Lines of mice with chronically elevated baseline corticosterone levels are more susceptible to a parasitic nematode infection

Chronically elevated circulating plasma glucocorticoid concentrations can have suppressive effects on immune function in mammals. House mice (Mus domesticus) that have been selectively bred for high voluntary wheel running exhibit chronically elevated (two-fold, on average) plasma corticosterone (CORT) levels and hence are an interesting model to study possible glucocorticoid-induced immune suppression. As an initial test of their immunocompetence, we compared the four replicate high runner (HR) lines with their four non-selected control (C) lines by subjecting them to infection by a parasitic nematode, Nippostrongylus brasiliensis. At generation 36 of the selection experiment, 10 adult males from each of the eight lines were inoculated subcutaneously with approximately 600 third-stage larval N. brasiliensis, and then sacrificed 12 days after injection. Neither spleen mass nor number of adult nematodes in the small intestine differed significantly between HR and C lines. However, the eight lines differed significantly in nematode counts, and the line means for nematode infestation were significantly positively related to baseline circulating CORT concentration measured in males from generations 34 and 39. Therefore, although selective breeding for high locomotor activity may not have resulted in a generally compromised immune response, results of this study are consistent with the hypothesis that glucocorticoids can have immunosuppressive effects.     

Prenatal exposure to dexamethasone alters hippocampal drive on hypothalamic-pituitary-adrenal axis activity in adult male rats

Glucocorticoids are essential for normal hypothalamic-pituitary-adrenal (HPA) axis activity; however, recent studies warn that exposure to excess endogenous or synthetic glucocorticoid during a specific period of prenatal development adversely affects HPA axis stability. We administered dexamethasone (DEX) to pregnant rats during the last week of gestation and investigated subsequent HPA axis regulation in adult male offspring in unrestrained and restraint-stressed conditions. With the use of real-time PCR and RIA, we examined the expression of regulatory genes in the hippocampus, hypothalamus, and pituitary, including corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), glucocorticoid receptors (GR), mineralcorticoid receptors (MR), and 11-beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1), as well as the main HPA axis hormones, adrenal corticotropic hormone (ACTH) and corticosterone (CORT). Our results demonstrate that the DEX-exposed group exhibited an overall change in the pattern of gene expression and hormone levels in the unrestrained animals. These changes included an upregulation of CRH in the hypothalamus, a downregulation of MR with a concomitant upregulation of 11beta-HSD-1 in the hippocampus, and an increase in circulating levels of both ACTH and CORT relative to unrestrained control animals. Interestingly, both DEX-exposed and control rats exhibited an increase in pituitary GR mRNA levels following a 1-h recovery from restraint stress; however, the increased expression in DEX-exposed rats was significantly less and was associated with a slower return to baseline CORT compared with controls. In addition, circulating levels of ACTH and CORT as well as hypothalamic CRH and hippocampal 11beta-HSD-1 expression levels were significantly higher in the DEX-exposed group compared with controls following restraint stress. Taken together, these data demonstrate that late-gestation DEX exposure in rats is associated with persistent changes in both the modulation of HPA axis activity and the HPA axis-mediated response to stress.     

Transient sex-related changes in the mice hypothalamo-pituitary-adrenal (HPA) axis during the acute phase of the inflammatory process

The potential role of endogenous sex hormones in regulating hypothalamo-pituitary-adrenal (HPA) axis function was investigated after a single injection of endotoxin in adult (8 week old) BALB/c mice of both sexes. The effect of LPS on plasma ACTH, corticosterone (B), testosterone and oestradiol (E) levels and on anterior pituitary (AP) ACTH and adrenal B contents at different times after treatment was studied. The results indicate that: (a) basal B but not ACTH plasma levels were significantly higher in female than in male mice; (b) LPS significantly increased both ACTH and B plasma levels over the baseline 2 h after injection, both hormone levels being higher in female than in male mice; (c) although plasma ACTH concentrations recovered the basal value at 72 h after LPS in animals of both sexes, plasma B levels returned to the baseline only at 120 h after treatment; (d) E plasma levels significantly increased 2 h after LPS and returned to the baseline at 72 h post-treatment, in both sexes; (e) at 2 h after LPS, testosterone plasma levels significantly decreased in male mice and increased in female mice, recovering the baseline level at 120 and 72 h after LPS, respectively; (f) AP ACTH content was similar in both sexes in basal condition and it was significantly diminished 72 h post-treatment without sex difference; whereas AP ACTH returned to basal content 120 h after LPS in males, it remained significantly decreased in females; (g) basal adrenal B content was higher in female than in male mice, and it significantly increased in both sexes 2 h post-LPS, maintaining this sex difference. Whereas adrenal B returned to basal content 72 h after treatment in male mice, it remained significantly enhanced up to 120 h post-LPS in female animals. The data demonstrate the existence of a clear sexual dimorphism in basal condition and during the acute phase response as well as in the recovery of the HPA axis function shortly after infection.     

Characterization of CRF, AVT, and ACTH cDNA and pituitary-adrenal axis function in Japanese quail divergently selected for tonic immobility

Higher corticosterone (CORT) responses to acute stress have previously been reported in quail selected for short (STI) duration of tonic immobility (TI) than for long TI (LTI), although behavioral studies indicated that LTI quail were more fearful. To investigate adrenal and pituitary function in these quail lines and their possible involvement in the differences in hypothalamic-pituitary-adrenal (HPA) axis reactivity, we measured CORT responses to adrenocorticotropin (1-24 ACTH), corticotropin-releasing factor (CRF), and arginine vasotocin (AVT) after characterizing the nucleotide acid sequences of these peptides in quail. Although maximum adrenal responses, assessed by ACTH challenge, were higher in STI quail, adrenal sensitivity was comparable for the two genotypes. It is therefore unlikely that differences in HPA axis reactivity involved the adrenal level. AVT and ACTH induced comparable CORT responses in both genotypes, whereas those induced by CRF were much lower. AVT is thus more potent than CRF in quail, but the respective maximum pituitary capacity of both genotypes to secrete ACTH was similar, and it is doubtful that the AVT pathway is involved in the difference in HPA axis reactivity between genotypes. On the other hand, the higher CORT responses induced by CRF in STI quail suggest that CRF might be involved in the differences in HPA axis reactivity between LTI and STI genotypes.     

Disruption of mineralocorticoid receptor function increases corticosterone responding to a mild, but not moderate, psychological stressor

Glucocorticoid negative feedback regulation of the hypothalamic-pituitary-adrenal (HPA) axis is mediated by corticosteroid receptors. It is widely thought that during stress, glucocorticoid receptors (GR) are essential for this negative feedback. In contrast, mineralocorticoid receptors (MR) are associated with HPA axis regulation in basal, nonstress conditions. Notions about the relative roles of MR and GR for HPA axis regulation during stressor challenge may not be complete. Recent work in our laboratory suggests that previous estimates of MR occupancy at resting plasma levels of corticosterone (CORT) may be overestimated. It is possible that a significant number of MR may be available to mediate negative feedback during stressor challenge. We hypothesized that this may be especially the case during mild stressor challenge when the plasma CORT response is weak. In the present studies, adult male Sprague-Dawley rats were first treated systemically or centrally with the selective MR antagonist RU28318 (50 mg/kg sc or 500 ng.10 microl(-1).2 h(-1) icv) or vehicle (300 microl propylene glycol sc or 10 microl/2 h sterile saline icv) and then challenged with 60-min novel environment or restraint. In vehicle controls, restraint resulted in a greater plasma CORT response than novel environment. Both systemic and central treatment with RU28318 significantly increased CORT responding to novel environment relative to vehicle controls. However, RU28318 treatment did not increase the CORT response to restraint. These data suggest that MR may be necessary for glucocorticoid regulation of HPA axis activity during mild stressors, but not during stressors that result in a more robust CORT response.     

Shape‐shift: Semicircular canal morphology responds to selective breeding for increased locomotor activity

Variation in semicircular canal morphology correlates with locomotor agility among species of mammals. An experimental evolutionary mouse model was used to test the hypotheses that semicircular canal morphology (1) evolves in response to selective breeding for increased locomotor activity, (2) exhibits phenotypic plasticity in response to early‐onset chronic exercise, and (3) is unique in individuals possessing the minimuscle phenotype. We examined responses in canal morphology to prolonged wheel access and selection in laboratory mice from four replicate lines bred for high voluntary wheel‐running (HR) and four nonselected control (C) lines. Linear measurements and a suite of 3D landmarks were obtained from 3D reconstructions of μCT‐scanned mouse crania (μCT is microcomputed tomography). Body mass was smaller in HR than C mice and was a significant predictor of both radius of curvature and 3D canal shape. Controlling for body mass, radius of curvature did not differ statistically between HR and C mice, but semicircular canal shape did. Neither chronic wheel access nor minimuscle affected radius of curvature or canal shape These findings suggest that semicircular canal morphology is responsive to evolutionary changes in locomotor behavior, but the pattern of response is potentially different in small‐ versus large‐bodied species.     

Evolution of hindlimb bone dimensions and muscle masses in house mice selectively bred for high voluntary wheel‐running behavior

We have used selective breeding with house mice to study coadaptation of morphology and physiology with the evolution of high daily levels of voluntary exercise. Here, we compared hindlimb bones and muscle masses from the 11th generation of four replicate High Runner (HR) lines of house mice bred for high levels of voluntary wheel running with four non‐selected control (C) lines. Mass, length, diameter, and depth of the femur, tibia‐fibula, and metatarsal bones, as well as masses of gastrocnemius and quadriceps muscles, were compared by analysis of covariance with body mass or body length as the covariate. Mice from HR lines had relatively wider distal femora and deeper proximal tibiae, suggesting larger knee surface areas, and larger femoral heads. Sex differences in bone dimensions were also evident, with males having thicker and shorter hindlimb bones when compared with females. Several interactions between sex, linetype, and/or body mass were observed, and analyses split by sex revealed several cases of sex‐specific responses to selection. A subset of the HR mice in two of the four HR lines expressed the mini‐muscle phenotype, characterized mainly by an ～50% reduction in hindlimb muscle mass, caused by a Mendelian recessive mutation, and known to have been under positive selection in the HR lines. Mini‐muscle individuals had elongated distal elements, lighter and thinner hindlimb bones, altered 3rd trochanter muscle insertion positions, and thicker tibia‐fibula distal widths. Finally, several differences in levels of directional or fluctuating asymmetry in bone dimensions were observed between HR and C, mini‐ and normal‐muscled mice, and the sexes. This study demonstrates that skeletal dimensions and muscle masses can evolve rapidly in response to directional selection on locomotor behavior.     

Baseline glucocorticoids are drivers of body mass gain in a diving seabird

Life‐history trade‐offs are influenced by variation in individual state, with individuals in better condition often completing life‐history stages with greater success. Although resource accrual significantly impacts key life‐history decisions such as the timing of reproduction, little is known about the underlying mechanisms driving resource accumulation. Baseline corticosterone (CORT, the primary avian glucocorticoid) mediates daily and seasonal energetics, responds to changes in food availability, and has been linked to foraging behavior, making it a strong potential driver of individual variation in resource accrual and deposition. Working with a captive colony of white‐winged scoters (Melanitta fusca deglandi), we aimed to causally determine whether variation in baseline CORT drives individual body mass gains mediated through fattening rate (plasma triglycerides corrected for body mass). We implanted individuals with each of three treatment pellets to elevate CORT within a baseline range in a randomized order: control, low dose of CORT, high dose of CORT, then blood sampled and recorded body mass over a two‐week period to track changes in baseline CORT, body mass, and fattening rates. The high CORT treatment significantly elevated levels of plasma hormone for a short period of time within the biologically relevant, baseline range for this species, but importantly did not inhibit the function of the HPA (hypothalamic–pituitary–adrenal) axis. Furthermore, an elevation in baseline CORT resulted in a consistent increase in body mass throughout the trial period compared to controls. This is some of the first empirical evidence demonstrating that elevations of baseline CORT within a biologically relevant range have a causal, direct, and positive influence on changes in body mass.     

Evaluating the Stress Response as a Bioindicator of Sub-Lethal Effects of Crude Oil Exposure in Wild House Sparrows (Passer domesticus)

Petroleum can disrupt endocrine function in humans and wildlife, and interacts in particularly complex ways with the hypothalamus-pituitary-adrenal (HPA) axis, responsible for the release of the stress hormones corticosterone and cortisol (hereafter CORT). Ingested petroleum can act in an additive fashion with other stressors to cause increased mortality, but it is not clear exactly why—does petroleum disrupt feedback mechanisms, stress hormone production, or both? This laboratory study aimed to quantify the effects of ingested Gulf of Mexico crude oil on the physiological stress response of house sparrows (Passer domesticus). We examined baseline and stress-induced CORT, negative feedback, and adrenal sensitivity in house sparrows given a 1% oil or control diet (n = 12 in each group). We found that four weeks on a 1% oil diet did not alter baseline CORT titers or efficacy of negative feedback, but significantly reduced sparrows'' ability to secrete CORT in response to a standardized stressor and adrenocorticotropin hormone injection, suggesting that oil damages the steroid-synthesizing cells of the adrenal. In another group of animals on the same 1% oil (n = 9) or control diets (n = 8), we examined concentrations of eight different blood chemistry parameters, and CORT in feathers grown before and during the feeding experiments as other potential biomarkers of oil exposure. None of the blood chemistry parameters differed between birds on the oil and control diets after two or four weeks of feeding, nor did feather CORT differ between the two groups. Overall, this study suggests that the response of CORT to stressors, but not baseline HPA function, may be a particularly sensitive bioindicator of sub-lethal chronic effects of crude oil exposure.     

Pharmacological studies on the anxiolytic effect of standardized Schisandra lignans extract on restraint-stressed mice

Fruits of Fructus Schisandrae were used as sedatives and hypnotics in traditional Chinese medicine for a long history. In this study, we investigated the effects of schisandra lignans extract (SLE) on anxiety disorder in restraint-stressed mice using light-dark (L-D) test. The influences of restraint stress on the levels of monoamines: noradrenaline (NE), dopamine (DA) and serotonin (5-HT) in cerebral cortex, as well as plasma corticosterone (CORT) were studied in mice. The HPLC fingerprint of SLE was recorded and the percentage composition of Schisandra lignans was determined as 82.63%. In L-D test, it was found out that 18 h of restraint stress significantly decreased the anxiolytic parameters (explorative behaviors, e.g. number of entries, time spent) in light area indicating high state of anxiety in stressed mice. In addition, restraint stress elevated NE, DA, and 5-HT levels in cerebral cortex of anxiety mice. Plasma CORT level was also increased. Oral administration of SLE (100 and 200 mg/kg/day, 8 days) emolliating the level of stress-induced anxiety by significantly increasing the anxiolytic parameters mentioned above. We also observed decreases in cerebral cortex monoamines levels, as well as plasma CORT level in stressed mice. These results suggested that SLE reversed stress-induced anxiety level, changes of cortex monoamine transmitters and plasma CORT. The anxiolytic effects of SLE might be related to its anti-stress activity by modulation of hyperactive HPA axis.     

“Green odor” inhalation by stressed rat dams reduces behavioral and neuroendocrine signs of prenatal stress in the offspring

Chronic maternal stress during pregnancy results in the “prenatally stressed” offspring displaying behavioral and neuroendocrine alterations that persist into adulthood. We investigated how inhalation of green odor (a mixture of equal amounts of trans-2-hexenal and cis-3-hexenol) by stressed dams might alter certain indices of prenatal stress in their offspring. These indices were depression-like behavior (increased immobility time in the forced-swim test) and acute restraint stress-induced changes in hypothalamo-pituitary-adrenocortical (HPA) axis activity [plasma corticosterone (CORT) and ACTH levels and the number of Fos-immunoreactive cells in the hypothalamic paraventricular nucleus (an index of neuronal activity)]. Pregnant rats were exposed to restraint stress for 60 min/day for 10 days (gestational days 10-19). The prenatally stressed offspring exhibited significant increases in depression-like behavior and in restraint stress-induced ACTH, CORT, and Fos responses, unless their dam had been exposed to green odor. The behavioral effect of the odor was also seen in offspring that were fostered by unstressed dams. The results obtained in the dams themselves were as follows. In vehicle-exposed stressed dams, but not in green odor-exposed ones, total body and adrenal weights were significantly decreased or increased, respectively. Depression-like behavior was not observed in the vehicle-exposed stressed dams themselves. Green odor inhalation prevented the impairment of maternal behavior induced by restraint stress. Thus, exposure of dams to stress may affect both the fetal brain and fetal HPA axis, and also maternal behavior, leading to altered behavioral and neuroendocrine responses in the offspring. Such effects may be prevented by the stressed dams inhaling green odor.     

Selection for fast and slow exploration affects baseline and stress-induced corticosterone excretion in Great tit nestlings,Parus major

In nestlings, glucocorticoid (GC) secretion has short-term and long-term f itness consequences. For example, short-time elevations trigger begging activity, whereas chronically elevated GC levels impair body condition, growth and cognitive abilities. Despite a growing body of literature on personality traits, the effects of selection for fast and slow exploration on GC secretion have received little attention. We compared baseline and stress-induced hypothalamic–pituitary–adrenal (HPA) axis activity of hand-reared great tit nestlings of lines selected for fast and slow exploration. Nestling droppings were collected under three conditions: control, test (following handling stress, day 14 after hatching) and the following day. The concentrations of excreted immunoreactive corticosterone metabolites (CM) were determined via an enzyme immunoassay. We also observed nestlings' begging behaviour. CM differed significantly between the lines. Nestlings of the fast line excreted lower CM than slow-line birds. In response to handling stress, nestlings excreted significantly higher concentrations of CM than during the control and on the day after handling. Sex and begging activity were not related to CM levels. Under the control condition, but not after handling, males begged significantly more often than females. In both lines, adults excreted significantly less CM compared to nestlings. Both nestlings and adults of the slow line produced higher baseline CM values than fast-line birds. Fast-line nestlings excreted lower baseline CM than nestlings of a wild population not selected for fast or slow exploration. Slow-line nestlings did not. Our results show that selection on the basis of exploratory behaviour affected HPA axis reactivity.     

Selection for fast and slow exploration affects baseline and stress-induced corticosterone excretion in Great tit nestlings, Parus major

In nestlings, glucocorticoid (GC) secretion has short-term and long-term f itness consequences. For example, short-time elevations trigger begging activity, whereas chronically elevated GC levels impair body condition, growth and cognitive abilities. Despite a growing body of literature on personality traits, the effects of selection for fast and slow exploration on GC secretion have received little attention. We compared baseline and stress-induced hypothalamic–pituitary–adrenal (HPA) axis activity of hand-reared great tit nestlings of lines selected for fast and slow exploration. Nestling droppings were collected under three conditions: control, test (following handling stress, day 14 after hatching) and the following day. The concentrations of excreted immunoreactive corticosterone metabolites (CM) were determined via an enzyme immunoassay. We also observed nestlings' begging behaviour. CM differed significantly between the lines. Nestlings of the fast line excreted lower CM than slow-line birds. In response to handling stress, nestlings excreted significantly higher concentrations of CM than during the control and on the day after handling. Sex and begging activity were not related to CM levels. Under the control condition, but not after handling, males begged significantly more often than females. In both lines, adults excreted significantly less CM compared to nestlings. Both nestlings and adults of the slow line produced higher baseline CM values than fast-line birds. Fast-line nestlings excreted lower baseline CM than nestlings of a wild population not selected for fast or slow exploration. Slow-line nestlings did not. Our results show that selection on the basis of exploratory behaviour affected HPA axis reactivity.     

Effect of voluntary wheel running on circadian corticosterone release and on HPA axis responsiveness to restraint stress in Sprague-Dawley rats.

Adaptations of the hypothalamic-pituitary-adrenal (HPA) axis to voluntary exercise in rodents are not clear, because most investigations use forced-exercise protocols, which are associated with psychological stress. In the present study, we examined the effects of voluntary wheel running on the circadian corticosterone (Cort) rhythm as well as HPA axis responsiveness to, and recovery from, restraint stress. Male Sprague-Dawley rats were divided into exercise (E) and sedentary (S) groups, with E rats having 24-h access to running wheels for 5 wk. Circadian plasma Cort levels were measured at the end of each week, except for week 5 when rats were exposed to 20 min of restraint stress, followed by 95 min of recovery. Measurements of glucocorticoid receptor content in the hippocampus and anterior pituitary were performed using Western blotting at the termination of the restraint protocol. In week 1, circadian Cort levels were twofold higher in E compared with S animals, but the levels progressively decreased in the E group throughout the training protocol to reach similar values observed in S by week 4. During restraint stress and recovery, Cort values were similar between E and S, as was glucocorticoid receptor content in the hippocampus and pituitary gland after death. Compared with E, S animals had higher plasma ACTH levels during restraint. Taken together, these data indicate that 5 wk of wheel running are associated with normal circadian Cort activity and normal negative-feedback inhibition of the HPA axis, as well as with increased adrenal sensitivity to ACTH after restraint stress.     

Effect of "rose essential oil" inhalation on stress-induced skin-barrier disruption in rats and humans

In stressed animals, several brain regions (e.g., hypothalamic paraventricular nucleus [PVN]) exhibit neuronal activation, which increases plasma adrenocorticotropic hormone (ACTH) and glucocorticoids. We previously reported that so-called "green odor" inhibits stress-induced activation of the hypothalamo-pituitary-adrenocortical axis (HPA axis) and thereby prevents the chronic stress-induced disruption of the skin barrier. Here, we investigated whether rose essential oil, another sedative odorant, inhibits the stress-induced 1) increases in PVN neuronal activity in rats and plasma glucocorticoids (corticosterone [CORT] in rats and cortisol in humans) and 2) skin-barrier disruption in rats and humans. The results showed that in rats subjected to acute restraint stress, rose essential oil inhalation significantly inhibited the increase in plasma CORT and reduced the increases in the number of c-Fos-positive cells in PVN. Inhalation of rose essential oil significantly inhibited the following effects of chronic stress: 1) the elevation of transepidermal water loss (TEWL), an index of the disruption of skin-barrier function, in both rats and humans and 2) the increase in the salivary concentration of cortisol in humans. These results suggest that in rats and humans, chronic stress-induced disruption of the skin barrier can be limited or prevented by rose essential oil inhalation, possibly through its inhibitory effect on the HPA axis.     

Caffeine-induced activated glucocorticoid metabolism in the hippocampus causes hypothalamic-pituitary-adrenal axis inhibition in fetal rats

Epidemiological investigations have shown that fetuses with intrauterine growth retardation (IUGR) are susceptible to adult metabolic syndrome. Clinical investigations and experiments have demonstrated that caffeine is a definite inducer of IUGR, as children who ingest caffeine-containing food or drinks are highly susceptible to adult obesity and hypertension. Our goals for this study were to investigate the effect of prenatal caffeine ingestion on the functional development of the fetal hippocampus and the hypothalamic-pituitary-adrenal (HPA) axis and to clarify an intrauterine HPA axis-associated neuroendocrine alteration induced by caffeine. Pregnant Wistar rats were intragastrically administered 20, 60, and 180 mg/kg·d caffeine from gestational days 11-20. The results show that prenatal caffeine ingestion significantly decreased the expression of fetal hypothalamus corticotrophin-releasing hormone. The fetal adrenal cortex changed into slight and the expression of fetal adrenal steroid acute regulatory protein (StAR) and cholesterol side-chain cleavage enzyme (P450scc), as well as the level of fetal adrenal endogenous corticosterone (CORT), were all significantly decreased after caffeine treatment. Moreover, caffeine ingestion significantly increased the levels of maternal and fetal blood CORT and decreased the expression of placental 11β-hydroxysteroid dehydrogenase-2 (11β-HSD-2). Additionally, both in vivo and in vitro studies show that caffeine can downregulate the expression of fetal hippocampal 11β-HSD-2, promote the expression of 11β-hydroxysteroid dehydrogenase 1 and glucocorticoid receptor (GR), and enhance DNA methylation within the hippocampal 11β-HSD-2 promoter. These results suggest that prenatal caffeine ingestion inhibits the development of the fetal HPA axis, which may be associated with the fetal overexposure to maternal glucocorticoid and activated glucocorticoid metabolism in the fetal hippocampus. These results will be beneficial in elucidating the developmental toxicity of caffeine and in exploring the fetal origin of adult HPA axis dysfunction and metabolic syndrome susceptibility for offspring with IUGR induced by caffeine.     

Effects of repeated investigator handling of Leach's Storm‐Petrel chicks on growth rates and the acute stress response

Disturbance during development may have lasting effects on the growth rates and stress physiology of birds. Although repeated handling by researchers is often necessary, the possible effects of such handling on the development of semi‐altricial young are unclear. We examined the effect of daily handling on growth rates and plasma corticosterone levels of Leach's Storm‐Petrel (Oceanodroma leucorhoa) chicks on Kent Island in the Bay of Fundy, New Brunswick, Canada, during the 2011 nesting season. From post‐hatch day 7 to post‐hatch days 14–36, birds in the experimental group were extracted from burrows and measured (wing, tarsus, and mass) for ～3 min every day, whereas birds in the control group were left undisturbed. After the treatment period, blood was collected from birds in both groups within 3 min of initially reaching into burrows (baseline) and after a 30‐min restraint stress test to assess the effect of early life disturbance on programming of the hypothalamic‐pituitary‐adrenal (HPA) axis. A second acute restraint stress test was conducted three weeks after the end of the treatment period to investigate possible longer term effects of early life disturbance. Growth rates of wings and tarsi were similar for handled chicks (N = 18) and non‐handled control chicks (N = 21), as were baseline and 30‐min acute restraint stress‐induced corticosterone levels. As also reported in previous studies of other altricial and semi‐altricial species, older chicks (42–64 d old) had higher plasma corticosterone levels than younger chicks (21–43 d old) after acute restraint stress tests, reflecting delayed development of the HPA axis. The age‐related increase in HPA axis sensitivity observed prior to fledging could facilitate foraging and predator avoidance behaviors while minimizing exposure to high levels of corticosterone earlier in development. Overall, we found no evidence that repeated disturbance influenced either growth rates or HPA axis programming of Leach's Storm‐Petrel chicks.     

Genetic differences in coping strategies in response to prolonged and repeated restraint in Japanese quail divergently selected for long or short tonic immobility

Exposure to fearful situations elicits behavioral and Hypothalamic–Pituitary–Adrenal (HPA) axis responses characteristic of the coping response of individual animals to counteract environmental challenges. The aim of this study was to investigate behavioral and corticotropic responses concomitantly following prolonged or repeated restraint stress by placing two genotypes of Japanese quail divergently selected for long (LTI) or short (STI) duration of tonic immobility (TI) in a crush cage. In our study, STI quail exhibited higher corticosterone (CORT) levels than LTI quail in response to prolonged restraint. STI quail struggled sooner and much more than LTI quail, and struggling behavior in STI quail progressively decreased during the course of restraint whereas LTI quail displayed very little struggling behavior in the crush cage. LTI quail are thus more likely to adopt a passive behavior coping strategy upon exposure to threat whereas STI quail behave more as active copers. The corticosterone responses shown by LTI and STI quail under restraint stress suggest that adrenocortical correlates of coping behavior in these genotypes of quail may be different from the coping styles previously described in other species. Repeated restraint slightly decreased CORT responses to stress in all experimental groups, but more markedly in male STI quail, whereas adrenal sensitivity and maximum adrenal corticosterone response capacity did not change in any group. On the other hand, neither behavioral habituation nor sensitization processes occurred in the context of repeated restraint in female and male LTI quail and female STI quail, whereas the decreases observed in some behavioral responses were interpreted to be the result of a habituation process in male STI quail.     

Rat Strain Differences in Responses of Plasma Prolactin and PRL mRNA Expression After Acute Amphetamine Treatment or Restraint Stress

1. The aim of this study was to compare the effects of acute amphetamine (AMPH) treatment and restraint stress on plasma level of prolactin (PRL) and PRL mRNA expression in the adenohypophysis in Sprague–Dawley and Lewis male rats, the latter known to have a deficient hypothalamo–pituitary-adrenal (HPA) axis.2. Both restraint stress and AMPH treatment (i.p. in a dose of 8 mg/kg of b.w.) were applied 15 or 30 min before termination of the experiment. Plasma PRL and corticosterone (CORT) were determined by radioimmunoassay. PRL mRNA expression was estimated by a dot-blot hybridization.3. Restraint stress and AMPH treatment induced a significant increase in theCORT plasma level, as an indicator of stress response. Compared to Sprague–Dawley rats, the magnitude of CORT increase after both stimuli was significantly lower in Lewis rats.4. Although restraint stress significantly increased the PRL plasma levels in both rat strains, AMPH treatment reduced the PRL levels in both rat strains. However, the changes of PRL plasma levels had another pattern in Lewis rats than in Sprague–Dawley rats. Control plasma PRL levels were significantly higher in Lewis rats, and in this rat strain AMPH treatment for 30 min increased the PRL levels as compared to the values obtained after AMPH treatment for 15 min.5. Expression of PRL mRNA in adenohypophysis by restraint stress and AMPH treatment had a similar pattern. After a 15-min lasting restraint stress, the expression of PRL mRNA was decreased insignificantly in both rat strains. AMPH treatment induced in Sprague–Dawley rats a significant decrease of PRL mRNA after a 15-min interval while after 30 min there was a significant increase. However, in Lewis rats AMPH failed to significantly change PRL mRNA.6. The results from the present study indicate that the mechanisms mediatingthe effects of acute restraint stress and acute AMPH treatment differ in PRL response in Sprague–Dawley and Lewis male rat strains. Differences in the observed responses in Lewis rats could be related to the deficient activity of HPA axis in this rat strain.