Neuroendocrine mechanisms of innate states of attenuated responsiveness of the hypothalamo-pituitary adrenal axis to stress

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

Reduced cortisol and metabolic responses of thin ewes to an acute cold challenge in mid-pregnancy: implications for animal physiology and welfare

BACKGROUND

Low food availability leading to reductions in Body Condition Score (BCS; 0 indicates emaciation and 5 obesity) in sheep often coincides with low temperatures associated with the onset of winter in New Zealand. The ability to adapt to reductions in environmental temperature may be impaired in animals with low BCS, in particular during pregnancy when metabolic demand is higher. Here we assess whether BCS affects a pregnant animal's ability to cope with cold challenges.

METHODS

Eighteen pregnant ewes with a BCS of 2.7±0.1 were fed to attain low (LBC: BCS2.3±0.1), medium (MBC: BCS3.2±0.2) or high BCS (HBC: BCS3.6±0.2). Shorn ewes were exposed to a 6-h acute cold challenge in a climate-controlled room (wet and windy conditions, 4.4±0.1°C) in mid-pregnancy. Blood samples were collected during the BCS change phase, acute cold challenge and recovery phase.

RESULTS

During the BCS change phase, plasma glucose and leptin concentrations declined while free fatty acids (FFA) increased in LBC compared to MBC (P<0.01, P<0.01 and P<0.05, respectively) and HBC ewes (P<0.05, P<0.01 and P<0.01, respectively). During the cold challenge, plasma cortisol concentrations were lower in LBC than MBC (P<0.05) and HBC ewes (P<0.05), and FFA and insulin concentrations were lower in LBC than HBC ewes (P<0.05 and P<0.001, respectively). Leptin concentrations declined in MBC and HBC ewes while remaining unchanged in LBC ewes (P<0.01). Glucose concentrations and internal body temperature (T(core)) increased in all treatments, although peak T(core) tended to be higher in HBC ewes (P<0.1). During the recovery phase, T4 concentrations were lower in LBC ewes (P<0.05).

CONCLUSION

Even though all ewes were able to increase T(core) and mobilize glucose, low BCS animals had considerably reduced cortisol and metabolic responses to a cold challenge in mid-pregnancy, suggesting that their ability to adapt to cold challenges through some of the expected pathways was reduced.

Relationship between psychological stress and recurrent miscarriage

Stress arousal may compromise the feedback regulation of the hypothalamo-pituitary-adrenal axis, releasing stress-related biomarkers and thereby affecting establishment of pregnancy. This study examined the relationship between stress and recurrent miscarriage (RM) and the impact of stress on establishment of pregnancy. The stress status of 45 patients with unexplained RM and 40 fertile women was investigated with the Fertility Problem Inventory (FPI), Perceived Stress Scale (PSS), Positive and Negative Affect Schedule, peripheral natural killer (NK) cells and cortisol. Patients with unexplained RM had significantly higher scores on the FPI (P<0.05, adjusted OR 1.02), PSS (P<0.05, adjusted OR 1.13) and Negative Affect scale (P<0.05, adjusted OR 1.12) and lower scores on the Positive Affect scale (P<0.05, adjusted OR 0.89) than fertile controls. Patients who had live births (n=20) during the study period had significantly lower scores in the Positive Affect scale (P<0.05, adjusted OR 1.17) than those who miscarried (n=10). There was a little association between psychological stress measurements and biochemical stress measurements. These results suggest that stress is a risk factor of RM. Within women with RM, moderate stress appears to be associated with improved pregnancy outcome.

From stress to postpartum mood and anxiety disorders: how chronic peripartum stress can impair maternal adaptations

The peripartum period, in all mammalian species, is characterised by numerous adaptations at neuroendocrine, molecular and behavioural levels that prepare the female for the challenges of motherhood. These changes have been well characterised and, while they are necessary to ensure the survival and nurturance of the offspring, there is growing belief that they are also required for maternal mental health. Thus, while increased calmness and attenuated stress responsivity are common characteristics of the peripartum period, it also represents a time of increased susceptibility to mood disorders. While a number of risk factors for these disorders are known, their underlying aetiology remains poorly understood, due at least in part to a lack of appropriate animal models. One translatable risk factor is stress exposure during the peripartum period. In the following review we first describe common peripartum adaptations and the impact postpartum mood disorders have on these. We then discuss the known consequences of peripartum stress exposure on such maternal adaptations that have been described in basic research.

The possible involvement of salsolinol and hypothalamic prolactin in the central regulatory processes in ewes during lactation

Salsolinol, a dopamine-related compound and prolactin-producing cells were found in the ovine hypothalamus. This study was designed to test the hypothesis that salsolinol, acting from the CNS level, is able to stimulate pituitary prolactin release as well as prolactin mRNA expression in the anterior pituitary cells (AP) and in the mediobasal hypothalamus (MBH) in lactating ewes. The intracerebroventricular infusions of salsolinol in two doses, total of 50 ng or 5 μg, were performed in a series of five 10-min infusions at 20-min intervals. All infusions were made from 12:30 to 15:00 and the pre-infusion period was from 10:00 to 12.30 h. The prolactin concentration in plasma samples, collected every 10 min, was determined by radioimmunoassay; prolactin mRNA expression in AP and MBH tissues was determined by real-time PCR. The obtained results showed that salsolinol infused at the higher dose significantly (p < 0.001) increased plasma prolactin concentration in lactating ewes, when compared with the concentration noted before the infusion and with that in lactating controls. In lactating ewes, the relative levels of prolactin mRNA expression in the AP and MBH were up to twofold and fivefold higher respectively than in non-lactating ewes (p < 0.05). In our experimental design, salsolinol did not significantly affect the ongoing process of prolactin gene expression in these tissues. We conclude that in ewes, salsolinol may be involved, at least, in the process of stimulation of prolactin release during lactation and that hypothalamic prolactin plays an important role in the central mechanisms of adaptation to lactation.

Anxiety and hypothalamic-pituitary-adrenal axis responses to psychological stress are attenuated in male rats made lean by large litter rearing

An excellent strategy to treat overactive responses to stress is to exploit the body's inherent stress-inhibitory mechanisms. Stress responses are known to differ between individuals depending upon their level and distribution of adiposity and their experiences in early life. For instance, we have recently shown that female rats made obese by overfeeding during the neonatal period have exacerbated responses to psychological stress. The converse may be true for those that are underfed during this period. In this investigation we hypothesized that rats made lean by neonatal underfeeding would have reduced anxiety and attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress. Our findings show that male (but not female) rats, made smaller by being suckled in a large litter, show reduced anxiety-related behaviour compared with those from normal litters when tested in the elevated plus maze. These smaller males also have attenuated activation of the paraventricular nucleus of the hypothalamus in response to the psychological stress, restraint, and corticosterone responses to restraint that return more quickly to baseline than controls. These findings are exciting from the perspective of understanding and potentially exploiting the body's inherent stress-inhibitory mechanisms to treat overactive responses to stress. They also provide an indication that being lean may be able to ameliorate overactive stress responses. Understanding the mechanisms by which these stress responses are attenuated in lean animals will be important for future strategies to treat diseases associated with overactive HPA axes in humans.

Oestrogen: an overlooked mediator in the neuropsychopharmacology of treatment response?

Major depression (MD) and anorexia nervosa (AN) often present comorbidly and both share some affective symptoms, despite obvious phenotypic differences. In the illness phase, pathophysiological evidence indicates similar abnormalities in both clinical groups including dysfunction in the serotonin (5-HT) system (of which some abnormalities persist following recovery) and between 60% and 80% of patients in both groups present with significant hyperactivity of the hypothalamo-pituitary-adrenal (HPA) axis. First-line approach to treatment for MD involves modulation of the 5-HT system using selective serotonin reuptake inhibitors (SSRIs). For AN, treatment with SSRIs has been shown to be considerably less effective compared to MD. Both illnesses show marked dysregulation in the HPA axis. A consequence of SSRI treatment is a reduction and/or normalization of indices of the HPA axis [i.e. cortisol, adrenocorticotropic hormone (ACTH)], which is consistent with recovery levels in both clinical groups. Oestrogen (in high doses) has been shown to exert antidepressant effects and positively impact on MD symptoms as a treatment in its own right, or in combination with antidepressants, in women of menopausal age. It is proposed that a combination of SSRIs and oestrogen therapy may facilitate physiological normalization in MD in women of non-menopausal age and in AN. Preliminary evidence suggests oestrogen treatment alone is of some benefit to patients and it is proposed that a combination of SSRI and oestrogen will precipitate and potentially accelerate symptomatic remission. Should this approach be successful, it offers the capacity for improvement over traditional antidepressant use in women diagnosed with MD and a novel strategy for the treatment of AN, a serious clinical illness associated with the highest mortality of any psychiatric condition.

Evidence that RF-amide related peptide-3 is not a mediator of the inhibitory effects of psychosocial stress on gonadotrophin secretion in ovariectomised ewes

It is well known that stress inhibits normal reproductive function, including gonadotrophin secretion; however, the mechanisms and mediators involved are largely unknown. Stress impairs the secretion of luteinising hormone (LH), and it has been suggested that the RF-amide gonadotrophin-inhibitory hormone (GnIH), known as RF-amide related peptide-3 (RFRP-3) in mammalian species, may mediate this inhibitory effect of stress. If this is the case, the GnIH/RFRP system would likely be up-regulated during stress. We tested this hypothesis in ovariectomised ewes using a psychosocial stressor: isolation/restraint. Ewes were randomly allocated to control or stress (n=5 per group). Isolation/restraint stress was imposed for 90 min after control sampling for 4 h, whereas control ewes were sampled continuously for 5.5 h. All ewes were then euthanased and brains were collected. As expected, plasma concentrations of cortisol were increased significantly (P<0.05) by stress and plasma concentrations of LH were significantly (P<0.05) reduced. Immunohistochemistry and in situ hybridisation were conducted for RFRP-3 peptide and RFRP mRNA expression, respectively, in the paraventricular nucleus/dorsal medial hypothalamus region of the hypothalamus. There was no significant effect of stress on RFRP-3 peptide or mRNA levels, with no differences between control or stress ewes. Furthermore, there was no difference in the number of RFRP-3 cells double-labelled for Fos between control and stress ewes and there was no difference in the cellular expression of RFRP mRNA between groups. These results indicate that the GnIH/RFRP system is not activated by psychosocial stress in ewes, suggesting that it is an unlikely mediator of the effects of stress on LH secretion.

Sex differences precipitating anorexia nervosa in females: the estrogen paradox and a novel framework for targeting sex-specific neurocircuits and behavior

In anorexia nervosa (AN), reward contamination likely plays a significant role in maintenance of the illness. Reward contamination is a context in which patients' behaviors of self-starvation and excessive exercise, while initially rewarding, become aversive, even punishing; but patients may not recognize the punishing and conflicted/contaminated behaviors. An emerging neurocircuit encompassing the anterior cingulate cortex (ACC) has been functionally linked to symptoms including reward contamination and body dysmorphic processing. Owing to the significantly greater prevalence of AN in females, evidence from clinical literature and preclinical models is spearheaded to provide a novel rationale for estrogen triggering sensitivity to the experience of stress and reward, precipitating AN disproportionately in females at the time of puberty. Paradoxically, however, estrogen may facilitate response to pharmacological interventions and (desensitization of the identified neurocircuits) via its contribution to serotonin modulation, hypothalamo-pituitary adrenal (HPA)-axis attenuation, and effects on dopamine.

Stressor specificity of sex differences in hypothalamo-pituitary-adrenal axis activity: cortisol responses to exercise, endotoxin, wetting, and isolation/restraint stress in gonadectomized male and female sheep

Sex differences in the stress-induced activity of the hypothalamo-pituitary-adrenal axis in sheep appear to be dependent on the stressor encountered and occur irrespective of the presence of gonadal steroids. We tested the hypotheses that cortisol responses to exercise, endotoxin, wetting (experiment 1), and isolation/restraint (experiment 2) stress differ between gonadectomized male and female sheep. At weekly intervals (in experiment 1), we subjected gonadectomized rams and ewes (n = 6/group) to control conditions, to exercise stress, to iv injection of endotoxin, and to wetting stress. In a second experiment (experiment 2), we subjected gonadectomized rams and ewes (n = 5/group) to control conditions or to isolation/restraint stress. In both experiments, we measured plasma concentrations of cortisol before, during, and after stress at a frequency of at least 15 min with samples collected (from an indwelling jugular catheter) at a greater frequency around the time of the stressor. Cortisol responses to wetting (experiment 1) and isolation/restraint (experiment 2) stress were significantly higher in females compared with males but in response to exercise (experiment 1) and endotoxin (experiment 1) stress, there were no differences between the sexes. For some stressors, there are sex differences in sheep in the stress-induced activity of the hypothalamo-pituitary-adrenal axis that are independent of the presence of the sex steroids, but the existence of these sex differences and the direction of these sex differences differs, depending on the stressor imposed.

The impact of treatment on HPA axis activity in unipolar major depression

Dysregulation of hypothalamic-pituitary-adrenal axis activity in major depressive disorder has been found to normalize with successful treatment, though inconsistencies exist. To determine the magnitude of change in cortisol levels from pre to post-treatment in individuals with unipolar depression quantitative methods of meta-analysis were applied. Thirty-four studies met inclusion criteria and consisted of a total of 1049 depressed patients across study samples. The overall mean effect size of pre-post-treatment cortisol measures indicated that approximately 56% of depressed participants had similar cortisol levels before and after treatment regardless of symptom improvement. The mean effect size of pre-post cortisol measures for those who responded to treatment was larger than the mean effect size of non-responders; however, this difference did not reach statistical significance. As well, no significant differences in mean effect size of pre-post cortisol measures based on type of treatment (e.g. antidepressant vs. ECT) were found. Subtype of depressive illness and length of treatment may contribute to the magnitude of change in cortisol measure before and after treatment. Inconsistent findings within the reviewed literature may confound the overall results. The type of treatment and response to treatment do not appear to impact the magnitude of change in cortisol level pre to post-treatment. Our findings suggest that the utility of cortisol as an outcome measure may be limited to specific subsets of the depressed population, and that given the variability in HPA results between studies, it is premature to state that cortisol is not a good outcome measure.

A single exposure to an acute stressor has lasting consequences for the hypothalamo-pituitary-adrenal response to stress in free-living birds

In vertebrates, activation of the hypothalamo-pituitary-adrenal (HPA) axis in response to unpredictable events results in elevated glucocorticoid secretion. Repeated exposure to stressors alters subsequent glucocorticoid secretion, either by inducing chronic stress or as a result of habituation. However, most studies of repeated stress focus on the impacts of multiple and frequent exposures to acute stressors, and few have been carried out in free-living animals. We investigated whether a single exposure to a novel stressor was sufficient to produce long-lasting alterations in HPA function in free-living eastern bluebirds (Sialia sialis). We subjected adult females to a capture/restraint protocol in which we collected serial blood samples over an hour of restraint to be analyzed for corticosterone. We administered this protocol to three groups of females during the nestling phase of their first and/or second brood of the season: Repeaters (sampled during brood 1 and brood 2), Naïve-Brood 1 (sampled only during brood 1), and Naïve-Brood 2 (sampled only during brood 2). Repeaters had attenuated corticosterone responses to the second restraint bout compared to the first, and in brood 2, Repeaters had lower responses than Naïve-Brood 2 females. However, Naïve-Brood 1 and Naïve-Brood 2 birds did not differ in their responses to restraint. Thus, as little as one prior experience with an acute stressor was sufficient to alter subsequent HPA responsiveness, and this effect was not due to a natural change in HPA responsiveness as the breeding season progressed. These data may have important implications for understanding how acute stressors can alter a free-living animal's ability to cope in the face of subsequent stressors, and for longitudinal field studies in which individuals are repeatedly sampled for glucocorticoid responsiveness.

Neonatal overfeeding alters adult anxiety and stress responsiveness

The neonatal nutritional environment is critical for programming the systems regulating body weight, and an inappropriate nutritional environment in early life can lead to overweight or obesity later on. In this study we demonstrate that changes to the neonatal nutritional environment, induced by changing the litter size in which the animal is raised, can alter not only body weight into adulthood, but also anxiety behaviours and stress responsiveness. These effects appear to be somewhat sex-dependent, affecting female rats more strongly than males. Thus, Wistar rats raised in small litters, where they have greater access to their mothers' milk, weigh more in adulthood than those raised in large litters. Females from these small litters show enhanced exploratory behaviour and reduced anxiety in the elevated plus maze, entering the open arms more often. They also display enhanced central responses to restraint stress including greater activation of the paraventricular nucleus of the hypothalamus and paraventricular nucleus of the thalamus, possibly indicating that the changes we see are related to enhanced arousal. Thus, while neonatal litter size affects long-term body weight regulation, it can also alter long-term activity, anxiety and stress responsiveness, and the degree to which it does so appears to be sex-dependent.

Cortisol disrupts the ability of estradiol-17beta to induce the LH surge in ovariectomized ewes

Stress disrupts the preovulatory luteinizing hormone (LH) surge in females, but the mechanisms are unknown. We tested the hypothesis that cortisol compromises the ability of estrogen to induce a preovulatory-like LH surge in ovariectomized ewes in both the breeding and nonbreeding season. Luteinizing hormone surges were induced in ovariectomized ewes by treatment with progesterone followed by a surge-inducing estradiol-17beta (E2) stimulus using a crossover design. The experiment was replicated in the breeding and nonbreeding seasons. Cortisol reduced the incidence of LH surges irrespective of season. Cortisol increased the latency from E2 stimulus to the onset of the surge in the breeding season only and suppressed the LH surge amplitude during both seasons (P<0.01). We conclude that cortisol can interfere with the LH surge in several ways: delay, blunt, and in extreme cases prevent the E2-induced LH surge. Furthermore, the effect of cortisol to delay the E2-induced LH surge is more pronounced in the breeding season. These results show that cortisol disrupts the positive feedback effect of E2 to trigger an LH surge and suggest the involvement of multiple mechanisms.

Role of various neurotransmitters in mediating the long-term endocrine consequences of prenatal alcohol exposure

Adult rats and mice born to dams exposed to alcohol (fetal alcohol-exposed [FAE]) exhibit enhanced activity of their hypothalamic-pituitary-adrenal (HPA) axis when exposed to stressors. However, the mechanisms responsible for this phenomenon remain incompletely understood. Here two possibilities are reviewed: one that pertains to nitric oxide (NO), an unstable gas that stimulates the HPA axis; and one that focuses on catecholamines, which also stimulate this axis. Significant alterations were not observed in levels of NO synthase, the enzyme responsible for NO formation, in the paraventricula nucleus (PVN) of FAE rats. However, the stimulatory influence of this gas on the hypothalamic-pituitary-adrenal (HPA) axis was enhanced in these animals, thereby providing a mechanism likely to participate in the neuroendocrine hyperactivity that is the hallmark of this model. It was also recently shown that, while the ability of catecholamines to release adrenocorticotropic hormone (ACTH) was comparable in control rats and rats exposed to alcohol during embryonic development, there was a significant upregulation of the C1 brain-stem region when these latter animals were exposed to mild footshocks. Since this region sends prominent projections to the PVN, its increased activity may participate in the HPA axis hyperactivity observed in FAE offspring. Finally, microarray technology was used to search for potential differences in genes present in the brains of control and FAE mice. When these brains were collected on day 17.5 of embryonic development, several genes were upregulated, while others were downregulated, which may provide potential new candidates that mediate the influence of prenatal alcohol on the HPA axis of adult offspring.

Psychosocial stress inhibits amplitude of gonadotropin-releasing hormone pulses independent of cortisol action on the type II glucocorticoid receptor

Our laboratory has developed a paradigm of psychosocial stress (sequential layering of isolation, blindfold, and predator cues) that robustly elevates cortisol secretion and decreases LH pulse amplitude in ovariectomized ewes. This decrease in LH pulse amplitude is due, at least in part, to a reduction in pituitary responsiveness to GnRH, caused by cortisol acting via the type II glucocorticoid receptor (GR). The first experiment of the current study aimed to determine whether this layered psychosocial stress also inhibits pulsatile GnRH release into pituitary portal blood. The stress paradigm significantly reduced GnRH pulse amplitude compared with nonstressed ovariectomized ewes. The second experiment tested if this stress-induced decrease in GnRH pulse amplitude is mediated by cortisol action on the type II GR. Ovariectomized ewes were allocated to three groups: nonstress control, stress, and stress plus the type II GR antagonist RU486. The layered psychosocial stress paradigm decreased GnRH and LH pulse amplitude compared with nonstress controls. Importantly, the stress also lowered GnRH pulse amplitude to a comparable extent in ewes in which cortisol action via the type II GR was antagonized. Therefore, we conclude that psychosocial stress reduces the amplitude of GnRH pulses independent of cortisol action on the type II GR. The present findings, combined with our recent observations, suggest that the mechanisms by which psychosocial stress inhibits reproductive neuroendocrine activity at the hypothalamic and pituitary levels are fundamentally different.

Neonatal handling and the maternal odor preference in rat pups: involvement of monoamines and cyclic AMP response element-binding protein pathway in the olfactory bulb

Early-life environmental events, such as the handling procedure, can induce long-lasting alterations upon several behavioral and neuroendocrine systems. However, the changes within the pups that could be causally related to the effects in adulthood are still poorly understood. In the present study, we analyzed the effects of neonatal handling on behavioral (maternal odor preference) and biochemical (cyclic AMP response element-binding protein (CREB) phosphorylation, noradrenaline (NA), and serotonin (5-HT) levels in the olfactory bulb (OB)) parameters in 7-day-old male and female rat pups. Repeated handling (RH) abolished preference for the maternal odor in female pups compared with nonhandled (NH) and the single-handled (SH) ones, while in RH males the preference was not different than NH and SH groups. In both male and female pups, RH decreased NA activity in the OB, but 5-HT activity increased only in males. Since preference for the maternal odor involves the synergic action of NA and 5-HT in the OB, the maintenance of the behavior in RH males could be related to the increased 5-HT activity, in spite of reduction in the NA activity in the OB. RH did not alter CREB phosphorylation in the OB of both male and females compared with NH pups. The repeated handling procedure can affect the behavior of rat pups in response to the maternal odor and biochemical parameters related to the olfactory learning mechanism. Sex differences were already detected in 7-day-old pups. Although the responsiveness of the hypothalamic-pituitary-adrenal axis to stressors is reduced in the neonatal period, environmental interventions may impact behavioral and biochemical mechanisms relevant to the animal at that early age.

Tail skin temperatures reflect coping styles in rats

This study was carried out to elucidate the predictive value of tail skin temperatures (TSTs) assessed in naïve rats as a non-invasive pre-experimental method of classification of coping style. Male Lewis rats were classified according to tail skin temperatures (TST), and relative size within cage-groups. TSTs were monitored over two-hour periods following exposure to physical and emotional stressors. Bodyweight-shifts associated to the experiments were analysed. Six organs of neuroendocrine relevance to allostasis were weighed. Challenge-specific TST-profiles were size-related and consistent with proactive or reactive coping. Pro-active (A) rats showed a more pronounced TST-response to unknown conspecifics, but reactive (B) rats to environmental novelties. B-rats showed challenge-specific weight-losses while A-rats gained more after experiments. Second size males showed rapidly decreased TSTs (vasoconstriction) after nociceptive stimulation. Males that showed the highest basal TSTs and weight-loss in emotionality tests had lost a first rank position during a pre-experimental period, suggesting long-lasting effects of social defeat. Pre-experimental growth correlated positively to adiposisity post-experimentally, but negatively to testes relative weight in B-rats. Scaling effects explained heart-size in B-rats and pituitary-size in A-rats. The overall patterns that emerged, in factor analyses including organ sizes, were consistent with pro-active coping in A-rats and reactive in B-rats. Our results, controlling for rank-effects, suggest that non-invasively assessed TSTs may predict individual stress-coping phenotypes pre-experimentally in rats housed in groups.

Oxytocin alleviates the neuroendocrine and cytokine response to bacterial endotoxin in healthy men

Oxytocin is a hormone and neurotransmitter found to have anti-inflammatory functions in rodents. Here we used experimental bacterial endotoxinemia to examine the role of exogenous oxytocin administration on innate immune responses in humans. Ten healthy men received, in a randomized, placebo-controlled, crossover design, placebo, oxytocin, LPS, and LPS + oxytocin. Oxytocin treatment resulted in a transient or prolonged reduction of endotoxin-induced increases in plasma ACTH, cortisol, procalcitonin, TNF-alpha, IL-1 receptor antagonist, IL-4, IL-6, macrophage inflammatory protein-1alpha, macrophage inflammatory protein-1beta, monocyte chemoattractant protein-1 (MCP-1), interferon-inducible protein 10, and VEGF. In vitro, oxytocin had no impact on LPS effects in releasing TNF-alpha, IL-6, and MCP-1 in monocytes and peripheral blood mononuclear cells from healthy human donors. In summary, oxytocin decreases the neuroendocrine and cytokine activation caused by bacterial endotoxin in men, possibly due to the pharmacological modulation of the cholinergic anti-inflammatory pathway. Oxytocin might be a candidate for the therapy of inflammatory diseases and conditions associated with high cytokine and VEGF levels.

Adaptive responses of the maternal hypothalamic-pituitary-adrenal axis during pregnancy and lactation

Over the past 40 years, it has been recognised that the maternal hypothalamic-pituitary-adrenal (HPA) axis undergoes adaptations through pregnancy and lactation that might contribute to avoidance of adverse effects of stress on the mother and offspring. The extent of the global adaptations in the HPA axis has been revealed and the underlying mechanisms investigated within the last 20 years. Both basal, including the circadian rhythm, and stress-induced adrenocorticotrophic hormone and glucocorticoid secretory patterns are altered. Throughout most of pregnancy, and in lactation, these changes predominantly reflect reduced drive by the corticotropin-releasing factor (CRF) neurones in the parvocellular paraventricular nucleus (pPVN). An accompanying profound attenuation of HPA axis responses to a wide variety of psychological and physical stressors emerges after mid-pregnancy and persists until the end of lactation. Central to this suppression of stress responsiveness is reduced activation of the pPVN CRF neurones. This is consequent on the reduced effectiveness of the stimulation of brainstem afferents to these CRF neurones (for physical stressors) and of altered processing by limbic structures (for emotional stressors). The mechanism of reduced CRF neurone responses to physical stressors in pregnancy is the suppression of noradrenaline release in the PVN by an up-regulated endogenous opioid mechanism, which is induced by neuroactive steroid produced from progesterone. By contrast, in lactation suckling the young provides a neural stimulus that dampens the HPA axis circadian rhythm and reduces stress responses. Reduced noradrenergic input activity is involved in reduced stress responses in lactation, although central prolactin action also appears important. Such adaptations limit the adverse effects of excess glucocorticoid exposure on the foetus(es) and facilitate appropriate metabolic and immune responses.

Responses of the hypothalamopituitary adrenal axis and the sympathoadrenal system to isolation/restraint stress in sheep of different adiposity

There is evidence that levels of adipose tissue can influence responses of the hypothalamopituitary-adrenal (HPA) axis to stress in humans and rats but this has not been explored in sheep. Also, little is known about the sympathoadrenal responses to stress in individuals with relatively different levels of adipose tissue. We tested the hypothesis that the stress-induced activation of the HPA axis and sympathoadrenal system is lower in ovariectomized ewes with low levels of body fat (lean) than ovariectomized ewes with high levels of body fat (fat). Ewes underwent dietary manipulation for 3 months to yield a group of lean ewes (n = 7) with a mean (+/-SEM) live weight of 39.1 +/- 0.9 kg and body fat of 8.9 +/- 0.6% and fat ewes (n = 7) with a mean (+/-SEM) live weight of 69.0 +/- 1.8 kg and body fat of 31.7 +/- 3.4%. Fat ewes also had higher circulating concentrations of leptin than lean ewes. Blood samples were collected every 15 min over 8 h when no stress was imposed (control day) and on a separate day when 4 h of isolation/restraint was imposed after 4 h of pretreatment sampling (stress day). Plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol, epinephrine and norepinephrine did not change significantly over the control day and did not differ between lean and fat ewes. Stress did not affect plasma leptin levels. All stress hormones increased significantly during isolation/restraint stress. The ACTH, cortisol and epinephrine responses were greater in fat ewes than lean ewes but norepinephrine responses were similar. Our results suggest that relative levels of adipose tissue influence the stress-induced activity of the hypothalamopituitary-adrenal axis and some aspects of the sympathoadrenal system with fat animals having higher responses than lean animals.