Hypothalamo-pituitary-adrenal Axis Research Articles

Glucocorticoids Down-Regulate Lipopolysaccharide-Induced de novo Production of Neurotensin mRNA in the Rat Hypothalamic, Paraventricular, Corticotrophin-Releasing Hormone Neurons

Objective: Intraperitoneal injection of the endotoxin lipopolysaccharide (LPS) produces inflammation accompanied by activation of the immune system and the secretion of cytokines. Cytokines stimulate the hypothalamo-pituitary-adrenal (HPA) axis to release the anti-inflammatory corticosterone which controls its own production by acting on the HPA axis. Upstream in the HPA axis are neuroendocrine corticotrophin-releasing hormone (CRH) neurons located in the paraventricular nucleus (PVN), whose multipeptidergic phenotype changes during inflammation: while CRH mRNA is up-regulated in these conditions, neurotensin (NT) mRNA expression is induced de novo. The negative feedback control of glucocorticoids on CRH production is well documented; however, their action on NT production in the PVN of the hypothalamus is poorly documented. The aim of this study was to determine if glucocorticoids modulate the de novo production of NT during inflammation. Methods: Using quantitative in situ hybridization histochemistry, we examined whether the absence (adrenalectomy) or excess (corticosterone implants) of glucocorticoids modulate de novo production of NT mRNA in the PVN during inflammation induced by LPS treatment. Results: A relatively low dose of LPS (50 µg/kg) that is not efficient to induce NT mRNA production in the PVN becomes efficient after adrenalectomy. Moreover, corticosterone excess reduces LPS-induced production of NT mRNA in the PVN. Conclusion: Glucocorticoids exert a negative control on NT mRNA production in the PVN of the hypothalamus, and this effect requires that NT mRNA production be triggered, such as during inflammation.

Rebuttal: Depression is Not a Brain Disease

Joanna Moncrieff, MBBS, MRCPysch, MSc, MD1 (Can J Psychiatry 2007;52:100-101) Psychiatrists have been trying to construct a biological theory of depression for decades. Numerous candidates have been proposed, from noradrenalin and serotonin abnormalities to cortisol excess, hippocampal insufficiency, and neurotrophic factor. In all cases, results are inconsistent, and where abnormalities are found, they have not been shown to be specific or causal. For example, contrary to Dr Ravindran and Dr Kennedy's suggestions, the evidence on hippocampal volume is weak. Numerous studies show no difference between subjects with depression and control subjects, and I could not find studies supporting their assertion that duration of untreated illness correlates with volume reduction. In contrast, studies show that duration of treated illness predicts volume reduction.1,2 This raises the possibility that drug treatments for depression reduce brain volume in the same fashion as antipsychotics have been shown to do in patients with psychosis.3 In addition, loss of hippocampal volume is also found in first-episode psychosis4 and posttraumatic stress disorder5 and was recently shown in women diagnosed with dissociative identity disorder.6 Metabolic abnormalities sometimes found in depression are also not specific. For example, acute psychosis is also associated with increased hypothalamopituitary-adrenal axis function.7 Even if biochemical or structural abnormalities were found to be associated with depression, this would not imply that they were causal. If I experience an adverse event, I will feel sad, and if this emotion is strong enough, there are likely to be associated biochemical changes-but it is the event that has made me sad, not the chemical fluctuations. They are best viewed as an accompaniment, or a biological correlation, of the emotional state. In my first piece, I concentrated on placebo-controlled studies because it is difficult to show any real-world benefits from the use of antidepressants. In fact, their increased use is associated with increasing prevalence and duration of depressive episodes. The naturalistic Sequenced Treatment Alternatives to Relieve Depression trial found remission rates that are unimpressive in a naturally remitting condition, although the fact that this study did not include a placebo group means this valuable opportunity to evaluate the effectiveness of antidepressants was wasted.8 The study on absence due to sickness quoted by Ravindran and Kennedy actually found that individuals treated with antidepressants were less likely to return to work than those who were not treated with them (P Findings that patients who comply with optimal or adequate dosages do better than those who do not probably reflect the fact that individuals who comply with any treatment, including placebo, have better outcomes than those who do not.10 The study of quality of life was a discontinuation study that demonstrated a deterioration in individuals who had improved on drug treatment and were then randomized to placebo. As such, it provides no information on the benefits of antidepressants when they are compared with prospectively started placebo treatment.11 We do indeed live in an age characterized by an epidemic of psychological disorders.12, p 40 However, the mass prescribing of antidepressants and the concomitant message that depression is a brain disease have helped to create this situation, not to improve it. By persuading people that their thoughts and feelings originate from a biological defect, we are preventing them from finding real solutions to the complex problems of modern living.

Pathophysiology of hypercortisolism in depression

The mechanisms mediating hypercortisolemia in depression remain controversial. Adopting the biomarker strategy, we studied adrenocorticotropin (ACTH) and cortisol dynamics in hypercortisolemic and non-hypercortisolemic depressed in-patients, and in normal volunteers. Deconvolution analysis of 24-h pulsatile secretion, approximate entropy (ApEn) estimation of secretory regularity, cross-ApEn quantitation of forward and reverse ACTH-cortisol synchrony, and cosine regression of 24-h rhythmicity. Hypercortisolemia was strongly associated with melancholic and psychotic depressive subtypes. Hypercortisolemic patients had elevated ACTH and cortisol secretion, mediated chiefly by increased burst masses. Basal ACTH secretion was increased, ACTH half-life was reduced, and mean 24-h ACTH concentration was normal. Cortisol secretion was increased in a highly irregular pattern (high ApEn), with high ACTH --> cortisol cross-ApEn (impaired feedforward coupling). Cortisol-mediated feedback on the secretory pattern of ACTH was normal. Hypercortisolemic depressed patients had normal programming of the central hypothalamo-pituitary-adrenal (HPA) axis pulse generator: ACTH pulse frequency, cortisol pulse frequency, circadian acrophases, and ApEn of ACTH secretion were normal. Responsiveness of the adrenal cortex to endogenous ACTH was normal. Non-hypercortisolemic patients resembled hypercortisolemic patients on ACTH regulatory parameters but had low total cortisol secretion. Increased ACTH secretion occurs in depressed in-patients regardless of cortisolemic status, confirming central HPA axis overdrive in severe depression. Depressive hypercortisolemia results from an additional change in the adrenal cortex that causes ACTH-independent, disorderly basal cortisol release, a sign of physiological stress in melancholic/psychotic depression.

The hypothalamo–pituitary–adrenal axis in chronic fatigue syndrome and fibromyalgia syndrome

The hypothalamo–pituitary–adrenal (HPA) axis plays a major role in the regulation of responses to stress. Human stress-related disorders such as chronic fatigue syndrome (CFS), fibromyalgia syndrome (FMS), chronic pelvic pain and post-traumatic stress disorder are characterized by alterations in HPA axis activity. However, the role of the HPA axis alterations in these stress-related disorders is not clear. Most studies have shown that the HPA axis is underactive in the stress-related disorders, but contradictory results have also been reported, which may be due to the patients selected for the study, the methods used for the investigation of the HPA axis, the stage of the syndrome when the tests have been done and the interpretation of the results. There is no structural abnormality in the endocrine organs which comprise the HPA axis, thus it seems that hypocortisolemia found in the patients with stress-related disorder is functional. It may be also an adaptive response of the body to chronic stress. In this review, tests used in the assessment of HPA axis function and the HPA axis alterations found in CFS and FMS are discussed in detail.

“Buffalo” hump in nonalcoholic fatty liver disease

I read with interest the recent article by Cheung et al.1 regarding the impact of fat distribution, as estimated by several anthropometric parameters, on the severity of nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome in obese NAFLD patients. Notably, they found that dorsocervical lipohypertrophy (“buffalo” hump) was the single greatest predictor of the histological severity of NAFLD, whereas waist circumference was the greatest predictor of the severity of metabolic syndrome.1 Dorsocervical lipohypertrophy (DCL) was diagnosed only clinically but no quantitative measure (for example, ultrasound imaging) was used for diagnosing the “hump” at the base of the neck. Obviously, this is a major limitation of the study. Additionally, it is conceivable that the differential impact of DCL and waist circumference on the severity of NAFLD histology and metabolic syndrome is simply due to the fact that they are only indirect and crude indices of abdominal visceral fat distribution.2 A direct and more accurate measure of abdominal visceral fat, obtained by computed tomography or magnetic resonance imaging,2 would be useful to explore this issue adequately. However, the authors have interestingly shown that DCL, which is commonly seen in Cushing's syndrome, is a highly prevalent condition (28.5%) in obese NAFLD patients,1 thus suggesting an underlying subclinical hypercortisolism in NAFLD. Regarding this, recent studies have consistently shown a subclinical hypothalamo-pituitary-adrenal (HPA) axis dysfunction in NAFLD. Westerbacka et al.3 reported that obese men with higher liver fat content (as evaluated by magnetic resonance imaging spectroscopy) have a selective increase in 24-hour urinary excretion of 5-beta-reduced cortisol metabolites and a lower ratio of urinary cortisol/cortisone metabolites than men with lower liver fat content. Saruc et al.4 found that postmenopausal women with NAFLD, as assessed by ultrasound, have higher plasma dehydroepiandrosterone levels than controls. Others have shown that obese individuals5 and overweight type 2 diabetic patients6 with ultrasonographically diagnosed NAFLD have higher 24-hour urinary free cortisol excretion and postdexamethasone suppression cortisol concentrations than nonsteatotic controls. More importantly, we have recently demonstrated that overweight patients with biopsy-proven NAFLD have a subclinical, chronic HPA axis activation (as reflected by the increased, albeit still normal, 24-hour urinary free cortisol values and the blunted suppression of cortisol levels by 1.0 mg-dexamethasone with normal serum corticosteroid-binding globulin concentrations) that is correlated to the histopathological severity of NAFLD (that is, necro-inflammatory grade and fibrosis stage) independently of multiple potential confounders, including insulin resistance and metabolic syndrome components.7 Overall, therefore, the evidence from these studies,3-7 although only correlative in nature, suggests the hypothesis that overweight/obese NAFLD patients have a subtle HPA axis dysfunction that is strongly correlated with the severity of NAFLD histology, leading to subclinical cortisol overproduction that might be implicated in the development/progression of NAFLD. Future prospective and interventional (by using a cortisol inhibitor or specific 11beta-hydroxysteroid dehydrogenase-type 1 inhibitors) studies are obviously needed to validate this hypothesis and to better understand the underlying biological mechanisms linking HPA axis dysfunction to the development of NAFLD. Giovanni Targher M.D.*, * Section of Endocrinology, Department of Biomedical and Surgical Sciences, University Hospital, Verona, Italy.

Acute and chronic neuroendocrine effects of interferon‐β 1a in multiple sclerosis

Treatment of multiple sclerosis with interferon-beta (IFN-beta) results in variable responses interindividually. Cytokine-hormone interactions may modulate the therapeutic effects of IFN-beta. Since hyperactivity of the hypothalamo-pituitary-adrenal (HPA) axis and other neuroendorine disturbances occur in multiple sclerosis, we determined the detailed neuroendocrine response of patients with multiple sclerosis to IFN-beta. Longitudinal open-label study. Eight patients with relapsing-remitting multiple sclerosis (four women, age 31.9 +/- 1.5 years, EDSS 1.5-2.5). Plasma ACTH, cortisol, prolactin, GH, TSH, LH and FSH were determined in 30-min intervals during 8 h on four occasions: after intramuscular injection of saline; after the first dose of IFN-beta 1a; after the second IFN-beta dose with oral indomethacin pretreatment; and after 3 months of IFN-beta therapy. Dexamethasone-corticotropin-releasing hormone test was performed before and at 3 months on IFN-beta. Compared to saline, IFN injection resulted in marked rise in plasma ACTH (mean, 370% of baseline), cortisol (214%), prolactin (253%) and GH (756%), between 2 and 6 h after injection. With indomethacin, hormone secretion occurred with reduced peak values. Endocrine response adapted partially after 3 months of treatment. HPA axis activity decreased in most patients, but increased in one patient with frequent relapses. Marked neuroendocrine effects occur in response to IFN-beta in multiple sclerosis. Upon prolonged treatment, these effects partially adapt, and HPA axis hyperactivity is reduced. Prospective studies to determine the relation to individual treatment response can be based on these findings.

CP-154,526, a CRF type-1 receptor antagonist, attenuates the cue-and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior in rats

Previous studies from our laboratory and others have indicated a role for the hypothalamo-pituitary-adrenal (HPA) axis in the extinction/reinstatement animal model of cocaine relapse This present study was designed to investigate the potential role for the HPA axis in the cue- and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior by determining the effects of ketoconazole and the corticotropin-releasing hormone (CRF) type 1 receptor antagonist, CP-154,526, on these behaviors. Male Wistar rats were trained to self-administer methamphetamine (0.03 mg/kg/infusion). The delivery of methamphetamine was paired with the presentation of a tone and the illumination of a house light. Once stable responding was reached, the rats were placed into extinction. The effects of pretreatment with ketoconazole (25, 50, or 100 mg/kg, i.p.) or CP-154,526 (20 or 40 mg/kg, i.p.; 3 micro g, i.c.v) on cue-induced reinstatement were then evaluated. Cue-induced reinstatement was not significantly attenuated by pretreatment with peripherally administered CP-154,526 or by pretreatment with ketoconazole. However, centrally administered CP-154,526 (3 micro g, i.c.v.) significantly attenuated cue-induced reinstatement. In a separate group of rats, CP-154,526 (20 mg/kg, i.p.) attenuated methamphetamine-induced reinstatement (0.12 mg/kg priming infusion); whereas a higher dose (40 mg/kg) was necessary to attenuate reinstatement induced by a priming infusion of 0.24 mg/kg/infusion. Ketoconazole (50 mg/kg) did not affect reinstatement induced by a 0.12 mg/kg priming infusion and, therefore, was not tested at the higher methamphetamine priming dose. These data suggest an important role for CRF in the cue- and methamphetamine-induced reinstatement of extinguished methamphetamine-seeking behavior.

Effects of the Short Chain Sugar Acid 2‐Buten‐4‐Olide on the Hypothalamo‐Pituitary‐Adrenal Axis in Normal and Adjuvant‐Induced Arthritic Rats

The effects of intraperitoneal (i.p.) administration of 2-buten-4-olide (2-B4O), an endogenous sugar acid, on the hypothalamo-adenohypophysial system were examined in Lewis rats that were normal and in adjuvant-induced arthritic (AA) rats. In comparison with vehicle-treated rats, the plasma corticosterone and c-fos mRNA levels in the paraventricular nucleus (PVN) of normal rats increased significantly after i.p. administration of 2-B4O. Dual immunostaining revealed that almost all corticotrophin-releasing factor (CRF)-immunopositive neurones in the parvocellular division of the PVN exhibited Fos-like immunoreactivity (LI) 120 min after i.p. administration of 2-B4O (100 mg/kg). In the AA rats, repeated i.p. administration of 2-B4O (100 mg/kg) after immunisation significantly suppressed the expression of clinical symptoms and significantly increased plasma concentrations of corticosterone. Further, repeated i.p. administration of 2-B4O significantly increased CRF mRNA levels in the PVN and pro-opiomelanocortin mRNA levels in the anterior pituitary; however, they did not change arginine vasopressin mRNA levels in the parvocellular division of the PVN. These results suggest that i.p. administration of 2-B4O activates the hypothalamo-pituitary-adrenal (HPA) axis via the activation of CRF neurones in the PVN, and the activation of the HPA axis by i.p. administration of 2-B4O may be associated with the inhibition of AA in rats.

Role of Brg1 and HDAC2 in GR trans-repression of the pituitary POMC gene and misexpression in Cushing disease

Negative feedback regulation of the proopiomelanocortin (POMC) gene by the glucocorticoid (Gc) receptor (GR) is a critical feature of the hypothalamo-pituitary-adrenal axis, and it is in part exerted by trans-repression between GR and the orphan nuclear receptors related to NGFI-B. We now show that Brg1, the ATPase subunit of the Swi/Snf complex, is essential for this trans-repression and that Brg1 is required in vivo to stabilize interactions between GR and NGFI-B as well as between GR and HDAC2. Whereas Brg1 is constitutively present at the POMC promoter, recruitment of GR and HDAC2 is ligand-dependent and results in histone H4 deacetylation of the POMC locus. In addition, GR-dependent repression inhibits promoter clearance by RNA polymerase II. Thus, corecruitment of repressor and activator at the promoter and chromatin modification jointly contribute to trans-repression initiated by direct interactions between GR and NGFI-B. Loss of Brg1 or HDAC2 should therefore produce Gc resistance, and we show that approximately 50% of Gc-resistant human and dog corticotroph adenomas, which are the hallmark of Cushing disease, are deficient in nuclear expression of either protein. In addition to providing a molecular basis for Gc resistance, these deficiencies may also contribute to the tumorigenic process.

Chronic restraint or variable stresses differently affect the behavior, corticosterone secretion and body weight in rats

Organisms are constantly subjected to stressful stimuli that affect numerous physiological processes and activate the hypothalamo-pituitary-adrenal (HPA) axis, increasing the release of glucocorticoids. Exposure to chronic stress is known to alter basic mechanisms of the stress response. The purpose of the present study was to compare the effect of two different stress paradigms (chronic restraint or variable stress) on behavioral and corticosterone release to a subsequent exposure to stressors. Considering that the HPA axis might respond differently when it is challenged with a novel or a familiar stressor we investigated the changes in the corticosterone levels following the exposure to two stressors: restraint (familiar stress) or forced novelty (novel stress). The changes in the behavioral response were evaluated by measuring the locomotor response to a novel environment. In addition, we examined changes in body, adrenals, and thymus weights in response to the chronic paradigms. Our results showed that exposure to chronic variable stress increased basal plasma corticosterone levels and that both, chronic restraint and variable stresses, promote higher corticosterone levels in response to a novel environment, but not to a challenge restraint stress, as compared to the control (non-stressed) group. Exposure to chronic restraint leads to increased novelty-induced locomotor activity. Furthermore, only the exposure to variable stress reduced body weights. In conclusion, the present results provide additional evidence on how chronic stress affects the organism physiology and point to the importance of the chronic paradigm and challenge stress on the behavioral and hormonal adaptations induced by chronic stress.

Cannabinoid CB 1 receptor antagonism modulates plasma corticosterone in rodents

Although the involvement of cannabinoids and the endogenous cannabinoid system in the regulation of the hypothalamo–pituitary–adrenal axis in rodents is well documented, the precise role played by the cannabinoid type one (CB 1) receptor in this effect has not been fully elucidated. Consequently, we investigated the role of CB 1 receptor in modulating plasma corticosterone concentrations through use of the potent and selective CB 1 receptor antagonist SR141716A and CB 1 receptor knockout mice. Rats were administered SR141716A (0.1, 0.3, and 1 mg/kg, i.v.) and blood was sampled at 0, 15, 60, 90 and 120 min postinjection. SR141716A dose- and time-dependently increased plasma corticosterone levels and maximum effects were obtained with the 1 mg/kg dose 60 min postinjection. In mice, SR141716A (0.1, 0.3, 1, 3, and 10 mg/kg, i.p.) also induced a dose-dependent rise in corticosterone levels 60 min postinjection; this rise reached plateau levels with the 0.3–1 mg/kg doses. The stimulatory effect of SR141716A (1 mg/kg, i.p.) on plasma corticosterone 60 min postinjection was abolished in the CB 1 receptor knockout mice, which did not show any difference in basal corticosterone levels as compared to their wild-type controls. Finally, the stimulatory effects of SR141716A (10 mg/kg, i.p.) on plasma corticosterone 60 min postinjection were retained after subchronic dosing (5 days, once daily) in mice. The present results indicate that SR141716A increases plasma corticosterone in rats and mice possibly through blockade of CB 1 receptors, an effect that is retained after subchronic dosing in mice. These data provide support for the notion that changes in plasma corticosterone concentrations may be used in the laboratory and the clinic to assess the effects of CB 1 receptor antagonism.

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.

Atomoxetine increases salivary cortisol in healthy volunteers

It has been proposed that acute hypothalamo-pituitary-adrenal (HPA) axis challenge using noradrenergic drugs may be of utility in assessing the functional integrity of central noradrenaline pathways. Atomoxetine (formerly tomoxetine) is a highly selective noradrenaline reuptake inhibitor, which has recently been licensed for the treatment of attention deficit hyperactivity disorder (ADHD). The aim of this study was to assess the effects of acute atomoxetine on salivary cortisol levels for the first time.A total of 60 healthy male volunteers received 60 mg atomoxetine, 30 mg citalopram, or placebo per os in a double-blind parallel groups design (n = 20 per group). Salivary cortisol, blood pressure and pulse rates were recorded at baseline and at +1.0, +1.5, +2.5 and +3.5 hours after capsule administration.60 mg atomoxetine led to highly significant increases in salivary cortisol and a moderate increase in pulse rate, in the absence of significant effects on blood pressure. 30 mg citalopram had no significant effects on cortisol or cardiovascular parameters. These data support the utility of atomoxetine neuroendocrine challenge for evaluating central noradrenaline pathways, which may be of future use in neuropsychiatric patient studies. Furthermore, the effects of atomoxetine on HPA axis function may have clinical implications given the use of this agent in the treatment of ADHD.

Immunocytochemical Detection of Cholecystokinin and Corticotrophin‐Releasing Hormone Neuropeptides in the Hypothalamic Paraventricular Nucleus of the Jerboa (Jaculus orientalis): Modulation by Immobilisation Stress

The hypothalamic response to an environmental stress implicates the corticotrophin-releasing hormone (CRH) neuroendocrine system of the hypothalamic parvicellular paraventricular nucleus (PVN) in addition to other neuropeptides coexpressed within CRH neurones and controlling the hypothalamo-pituitary-adrenal (HPA) axis activity as well. Such neuropeptides are vasopressin, neurotensin and cholecystokinin (CCK). It has previously been demonstrated that the majority of the CRH neuronal population coexpresses CCK after a peripheral stress in rats. In the present study, we explored such neuroendocrine plasticity in the jerboa in captivity as another animal model. In particular, we studied CCK and CRH expression within the hypothalamic PVN by immunocytochemistry in control versus acute immobilisation stress-submitted jerboas. The results show that CCK- and CRH-immunoreactive neuronal systems are located in the hypothalamic parvicellular PVN. The number of CCK-immunoreactive neurones within the PVN was significantly increased (138% increase) in stressed animals compared to controls. Similarly, the number of CRH-containing neurones was higher in stressed jerboas (128%) compared to controls. These results suggest that the neurogenic stress caused by immobilisation stimulates CCK as well as CRH expression in jerboas, which correlates well with previous data obtained in rats using other stressors. The data obtained also suggest that, in addition to CRH, CCK is another neuropeptide involved in the response to stress in jerboa, acting by controlling HPA axis activity. Because CCK is involved in the phenotypical plasticity of CRH-containing neurones in response to an environmental stress, we also explored their coexpression by double immunocytochemistry within the PVN and the median eminence (i.e. the site of CRH and CCK corelease in the rat) following jerboa immobilisation. The results show that CCK is not coexpressed within CRH neurones in either control or stressed jerboa, suggesting differences between jerboas and rats in the neuroendocrine regulatory mechanisms of the stress response involving CRH and CCK. The adaptative physiological mechanisms to environmental conditions might vary from one mammal species to another.

Effects of Morris water maze testing on the neuroendocrine stress response and intrahypothalamic release of vasopressin and oxytocin in the rat

Adult male Wistar rats were trained in the Morris water maze (MWM) on 3 consecutive days to find a visible platform. Concomitantly, microdialysis samples from the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei were collected in order to monitor local release of the neuropeptides vasopressin (AVP) and oxytocin (OXT), respectively, during controllable swim stress. Additionally, a separate set of animals was equipped with chronic jugular venous catheters to collect blood samples for analyzing plasma concentrations of corticotropin (ACTH) and corticosterone during training in the MWM. As measured by microdialysis, swimming in the MWM caused a significantly increased release of AVP within the PVN and of OXT within the SON on each of the 3 test sessions. In contrast to OXT in the SON, basal AVP concentrations in the PVN tended to rise from day to day. Plasma ACTH and corticosterone were found to be similarly elevated in response to MWM exposure on each of the test sessions. Taken together, these data demonstrate that testing in the MWM is not only associated with a significant activation of the hypothalamo–pituitary–adrenal axis but also with an intrahypothalamic release of AVP and OXT. If compared with findings using repeated forced swimming as an uncontrollable stressor (Wotjak, C.T., Ganster, J., Kohl, G., Holsboer, F., Landgraf, R., Engelmann, M., 1998. Dissociated central and peripheral release of vasopressin, but not oxytocin, in response to repeated swim stress: new insights into the secretory capacities of peptidergic neurons. Neuroscience 85, 1209–1222), the present results suggest that (1) similarities in the release profiles of AVP in the PVN and plasma hormone levels are fairly independent from the controllability of the stressor and seem, thus, to primarily relate to the physical demands of the task, whereas (2) the different intra-SON OXT release profiles might be linked to the controllability of the stressor.

Hydroxyurea induces vasopressin release and cytokine gene expression in the rat hypothalamus

We previously showed that the cytostatic drug hydroxyurea (HU) activates the hypothalamo–pituitary–adrenal (HPA) axis in intact rats, whereas it is lethal in rats with impaired HPA function. In these animals, HU toxicity is mediated by increased circulating levels of proinflammatory cytokines, whose secretion cannot be counteracted by glucocorticoids, suggesting that HPA activation blunts HU toxicity. Here we investigated the mechanisms through which HU activates the HPA axis, looking at the direct effects of the drug on the isolated hypothalamus. We found that HU significantly increases the release of arginine vasopressin but not that of corticotrophin-releasing hormone in short-term incubation experiments. The levels of arginine vasopressin are also increased in the hypothalamus and systemic circulation 2 h after the in vivo administration of the drug. Furthermore, HU increased significantly the expression of interleukin-6 and, to a lesser extent, interleukin-1β in the hypothalamus. Interestingly, experiments with HU on primary cultures of rat microglia and astrocytes suggested that the increase in cytokine gene expression observed in hypothalamic explants is not accounted for by glial cells. Since both vasopressin and cytokines can activate the HPA axis, our present findings provide a reasonable explanation of the HPA activation elicited by HU in vivo in the rat.

Lack of Trimethyltin (TMT)‐Induced Elevation of Plasma Corticosterone in PACAP‐Deficient Mice

Accumulating evidence implicates pituitary adenylate cyclase-activating polypeptide (PACAP) in a number of stress responses. By using PACAP-deficient mice, PACAP has been shown to have an in vivo role in the regulation of the sympathoadrenal axis, but a role in regulating the hypothalamo-pituitary-adrenal (HPA) axis has not been fully addressed. To elucidate the role of endogenous PACAP in HPA axis regulation during pathological conditions, mice lacking the Adcyap1 gene encoding the neuropeptide PACAP (Adcyap1-/-) were injected with trimethyltin (TMT), a neurotoxin known to induce neuronal damage and several systemic responses including elevated plasma corticosterone levels. In wild-type controls, TMT induced transient decreases in water and food intake, with a concomitant decrease in body weight; however, no significant changes were observed in Adcyap1-/- mice. Basal corticosterone levels were not significantly different between the mutant and wild-type mice. TMT induced a marked elevation of plasma corticosterone above basal levels in wild-type mice but no significant increase was seen in Adcyap1-/- mice. The present article suggests that PACAP is involved in the corticosterone release in some pathological conditions but not in the basal state.

Intrathecal clonidine suppresses zymosan-induced peripheral leukocyte migration in a mouse air pouch model via activation of spinal muscarinic type 2 receptors and sympathoadrenal medullary activity

These studies were performed to examine the potential anti-inflammatory effect of intrathecal (IT) clonidine (an α 2-adrenoceptor agonist) on zymosan-induced leukocyte migration in a mouse air pouch model. IT clonidine dose-dependently suppressed zymosan-induced leukocyte migration and this effect was blocked by IT idazoxan (an α 2-adrenoceptor antagonist) pretreatment. Since a number of studies have previously shown that spinal α 2-adrenoceptors are functionally associated with spinal cholinergic activity, we next examined whether spinal acetylcholine (ACh) receptors were also involved in mediating this anti-inflammatory effect of IT clonidine. IT pretreatment with atropine (a muscarinic receptor antagonist), but not hexamethonium (a nicotinic receptor antagonist) completely blocked the anti-migratory effect of IT clonidine. Subsequent experiments showed that IT pretreatment with methoctramine (a muscarinic M 2 antagonist), but not pirenzepine (an M 1 antagonist) or 4-DAMP (an M 3 antagonist), suppressed clonidine's anti-inflammatory effect. Finally, we studied the potential roles of the sympathetic nervous system and the hypothalamo-pituitary–adrenal axis in clonidine's anti-inflammatory effect. Adrenalectomy or systemic injection of propranolol (a β-adrenoceptor antagonist) blocked clonidine's effect. However, pretreatment with RU486 (a corticosteroid antagonist) or peripheral sympathetic denervation using 6-hydroxydopamine had no effect. Furthermore, IT clonidine increased Fos expression in zymosan treated mice exclusively in T7–T11 sympathetic preganglionic neurons (which mainly project to the adrenal medulla), but not those of the T1–T6 or T12–L2 spinal segments. Moreover, IT methoctramine significantly reduced this increase in Fos expression. Collectively, these findings suggest that IT clonidine suppresses peripheral leukocyte migration via a sympathoadrenal medullary pathway, and that this suppressive effect is mediated by spinal M 2 receptors.

A comparison between the effects of low (1 µg) and standard dose (250 µg) ACTH stimulation tests on adrenal cortex functions with Behçet's disease

Behçet's disease is a rare, chronic disorder. The cause of Behçet's disease is unknown. It is believed to be caused by an autoimmune reaction. As in other chronic autoimmune diseases, Behçet's disease may show a subclinical adrenal failure and some changes in cortisol levels. We aimed to evaluate adrenal gland function in Behçet's disease patients. This study included 18 Behçet's disease patients and 15 healthy controls. Patient and control groups were administered i.v. 1 microg low dose test (LDT) and 250 microg standard dose test (SDT) adrenocorticotropic hormone (ACTH) stimulation test after 12 h of night fasting with an interval of 3-days and cortisol responses in the 0th, 30th and 60th minutes were evaluated. There was no statistically significant difference between basal cortisol values of Behçet's disease and control groups. Cortisol values in the 60th minute in LDT were significantly lower in Behçet's disease group than in the control group. In the peak cortisol responses to LDT, a significant decrease was found in Behçet's disease group. These findings suggest that hypothalamo-pituitary adrenal axis is partially suppressed in Behçet's disease.

Stress et obésité

Stress is often a subjective idea. Clinical data suggest that stressful situations may exert an influence upon the weight. Many epidemiological studies have shown a link between stress and weight gain; this may be in accordance with a symbolic stress such as social or mental stress from working conditions. A relationship occurs between socio-economic class and obesity and could be due to the social stress. The mechanisms which are involved are dietary behaviour and food intake, in case of stressful situations changes, particulary in restreint subjects. Many other data are concerning the hypothalamo pituitary adrenal axis and the nervous sympathic system which are stimulated by stress. Although the plasma cortisol concentrations are normal in obesity, there is an overproduction and an high reactivity of cortisol in obesity. The loco-regional synthesis of cortisol in the visceral adipose tissue with the 11 beta-hydroxysteroid-deshydrogenase may contribute to increase the adipocyte differenciation and proliferation. This may particularly explain the higher metabolic and cardiovascular risk in stressed subjects. Other hormonal disturbances including leptin, resistine, melanocortin are observed. The permanent sympathic stimulation may induces a beta adrenergic desensitization effect. Omega 3 fatty acids may be useful for decreasing stress and some metabolic effects of stress.