Differential involvement of rat medial prefrontal cortex dopamine receptors in modulation of hypothalamic-pituitary-adrenal axis responses to different stressors

Recent investigations have implicated the medial prefrontal cortex (mPFC) in modulation of subcortical pathways that contribute to the generation of behavioural, autonomic and endocrine responses to stress. However, little is known of the mechanisms involved. One of the key neurotransmitters involved in mPFC function is dopamine, and we therefore aimed, in this investigation, to examine the role of mPFC dopamine in response to stress in Wistar rats. In this regard, we infused dopamine antagonists SCH23390 or sulpiride into the mPFC via retrodialysis. We then examined changes in numbers of cells expressing the c-fos immediate-early gene protein product, Fos, in subcortical neuronal populations associated with regulation of hypothalamic-pituitary-adrenal (HPA) axis stress responses in response to either of two stressors; systemic injection of interleukin-1beta, or air puff. The D-1 antagonist, SCH23390, and the D-2 antagonist, sulpiride, both attenuated expression of Fos in the medial parvocellular hypothalamic paraventricular nucleus (mpPVN) corticotropin-releasing factor cells at the apex of the HPA axis, as well as in most extra-hypothalamic brain regions examined in response to interleukin-1beta. By contrast, SCH23390 failed to affect Fos expression in response to air puff in any brain region examined, while sulpiride resulted in an attenuation of the air puff-induced response in only the mpPVN and the bed nucleus of the stria terminalis. These results indicate that the mPFC differentially processes the response to different stressors and that the two types of dopamine receptor may have different roles.

Evaluation of random plasma cortisol and the low dose corticotropin test as indicators of adrenal secretory capacity in critically ill patients: A prospective study

It is unclear whether a random plasma cortisol measurement and the corticotropin (ACTH) test adequately reflect glucocorticoid secretory capacity in critical illness. This study aimed to determine whether these tests provide information representative of the 24 hour period. Plasma cortisol was measured hourly for 24 hours in 21 critically ill septic patients followed by a corticotropin test with 1 μ g dose administered intravenously. Serum and urine were analysed for ACTH and free cortisol respectively. Marked hourly variability in plasma cortisol was evident (coefficient of variation 8-30%) with no demonstrable circadian rhythm. The individual mean plasma cortisol concentrations ranged from 286 59 nmol/l to 796 &PLUSMN; 83 nmol/l. The 24 hour mean plasma cortisol was strongly correlated with both random plasma cortisol (r(2) 0.9, P< 0.0001) and the cortisol response to corticotropin (r(2) 0.72, P< 0.001). Only nine percent of patients increased their plasma cortisol by 250 nmol/l after corticotropin (euadrenal response). However, 35% of non-responders had spontaneous hourly rises > 250 nmol/l thus highlighting the limitations of a single point corticotropin test. Urinary free cortisol was elevated (865&PLUSMN; 937 nmol) in both corticotropin responders and non-responders suggesting elevated plasma free cortisol. No significant relationship was demonstrable between plasma cortisol and ACTH. We conclude that although random cortisol measurements and the low dose corticotropin tests reliably reflect the 24 hour mean cortisol in critical illness, they do not take into account the pulsatile nature of cortisol secretion. Consequently, there is the potential for erroneous conclusions about adrenal function based on a single measurement. We suggest that caution be exercised when drawing conclusions on the adequacy of adrenal function based on a single random plasma cortisol or the corticotropin test.

Prolactin and the expression of suppressor of cytokine signaling-3 in the sheep adrenal gland before birth

Prolactin and the expression of suppressor of cytokine signaling-3 in the sheep adrenal gland before birth. Am J Physiol Regul Integr Comp Physiol 291: R1399-R1405, 2006. First published June 29, 2006; doi: 10.1152/ajpregu.00252.2006.-The fetal pituitary-adrenal axis plays a key role in the fetal response to intrauterine stress and in the timing of parturition. The fetal sheep adrenal gland is relatively refractory to stimulation in midgestation (90-120 days) before the prepartum activation, which occurs around 135 days gestation (term = 147 +/- 3 days). The mechanisms underlying the switch from adrenal quiescence to activation are unclear. Therefore, we have investigated the expression of suppressor of cytokine signaling-3 (SOCS-3), a putative inhibitor of tissue growth in the fetal sheep adrenal between 50 and 145 days gestation and in the adrenal of the growth-restricted fetal sheep in late gestation. SOCS-3 is activated by a range of cytokines, including prolactin (PRL), and we have, therefore, determined whether PRL administered in vivo or in vitro stimulates SOCS-3 mRNA expression in the fetal adrenal in late gestation. There was a decrease (P < 0.005) in SOCS-3 expression in the fetal adrenal between 54 and 133 days and between 141 and 144 days gestation. Infusion of the dopaminergic agonist, bromocriptine, which suppressed fetal PRL concentrations but did not decrease adrenal SOCS-3 mRNA expression. PRL administration, however, significantly increased adrenal SOCS-3 mRNA expression (P < 0.05). Similarly, there was an increase (P < 0.05) in SOCS-3 mRNA expression in adrenocortical cells in vitro after exposure to PRL (50 ng/ml). Placental and fetal growth restriction had no effect on SOCS-3 expression in the adrenal during late gestation. In summary, the decrease in the expression of the inhibitor SOCS-3 after 133 days gestation may be permissive for a subsequent increase in fetal adrenal growth before birth. We conclude that factors other than PRL act to maintain adrenal SOCS-3 mRNA expression before 133 days gestation but that acute elevations of PRL can act to upregulate adrenal SOCS-3 expression in the sheep fetus during late gestation.

Variability of cortisol assays can confound the diagnosis of adrenal insufficiency in the critically ill population

Objective: To compare the total plasma cortisol values obtained from three widely used immunoassays and a high pressure liquid chromatography (HPLC) technique on samples obtained from patients with sepsis. Design and setting: Observational interventional in the general intensive care unit of a metropolitan hospital. Patients and participants: Patients admitted to the intensive care unit with a diagnosis of sepsis and fulfilling criteria of systemic inflammatory response syndrome. Interventions: Standard short synacthen test performed with 250 mu g cosyntropin. Measurements and results: Two of the three immunoassays returned results significantly higher than those obtained by HPLC: Immulite by 95% (95%CI 31-188%) and TDx by 79% (21-165%). The limits of agreement for all three immunoassays with HPLC ranged from -62% to 770%. In addition, by classifying the patients into responders and non-responders to ACTH by standard criteria there was concordance in all assays in only 44% of patients. Conclusions: Immunoassay estimation of total plasma cortisol in septic patients shows wide assay related variation that may have significant impact in the diagnosis of relative adrenal insufficiency.

Systemic apomorphine alters HPA axis responses to interleukin-1 beta adminstration but not sound stress

Apomorphine is a dopamine receptor agonist that was recently licensed for the treatment of erectile dysfunction. However, although sexual activity can be stressful, there has been little investigation into whether treatments for erectile dysfunction affect stress responses. We have examined whether a single dose of apomorphine, sufficient to produce penile erections (50 mug/kg, i.a.), can alter basal or stress-induced plasma ACTH levels, or activity of central pathways thought to control the hypothalamic-pituitary-adrenal axis in rats. An immune challenge (interleukin-1beta, 1 mug/kg, i.a.) was used as a physical stressor while sound stress (100 dB white noise, 30 min) was used as a psychological stressor. Intravascular administration of apomorphine had no effect on basal ACTH levels but did substantially increase the number of Fos-positive amygdala and nucleus tractus solitarius catecholamine cells. Administration of apomorphine prior to immune challenge augmented the normal ACTH response to this stressor at 90 min and there was a corresponding increase in the number of Fos-positive paraventricular nucleus corticotropin-releasing factor cells, paraventricular nucleus oxytocin cells and nucleus tractus solitarius catecholamine cells. However, apomorphine treatment did not alter ACTH or Fos responses to sound stress. These data suggest that erection-inducing levels of apomorphine interfere with hypothalamic-pituitary-adrenal axis inhibitory feedback mechanisms in response to a physical stressor, but have no effect on the response to a psychological stressor. Consequently, it is likely that apomorphine acts on a hypothalamic-pituitary-adrenal axis control pathway that is unique to physical stressors. A candidate for this site of action is the nucleus tractus solitarius catecholamine cell population and, in particular, A2 noradrenergic neurons. (C) 2003 Elsevier Science Ltd. All rights reserved.

Evidence that the Bed Nucleus of the Stria Terminalis Contributes to the Modulation of Hypophysiotropic Corticotropin-Releasing Factor Cell Responses to Systemic Interleukin-1β

Systemic infection activates the hypothalamic-pituitary-adrenal (HPA) axis, and brainstem catecholamine cells have been shown to contribute to this response. However, recent work also suggests an important role for the central amygdala (CeA). Because direct connections between the CeA and the hypothalamic apex of the HPA axis are minimal, the present study investigated whether the bed nucleus of the stria terminalis (BNST) might act as a relay between them. This was done by using an animal model of acute systemic infection involving intravascular delivery of the proinflammatory cytokine interleukin-1 (IL-1, 1 g/kg). Unilateral ibotenic acid lesions encompassing the ventral BNST significantly reduced both IL-1-induced increases in Fos immunoreactivity in corticotropin-releasing factor (CRF) cells of the hypothalamic paraventricular nucleus (PVN) and corresponding increases in adrenocorticotropic hormone (ACTH) secretion. Similar lesions had no effect on CRF cell responses to physical restraint, suggesting that the effects of BNST lesions were not due to a nonspecific effect on stress responses. In further studies, we examined the functional connections between PVN, BNST, and CeA by combining retrograde tracing with mapping of IL-1-induced increases in Fos in BNST and CeA cells. In the case of the BNST, these studies showed that systemic IL-1 administration recruits ventral BNST cells that project directly to the PVN. In the case of the CeA, the results obtained were consistent with an arrangement whereby lateral CeA cells recruited by systemic IL-1 could regulate the activity of medial CeA cells projecting directly to the BNST. In conclusion, the present findings are consistent with the hypothesis that the BNST acts as a relay between the CeA and PVN, thereby contributing to CeA modulation of hypophysiotropic CRF cell responses to systemic administration of IL-1.

Medial prefrontal cortex suppression of the hypothalamic–pituitary–adrenal axis response to a physical stressor, systemic delivery of interleukin-1β

Previous studies have shown that the medial prefrontal cortex can suppress the hypothalamic-pituitary-adrenal axis response to stress. However, this effect appears to vary with the type of stressor. Furthermore, the absence of direct projections between the medial prefrontal cortex and corticotropin-releasing factor cells at the apex of the hypothalamic-pituitary-adrenal axis suggest that other brain regions must act as a relay when this inhibitory mechanism is activated. In the present study, we first established that electrolytic lesions involving the prelimbic and infralimbic medial prefrontal cortex increased plasma adrenocorticotropic hormone levels seen in response to a physical stressor, the systemic delivery of interleukin-1beta. However, medial prefrontal cortex lesions did not alter plasma adrenocorticotropic hormone levels seen in response to a psychological stressor, noise. To identify brain regions that might mediate the effect of medial prefrontal cortex lesions on hypothalamic-pituitary-adrenal axis responses to systemic interleukin-1beta, we next mapped the effects of similar lesions on interleukin-1beta-induced Fos expression in regions previously shown to regulate the hypothalamic-pituitary-adrenal axis response to this stressor. It was found that medial prefrontal cortex lesions reduced the number of Fos-positive cells in the ventral aspect of the bed nucleus of the stria terminalis. However, the final experiment, which involved combining retrograde tracing with Fos immunolabelling, revealed that bed nucleus of the stria terminalis-projecting medial prefrontal cortex neurons were largely separate from medial prefrontal cortex neurons recruited by systemic interleukin-1beta, an outcome that is difficult to reconcile with a simple medial prefrontal cortex-bed nucleus of the stria terminalis-corticotropin-releasing factor cell control circuit.

Increased diagnosis of primary aldosteronism, including surgically correctable forms, in centers from five continents

Primary aldosteronism (PA) is a common form of endocrine hypertension previously believed to account for less than 1% of hypertensive patients. Hypokalemia was considered a prerequisite for pursuing diagnostic tests for PA. Recent studies applying the plasma aldosterone/plasma renin activity ratio (ARR) as a screening test have reported a higher prevalence. This study is a retrospective evaluation of the diagnosis of PA from clinical centers in five continents before and after the widespread use of the ARR as a screening test. The application of this strategy to a greater number of hypertensives led to a 5- to 15-fold increase in the identification of patients affected by PA. Only a small proportion of patients ( between 9 and 37%) were hypokalemic. The annual detection rate of aldosterone-producing adenoma (APA) increased in all centers ( by 1.3-6.3 times) after the wide application of ARR. Aldosterone-producing adenomas constituted a much higher proportion of patients with PA in the four centers that employed adrenal venous sampling ( 28 - 50%) than in the center that did not (9%). In conclusion, the wide use of the ARR as a screening test in hypertensive patients led to a marked increase in the detection rate of PA. Copyright © 2004 by The Endocrine Society

Primary aldosteronism - careful investigation is essential and rewarding

Once considered rare, primary aldosteronism (PAL) is now regarded as the commonest potentially curable and specifically treatable form of hypertension. At Greenslopes Hospital Hypertension Unit (GHHU), the decision in 1991 to screen all (and not just hypokalemic or resistant) hypertensives by aldosterone/renin ratio (ARR) testing led to a 10-fold increase in detection rate of PAL and four-fold increase in removal rate of aldosterone-producing adenomas (APAs). The GHHU/Princess Alexandra Hospital Hypertension Unit PAL series stands at 977 patients and 250 APAs removed with hypertension cured in 50-60% (remainder improved). Reliable detection requires that interfering medications are withdrawn (or their effects considered) before ARR measurement, and reliable methods (such as fludrocortisone suppression testing) to confirm PAL. Adrenal venous sampling is the only dependable way to differentiate APA from bilateral adrenal hyperplasia. Genetic testing has facilitated detection of alucocorticoid-remediable, familial PAL. Identification of mutations causing the more common familial variety described by GHHU in 1991 should further aid in detection of PAL. (C) 2003 Elsevier Ireland Ltd. All rights reserved.

The aldosterone-renin ratio in screening for primary aldosteronism

Recognition that primary aldosteronism (PAL) is a common specifically treatable form of hypertension and that most patients are normokalemic has led to a marked increase in demand for aldosterone/renin ratio (ARR) testing as a means of screening for this disorder. The value of this screening test depends on an appreciation of many factors (such as diet, posture, time of day, presence of hypokalemia, medications, age, and renal function), which can affect the results, on the care with which these factors are either controlled or their effects taken into account, and on access to reliable and reproducible assays for renin and aldosterone. Even then, physiological day-to-day variability reduces the value of a single estimation, and repeated testing is necessary before a decision that PAL is highly likely (warranting further testing) or highly unlikely can be made. Provided that testing of aldosterone suppressibility is always carried out to confirm or exclude the diagnosis, and the subtype is determined by hybrid gene testing and adrenal venous sampling, wide application of the ARR can have a major beneficial clinical impact with improved therapeutic outcomes, including possible cure in those with unilateral disease.

Association between chronic fatigue syndrome and the corticosteroid-binding globulin gene ALA SER224 polymorphism

Chronic fatigue syndrome (CFS) is characterized by idiopathic fatigue of greater than 6 months' duration with postexertional exacerbation and many other symptoms. A trend toward relative hypocortisolism is described in CFS. Twin and family studies indicate a substantial genetic etiologic component to CFS. Recently, severe corticosteroid-binding globulin (CBG) gene mutations have been associated with CFS in isolated kindreds. Human leukocyte elastase, an enzyme important in CBG catabolism at inflammatory sites, is reported to be elevated in CFS. We hypothesized that CBG gene polymorphisms may act as a genetic risk factor for CFS. A total of 248 patients with CFS defined by Centers for Disease Control criteria, and 248 controls were recruited. Sequencing and restriction enzyme testing of the CBG gene coding region allowed detection of severe CBG gene mutations and a common exon 3 polymorphism (c.825G --> T, Ala-Ser(224)). Plasma CBG levels were measured in 125 CFS patients and 198 controls by radioimmunoassay. Total and free (calculated and measured) cortisol levels were ascertained in single samples between 8-10 a.m. The age of onset (mid 30s) and gender ratio (2.2:1, female:male) of the patients were similar to those reported in U.S. epidemiologic studies. A trend toward a preponderance of serine(224) homozygosity among the CFS patients was noted, compared with controls (chi(2) = 5.31, P = 0.07). Immunoreactive-CBG (IR-CBG) levels were higher in Serine/Alanine (Ser/Ala) than Ala/Ala subjects and higher again in Ser/Ser subjects, this effect was strongest in controls; Ser/Ser: 46.1 +/- 1.8 (n = 31, P = 0.03) vs. Ser/Ala: 42.4 +/- 1.0 (n = 56, P = 0.05) vs. Ala/Ala: 40.8 +/- 1.7 mug/mL (n = 21). Despite higher CBG levels, there was a nonsignificant trend toward lower total and free plasma cortisol in serine allele positive patients, total cortisol: Ser/Ser: 13.3 +/- 1.4 (n = 34) vs. Ser/Ala: 14.0 +/- 0.7 (n = 66) vs. Ala/Ala: 15.4 +/- 1.0 (n = 23). Homozygosity for the serine allele of the CBG gene may predispose to CFS, perhaps due to an effect on hypothalamic-pituitary-adrenal axis function related to altered CBG-cortisol transport function or immune-cortisol interactions.

Hypothalamic paraventricular nucleus neurons regulate medullary catecholamine cell responses to restraint stress

Both physical and psychological stressors recruit catecholamine cells (CA) located in the ventrolateral medulla (VLM) and the nucleus of the solitary tract (NTS). In the case of physical stressors, this effect is initiated by signals that first access the central nervous system at or below the level of the medulla. For psychological stressors, however, CA cell recruitment depends on higher structures within the neuraxis. Indeed, we have recently provided evidence of a pivotal role for the medial amygdala (MeA) in this regard, although such a role must involve a relay, as MeA neurons do not project directly to the medulla. However, some of the MeA neurons that respond to psychological stress have been found to project to the hypothalamic paraventricular nucleus (PVN), a structure that provides significant input to the medulla. To determine whether the PVN might regulate medullary CA cell responses to psychological stress, animals were prepared with unilateral injections of the neurotoxin ibotenic acid into the PVN (Experiment 1), or with unilateral injections of the retrograde tracer wheat germ agglutinin-gold (WGA-Au) into the CA cell columns of the VLM or NTS (Experiment 2). Seven days later, animals were subjected to a psychological stressor (restraint; 15 minutes), and their brains were subsequently processed for Fos plus appropriate cytoplasmic markers (Experiment 1), or Fos plus WGA-Au (Experiment 2). PVN lesions significantly suppressed the stress-related induction of Fos in both VLM and NTS CA cells, whereas tracer deposits in the VLM or NTS retrogradely labeled substantial numbers of PVN cells that were also Fos-positive after stress. Considered in concert with previous results, these data suggest that the activation of medullary CA cells in response to psychological stress may involve a critical input from the PVN. (C) 2004 Wiley-Liss, Inc.

Role of catecholaminergic inputs to the medial prefrontal cortex in local and subcortical expression of Fos after psychological stress

A wide variety of stressors elicit Fos expression in the medial prefrontal cortex (mPFC). No direct attempts, however, have been made to determine the role of the inputs that drive this response. We examined the effects of lesions of mPFC catecholamine terminals on local expression of Fos after exposure to air puff, a stimulus that in the rat acts as an acute psychological stressor. We also examined the effects of these lesions on Fos expression in a variety of subcortical neuronal populations implicated in the control of adrenocortical activation, one classic hallmark of the stress response. Lesions of the mPFC that were restricted to dopaminergic terminals significantly reduced numbers of Fos-immunoreactive (Fos-IR) cells seen in the mPFC after air puff, but had no significant effect on stress-induced Fos expression in the subcortical structures examined. Lesions of the mPFC that affected both dopaminergic and noradrenergic terminals also reduced numbers of Fos-IR cells observed in the mPFC after air puff. Additionally, these lesions resulted in a significant reduction in stress-induced Fos-IR in the ventral bed nucleus of the stria terminalis. These results demonstrate a role for catecholaminergic inputs to the mPFC, in the generation of both local and subcortical responses to psychological stress. (C) 2004 Wiley-Liss, Inc.

A critical role for the parabrachial nucleus in generating central nervous system responses elicited by a systemic immune challenge

Using Fos immunolabelling as a marker of neuronal activation, we investigated the role of the parabrachial nucleus in generating central neuronal responses to the systemic administration of the proinflarnmatory cytokine interleukin-1beta (1 mug/kg, i.a.). Relative to intact animals, parabrachial nucleus lesions significantly reduced the number of Fos-positive cells observed in the central amygdala (CeA), the bed nucleus of the stria terminalis (BNST), and the ventrolateral medulla (VLM) after systemic interleukin-1beta. In a subsequent experiment in which animals received parabrachial-directed deposits of a retrograde tracer, it was found that many neurons located in the nucleus tractus solitarius (NTS) and the VLM neurons were both retrogradely labelled and Fos-positive after interleukin-1beta administration. These results suggest that the parabrachial nucleus plays a critical role in interleukin-1beta-induced Fos expression in CeA, BNST and VLM neurons and that neurons of the NTS and VLM may serve to trigger or at least influence changes in parabrachial nucleus activity that follows systemic interleukin-1beta administration. (C) 2004 Elsevier B.V. All rights reserved.