Activation Of Hypothalamo-pituitary-adrenal Axis Research Articles

Acute Mono-Arthritis Activates the Neurohypophysial System and Hypothalamo-Pituitary Adrenal Axis in Rats.

Various types of acute/chronic nociceptive stimuli cause neuroendocrine responses such as activation of the hypothalamo-neurohypophysial [oxytocin (OXT) and arginine vasopressin (AVP)] system and hypothalamo-pituitary adrenal (HPA) axis. Chronic multiple-arthritis activates the OXT/AVP system, but the effects of acute mono-arthritis on the OXT/AVP system in the same animals has not been simultaneously evaluated. Further, AVP, not corticotropin-releasing hormone (CRH), predominantly activates the HPA axis in chronic multiple-arthritis, but the participation of AVP in HPA axis activation in acute mono-arthritis remains unknown. Therefore, we aimed to simultaneously evaluate the effects of acute mono-arthritis on the activity of the OXT/AVP system and the HPA axis. In the present study, we used an acute mono-arthritic model induced by intra-articular injection of carrageenan in a single knee joint of adult male Wistar rats. Acute mono-arthritis was confirmed by a significant increase in knee diameter in the carrageenan-injected knee and a significant decrease in the mechanical nociceptive threshold in the ipsilateral hind paw. Immunohistochemical analysis revealed that the number of Fos-immunoreactive (ir) cells in the ipsilateral lamina I–II of the dorsal horn was significantly increased, and the percentage of OXT-ir and AVP-ir neurons expressing Fos-ir in both sides of the supraoptic (SON) and paraventricular nuclei (PVN) was increased in acute mono-arthritic rats. in situ hybridization histochemistry revealed that levels of OXT mRNA and AVP hnRNA in the SON and PVN, CRH mRNA in the PVN, and proopiomelanocortin mRNA in the anterior pituitary were also significantly increased in acute mono-arthritic rats. Further, plasma OXT, AVP, and corticosterone levels were significantly increased in acute mono-arthritic rats. These results suggest that acute mono-arthritis activates ipsilateral nociceptive afferent pathways at the spinal level and causes simultaneous and integrative activation of the OXT/AVP system. In addition, the HPA axis is activated by both AVP and CRH in acute mono-arthritis with a distinct pattern compared to that in chronic multiple-arthritis.

92 Intra-nasal oxytocin treatment does not attenuate the hypothalamo-pituitary-adrenal axis in beef heifers subjected to isolation stress or restraint and isolation stress

Abstract Changes in the physiological, psychological, and behavioral manifestations of stress are observed in association with increases in circulating oxytocin. Providing oxytocin intra-nasally attenuates stressor-induced hypothalamo-pituitary-adrenal (HPA) axis activation in humans and rodents. The present study was conducted to investigate effects of intra-nasal oxytocin supplementation on stressor-induced activation of the HPA axis in beef cattle. We hypothesized that oxytocin would attenuate activation of the HPA axis, ultimately decreasing plasma cortisol. Bos taurus heifers (n = 28) were blocked by bodyweight and randomly allocated to one of four treatment groups, in a 2 × 2 factorial arrangement: 1) Saline, isolated, standing, and unrestrained (S-IS, 0.015mL/kg BW 0.9% isotonic saline, n = 7); 2) Saline, isolated, and restrained (S-RIS; 0.015 ml/kg BW 0.9% isotonic saline; n = 7); 3) Oxytocin, IS (OXT-IS, 0.3 IU/kg BW oxytocin; n = 7); and 4) Oxytocin and isolated and restrained (OXT-RIS, 0.3 IU/kg BW oxytocin; n = 7). Oxytocin and saline were administered intra-nasally. Appropriate stressors were applied 30 minutes following intra-nasal treatment. Blood samples were collected directly following imposing the stressor, and every 10 minutes thereafter, for 2 h. Cortisol concentrations increased over time in animals exposed to restraint and isolation stress (P < 0.01) and decreased over time in animals exposed to isolation stress (P < 0.01). In the present study, oxytocin did not affect measured indicators of HPA axis activation. Greater plasma oxytocin concentrations were observed in restrained animals administered saline, compared with their standing counterparts administered oxytocin (P < 0.01), indicating some endogenous release of oxytocin in response to restraint stress. Overall, restraint stress increased cortisol and oxytocin in Bos taurus heifers compared with heifers subjected only to isolation. Finding a more intermediate stress model may allow for more precise detection of effects of oxytocin on the stress response.

Intranasal oxytocin treatment does not attenuate the hypothalamo-pituitary-adrenal axis in beef heifers subjected to isolation stress or restraint and isolation stress

Changes in the physiological, psychological, and behavioral manifestations of stress have been observed in association with increases in circulating oxytocin (OXT). Providing OXT intranasally has been shown to attenuate stressor-induced hypothalamo-pituitary-adrenal (HPA) axis activation in humans and rodents; however, anxiolytic effects may be context and species specific. The present study aimed to investigate the effect of intranasal OXT supplementation on stressor-induced activation of the HPA axis in beef cattle. We hypothesized that OXT would attenuate activation of the HPA axis, ultimately decreasing plasma cortisol and adrenocorticotropic hormone (ACTH). Twenty-eight Bos taurus heifers were blocked by bodyweight and randomly allocated to one of four treatment groups, in a 2 × 2 factorial arrangement: (1) saline, isolated, standing, and unrestrained (S-isolation stress [IS], 0.015 mL/kg BW 0.9% isotonic saline, n = 7); (2) saline, isolated, and restrained (S-restraint and isolation stress [RIS]; 0.015 mL/kg BW 0.9% isotonic saline; n = 7); (3) OXT, IS (OXT-IS, 0.3 IU/kg BW oxytocin; n = 7); and (4) OXT and RIS (OXT-RIS, 0.3 IU/kg BW oxytocin; n = 7). Oxytocin and saline were administered intranasally. Intranasal treatments were given followed by a waiting time of 30 min when each of the stress treatments was applied for 2 h. Blood samples were collected via jugular catheters directly after stressor application and every 10 min thereafter, for 2 h. Cortisol concentrations increased over time in animals exposed to RIS (P < 0.01) and decreased over time in animals exposed to IS (P < 0.01). Concentrations of ACTH decreased over time for the IS-treated heifers but remained elevated for the RIS-treated heifers (P < 0.01). Under the conditions of the present study, OXT treatment did not affect measured indicators of HPA axis activation. A treatment × time interaction (P < 0.01) was detected for OXT, such that OXT heifers exhibited greater initial OXT concentrations followed by a decline; saline-treated heifers had consistently stable oxytocin concentrations. The RIS-treated heifers increased their glucose (P < 0.01) and lactate (P < 0.01) concentrations throughout the application of the stressors compared with the IS-treated heifers. Overall, restraint stress increased cortisol and oxytocin in B taurus heifers compared with heifers subjected only to isolation. Finding a more intermediate stress model may better allow for detection of the effects of oxytocin on the stress response.

Roles of Hippocampal Somatostatin Receptor Subtypes in Stress Response and Emotionality.

Altered brain somatostatin functions recently appeared as key elements for the pathogenesis of stress-related neuropsychiatric disorders. The hippocampus exerts an inhibitory feedback on stress but the mechanisms involved remain unclear. We investigated herein the role of hippocampal somatostatin receptor subtypes in both stress response and behavioral emotionality using C57BL/6, wild type and sst2 or sst4 knockout mice. Inhibitory effects of hippocampal infusions of somatostatin agonists on stress-induced hypothalamo-pituitary-adrenal axis (HPA) activity were tested by monitoring peripheral blood and local hippocampus corticosterone levels, the latter by using microdialysis. Anxiolytic and antidepressant-like effects were determined in the elevated-plus maze, open field, forced swimming, and stress-sensitive beam walking tests. Hippocampal injections of somatostatin analogs and sst2 or sst4, but not sst1 or sst3 receptor agonists produced rapid and sustained inhibition of HPA axis. sst2 agonists selectively produced anxiolytic-like behaviors whereas both sst2 and sst4 agonists had antidepressant-like effects. Consistent with these findings, high corticosterone levels and anxiety were found in sst2KO mice and depressive-like behaviors observed in both sst2KO and sst4KO strains. Both hippocampal sst2 and sst4 receptors selectively inhibit stress-induced HPA axis activation but mediate anxiolytic and antidepressive effects through distinct mechanisms. Such results are to be accounted for in development of pathway-specific somatostatin receptor agents in the treatment of hypercortisolism (Cushing's disease) and stress-related neuropsychiatric disorders.

Blunted hypothalamo-pituitary adrenal axis response to predator odor predicts high stress reactivity

Individuals with trauma- and stress-related disorders exhibit increases in avoidance of trauma-related stimuli, heightened anxiety and altered neuroendocrine stress responses. Our laboratory uses a rodent model of stress that mimics the avoidance symptom cluster associated with stress-related disorders. Animals are classified as ‘Avoiders’ or ‘Non-Avoiders’ post-stress based on avoidance of predator-odor paired context. Utilizing this model, we are able to examine subpopulation differences in stress reactivity. Here, we used this predator odor model of stress to examine differences in anxiety-like behavior and hypothalamo-pituitary adrenal (HPA) axis function in animals that avoid a predator-paired context relative to those that do not. Rats were exposed to predator odor stress paired with a context and tested for avoidance (24h and 11days), anxiety-like behavior (48h and 5days) and HPA activation following stress. Control animals were exposed to room air. Predator odor stress produced avoidance in approximately 65% of the animals at 24h that persisted 11days post-stress. Both Avoiders and Non-Avoiders exhibited a heightened anxiety-like behavior at 48h and 5days post-stress when compared to unstressed Controls. Non-Avoiders exhibited significant increases in circulating adrenocorticotropin hormone (ACTH) and corticosterone (CORT) concentrations immediately following predator odor stress compared to Controls and this response was significantly attenuated in Avoiders. There was an inverse correlation between circulating ACTH/CORT concentrations and avoidance, indicating that lower levels of ACTH/CORT predicted higher levels of avoidance. These results suggest that stress effects on HPA stress axis activation predict long-term avoidance of stress-paired stimuli, and build on previous data showing the utility of this model for exploring the neurobiological mechanisms of trauma- and stress-related disorders.

Serum cortisol concentrations during induced hypothermia for perinatal asphyxia are associated with neurological outcome in human infants

Birth asphyxia is a cause of neonatal death or adverse neurological sequelae. Biomarkers can be useful to clinicians in order to optimize intensive care management and communication of prognosis to parents. During perinatal adverse events, increased cortisol secretion is due to hypothalamo–pituitary–adrenal axis activation. We aimed to investigate if cortisol variations during therapeutic hypothermia are associated with neurodevelopmental outcome. We compared 18 cases (neonates with birth asphyxia) with 18 controls (healthy term newborns) and confirmed increased serum cortisol concentrations following the peri-partum adverse event. Among cases, we stratified patients according to neurological outcome at 18 months (group A – good; group B – adverse) and found that after 24 h of therapeutic hypothermia serum cortisol concentration was significantly lower in group A vs group B (28.7 ng/mL vs 344 ng/mL, *p = 0.01). In group B serum, cortisol concentration decreased more gradually during therapeutic hypothermia. We conclude that monitoring serum cortisol concentration during neonatal therapeutic hypothermia can add information to clinical evaluation of neonates with birth asphyxia; cortisol values after the first 24 h of hypothermia can be a biomarker associated with neurodevelopmental outcome at 18 months of age.

Up-Regulation of the Fetal Baboon Hypothalamo-Pituitary-Adrenal Axis in Intrauterine Growth Restriction: Coincidence with Hypothalamic Glucocorticoid Receptor Insensitivity and Leptin Receptor Down-Regulation

Intrauterine growth restriction (IUGR) is an important fetal developmental problem resulting from 2 broad causes: maternal undernutrition and/or decreased fetal nutrient delivery to the fetus via placental insufficiency. IUGR is often accompanied by up-regulation of the hypothalamo-pituitary-adrenal axis (HPAA). Sheep studies show fetal HPAA autonomy in late gestation. We hypothesized that IUGR, resulting from poor fetal nutrient delivery, up-regulates the fetal baboon HPAA in late gestation, driven by hypothalamo-pituitary glucocorticoid receptor (GR) insensitivity and decreased fetal leptin in peripheral plasma. Maternal baboons were fed as ad libitum controls or nutrient restricted to produce IUGR (fed 70% of the control diet) from 0.16 to 0.9 gestation. Peripheral ACTH, cortisol, and leptin were measured by immunoassays. CRH, arginine vasopressin (AVP), GR, leptin receptor (ObRb), and pro-opiomelanocortin peptide expression were determined immunohistochemically. IUGR fetal peripheral cortisol and ACTH, but not leptin, were increased (P < .05). IUGR increased CRH peptide expression, but not AVP, in the fetal hypothalamic paraventricular nucleus (PVN) and median eminence (P < .05). PVN ObRb peptide expression, but not GR, was decreased (P < .05) with IUGR. ObRb and pro-opiomelanocortin were robustly expressed in the anterior pituitary gland, but ∼1% of cells showed colocalization. We conclude that (1) CRH, not AVP, is the major releasing hormone driving ACTH and cortisol secretion during primate IUGR, (2) fetal HPAA activation was aided by GR insensitivity and decreased ObRb expression in the PVN, and (3) the anterior pituitary is not a site for ObRb effects on the HPAA.

New Aspects of the Immunoregulation by the Hypothalamo-Pituitary-Adrenal (HPA) Axis

One of the basic neuro-immune-endocrine interaction is the hypothalamo-pituitary-adrenal axis (HPA) to harmonize immune response to inflammatory stressors. Immune defense mechanisms mediated by cytokines and other humoral factors play particularly important roles in this communication. They are also potent activators in the CNS and factors of the HPA axis, like an increased secretion of glucocorticoids (GC). They can act as major feedback regulator of the vertebrate immune response via suppression of a wide range of cytokines, as well as interferons. Increases in systemic GC levels, however, often play dual role: do not suppress all cytokines since inhibition of a particular cytokine may result in elevated production of others. External stimuli/acute stress can compromise activation of the HPA axis and activate immune processes for defense, redirecting leukocytes from the circulation to the environment/organism interface. Overall it results in release of danger-associated molecular patterns (DAMPs) to activate cells of the innate immune system, which is resolved by neural, hormonal or immune mechanisms. The chronic stress leads to chronic immune arousal and subsequent sterile, low-grade inflammation, which has been identified in most stress-related or civilized disorders in humans. The role of pituitary-gonadal axis in the activation of HPA axis results in a gender difference in HPA response to immunological challenges: e.g. can be varied during the estrus cycle, pregnancy or lactation. That corresponds to the results of recent experimental data that reveals an important role of certain neurotramsitters (such as dopamine) in immune regulation. Internal constitutional-factors of neuro-immune-endocrine interaction, such as corticotropin-releasing hormone (CRH) and its receptors (CRF-R1 and CRF-R2), melanocortin peptides, glucocorticoids or pro-inflammatory cytokines can also act as an immunoregulator, since their receptors is present in lymphoid organs, also in peripheral blood and organs that are enhanced under inflammatory conditions. In spite of series experimental data, the role of CRH and other members of its family, as well as its receptors in inflammation are still controversial. This dual role may be due to different CRF receptors and altered functionality. There are several putative mechanisms or ports of entry, in which the cytokines may affect HPA activity and CRH release. Some influences of cytokines on the HPA axis may be exerted by an indirect way. The aim of our review was to summarize and outline of key interacting agents based upon recent experimental results.

Increased plasma corticosterone levels after periaqueductal gray stimulation-induced escape reaction or panic attacks in rats

The hypothalamo–pituitary–adrenal (HPA) axis is involved in stress, depression and anxiety. Controversy exists on HPA axis activation during panic attacks (PAs). We examined whether the HPA axis is involved in the escape or panic-like response in an animal model of PAs induced by electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats. Additionally, rats were also treated with chronic administration of buspirone (BUSP) and escitalopram (ESCIT), respectively; and they were stimulated in the open-field arena for panic-like reaction. Levels of stress hormone corticosterone were measured following 30min after escape or panic condition. Our results demonstrated that the levels of plasma corticosterone were significantly increased after the induction of escape or panic-like response in comparison with the sham animals. The levels of corticosterone were significantly decreased in the dlPAG stimulated groups after rats were treated chronically with the ESCIT but not the BUSP as compared to the saline treated animals. Importantly, the increase of corticosterone level after escape or panic-like response was paralleled by an increase of neuronal activation of c-Fos in both the parvocellular and magnocellular paraventricular nucleus of the hypothalamus. Moreover, the c-Fos data also showed a decrease in the number of positive cells particularly for the ESCIT as well as the BUSP in comparison with the saline stimulated animals. In conclusion, the present study clearly demonstrated that PA or escape response activates the HPA axis and it remains difficult to anticipate the mechanism underlying HPA axis during PAs and its relationship with 5-HT drugs.

Food, stress, and reproduction: Short-term fasting alters endocrine physiology and reproductive behavior in the zebra finch

Stress is thought to be a potent suppressor of reproduction. However, the vast majority of studies focus on the relationship between chronic stress and reproductive suppression, despite the fact that chronic stress is rare in the wild. We investigated the role of fasting in altering acute stress physiology, reproductive physiology, and reproductive behavior of male zebra finches ( Taeniopygia guttata) with several goals in mind. First, we wanted to determine if acute fasting could stimulate an increase in plasma corticosterone and a decrease in corticosteroid binding globulin (CBG) and testosterone. We then investigated whether fasting could alter expression of undirected song and courtship behavior. After subjecting males to fasting periods ranging from 1 to 10 h, we collected plasma to measure corticosterone, CBG, and testosterone. We found that plasma corticosterone was elevated, and testosterone was decreased after 4, 6, and 10 h of fasting periods compared with samples collected from the same males during nonfasted (control) periods. CBG was lower than control levels only after 10 h of fasting. We also found that, coincident with these endocrine changes, males sang less and courted females less vigorously following short-term fasting relative to control conditions. Our data demonstrate that acute fasting resulted in rapid changes in endocrine physiology consistent with hypothalamo–pituitary–adrenal axis activation and hypothalamo–pituitary–gonadal axis deactivation. Fasting also inhibited reproductive behavior. We suggest that zebra finches exhibit physiological and behavioral flexibility that makes them an excellent model system for studying interactions of acute stress and reproduction.

In Vivo Cerebrovascular Effects of Cocaine- and Amphetamine-Regulated Transcript (CART) Peptide

Cocaine- and amphetamine-regulated transcript (CART) and its associated peptides have been implicated in a number of physiologic processes including modulation of the hypothalamo-pituitary-adrenal (HPA) axis and cardiovascular regulation. Recently, we reported that in isolated cerebral arterioles, CART peptide (CARTp) acts directly to produce endothelium-dependent constriction via the endothelin signaling pathway. We used the rat closed cranial window model to determine the in vivo effects of CARTp on pial arteriolar diameter. Intravenous administration of 30 microg/kg CARTp produced a significant pressor effect and constriction of pial arterioles. The pressor response to systemic CARTp was blocked by the beta-adrenergic receptor antagonist propranolol (2 mg/kg IV). Direct application of 0.1 nM-1 microM CARTp to pial arterioles produced a dose-dependent and long-lasting constriction to approximately 88% of baseline diameter. The constriction response to topically applied 100 nM CARTp was blocked by both the endothelin A (ETA) receptor antagonist BQ-123 (10 microM) and the inhibitor of endothelin-converting enzyme, phosphoramidon (100 nM). These results demonstrate for the first time that CARTp constricts cerebral vessels in vivo, an action mediated by its effects on the endothelin system, specifically via activation of ETA receptors. This supports the notion that CARTp plays a physiologic role in cerebrovascular regulation, particularly during times of HPA axis activation.

Erythropoietin Inhibits Basal and Stimulated Corticotropin-Releasing Hormone Release from the Rat Hypothalamus via a Nontranscriptional Mechanism

Brain hypoxia-ischemia induces a local increase in the levels of erythropoietin (EPO) and vascular endothelial growth factor (VEGF); this condition is also associated with acute activation of the hypothalamo-pituitary-adrenal (HPA) axis, suggesting that increased levels of EPO and VEGF in the hypothalamus may play a role in the control of HPA function. Thus, in this study we used rat hypothalamic explants to investigate whether EPO and VEGF can directly modulate CRH release; the latter was assessed by RIA measurement of the peptide in the incubation medium and hypothalamic tissue. EPO and VEGF effects were studied in short-term (1-3 h) experiments under basal conditions or after stimulation with 56 mM KCl or 10 microM veratridine. We observed that EPO (1-10 nm) significantly reduced CRH release and, in parallel, increased intrahypothalamic CRH content. VEGF tended to reduce CRH release without reaching statistical significance. Moreover, EPO, but not VEGF, inhibited KCl- and veratridine-stimulated CRH release and counteracted the parallel decrease in intrahypothalamic CRH induced by the two secretagogues. EPO effects were not mediated by modification of CRH gene expression, either in the absence or the presence of KCl or veratridine; in this paradigm, KCl and veratridine per se did not modify CRH gene expression. Our findings suggest that EPO contributes to the regulation of the HPA axis activation; in pathological conditions such as brain ischemia, this growth factor may control the HPA axis function, preventing possible detrimental effects of HPA overactivation.

Interleukin-6 levels and HPA axis activation in breast cancer patients with major depressive disorder

An association or a casual link has been proposed between the neuroendocrinological and neuroimmunological changes attributed to either depression or cancer. This study investigated whether breast cancer patients with and without major depression exhibit plasma interleukin-6 abnormalities and dexamethasone suppression test results. Four groups, each consisting of 30 women (1—healthy women, 2—patients with major depression, 3—breast cancer patients without major depression, 4—breast cancer patients with major depression), were compared to each other. Psychiatric evaluations were made by structured clinical interview for DSM-IV. Severity of depression was measured with the Hamilton Depression Rating Scale. Plasma levels of interleukin-6 were measured. A dexamethasone suppression test was applied. Breast cancer patients with major depression had markedly higher plasma levels of interleukin-6 than the other group. All breast cancer patients with depression had abnormal dexamethasone suppression test results. These findings suggest a hypothalamo-pituitary–adrenal axis activation and plasma levels of interleukin-6 and plasma interleukin-6 elevation and plasma levels if interleukin-6 and plasma levels of post cortisol concentrations. Evidence for a casual link or association of major depression with immune and endocrinological activation needs to be investigated further.

Glucocorticoid Resistance following Herpes Simplex-1 Infection: Role of Hippocampal Glucocorticoid Receptors

Herpes simplex-1 (HSV-1) is a sporadic cause of viral encephalitis. We have previously demonstrated that corneal HSV inoculation markedly activates the hypothalamo-pituitary-adrenal (HPA) axis. This activation depends on host derived brain interleukine-1 and was resistant to pretreatment with dexamethasone (dex), possibly because immune factors such as pro-inflammatory cytokines can modify the binding capacity of glucocorticoids in the hippocampus. In the present study, we examined whether resistance of the HPA axis activation following intracerebral HSV-1 infection to dex-induced suppression is associated with modifications in hippocampal or pituitary glucocorticoids (GC) receptors or GC receptors in cultured astrocytes. Male rats were injected intracerebroventricularly with purified HSV-1 or vehicle. 48 h later, dex or vehicle was injected intraperitoneally. Rats were sacrificed 3.5 h later. ACTH and corticosterone (CS) were measured in the serum. Specific binding of ³H-dex was measured in the cytosolic fraction of the hippocampus and the pituitary. Dex failed to reduce ACTH and CS responses to HSV-1 infection. In contrast, dex significantly reduced ACTH and CS responses to acoustic neural stimuli. Infection with HSV-1 markedly reduced the hippocampal maximal specific binding of dex with no effect on the dissociation constant (K_d) values. HSV-1 had no effect on the binding of dex in the pituitary. Infection of cultured astrocytes with HSV-1 also reduced the maximal specific binding of dex, but increased the K_dvalue. The results suggest that HSV-1 induced GC resistance may be mediated by downregulation of GC receptors in hippocampal tissue. These results may clarify a mechanism responsible for GC resistance following immune challenges.

High glucose activates pituitary proopiomelanocortin gene expression: possible role of free radical‐sensitive transcription factors

Hyperglycemia is recognized as a metabolic stress, and indeed it is known to stimulate hypothalamo-pituitary-adrenal (HPA) axis, a representative anti-stress system, in patients with diabetes mellitus or in animal models of hyperglycemia. Thus, we tried to clarify the molecular mechanism of glucose-induced HPA axis activation. We studied the effect of high glucose on the transcriptional regulation of proopiomelanocortin (POMC) gene that encodes adrenocorticotropic hormone, a central mediator of HPA axis, using AtT20 corticotroph cell line in vitro. We found that high glucose concentration (24 mM) significantly stimulated the 5'-promoter activity of POMC gene. The effect was promoter-specific, and was mimicked by nuclear factor-kappaB (NF-kappaB)- or AP1-responsive promoters but not by cAMP-responsive element or serum-response element-containing promoters. Furthermore, the stimulatory effect of high glucose on POMC gene was eliminated by NF-kappaB and AP1 inhibitors, suggesting the involvement of the transcriptional factors. The POMC 5'-promoter has the canonical NF-kappaB consensus sequence, and gel shift assay showed the binding of NF-kappaB to the element. Finally, the effect of high glucose was completely abolished by treatment with a radical quencher 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL). Our data suggest that hyperglycemia activates POMC gene expression, at least partly, via NF-kappaB/AP1, and that high-glucose-induced free radical generation may mediate the activation of these transcription factors, which in turn stimulates the transcription of POMC gene.

Involvement of Corticotropin-Releasing Hormone- and Interleukin (IL)-6-Dependent Proopiomelanocortin Induction in the Anterior Pituitary during Hypothalamic-Pituitary-Adrenal Axis Activation by IL-1α

IL-1alpha/beta and IL-6 are endogenous modulator of hypothalamo-pituitary-adrenal axis (HPAA) and are thought to play key roles in immune-neuroendocrine interactions during inflammation. Here, we show IL-1alpha induced a normal HPAA activation in IL-1alpha/beta knockout (KO) and IL-6 KO mice at 1 h; however, at 6 h HPAA activation was reduced relative to wild-type mice, indicating a role for endogenous IL-1alpha/beta and IL-6 in prolonged HPAA activation. We found that the induction of proopiomelanocortin (POMC) transcript in the anterior pituitary (AP) at 6 h in response to IL-1alpha was reduced in IL-1alpha/beta KO and IL-6 KO mice, as well as in CRH KO mice, suggesting IL-1alpha/beta, IL-6, and CRH are all required for POMC induction. The induction of CRH transcript in the paraventricular nucleus at 6 h and plasma IL-6 levels, in response to IL-1alpha, were reduced in IL-1alpha/beta KO mice. Because IL-1alpha-induced activation of signal transducer and activator of transcription 3 in the AP was also suppressed in IL-6 KO mice, we suggest that plasma IL-6 is first induced by IL-1alpha, and IL-6 activates signal transducer and activator of transcription 3 in the AP, leading to the induction of POMC in concert with CRH. Our results suggest a role for IL-1alpha/beta in the induction of POMC in the AP through the induction of two independent pathways, CRH and IL-6.

The role of vasopressin in hypothalamo-pituitary-adrenal axis activation during stress: an assessment of the evidence.

The hypothalamo-pituitary-adrenal (HPA) axis is a key component of the stress reaction. Most contemporary reviews mention the corticotropin-releasing hormone and arginine vasopressin (AVP)-containing parvocellular neurons of the hypothalamic paraventricular nucleus as the endocrinomotor component of the system. Although there are many studies about the role of AVP in the stress activation, there is evidence consistent and inconsistent with the general view on the importance of AVP. We propose a list of experiments that may provide critical evidence for or against the widely held opinion. The naturally AVP-deficient Brattleboro rat seems to be a good tool for studying the role of AVP. Our experiments on Brattleboro rats with restraint and ip hypertonic saline injection did not support the prominent role of AVP in acute stress, although in forced swim the lack of AVP influenced the HPA axis activation. Among different chronic stress situations (14 days' restraint, chronic morphine or ip hypertonic saline treatment, streptozotocin-induced diabetes mellitus), the role of AVP was not confirmed by changes in somatic parameter (i.e., body, thymus, and adrenal weight changes).

The role of endogenous interleukin-1 in stress-induced adrenal activation and adrenalectomy-induced adrenocorticotropic hormone hypersecretion.

To examine the role of IL-1 in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis, mice with knockout of the IL-1 receptor type I (IL-1rKO) were exposed to psychological and metabolic stressors. When exposed to mild stressors (auditory stress or a low dose of 2-deoxyglucose), IL-1rKO mice displayed a significantly diminished corticosterone secretion, compared with wild-type (WT) controls. In response to more severe stressors (60-min restraint or a high dose of 2-deoxyglucose), both groups exhibited a similar increase in corticosterone secretion. To examine the role of IL-1 in HPA axis feedback regulation, serum ACTH levels were measured after adrenalectomy (ADX) in IL-1rKO mice and in mice with transgenic overexpression of IL-1 receptor antagonist within the brain (IL-1raTG). As expected, WT controls exhibited ADX-induced ACTH hypersecretion, whereas IL-1rKO and IL-1raTG mice showed no increase in ACTH levels, suggesting that brain IL-1 has a critical role in ADX-associated ACTH hypersecretion. Similarly, WT mice that were chronically exposed to IL-1ra in utero displayed a diminished ADX-induced ACTH hypersecretion, compared with vehicle-treated controls, suggesting a developmental role of IL-1 in HPA axis regulation. In conclusion, our results suggest that endogenous IL-1 plays a critical role in HPA axis activation after stress and ADX.

HPA axis activation and neurochemical responses to bacterial translocation from the gastrointestinal tract.

Stress can cause migration of indigenous bacterial flora from the gut to the peritoneum, a phenomenon known as bacterial translocation. Destruction of the cell walls of gram-negative bacteria can result in the production of endotoxin (lipopolysaccharide, LPS), which is the likely cause of sepsis. Exogenously administered LPS can activate the hypothalamo-pituitary-adrenal (HPA) axis as well as brain noradrenergic and indoleaminergic systems. Thus, it is possible that activations of these systems associated with laboratory stressors in rats and mice could be attributed to bacterial translocation and LPS production. To test this hypothesis we conducted experiments on the time course of bacterial translocation in response to restraint in mice, while measuring HPA and neurochemical responses. These experiments failed to show good correlations between the occurrence of bacterial translocation and HPA and neurochemical activations, suggesting that the later responses were not linked to bacterial translocation. This conclusion was supported by the observation of normal neurochemical responses to restraint in germ-free mice. In further experiments, translocation of Salmonella typhimurium, a bacterium that readily translocates in unstressed animals, was associated with HPA activation and noradrenergic and indoleaminergic responses, indicating that bacterial translocation can indeed activate the HPA axis and brain amines. However, the above experiments suggest that this is not the mechanism by which restraint activates these systems.

Impaired adrenocorticotropic hormone response to bacterial endotoxin in mice deficient in prostaglandin E receptor EP1 and EP3 subtypes.

Sickness evokes various neural responses, one of which is activation of the hypothalamo-pituitary-adrenal (HPA) axis. This response can be induced experimentally by injection of bacterial lipopolysaccharide (LPS) or inflammatory cytokines such as IL-1. Although prostaglandins (PGs) long have been implicated in LPS-induced HPA axis activation, the mechanism downstream of PGs remained unsettled. By using mice lacking each of the four PGE receptors (EP1-EP4) and an EP1-selective antagonist, ONO-8713, we showed that both EP1 and EP3 are required for adrenocorticotropic hormone release in response to LPS. Analysis of c-Fos expression as a marker for neuronal activity indicated that both EP1 and EP3 contribute to activation of neurons in the paraventricular nucleus of the hypothalamus (PVN). This analysis also revealed that EP1, but not EP3, is involved in LPS-induced activation of the central nucleus of the amygdala. EP1 immunostaining in the PVN revealed its localization at synapses on corticotropin-releasing hormone-containing neurons. These findings suggest that EP1- and EP3-mediated neuronal pathways converge at corticotropin-releasing hormone-containing neurons in the PVN to induce HPA axis activation upon sickness.