Hormonal interactions within the hypothalamus and pituitary with respect to stress and reproduction in sheep

Endocrine systems may be used as indicators of stress in two ways. The primary role of a hormone may be as part of the homeostatic response to a stimulus (e.g., adrenaline, corticosteroids). The amplitude of hormone response may correlate with the severity of the stimulus and any change indicate that the body is responding. Alternatively, a hormone may have a key role in normal body function (e.g., reproduction) and stress may deleteriously alter the hormone signal prevent normal function. This demonstrates that the stimulus was sufficiently severe that homeostatic mechanisms were unable to maintain normal function. Stress may effect reproduction by reducing both LH pulse amplitude and frequency. The LH surge may also be delayed. Several mechanisms may account for these effects both at the hypothalamus and pituitary. Corticosteroids have a broad, yet fundamental, role in homeostasis and have been used as primary indicators of stress for many years. Excess corticosteroid can be detrimental so the concentration is controlled via the hypothalamus-pituitary-adrenal (HPA) axis by multi-level feedback mechanisms. Under field and experimental conditions, after an initial large response prolonged stimulation leads to a gradually reducing plasma corticosteroid concentrations. This has been interpreted as a reduction in perceived stimulus severity or habituation to the stimulus and the animal deemed "less stressed" and its welfare "better." However, this reduction may be due to the intrinsic control mechanisms designed to prevent prolonged increases in corticosteroid concentrations. The stress signal at higher brain levels may still be present and the animal may still be experiencing the stimulus as aversive. Thus, the welfare interpretation of a corticosteroid concentration may differ during the time course of a stress response. A greater understanding of the mechanisms controlling corticosteroid secretion at each level of the HPA is required to determine what is the correct interpretation at any time point. To address these issues, we have used mathematical modelling to produce representations of possible control mechanisms at each level of the HPA. The starting point was to measure AVP and CRH concentrations in hypophysial portal blood and ACTH and cortisol concentrations in jugular blood in conscious sheep during 2h road transport (a cognitive stimulus). Modelling identified the signal inputs that were most likely to explain the secretion rate of each hormone. Modelling suggested that the reduction in AVP and CRH secretion observed during transport was most likely due to a reduction in stimulus input, with a significant contribution from cortisol negative feedback only on AVP secretion. At the pituitary level, ACTH secretion was stimulated more by AVP than by CRH (ratio 2.3:1) and there was also a stimulatory effect related to cortisol concentration at the time of sampling. However, the responses to both stimuli were curtailed by cortisol negative feedback and an inhibitory effect of prior CRH concentration. These are complex effects, but the modelling does suggest that while "stress" inputs may reduce over time hormone negative feedback is a major factor reducing hormone responses. When interpreting hormone data for animal welfare purposes, it is important not to interpret a reduction in hormone concentration due to intrinsic hormone control mechanisms as a reduction due to a decrease in the stress stimulus.     

Stress and the endocrine hypothalamus-pituitary-testis system: a review

Stressors generally induce a depression of the hypothalamus-pituitary-testis (HPT) system, mediated by the activated hypothalamus-pituitary-adrenocortical (HPA) system, resulting in a fall in plasma luteinising hormone (LH) and testosterone levels. Hypothalamic gonadotrophin-releasing hormone (GnRH) secretion may be suppressed by endogenous opioid peptides (EOP) and/or corticosteroids. The latter dramatically enhance the negative feedback effects of testosterone on both the hypothalamus and pituitary. Pituitary gonadotrophin secretion may be reduced by adrenocorticotrophic hormone or by EOP of hypothalamic or pituitary origin. Decreases in plasma concentrations of testosterone, independent of gonadotrophins, can be induced by corticosteroids. These hormones might reduce the number of Leydig-cell LH-receptors or occupation of LH-receptors. Testicular steroidogenesis may also be inhibited by pro-opiomelanocortin-derived (opioid) peptides secreted by the Leydig cells. There are some indications of increases in LH and testosterone during acute stress and, in dominant male animals, during the stress of social conflict. The latter finding indicates a difference in stress response between dominant and subordinate males. In subordinate males, decreased feedback sensitivity may allow hypersecretion throughout the HPA system. As a result, corticotrophin releasing hormone may induce the release of EOP from the hypothalamus, which inhibit the HPT axis. This inhibition may be enhanced by a corticosteroid-induced decrease in testosterone feedback.     

Central and peripheral effects of repeated noise stress on hypothalamic-pituitary-adrenocortical axis in pigs

The present study was performed to examine the effects of a repeated noise exposure (4 weeks) on basal and noise-induced plasma adrenocorticotrophin (ACTH), cortisol and corticosteroid binding globulin (CBG) levels, brain glucocorticoid receptors (GR) and corticotropin-releasing hormone (CRH) concentrations as well as on the morphology of adrenal glands in German Landrace pigs. Chronically cannulated pigs were exposed to either a daily stimulation with broad-band noise (2 h, 90 dB) (N1), or to the same stimulus three times a week (N2), or to an equal handling procedure without noise stimulation. Noise exposure caused an increase of basal CBG concentrations in N1 animals in the first week. During noise session, an increase of plasma ACTH and cortisol levels in N1 animals was measured in week 1 followed by a subsequent decrease until week 4. The ACTH and cortisol response of the N2 animals increased after week 1 and was significantly elevated in week 4. Furthermore, noise stress caused an increased hippocampal GR binding of N2 pigs, but had no effects on GR binding in the amygdala and on hypothalamic CRH levels. There were also significant structural modifications in the adrenal gland of N1 pigs resulting in differentiated effects on the adrenal cortex and medulla. The present results show that repeated noise exposure of pigs causes considerable alterations at different levels of the HPA system in association with the frequency of noise stimulation. This may have substantial impact on the general vulnerability of the animal with respect to productivity, health and welfare.     

Hypothalamo‐pituitary‐adrenocortical axis in stress‐susceptible and stress‐resistant pigs: endocrine responses to corticotrophin‐releasing factor and vasopressin*

Swiss Landrace pigs selected into genetically well‐characterized low and high tissue fat lines (f and F respectively) react differently to exogenous and endogenous stressors. Response of the hypothalamo‐pituitary‐adrenocortical (HPA) axis to i.v. administered ovine corticotrophin‐releasing factor (oCRF) and lysine vasopressin (LVP) in young females, intact and pretreated with dexamethasone or metyrapone, leads to the conclusion that different stress susceptibility of the two lines correlates with the sensitivity of pituitary corticotrophs to oCRF stimulation. Total amount of ACTH released after stimulation with submaximal oCRF doses was roughly equal in both lines, and cortisol level is even lower in the f‐line, most likely due to the considerably enhanced metabolic clearance rate of cortisol (lower half‐life of plasma cortisol compared with F‐line). LVP‐stimulated ACTH release is comparable with that of oCRF is stronger in the f‐line. Combined effect of oCRF and LVP is rather additive than synergistic but the half‐life ratio cortisol/ACTH after this stimulation is about four times higher than for stimulation by LVP and oCRF separately. In cases of externally stimulated HPA axis, cortisol plasma concentration tightly cross‐correlates with that of ACTH.     

The effect of stress conditions on exocrine pancreatic secretion in growing pigs

Introduction   Competition and aggression in pigs is known to reduce daily weight gain (DWG) (R und GREN and L& ouml ; fqvist 1989; H yun et al. 1998; L und et al. 1998), and to impair feed conversion ratio (W alker 1991; L und et al. 1998). The exact biological mechanisms behind these effects are not fully understood. Aggression and competition activate a cascade of reactions of biological relevance, such as inhibition of the parasympathetic nervous system, stimulation of the sympathetic nervous system, including the adrenal medulla (A xelrod et al. 1970; D alin et al. 1993a, 1993b), and activation of the hypothalamo-hypophyseal-adrenal (HHA) axis resulting in higher adrenocorticotropic hormone (ACTH) and higher cortisol concentrations in the plasma (D alin et al. 1993b; O lsson and S vendsen 1997). These responses as well as muscular activity increase metabolic losses (S chrama et al. 1993).
Hyper-physiological treatment with glucocorticoids stimulates pancreatic amylase activities in piglets (B aintner and N emeth 1982; C happle et al. 1989a, 1989b, 1989c), but no observations in growing pigs have been published. Inhibition of the parasympathetic nervous system (C hey et al. 1979) and stimulation of the sympathetic nervous system (C hey 1991) reduce exocrine pancreatic secretion. So, there might be some conflicting physiological responses of the exocrine pancreas to stress conditions. In order to increase our understanding of the animal's physiological responses to conditions of stress, we tested the hypothesis that conditions associated with stress (mixing with unfamiliar pigs, frustration and ACTH treatment) reduce exocrine pancreatic secretion. In addition, we tested the effect of treatment with Amperozide (a neurolepticum which reduces aggression and the effects of stress in pigs) on exocrine pancreatic secretion.     

Factors regulating ovarian function in pigs

The hormonal interactions of the hypothalamic-pituitary-ovarian-uterine axis are accountable for a normal reproduction in female pigs. It is of importance to have knowledge of estrous symptoms and hormonal profiles around ovulation. The introduction of the transrectal ultrasonography in sows has given us the possibility to study ovarian activity in conscious animals and relate the timing of estrus to ovulation. Combining this technique with measuring of several hormones like luteinizing hormone (LH), follicle-stimulating hormone (FSH), inhibin, estradiol, progesterone, insulin-like growth hormone I (IGF-I), prostaglandin F2alpha (PGF2alpha) metabolite, oxytocin, facilitate our knowledge about the sequence of ovarian events. Evidence suggests that activation of the hypothalamic-pituitary-adrenal axis may hamper the normal gonadotropin secretion and in consequence, the ovarian function. The metabolic status during lactation, weaning of piglets and social stress might affect onset of ovarian activity and the related estrous behavior. The role of seminal plasma, artificial insemination and presence of the boar might also be included as factors regulating the temporal kinetics of ovulation, corpus luteum development, uterine function and steroid production in the ovary. Studies using a simulated stress by means of adrenocorticotrophic hormone (ACTH) administration or food deprivation are tools in understanding how the ovary is susceptible to impairment. The intention of this paper is to review current knowledge concerning the endocrine aspects of normal and stress-influenced ovarian function in pigs.     

Susceptibility of reproduction in female pigs to impairment by stress or elevation of cortisol

It is generally agreed that stress can impair reproduction. Furthermore, it is often thought that cortisol, which is secreted during stress as a result of activation of the hypothalamo-pituitary adrenal axis, is associated with this stress-induced impairment of reproduction. It has been hypothesized that reproduction in females is particularly susceptible to disruption by acute stress during the series of endocrine events that induce estrus and ovulation. Nevertheless, we found no support for this conjecture when we subjected female pigs to repeated acute stress or repeated acute elevation of cortisol during the period leading up to estrus and ovulation. Conversely, studies have demonstrated that prolonged stress and sustained elevation of cortisol can disrupt reproductive processes in female pigs. Nevertheless, in each study that demonstrated this effect, there were some animals subjected to the prolonged stressor or the sustained elevation of cortisol in which the reproductive parameters that were measured were not affected by the treatment. We propose that reproduction in female pigs is resistant to the effects of acute or repeated acute stress or acute or repeated acute elevation of cortisol even if these occur during the series of endocrine events that induce estrus and ovulation. Furthermore, while reproductive processes in some individuals are compromised, reproduction in a proportion of female pigs appears to be resistant to the effects of prolonged stress or sustained elevation of cortisol.     

Association study of molecular polymorphisms in candidate genes related to stress responses with production and meat quality traits in pigs

The hypothalamic-pituitary-adrenal (HPA) axis exerts a large range of effects on metabolism, the immune system, inflammatory processes, and brain functions. Together with the sympathetic nervous system, it is also the most important stress-responsive neuroendocrine system. Both systems influence production traits, carcass composition, and meat quality. The HPA axis may be a critical target for genetic selection of more robust animals. Indeed, numerous studies in various species have demonstrated the importance of genetic factors in shaping the individual HPA axis phenotype, and genetic polymorphism can be found at each level of the axis, including hormone production by the adrenal cortices under stimulation by adrenocorticotropic hormone (ACTH), hormone bioavailability, or receptor and postreceptor mechanisms. The aim of the present experiment was to extend these findings to the brain neurochemical systems involved in stress responses. To this end, a number of candidate genes were sequenced for molecular polymorphisms and their association was studied with stress neuroendocrine and production traits in a genetically diverse population consisting of 100 female pigs from an advanced intercross (F10-F12) between 2 highly divergent breeds, Large White (LW) and Meishan (MS). The LW breed has a high production potential for lean meat and a low HPA axis activity, and the MS breed has low growth rate, fat carcasses—but large litters of highly viable piglets—and a high HPA axis activity. Candidate genes were chosen in the catecholaminergic and serotonergic pathways, in the pituitary control of cortisol production, among genes previously demonstrated to be differentially expressed in ACTH-stimulated adrenal glands from LW and MS pigs, and in cortisol receptors. Sixty new polymorphisms were found. The association study with carcass and meat quality traits and with endocrine traits showed a number of significant results, such as monoamine oxidase (MAOA) polymorphisms with growth rate (P = 0.01); lean content and intramuscular fat (P < 0.01), which are the most important traits for carcass value; dopamine receptor D3 (DRD3) with carcass composition (P < 0.05); and vasopressin receptor 1B (AVPR1B) with meat quality traits (P ≤ 0.05). The effect of these polymorphisms on neuroendocrine parameters (eg DRD3 and HPA axis or AVPR1B and catecholamines) indicates information regarding their biological mechanism of action.     

Physiological and behavioural effects of an intracerebroventricular injection of corticotropin releasing hormone in goats

This study investigated the effects of an intracerebroventricular (ICV) injection of corticotropin releasing hormone (CRH) on physiological and behavioural responses in goats. In Experiment 1, saline (control) or saline plus 25 microg of ovine CRH was injected into the third ventricle of castrated male goats. CRH increased plasma cortisol (Cor) levels markedly within 15 min, but had little effect on plasma glucose (Glu). Compared with saline injected goats, CRH decreased the total duration of lying behaviour but increased its frequency, and suppressed rumination and self-grooming. In Experiment 2, the effects of an intravenous (IV) injection of human adrenocorticotropic hormone (ACTH) (1-24) (0.1mg) were examined and an IV injection of saline was used as control. ACTH increased plasma Cor levels markedly, but did not change any behaviour compared with controls. It was concluded that CRH mediated the response of the hypothalamus-pituitary-adrenal (HPA) axis and behaviour following stress in goats, although the CRH-induced behavioural changes were independent of the HPA axis and seemed to be the result of direct action within the central nervous system.     

脂多糖刺激对断奶仔猪下丘脑-垂体-肾上腺轴PPARγ表达的影响

研究脂多糖(LPS)对断奶仔猪下丘脑-垂体-肾上腺(HPA)轴过氧化物酶体增殖物活化受体γ(PPARγ)表达的影响。对照组注射生理盐水,试验组注射LPS。注射后1.5 h和3 h采血,3 h采血后屠宰。结果表明:LPS刺激后1.5 h,中性粒细胞含量及其比例显著下降(P<0.05);LPS刺激后3 h,白细胞、淋巴细胞、中性粒细胞含量显著下降(P<0.05)。LPS刺激后1.5 h,血浆肿瘤坏死因子(TNF)-α、皮质醇和促肾上腺皮质激素释放素激素(CRH)含量显著上升(P<0.05);LPS刺激后3 h,血浆TNF-α、皮质醇和促肾上腺皮质激素(ACTH)含量显著上升(P<0.05);LPS刺激导致下丘脑、腺垂体、肾上腺皮质和髓质中PPARγ阳性细胞百分率显著升高(P<0.05)。这表明LPS导致免疫应激,激活HPA轴,诱导HPA轴PPARγ的表达。     

Hypothalamic-pituitary-adrenal axis responsiveness to insulin-induced hypoglycaemia is modified by trypanosome infection in Boran (Bos indicus) cattle.

Ten Boran (Bos indicus) cattle were used to study the stress responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis during trypanosome infection. Five cattle were infected with Trypanosoma congolense IL 1180 by tsetse challenge and five cattle served as controls. All infected animals developed acute trypanosomiasis. Insulin-induced hypoglycaemia (50 per cent of pre-insulin glucose concentration) was used as a stress factor. Acute hypoglycaemia was observed in three infected and three control animals after insulin challenge. Two animals from each group either did not respond or responded slowly. Hypoglycaemia in infected animals completely failed to induce an HPA axis response, while in control animals an HPA axis response was indicated by a significant increase in plasma adrenocorticotrophic hormone (ACTH) and cortisol concentrations (P less than 0.01). The results show that trypanosomiasis in Boran cattle can cause a decrease in the stress responsiveness of the HPA axis as indicated by a blunted ACTH/cortisol response to insulin-induced hypoglycaemia.     

The Effect of Piglet Expulsion in the Sow on Plasma Cortisol, Adrenocorticotropic Hormone and β-endorphin

Contents
Previous studies have shown an increase in plasma cortisol in gilts over farrowing irrespective of environment suggesting that factor(s) associated with parturition itself cause physiological stress. Factors involved in mediating the hypathalomo–pituitary–adrenal (HPA) axis at parturition are not well understood. This study examines the effect of piglet expulsion on the pituitary–adrenal axis by measurement of plasma cortisol, adrenocorticotropic hormone (ACTH) and β-endorphin. The effect of farrowing environment in modulating the acute response to piglet expulsion is also investigated. Twelve second parity sows, with indwelling jugular catheters, were moved into either a farrowing crate or a straw-bedded pen 5 days before their expected parturition date (EPD). Blood samples were taken from each sow during a prefarrowing baseline period and then rapid samples (2.5 mins) were taken for 10 min following the birth of two piglets. No effect of environment was found on any of the hormonal variables which reinforces the hypothesis that the physiological stress seen in parturient pigs is due to some intrinsic factor of parturition. Plasma cortisol, ACTH and β-endorphin did not change significantly in the period following piglet expulsion suggesting that individual piglet expulsions do not play a major role in 'parturition stress'. There was however, an increase in plasma cortisol, ACTH and β-endorphin in response to increasing piglet number which is consistent with previous studies of general farrowing in which cortisol increased as farrowing progressed. Therefore this study reinforces the hypothesis that physiological stress increases with ongoing parturition although this does not appear to be a result of piglet expulsion. The potential role of other factors which may be involved in causing 'parturition stress' should be investigated.     

Administration of ACTH to restrained, pregnant sows alters their pigs' hypothalamic-pituitary-adrenal (HPA) axis

This study was designed to examine the physiology and behavior of pigs whose dams were snared and then injected with ACTH during gestation. Administration of ACTH to dams during pregnancy has been shown to replicate the effects of prenatal stress in other species. Control sows (n = 8) were given no treatment, whereas the treatment sows (ACTH, n = 8) were immobilized by snaring the snout and then administered an i.v. injection of ACTH (1 IU/kg BW) weekly from 6 to 12 wk of gestation. A pig was killed from each sow at 1, 30, and 60 d of age. The hypothalamus, pituitary gland, adrenal glands, and liver were immediately obtained to determine the amounts of corticotropin-releasing hormone (CRH), beta-endorphin, and mRNA for pro-opiomelanocorticotropin (POMC), the ACTH receptor (ACTH-R), and insulin-like growth factor I (IGF-I). Pituitary corticotrope and somatotrope cell numbers and adrenal cortex-to-medulla area ratios (CORT:MED) were also determined. Pigs' behaviors were recorded at 6 and 8 wk of age. At 75 d of age, a blood sample was taken and a biopsy puncture was created on one pig from each litter, then pigs were stressed by mixing. Blood was sampled every other day for 10 d to determine plasma cortisol concentrations and differential leukocyte counts. Biopsy damage was evaluated for healing. At 1 d of age, control pigs tended to weigh more (P = .09), have a lower expression of ACTH-R mRNA (P = .01) and IGF-I mRNA (P = .01), and a lower CORT:MED (P = .04) than ACTH pigs. At 30 d of age, control pigs had a greater concentration of beta-endorphin (P = .01) and tended to have a lower concentration of CRH (P = .09) and IGF-I mRNA (P = .10) than ACTH pigs. At 60 d of age, control pigs tended to have lighter pituitary glands (P = .08), a lower expression of POMC mRNA (P = .02), and a CORT:MED (P = .003) than ACTH pigs. At 8 wk of age, control pigs performed a higher frequency of belly nosing (P = .07) and oral vice behaviors (P = .01) than ACTH pigs. In response to mixing stress, control pigs had lesser concentrations of plasma cortisol (P = .03) and healed faster (P = .006) than ACTH pigs. Thus, exogenous ACTH and restraint during gestation alters the HPA axis of the sow's offspring, and during stressful situations later in life health, and therefore welfare, may be compromised.     

Effects of dermal dexamethasone application on ACTH and both basal and ACTH-stimulated cortisol concentration in normal horses

There are no data available regarding the systemic (adverse) effects which might be induced by topical/dermal glucocorticoids (GCs) application in the horse. Besides their widespread use for the treatment of a variety of peripheral inflammatory disorders such as atopic dermatitis, eczemas or arthritis in the horse, their surreptitious application has become a concern in doping cases in competition/performance horses. Assessing both basal and ACTH‐stimulated plasma cortisol as well as basal ACTH concentrations following application of dexamethsone‐containing dermal ointment is necessary to determine influences on hypothalamus‐pituitary‐adrenal (HPA) axis. Ten clinically healthy adult standardbred horses (6 mares, 4 geldings) were rubbed twice daily each with 50 g dexamethasone‐containing ointment on a defined skin area (30 × 50 cm) for 10 days. RIA and chemiluminescent enzyme immuno‐metric assay were used to determine resting and ACTH‐stimulated plasma cortisol and basal ACTH concentrations, respectively. HPA feedback sensitivity and adrenal function were measured by a standard ACTH stimulation test. Dermal dexamethasone suppressed significantly the resting plasma cortisol level (to 75–98%) below baseline (P < 0.001) within the first 2 days and decreased further until day 10. ACTH stimulation test showed a markedly reduced rise in plasma cortisol concentrations (P < 0.001 vs. baseline). Plasma ACTH level decreased also during topical dexamethasone application. The number of total lymphocytes and eosinophil granulocytes was reduced, whereas the number of neutrophils increased. No significant change of serum biochemical parameters was noted. Dermal dexamethasone application has the potential to cause an almost complete and transient HPA axis suppression and altered leukocyte distribution in normal horses. The effects on HPA axis function should be considered in relation to the inability of animals to resist stress situations. The data further implicate that percutaneously absorbed dexamethasone (GCs) may cause systemic effects relevant to ‘doping’.     

Effects of castration, tooth resection, or tail docking on plasma metabolites and stress hormones in young pigs

Changes in the activity of the sympathetic nervous system or in the hypothalamo-pituitary-adrenal axis have been extensively used to evaluate pain induced by castration or tail docking in numerous species. Such data are missing in pigs. Therefore, three experiments were conducted to determine the effects of castration, tail docking, or tooth resection on stress hormones. Glucose and lactate also were measured because catecholamines stimulate mobilization of glycogen, which results in glucose and lactate release. In Exp.1, 18 male pigs from seven litters (two or three pigs per litter) were catheterized surgically into one jugular vein, under general anesthesia, at 5 or 6 d of age. Two days later, they were submitted either to bilateral castration, control handling, or no handling (n = 6 per group). Blood samples were collected before (- 15 and -2 min) and after (5, 15, 30, 60, 90, 180 min) the experimental treatment. In Exp. 2, 27 female pigs from 12 litters (one to four pigs per litter) were submitted either to tooth clipping with pliers, tooth resection with a grinder apparatus, control handling, or no handling (n = 6 or 7 per group) at 1 d of age. In Exp. 3, 17 female pigs from nine litters (one to three pigs per litter) were submitted to one of the following treatments: 1) tail docking with an electric-heated scissor docking iron, 2) control handling, and 3) no handling (n = 5 or 6 per group) at 1 d of age. Castration induced significant (P < 0.05) increases in adrenocorticotropin hormone (ACTH; from 5 to 60 min), cortisol (from 15 to 90 min), and lactate (from 5 to 30 min). These variations are indicative of stress and tissue damage following castration. In contrast, neither tail docking nor tooth resection had marked effects on plasma cortisol, ACTH, glucose, and lactate. Measurements of plasma cortisol, lactate, and ACTH could be useful for validating treatments designed to relieve the distress reaction induced by castration in pigs.     

Studies of endotoxin-dependent fever in pre-pubertal pigs following acute activation of the pituitary-adrenocortical axis: towards a new hypothesis of fever regulation

The possibility that adrenocortical activation might alter the pyretic effects of bacterial lipopolysaccharide endotoxin in growing pigs was investigated. In a series of four experiments, animals received increasing doses of porcine adrenocorticotrophic hormone ACTH (1.5, 4.5, 13.5 IU kg-1) or CRH (7 microg kg-1), all of which markedly affected cortisol release. Unexpectedly, these treatments tended to increase body temperature during the early and middle stages of the febrile response, although they did appear to induce an earlier deferscence. These results suggest that acute stress may not modify fever induced by immunological challenge, although a different situation could obtain during chronic stress. Furthermore, a hypothesis of fever regulation is proposed which attempts to reconcile the present findings with those from previous studies in swine.     

A model for assessing the impact of behavioral stress on domestic animals

Animal scientists need a reliable measure of behavioral stress in domestic animals if they are going to be able to assess the stress of various management practices and to answer public concern about the well-being of animals used in agriculture. Popular measures of stress, alterations in behavior or changes in hormone secretion, are not adequate because of a failure to establish any direct correlation between changes in these characteristics with adverse effects on animal well-being. Further complicating the use of these indicators of stress is the variation in their pattern of response to different kinds of stressors. Even the same stressor can elicit divergent responses in different animals because of inter-animal variation in the stress response. To address these problems, a model of animal stress is discussed and tested. From this model it is proposed that the best indicator of an animal suffering from stress is the development of a pre-pathological state; i.e., a stress-related change in biological function that threatens the animal's well-being. Examples of such pre-pathological states would be a suppression of the immune system, the loss of reproductive events critical for normal reproduction, or the development of behaviors that would lead to such undesirable acts as tail-biting or excessive fighting. Although determining the existence of such pre-pathological states is not convenient, their existence is currently the only defensible indicator of an animal suffering from behavioral stress.     

Force-feeding procedure and physiological indicators of stress in male mule ducks.

1. The effects of the force-feeding procedure and its different components on various physiological indicators of acute and chronic stress were investigated in male mule ducks before and during a 12-d cramming period. 2. The highest concentration of corticosterone were measured after injection of ACTH agonist, during the pre-experimental period when the ducks were still housed in collective floor pens and at the time of transfer. 3. During the cramming period, corticosterone measured before and after force-feeding did not differ significantly though there was a non-significant trend towards an increase in certain cases. 4. The different components of force-feeding, including manipulation, intubation, force-feeding with a standard or a large amount of food had no significant effect upon corticosterone concentrations. 5. There was no indication from ACTH agonist challenge either of a change in adrenal sensitivity or a change in its responsiveness. 6. The heterocyte-lymphocyte ratio measured before and at the end of the cramming period did not differ significantly. 7. In conclusion, we observed no significant indication that force-feeding is perceived as an acute or chronic stress by male mule ducks, in our experimental conditions. Nevertheless, it remains to be shown that their adrenocorticotropic axis is responsive to acute stressors.     

Aggressive and submissive behavior in young swine given exogenous acth

Ten replicates of two pigs each were used to determine the effects of 10 IU/kg i.m. adrenocorticotropin hormone (ACTH) or physiological saline on aggressive and submissive behaviors. Behavior was recorded for 90 minutes after pigs of each treatment were grouped. Both duration and latency to attack were similar for ACTH- and salinetreated pigs. Submissive behavior was greater for ACTH-treated pigs (P<.01). In this species, ACTH increased submissive behavior which resulted in domination of ACTH-treated pigs by control pigs.     

下丘脑-垂体-肾上腺轴参与动物采食调控的研究进展

采食是动物维持生命活动的基本生理过程，是动物生长发育的基础。畜禽采食量的高低直接影响到营养物质的摄入量及生产性能的发挥。在畜牧业生产中，影响采食的因素很多，而应激是其中一个非常重要的影响因素。动物机体的应激反应主要由下丘脑-垂体-肾上腺（HPA）轴来调控。下丘脑、垂体和肾上腺皮质通过释放促肾上腺皮质激素释放激素（CRH）、促肾上腺皮质激素（ACTH）和糖皮质激素（GC）这3种应激激素来协同调控动物的应激反应。应激激素对采食行为的调节是一个非常复杂的过程，主要通过稳态和非稳态途径来调节采食，可以双向调控食物的摄入量。稳态途径指的是通过调控机体能量稳态而调控采食。CRH和ACTH通过抑制下丘脑促食欲肽的表达而抑制采食；而GC在中枢和外周发挥着完全相反的作用。非稳态途径指的是通过影响中脑奖赏系统调控采食的愉悦感，是近年来食欲调控研究的热点，越来越多的研究证明了应激激素与奖赏系统的联系。作者针对应激激素调控采食的最新研究报道进行综述，以期为生产实践中新型的采食调控技术研发提供一定的参考。