Corticotropin-releasing Hormone Secretion Research Articles

Interleukin-1β depolarizes magnocellular neurons in the paraventricular nucleus of the hypothalamus through prostaglandin-mediated activation of a non selective cationic conductance

Interleukin-1β (IL-1β) is involved in hypothalamic regulation of the neuroimmune response by influencing the synthesis and secretion of corticotropin releasing hormone (CRH), vasopressin (VP) and other stress-related mediators. VP secretion from magnocellular (MNC) neurons of the paraventricular nucleus (PVN) of the hypothalamus at the posterior pituitary and/or median eminence contributes to increasing adrenocorticotropin hormone (ACTH) output and ultimately glucocorticoid release, which then contributes to the stress response. In this study, using whole-cell patch clamp recordings from neurons in a slice preparation of the rat PVN, we show that MNC neurons are also influenced by IL-1β. In response to 1 nM IL-1β, 62% of MNC neurons tested depolarized (mean depolarization=10.9±1.4 mV); effects which were maintained in the presence of a sodium channel blocker, tetrodotoxin (TTX). The effects of IL-1β on MNC neurons were blocked in the presence of a specific cyclooxygenase (COX)-2 inhibitor, NS-398, indicating a dependence on prostaglandins (PG) in mediating these effects. In response to direct application of 1 μM PGE 2, 57% of MNC neurons depolarized, exhibiting a membrane potential change similar to that induced by IL-1β (mean depolarization=7.8±1.1 mV). Voltage clamp experiments examining the effects of PGE 2 on the currents evoked by slow voltage ramps revealed activation of a conductance characteristic of a non-selective cationic conductance (NSCC) (voltage-independent, with a reversal potential of −41.8±7.6 mV), suggesting that this prostanoid directly modifies cationic currents in MNC neurons. These data provide evidence that IL-1β depolarizes MNC neurons in the PVN as a result of prostaglandin-mediated activation of a NSCC.

Provocation of Kainic Acid Receptor mRNA Changes in the Rat Paraventricular Nucleus by Insulin‐Induced Hypoglycaemia

Hypoglycaemia induced by insulin injection is a powerful stimulus to the hypothalamic-pituitary-adrenal (HPA) axis and drives the secretion of corticotropin-releasing hormone and vasopressin from the neurones in the paraventricular nucleus (PVN), as well as the downstream hormones, adrenocorticotropic hormone and corticosterone. In some brain regions, hypoglycaemia also provokes increases in extracellular fluid concentrations of glutamate. Regulation of glutamatergic mechanisms could be involved in the control of the HPA axis during hypoglycaemic stress and one potential site of regulation might be at the receptors for glutamate, which are expressed in the PVN. Insulin (2.0 IU/kg, i.p.) or saline was administered to adult male Sprague-Dawley rats and the animals were sacrificed 30 min, 180 min and 24 h after injection. The amount of several kainic acid-preferring glutamate receptor mRNAs (i.e. KA2, GluR5 and GluR6) were assessed in the PVN by in situ hybridisation histochemistry. Injection of insulin induced a rapid fall in plasma glucose concentrations, which was mirrored by an increase in plasma corticosterone concentrations. KA2 and GluR5 mRNAs are highly expressed within the rat PVN, and responded to hypoglycaemia with robust increases in expression that endured beyond the period of hypoglycaemia itself. However, GluR6 mRNA is expressed in the areas adjacent to the PVN and hypoglycaemic stress failed to alter expression of this mRNA. These experiments suggest that kainic acid-preferring glutamate receptors are responsive to changes in plasma glucose concentrations and may participate in the activation of the PVN neurones during hypoglycaemic stress.

Metyrapone tests in patients with panic disorder

Studies of hypothalamic secretion of corticotropin-releasing hormone (CRH) in patients with panic disorder in the nonpanic state (using CRH tests) are contradictory. No data about the hypothalamic-pituitary response to metyrapone are available. Study participants included 14 patients with panic disorder (DSM-IV criteria) and 14 healthy control subjects who underwent a standard overnight metyrapone test and a combined metyrapone/low-dose dexamethasone test. Significant treatment effects of metyrapone and combined metyrapone/dexamethasone were found on plasma corticotropin, cortisol, and 11-deoxycortisol, but no differences between patients and control subjects emerged. Considering visual analogue scale ratings of anxiety, tension, restlessness, and Beck Depression Inventory scores as covariates, no group effects were detected. Standard overnight metyrapone tests do not support a hypersecretion of hypothalamic CRH in panic disorder. Furthermore, no evidence for increased glucocorticoid negative feedback in panic was found. Hypothalamic CRH secretion in the nonpanic state needs further research.

Impaired hypothalamic-pituitary-adrenocortical (HPA) system is related to severity of benzodiazepine withdrawal in patients with depression

A concatenation of data indicates that the pathogenesis of depression is related to an increased production and secretion of corticotropin-releasing hormone (CRH). Benzodiazepines profoundly suppress the basal and stress-related activation of the hypothalamic-pituitary-adrenocortical (HPA) system and discontinuation of these drugs results in rebound activation. We therefore investigated whether the extent of HPA system dysregulation is related to the severity of benzodiazepine withdrawal in patients with depression. We performed the combined dexamethasone/CRH test before benzodiazepine discontinuation (taper-off max. 5 mg diazepam-equivalents/week) in 14 depressed patients (13 f, 1 m, mean age 54.6 +/- 14.6) who responded to the antidepressant treatment. The severity of withdrawal symptoms was measured using the Clinical Institute Withdrawal Assessment-Benzodiazepines (CIWA-B) questionnaire. The depressive psychopathology was monitored using the Hamilton Depression Rating Scale, Montgomery Asberg Depression Rating Scale and Beck Depression Inventory. Patients with more severe benzodiazepine withdrawal (CIWA-B-increase > 14 pts; n = 7) showed a significant higher cortisol and ACTH response in the dexamethasone/CRH test preceding the discontinuation of benzodiazepines than patients displaying less severe withdrawal symptoms (CIWA-B-increase <14 pts.; n = 7) (ANCOVA, p < 0.05). Both groups did not differ in the pre-taper psychopathology ratings and their basal neuroendocrine activity. In view of the GABAergic inhibition of HPA system activity and the anxiogenic effect of CRH, benzodiazepine withdrawal symptoms may be partly due to a disinhibition of the HPA system during discontinuation of benzodiazepines.

Regulatory mechanisms of corticotropin-releasing hormone and vasopressin gene expression in the hypothalamus.

Tuberoinfundibular corticotropin-releasing hormone (CRH) neurones are the principal regulators of the hypothalamic-pituitary-adrenal (HPA)-axis. Vasopressin is primarily a neurohypophysial hormone, produced in magnocellular neurones of the hypothalamic paraventricular and supraoptic nuclei, but parvocellular CRH neurones also coexpress vasopressin, which acts as a second 'releasing factor' for adrenocorticotropic hormone along with CRH. All stress inputs converge on these hypothalamic neuroendocrine neurones, and the input signals are integrated to determine the output secretion of CRH and vasopressin. Aminergic, cholinergic, GABAergic, glutamatergic and a number of peptidergic inputs have all been implicated in the regulation of CRH/vasopressin neurones. Glucocorticoids inhibit the HPA-axis activity by negative feedback. Interleukin-1 stimulates CRH and vasopressin gene expression, and is implicated in immune-neuroendocrine regulation. cAMP-response element-binding protein phosphorylation may mediate transcriptional activation of both CRH and vasopressin genes, but the roles of AP-1 and other transcription factors remain controversial. Expression profiles of the CRH and vasopressin genes are not uniform after stress exposure, and the vasopressin gene appears to be more sensitive to glucocorticoid suppression.

Reproductive functions of corticotropin-releasing hormone. Research and potential clinical utility of antalarmins (CRH receptor type 1 antagonists).

The hypothalamic-pituitary-adrenal (HPA) axis exerts a complex, mostly inhibitory, effect on the female reproductive system. In addition, the principal regulator of this axis, the hypothalamic neuropeptide corticotropin-releasing hormone (CRH) and its receptors have been identified in most female reproductive tissues, including the ovary, uterus, and placenta. Furthermore, CRH is secreted in peripheral inflammatory sites where it exerts strong inflammatory actions. Antalarmins (CRH receptor type 1 antagonists) have been used to elucidate the roles of CRH in stress, inflammation and reproduction. We review existing data on the effects of CRH in the female reproductive system. Ovarian CRH participates in female sex steroid production, follicular maturation, ovulation and luteolysis. Uterine CRH participates in decidualization, implantation, and early maternal tolerance. Placental CRH participates in the physiology of pregnancy and the onset of parturition. Circulating placental CRH is secreted mostly during the latter half of pregnancy and is responsible for the concurrently increasing physiologic hypercortisolism of this period. After labor and delivery, this hypercortisolism is ensued by a transient suppression of hypothalamic CRH secretion, which may explain the postpartum blues and depression and the increased autoimmune manifestations depression of period, the postpartum period. These data show that CRH is present in female reproductive tissues, and is regulating key reproductive functions with an inflammatory component, such as ovulation, luteolysis, implantation, and parturition.

Impaired hypothalamic-pituitary-adrenocortical (HPA) system is related to severity of benzodiazepine withdrawal in patients with depression

A concatenation of data indicates that the pathogenesis of depression is related to an increased production and secretion of corticotropin-releasing hormone (CRH). Benzodiazepines profoundly suppress the basal and stress-related activation of the hypothalamic-pituitary-adrenocortical (HPA) system and discontinuation of these drugs results in rebound activation. We therefore investigated whether the extent of HPA system dysregulation is related to the severity of benzodiazepine withdrawal in patients with depression. We performed the combined dexamethasone/CRH test before benzodiazepine discontinuation (taper-off max. 5 mg diazepam-equivalents/week) in 14 depressed patients (13 f, 1 m, mean age 54.6 ± 14.6) who responded to the antidepressant treatment. The severity of withdrawal symptoms was measured using the Clinical Institute Withdrawal Assessment-Benzodiazepines (CIWA-B) questionnaire. The depressive psychopathology was monitored using the Hamilton Depression Rating Scale, Montgomery Asberg Depression Rating Scale and Beck Depression Inventory. Patients with more severe benzodiazepine withdrawal (CIWA-B-increase > 14 pts.; n=7) showed a significant higher cortisol and ACTH response in the dexamethasone/CRH test preceding the discontinuation of benzodiazepines than patients displaying less severe withdrawal symptoms (CIWA-B-increase <14 pts.; n = 7) (ANCOVA, p < 0.05). Both groups did not differ in the pre-taper psychopathology ratings and their basal neuroendocrine activity. In view of the GABAergic inhibition of HPA system activity and the anxiogenic effect of CRH, benzodiazepine withdrawal symptoms may be partly due to a disinhibition of the HPA system during discontinuation of benzodiazepines.

IL-1β-mediated neuropeptide and immediate early gene mRNA induction is defective in Lewis hypothalamic cell cultures

We previously found that Lewis (LEW/N) hypothalamic cells respond to interleukin-1β (IL-1β) with reduced corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) peptide synthesis and secretion compared to Fischer (F344/N) cells. To investigate whether this peptide hyporesponsiveness in LEW/N cells is secondary to their deficient mRNA expression, temporal mRNA expression patterns of CRH, AVP, and several hypothalamic neuropeptides induced by IL-1β in LEW/N and F344/N hypothalamic dissociated cell cultures were delineated by quantitative real-time polymerase chain reaction (RT-PCR). To investigate the molecular mechanisms underlying neuropeptide mRNA induction in cells of both strains, temporal mRNA expression patterns of immediate early genes (IEGs) and several signal transduction-associated molecules were also examined. We found that LEW/N hypothalamic cells were hyporesponsive to IL-1β induction of neuropeptide and IEG mRNA, while LEW/N cells transcribed more IL-1 receptor and inducible nitric oxide synthase (iNOS) compared to F344N/N cells, suggesting that LEW/N and F344/N hypothalamic cells are differentially activated by IL-1β.

Modulation of sympathetic activity by corticotropin-releasing hormone and atrial natriuretic peptide

Background: Heart rate variability represents a reliable marker to delineate the status of autonomic nervous system (ANS) function and alterations due to stress in vivo. Interestingly, up to now the effects of corticotropin-releasing hormone (CRH), a key regulator of the stress hormone system, upon heart rate variability are not sufficiently described. Hence, we attempted to investigate the ANS-effects of a CRH bolus and the modulatory influences of atrial natriuretic peptide (ANP), one of the most important functional antagonist of CRH actions. Methods: 12 healthy male volunteers were administered 100 μg CRH as bolus injection at 15:00. Six randomly chosen subjects received 150 μg ANP dissolved in normal saline and six subjects a normal saline infusion from 14:45 to 15:15. From 13:00 to 17:00 an ECG was recorded and mean heart rate (HR), total power (TP), very low frequency (VLF), low frequency (LF), LF in normalized units (LF [nu]), high frequency (HF) domains and the LF/HF-ratio in the interval from 14:00 to 16:00 were determined. Results: After administration of CRH a significant increase in HR and a fast reduction of TP were observed, which lasted about 1 h. Based upon spectral domain analyses the sympathetic activity after CRH administration as indicated by LF [nu] increased by 31% (mean location) during saline. Applying ANP this increase was reduced to 19% (mean location). The VLF component, which is considered to be based in part also on sympathetic influences, indicates comparable effect. During saline the VLF after CRH bolus remained largely unchanged, but was reduced to 66% by ANP. Though the vagal activity indicated by the HF component was reduced after CRH, no significant differences emerged between both treatments. The changes of the LF/HF-ratio were pronounced in both groups. During saline this ratio increased by about 111%, during ANP only by 43% (mean location). Conclusions: Based upon HRV analysis the CRH administration induced sympathotonic effects which were antagonized by ANP. The observed vagal changes were less pronounced and need further investigation. Further studies of autonomic effects by alterations of CRH secretion in depression and anxiety disorder are strongly warranted.

Maternal and Fetal Hypothalamic‐Pituitary‐Adrenal Axes During Pregnancy and Postpartum

The principal modulators of the hypothalamic-pituitary-adrenal (HPA) axis are corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Corticotropin-releasing hormone is not exclusively produced in the hypothalamus. Its presence has been demonstrated at peripheral inflammatory sites. Ovulation and luteolysis bear characteristics of an aseptic inflammation. CRH was found in the theca and stromal cells as well as in cells of the corpora lutea of human and rat ovaries. The cytoplasm of the glandular epithelial cells of the endometrium has been shown to contain CRH and the myometrium contains specific CRH receptors. It has been suggested that CRH of fetal and maternal origin regulates FasL production, thus affecting the invasion (implantation) process through a local auto-paracrine regulatory loop involving the cytotrophoblast cells. Thus, the latter may regulate their own apoptosis. During pregnancy, the plasma level of circulating maternal immunoreactive CRH increases exponentially from the first trimester of gestation due to the CRH production in the placenta, decidua, and fetal membranes. The presence in plasma and amniotic fluid of a CRH-binding protein (CRHbp) that reduces the bioactivity of circulating CRH by binding is unique to humans. Maternal pituitary ACTH secretion and plasma ACTH levels rise during pregnancy-though remaining within normal limits-paralleling the rise of plasma cortisol levels. The maternal adrenal glands during pregnancy gradually become hypertrophic. Pregnancy is a transient, but physiologic, period of hypercortisolism. The diurnal variation of plasma cortisol levels is maintained in pregnancy, probably due to the secretion of AVP from the parvicellular paraventricular nuclei. CRH is detected in the fetal hypothalamus as early as the 12th week of gestation. CRH levels in fetal plasma are 50% less than in maternal plasma. The circulating fetal CRH is almost exclusively of placental origin. The placenta secretes CRH at a slower rate in the fetal compartment. AVP is detected in some neurons of the fetal hypothalamus together with CRH. AVP is usually detectable in the human fetal neurohypophysis at 11 to 12 weeks gestation and increases over 1000-fold over the next 12 to 16 weeks. The role of fetal AVP is unclear. Labor appears to be a stimulus for AVP release by the fetus. The processing of POMC differs in the anterior and intermediate lobes of the fetal pituitary gland. Corticotropin (ACTH) is detectable by radioimmunoassay in fetal plasma at 12 weeks gestation. Concentrations are higher before 34 weeks gestation, with a significant fall in late gestation. The human fetal adrenal is enormous relative to that of the adult organ. Adrenal steroid synthesis is increased in the fetus. The major steroid produced by the fetal adrenal zone is sulfoconjugated dehydroepiandrosterone (DHEAS). The majority of cortisol present in the fetal circulation appears to be of maternal origin, at least in the nonhuman primate. The fetal adrenal uses the large amounts of progesterone supplied by the placenta to make cortisol. Another source of cortisol for the fetus is the amniotic fluid where cortisol converted from cortisone by the choriodecidua, is found. In humans, maternal plasma CRH, ACTH, and cortisol levels increase during normal labor and drop at about four days postpartum; however, maternal ACTH and cortisol levels at this stage are not correlated. In sheep, placental CRH stimulates the fetal production of ACTH, which in turn leads to a surge of fetal cortisol secretion that precipitates parturition. The 10-day-long intravenous administration of antalarmin, a CRH receptor antagonist, significantly prolonged gestation compared to the control group of animals. Thus, CRH receptor antagonism in the fetus can also delay parturition. The HPA axis during the postpartum period gradually recovers from its activated state during pregnancy. The adrenals are mildly suppressed in a way analogous to postcure Cushing's syndrome. Provocation testing has shown that hypothalamic CRH secretion is transiently suppriently suppressed at three and six weeks postpartum, normalizing at 12 weeks.

Increased corticortropin-releasing hormone release in ovariectomized rats’ paraventricular nucleus: effects of electroacupuncture

Utilizing push-pull perfusion, we examined secretary profiles of corticotropin-releasing hormone (CRH) in the nucleus paraventricularis (PVN) of freely moving intact (INT) and ovariectomized (OVX) rats, and in the meanwhile the effects of electroacupuncture (EA) on the release patterns of CRH were observed. The PVN was perfused with artificial cerebrospinal fluid between 08:00 and 12:00 h, and perfusates were collected every 10 min. The average CRH output was significantly larger in OVX rats than that in INT and INT with EA (INT+EA) groups. Interestingly enough, the CRH output showed a significant elevation in OVX with EA (OVX+EA) group during the EA procedure and further increase immediately after the EA. It is the first time to present the temporal profiles of CRH secretion in the PVN of OVX and OVX+EA rats.

Acute Stress Results in Skin Corticotropin-Releasing Hormone Secretion, Mast Cell Activation and Vascular Permeability, an Effect Mimicked by Intradermal Corticotropin-Releasing Hormone and Inhibited by Histamine-1 Receptor Antagonists

Background: Mast cells play an important role in allergic inflammation by releasing vasoactive molecules, proteases and cytokines. Corticotropin-releasing hormone (CRH) and its structural analogue urocortin (Ucn) were shown to trigger skin mast cell activation and vascular permeability. We investigated the effect of acute stress on rat skin vascular permeability and CRH secretion, as well as the effect of intradermal CRH, and that of two histamine-1 receptor antagonists, azelastine and olopatadine, on vascular permeability. Methods: Rats were stressed by restraint and vascular permeability was assessed by extravasation of ⁹⁹Tc-gluceptate, while mast cell activation was determined by skin rat mast cell protease-1 (RMCP-1) content. Skin CRH content was evaluated by ELISA. The effect of intradermal injection of CRH and Ucn, as well as that of two histamine-1 receptor antagonists, azelastine and olopatadine, was assessed by Evan’s blue extravasation. Purified rat peritoneal mast cells (RPMCs) were also pretreated with azelastine (24 µM) or olopatadine (133 µM) for 5 min before challenge with compound 48/80 (0.5 µg/ml) for 30 min. Histamine secretion was measured fluorometrically. Intracellular Ca²⁺ ions were evaluated in RPMCs loaded with calcium crimson and stimulated with compound 48/80. Results: Acute stress increased skin vascular permeability and CRH content, while it decreased RMCP-1. Intradermal injection of CRH or Ucn induced substantial Evan’s blue extravasation that was inhibited by pretreatment with azelastine (24 µM) and olopatadine (133 µM). Both antihistamines also inhibited histamine release and intracellular increase of Ca²⁺ ions from RPMCs stimulated by compound 48/80. Conclusions: These results indicate that acute stress increases skin CRH that can trigger mast cell-dependent vascular permeability, effects inhibited by certain histamine-1 receptor antagonists, possibly acting to reduce intracellular Ca²⁺ ion levels.

Increased corticotropin-releasing hormone immunoreactivity in monoamine-containing pontine nuclei of depressed suicide men.

A number of clinical investigations and postmortem brain studies have provided evidence that excessive corticotropin-releasing hormone (CRH) secretion and neurotransmission is involved in the pathophysiology of depressive illness, and several studies have suggested that the hyperactivity in CRH neurotransmission extends beyond the hypothalamus involving several extra-hypothalamic brain regions. The present study was designed to test the hypothesis that CRH levels are increased in specific brainstem regions of suicide victims with a diagnosis of major depression. Frozen tissue sections of the pons containing the locus coeruleus and caudal raphe nuclei from 11 matched pairs of depressed suicide and control male subjects were processed for radioimmunocytochemistry using a primary antiserum to CRH and a ([125])I-IgG secondary antibody. The optical density corresponding to the level of CRH-immunoreactivity (IR) was quantified in specific pontine regions from the film autoradiographic images. The level of CRH-IR was increased by 30% in the locus coeruleus, 39% in the median raphe and 45% in the caudal dorsal raphe in the depressed suicide subjects compared to controls. No difference in CRH-IR was found in the dorsal tegmentum or medial parabrachial nucleus between the subject groups. These findings reveal that CRH-IR levels are specifically increased in norepinephrine- and serotonin-containing pontine nuclei of depressed suicide men, and thus they are consistent with the hypothesis that CRH neurotransmission is elevated in extra-hypothalamic brain regions of depressed subjects.

Endogenous activation of group-II metabotropic glutamate receptors inhibits the hypothalamic–pituitary–adrenocortical axis

Systemic injection of the mGlu2/3 receptor antagonist, LY341495 (1 mg/kg, i.p.), increased plasma corticosterone in mice to an extent similar to that induced by the despair test. Treatment with the mGlu2/3 receptor agonist, LY379268 (1 mg/kg, i.p.), or the non-competitive mGlu5 receptor antagonist, MPEP (5 mg/kg, i.p.), failed to induce significant changes in corticosterone levels. Searching for a site of action of LY341495, we examined the expression of mGlu receptor subtypes in the various anatomical regions of the mouse hypothalamic–pituitary–adrenal (HPA) axis. Only mGlu5 and -7 receptor mRNAs were detected in the adrenal gland by RT-PCR, whereas mGlu -1, -3, -4, -5, -7 and -8 receptor mRNAs were detected in the anterior pituitary. All transcripts (with the exception of mGlu5 and mGlu6 receptor mRNAs) were detected in the hypothalamus. However, Western blot analysis showed the presence of mGlu2/3 receptor proteins only in the hypothalamus and not in the anterior pituitary. This was consistent with functional data showing that LY341495 (0.1 and 1 μM) failed to affect ACTH secretion from isolated mouse anterior pituitaries. Moving from these observations, we examined whether LY341495 could activate the HPA axis by inhibiting mGlu2/3 receptors at hypothalamic level. We measured the release of corticotropin releasing hormone (CRH) in isolated mouse hypothalami incubated in the presence of subtype-selective mGlu receptor agonists or antagonists. Among all the drugs we have tested, only LY341495 was able to increase CRH secretion. With high concentrations of LY341495 (1 μM) this increase was similar to that induced by 50 mM K +. The action of LY341495 was prevented by the combined application of the mGlu2/3 receptor agonist, LY379268. We conclude that group-II mGlu receptors tonically regulate the HPA axis by controlling CRH secretion at hypothalamic level.

Reduced attention in mice overproducing corticotropin-releasing hormone

Data from several studies suggest that unrestrained secretion of corticotropin-releasing hormone in the CNS produces several signs and symptoms of depression. Recent evidence indicates that blockade of the CRH receptor 1 reduced depression scores in depressed patients. One of the symptoms that occur is depression is impairment in attentional processes. Whether these impairments are due to alterations in the CRH system are so far unknown. In order to investigate whether overproduction of CRH alters attentional process, transgenic mice overproducing CRH were tested on an operant five choice serial reaction time task, a task which taxes sustained and divided attention. Mutants showed impaired autoshaping. During initial discrimination learning, transgenics performed below wildtype level, but with extended training with long stimulus durations, transgenic animals reached similar accuracy levels as wildtype mice. When animals were tested at shortest stimulus duration (0.5 s), a mild but significant impairment in accurate responding emerged in transgenics. This was accompanied by longer correct response latencies, while incorrect latencies did not differ between groups, suggesting attentional impairment in CRH transgenics. Because these animals have been reported to also show increased anxiety-related behaviour, animals were treated with the anxiolytic benzodiazepine diazepam. Diazepam failed to affect accuracy, but transgenic mice showed a stronger behavioural disinhibition. This suggests that the attentional impairment seen in CRH overexpressors is independent of alterations in anxiety-like behaviour. These findings may have implications for understanding the pathophysiology of psychiatric disorders such as depression, where it has been suggested that an overactivity of the CRH system accounts for a variety of symptoms, including hyper-arousal and attentional impairment.

Interleukin-1 beta depolarizes paraventricular nucleus parvocellular neurones.

Interleukin-1 beta (IL-1 beta) is involved in hypothalamic regulation of corticotropin releasing hormone (CRH) secretion and consequent downstream modulation of the neuroimmune response. In this study, whole-cell patch clamp recordings of rat parvocellular neurones in a slice preparation of the paraventricular nucleus (PVN) of the hypothalamus were performed to examine the cellular effects of IL-1 beta. In response to 1 nm IL-1 beta, 65% of parvocellular neurones tested exhibited a clear depolarization, which was abolished in the presence of tetrodotoxin (TTX). This depolarization was partially dependent on nitric oxide formation, as demonstrated by attenuation of the response in the presence of N-omega-nitro-L-arginine methylester, a nitric oxide synthase inhibitor. The effects of IL-1 beta on responsive parvocellular neurones were associated with a decrease in the frequency of inhibitory post synaptic potentials (IPSPs). Bicuculline administration blocked the effects of IL-1 beta, suggesting that this cytokine modulates GABA-ergic output, resulting in a decrease in inhibitory input (IPSPs) and consequent depolarization. These data support the conclusion that IL-1 beta influences the excitability of parvocellular neurones in the PVN, as a secondary consequence of nitric oxide generation and modulation of GABAergic inhibitory input to these cells. They elucidate cellular correlates underlying the well-established neuroimmune roles of IL-1 beta in the paraventricular nucleus of the hypothalamus.

Specific up-regulation of CRH or AVP secretion by acetylcholine or lipopolysaccharide in inflammatory susceptible Lewis rat fetal hypothalamic cells

Lewis (LEW/N) rats, compared to Fischer (F344/N) rats, are susceptible to inflammatory/autoimmune diseases, in part, as a result of their blunted hypothalamic–pituitary–adrenal (HPA) axis responses. We examined regulation of LEW/N and F344/N fetal hypothalamic cell secretion of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), two major HPA axis mediators, by inflammatory and neurotransmitter stimuli. Interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and protein kinase A (PKA) and protein kinase C (PKC) activators did not affect LEW/N basal secretion. Compared to F344/N, LEW/N cells were hyporesponsive to lipopolysaccharide (LPS), serotonin (5-HT), and acetylcholine chloride (ACh). However, LPS-induced AVP release and ACh-evoked CRH secretion in LEW/N were comparable with those of F344/N. Our findings suggest that the blunted LEW/N neuropeptide response was more likely related to components of second messenger systems, rather than to any one specific stimulus.

Steroids.

Corticosteroids are considered to be essential stress hormones. They are secreted together with adrenocorticotropic hormone (ACTH) in response to the pulsatile secretion of corticotropin-releasing hormone from the paraventricular nucleus of the hypothalamus. Changes in pulse amplitude are responsible for the diurnal rhythm in circulating ACTH and cortisol levels. Steroid levels increase immediately after injury, pain, fever, and hypovolemia in response to the stimulation of corticotropin-releasing hormone secretion by various cytokines. The increase in steroid levels is typically proportional to the magnitude of stress, with serum cortisol values being highest in moribund patients and shortly before death. With severe and prolonged stress, steroid levels are increased for weeks to months and may be associated with hypertrophy of the adrenal cortex. Cortisol acts in concert with catecholamines to maintain the vascular tone, endothelial integrity, vascular permeability, and the distribution of total body water within the vascular compartment. It also potentiates the vasoconstrictor effects of catecholamines. Cortisol helps to stimulate lipolysis, inhibit protein synthesis, facilitate amino acid mobilization from muscle, induce the enzymes of gluconeogenesis, enhance secretion of glucagon, inhibit insulin secretion, and stimulate conversion of lactic acid to glycogen. Because of their anti-inflammatory properties, steroids have been proposed as therapeutic adjuvants in systemic inflammation and may protect the host against overshooting defense reactions by reducing the migration of leukocytes to the inflammatory sites and the incidence of neutrophil-mediated tissue injury and organ dysfunction.

The CRH1 receptor antagonist R121919 attenuates stress-elicited sleep disturbances in rats, particularly in those with high innate anxiety

Excessive corticotropin-releasing hormone (CRH) secretion in limbic and prefrontal brain areas has been postulated to underly stress-related clinical conditions. Studies in mice with deleted or pharmacologically compromized CRH type 1 receptors (CRH-R1) point to a key role of the CRH/CRH-R1 signaling cascade as a potential drug target. Therefore, we compared the effect of a selective high affinity CRH-R1 antagonist (R121919) on sleep–wake behavior in two rat lines selectively bred for either high or low innate anxiety. We found that the subcutaneous injection of the solvent of R121919, a citrate buffer solution, transiently increased circulating levels of the stress hormones ACTH and corticosterone and reduced sleep, especially in high-anxiety animals. When R121919 was added to the solvent, hormone levels and sleep patterns returned to baseline and were indistinguishable between the rat lines. This finding is in accord with previous observations from a clinical trial in depressed patients and studies in rats with high innate anxiety that suggested major effects of CRH-R1 antagonism in the presence of a pathological (i.e. CRH hypersecretion) condition only.

Glucose metabolism in the amygdala in depression: Relationship to diagnostic subtype and plasma cortisol levels

In a previous positron emission tomography (PET) study of major depression, we demonstrated that cerebral blood flow was increased in the left amygdala in unipolar depressives with familial pure depressive disease (FPDD) relative to healthy controls [J. Neurosci. 12 (1992) 3628.]. These measures were obtained from relatively low-resolution PET images using a stereotaxic method based upon skull X-ray landmarks. The current experiments aimed to replicate and extend these results using higher-resolution glucose metabolism images and magnetic resonance imaging (MRI)-based region-of-interest (ROI) analysis. The specificity of this finding to FPDD was also investigated by assessing depressed samples with bipolar disorder (BD-D) and depression spectrum disease (DSD). Finally, the relationship between amygdala metabolism and plasma cortisol levels obtained during the scanning procedure was assessed. Glucose metabolism was measured using PET and 18F-fluorodeoxyglucose ( 18FDG) in healthy control ( n=12), FPDD ( n=12), DSD ( n=9) and BD-D ( n=7) samples in the amygdala and the adjacent hippocampus. The left amygdala metabolism differed across groups ( P<.001), being increased in both the FPDD and BD-D groups relative to the control group. The left amygdala metabolism was positively correlated with stressed plasma cortisol levels in both the unipolar ( r=.69; P<.005) and the bipolar depressives ( r=0.68; .1< P<.05). In contrast, neither significant main effects of diagnosis nor significant relationships with plasma cortisol were evident in post hoc analyses of metabolism in the right amygdala or the hippocampus. Preliminary assessment of BD subjects imaged during remission suggested that amygdala metabolism is also elevated in remitted subjects who are not taking mood-stabilizing drugs, but within the normal range in subjects taking mood stabilizers. These data confirm our previous finding that neurophysiological activity is abnormally increased in FPDD, and extend it to BD-D. These abnormalities were not accounted for by spilling in of radioactivity from the adjacent hippocampus. The correlation between left amygdala metabolism and stressed plasma cortisol levels may conceivably reflect either the effect of amygdala activity on corticotropin-releasing hormone (CRH) secretion or the effect of cortisol on amygdala function.