Sex differences in plasma corticosterone release in undisturbed chickens (Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

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.

Heat stress and poultry production: a comprehensive review

The impact of global warming on poultry production has gained significant attention over the years. However, our current knowledge and understanding of the mechanisms through which heat stress (HS) resulting from global warming affects the welfare, behavior, immune response, production performance, and even transgenerational effects in poultry are still incomplete. Further research is needed to delve deeper into these mechanisms to gain a comprehensive understanding. Numerous studies have investigated various biomarkers of stress in poultry, aiming to identify reliable markers that can accurately assess the physiological status and well-being of birds. However, there is a significant amount of variation and inconsistency in the results reported across different studies. This inconsistency highlights the need for more standardized methods and assays and a clearer understanding of the factors that influence these biomarkers in poultry. This review article specifically focuses on 3 main aspects: 1) the neuroendocrine and behavioral responses of poultry to HS, 2) the biomarkers of HS and 3) the impact of HS on poultry production that have been studied in poultry. By examining the neuroendocrine and behavioral changes exhibited by poultry under HS, we aim to gain insights into the physiological impact of elevated temperatures in poultry.

Interaction between the hypothalamo-pituitary-adrenal and thyroid axes during immobilization stress

The location of corticotropin-releasing hormone receptor 2 (CRH-R2) on thyrotropes within the avian anterior pituitary (APit) and its activation by different stressors indicate a possible communication between hypothalamo-pituitary-adrenal (HPA) and thyroid (HPT) axes. Therefore, an experiment was designed to 1) compare the timing of major components of the HPT axis to those of the HPA axis; 2) address whether stressors activating the HPA axis may simultaneously upregulate components of the HPT axis. Blood, brain, and APit were sampled from chicks prior to stress (control) and 15, 30, 60, 90, and 120 min following immobilization (IM) stress. The nucleus of the hippocampal commissure (NHpC) and paraventricular nucleus (PVN) were cryo-dissected from brains for RT-qPCR. Gene expression of thyrotropin-releasing hormone (TRH) and its receptors (TRH-R1 and TRH-R3), urocortin3 (UCN3), deiodinase 2 (D2), and the second type of corticotropin-releasing hormone (CRH2) within the NHpC and PVN was measured. Additionally, gene expression of TRH receptors, thyroid stimulating hormone subunit beta (TSHβ), and D2 was determined in the APit and corticosterone assayed in blood. In brains, a significant upregulation in examined genes occurred at different times of IM. Specifically, UCN3 and CRH2 which have a high affinity to CRH-R2 showed a rapid increase in their mRNA levels that were accompanied by an early upregulation of TRHR1 in the NHpC. In the APit, a significant increase in gene expression of TSHβ and TRH receptors was observed. Therefore, results supported concurrent activation of major brain and APit genes associated with the HPA and HPT axes following IM. The initial neural gene expression originating within the NHpC resulted in the increase of TSHβ mRNA in the APit. Specifically, the rapid upregulation of UCN3 in the NHpC appeared responsible for the early activation of TSHβ in the APit. While sustaining TSHβ activation appeared to be due to both CRH2 and TRH. Therefore, data indicate that CRH-producing neurons and corticotropes as well as CRH- and TRH-producing neurons and thyrotropes are activated to produce the necessary energy required to maintain homeostasis in birds undergoing stress. Overall, data support the inclusion of the NHpC in the classical avian HPA axis and for the first time show the concurrent activation of the HPA axis and components of the HPT axis following a psychogenic stressor.

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.

Stress, health and the welfare of laying hens

It is essential to understand responses to stress and the impact of stress on physiological and behavioural functioning of hens, so as to assess their welfare. The current understanding of stress in laying hens is comprehensively reviewed here. Most research on stress in hens has focussed on the activity of the adrenal glands, with the most common approach being to measure corticosterone, which is the predominant glucocorticoid produced by birds in response to stress. While these measures are useful, there is a need to understand how the brain regulates stress responses in hens. A greater understanding of the sympathoadrenal system and its interaction with the hypothalamo–pituitary–adrenal axis is required. There is also a lack of knowledge about the many other peptides and regulatory systems involved in stress responses in hens. The usefulness of understanding stress in hens in terms of assessing welfare depends on appreciating that different stressors elicit different responses and that there are often differences in responses to, and impacts of, acute and chronic stress. It is also important to establish the actions and fate of stress hormones within target tissues. It is the consequences of these actions that are important to welfare. A range of other measures has been used to assess stress in hens, including a ratio of heterophils to lymphocytes and haematocrit:packed cell-volume ratio and measures of corticosterone or its metabolites in eggs, excreta, feathers and the secretions of the uropygial gland. Measures in eggs have proffered varying results while measures in feathers may be useful to assess chronic stress. There are various studies in laying hens to indicate impacts of stress on the immune system, health, metabolism, appetite, and the quality of egg production, but, generally, these are limited, variable and are influenced by the management system, environment, genetic selection, type of stressor and whether or not the birds are subjected to acute or chronic stress. Further research to understand the regulation of stress responses and the impact of stress on normal functioning of hens will provide important advances in the assessment of stress and, in turn, the assessment of welfare of laying hens.

Spontaneous intake of essential oils after a negative postnatal experience has long-term effects on blood transcriptome in chickens

Chicks subjected to early stressful factors could develop long-lasting effects on their performances, welfare and health. Free access to essential oils (EO) in poultry farming could mitigate these effects and potentially reduce use of antimicrobial drugs. This study on chicken analyzed long-lasting effects of post-hatch adverse conditions (Delayed group), and the impact of EO intake on blood physiological parameters and transcriptome. Half of the Control and Delayed groups had free access to EO, while the other half had only water for the first 13 days post-hatching. Blood analyses of metabolites, inflammation and oxidative stress biomarkers, and mRNA expression showed sex differences. Long-lasting effects of postnatal experience and EO intake persisted in blood transcriptome at D34. The early adverse conditions modified 68 genes in males and 83 genes in females. In Delayed males six transcription factors were over-represented (NFE2L2, MEF2A, FOXI1, Foxd3, Sox2 and TEAD1). In females only one factor was over-represented (PLAG1) and four under-represented (NFIL3, Foxd3, ESR2 and TAL1::TCF3). The genes showing modified expression are involved in oxidative stress, growth, bone metabolism and reproduction. Remarkably, spontaneous EO intake restored the expression levels of some genes affected by the postnatal adverse conditions suggesting a mitigating effect of EO intake.

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.

Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

The fact that body temperature can rise or fall following exposure to stressors has been known for nearly two millennia; however, the functional value of this phenomenon remains poorly understood. We tested two competing hypotheses to explain stress-induced changes in temperature, with respect to surface tissues. Under the first hypothesis, changes in surface temperature are a consequence of vasoconstriction that occur to attenuate blood loss in the event of injury and serve no functional purpose per se; defined as the 'haemoprotective hypothesis'. Under the second hypothesis, changes in surface temperature reduce thermoregulatory burdens experienced during activation of a stress response, and thus hold a direct functional value: the 'thermoprotective hypothesis'. To understand whether stress-induced changes in surface temperature have functional consequences, we tested predictions of these two hypotheses by exposing black-capped chickadees (n=20) to rotating stressors across an ecologically relevant ambient temperature gradient, while non-invasively monitoring surface temperature (eye region temperature) using infrared thermography. Our results show that individuals exposed to rotating stressors reduce surface temperature and dry heat loss at low ambient temperature and increase surface temperature and dry heat loss at high ambient temperature, when compared with controls. These results support the thermoprotective hypothesis and suggest that changes in surface temperature following stress exposure have functional consequences and are consistent with an adaptation. Such findings emphasize the importance of the thermal environment in shaping physiological responses to stressors in vertebrates, and in doing so, raise questions about their suitability within the context of a changing climate.

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.

Some aspects of the hypothalamic and pituitary development, metamorphosis, and reproductive behavior as studied in amphibians

In this review article, information about the development of the hypothalamo-hypophyseal axis, endocrine control of metamorphosis, and hormonal and pheromonal involvements in reproductive behavior in some amphibian species is assembled from the works conducted mainly by our research group. The hypothalamic and pituitary development was studied using Bufo embryos and larvae. The primordium of the epithelial hypophysis originates at the anterior neural ridge and migrates underneath the brain to form a Rathke's pouch-like structure. The hypothalamo-hypophyseal axis develops under the influence of thyroid hormone (TH). For the morphological and functional development of the median eminence, which is a key structure in the transport of regulatory hormones to the pituitary, contact of the adenohypophysis with the undeveloped median eminence is necessary. For the development of proopiomelanocortin-producing cells, contact of the pituitary primordium with the infundibulum is required. The significance of avascularization in terms of the function of the intermediate lobe of the pituitary was evidenced with transgenic Xenopus frogs expressing a vascular endothelial growth factor in melanotropes. Metamorphosis progresses via the interaction of TH, adrenal corticosteroids, and prolactin (PRL). We emphasize that PRL has a dual role: modulation of the speed of metamorphic changes and functional development of organs for adult life. A brief description about a novel type of PRL (1B) that was detected was made. A possible reason why the main hypothalamic factor that stimulates the release of thyrotropin is not thyrotropin-releasing hormone, but corticotropin-releasing factor is considered in light of the fact that amphibians are poikilotherms. As regards the reproductive behavior in amphibians, studies were focused on the courtship behavior of the newt, Cynops pyrrhogaster. Male newts exhibit a unique courtship behavior toward sexually developed conspecific females. Hormonal interactions eliciting this behavior and hormonal control of the courtship pheromone secretion are discussed on the basis of our experimental results.

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.

No evidence for sex-specific effects of the maternal social environment on offspring development in Japanese quail (Coturnix japonica)

The social environment of reproducing females can cause physiological changes, with consequences for reproductive investment and offspring development. These prenatal maternal effects are often found to be sex-specific and may have evolved as adaptations, maximizing fitness of male and female offspring for their future environment. Female hormone levels during reproduction are considered a potential mechanism regulating sex allocation in vertebrates: high maternal androgens have repeatedly been linked to increased investment in sons, whereas high glucocorticoid levels are usually related to increased investment in daughters. However, results are not consistent across studies and therefore still inconclusive. In Japanese quail (Coturnix japonica), we previously found that pair-housed females had higher plasma androgen levels and tended to have higher plasma corticosterone levels than group-housed females. In the current study we investigate whether these differences in maternal social environment and physiology affect offspring sex allocation and physiology. Counter to our expectations, we find no effects of the maternal social environment on offspring sex ratio, sex-specific mortality, growth, circulating androgen or corticosterone levels. Also, maternal corticosterone or androgen levels do not correlate with offspring sex ratio or mortality. The social environment during reproduction therefore does not necessarily modify sex allocation and offspring physiology, even if it causes differences in maternal physiology. We propose that maternal effects of the social environment strongly depend upon the type of social stimuli and the timing of changes in the social environment and hormones with respect to the reproductive cycle and meiosis.

Anatomical and functional implications of corticotrophin-releasing hormone neurones in a septal nucleus of the avian brain: an emphasis on glial-neuronal interaction via V1a receptors in vitro

Previously, we showed that corticotrophin-releasing hormone immunoreactive (CRH-IR) neurones in a septal structure are associated with stress and the hypothalamic-pituitary-adrenal axis in birds. In the present study, we focused upon CRH-IR neurones located within the septal structure called the nucleus of the hippocampal commissure (NHpC). Immunocytochemical and gene expression analyses were used to identify the anatomical and functional characteristics of cells within the NHpC. A comparative morphometry analysis showed that CRH-IR neurones in the NHpC were significantly larger than CRH-IR parvocellular neurones in the paraventricular nucleus of the hypothalamus (PVN) and lateral bed nucleus of the stria terminalis. Furthermore, these large neurones in the NHpC usually have more than two processes, showing characteristics of multipolar neurones. Utilisation of an organotypic slice culture method enabled testing of how CRH-IR neurones could be regulated within the NHpC. Similar to the PVN, CRH mRNA levels in the NHpC were increased following forskolin treatment. However, dexamethasone decreased forskolin-induced CRH gene expression only in the PVN and not in the NHpC, indicating differential inhibitory mechanisms in the PVN and the NHpC of the avian brain. Moreover, immunocytochemical evidence also showed that CRH-IR neurones reside in the NHpC along with the vasotocinergic system, comprising arginine vasotocin (AVT) nerve terminals and immunoreactive vasotocin V1a receptors (V1aR) in glia. Hence, we hypothesised that AVT acts as a neuromodulator within the NHpC to modulate activity of CRH neurones via glial V1aR. Gene expression analysis of cultured slices revealed that AVT treatment increased CRH mRNA levels, whereas a combination of AVT and a V1aR antagonist treatment decreased CRH mRNA expression. Furthermore, an attempt to identify an intercellular mechanism in glial-neuronal communication in the NHpC revealed that brain-derived neurotrophic factor (BDNF) and its receptor (TrkB) could be involved in the signalling mechanism. Immunocytochemical results further showed that both BDNF and TrkB receptors were found in glia of the NHpC. Interestingly, in cultured brain slices containing the NHpC, the use of a selective TrkB antagonist decreased the AVT-induced increase in CRH gene expression levels. The results from the present study collectively suggest that CRH neuronal activity is modulated by AVT via V1aR involving BDNF and TrkB glia in the NHpC.

Arginine vasotocin is the major adrenocorticotropic hormone-releasing factor in the bullfrog Rana catesbeiana

In a previous study, we showed that corticotropin-releasing factor (CRF) is the major thyroid-stimulating hormone (TSH)-releasing factor in the bullfrog (Rana catesbeiana) hypothalamus. Our findings prompted us to ascertain whether CRF or arginine vasotocin (AVT), a known adrenocorticotropic hormone (ACTH) secretagogue in several vertebrates, is the main stimulator of the release of ACTH from the bullfrog pituitary. Both the frog CRF and AVT stimulated the release of immunoassayable ACTH from dispersed anterior pituitary cells in vitro in a concentration-dependent manner. AVT, however, exhibited far more potent ACTH-releasing activity than CRF. Although CRF by itself weakly stimulated ACTH release, it acted synergistically with AVT to enhance the release of ACTH markedly. Mesotocin and AVT-related peptides such as hydrin 1 and hydrin 2 showed relatively weak ACTH-releasing activity. Subsequently, cDNAs encoding the bullfrog AVT V1a-type and V1b-type receptors were molecularly cloned. Reverse transcriptase-PCR using specific primers revealed that the anterior lobe of the pituitary predominantly expressed AVT V1b-type receptor mRNA but scarcely expressed AVT V1a-type receptor mRNA. Abundant signals for V1b-type receptor mRNA in the corticotropes were also detected by in situ hybridization. The results obtained by the experiments with the bullfrog pituitary indicate that AVT acts as the main ACTH-releasing factor through the AVT V1b-type receptor and that CRF acts synergistically with AVT to enhance the release of ACTH.

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.

Diencephalic and septal structures containing the avian vasotocin receptor (V1aR) involved in the regulation of food intake in chickens, Gallus gallus

Recently, it was found that the avian central vasotocin receptor (V1aR) is associated with the regulation of food intake. To identify V1aR-containing brain structures regulating food intake, a selective V1aR antagonist SR-49059 that induced food intake was administrated intracerebroventricularly in male chickens followed by detection of brain structures using FOS immunoreactivity. Particularly, the hypothalamic core region of the paraventricular nucleus, lateral hypothalamic area, dorsomedial hypothalamic nucleus, a subnucleus of the central extended amygdalar complex [dorsolateral bed nucleus of the stria terminalis], medial septal nucleus and caudal brainstem [nucleus of the solitary tract] showed significantly increased FOS-ir cells. On the other hand, the supraoptic nucleus of the preoptic area and the nucleus of the hippocampal commissure of the septum showed suppressed FOS immunoreactivity in the V1aR antagonist treatment group. Further investigation revealed that neuronal activity of arginine vasotocin (AVT-ir) magnocellular neurons in the supraoptic nucleus, preoptic periventricular nucleus, paraventricular nucleus and ventral periventricular hypothalamic nucleus and most likely corticotropin releasing hormone (CRH-ir) neurons in the nucleus of the hippocampal commissure were reduced following the antagonist treatment. Dual immunofluorescence labeling results showed that perikarya of AVT-ir magnocellular neurons in the preoptic area and hypothalamus were colabeled with V1aR. Within the nucleus of the hippocampal commissure, CRH-ir neurons were shown in close contact with V1aR-ir glial cells. Results of the present study suggest that the V1aR plays a role in the regulation of food intake by modulating neurons that synthesize and release anorectic neuropeptides in the avian brain.

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.

Early stress causes sex-specific, life-long changes in behaviour, levels of gonadal hormones, and gene expression in chickens

Early stress can have long-lasting phenotypic effects. Previous research shows that male and female chickens differ in many behavioural aspects, and respond differently to chronic stress. The present experiment aimed to broadly characterize long-term sex differences in responses to brief events of stress experienced during the first weeks of life. Chicks from a commercial egg-laying hybrid were exposed to stress by inducing periods of social isolation during their first three weeks of life, followed by a broad behavioural, physiological and genomic characterization throughout life. Early stressed males, but not females, where more anxious in an open field-test, stayed shorter in tonic immobility and tended to have delayed sexual maturity, as shown by a tendency for lower levels of testosterone compared to controls. While early stressed females did not differ from non-stressed in fear and sexual maturation, they were more socially dominant than controls. The differential gene expression profile in hypothalamus was significantly correlated from 28 to 213 days of age in males, but not in females. In conclusion, early stress had a more pronounced long-term effect on male than on female chickens, as evidenced by behavioral, endocrine and genomic responses. This may either be attributed to inherent sex differences due to evolutionary causes, or possibly to different stress related selection pressures on the two sexes during commercial chicken breeding.

Adding ‘epi-’ to behaviour genetics: implications for animal domestication

In this review, it is argued that greatly improved understanding of domestication may be gained from extending the field of behaviour genetics to also include epigenetics. Domestication offers an interesting framework of rapid evolutionary changes caused by well-defined selection pressures. Behaviour is an important phenotype in this context, as it represents the primary means of response to environmental challenges. An overview is provided of the evidence for genetic involvement in behavioural control and the presently used methods for finding so-called behaviour genes. This shows that evolutionary changes in behaviour are to a large extent correlated to changes in patterns of gene expression, which brings epigenetics into the focus. This area is concerned with the mechanisms controlling the timing and extent of gene expression, and a lot of focus has been placed on methylation of cytosine in promoter regions, usually associated with genetic downregulation. The review considers the available evidence that environmental input, for example stress, can modify methylation and other epigenetic marks and subsequently affect behaviour. Furthermore, several studies are reviewed, demonstrating that acquired epigenetic modifications can be inherited and cause trans-generational behaviour changes. In conclusion, epigenetics may signify a new paradigm in this respect, as it shows that genomic modifications can be caused by environmental signals, and random mutations in DNA sequence are therefore not the only sources of heritable genetic variation.

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 15 min and then decreased at 1 h and 6 h 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 (10 ng/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.

Identification of arginine vasotocin (AVT) neurons activated by acute and chronic restraint stress in the avian septum and anterior diencephalon

Effects of acute and chronic psychological stress in the brain of domestic avian species have not been extensively studied. Experiments were performed using restraint stress to determine groups of neurons activated in the septum and diencephalon of chickens. Using FOS immunoreactivity six brain structures were shown activated by acute stress including: the lateral hypothalamic area (LHy), ventrolateral thalamic nucleus (VLT), lateral septum (LS), lateral bed nucleus of the stria terminalis (BSTL), nucleus of the hippocampal commissure (NHpC) and the core region of the paraventricular nucleus (PVNc). Additionally, the LHy and PVNc showed increased FOS immunoreactive (-ir) cells in the birds chronically stressed when compared to controls. In contrast, the NHpC showed decreased FOS-ir cells following the 10day chronic stress imposed. Thereafter, restraint stress experiments were performed to identify activated arginine vasotocin (AVT) neurons (parvocellular or magnocellular) using immunocytochemistry. Of the six FOS activated structures, the PVN was known to contain distinct size groups of AVT-ir neurons, parvocellular (small), medium sized and magnocellular (large). Using dual immunostaining (AVT/FOS), AVT-ir parvocellular neurons in the PVNc were found activated in both acute and chronic stress. To determine whether these AVT-ir parvocellular neurons are co-localized with corticotropin releasing hormone (CRH), an attempt was made to visualize CRH-ir neurons using colchicine. Although AVT-ir and CRH-ir parvocellular neurons occur in the PVNc, only a few neurons were shown co-localized with AVT and CRH after acute restraint stress. Results of this study suggest that the NHpC, LS, VLT, BSTL, LHy and AVT-ir parvocellular neurons in the PVNc are associated with psychological stress in birds.

A possible mechanism contributing to the synergistic action of vasotocin (VT) and corticotropin-releasing hormone (CRH) receptors on corticosterone release in birds

Arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) are two neuronal regulators in the hypothalamic-pituitary-adrenal (HPA) axis that modulate biological responses to stress in avian species. When AVT and CRH are administered together in vitro or in vivo, levels of adrenocorticotropic hormone (ACTH) or plasma corticosterone (CORT) are released, respectively, in a synergistic manner. The underlying mechanism of this greater than additive stress response was investigated by expressing the vasotocin receptor type 2 (VT2R) and CRH receptor type 1 (CRH-R1), both G-protein coupled receptors, in HeLa cells. Fluorescence resonance energy transfer (FRET) analysis provided the evidence for heterodimerization of the VT2R/CRH-R1 in the presence of their respective ligands, AVT and CRH. The VT2R and CRH-R1 were tagged at the C-terminal ends with either cyan fluorescent protein (CFP) or yellow fluorescent protein (YFP), and a VT2R chimera was constructed by replacing the fourth transmembrane region (TM4) of the VT2R with TM-IV of the β2-adrenergic receptor (β2AR). When VT2R/β2AR chimera and CRH-R1 were expressed in HeLa cells, heterodimerization was partly disrupted. Taken together, these data indicate that TM-IV of the VT2R may provide an important interface for effective receptor dimerization, suggesting that direct molecular interaction between VT2R and CRH-R1 receptors plays a role in mediating an enhanced interaction between these two receptors. Their interaction at the anterior pituitary level may potentiate the endocrine output of the avian HPA system.

Identification of antagonists to the vasotocin receptor sub-type 4 (VT4R) involved in stress by molecular modelling and verification using anterior pituitary cells

The vasotocin receptor family is homologous to the mammalian vasopressin G-protein coupled receptor (GPCR) family. The vasotocin receptor 2 (VT2R) and 4 (VT4R) have recently been shown to play important role(s) in the neuroendocrine regulation of stress in birds. A homology-based structural model of VT4R of the domestic chicken, Gallus gallus, was built using the sophisticated SYBYL-X suite. The structure of VT4R built with and without extra- and intracellular unstructured loops showed a seven-helix transmembrane domain, which is a characteristic feature of GPCRs. Several agonists and antagonists were screened by molecular docking to map their potential binding sites on the structure of VT4R. Interestingly, the presence of the N-terminal, intracellular and extracellular loops and C-terminal amino acid sequences emerging from the transmembrane domains during molecular docking appeared to influence the binding interface of the peptide agonists and peptide/non-peptide antagonists on the VT4R. The presence of unstructured loops, however, did not affect the relative binding affinity ranking of the peptide antagonists to VT4R. In general, the natural ligand, arginine vasotocin and the peptide/non-peptide antagonists were observed to be more deeply buried in the receptor. Results of in vitro inhibition experiments, using cultured anterior pituitary cells, showed excellent agreement with the binding affinity of the antagonists predicted by molecular docking. The results of this study provide valuable clues for the rational design of novel pharmaceutical compounds capable of blocking or attenuating the stress response.

Distribution of the Vasotocin Subtype Four Receptor (VT4R) in the Anterior Pituitary Gland of the Chicken, Gallus gallus, and its Possible Role in the Avian Stress Response

The neurohormone arginine vasotocin (AVT) in non mammalian vertebrates is homologous to arginine vasopressin (AVP) in mammals. Its actions are mediated via G protein-coupled receptors that belong to the vasotocin/mesotocin family. Because of the known regulatory effects of nonapeptide hormones on anterior pituitary functions, receptor subtypes in that family have been proposed to be located in anterior pituitary cells. Recently, an avian vasotocin receptor subtype designated VT4R has been cloned, which shares 69% sequence homology with a human vasopressin receptor, the V1aR. In the present study, a polyclonal antibody to the VT4R was developed and validated to confirm its specificity to the VT4R. The antibody was used to test the hypothesis that the VT4R is present in the avian anterior pituitary and is specifically associated with certain cell types, where its expression is modulated by acute stress. Western blotting of membrane protein extracts from pituitary tissue, the use of HeLa cells transfected with the VT4R and peptide competition assays all confirmed the specificity of the antibody to the VT4R. Dual-labelling immunofluorescence microscopy was utilised to identify pituitary cell types that contained immunoreactive VT4R. The receptor was found to be widely distributed throughout the cephalic lobe but not in the caudal lobe of the anterior pituitary. Immunoreactive VT4R was associated with corticotrophs. Approximately 89% of immunolabelled corticotrophs were shown to contain the VT4R. The immunoreactive VT4R was not found in gonadotrophs, somatotrophs or lactotrophs. To determine a possible functional role of the VT4R and previously characterised VT2R, gene expression levels in the anterior pituitary were determined after acute immobilisation stress by quantitative reverse transcriptase-polymerase chain reaction. The results showed a significant increase in plasma corticosterone levels (three- to four-fold), a significant reduction of VT4R mRNA and an increase of VT2R mRNA (P < 0.05) in acutely immobilised chicks compared to controls. The data suggest a role of the VT4R in the avian stress response.

Roles of arginine vasotocin receptors in the brain and pituitary of submammalian vertebrates

This chapter reviews the functions of arginine vasotocin (AVT) and its receptors in the central nervous system (CNS) of primarily submammalian vertebrates. The V1a-type receptor, which is widely distributed in the CNS of birds, amphibians, and fish, is one of the most important receptors involved in the expression of social and reproductive behaviors. In mammals, the V1b receptor of arginine vasopressin, an AVT ortholog, is assumed to be involved in aggression, social memory, and stress responses. The distribution of the V1b-type receptor in the brain of submammalian vertebrates has only been reported in an amphibian species, and its putative functions are discussed in this review. The functions of V2-type receptor in the CNS are still unclear. Recent phylogenetical and pharmacological analyses have revealed that the avian VT1 receptor can be categorized as a V2b-type receptor. The distribution of this newly categorized VT1 receptor in the brain of avian species should contribute to our knowledge of the possible roles of the V2b-type receptor in the CNS of other nonmammalian vertebrates. The functions of AVT in the amphibian and avian pituitaries are also discussed, focusing on the V1b- and V1a-type receptors.

Transgenerational effects of early experience on behavioral, hormonal and gene expression responses to acute stress in the precocial chicken

Stress during early life can profoundly influence an individual's phenotype. Effects can manifest in the short-term as well as later in life and even in subsequent generations. Transgenerational effects of stress are potentially mediated via modulation of the hypothalamic-pituitary-adrenal axis (HPA) as well as epigenetic mechanisms causing heritable changes in gene expression. To investigate these pathways we subjected domestic chicken (Gallus gallus) to intermittent social isolation for the first three weeks of life. The early life stress resulted in a dampened corticosterone response to restraint stress in affected birds and in their male offspring. Stress-specific genes, such as early growth response 1 (EGR1) and corticotropin releasing hormone receptor 1 (CRHR1), were upregulated immediately after restraint stress, but not under baseline conditions. Treatment differences in gene expression were also correlated across generations which indicate transgenerational epigenetic inheritance. In an associative learning test early stressed birds made more correct choices suggesting a higher coping ability in stressful situations. This study is the first to show transgenerational effects of early life stress in a precocial species by combining behavioral, endocrinological, and transcriptomic measurements.

Effects of dietary yeast extract on turkey stress response and heterophil oxidative burst activity

1. Effective nutritional approaches to counteract the negative effects of stress may provide food animal producers with useful alternatives to antibiotics. In this study, turkeys were fed on a standard diet, or the same diet supplemented with yeast extract (YE), to determine if YE would improve disease resistance in a stress model. 2. At 16 weeks of age, half of the birds were exposed to a bacterial challenge using a coarse spray of the pen environment. A subset of control and challenged birds was also treated with dexamethasone (Dex) prior to challenge (Dex/challenge). At 18 weeks, another subset was subjected to a 12?h transport stress protocol (Challenge/transport). All birds were bled and necropsied the morning after transport. The numbers and proportions of blood cells and the heterophil oxidative burst activity (OBA) were determined. Serum corticosterone (Cort) levels of male birds were measured using a commercial ELISA kit. Body weight and gain were increased by YE during week 1. 3. YE decreased mortality and bacterial isolation following Dex/challenge only in females. Cort levels in male turkeys were decreased by YE and Dex treatment. OBA was higher in males and in birds given YE and was reduced by challenge and transport. 4. These results suggest there may be gender differences in the turkey stress response and that dietary YE has potential for modulating the impact of stress on innate immunity of turkeys.

Time course changes in selected biochemical indices of broilers in response to pretransport handling

Two experiments were conducted to assess the stress response of broilers to catching and pretransport handling followed by different periods of crating. The short-term changes in selected biochemical indices were monitored at 1-min intervals within 10 min of crating after the catching and handling of broilers (experiment 1). These indices were further monitored at 15-min intervals for 2 h of crating after the catching and handling of broilers (experiment 2). Increased (P < 0.001) corticosterone concentrations were observed immediately after the broilers were caught, handled, and placed in crates. They continued to increase until 7 min after crating and then slowly decreased, but even at 120 min after handling, corticosterone concentrations were higher (P < 0.001) in crated broilers than in control broilers. In addition, lactate concentrations increased (P < 0.001) immediately in comparison with those of broilers with no additional handling except for catching and blood sampling, but 15 min later, the lactate concentrations had decreased to the precrating level. Lactate dehydrogenase concentrations increased (P = 0.042) 30 min after crating and continued to increase for the rest of the monitored period. A decreased level of cholesterol (P = 0.017) and increased concentration of uric acid (P = 0.041) were found 1 min after crating. The decrease in cholesterol was visible up to 9 min after crating; it then returned to its original value except for the period from 75 to 90 min after crating, when a decrease (P < 0.05) was again detected. Higher (P < 0.01) concentrations of uric acid were found continuously from 4 to 75 min after crating. Glucose concentrations were increased (P = 0.017) 2 min after crating, but the stress-induced increase was not consistent over the course of the next few minutes after crating. Glucose concentrations were not different from those of control broilers from 10 to 120 min after crating, although they showed a decreasing pattern. A decrease (P = 0.031) in triglyceride concentrations was detected 75 min after crating.

Testosterone modulates pituitary vasotocin receptor expression and adrenal activity in osmotically stressed chicken

Regulation of arginine vasotocin (AVT), avian neurohypophyseal hormone, is an important component of the hypothalamo-pituitary-adrenal axis. Changes in plasma osmolality levels and sex steroids are known to affect AVT gene expression. The present study reports the effect of water deprivation and testosterone treatment independently, as well as simultaneously, on the pituitary vasotocin receptor VT2R expression and adrenal steroidogenic activity in sexually immature male chicken (Gallus gallus). Birds were divided into four groups- control, water deprived (WD), testosterone injected (TE) and TE treated water deprived (TE+WD). WD decreased and TE treatment alone or in combination with WD (TE+WD) increased VT2R expression compared to the control. Expression of pro-opiomelanocortin (POMC) was also studied since this gene is a polypeptide precursor of ACTH and is under the negative feedback of adrenal corticoids. TE treatment as well as WD separately or when coupled together decreased the POMC mRNA expression in the pituitary but stimulated adrenal steroidogenic activity. Further, VT2R expression decreased in TE+WD compared to TE group, but it was not different from the vehicle treated control group suggesting that the suppressive effect of WD on VT2R expression was inhibited by the stimulatory effect of testosterone. Similarly, although both TE and WD decreased POMC expression and increased steroidogenic activity, no further decrease or increase in these parameters was observed when these two (WD and TE) treatments were combined together. Although, the exact mechanism is not clear, data indicate a stimulatory action of testosterone on VT2R expression and adrenal function despite a decreased expression of POMC mRNA. Results also suggest that testosterone treatment to sexually immature birds, in addition to its effect on hypothalamic AVT neurons (earlier study) and pituitary VT2R expression (present study), masks or inhibits osmotic stress-induced alterations in pituitary-adrenal activity.

Initial transference of wild birds to captivity alters stress physiology

Maintaining wild animals in captivity has long been used for conservation and research. While often suggested that captivity causes chronic stress, impacts on the underlying stress physiology are poorly understood. We used wild-caught chukar (Alectoris chukar) as a model avian species to assess how the initial 10 days of captivity alters the corticosterone (CORT) secretory pathway. In the first few days of captivity, birds lost weight, had lower hematocrit and demonstrated changes in CORT concentrations. Both baseline and restraint-stress-induced CORT concentrations decreased by days 3-5 of captivity and remained significantly lower throughout the 10 days although stress-induced concentrations began to recover by day 9. To delineate potential mechanisms underlying these CORT changes, we evaluated alterations to the hypothalamic-pituitary-adrenal (HPA) axis. Although chukar appear to be resistant to arginine vasotocin's (AVT) effects on CORT release, adrenocorticotropin hormone (ACTH) stimulated CORT release; however, ACTH stimulation did not differ during the 10 days of captivity. In contrast, negative feedback axis sensitivity, as determined by both dexamethasone suppression as well as endogenous negative feedback, decreased by day 5 but was regained by day 9. In addition, the combined stressors of capture and long distance transport eliminated the animals' ability to mount an acute CORT response on the day following the move. Therefore, introduction into captivity appeared to shift the chukar into a temporary state of chronic stress that began to recover within 9days. The duration of these alterations likely varies due to differences in capture techniques, transport distance, and species studied.