measured. The results showed a significant effect of feed restriction on blood HLR and plasma CORT, GHR, 5-HT, DA, and brain HSP 70 levels. However, feed restriction had no effect on serum levels of APP of alpha-1 acid glycoprotein, ovotransferin, and ceruloplasmin. Serum levels of 5-HT and GHR varied curvilinearly with the feed restriction level. The relationship between brain HSP 70 and level of feed restriction was negligible. However, significant linear relationships between HLR, CORT, DA, and the level of feed restriction were noted. Thus, these 3 parameters appear to represent a straight forward relation with severity of feed restriction.

Common effects of fat, ethanol, and nicotine on enkephalin in discrete areas of the brain

Fat, ethanol, and nicotine share a number of properties, including their ability to reinforce behavior and produce overconsumption. To test whether these substances act similarly on the same neuronal populations in specific brain areas mediating these behaviors, we administered the substances short-term, using the same methods and within the same experiment, and measured their effects, in areas of the hypothalamus (HYPO), amygdala (AMYG), and nucleus accumbens (NAc), on mRNA levels of the opioid peptide, enkephalin (ENK), using in situ hybridization and on c-Fos immunoreactivity (ir) to indicate neuronal activity, using immunofluorescence histochemistry. In addition, we examined for comparison another reinforcing substance, sucrose, and also took measurements of stress-related behaviors and circulating corticosterone (CORT) and triglycerides (TG), to determine if they contribute to these substances’ behavioral and physiological effects. Adult Sprague–Dawley rats were gavaged three times daily over 5days with 3.5mL of water, Intralipid (20% v/v), ethanol (12% v/v), nicotine (0.01% w/v) or sucrose (22% w/v) (approximately 7kcal/dose), and tail vein blood was collected for measurements of circulating CORT and TG. On day five, animals were sacrificed, brains removed, and the HYPO, AMYG, and NAc processed for single- or double-labeling of ENK mRNA and c-Fos-ir. Fat, ethanol, and nicotine, but not sucrose, increased the single- and double-labeling of ENK and c-Fos-ir in precisely the same brain areas, the middle parvocellular but not lateral area of the paraventricular nucleus, central but not basolateral nucleus of the AMYG, and core but not shell of the NAc. While having little effect on stress-related behaviors or CORT levels, fat, ethanol, and nicotine all increased circulating levels of TG. These findings suggest that the overconsumption of these three substances and their potential for abuse are mediated by the same populations of ENK-expressing neurons in specific nuclei of the hypothalamus and limbic system.

Regulation of gene expression of vasotocin and corticotropin-releasing hormone receptors in the avian anterior pituitary by corticosterone

The effect of chronic stress (CS) on gene expression of the chicken arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) receptors [VT2R, VT4R, CRH-R1, and CRH-R2] was examined by measuring receptor mRNA levels in the anterior pituitary gland of the chicken after chronic immobilization stress compared to acute stress (AS). Radioimmunoassay results showed that blood circulating corticosterone (CORT) levels in the CS group were significantly decreased compared to that of birds in the AS group (P<0.05). The VT2R and CRH-R2 mRNA in CS birds were significantly decreased to that of controls. The VT4R mRNA was significantly decreased compared to controls in AC birds and was further decreased in the CS group compared to controls (P<0.05). The CRH-R1 mRNA was significantly decreased in the AS birds compared to controls. However, there was no significant difference of CRH-R1 mRNA between acute stress and chronic stress birds. Using primary anterior pituitary cell cultures, the effect of exogenous CORT on VT/CRH receptor gene expression was examined. Receptor mRNA levels were measured after treatment of CORT followed by AVT/CRH administration. The CORT pretreatment resulted in a dose-dependent decrease of proopiomelanocortin heteronuclear RNA, a molecular marker of a stress-induced anterior pituitary. Without CORT pretreatment of anterior pituitary cell cultures, the VT2R, VT4R and CRH-R1mRNA levels were significantly increased within 15min and then decreased at 1h and 6h by AVT/CRH administration (P<0.05). Pretreatment of CORT in anterior pituitary cells induced a dose-dependent increase of VT2R, VT4R and CRH-R2 mRNA levels, and a significant decrease of CRH-R1 mRNA levels at only the high dose (10ng/ml) of CORT (P<0.05).Taken together, results suggest a modulatory role of CORT on the regulation of VT/CRH receptor gene expression in the avian anterior pituitary gland dependent upon CORT levels.