Corticosterone differentially modulates expression of corticotropin releasing factor and arginine vasopressin mRNA in the hypothalamic paraventricular nucleus following either acute or repeated restraint stress

Molecular Derangements and the Diagnosis of ACTH-Dependent Cushing's Syndrome

Endogenous Cushing's syndrome (CS) is associated with morbidities (diabetes, hypertension, clotting disorders) and shortens life because of infections, pulmonary thromboembolism, and cardiovascular disease. Its clinical presentation is immensely variable, and diagnosis and treatment are often delayed. Thus, there are many opportunities for basic and clinical research leading to better tests, faster diagnosis, and optimized medical treatments. This review focuses on CS caused by excessive adrenocorticotropin (ACTH) production. It describes current concepts of the regulation of ACTH synthesis and secretion by normal corticotropes and mechanisms by which dysregulation occurs in corticotrope (termed "Cushing's disease") and noncorticotrope (so-called ectopic) ACTH-producing tumors. ACTH causes adrenal gland synthesis and pulsatile release of cortisol; the excess ACTH in these forms of CS leads to the hypercortisolism of endogenous CS. Again, the differences between healthy individuals and those with CS are highlighted. The clinical presentations and their use in the interpretation of CS screening tests are described. The tests used for screening and differential diagnosis of CS are presented, along with their relationship to cortisol dynamics, pathophysiology, and negative glucocorticoid feedback regulation in the two forms of ACTH-dependent CS. Finally, several gaps in current understanding are highlighted in the hope of stimulating additional research into this challenging disorder.

Stressed rats fail to exhibit avoidance reactions to innately aversive social calls

Disruptions in amygdalar function, a brain area involved in encoding emotionally salient information, has been implicated in stress-related affective disorders. Earlier animal studies on the behavioral consequences of stress-induced abnormalities in the amygdala focused on learned behaviors using fear conditioning paradigms. If and how stress affects unconditioned, innate fear responses to ethologically natural aversive stimuli remains unexplored. Hence, we subjected rats to aversive ultrasonic vocalization calls emitted on one end of a linear track. Unstressed control rats exhibited a robust avoidance response by spending more time away from the source of the playback calls. Unexpectedly, prior exposure to chronic immobilization stress prevented this avoidance reaction, rather than enhancing it. Further, this stress-induced impairment extended to other innately aversive stimuli, such as white noise and electric shock in an inhibitory avoidance task. However, conditioned fear responses were enhanced by the same stress. Inactivation of the basolateral amygdala (BLA) in control rats prevented this avoidance reaction evoked by the playback. Consistent with this, analysis of the immediate early gene cFos revealed higher activity in the BLA of control, but not stressed rats, after exposure to the playback. Further, in vivo recordings in freely behaving control rats exposed to playback showed enhanced theta activity in the BLA, which also was absent in stressed rats. These findings offer a new framework for studying stress-induced alterations in amygdala-dependent maladaptive responses to more naturally threatening and emotionally relevant social stimuli. The divergent impact of stress on defensive responses--impaired avoidance responses together with increased conditioned fear--also has important implications for models of learned helplessness and depression.

Neuroendocrine Regulation of Plasma Cortisol Levels During Smoltification and Seawater Acclimation of Atlantic Salmon

Diadromous fishes undergo dramatic changes in osmoregulatory capacity in preparation for migration between freshwater and seawater. One of the primary hormones involved in coordinating these changes is the glucocorticoid hormone, cortisol. In Atlantic salmon (Salmo salar), cortisol levels increase during the spring smoltification period prior to seawater migration; however, the neuroendocrine factors responsible for regulating the hypothalamic-pituitary-interrenal (HPI) axis and plasma cortisol levels during smoltification remain unclear. Therefore, we evaluated seasonal changes in circulating levels of cortisol and its primary secretagogue-adrenocorticotropic hormone (ACTH)-as well as transcript abundance of the major regulators of HPI axis activity in the preoptic area, hypothalamus, and pituitary between migratory smolts and pre-migratory parr. Smolts exhibited higher plasma cortisol levels compared to parr across all timepoints but circulating ACTH levels were only elevated in May. Transcript abundance of preoptic area corticotropin-releasing factor b1 and arginine vasotocin were ~2-fold higher in smolts compared to parr in February through May. Smolts also had ~7-fold greater hypothalamic transcript abundance of urotensin 1 (uts-1a) compared to parr in May through July. When transferred to seawater during peak smolting in May smolts rapidly upregulated hypothalamic uts-1a transcript levels within 24 h, while parr only transiently upregulated uts-1a 96 h post-transfer. In situ hybridization revealed that uts-1a is highly abundant in the lateral tuberal nucleus (NLT) of the hypothalamus, consistent with a role in regulating the HPI axis. Overall, our results highlight the complex, multifactorial regulation of cortisol and provide novel insight into the neuroendocrine mechanisms controlling osmoregulation in teleosts.

Amygdala Arginine Vasopressin Modulates Chronic Ethanol Withdrawal Anxiety-Like Behavior in the Social Interaction Task

BACKGROUND

Chronic ethanol (EtOH) exposure induces neurobehavioral maladaptations in the brain though the precise changes have not been fully explored. The central nucleus of the amygdala (CEA) regulates anxiety-like behavior induced by withdrawal from chronic intermittent EtOH (CIE) exposure, and the arginine vasopressin (AVP) system within the CEA regulates many anxiety-like behaviors. Thus, adaptations occur in the CEA AVP system due to chronic EtOH exposure, which lead to anxiety-like behaviors in rats.

METHODS

Chronic exposure to a low-dose EtOH (4.5% wt/vol) induces anxiety-like behavior in rats. Wistar or Sprague Dawley rats were exposed to a modified CIE or CIE, while intra-CEA microinjections of AVP or a V1b receptor antagonist were used to elicit or block withdrawal-induced anxiety. Additionally, AVP microinjections into the CEA were given 24 hours following 15 days of continuous high-dose EtOH (7% wt/vol), a time period when rats no longer express anxiety. Chemogenetics was also used to activate the basolateral amygdala (BLA) or deactivate the dorsal periaqueductal gray=(dm/dlPAG) therefore PAG=periaqueductal gray to elicit or block withdrawal-induced anxiety.

RESULTS

AVP microinjected into the CEA in lieu of exposure to the first 2 cycles of CIE was sufficient to induce anxiety-like behavior in these commonly used rat strains. The V1b receptor antagonist, but not an oxytocin receptor agonist, into the CEA during the first 2 withdrawal cycles suppressed anxiety. However, activation of the BLA in lieu of exposure to the first 2 cycles of CIE was insufficient to induce anxiety-like behavior. AVP microinjection into the CEA 24 hours into withdrawal reelicited anxiety-like behavior, and deactivation of the dm/dlPAG reduced this effect of CEA AVP.

CONCLUSIONS

Taken together, this study demonstrates a role of CEA AVP and a CEA-dm/dlPAG circuit in the development of anxiety induced by CIE. Such information is valuable for identifying novel therapeutic targets for alcohol- and anxiety-associated disorders.

Chronic variable stress alters hypothalamic-pituitary-adrenal axis function in the female mouse

Chronic stress is often associated with a dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which can greatly increase risk for a number of stress-related diseases, including neuropsychiatric disorders. Despite a striking sex-bias in the prevalence of many of these disorders, few preclinical studies have examined female subjects. Hence, the present study aimed to explore the effects of chronic stress on the basal and acute stress-induced activity of the HPA axis in the female C57BL/6 mouse. We used a chronic variable stress (CVS) paradigm in these studies, which successfully induces physiological and behavioral changes that are similar to those reported for some patients with mood disorders. Using this model, we found pronounced, time-dependent effects of chronic stress on the HPA axis. CVS-treated females exhibited adrenal hypertrophy, yet their pattern of glucocorticoid secretion in the morning resembled that of controls. CVS-treated and control females had similar morning basal corticosterone (CORT) levels, which were both significantly elevated following a restraint stressor. Although morning basal gene expression of the key HPA-controlling neuropeptides corticotropin releasing hormone (CRH), arginine vasopressin (AVP) and oxytocin (OT) was unaltered within the paraventricular nucleus (PVN) by CVS, CVS altered the PVN OT and AVP mRNA responses to acute restraint. In control females, acute stress decreased AVP, but not OT mRNA; whereas, in CVS females, it decreased OT, but not, AVP mRNA. Unlike the morning pattern of HPA activity, in the evening, CVS-treated females showed increased basal CORT with hypoactive responses of CORT and PVN c-Fos immunoreactivity to restraint stress. Furthermore, CVS elevated evening PVN CRH and OT mRNAs in the PVN, but it did not influence anxiety- or depressive-like behavior after a light/dark box or tail suspension test. Taken together, these findings indicate that CVS is an effective model for HPA axis dysregulation in the female mouse and may be relevant for stress-related diseases.

Vasopressin and alcohol: a multifaceted relationship

BACKGROUND

Arginine vasopressin (VP) has been implicated in a number of neuropsychiatric disorders with an emphasis on situations where stress increased the severity of the disorder. Based on this hypothesized role for VP in neuropsychiatric disorders, much research is currently being undertaken in humans and animals to test VP as a target for treatment of a number of these disorders including alcohol abuse.

OBJECTIVES

To provide a summary of the literature regarding the role of VP in alcohol- and stress-related behaviors including the use of drugs that target VP in clinical trials.

RESULTS

Changes in various components of the VP system occur with alcohol and stress. Manipulating VP or its receptors can alter alcohol- and stress-related behaviors including tolerance to alcohol, alcohol drinking, and anxiety-like behavior. Finally, the hypothalamic-pituitary-adrenal axis response to alcohol is also altered by manipulating the VP system. However, clinical trials of VP antagonists have had mixed results.

CONCLUSIONS

A review of VP's involvement in alcohol's actions demonstrates that there is much to be learned about brain regions involved in VP-mediated effects on behavior. Thus, future work should focus on elucidating relevant brain regions. By using previous knowledge of the actions of VP and determining the brain regions and/or systems involved in its different behavioral effects, it may be possible to identify a specific receptor subtype target, drug treatment combination, or specific clinical contexts that may point toward a more successful treatment.

Stress axis regulation during social ascension in a group-living cichlid fish

Animals living in groups often form social hierarchies, with characteristic behaviours and physiologies associated with rank. However, when social opportunities arise and a subordinate ascends into a dominant position, quick adjustments are necessary to secure this position. Such periods of social transition are typically associated with elevated glucocorticoid production, but the precise regulation of the stress axis during these occasions is not well understood. Using the group-living cichlid, Neolamprologus pulcher, the effects of social ascension on the stress axis were assessed. Ascenders rapidly filled experimentally created vacancies, adopting a dominant behavioural phenotype within 72 h-elevating aggression, activity, and workload, while receiving high rates of affiliative behaviours from their group members. Despite assuming behavioural dominance within their groups, ascenders displayed higher cortisol levels than dominants three days post-ascension. Additionally, compared to subordinates, ascenders had increased transcript abundance of steroidogenic acute regulatory protein (star) and cytochrome p450 side-chain cleavage enzyme (p450scc) in the head kidney, indicating activation of the stress axis. Cortisol levels were lowest in ascenders that displayed low rates of aggression, potentially reflecting the reestablishment of social stability in these groups. Increased transcript abundance of both glucocorticoid receptors (gr1 and gr2) in the brain's preoptic area (POA) of ascenders compared to dominants suggested an enhanced capacity for cortisol regulation via negative feedback. Our results reveal a regulatory cascade of behavioural and physiological interactions and highlight the importance of investigating the underlying mechanisms regulating the stress axis.

Expression of stress hormones AVP and CRH in the hypothalamus of Mus musculus following water and food deprivation

Neurohypophyseal hormone, arginine vasopressin (AVP), in addition to acting as antidiuretic hormone is also considered to be stress hormone like hypothalamic corticotropin-releasing hormone (CRH). Present study was designed to investigate the relative response of these stress hormones during water and food deprivation. In this study, male laboratory mice of Swiss strain were divided in 5 groups, control - provided water and food ad libitum, two experimental groups water deprived for 2 and 4days respectively (WD2 and WD4) and another two groups food deprived for 2 and 4days respectively (FD2 and FD4). Results indicate an increased expression of AVP mRNA as well as peptide in the hypothalamus of WD2 mice and the expression was further upregulated after 4days of water deprivation but the expression of CRH remained unchanged compare to their respective controls. On the other hand no change was observed in the expression of hypothalamic AVP mRNA while AVP peptide increased significantly in FD2 and FD4 mice compare to control. Further, the expression of CRH mRNA although increased in hypothalamus of both FD2 and FD4 mice, the immunofluorescent staining shows decreased expression of CRH in PVN of food deprived mice. Based on these findings it is concluded that since during osmotic stress only AVP expression is upregulated but during metabolic stress i.e. food deprivation transcription and translation of both the stress hormones are differentially regulated. Further, it is suggested that role of AVP and CRH may be stress specific.

Testing the critical window of estradiol replacement on gene expression of vasopressin, oxytocin, and their receptors, in the hypothalamus of aging female rats

The current study tested the "critical window" hypothesis of menopause that postulates that the timing and duration of hormone treatment determine their potential outcomes. Our focus was genes in the rat hypothalamus involved in social and affiliative behaviors that change with aging and/or estradiol (E2): Avp, Avpr1a, Oxt, Oxtr, and Esr2 in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Rats were reproductively mature or aging adults, ovariectomized, given E2 or vehicle treatment of different durations, with or without a post-ovariectomy delay. Our hypothesis was that age-related changes in gene expression are mitigated by E2 treatments. Contrary to this, PVN Oxtr increased with E2, and Avpr1a increased with age. In the SON, Avpr1a increased with age, Oxtr with age and timing, and Avp was altered by duration. Thus, chronological age and E2 have independent actions on gene expression, with the "critical window" hypothesis supported by the observed timing and duration effects.

Ancestral experience as a game changer in stress vulnerability and disease outcomes

Stress is one of the most powerful experiences to influence health and disease. Through epigenetic mechanisms, stress may generate a footprint that propagates to subsequent generations. Programming by prenatal stress or adverse experience in parents, grandparents, or earlier generations may thus be a critical determinant of lifetime health trajectories. Changes in regulation of microRNAs (miRNAs) by stress may enhance the vulnerability to certain pathogenic factors. This review explores the hypothesis that miRNAs represent stress-responsive elements in epigenetic regulation that are potentially heritable. Recent findings suggest that miRNAs are key players linking adverse early environments or ancestral stress with disease risk, thus they represent useful predictive disease biomarkers. Since miRNA signatures of disease are potentially heritable, big data management platforms will be vital to harness multi-generational information and capture succinct yet potent biomarkers capable of directing preventative treatments. This feature would offer a unique window of opportunity to advance personalized medicine.

Estradiol regulates effects of hindbrain activator 5-aminoimidazole-4-carboxamide-riboside administration on hypothalamic adenosine 5'-monophosphate-activated protein kinase activity and metabolic neurotransmitter mRNA and protein expression

Hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) activation alters hypothalamic neuronal genomic activity in an estradiol (E)-dependent manner. This study examines the premise that E regulates metabolic effector neuron reactivity to hindbrain AMPK. Paraventricular (PVH), arcuate (ARH), and ventromedial (VMH) nuclei were micropunched from brains of E- or oil (O)-implanted ovariectomized female rats that had been injected, into the fourth ventricle, with the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR; A) or saline (S) and analyzed by quantitative polymerase chain reaction and Western blotting for neurotransmitter mRNA and protein expression. PVH corticotrophin-releasing hormone gene and protein profiles were decreased in O/A and E/A animals. ARH pro-opiomelanocortin (POMC) mRNA and protein were both elevated in O/A but were diminished or unchanged, respectively, in E/A animals; ARH neuropeptide Y (NPY) transcription was inhibited in O/A and E/A animals, but neuropeptide content was augmented in E/A only. VMH SF-1 mRNA and protein were reduced in O and E animals. AICAR did not alter AMPK protein in any structure but elevated PVH (↑E), did not alter ARH, and decreased VMH (↓O,↓E) pAMPK. Results demonstrate hypothalamic metabolic neurotransmitter and AMPK reactivity to hindbrain AMPK activation, including E-dependent adjustments in POMC and NPY transcription and protein expression. Dissimilar POMC (↑O vs. ↔E) and NPY (↓O vs. ↑E) neuropeptide responses to caudal fourth ventricle AICAR indicate E regulation of hindbrain AMPK signaling and/or target receptivity, implying that ARH-controlled metabolic responses may differ in the presence vs. absence of E. Evidence for variable changes in hypothalamic AMPK activity resulting from hindbrain sensor manipulation suggests that individual (or region-based groups of) AMPK-expressing neuron populations are uniquely impacted by hindbrain AMPK.

Chronic unpredictable stress and long-term ovariectomy affect arginine-vasopressin expression in the paraventricular nucleus of adult female mice

Arginine-Vasopressin (AVP) may regulate the hypothalamic-pituitary-adrenal axis (HPA) and its effects on depressive responses. In a recent study, we demonstrated that Chronic Unpredictable Stress (CUS) depressive effects are enhanced by long-term ovariectomy (a model of post-menopause). In the present study, we investigated the effects of long-term ovariectomy and CUS on AVP expression in different subdivision of the paraventricular nucleus (PVN) of female mice. Both long-term ovariectomy and CUS affect AVP immunoreactivity in some of the PVN subnuclei of adult female mice. In particular, significant changes on AVP immunoreactivity were observed in magnocellular subdivisions, the paraventricular lateral magnocellular (PaLM) and the paraventricular medial magnocellular (PaMM), the 2 subnuclei projecting to the neurohypophysis for the hormonal regulation of body homeostasis. AVP immunoreactivity was decreased in the PaLM by both the long-term deprivation of ovarian hormones and the CUS. In contrast, AVP immunoreactivity was increased in the PaMM by CUS, whereas it was decreased by ovariectomy. Therefore, present results suggest morphological and functional differences among the PVN's subnuclei and complex interactions among CUS, gonadal hormones and AVP immunoreactivity.

Regulation of gene expression of vasotocin and corticotropin-releasing hormone receptors in the avian anterior pituitary by corticosterone

The effect of chronic stress (CS) on gene expression of the chicken arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) receptors [VT2R, VT4R, CRH-R1, and CRH-R2] was examined by measuring receptor mRNA levels in the anterior pituitary gland of the chicken after chronic immobilization stress compared to acute stress (AS). Radioimmunoassay results showed that blood circulating corticosterone (CORT) levels in the CS group were significantly decreased compared to that of birds in the AS group (P<0.05). The VT2R and CRH-R2 mRNA in CS birds were significantly decreased to that of controls. The VT4R mRNA was significantly decreased compared to controls in AC birds and was further decreased in the CS group compared to controls (P<0.05). The CRH-R1 mRNA was significantly decreased in the AS birds compared to controls. However, there was no significant difference of CRH-R1 mRNA between acute stress and chronic stress birds. Using primary anterior pituitary cell cultures, the effect of exogenous CORT on VT/CRH receptor gene expression was examined. Receptor mRNA levels were measured after treatment of CORT followed by AVT/CRH administration. The CORT pretreatment resulted in a dose-dependent decrease of proopiomelanocortin heteronuclear RNA, a molecular marker of a stress-induced anterior pituitary. Without CORT pretreatment of anterior pituitary cell cultures, the VT2R, VT4R and CRH-R1mRNA levels were significantly increased within 15 min and then decreased at 1 h and 6 h by AVT/CRH administration (P<0.05). Pretreatment of CORT in anterior pituitary cells induced a dose-dependent increase of VT2R, VT4R and CRH-R2 mRNA levels, and a significant decrease of CRH-R1 mRNA levels at only the high dose (10 ng/ml) of CORT (P<0.05).Taken together, results suggest a modulatory role of CORT on the regulation of VT/CRH receptor gene expression in the avian anterior pituitary gland dependent upon CORT levels.

Corticotropin releasing factor in neuroplasticity

Stress is among the strongest signals promoting neuroplasticity: Stress signals, indicating real or perceived danger, lead to alterations of neuronal function and often structure, designed to adapt to the changed conditions and promote survival. Corticotropin releasing factor (CRF) is expressed and released in several types of neuronal populations that are involved in cognition, emotion and the regulation of autonomic and endocrine function. CRF expressing neurons undergo functional and structural plasticity during stress and, in addition, the peptide acts via specific receptors to promote plasticity of target neurons.

Effect of various physical stress models on serum cortisol level in wistar rats

BACKGROUND

Stress indicates the response or reaction of an organism to the environmental circumstances and their outcomes. Acute stress is well known to trigger several hormonal alterations in animals. An increase in glucocorticoid concentration can represent intensity of discomfort or distress experienced by an animal. The study was undertaken to evaluate the effects of various physical stress models on serum cortisol level in Wistar male rats.

METHODOLOGY

In this study six Wistar male rats weighing 150-200 gm were randomly selected. Animals were exposed to 'forced swim test' and 'restraint test'. Their serum cortisol level was measured by ELISA test using alpha prime ELISA system before and after the tests respectively.

RESULTS

RESULTS were analyzed by students paired t-test. Serum cortisol level was significantly higher after forced swim test as well as after restraint test. When both the physical activities were compared, serum cortisol level was increased more after restraint stress than after forced swim test however, the difference was not significant statistically.

INTERPRETATION AND CONCLUSION

The rise in serum cortisol level was observed in both the physical activity models . Rise in serum cortisol level was significantly higher after restraint test than exposing them to forced swim test. This indicates that restraining the rats produced more stress than making them forcefully swim.

Behavioral and physiological responses of female prairie voles (Microtus ochrogaster) to various stressful conditions

Stressful life events elicit hypothalamic-pituitary-adrenal (HPA) axis activation, which may alter psychological states or behavioral routines. Therefore, the current study focused on the HPA axis response to better understand such manifestations in female prairie voles (Microtus ochrogaster). In Experiment 1, females were stressed for 1 h via one of the four stressors: exposure to a novel environment, immobilization ("plastic mesh"), brief social defeat, or prolonged social defeat. Following a 30-min recovery, the females received a 5-min elevated plus maze (EPM) test and, subsequently, blood was collected to measure plasma corticosterone concentrations. Only immobilization stress induced an anxiety-like behavioral response in the EPM test and elevated plasma corticosterone levels compared to the control groups. Corticosterone concentrations were also significantly elevated following exposure to prolonged social defeat compared to the control conditions, but not after novel environment stress or short social defeat. In Experiment 2, females were exposed to immobilization stress over 1, 3, or 7 days in a daily (predictable; pIMO) or irregular (unpredictable; uIMO) schedule. The biobehavioral stress response in females exposed to pIMO for 3 or 7 days did not differ significantly from controls, suggesting these females habituated. By comparison, females exposed to uIMO over 3 or 7 days did not habituate behaviorally or physiologically, even producing augmented corticosterone levels. In both experiments, positive correlations were found between corticosterone levels and anxiety-like behaviors in the EPM test. Together, our data suggest that the stress response by female prairie voles is dependent on stress intensity, source, previous experience, and predictability. Furthermore, the HPA axis response, as evident by corticosterone levels, is associated with the impact that these factors have on behavioral routine.

Effects of experimentally induced hyperthyroidism on central hypothalamic-pituitary-adrenal axis function in rats: in vitro and in situ studies

Hyperthyroidism is associated with hypercorticosteronemia, although the locus that is principally responsible for the hypercorticosteronism remains unclear. The purpose of this study was to assess the effects of hyperthyroidism on the functional integrity of the hypothalamic-pituitary-adrenal (HPA) axis, to identify the locus in the HPA axis that is principally affected, and address the time-dependent effects of alterations in thyroid status. The functional integrity of each component of the HPA axis was examined in vitro and in situ in sham-thyroidectomized male Sprague-Dawley rats given placebo or in thyroidectomized rats given pharmacological dose (50 μg) of thyroxin for 7 or 60 days. Basal plasma corticosterone and corticosterone binding globulin (CBG) concentrations were significantly increased in short- and long-term hyperthyroid rats, and by 60 days. Basal plasma ACTH levels were similar to controls. Both hypothalamic CRH content and the magnitude of KCL- and arginine vasopressin (AVP)-induced CRH release from hypothalamic culture were increased in long-term hyperthyroid rats. There was a significant increase in the content of both ACTH and β-endorphin in the anterior pituitaries of both short- and long-term hyperthyroid animals. Short-term hyperthyroid rats showed a significant increase in basal POMC mRNA expression in the anterior pituitary, and chronically hyperthyroid animals showed increased stress-induced POMC mRNA expression. Adrenal cultures taken from short-term hyperthyroid rats responded to exogenous ACTH with an exaggerated corticosterone response, while those taken from 60-day hyperthyroid animals showed responses similar to controls. The findings show that hyperthyroidism is associated with hypercorticosteronemia and HPA axis dysfunction that becomes more pronounced as the duration of hyperthyroidism increases. The evidence suggests that experimentally induced hyperthyroidism is associated with central hyperactivity of the HPA axis.

Effects of corticotropin-releasing factor 1 receptor antagonism on the hypothalamic-pituitary-adrenal axis of rodents

Corticotropin-releasing factor (CRF) is the major hypothalamic neuropeptide responsible for stimulation of the hypothalamic-pituitary-adrenal axis (HPAA), resulting in the synthesis and release of glucocorticoids from the adrenal cortex. In a recent study, we reported the discovery of the CRF1 receptor antagonist, 3-(4-chloro-2-morpholin-4-yl-thiazol-5-yl)-8-(1-ethylpropyl)-2,6-dimethyl-imidazo[1,2-b]pyridazine (MTIP), which has efficacy in preclinical models of stress-induced alcohol consumption. Because CRF1 is important in HPAA activation, we evaluated the effects of MTIP administration on rodent HPAA function. Initial studies established the MTIP doses required for brain and pituitary CRF1 occupancy and those associated with the inhibition of intracerebroventricular CRF on the HPAA in mice. Then, rat basal plasma corticosterone (CORT) concentrations were measured hourly by radioimmunoassay for 24 h after three daily doses of MTIP or vehicle. In these studies, the early phase of the nocturnal CORT surge was reduced; however, the area under the CORT curve was identical for the 24-h period. In subsequent studies, increases in plasma CORT due to direct pharmacological manipulation of the HPAA axis or by stressors were evaluated after MTIP treatment in mice. MTIP attenuated CORT responses generated by immediate bolus administration of insulin or ethanol; however, MTIP did not affect activation of the HPAA by other stressors and pharmacological agents. Therefore, MTIP can modulate basal HPAA activity during the CORT surge and reduced activation after a select number of stressors but does not produce a lasting suppression of basal CORT. The ability of MTIP to modulate plasma CORT after hyperinsulinemia may provide a surrogate strategy for a target occupancy biomarker.

Effects of repeated stress on distal airway inflammation, remodeling and mechanics in an animal model of chronic airway inflammation

BACKGROUND/AIMS

Epidemiological studies suggest that stress has an impact on asthmatic exacerbations. We evaluated if repeated stress, induced by forced swimming, modulates lung mechanics, distal airway inflammation and extracellular matrix remodeling in guinea pigs with chronic allergic inflammation.

METHODS

Guinea pigs were submitted to 7 ovalbumin or saline aerosols (1-5 mg/ml during 4 weeks; OVA and SAL groups). Twenty-four hours after the 4th inhalation, guinea pigs were submitted to the stress protocol 5 times a week during 2 weeks (SAL-S and OVA-S groups). Seventy-two hours after the 7th inhalation, guinea pigs were anesthetized and mechanically ventilated. Resistance and elastance of the respiratory system were obtained at baseline and after ovalbumin challenge. Lungs were removed, and inflammatory and extracellular matrix remodeling of distal airways was assessed by morphometry. Adrenals were removed and weighed.

RESULTS

The relative adrenal weight was greater in stressed guinea pigs compared to non-stressed animals (p < 0.001). Repeated stress increased the percent elastance of the respiratory system after antigen challenge and eosinophils and lymphocytes in the OVA-S compared to the OVA group (p < 0.001, p = 0.003 and p < 0.001). Neither collagen nor elastic fiber contents were modified by stress in sensitized animals.

CONCLUSIONS

In this animal model, repeated stress amplified bronchoconstriction and inflammatory response in distal airways without interfering with extracellular matrix remodeling.

Vasopressin modulates hypothalamo-pituitary activity by paracrine action during acute and chronic immobilization stress in rats

The aim of the study was to examine changes in corticotropin releasing hormone (CRH), vasopressin (VP), adrenocorticotropin (ACTH) as well as VP3 receptor protein concentration in the hypothalamus and the pituitary of rats exposed to acute (3 h) and chronically repeated (3 h daily for 7 days) immobilization stress. Our results show that, unlike the increase in ACTH, there were no changes in serum VP despite the significant changes in this hormone and its receptor concentrations in the hypothalamus and pituitary (HP). This suggests that VP regulates HP activity by predominantly acting in a paracrine manner under the examined stress condition.

The importance of corticosterone in mediating restraint-induced weight loss in rats

I. J. Scherer, P. V. Holmes, R. B.S. Harris. The importance of corticosterone in mediating restraint-induced weight loss in rats. PHYSIOL BEHAV 00 (0) 000-000, 2010. Rats restrained for 3 h/day for 3d ays (RR) lose weight and do not return to the weight of non-restrained controls once restraint has ended. This study tested the importance of restraint-induced corticosterone release in mediating the change in body weight by injecting ADX rats with 2.0mg corticosterone/kg before each restraint to replicate the restraint-induced surge in circulating corticosterone. Restrained adrenalectomized (ADX) rats injected with corticosterone had the same initial weight loss as intact restrained rats, whereas corticosterone injection in non-restrained ADX rats and restraint of ADX rats injected with saline each produced only half as much initial weight loss. Sustained weight loss, measured for 14 days after the end of RR, was the same for restrained intact rats and restrained ADX rats injected with corticosterone whereas restrained ADX rats injected with saline achieved the same weight gain as their controls. Corticosterone injections had no effect on weight gain of non-restrained intact rats. In situ hybridization showed that corticotropin releasing factor (CRF) mRNA expression in the paraventricular nucleus of the hypothalamus (PVN) was increased by the same degree in ADX rats and restrained intact rats and was not modified by corticosterone injections. There was no significant effect of restraint, ADX or corticosterone injection on PVN arginine vasopressin (AVP) mRNA expression. These data indicate that a surge in corticosterone causes sustained weight loss in ADX rats through a mechanism that can be compensated for in intact rats and is independent of changes in PVN CRF or AVP mRNA expression.

A subchronic application period of glucocorticoids leads to rat cognitive dysfunction whereas physostigmine induces a mild neuroprotection

The cholinergic neurotransmitter system and prolonged glucocorticoid-induced stress can affect cognitive functions in opposite ways. While pharmacological enhancement of cholinergic neurotransmission is known to induce neuroprotective effects, chronic glucocorticoids impair cognitive functions. Up to now, there is no consensus as to whether a subchronic stress period of several days would affect cognitive function. The goal of this study was to investigate whether or not repeated applications of physostigmine over 3 days lead to protective effects on rat spatial cognitive abilities in contrast to the deteriorating effect on rat cognitive function after corticosterone treatment. Furthermore, we wanted to investigate in what extent this cognition-modulating effect is associated with rat cerebral acetylcholinergic system. Male adult rats (n = 40) were randomly divided into four groups with n = 10 per group: (I) placebo-, (II) corticosterone- (15 mg/day), (III) physostigmine- (0.014 mg/day), and (IV) physostigmine + corticosterone-treated rats. Body mass and plasma corticosterone concentrations were measured. Psychometric investigations were conducted using a Morris water maze before and after a subchronic treatment. In cerebral tissue, ACh and acetylcholinesterase (AChE) content and ACh receptor density were determined. Tissue corticosterone concentration was measured in cerebral cortex, hippocampus, and adrenal glands. In corticosterone-treated rats, reduced spatial cognitive abilities were associated with a significant increase in plasma (+25%) and cerebral corticosterone levels (+350%) parallelled by a significant reduction in adrenal gland concentrations (-84%) as compared to placebo. Repeated physostigmine injections improved rats' spatial memory and increased cerebral ACh and AChE content (p < 0.05). When physostigmine was administered at the same time as corticosterone (group IV), it was not able to reverse the corticosterone effect. A significant correlation was detected between cerebral AChE and corticosterone concentrations as well as between AChE and psychometric parameters. We conclude that subchronic exogenous corticosterone administration induces memory dysfunction whereas physostigmine exerts cognitive-enhancing effects if given for 3 days. An apparently existing interaction between glucocorticoid excess and ACh metabolism is discussed.

A comparison of two repeated restraint stress paradigms on hypothalamic-pituitary-adrenal axis habituation, gonadal status and central neuropeptide expression in adult male rats

The available evidence continues to illustrate an inhibitory influence of male gonadal activity on the hypothalamic-pituitary-adrenal (HPA) axis under acute stress. However, far less is known about how these systems interact during repeated stress. Because HPA output consistently declines across studies examining repeated restraint, the potential mechanisms mediating this habituation are often inferred as being equivalent, even though these studies use a spectrum of restraint durations and exposures. To test this generalisation, as well as to emphasise a potential influence of the male gonadal axis on the process of HPA habituation, we compared the effects of two commonly used paradigms of repeated restraint in the rodent: ten daily episodes of 0.5 h of restraint and five daily episodes of 3 h of restraint. Both paradigms produced comparable declines in adrenocorticotrophic hormone and corticosterone between the first and last day of testing. However, marked differences in testosterone levels, as well as corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) expression, occurred between the two stress groups. Plasma testosterone levels remained relatively higher in animals exposed to 0.5 h of restraint compared to 3 h of restraint, whereas forebrain gonadotrophin-releasing hormone (GnRH) cell counts increased in both groups. AVP mRNA was increased after 3 h, but not after 0.5 h of repeated restraint, in the medial parvicellular paraventricular nucleus and in the posterior bed nucleus of the stria terminalis (BST), and increased with 0.5 h of repeated restraint in the medial amygdala. CRH mRNA was increased after 3 h, but not after 0.5 h of repeated restraint, in the central amygdala and anterior BST. The data obtained illustrate that, despite comparable declines in HPA responses, the pathways recruited for stress adaptation appear to be distinct between restraint groups. Given the extreme sensitivity of limbic AVP to testosterone, and conversely CRH to circulating glucocorticoids, whether differences in endocrine profiles might explain these neuropeptide differences remains to be seen. Nonetheless, the present study provides several new entry points for testing gonadal influences on stress-specific HPA habituation.

Differential glucocorticoid effects on stress-induced gene expression in the paraventricular nucleus of the hypothalamus and ACTH secretion in the rat

Although previous studies have examined the extent to which adrenocorticotropic hormone (ACTH) secretion depends on endogenous glucocorticoid levels, few have examined the parallel glucocorticoid dependency of gene expression within the corticotropin releasing hormone (CRH) neuron containing subregion of the hypothalamic paraventricular nucleus (PVN). This study examined resting and stress-induced expression of three immediate early genes (c-fos, zif268, and NGFI-B mRNAs) and two phenotypic restricted immediate early genes that code for ACTH secretagogues (CRH and arginine vasopressin [AVP] hnRNAs) in the PVN of adrenalectomized (ADX) rats given either 0.9% saline to drink for 5 days or saline with corticosterone (CORT; 25 microg/ml). CORT-containing saline was replaced with saline 18 h before testing to ensure clearance of CORT at the time of testing. Dependent measures were examined 0, 15, 30, 60, or 120 min after 30 min restraint. Compared to sham surgery, ADX produced a large upregulation of basal ACTH secretion but only a trend for an increase in basal PVN CRH and parvocellular (mp) PVN AVP hnRNA expression, and a marked augmentation of restraint-induced ACTH secretion and the expression of all five genes examined. CORT containing saline partially normalized basal and restraint-induced ACTH secretion and restraint-induced AVP hnRNA, c-fos mRNA, and zif268 mRNA in the PVN in ADX rats. In contrast, expression patterns of restraint-induced PVN CRH hnRNA and NGFI-B mRNA were not different between ADX rats with or without CORT replacement. Given that there was no circulating CORT present at the time of restraint challenge in either group of ADX rats, the differential impact of CORT replacement on restraint-induced PVN gene expression must reflect differential dependency of the expression of these genes in the PVN on the prior presence of CORT.

Adaptation to mild, intermittent stress delays development of hyperglycemia in the Zucker diabetic Fatty rat independent of food intake: role of habituation of the hypothalamic-pituitary-adrenal axis

Hypothalamic-pituitary-adrenal (HPA) axis hyperactivity occurs in type 2 diabetes, and stress is assumed to play a causal role. However, intermittent restraint stress, a model mimicking some mild stressors, delays development of hyperglycemia in Zucker diabetic fatty (ZDF) rats. We examine whether such stress delays hyperglycemia independent of stress-induced reductions in hyperphagia and is due to adaptations in gene expression of HPA-related peptides and receptors that ameliorate corticosteronemia and thus hyperglycemia. ZDF rats were intermittently restraint stressed (1 h/d, 5 d/wk) for 13 wk and compared with obese control, pair fed, and lean ZDF rats. After 13 wk, basal hormones were repeatedly measured over 24 h, and HPA-related gene expression was assessed by in situ hybridization. Although restraint initially induced hyperglycemia, this response habituated over time, and intermittent restraint delayed hyperglycemia. This delay was partly related to 5-15% decreased hyperphagia, which was not accompanied by decreased arcuate nucleus NPY or increased POMC mRNA expression, although expression was altered by obesity. Obese rats demonstrated basal hypercorticosteronemia and greater corticosterone responses to food/water removal. Basal hypercorticosteronemia was further exacerbated after 13 wk of pair feeding during the nadir. Importantly, intermittent restraint further delayed hyperglycemia independent of food intake, because glycemia was 30-40% lower than after 13 wk of pair feeding. This may be mediated by increased hippocampal MR mRNA, reduced anterior pituitary POMC mRNA levels, and lower adrenal sensitivity to ACTH, thus preventing basal and stress-induced hypercorticosteronemia. In contrast, 24-h catecholamines were unaltered. Thus, rather than playing a causal role, intermittent stress delayed deteriorations in glycemia and ameliorated HPA hyperactivity in the ZDF rat.

Stress and memory: behavioral effects and neurobiological mechanisms

Stress is a potent modulator of learning and memory processes. Although there have been a few attempts in the literature to explain the diversity of effects (including facilitating, impairing, and lack of effects) described for the impact of stress on memory function according to single classification criterion, they have proved insufficient to explain the whole complexity of effects. Here, we review the literature in the field of stress and memory interactions according to five selected classifying factors (source of stress, stressor duration, stressor intensity, stressor timing with regard to memory phase, and learning type) in an attempt to develop an integrative model to understand how stress affects memory function. Summarizing on those conditions in which there was enough information, we conclude that high stress levels, whether intrinsic (triggered by the cognitive challenge) or extrinsic (induced by conditions completely unrelated to the cognitive task), tend to facilitate Pavlovian conditioning (in a linear-asymptotic manner), while being deleterious for spatial/explicit information processing (which with regard to intrinsic stress levels follows an inverted U-shape effect). Moreover, after reviewing the literature, we conclude that all selected factors are essential to develop an integrative model that defines the outcome of stress effects in memory processes. In parallel, we provide a brief review of the main neurobiological mechanisms proposed to account for the different effects of stress in memory function. Glucocorticoids were found as a common mediating mechanism for both the facilitating and impairing actions of stress in different memory processes and phases. Among the brain regions implicated, the hippocampus, amygdala, and prefrontal cortex were highlighted as critical for the mediation of stress effects.

Stress sensitivity and resilience in the chronic mild stress rat model of depression; an in situ hybridization study

We used the validated chronic mild stress (CMS) paradigm to induce anhedonia, a core symptom of major depression, in rats. Thirty percent of animals exposed to CMS are resistant to the development of anhedonia, whereas the remaining are responsive, CMS resilient and CMS sensitive, respectively. We used in situ hybridization to elucidate the molecular mechanisms, which may be involved in the development of anhedonia during CMS. In the CA3 of the ventral hippocampus, we found upregulation of brain-derived neurotrophic factor (BDNF) mRNA in the CMS resilient group indicating protective role of BDNF in stress. Moreover, in the CA3 we found downregulation of vascular endothelial growth factor (VEGF) mRNA in the CMS sensitive group. Downregulation of VEGF suggests impaired hippocampal function, caused by loss of trophic factor neuroprotective support, as part of a previously uncharacterized mechanism for development of anhedonia. CMS induced anhedonia was not related to mRNA expression differences of the dopamine receptors D(1) and D(2), enkephalin, dynorphin, the NMDA receptor subtype NR2B in the ventral striatum, BDNF expression in the dentate gyrus, nor corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) in the paraventricular nucleus of the hypothalamus. In particular, HPA axis seems to be activated in the CMS resilient group suggesting other pathways protecting against stress sensitivity. We applied the restraint stress procedure to compare effects of a faster and simpler form of stress to CMS and found the latter to be more valid as rats probably easier adapt to restraint stress. Finally, we used the conditioned place preference model to demonstrate a clear tendency towards a distinct morphine induced behavioral difference between CMS resilient and CMS sensitive animals.

Stress and memory: behavioral effects and neurobiological mechanisms

Stress is a potent modulator of learning and memory processes. Although there have been a few attempts in the literature to explain the diversity of effects (including facilitating, impairing, and lack of effects) described for the impact of stress on memory function according to single classification criterion, they have proved insufficient to explain the whole complexity of effects. Here, we review the literature in the field of stress and memory interactions according to five selected classifying factors (source of stress, stressor duration, stressor intensity, stressor timing with regard to memory phase, and learning type) in an attempt to develop an integrative model to understand how stress affects memory function. Summarizing on those conditions in which there was enough information, we conclude that high stress levels, whether intrinsic (triggered by the cognitive challenge) or extrinsic (induced by conditions completely unrelated to the cognitive task), tend to facilitate Pavlovian conditioning (in a linear-asymptotic manner), while being deleterious for spatial/explicit information processing (which with regard to intrinsic stress levels follows an inverted U-shape effect). Moreover, after reviewing the literature, we conclude that all selected factors are essential to develop an integrative model that defines the outcome of stress effects in memory processes. In parallel, we provide a brief review of the main neurobiological mechanisms proposed to account for the different effects of stress in memory function. Glucocorticoids were found as a common mediating mechanism for both the facilitating and impairing actions of stress in different memory processes and phases. Among the brain regions implicated, the hippocampus, amygdala, and prefrontal cortex were highlighted as critical for the mediation of stress effects.

The effects of acute corticosterone administration on anxiety, endogenous corticosterone, and c-Fos expression in the rat brain

The effects of acute pretreatment of rats with corticosterone (5 and 20 mg/kg, s.c.) on emotional behavior, expression of c-Fos protein in brain structures, and serum concentration of corticosterone were studied to model the short-term glucocorticoid-dependent changes in brain functions. Corticosterone was administered 90 min before training of a conditioned fear reaction (a freezing response), and behavioral, hormonal and immunocytochemical effects were examined 1 day later, on the test day. Pretreatment of rats with corticosterone significantly attenuated the freezing reaction in the conditioned fear test. The effect of the corticosterone was accompanied by a selective enhancement of the aversive context-induced c-Fos expression in some brain structures: the parvocellular and magnocellular neurons of the paraventricular hypothalamic nucleus (pPVN and mPVN), the medial amygdala nucleus (MeA), and the cingulate cortex, area 1 (Cg1), as well as an increase in the concentration of aversive context-induced endogenous serum glucocorticoid, 1.5 h and 10 min after the test session, respectively. It is suggested that the behavioral effects of acute pretreatment of rats with corticosterone could be due to changes in the mnemonic processes in the brain, inhibition of brain corticotropin releasing factor (CRF) synthesis, or stimulation of GABA-A receptor modulating neurosteroids synthesis. It is hypothesized that the enhanced activity of Cg1, MeA, pPVN, and mPVN, and the hypothalamic-pituitary-adrenal axis with concomitant increased serum glucocorticoid concentration, might serve to facilitate active coping behavior in a threatening situation.

Corticotropin releasing hormone receptor alterations elicited by acute and chronic unpredictable stressor challenges in stressor-susceptible and resilient strains of mice

Stressors increase corticotropin releasing hormone (CRH) functioning in hypothalamic and frontal cortical brain regions, and thus may contribute to the provocation of anxiety and depressive disorder. As the effects of stressors on these behavioral changes are more pronounced in some strains of mice (e.g., BALB/cByJ) than in others (e.g., C57BL/6ByJ), the present investigation assessed whether acute and chronic stressors would differentially influence CRH receptor immunoreactivity (ir-CRHr) and CRH receptor mRNA expression (CRH(1) and CRH(2)) in the orbital frontal cortex (OFC) of these strains. An acute noise stressor, and to a greater extent a chronic, variable stressor regimen reduced ir-CRHr in BALB/cByJ mice. In contrast, in the hardier C57BL/6ByJ mice the acute stressor increased ir-CRHr in portions of the OFC, whereas a chronic stressor tended to reduce ir-CRHr. However, whereas the acute stressor did not influence CRH(1) mRNA expression, the chronic stressor increased CRH(1) mRNA expression in both mouse strains. The CRH(2) expression appeared in low abundance in both strains and was unaltered by the stressor. In addition to the OFC variations, quantitative immunohistochemistry indicated that the chronic stressor treatment increased CRH immunoreactivity in the median eminence of C57BL/6ByJ mice, but co-expression of CRH and arginine vasopressin (AVP) immunoreactivity was not provoked by the stressors. The data support the view that stressors provoke marked variations of ir-CRHr in the OFC that might contribute to the differential anxiety/depression-like profiles ordinarily apparent in the stressor-vulnerable and -resilient mouse strains.

Do corticosteroids damage the brain?

Corticosteroids are an essential component of the body's homeostatic system. In common with other such systems, this implies that corticosteroid levels in blood and, more importantly, in the tissues remain within an optimal range. It also implies that this range may vary according to circumstance. Lack of corticosteroids, such as untreated Addison's disease, can be fatal in humans. In this review, we are principally concerned with excess or disturbed patterns of circulating corticosteroids in the longer or shorter term, and the effects they have on the brain.

Habituation to repeated restraint stress is associated with lack of stress-induced c-fos expression in primary sensory processing areas of the rat brain

Rats repeatedly exposed to restraint show a reduced hypothalamic-pituitary-adrenal axis response upon restraint re-exposure. This hypothalamic-pituitary-adrenal axis response habituation to restraint does not generalize to other novel stressors and is associated with a decrease in stress-induced c-fos expression in a number of stress-reactive brain regions. We examined whether habituation to repeated restraint is also associated with adaptation of immediate early gene expression in brain regions that process and relay primary sensory information. These brain regions may not be expected to show gene expression adaptation to repeated restraint because of their necessary role in experience discrimination. Rats were divided into a repeated restraint group (five 1-hour daily restraint sessions) and an unstressed group (restraint naïve). On the sixth day rats from each group were either killed with no additional stress experience or at 15, 30 or 60 min during restraint. Immediate early gene expression (corticotrophin-releasing hormone heteronuclear RNA, c-fos mRNA, zif268 mRNA) was determined by in situ hybridization. A reduction in stress-induced hypothalamic-pituitary-adrenal axis hormone secretion (plasma corticosterone and adrenocorticotropic hormone) and immediate early gene expression levels in the paraventricular nucleus of the hypothalamus, the lateral septum and the orbital cortex was observed in repeated restraint as compared with restraint naïve animals. This reduction was already evident at 15 min of restraint. Unexpectedly, we also found in repeated restraint rats a reduction in restraint-induced c-fos expression in primary sensory-processing brain areas (primary somatosensory cortex, and ventroposteriomedial and dorsolateral geniculate nuclei of thalamus). The overall levels of hippocampal mineralocorticoid receptor heteronuclear RNA or glucocorticoid receptor mRNA were not decreased by repeated restraint, as may occur in response to severe chronic stress. We propose that repeated restraint leads to a systems-level adaptation whereby re-exposure to restraint elicits a rapid inhibitory modulation of primary sensory processing (i.e. sensory gating), thereby producing a widespread attenuation of the neural response to restraint.

Increased body fat in mice with a targeted mutation of the paternally expressed imprinted gene Peg3

Peg3 encodes a C2H2 type zinc finger protein that is implicated in a novel physiological pathway regulating core body temperature, feeding behavior, and obesity in mice. Peg3+/- mutant mice develop an excess of abdominal, subcutaneous, and intra-scapular fat, despite a lifetime of lower food intake than wild-type animals. However, they start life with reduced fat reserves and are slower to enter puberty. These mice maintain a lower core body temperature, fail to respond to a cold challenge, and have lower metabolic activity as measured by oxygen consumption. Plasma leptin levels are significantly higher than in wild types, and Peg3+/- mice appear to have developed leptin resistance. Administration of exogenous leptin resulted in a significant reduction in food intake in wild-type mice that was not observed in Peg3+/- mutants. This mutation, which is strongly expressed in hypothalamic tissue during development, has the capacity to regulate multiple events relating to energy homeostasis.

Stress induces CRF release in the paraventricular nucleus, and both CRF and GABA release in the amygdala

In the hypothalamus, corticotropin-releasing factor (CRF) initiates the hypothalamic-pituitary-adrenal (HPA) axis response to stress, resulting in the release of glucocorticoids, including cortisol. Extrahypothalamic CRF, particularly in the limbic system, also appears to play a role in the stress response. To further define brain CRF response to stress, immunosensor-based microdialysis probes were used to measure the extracellular levels of CRF in the paraventricular nucleus of the hypothalamus (PVN) and in the amygdala of sheep during a predator (dog) exposure stress. In addition, gamma amino butyric acid (GABA) was measured in the amygdala and cortisol was measured in venous blood. Exposure to the predator stress increased CRF in the PVN and both CRF and GABA in the amygdala. These were followed in time by a rise in venous cortisol. Application of a CRF antagonist to the amygdala, immediately prior to stress, had a small effect on the subsequent observed stress responses. This treatment, however, significantly reduced the responses to a repeat stress administered 2 days later, compared to nontreated animals. Application of a GABA antagonist to the amygdala prior to stress had no effect on the subsequent observed stress response but increased the response to the stress repeated 2 days later. Perfusion with 4-aminopyridine, a neuronal depolarising agent, into the PVN induced a release of CRF accompanied shortly thereafter by a small increase in CRF in the amygdala, and 5-10 min later by an increase in venous cortisol. Perfusion into the amygdala increased the levels of both CRF and GABA but had no effect on either PVN CRF or venous cortisol. These data support roles for both the PVN and amygdala in stress responsiveness. It suggests further that actions at the amygdala can strongly influence subsequent responsiveness to a further stress, mediated in part by both CRF and GABA actions.

A single exposure to severe stressors causes long-term desensitisation of the physiological response to the homotypic stressor

Although some laboratories have reported that a single session of stress is able to induce a long-lasting sensitisation of the hypothalamic-pituitary-adrenal (HPA) response to further exposures to stress, we have found that a single exposure to severe emotional (immobilisation, restraint or shock) or systemic (endotoxin) stressors reduces the responsiveness of the HPA to the same, but not to a novel (heterotypic), stressor, in which case a slight sensitisation was observed. Long-term desensitisation has been found to reduce not only secretion of peripheral HPA hormones (ACTH and corticosterone), but also to reduce responses of central components of the HPA axis (c-fos and CRF gene expression at the level of the paraventricular nucleus of the hypothalamus, PVN). In addition, desensitisation also applies to the impact of the stressor on food intake and, probably, to stress-induced hyperglycaemia. The development of long-term desensitisation of the HPA axis does not appear to be a universal consequence of exposure to severe stressors as it was not observed in response to insulin-induced hypoglycaemia. Whether or not the development of long-term effects of stress depend on the specific pathways activated by particular stressors remains to be tested. The observed desensitisation of the HPA axis in response to the homotypic stressor shows two special features which makes it difficult to be interpreted in terms of an habituation-like process: (a) the effect increased with time (days to weeks) elapsed between the first and second exposure to the stressor, suggesting a progressive maturational process; and (b) the stronger the stressor the greater the long-term desensitisation. Therefore, it is possible that desensitisation of the HPA axis is the sum of two different phenomena: long-term effects and habituation-like processes. The contribution of the former may be more relevant with severe stressors and longer inter-stress intervals, and that of the latter with mild stressors and repeated exposures. Long-term stress-induced changes may not take place at the level of the PVN itself, but in brain nuclei showing synaptic plasticity and putatively involved in the control of the HPA axis and other physiological responses. As for the precise areas involved, these remain to be characterized.

17Beta-oestradiol modulates glucocorticoid, neural and behavioural adaptations to repeated restraint stress in female rats

Sex steroids have a role in modulating responses that extends beyond reproduction. The current study investigated the influence of the sex steroid 17beta-oestradiol on hypothalamic-pituitary-adrenal (HPA) and behavioural responses to acute or repeated restraint stress. Ovariectomized rats treated with 17beta-oestradiol or peanut oil via a subcutaneous silastic capsule were subjected to daily handling (non stressed), acute (single, 1 h) or daily (10 days, 1 h/day) restraint stress. Blood collected at the end of stress revealed that 17beta-oestradiol treatment augmented the corticosterone response to acute restraint. After daily exposure to restraint, the corticosterone response was noticeably diminished in untreated females but 17beta-oestradiol-treated rats still showed an exaggerated response compared to castrated, untreated females. Brain tissue collected 3 h after the end of restraint was probed using isotopic in situ hybridization for corticotropin-releasing factor (CRF) and vasopressin gene expression in the paraventricular nucleus (PVN) of the hypothalamus. 17beta-oestradiol treatment at the higher dose (120 microg/ml) decreased basal CRF mRNA. Stress caused an increase in CRF mRNA expression in 17beta-oestradiol-treated rats but not in the vehicle group. Repeated restraint stress caused an increase in PVN parvocellular vasopressin gene expression, which was more pronounced in 17beta-oestradiol-replaced rats. Animals were exposed to the elevated plus maze for 5 min as a test for anxiety. Non-stressed control rats with or without 17beta-oestradiol replacement spent the same percentage amount of time exploring the open arms of the maze. Previous exposure to acute restraint stress caused a marked reduction in the time spent exploring the open arms, indicating an increase in anxiety levels in these rats; this effect was observed in both vehicle and 17beta-oestradiol-treated rats. After repeated restraint stress, 17beta-oestradiol-replaced rats spent as much time exploring the open arms of the maze as controls, indicating adaptation. By contrast, nonreplaced rats were still showing a significant reduction in open arm exploration after repeated restraint. The present study presents novel data showing that the HPA axis remains reactive to repeated stress in 17beta-oestradiol-treated ovariectomized rats, but stress-induced anxiety behaviour is reduced.

Effects of repeated restraint stress on hypothalamo-pituitary-adrenocortical function in vasopressin deficient Brattleboro rats

Arginine-vasopressin (AVP) has been proposed to be an important mediator during chronic stress in the regulation of the hypothalamo-pituitary-adrenal axis. In the present study we addressed the role of AVP in maintaining adrenocortical responsiveness during chronic stress using the AVP deficient mutant Brattleboro rat. Heterozygous Brattleboro rats (di/+) served as controls and were compared to homozygous rats (di/di) with diabetes insipidus. Sixty minutes daily restraint was repeated for 5, 8, 11 or 15 days and organ weights, plasma adrenocorticotropin (ACTH) and corticosterone levels and anterior pituitary proopiomelanocortin (POMC) mRNA and ACTH content were measured. The body, adrenal and thymus weight changes induced by chronic stress became significant between 5 and 8 repetition and AVP deficiency had no effect on these parameters. The first indication that AVP has a role to play appears after 11 repetitions. In the di/di group at the end of 11th restraint, the plasma ACTH was decreased when compared to the di/+ rats. In animals with indwelling cannulas some adaptation could be seen in ACTH response without any difference between di/+ and di/di rats after 15 restraints. The corticosterone- and prolactin-elevations induced by restraint did not habituate in the di/+ and the di/di rats. Chronic stress increased POMC mRNA in the anterior pituitary similarly in di/+ and di/di rats. Although AVP seems to be necessary for a full ACTH response, most of the other signs of chronic stress after repeated restraint occur unchanged in the absence of AVP in both genders. This suggests that either AVP is not indispensable for activating the hypothalamo-pituitary-adrenocortical system by chronic stress or the absence of AVP is compensated by other mediators in Brattleboro rats.

Secretion of tumor necrosis factor-alpha from human placental tissues induced by hypoxia-reoxygenation causes endothelial cell activation in vitro: a potential mediator of the inflammatory response in preeclampsia

Preeclampsia is a hypertensive complication of human pregnancy characterized by generalized maternal endothelial cell activation. Circulating pro-inflammatory cytokines derived from the placenta are thought to play a key role. We recently demonstrated that hypoxia-reoxygenation (H/R) of placental tissues in vitro causes equivalent oxidative stress to that seen in preeclampsia. Our aim was to determine whether H/R also increases production of tumor necrosis factor-alpha (TNF-alpha), and whether conditioned media from samples exposed to H/R causes activation of human umbilical vein endothelial cells (HUVECs). Concentrations of mRNA encoding TNF-alpha were significantly higher in placental tissues subjected to H/R compared to hypoxic or normoxic controls. Although there was no difference in the concentrations of TNF-alpha protein in tissue homogenates, levels of TNF-alpha protein in the medium were significantly higher after H/R compared to controls, indicating increased secretion. Furthermore, conditioned medium from samples subjected to H/R caused increased expression of E-selectin by HUVECs, and the addition of anti-TNF-alpha antibodies significantly reduced that activation. These results are consistent with our hypothesis that intermittent perfusion of the placenta, secondary to reduced trophoblast invasion, causes increased secretion of TNF-alpha, and that this contributes to the activation of maternal endothelial cells that characterizes preeclampsia.

Mice lacking pro-opiomelanocortin are sensitive to high-fat feeding but respond normally to the acute anorectic effects of peptide-YY(3-36)

Inactivating mutations of the pro-opiomelanocortin (POMC) gene in both mice and humans leads to hyperphagia and obesity. To further examine the mechanisms whereby POMC-deficiency leads to disordered energy homeostasis, we have generated mice lacking all POMC-derived peptides. Consistent with a previously reported model, Pomc(-/-) mice were obese and hyperphagic. They also showed reduced resting oxygen consumption associated with lowered serum levels of thyroxine. Hypothalami from Pomc(-/-) mice showed markedly increased expression of melanin-concentrating hormone mRNA in the lateral hypothalamus, but expression of neuropeptide Y mRNA in the arcuate nucleus was not altered. Provision of a 45% fat diet increased energy intake and body weight in both Pomc(-/-) and Pomc(+/-) mice. The effects of leptin on food intake and body weight were blunted in obese Pomc(-/-) mice whereas nonobese Pomc(-/-) mice were sensitive to leptin. Surprisingly, we found that Pomc(-/-) mice maintained their acute anorectic response to peptide-YY(3-36) (PYY(3-36)). However, 7 days of PYY(3-36) administration had no effect on cumulative food intake or body weight in wild-type or Pomc(-/-) mice. Thus, POMC peptides seem to be necessary for the normal response of energy balance to high-fat feeding, but not for the acute anorectic effect of PYY(3-36) or full effects of leptin on feeding. The finding that the loss of only one copy of the Pomc gene is sufficient to render mice susceptible to the effects of high fat feeding emphasizes the potential importance of this locus as a site for gene-environment interactions predisposing to obesity.

Does the amygdala modulate adaptation to repeated stress?

Exposure of the rat to restraint results in activation of the hypothalamic-pituitary-adrenal (HPA) axis, a characteristic pattern of c-fos expression in the brain and increased cardiovascular function. These responses adapt with repeated exposure of an individual to the same stress. Corticosterone secretion habituates, and c-fos mRNA expression in the paraventricular nucleus of the hypothalamus (PVN) decreases. The increased expression of corticotropin releasing hormone mRNA in the PVN also becomes less prominent, whereas vasopressin mRNA progressively increases. The neural mechanisms responsible for this adaptation remain obscure. Because of its role in conditioned learning, we have hypothesised that the amygdala might be involved in this adaptive process. Here we show that large neurotoxic lesions of the amygdala in male rats do not prevent acute stress activation of the HPA axis following 30 min restraint, whilst more discrete lesions of the central nucleus actually exacerbate the acute response. Rats with large amygdala lesions demonstrate delayed habituation of corticosterone and c-fos to repeated restraint, an affect not apparent with central nucleus lesions. Furthermore we show that neither type of lesion significantly reduced tachycardiac responses to single or repeated restraint as measured by telemetry. We conclude that the amygdala and the central nucleus are not necessary for HPA and cardiovascular activation in response to stress (though the central nucleus may modulate it), and that adaptation to repeated stress is only modestly dependent upon the amygdala.

Role of hypothalamic inputs in maintaining pituitary-adrenal responsiveness in repeated restraint

The role of hypothalamic structures in the regulation of chronic stress responses was studied by lesioning the mediobasal hypothalamus or the paraventricular nucleus of hypothalamus (PVH). Rats were acutely (60 min) and/or repeatedly (for 7 days) restrained. In controls, a single restraint elevated the plasma adrenocorticotropin (ACTH), corticosterone, and prolactin levels. Repeated restraint produced all signs of chronic stress, including decreased body and thymus weights, increased adrenal weight, basal corticosterone levels, and proopiomelanocortin (POMC) mRNA expression in the anterior pituitary. Some adaptation to repeated restraint of the ACTH response, but not of other hormonal responses, was seen. Lesioning of the mediobasal hypothalamus abolished the hormonal response and POMC mRNA activation to acute and/or repeated restraint, suggesting that the hypothalamo-pituitary-adrenal axis activation during repeated restraint is centrally driven. PVH lesion inhibited the ACTH and corticosterone rise to the first restraint by approximately 50%. In repeatedly restrained rats with PVH lesion, the ACTH response to the last restraint was reduced almost to basal control levels, and the elevation of POMC mRNA level was prevented. PVH seems to be important for the repeated restraint-induced ACTH and POMC mRNA stimulation, but it appears to partially mediate other restraint-induced hormonal changes.

Quantitative analysis of corticotropin-releasing factor and arginine vasopressin mRNA in the hypothalamus during chronic morphine treatment in rats: an in situ hybridization study

The content of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) in the hypothalamic paraventricular nucleus (PVN) increases during chronic morphine treatment. Because these experiments cannot distinguish between increased synthesis or reduced release, the present study measured changes in CRF and AVP mRNAs in the PVN by in situ hybridization. Concomitantly, changes in noradrenaline turnover in the PVN and changes in plasma corticosterone release were determined. Male rats were implanted with placebo (naive) or morphine pellets for 7 days. On day 7, groups of rats received an acute injection of either saline i.p. or morphine (30 mg/kg, i.p.). Acute morphine injection did not change the total size of the labelled area for CRF mRNA in the PVN of naive or morphine-pelleted rats, indicating that the number of CRF-containing neurones was unchanged. On the other hand, in rats chronically treated with morphine, the intensity of labelling for CRF mRNA was significantly reduced, suggesting a decrease in the synthesis of CRF. In placebo rats, injection of saline or morphine did not affect the surface hybridized for AVP mRNA. By contrast, in the morphine-group injected with saline, there was a significant reduction in the number of labelled neurones, measured by the size of labelled area. Similarly, there was a decrease in intensity of AVP mRNA expression in the parvocellular and magnocellular neurones of the PVN in the morphine-group injected with saline, suggesting a decreased synthesis of AVP in these neurones. In parallel with the decrease in the expression of CRF and AVP mRNAs in the PVN, there was a pronounced decrease in noradrenaline turnover and in the release of corticosterone in the morphine-pelleted rats. In conclusion, present results show that, in addition to modifications in corticosterone secretion and in noradrenaline turnover, chronic morphine administration produces a reduction in the synthesis of CRF and AVP.

Involvement of the brain oxytocin system in stress coping: interactions with the hypothalamo-pituitary-adrenal axis

In response to various ethologically relevant stressors, oxytocin is released not only from neurohypophysial terminals into the blood, but also within distinct brain regions, for example the hypothalamic supraoptic and paraventricular nuclei, the septum and the amygdala in dependence on the quality and intensity of the stressor. Thus, oxytocin secretory activity may accompany the response of the hypothalamo-pituitary-adrenal (HPA) axis to a given stressor. In the present chapter, I try to summarize our efforts to reveal the physiological significance of intracerebrally released oxytocin in rats with respect to the regulation of the HPA axis under basal and stress conditions as well as with respect to behavioural stress responses. The effects of oxytocin appear to depend on the brain region studied and the state of activity of the animal (basal versus stress). In order to reveal interactions between the oxytocin system and the HPA axis, preliminary results are presented pointing towards a differential action of glucocorticoids on intracerebral and peripheral oxytocin release.

Effect of naloxone-precipitated morphine withdrawal on CRH and vasopressin mRNA expression in the rat hypothalamic paraventricular nucleus

Morphine withdrawal is characterized by an increase in the hypothalamus-pituitary-adrenocortical (HPA) axis activity. Here, by means of in situ hybridization, the changes in CRH and vasopressin (AVP) mRNAs have been analysed within the rat hypothalamic paraventricular nucleus (PVN) during morphine dependence and after naloxone-precipitated morphine withdrawal. CRH and AVP mRNA expression were analysed 30 min following administration of saline or naloxone to control groups and to morphine dependent rats. The data for in situ hybridization analysis of PVN neurons show that there were no changes in the total size of labelled area for CRH or AVP mRNA during morphine withdrawal, indicating that dependence on morphine does not involve alterations in the number of neurons expressing CRH or AVP mRNA. However, levels of mRNA encoding for CRH were decreased in the PVN during morphine dependence and withdrawal. By contrast, injection of saline or naloxone to morphine dependent rats did not affect the intensity of AVM mRNA expression. All these findings are discussed in term of cellular events that couple morphine dependence-increased HPA axis activity with changes in gene expression in selective neurons of the PVN.