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

Sex differences in intestinal morphology and increase in diencephalic neuropeptide Y gene expression in female but not male Pekin ducks exposed to chronic heat stress

The impact of heat stress (HS) on production is intricately linked with feed intake. We investigated the effects of HS on intestines and diencephalic genes in Pekin ducks. One hundred and sixty adult ducks were allocated to two treatment rooms. The control room was maintained at 22°C and the HS room at 35°C for the first 10 h of the day then reduced to 29.5°C. After 3 weeks, 10 hens and 5 drakes were euthanized from each room and jejunum and ileum collected for histology. Brains were collected for gene expression analysis using qRT-PCR. Intestinal morphology data were analyzed with two-way ANOVA and diencephalic gene data were analyzed with Kruskal-Wallis test. There was an increase in villi width in the ileum (p = .0136) and jejunum (p = .0019) of HS hens compared to controls. HS drakes showed a higher crypt depth (CD) in the jejunum (p = .0198) compared to controls. There was an increase in crypt goblet cells (GC) count in the ileum (p = .0169) of HS drakes compared to HS hens. There was higher villi GC count (p = .07) in the jejunum of HS drakes compared to controls. There was an increase in the crypt GC density (p = .0054) in the ileum, not jejunum, of HS drakes compared to HS hens. Further, there were no differences in the proopiomelanocortin gene expression in either sex but there was an increase in the expression of neuropeptide Y (NPY) gene in HS hens (p = .031) only and a decrease in the corticotropin releasing hormone gene in the HS drakes (p = .037) compared to controls. These data show that there are sex differences in the effect of HS on gut morphology while the upregulation in NPY gene may suggest a role in mediating response to chronic HS.

Effects of Restraint Stress on Circulating Corticosterone and Met Enkephalin in Chickens: Induction of Shifts in Insulin Secretion and Carbohydrate Metabolism

This study examined the effects of acute restraint stress in the presence or absence of naltrexone on the circulating concentrations of insulin, glucose, Met-enkephalin and corticosterone in 14-week-old chickens [design: 2 sex × 2 stress/non-stress × 2 +/- naltrexone]. In chickens (five male and five females per treatment) subjected to restraint for 30 min, there were increases in the plasma concentrations of corticosterone and Met-enkephalin. The plasma concentrations of insulin and glucose were also increased in the chickens during restraint. Moreover, there were increases in the plasma concentrations of insulin and glucose in the chickens. The patterns of expression of the proenkephalin gene (PENK) in both the anterior pituitary gland and the adrenal gland were very similar to that of plasma Met-enkephalin. There were relationships between the plasma concentrations of corticosterone, Met-enkephalin, insulin and glucose after 30 min of restraint. The effects of naltrexone treatment on both untreated and stressed chickens were also examined, with naltrexone attenuating the stress-induced increases in the plasma concentrations of corticosterone, Met-enkephalin and glucose but not in those of insulin. The present study demonstrates that stress increases insulin secretion in chickens but also induces insulin resistance.

Chronic Heat Stress Part 2: Increased Stress and Fear Responses in F1 Pekin Ducks Raised from Parents That Experienced Heat Stress

The effects of HS on the welfare of poultry have been reported to have a transgenerational effect on phenotype plasticity. The goal of our experiment was to determine whether parental exposure to HS would impair the performance, HPA axis response, or behavior of their offspring. We treated adult drakes and hens (n = 80 ducks/treatment) at peak lay with HS or the control temperature for 3 weeks and incubated eggs collected from the last 3 days of the experiment. We utilized 76 ducklings/parental treatment group: control (CON-F1) and HS (HS-F1). Weekly data for body weights, body condition scores (BCSs), and novel object test (NOT) were collected. At 3 weeks of age, the ducks (n = 6/treatment) were subjected to adrenocorticotropic hormone (ACTH/cosyntropin, 0.0625 mg/kg) challenge or vehicle as the control. Blood samples were collected at 0, 1, 2, 3, and 4 h relative to treatment for serum glucocorticoid and heterophil-to-lymphocyte ratio (HLR) analyses. All injected birds were euthanized with pentobarbital on the second day relative to ACTH administration, and the spleen and bursa were removed and weighed immediately. Duck level analyses were completed using one- or two-way ANOVA as appropriate. BCSs were analyzed using a chi-squared test. The HS-F1 ducks had a lower hatch weight (p < 0.05) compared with the CON-F1 ducks but no significant difference in growth rates during the 5-week period. NOT (n = 4) analyses showed that the HS-F1 ducks had a greater fear response (p < 0.001) compared with the CON-F1 ducks. Similarly, an ACTH stimulation test showed that the HS-F1 ducks had significantly (p < 0.05) heightened corticosterone and HLR responses compared with the CON-F1 ducks. The HS-F1 ducks showed altered baseline and ACTH-stimulated levels of cortisol compared with the controls. Our data suggest that parental exposure to HS impacts the HPA response and fearfulness of the F1 generation in Pekin ducks.

Chronic treatment with glucocorticoids does not affect egg quality but increases cortisol deposition into egg albumen and elicits changes to the heterophil to lymphocyte ratio in a sex-dependent manner

During chronic stress, there is an initial increase in glucocorticoid (GC) levels, but they then return to low, albeit not baseline, levels. Recent studies have renewed interest in cortisol in that it may also have important roles in the stress response. The purpose of our study was to test the hypothesis that chronic treatment with low levels of either corticosterone or cortisol would alter HLR and immune organ morphometrics. Further, we wanted to determine if chronic treatment with either GC would elicit an increase in cortisol levels in egg albumen. To test our hypotheses, we implanted silastic capsules that contained corticosterone, cortisol, or empty capsules as controls (N = 5/sex/treatment). Blood serum, smears, body weights, and egg quality data were collected. Ducks were then euthanized and body weight, weights of spleens, livers, and the number of active follicles were recorded. Albumen GC levels were assessed using mass spectrometry. Data were analyzed using a 2- or 3-way ANOVA as appropriate and post-hoc with Fishers PLSD. No treatment elicited differences in egg quality measures or body weight compared to controls. Corticosterone treatment did elicit an increase in serum corticosterone (p &lt; 0.05), but not cortisol, levels compared to controls in both sexes. Both cortisol and corticosterone treatments increased (p &lt; 0.05) serum levels of cortisol compared to controls. Relative spleen weights were higher (p &lt; 0.05) in hens following corticosterone but not cortisol treatment. No other organs showed any differences among the treatment groups. Both GCs elicited an increase (p &lt; 0.001) in HLR in hens at all time-points over the 2-week treatment period compared to controls. Cortisol, not corticosterone, only elicited an increase in HLR for drakes (p &lt; 0.05) compared to controls but only at day 1 after implants. Chronic treatment with cortisol, but not corticosterone, elicited an increase (p &lt; 0.01) in egg albumen cortisol levels compared to other groups. Corticosterone was not detected in any albumen samples. Our results suggest that glucocorticoids elicit differential effects and although corticosterone has been stated to be the predominant GC in avian species, cortisol may provide critical information to further understand bird welfare.

Effects of a variable light intensity lighting program on the welfare and performance of commercial broiler chickens

Our previous variable-light intensity lighting program studies indicate the light intensity preference behavior of broilers for their daily activity including eating and resting. To evaluate the effects of variable-light intensity lighting program on performance and welfare of broilers, four commercial trials were conducted for looking at behaviors, mortality, leg-health, performance, and brain welfare indicator genes including tryptophan hydroxylase 2 and tyrosine hydroxylase (TH), glucocorticoid receptor (GR), brain-derived neurotropic factor (BDNF), and melanopsin (Opn4) gene expression. One-day-old broilers were housed in four commercial broiler houses. Each quadrant (section) of the house was placed with 4,800 chicks. A total of four lighting programs began on day 7 with 5 lux (lx), 20 lx, natural light (NL, 480 lx), and variable light (2-5/40 lx) using LED lights on a 16L:8D photoperiod. In the variable-light house, the number of dustbathing holes was significantly higher than that in natural-light houses and 5-lx and 20-lx houses. Daily physical activities, footpad condition, fear response to novel objects, body weight, feed conversion ratio, and the number of leg-problem induced culled birds were affected by the variable-light intensity lighting program. Expression of tryptophan hydroxylase 2 in the DRN and VTA of variable-light treated birds was lower than that of 5-lx- and 20-lx-treated birds on day 42 (p < 0.05). Higher expression of VTA-TH in 5-lx-treated birds than that in 20-lx-, NL-, and variable-light-treated birds suggests the high stress-susceptibility of 5-lx treated birds. Lower VTA-GR expression in 20-lx- and variable-light-treated birds indicates lower stress than that in NL- and 5-lx-treated birds (p < 0.05). The VTA-BDNF expression of NL-treated birds was 2.5 fold higher than that of 5-lx-, 20-lx-, and variable-light-treated birds (p < 0.05), and variable-light-treated birds showed the lowest level of BDNF expression (p < 0.05), suggesting the chronic social defeat stress in NL-treated birds. The result of VTA-Opn4 expression on day 42 suggests the possible role of VTA-Opn4 in broiler welfare through central light perception. Taken together, the variable-light intensity lighting program increased volunteer natural behaviors and physical activity, which may improve footpad condition and leg health of birds, consequently. Performance data including the increased daily weight gain and the lowered feed conversion ratio and results of brain welfare indicator gene expression showed the beneficial effect of the variable-light intensity lighting program on the performance and welfare of commercial broilers.

Effects of a variable light intensity lighting program on the welfare and performance of commercial broiler chickens

Our previous variable-light intensity lighting program studies indicate the light intensity preference behavior of broilers for their daily activity including eating and resting. To evaluate the effects of variable-light intensity lighting program on performance and welfare of broilers, four commercial trials were conducted for looking at behaviors, mortality, leg-health, performance, and brain welfare indicator genes including tryptophan hydroxylase 2 and tyrosine hydroxylase (TH), glucocorticoid receptor (GR), brain-derived neurotropic factor (BDNF), and melanopsin (Opn4) gene expression. One-day-old broilers were housed in four commercial broiler houses. Each quadrant (section) of the house was placed with 4,800 chicks. A total of four lighting programs began on day 7 with 5 lux (lx), 20 lx, natural light (NL, 480 lx), and variable light (2-5/40 lx) using LED lights on a 16L:8D photoperiod. In the variable-light house, the number of dustbathing holes was significantly higher than that in natural-light houses and 5-lx and 20-lx houses. Daily physical activities, footpad condition, fear response to novel objects, body weight, feed conversion ratio, and the number of leg-problem induced culled birds were affected by the variable-light intensity lighting program. Expression of tryptophan hydroxylase 2 in the DRN and VTA of variable-light treated birds was lower than that of 5-lx- and 20-lx-treated birds on day 42 (p < 0.05). Higher expression of VTA-TH in 5-lx-treated birds than that in 20-lx-, NL-, and variable-light-treated birds suggests the high stress-susceptibility of 5-lx treated birds. Lower VTA-GR expression in 20-lx- and variable-light-treated birds indicates lower stress than that in NL- and 5-lx-treated birds (p < 0.05). The VTA-BDNF expression of NL-treated birds was 2.5 fold higher than that of 5-lx-, 20-lx-, and variable-light-treated birds (p < 0.05), and variable-light-treated birds showed the lowest level of BDNF expression (p < 0.05), suggesting the chronic social defeat stress in NL-treated birds. The result of VTA-Opn4 expression on day 42 suggests the possible role of VTA-Opn4 in broiler welfare through central light perception. Taken together, the variable-light intensity lighting program increased volunteer natural behaviors and physical activity, which may improve footpad condition and leg health of birds, consequently. Performance data including the increased daily weight gain and the lowered feed conversion ratio and results of brain welfare indicator gene expression showed the beneficial effect of the variable-light intensity lighting program on the performance and welfare of commercial broilers.

Stress and steroid interaction modulates expression of estrogen receptor alpha in the brain, pituitary, and testes of immature Gallus gallus domesticus

In nature, food availability stimulates hypothalamo-pituitary-gonadal (HPG) axis while its scarcity induces stress, which further stimulates hypothalamo-pituitary-adrenal (HPA) axis producing a detrimental effect on the avian reproductive physiology. The present experiment was designed to examine the interaction of stress like food restriction and estradiol on male reproductive physiology with special emphasis on estrogen receptor alpha (ERα) as these play crucial role in reproduction. To achieve this, 60 day old White Leghorn immature cockrels were taken and divided into four groups (n  =  8 per group). One group was provided with food and water ad libitum. Second group was food restricted (FR) for 9 h/day after 5 days, third and fourth were administered with estradiol benzoate (EB 0.5 mg/100g/day) for 12 days. Fourth group was FR for 9 h/day after 5 days of EB treatment till last day of experiment (EB + FR). Immunofluorescent localization of ERα was principally in the pre-optic area and paraventricular nuclei of hypothalamus and in anterior pituitary gland. ERα expression was highly reduced (from 40 AU to 20 AU) after FR in testis but it increased (50 AU) after EB administration, EB + FR reflects a diminishing pattern in the increment after EB. FR decreased plasma estradiol while EB increased it. Increased plasma corticosterone, hydrogen peroxide, malondialdehyde, and decreased anti-oxidant enzymes in brain and testis of all groups indicate oxidative stress in the HPG axis. The increased ERα after EB and a decrease with FR and EB + FR support their reproductive function. Estrogen and its receptor alpha are responsible for maintaining epithelial morphology but FR along with EB administration modulates the testicular development by significantly decreasing its size (p<.0001) and seminiferous tubules (p<.0001) and no sperm formation via highly reduced expression of ir-ERα in HPG axis. Our findings led us to conclude that stress like FR and estradiol induces testicular regression immature male chickens by modulating ir-ERα expression in the HPG axis thereby resulting in reduction in reproductive physiology.

Possible roles of brain derived neurotrophic factor and corticotropin releasing hormone neurons in the nucleus of hippocampal commissure functioning within the avian neuroendocrine regulation of stress

Corticotropin releasing hormone (CRH) neurons located in the nucleus of hippocampal commissure (NHpC) have been proposed to be involved in the avian neuroendocrine regulation of stress and appeared to respond prior to CRH neurons in the hypothalamic paraventricular nucleus (PVN) when food deprivation stress was applied. Since the response of the NHpC was rapid and short-lived, was it regulated differentially from CRH neurons in the PVN? We, therefore, applied immobilization stress to test whether the NHpC response was stressor specific. Gene expression of CRH and stress-related genes in the NHpC, PVN, anterior pituitary (APit) as well as plasma corticosterone (CORT) were determined. Furthermore, brain derived neurotrophic factor (BDNF) and glucocorticoid receptor (GR) were examined regarding their possible roles in the regulation of CRH neurons. Data showed that rapid activation of CRH mRNA in the NHpC occurred and preceded a slower gene activation in the PVN, upregulation of proopiomelanocortin (POMC) transcripts in the APit and significant increases of CORT concentrations. Results suggested BDNF's role in negative feedback between CRH and CRHR1 in the NHpC and positive feedback between CRH and CRHR1 in the PVN. In the APit, V1bR activation appeared responsible for sustaining CORT release when stress persisted. Overall, data suggest that the NHpC functions as part of the HPA axis of birds and perhaps a comparable extra-hypothalamic structure occurs in other vertebrates.Lay SummaryThe nucleus of the hippocampal commissure, a structure outside of the hypothalamus, shows rapidly increased neural gene expression that appears to contribute to the early activation of the traditional hypothalamic-pituitary-adrenal (HPA) axis responsible for the production of stress hormones.

Effects of Dark Brooder Rearing and Age on Hypothalamic Vasotocin and Feather Corticosterone Levels in Laying Hens

Chickens cannot independently thermoregulate at hatch and lack opportunity to behaviorally thermoregulate with a hen in the egg layer industry, thus barns are heated to thermoneutral temperatures. Dark brooders are low-energy-consuming hot plates, which may be environmentally advantageous while providing welfare-enhancing aspects of maternal care (i.e., shelter and separation of active and inactive individuals). Dark brooder use has been demonstrated to decrease injurious pecking and mortality well into the production period of layers. To further understand hen development around lay onset and effects of dark brooders on the brain and HPA-axis, we examined effects of rearing with dark brooders on expression of vasotocin (AVT) in the hypothalamus and corticosterone (CORT) in the feathers of in total 48 layer Isa Warren hens at 16 w and 28 w of age (n = 12 per age and treatment). An age-dependent decreased number of AVT-positive neurons was seen in the medial preoptic area, medial preoptic nucleus, paraventricular nucleus, rostral part (prepeduncular hypothalamus), and lateral preoptic area. Trends to effects of brooder rearing were found in both anteromedial preoptic nucleus and supraoptic nucleus, with dark brooder reared animals showing higher mean counts of AVT-positive neurons in both areas. No interactions between brooder raising and age were observed in AVT-positive neuron count. CORT levels were higher in primary wing feathers from 28 week old hens than in those from 16 week hens. No main effects of rearing with dark brooders or interactions between age and treatment were found on CORT levels. The age-dependent effects seen in the hypothalamus and CORT aids in further understanding of the development of chickens around puberty. The use of brooders tended to increase AVT expression in the anteromedial preoptic nucleus and supraoptic nucleus, an indication that dark brooder rearing may affect physiological responses regulated by these areas. The lack of effect of dark brooders on CORT in feathers is at the least an indication that the use of dark brooders is not stressful; in combination with the benefits of dark brooders on injurious pecking, fearfulness and early mortality, this pleads for the use of dark brooders in on-farm situations.

Differential delayed responses of arginine vasotocin and its receptors in septo-hypothalamic brain structures and anterior pituitary that sustain hypothalamic-pituitary-adrenal (HPA) axis functions during acute stress

Recently, we proposed that corticotropin releasing hormone (CRH) neurons in the nucleus of hippocampal commissure (NHpC), located in the septum, function as a part of the traditional hypothalamic-pituitary-adrenal (HPA) axis in avian species. CRH and its receptor, CRHR1, are regulated differently in the NHpC compared to the paraventricular nucleus (PVN) following feed deprivation (FD). Therefore, we followed up our work by examining arginine vasotocin (AVT), the other major ACTH secretagogue, and its receptors, V1aR and V1bR, gene expression during FD stress in the NHpC, PVN, and ventral mediobasal hypothalamus/median eminence (MBHv/ME). The objectives were to 1) identify AVT perikarya, fibers and its two major receptors, V1aR and V1bR, in the NHpC, PVN, and MBHv/ME using immunohistochemistry, 2) determine the effect of stress on AVT, V1aR and V1bR mRNA expression in the same three brain structures, NHpC, PVN, and MBHv/ME; and, 3) ascertain the expression pattern of V1aR and V1bR mRNA in the anterior pituitary and measure plasma stress hormone, corticosterone (CORT), concentration following FD stress. Male chicks (Cobb 500), 14 days of age, were divided into six groups (10 birds/treatment) and subjected to different times of FD stress: (Control, 1 h, 2 h, 3 h, 4 h, and 8 h). For each bird, blood, brain, and anterior pituitary were sampled and frozen immediately. The NHpC, PVN, and MBHv/ME were micro-dissected for RT-PCR. Data were analyzed using one-way ANOVA followed by Tukey Kramer HSD test using a significance level of p < 0.05. Perikarya of AVT neurons were identified in the PVN but not in the NHpC nor MBHv/ME, and only V1aR-immunoreactivity (ir) was observed in the three structures, however, gene expression data for AVT and its two receptors were obtained in all structures. Both AVT and V1aR mRNA are expressed and increased significantly in the PVN following FD stress (p < 0.01). For the first time, V1bR mRNA was documented in the avian brain and specifically shown upregulated in the NHpC and PVN (p < 0.01) following stress. Additionally, delayed significant gene expression of AVT and its receptors in the PVN showed a positive feedback relationship responsible for maintaining CORT release. In contrast, a significant downregulation of AVT mRNA and upregulation of V1aR mRNA occurred in the NHpC (p < 0.01) during FD showing a negative feedback relationship between AVT and its receptors, V1aR and V1bR. Within the MBHv/ME and anterior pituitary, a gradual increase of AVT mRNA in PVN as well as MBHv/ME was associated with significant upregulation of V1bR (p < 0. 01) and downregulation of V1aR (p < 0.01) in both MBHv/ME and anterior pituitary indicating AVT regulates its receptors differentially to sustain CORT release and control overstimulation of the anterior pituitary during a stress response.

Effects of light intensity and dual light intensity choice on plasma corticosterone, central serotonergic and dopaminergic activities in birds, Gallus gallus

Light intensity plays an important role in the regulation of growth, behavior, reproduction, and welfare of avian species. Light intensity preference behavior has been suggested to be involved in welfare of birds. This study aims to investigate the effects of different light intensity and dual light intensity choice (DLIC) lighting program on plasma corticosterone (CORT), and tryptophan hydroxylase 2 (TPH2, the rate-limiting enzyme of serotonin biosynthesis) and tyrosine hydroxylase (TH, the rate-limiting enzyme of dopamine biosynthesis) gene expression in the brainstem of male chickens. Day old broilers were housed in two commercial houses, and placed in 24 pens. All the treatment groups were provided with 23 h light (L) /1 h dark (D) and 30 lx (lx) light intensity during the first week and then 18L:6D (10 lx) from day 7 to 14. Blood and brain were sampled at 14 days of age (10 lx) before the onset of light treatments. On day 15, four treatments (2, 10, 20, and 100 lx), and DLIC treatment (2/20 lx) were initiated. Samples were collected on days 15, 16, 17, 30 and 41. TPH2 expression in the dorsal raphe nucleus (DRN) and caudal raphe nucleus (CRN) of brainstem, and TPH2 and TH expression in ventral tegmental areas (VTN) of the midbrain were determined by qPCR. Results showed that bright light and DLIC lighting program temporarily attenuated plasma CORT, suggesting the short-term stress attenuating effect of bright light and DLIC lighting program. Differential TPH2 expression in the DRN and CRN observed in the DLIC birds indicate a significant effect of DLIC lighting program on the serotonergic activity in the avian brainstem. At the 41 days of age, the significant downregulation of TPH2 and TH expression occurred in the VTA of DLIC treated birds compared to the other group of birds. Taken together, temporal and spatial regulation of TPH2 and TH expression by DLIC lighting program indicate that compensatory regulation of serotonergic and dopaminergic activities might be involved in the light intensity preference behavior of birds, suggesting a possible beneficial effect of the DLIC lighting program on broiler welfare.

Feather HSP70: a novel non-invasive molecular marker for monitoring stress induced by heat exposure in broilers

Poultry well-being and economic burden due to heat stress (HS) are of great importance to the poultry industry. Efficient design and effective evaluation of any strategies to alleviate the adverse effects of HS on poultry production require an accurate measurement of stress. However, current methods for monitoring stress in poultry are less than ideal, as they are invasive or subjective, and therefore variable. Here, we demonstrated that HSP70, the well-established intracellular stress chaperone, is expressed in chicken feather and is responsive to HS, and could therefore be used as a stress marker. Growing feathers were collected from the same bird (Cobb500, n = 9) in the morning (barn temperature 24°C) and afternoon (barn temperature 29.5°C) in the summer (2016 June 21) in Arkansas, USA. In the afternoon, the birds were panting and their core body temperatures were significantly higher compared to the morning time, as illustrated by iButton data thermo-loggers. Concomitantly, blood HSP70 mRNA and feather HSP70 expression (mRNA and protein) were significantly increased in the afternoon compared to the morning time. Similarly, HSP70 protein expression in the duodenum was also significantly higher in the afternoon compared to the morning period. Together, these finding identify feather HSP70 as a novel non-invasive molecular signature that mirrors the intracellular and systemic stress, which can be useful to monitor well-being of chickens and other avian species under different challenges.

The vasotocinergic system and its role in the regulation of stress in birds

The regulation of stress in birds includes a complex interaction of neural systems affecting the hypothalamic-pituitary-adrenal (HPA) axis. In addition to the hypothalamic paraventricular nucleus, a structure called the nucleus of the hippocampal commissure likewise affects the output of pituitary stress hormones and appears to be unique to avian species. Within the anterior pituitary, the avian V1a and V1b receptors were found in corticotropes. Based on our studies with central administration of hormones in the chicken, corticotropic releasing hormone (CRH) is a more potent ACTH secretagogue than arginine vasotocin (AVT). In contrast, when applied peripherally, AVT is more efficacious. Co-administration of AVT and CRH peripherally, resulted in a synergistic stimulation of corticosterone release. Data suggest receptor oligomerization as one possible mechanism. In birds, vasotocin receptors associated with stress responses include the V1a and V1b receptors. Three-dimensional, homology-based structural models of the avian V1aR were built to test agonists and antagonists for each receptor that were screened by molecular docking to map their binding sites on each receptor. Additionally, binding affinity values for each available peptide antagonist to the V1aR and V1bR were determined. An anterior pituitary primary culture system was developed to determine how effective each antagonist blocked the function of each receptor in culture when stimulated by a combination of AVT/CRH administration. Use of an antagonist in subsequent in vivo studies identified the V1aR in regulating food intake in birds. The V1aR was likewise found in circumventricular organs of the brain, suggesting a possible function in stress.

Unpredictable Chronic Mild Stress Suppresses the Incorporation of New Neurons at the Caudal Pole of the Chicken Hippocampal Formation

In the mammalian brain, adult hippocampal neurogenesis (AHN) is suppressed by chronic stress, primarily at the ventral pole of the hippocampus. Based upon anatomy, we hypothesise that the caudal pole of the avian Hippocampal Formation (HF) presents a homologous subregion. We thus investigated whether AHN is preferentially suppressed in the caudal chicken HF by unpredictable chronic mild stress (UCMS). Adult hens were kept in control conditions or exposed to UCMS for 8 weeks. Hens experiencing UCMS had significantly fewer doublecortin-positive multipolar neurons (p < 0.001) and beaded axons (p = 0.021) at the caudal pole of the HF than controls. UCMS birds also had smaller spleens and lower baseline plasma corticosterone levels compared to controls. There were no differences in AHN at the rostral pole, nor were there differences in expression of genetic mediators of the HPA stress response in the pituitary or adrenal glands. Duration of tonic immobility and heterophil/lymphocyte (H/L) ratios were also not responsive to our UCMS treatment. These results support the hypothesised homology of the caudal pole of the avian HF to the ventral pole of the rodent hippocampus. Furthermore, quantifying neurogenesis in the caudal HF post-mortem may provide an objective, integrative measure of welfare in poultry, which may be more sensitive than current welfare measures.

Identification of avian vasotocin receptor subtype-specific antagonists involved in the stress response of the chicken, Gallus gallus

Vasotocin 1a and 1b receptors (V1aR and V1bR) have been shown to play important roles in the neuroendocrine regulation of stress responses via the anterior pituitary (AP) of birds. To identify effective subtype-specific antagonists for the chicken V1aR (cV1aR) and cV1bR, potential antagonists to the mammalian V1R were screened against the cV1aR and cV1bR 3D structural models by molecular docking analysis with determination of binding pocket/amino acid residues involved in the interaction. The antagonistic effects of the selected ligands were examined by measuring pro-opiomelanocortin (POMC) heteronuclear RNA (hnPOMC) levels following the in vitro stress administration to primary chicken AP cells. Results of in silico analysis showed that the Manning compound and several other antagonists were bound to cV1bR with higher affinity than the natural agonist, arginine vasotocin (AVT). Similarities and differences in the antagonist-receptor binding interface with receptors were characterized for each ligand. Non-peptide mammalian V1bR antagonists, SSR-149415 and L-368899, were shown to be effective and had an additive effect in blocking POMC hnRNA expression in pituitary cell culture studies. SR-49059 antagonized the effect(s) of AVT/CRH on the downregulation of the cV1aR and the upregulation of the cCRH-R2 expression but not the cV1bR and cCRH-R1. The Manning compound antagonized the downregulation of cV1aR, cV1bR and cCRH-R1 and the upregulation of cCRH-R2 expression. The specificity of antagonists apparently resulted from unique differences in the interacting residues and their binding affinities. Collectively, these results provide valuable leads for future development of novel compounds capable of blocking or attenuating the AP stress response of avian species and perhaps other non-mammalian vertebrates as well.

Tissue-Specific Expression of DNA Methyltransferases Involved in Early-Life Nutritional Stress of Chicken, Gallus gallus

DNA methylation was reported as a possible stress-adaptation mechanism involved in the transcriptional regulation of stress responsive genes. Limited data are available on effects of psychological stress and early-life nutritional stress on DNA methylation regulators [DNMTs: DNA (cytosine-5)-methyltransferase 1 (DNMT1), DNMT1 associated protein (DMAP1), DNMT 3 alpha (DNMT3A) and beta (DNMT3B)] in avian species. The objectives of this study were to: (1) investigate changes in expression of DNMT1, DMAP1, DNMT3A, and DNMT3B following acute (AS) or chronic immobilization stress (CS); (2) test immediate effect of early-life nutritional stress [food deprivation (FD) for 12 h (12hFD) or 36 h (36hFD) at the post-hatching period] on expression of DNA methylation regulators and glucocorticoid receptor (GR), and the long-term effect of early-life nutritional stress at 6 weeks of age. Expression of DNMTs and plasma corticosterone (CORT) concentration decreased by CS compared to AS (p < 0.05), indicating differential roles of DNA methylation regulators in the stress response. Plasma CORT at 12hFD and 36hFD birds increased compared to control birds (12hF and 36hF), but there were no significant differences in plasma CORT of 12hFD and 36hFD birds at 6 weeks of age compared to 6 week controls. DNMT1, DMAP1, and DNMT3B expression in the anterior pituitary increased by 12hFD, but decreased at 36hFD compared to their controls (P < 0.05). In liver, DNMT1, DNMT3A, and DNMT3B expression decreased by 12hFD, however, no significant changes occurred at 36hFD. Expression of DMAP1, DNMT3A, and DNMT3B in anterior pituitary and DMAP1 and DNMT3A expression in liver at 6 weeks of age were higher in 36hFD stressed birds compared to controls as well as 12hFD stressed birds. Hepatic GR expression decreased by 12hFD and increased by 36hFD (p < 0.05). Expression patterns of GR in the liver of FD stress-induced birds persisted until 6 weeks of age, suggesting the possible lifelong involvement of liver GR in early-life nutritional stress response of birds. Taken together, results suggest that DNA methylation regulator genes are tissue-specifically responsive to acute and chronic stress, and hepatic GR may play a critical role in regulating the early-life nutritional stress response of birds. In addition, the downregulation of DNMT1 and DMAP1 may be one of the adaptive mechanisms to chronic early-life nutritional stress via passive demethylation.

Differential responses of the vasotocin 1a receptor (V1aR) and osmoreceptors to immobilization and osmotic stress in sensory circumventricular organs of the chicken (Gallus gallus) brain

Past studies have shown that the avian vasotocin 1a receptor (V1aR) is involved in immobilization stress. It is not known whether the receptor functions in osmotic stress, and if sensory circumventricular organs may be involved. An experiment was designed with four treatment groups including a 1h immobilization acute stress (AS) group, an unstressed acute control (AC), a third given an intraperitoneal (ip) hypertonic saline injection (HS) and isotonic saline controls (IC) administered ip. One set of chick brains was perfused for immunohistochemistry while a second was sampled for quantitative RT-PCR. Plasma corticosterone (CORT) and arginine vasotocin (AVT) concentrations were significantly increased in the immobilized and hypertonic saline groups (p<0.01) compared to controls. Intense staining of the V1aR occurred throughout the organum vasculosum of the lamina terminalis (OVLT) and subseptal organ (SSO)/subfornical organ (SFO). The immunostaining allowed the boundaries of the two circumventricular organs (CVOs) to be described for the first time in avian species. Both treatment groups showed marked morphological changes in glia within the OVLT and SSO/SFO. The avian V1aR, angiotensin II type 1 receptor (AT1R), and transient receptor potential vanilloid receptor 1 (TRPV1) mRNA levels were increased in the SSO/SFO in hypertonic saline treated birds compared to isotonic controls. In contrast, the latter two genes (AT1R and TRPV1) were significantly decreased in the OVLT of birds subjected to hyperosmotic stress, while all three genes were significantly up-regulated after immobilization. Taken together, results show a possible differential function for the same receptors in two anatomically adjacent CVOs.

Central effect of vasotocin 4 receptor (VT4R/V1aR) antagonists on the stress response and food intake in chicks given neuropeptide Y (NPY)

Previous studies identified SR-49059 as a most effective antagonist of the avian vasotocin 4 receptor (VT4R) compared to other candidate blockers including the Manning compound using in silico 3 dimensional (3D) modeling/docking analysis of the chicken VT4R and an in vitro anterior pituitary cell culture study. The present experiments were designed to validate whether SR-49059 and the Manning compound would likewise be effective in vivo in blocking the VT4R when applied intracerebroventricularly (ICV) to chicks. Two treatments were tested, a stressor (immobilization) and administration of neuropeptide Y (NPY), a potent orexigenic compound. In the first experiment, birds were given the Manning compound, SR-49059 or physiological saline ICV followed by immobilization stress. Blood samples were taken and corticosterone (CORT) was determined by radioimmunoassay. It was hypothesized that both antagonists would reduce the stress response. A second experiment examined the role of the VT4R in food intake regulation. The Manning compound, SR-49059 or physiological saline was administered prior to NPY and food intake was monitored for 1h. It was hypothesized that each of the two antagonists coupled with NPY would augment food intake above the intake resulting from saline plus NPY administration. Related to the second experiment was a third that examined the difference between the effect of central administration of NPY versus SR-49059 in releasing CORT. Results of the first study showed that the Manning compound or SR-49059 prior to stress decreased CORT levels compared to controls while the second experiment showed that SR-49059 or the Manning compound plus NPY, enhanced food intake above that of the experimental group given saline and NPY. The last study showed that NPY increased plasma CORT above birds given SR-49059 centrally or saline administered controls. Taken together, results suggest that the avian VT4R is involved in the central neuroendocrine stress response as well as functions in appetite regulation by mediating an anorexigenic effect similar to what has been reported in mammals for the V1aR. In conclusion, similar to the past in silico and in vitro tests, the current in vivo experiments showed SR-49059 to be a most efficacious avian vasotocin receptor antagonist. Therefore based upon results of functional tests utilizing a highly specific mammalian antagonist, SR-49059, to the mammalian V1aR that likewise was most effective in blocking the avian VT4R and past reported high sequence homology between the mammalian V1aR and the VT4R, it is recommended that the chicken VT4R be renamed the avian V1aR to facilitate better communication among scientists involved in comparative studies.