Plasma Corticosterone Response Research Articles

Brown and white layer pullet hybrids show different fear responses towards humans, but what role does light during incubation play in that?

Good early life conditions are increasingly recognized as essential to animal welfare later in life. The use of light during incubation might improve coping capacities and welfare in later life in poultry, by more closely approximating chicken natural environments compared to the current conventional incubation in darkness. Previous studies showed that lighted incubation resulted in more lateralized chicks, a more pronounced daily behavior rhythm, earlier onset of melatonin rhythms, and lower stress reactions to various stressors after hatching. Most existing research, however, has been conducted on broilers, and little information on lighted incubation is available for laying hens. In the current research, Dekalb White and ISA Brown eggs were incubated in complete darkness or in a cycle of green 12 L:12D throughout incubation, and five fear of human tests were performed on the 387 chickens during the rearing phase. We expected dark-incubated chickens to show stronger fear responses than light-incubated chickens. That was only the case for one of 15 behavior measurements taken during the tests (p < 0.05). In addition, white layer hybrids are known to be flightier and more fearful than brown hybrids. In this study, white chickens indeed showed stronger fear responses than brown chickens in 12 of the 15 behavior measurements (p ≤ 0.002). Furthermore, we expected light during incubation to have stronger effects on white chickens than on brown chickens, because of the stronger transmission of light through white eggshells. However, the interaction between hybrid and incubation was never significant (p ≥ 0.18). Finally, contrary to our expectations, there was no effect of the incubation treatments or the hybrid on plasma corticosterone responses to a manual restraint test (p ≥ 0.36). Since there was a hybrid effect on behavior in this test, it is reasonable to think that behavior reflected coping style, rather than fear level. To conclude, the light regime used in this study does not seem as promising as expected to improve laying hen welfare. Finally, the brown hybrid was usually less fearful than the white hybrid, though there were some exceptions depending on the stressor, and that should be taken into account in research and in laying hen management.

Western diet-induced obesity interferes with the HPA axis-blunting effects of palatable food in male rats

Limited intermittent consumption of palatable food reduces HPA axis responses to stress in chow-fed rats, and this effect is dependent on the rewarding properties of the palatable food. However, obesity may be a state of reduced consummatory food reward, suggesting that palatable foods may be less effective at blunting HPA axis reactivity in the context of diet-induced obesity (DIO). To test this hypothesis, adult male Long-Evans rats were given unlimited access to Western (high-fat, high-sugar) diet (WD) vs. normal chow (controls). After 8 weeks of diet exposure, rats were given limited sucrose intake (LSI) consisting of additional twice-daily access to a small amount (4 ml) of either 3% or 30% sucrose drink, or water (controls) for 2 weeks. Rats then received an acute restraint stress challenge, with collection of tail blood samples for measurement of plasma corticosterone. WD-fed rats had increased caloric intake, body weight and adiposity, as expected. Rats offered LSI (3% or 30%) readily drank the maximal amount allowed (8 ml/day) and reduced their dietary intake to compensate for the sucrose calories, such that LSI did not alter body weight regardless of diet type. In chow-fed lean rats, LSI with either 3% or 30% sucrose reduced the plasma corticosterone response to restraint stress, but this effect was absent in WD-fed DIO rats. Together, these data support the hypothesis that obesity attenuates stress blunting by palatable foods and suggest the possibility that consequently, individuals with obesity may need to consume larger amounts of palatable food to obtain adequate stress relief.

Impacts of maternal separation stress on ethanol-related responses, anxiety- and depressive-like behaviors in adolescent mice

The present work evaluated the consequences of chronic maternal separation (MS), an animal model of early-life stress, on ethanol intake and striatal Fos expression induced by ethanol consumption. Furthermore, we analyzed MS impacts on anxiety- and depressive-like behaviors and on locomotor and plasma corticosterone responses to intraperitoneal treatment with ethanol in adolescent mice. For that, male and female C57BL/6J mice were exposed or not to MS stress, for 3 h per day, from postnatal day (PND) 1 to 14, and submitted to behavioral tests from PND 28. In Experiment 1, MS and control groups of mice were submitted to an involuntary ethanol intake protocol, and striatal Fos expression following ethanol exposure was analyzed. In Experiment 2, mice behavior was assessed in elevated plus-maze, sucrose splash, saccharin preference, and open field tests. Locomotor and plasma corticosterone responses induced by a systemic dose of ethanol (1.75 g/kg) were also evaluated. Our results demonstrated that MS increased ethanol intake only in an acute manner and did not impact ethanol-induced Fos expression in the dorsal striatum and nucleus accumbens (NAc) core and shell subregions. MS did not change the parameters analyzed during elevated plus-maze, sucrose splash, preference for saccharin, and open field tests. MS did not affect locomotor activity following ethanol injection nor plasma corticosterone response to the drug. Thus, our data showed that MS transiently increased ethanol intake. However, early-life stress did not impact Fos, locomotor, or plasma corticosterone responses to the drug. In addition, MS did not affect anxiety- and depressive-like behaviors in adolescent mice.

Cues associated with repeated ethanol exposure facilitate the corticosterone response to ethanol and immunological challenges in adult male Sprague Dawley rats: implications for neuroimmune regulation

ABSTRACT Background: We previously found a conditioned increase in central neuroinflammatory markers (Interleukin 6; IL-6) following exposure to alcohol-associated cues. Recent studies suggest (unconditioned) induction of IL-6 is entirely dependent on ethanol-induced corticosterone. Objectives: The goals of these present studies were to test whether alcohol-paired cues facilitated the hypothalamic-pituitary-adrenal (HPA) axis response to either a subthreshold priming alcohol dose or an immune or psychological stress challenge Methods: In Experiment 1 (N = 64), adult male Sprague Dawley rats were trained (paired or unpaired, four pairings total) with either vehicle or 2 g/kg alcohol [intragastric (i.g.) or intraperitoneal (i.p.)] injections. In Experiments 2 (N = 28) and 3 (N = 30), male rats were similarly trained but with 4 g/kg alcohol i.g. intubations. On test day, all rats were either administered a 0.5 g/kg alcohol dose (i.p. or i.g. Experiment 1), a 100 µg/kg i.p. lipopolysaccharide (LPS) challenge (Experiment 2), or a restraint challenge (Experiment 3), and exposed to alcohol-associated cues. Blood plasma was collected for analysis. Results: Alcohol-associated cues facilitated the plasma corticosterone response to a subthreshold dose of alcohol (F 1,28 = 4.85, p < .05) and an immune challenge (F 8,80 = 6.23, p < .001), but not a restraint challenge (F2,27 = 0.18, p > .05). Conclusion: These findings reveal that the impact of the cues associated with alcohol intoxication on the HPA axis may be context-specific. This work illustrates how HPA axis learning processes form in the early stages of alcohol use and has important implications for how the HPA and neuroimmune conditioning may develop in alcohol use disorder in humans and facilitate the response to a later immune challenge.

Transgenerational inheritance of fetal alcohol effects on proopiomelanocortin gene expression and methylation, cortisol response to stress, and anxiety-like behaviors in offspring for three generations in rats: Evidence for male germline transmission.

Previously it has been shown that fetal alcohol exposure increases the stress response partly due to lowering stress regulatory proopiomelanocortin (Pomc) gene expression in the hypothalamus via epigenetic mechanisms for multiple generations in mixed-breed rats. In this study we assess the induction of heritable epigenetic changes of Pomc-related variants by fetal alcohol exposure in isogenic Fischer 344 rats. Using transgenerational breeding models and fetal alcohol exposure procedures, we determined changes in hypothalamic Pomc gene expression and its methylation levels, plasma corticosterone hormone response to restraint stress, and anxiety-like behaviors using elevated plus maze tests in fetal alcohol-exposed offspring for multiple generations in isogenic Fischer rats. Fetal alcohol-exposed male and female rat offspring showed significant deficits in POMC neuronal functions with increased Pomc gene methylation and reduced expression. These changes in POMC neuronal functions were associated with increased plasma corticosterone response to restraint stress and increased anxiety-like behavior. These effects of fetal alcohol exposure persisted in the F1, F2, and F3 progeny of the male germline but not of the female germline. These data suggest that fetal alcohol exposure induces heritable changes in Pomc-related variants involving stress hyperresponsiveness and anxiety-like behaviors which perpetuate into subsequent generations through the male germline via epigenetic modifications.

Locus Coeruleus Noradrenergic Modulation of Diurnal Corticosterone, Stress Reactivity, and Cardiovascular Homeostasis in Male Rats

Introduction: Activation of the locus coeruleus-noradrenergic (LC-NA) system during awakening is associated with an increase in plasma corticosterone and cardiovascular tone. These studies evaluate the role of the LC in this corticosterone and cardiovascular response. Methods: Male rats, on day 0, were treated intraperitoneally with either DSP4 (50 mg/kg body weight) (DSP), an LC-NA specific neurotoxin, or normal saline (SAL). On day 10, animals were surgically prepared with jugular vein (hypothalamic-pituitary-adrenal [HPA] axis) or carotid artery (hemodynamics) catheters and experiments performed on day 14. HPA axis activity, diurnally (circadian) and after stress (transient hemorrhage [14 mL/kg body weight] or air puff-startle), and basal and post-hemorrhage hemodynamics were evaluated. On day 16, brain regions from a subset of rats were dissected for norepinephrine and corticotropin-releasing factor (CRF) assay. Results: In DSP rats compared to SAL rats, (1) regional brain norepinephrine was decreased, but there was no change in median eminence or olfactory bulb CRF content; (2) during HPA axis acrophase, the plasma corticosterone response was blunted; (3) after hemorrhage and air puff-startle, the plasma adrenocorticotropic hormone response was attenuated, whereas the corticosterone response was dependent on stressor category; (4) under basal conditions, hemodynamic measures exhibited altered blood flow dynamics and systemic vasodilation; and (5) after hemorrhage, hemodynamics exhibited asynchronous responses. Conclusion: LC-NA modulation of diurnal and stress-induced HPA axis reactivity occurs via distinct neurocircuits. The integrity of the LC-NA system is important to maintain blood flow dynamics. The importance of increases in plasma corticosterone at acrophase to maintain short- and long-term cardiovascular homeostasis is discussed.

Social buffering of plasma corticosterone and amygdala responses of young rats following exposure to periorbital shock: Implications for eyeblink conditioning development.

The developmental onset of aversive learning processes depends on complex interactions between endocrine, neural, and social influences. Emergence of avoidance conditioning in rat pups is triggered by elevated plasma corticosterone activating the amygdala. Further, the mother's ability to buffer the corticosterone response delays the onset of avoidance in ˜2-week-old pups. Eyeblink conditioning (EBC) also develops during the pre-weaning period. In previous work, little or no conditioning was observed on Day 17 for pups housed in the home cage with mother and littermates between training sessions, whereas pups isolated between training sessions did show some conditioning. This suggests that social buffering may also delay the onset of this form of aversive learning. In the present study with Day-17 pups, one session of periorbital shock, the typical EBC unconditioned stimulus for young rat pups, resulted in lower plasma corticosterone levels and neural activity in the central nucleus of the amygdale (CeA) of pups returned to the mother and homecage following the session as compared to pups isolated following the shock session. These findings demonstrate social buffering of the physiological response to aversive stimulus exposure under conditions of EBC and support the hypothesis that social buffering of early adverse experience may adjust the timing of emergence of EBC in rat pups. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Poly (I:C)-induced maternal immune activation modifies ventral hippocampal regulation of stress reactivity: prevention by environmental enrichment

Environmental enrichment (EE) has been successfully implemented in human rehabilitation settings. However, the mechanisms underlying its success are not understood. Incorporating components of EE protocols into our animal models allows for the exploration of these mechanisms and their role in mitigation. Using a mouse model of maternal immune activation (MIA), the present study explored disruptions in social behavior and associated hypothalamic pituitary adrenal (HPA) axis functioning, and whether a supportive environment could prevent these effects. We show that prenatal immune activation of toll-like receptor 3, by the viral mimetic polyinosinic-polycytidylic acid (poly(I:C)), led to disrupted maternal care in that dams built poorer quality nests, an effect corrected by EE housing. Standard housed male and female MIA mice engaged in higher rates of repetitive rearing and had lower levels of social interaction, alongside sex-specific expression of several ventral hippocampal neural stress markers. Moreover, MIA males had delayed recovery of plasma corticosterone in response to a novel social encounter. Enrichment housing, likely mediated by improved maternal care, protected against these MIA-induced effects. We also evaluated c-Fos immunoreactivity associated with the novel social experience and found MIA to decrease neural activation in the dentate gyrus. Activation in the hypothalamus was blunted in EE housed animals, suggesting that the putative circuits modulating social behaviors may be different between standard and complex housing environments. These data demonstrate that augmentation of the environment supports parental care and offspring safety/security, which can offset effects of early health adversity by buffering HPA axis dysregulation. Our findings provide further evidence for the viability of EE interventions in maternal and pediatric settings.

Effects of test experience, closed-arm wall color, and illumination level on behavior and plasma corticosterone response in an elevated plus maze in male C57BL/6J mice: a challenge against conventional interpretation of the test

The elevated plus maze test is a widely used test for assessing anxiety-like behavior and screening novel therapeutic agents in rodents. Previous studies have shown that a variety of internal factors and procedural variables can influence elevated plus maze behavior. Although some studies have suggested a link between behavior and plasma corticosterone levels, the relationships between them remain unclear. In this study, we investigated the effects of experience with a battery of behavioral tests, the wall color of the closed arms, and illumination level on the behavior and plasma corticosterone responses in the elevated plus maze in male C57BL/6J mice. Mice were either subjected to a series of behavioral tests, including assessments of general health and neurological function, a light/dark transition test, and an open field test, or left undisturbed until the start of the elevated plus maze test. The mice with and without test battery experience were allowed to freely explore the elevated plus maze. The other two independent groups of naïve mice were tested in mazes with closed arms with different wall colors (clear, transparent blue, white, and black) or different illumination levels (5, 100, and 800 lx). Immediately after the test, blood was collected to measure plasma corticosterone concentrations. Mice with test battery experience showed a lower percentage of open arm time and entries and, somewhat paradoxically, had lower plasma corticosterone levels than the mice with no test battery experience. Mice tested in the maze with closed arms with clear walls exhibited higher open arm exploration than mice tested in the maze with closed arms with black walls, while there were no significant differences in plasma corticosterone levels between the different wall color conditions. Illumination levels had no significant effects on any measure. Our results indicate that experience with other behavioral tests and different physical features of the maze affect elevated plus maze behaviors. Increased open arm time and entries are conventionally interpreted as decreased anxiety-like behavior, while other possible interpretations are considered: open arm exploration may reflect heightened anxiety and panic-like reaction to a novel situation under certain conditions. With the possibility of different interpretations, the present findings highlight the need to carefully consider the test conditions in designing experiments and drawing conclusions from the behavioral outcomes in the elevated plus maze test in C57BL/6J mice.

Effects of acute stressors experienced by five strains of layer breeders on measures of stress and fear in their offspring

Stressors experienced by layer breeders during egg production can lead to changes in the egg hormone content, potentially impacting their offspring, the commercial layers. Genetic differences might also affect the offspring's susceptibility to maternal experiences. In this study, we tested if maternal stress affects measures of stress and fear in five strains of layer breeders: commercial brown 1 & 2, commercial white 1 & 2 and a pure line White Leghorn. Each strain was equally separated into two groups: “Maternal Stress” (MS), where hens were subjected to a series of 8 consecutive days of acute psychological stressors, and “Control,” which received routine husbandry. Additional eggs from Control were injected either with corticosterone diluted in a vehicle solution (“CORT”) or just “Vehicle.” Stress- and fear-responses of the offspring were measured in a plasma corticosterone test and a combined human approach and novel object test. While the stress treatments did not affect the measured endpoints in the offspring, significant strain differences were found. The offspring of the white strains showed a higher physiological response compared to brown strains and the White 2 offspring was the least fearful strain in the human approach test. Our study found that neither the acute psychological stressors experienced by layer breeders nor the egg injections of corticosterone affected the parameters tested in their offspring. Post hoc power analyses suggest that the lack of treatment effects might be due to a small sample size (type II error). Although studies on larger flocks of layers are still needed, our results provide an initial understanding of an important subject, as in poultry production, layer breeders are often subjected to short-term stressors. In addition, our results suggest the dissociation between the physiological and behavioural parameters of stress response in laying hens, showing that increased concentrations of plasma corticosterone in response to stress might not be directly associated with high levels of fear.

Infrared Thermography Reveals Sex-Specific Responses to Stress in Mice.

Psychogenic hyperthermia is a stress-related condition reported mostly in women. Neuroendocrine responses to stress in females differ from those in males, and these differences cannot be explained solely based on hypothalamic-pituitary-adrenal (HPA) axis activity. Here, we used infrared (IR) thermographic imaging to record changes in cutaneous temperature following two types of stressful experiences in female and male mice. Mice were exposed to either single-session restraint stress or vertical exploration (rearing) deprivation and were monitored for exploratory activity and IR surface thermal changes. Females displayed higher rearing activity than males during the dark phase of the light cycle. Both sexes showed similar plasma corticosterone (CORT) responses after a challenge with restraint and rearing deprivation. However, only females responded to rearing deprivation with increased cutaneous temperature in the head and back, and a reduced thermal response in the tail. Circulating CORT levels were not correlated with the thermal variations. These findings, for the first time, provide evidence for sex-specific cutaneous thermal responses to short-term stress in mice following transient vertical-activity deprivation that may mimic clinical psychogenic hyperthermia.

Antidepressants of different classes cause distinct behavioral and brain pro- and anti-inflammatory changes in mice submitted to an inflammatory model of depression

BackgroundDepressed patients present increased plasma levels of lipopolysaccharide (LPS) and neuroinflammatory alterations. Here, we determined the neuroimmune effects of different classes of ADs by using the LPS inflammatory model of depression. MethodsMale rats received amitriptyline (AMI) a tricyclic, S-citalopram (ESC) a selective serotonin reuptake inhibitor, tranylcypromine (TCP) a monoamine oxidase inhibitor, vortioxetine (VORT) a multimodal AD or saline for ten days. One-hour after the last AD administration, rats were exposed to LPS 0.83 mg/kg or saline and 24 h later were tested for depressive-like behavior. Plasma corticosterone, brain levels of nitrite, pro- and anti-inflammatory cytokines, phospho-cAMP Response Element-Binding Protein (CREB) and nuclear factor (NF)-kB p 65 were determined. ResultsLPS induced despair-like, impaired motivation/self-care behavior and caused anhedonia. All ADs prevented LPS-induced despair-like behavior, but only VORT rescued impaired self-care behavior. All ADs prevented LPS-induced increase in brain pro-inflammatory cytokines [interleukin (IL)-1β and IL-6] and T-helper 1 cytokines [tumor necrosis factor (TNF)-α and interferon-γ]. VORT increased striatal and hypothalamic IL-4 levels. All ADs prevented LPS-induced neuroendocrine alterations represented by increased levels of hypothalamic nitrite and plasma corticosterone response. VORT and ESC prevented LPS-induced increase in NF-kBp65 hippocampal expression, while ESC, TCP and VORT, but not IMI, prevented the alterations in phospho-CREB expression. LimitationsLPS model helps to understand depression in a subset of depressed patients with immune activation. The levels of neurotransmitters were not determined. ConclusionThis study provides new evidence for the immunomodulatory effects of ADs, and shows a possible superior anti-inflammatory profile of TCP and VORT.

Coping with extremes: Remarkably blunt adrenocortical responses to acute stress in two sympatric snow finches on the Qinghai-Tibet Plateau during winter relative to other seasons

The extreme climatic conditions (ECCs) of the Qinghai-Tibet Plateau impose strong selective pressures on the evolution of phenotypic traits in free-living animals. It is not well understood how animals on the Qinghai-Tibet Plateau modify their adrenocortical functions in response to both predictable and unpredictable events of ECCs, especially when the available resources are lowest during the wintering life-history stage. To uncover potential physiological mechanisms, we studied the life history stage dependent features of morphology, the plasma corticosterone response to acute stress and brain glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) mRNA expression in two sympatric snow finches: the white-rumped snow finch (Onychostruthus taczanowskii, WRSF); and the rufous-necked snow finch, Pyrgilauda ruficollis, RNSF) in Qinghai Province, China. Our results showed that (a) baseline corticosterone and stressor-induced corticosterone levels significantly varied with life history stage, but not between the species; (b) in WRSF, GR mRNA expression in the paraventricular nucleus was higher in the wintering stage compared to the pre-basic molt stage. There were no differences in hippocampus MR mRNA expression between stages in either species; (c) in the wintering stage, the suppression of corticosterone secretion in both species was an unexpected strategy in free-living animals. Both convergent and divergent phenotypic traits of adrenocortical responses to acute stress in two sympatric snow finches contribute to our understanding of the coping mechanisms of closely related species in the severe winter on the Qinghai-Tibet Plateau.

Frequent range visits further from the shed relate positively to free-range broiler chicken welfare

Little is known about the implications of accessing an outdoor range for broiler chicken welfare, particularly in relation to the distance ranged from the shed. Therefore, we monitored individual ranging behaviour of commercial free-range broiler chickens and identified relationships with welfare indicators. The individual ranging behaviour of 305 mixed-sex Ross 308 broiler chickens was tracked on a commercial farm from the second day of range access to slaughter age (from 16 to 42 days of age) by radio frequency identification (RFID) technology. The radio frequency identification antennas were placed at pop-holes and on the range at 2.7 and 11.2 m from the home shed to determine the total number of range visits and the distance ranged from the shed. Chickens were categorised into close-ranging (CR) or distant-ranging (DR) categories based on the frequency of visits less than or greater than 2.7 m from the home shed, respectively. Half of the tracked chickens (n=153) were weighed at 7 days of age, and from 14 days of age their body weight, foot pad dermatitis (FPD), hock burn (HB) and gait scores were assessed weekly. The remaining tracked chickens (n=152) were assessed for fear and stress responses before (12 days of age) and after range access was provided (45 days of age) by quantifying their plasma corticosterone response to capture and 12 min confinement in a transport crate followed by behavioural fear responses to a tonic immobility (TI) test. Distant-ranging chickens could be predicted based on lighter BW at 7 and 14 days of age (P=0.05), that is before range access was first provided. After range access was provided, DR chickens weighed less every week (P=0.001), had better gait scores (P=0.01) and reduced corticosterone response to handling and confinement (P<0.05) compared to CR chickens. Longer and more frequent range visits were correlated with the number of visits further from the shed (P<0.01); hence distant ranging was correlated with the amount of range access, and consequently the relationships between ranging frequency, duration and distance were strong. These relationships indicate that longer, more frequent and greater ranging from the home shed was associated with improved welfare. Further research is required to identify whether these relationships between ranging behaviour and welfare are causal.

Interactions Between Gut Microbiota and Acute Restraint Stress in Peripheral Structures of the Hypothalamic-Pituitary-Adrenal Axis and the Intestine of Male Mice.

The gut microbiota play an important role in shaping brain functions and behavior, including the activity of the hypothalamus-pituitary-adrenocortical (HPA) axis. However, little is known about the effect of the microbiota on the distinct structures (hypothalamus, pituitary, and adrenals) of the HPA axis. In the present study, we analyzed the influence of the microbiota on acute restraint stress (ARS) response in the pituitary, adrenal gland, and intestine, an organ of extra-adrenal glucocorticoid synthesis. Using specific pathogen-free (SPF) and germ-free (GF) male BALB/c mice, we showed that the plasma corticosterone response to ARS was higher in GF than in SPF mice. In the pituitary, stress downregulated the expression of the gene encoding CRH receptor type 1 (Crhr1), upregulated the expression of the Fkbp5 gene regulating glucocorticoid receptor sensitivity and did not affect the expression of the proopiomelanocortin (Pomc) and glucocorticoid receptor (Gr) genes. In contrast, the microbiota downregulated the expression of pituitary Pomc and Crhr1 but had no effect on Fkbp5 and Gr. In the adrenals, the steroidogenic pathway was strongly stimulated by ARS at the level of the steroidogenic transcriptional regulator Sf-1, cholesterol transporter Star and Cyp11a1, the first enzyme of steroidogenic pathway. In contrast, the effect of the microbiota was significantly detected at the level of genes encoding steroidogenic enzymes but not at the level of Sf-1 and Star. Unlike adrenal Sf-1, the expression of the gene Lrh-1, which encodes the crucial transcriptional regulator of intestinal steroidogenesis, was modulated by the microbiota and ARS and this effect differed between the ileum and colon. The findings demonstrate that gut microbiota have an impact on the response of the pituitary, adrenals and intestine to ARS and that the interaction between stress and the microbiota during activation of glucocorticoid steroidogenesis differs between organs. The results suggest that downregulated expression of pituitary Pomc and Crhr1 in SPF animals might be an important factor in the exaggerated HPA response of GF mice to stress.

Effects of oxytocin receptor antagonism on social function and corticosterone release after adolescent social instability in male rats

Oxytocin influences social behaviour and hypothalamic-pituitary-adrenal (HPA) function. We previously found that social instability stress (SS) from postnatal day 30 to 45 increased oxytocin receptor (OTR) densities in the lateral septum and nucleus accumbens of adolescent male rats. Here, we investigated social behaviour and HPA function in adolescent male SS rats compared with age- and sex-matched controls after intraperitoneal treatment with an OTR antagonist L-368,899 (OTR-A). Regardless of OTR antagonism, adolescent SS rats spent more time in social approach (investigation through wire mesh) but less time in social interaction (physical interaction) with unfamiliar same-sex and same-age peers than did controls. However, OTR-A-treatment caused SS rats to be more socially avoidant than OTR-A-treated controls and saline-treated rats of the same condition. Additionally, the predicted rise in plasma corticosterone in response to OTR-A treatment was blunted in SS rats. Fos immunoreactivity (IR) was used as a marker of neural activation in social brain regions and oxytocin-IR was examined in the paraventricular nucleus of the hypothalamus (PVN) in response to interacting with unfamiliar peers in SS and control rats after OTR-A treatment. OTR-A treatment had little effect on Fos-IR and oxytocin-IR in the analyzed brain regions, but SS rats had lower Fos-IR and oxytocin-IR in the PVN and greater Fos-IR in subregions of the prefrontal cortex, and hippocampus, and lateral septum than did controls. Finally, binding density of OTR was measured in the PVN and hippocampus, and greater OTR binding density was found in the PVN of SS rats. Together, these data demonstrate a greater influence of OTR antagonism on social behaviour and a reduced influence of OTR antagonism on HPA responses after adolescent SS in male rats. The results also suggest that differences in neural functioning in the prefrontal cortex, hippocampus and lateral septum of adolescent SS rats may be involved in their altered social behaviour relative to that of controls.

A Long-Acting Neutralizing Monoclonal ACTH Antibody Blocks Corticosterone and Adrenal Gene Responses in Neonatal Rats.

The control of steroidogenesis in the neonatal adrenal gland is of great clinical interest. We have previously demonstrated that the postnatal day (PD) 2 rat exhibits a large plasma corticosterone response to hypoxia in the absence of an increase in plasma ACTH measured by RIA, whereas the corticosterone response to exogenous ACTH is intact. By PD8, the corticosterone response to hypoxia is clearly ACTH-dependent. We hypothesized that this apparently ACTH-independent response to hypoxia in the newborn rat is due to an increase in a bioactive, nonimmunoassayable form of ACTH. To evaluate this phenomenon, we pretreated neonatal rats with a novel, specific, neutralizing anti-ACTH antibody (ALD1611) (20 mg/kg or 1 mg/kg IP) on the morning of PD1, PD7, and PD14. Twenty-four hours later, we measured hypoxia- or ACTH-stimulated plasma ACTH and corticosterone. For long-term effects, ALD1611 was given on PD1 and pups were studied on PD8 and PD15. Pretreatment with ALD1611 significantly decreased baseline corticosterone and completely blocked the corticosterone response to hypoxia and exogenous ACTH stimulation at all ages. The effect of 1 mg/kg ALD1611 on PD1 had dissipated by PD15. The decrease in corticosterone in ALD1611-treated pups was associated with decreases in baseline and hypoxia- and ACTH-stimulated adrenal Ldlr, Mrap, and Star mRNA expression at all ages. The adrenal response to hypoxia in the newborn rat is ACTH-dependent, suggesting the release of nonimmunoassayable, biologically active forms of ACTH. ALD1611 is useful as a tool to attenuate stress-induced, ACTH-dependent adrenal steroidogenesis in vivo.

Genetic Factors Mediate the Impact of Chronic Stress and Subsequent Response to Novel Acute Stress.

Individual differences in physiological and biobehavioral adaptation to chronic stress are important predictors of health and fitness; genetic differences play an important role in this adaptation. To identify these differences we measured the biometric, neuroendocrine, and transcriptional response to stress among inbred mouse strains with varying degrees of genetic similarity, C57BL/6J (B), C57BL/6NJ (N), and DBA/2J (D). The B and D strains are highly genetically diverse whereas the B and N substrains are highly similar. Strain differences in hypothalamic-pituitary-adrenal (HPA) axis cross-sensitization were determined by plasma corticosterone (CORT) levels and hippocampal gene expression following 7-weeks of chronic mild stress (CMS) or normal housing (NH) and subsequent exposure to novel acute restraint. Fecal CORT metabolites and body and organ weights were also measured. All strains exposed to CMS had reduced heart weights, whereas body weight gain was attenuated only in B and N strains. Acute stress alone produced larger plasma CORT responses in the D and N strains compared to the B strain. CMS paired with acute stress produced cross-sensitization of the CORT response in the N strain. The N strain also had the largest number of hippocampal transcripts with up-regulated expression in response to stress. In contrast, the D strain had the largest number of transcripts with down-regulated expression following CMS and acute stress. In summary, we observed differential responses to CMS at both the physiological and molecular level among genetically diverse strains, indicating that genetic factors drive individual differences in experience-dependent regulation of the stress response.

Sustained corticosterone rise in the prefrontal cortex is a key factor for chronic stress-induced working memory deficits in mice

Exposure to prolonged, unpredictable stress leads to glucocorticoids-mediated long-lasting neuroendocrine abnormalities associated with emotional and cognitive impairments. Excessive levels of serum glucocorticoids (cortisol in humans, corticosterone in rodents) contribute notably to deficits in working memory (WM), a task which heavily relies on functional interactions between the medial prefrontal cortex (PFC) and the dorsal hippocampus (dHPC). However, it is unknown whether stress-induced increases in plasma corticosterone mirror corticosterone levels in specific brain regions critical for WM. After a 6 week-UCMS exposure, C57BL/6 J male mice exhibited increased anxiety- and depressive-like behaviors when measured one week later and displayed WM impairments timely associated with increased plasma corticosterone response. In chronically stressed mice, basal phosphorylated/activated CREB (pCREB) was markedly increased in the PFC and the CA1 area of the dHPC and WM testing did not elicit any further increase in pCREB in the two regions. Using microdialysis samples from freely-moving mice, we found that WM testing co-occurred with a rapid and sustained increase in corticosterone response in the PFC while there was a late, non-significant rise of corticosterone in the dHPC. The results also show that non-stressed mice injected with corticosterone (2 mg/kg i.p.) before WM testing displayed behavioral and molecular alterations similar to those observed in stressed animals while a pre-WM testing metyrapone injection (35 mg/kg i.p.), a corticosterone synthesis inhibitor, prevented the effects of UCMS exposure. Overall, the abnormal regional increase of corticosterone concentrations mainly in the PFC emerges as a key factor of enduring WM dysfunctions in UCMS-treated animals.

Chronic adolescent stress sex-specifically alters central and peripheral neuro-immune reactivity in rats

Adversity during development is a reliable predictor of psychiatric disorders such as depression and anxiety which are increasingly recognized to have an immune component. We have previously demonstrated that chronic adolescent stress (CAS) in rats leads to depressive-like behavior in adulthood along with long-lasting changes to the hypothalamic-pituitary-adrenal axis and pro-inflammatory cytokine induction in the hippocampus. However, the mechanisms by which CAS promotes hippocampal inflammation are not yet defined. Here we tested the hypothesis that a history of CAS exaggerates induction of the pro-inflammatory NFκB pathway in the adult rat hippocampus without compromising the peripheral immune response. We also assessed potential sex differences because it is unclear whether females, who are twice as likely to suffer from mood disorders as males, are disproportionally affected by stress-primed inflammation. Male and female adolescent rats underwent a CAS paradigm or received no stress. Six weeks following the last stressor, all rats received a single systemic injection of either lipopolysaccharide or vehicle to unmask possible immune-priming effects of CAS. An NFκB signaling PCR array demonstrated that CAS exaggerated the expression of NFκB-related genes in the hippocampus of both males and females. Interestingly, targeted qPCR demonstrated that CAS potentiated the induction of hippocampal IL1B and REL mRNA in female rats only, suggesting that some immune effects of CAS are indeed sex-specific. In contrast to the hippocampal findings, indices of peripheral inflammation such as NFκB activity in the spleen, plasma IL-1β, IL-6, TNF-α, and corticosterone were not impacted by CAS in female rats. Despite showing no pro-inflammatory changes to hippocampal mRNA, male CAS rats displayed lower plasma corticosterone response to LPS at 2 h after injection followed by an exaggerated plasma IL-1β response at 4 h. This potentially blunted corticosterone response coupled with excessive innate immune signaling in the periphery is consistent with possible glucocorticoid resistance in males. In contrast, the effects of CAS manifested as excessive hippocampal immune reactivity in females. We conclude that while a history of exposure to chronic adolescent stress enhances adult immune reactivity in both males and females, the mechanism and manifestation of such alterations are sex-specific.