Regulation of hypoxia-induced release of corticotropin-releasing factor in the rat hypothalamus by norepinephrine

Inhibition of peripheral chemoreceptors improves ventilatory efficiency during exercise in heart failure with preserved ejection fraction − a role of tonic activity and acute reflex response

Peripheral chemoreceptors (PChRs) play a significant role in maintaining adequate oxygenation in the bloodstream. PChRs functionality comprises two components: tonic activity (PChT) which regulates ventilation during normoxia and acute reflex response (peripheral chemosensitivity, PChS), which increases ventilation following a specific stimulus. There is a clear link between augmented PChS and exercise intolerance in patients with heart failure with reduced ejection fraction. It has been also shown that inhibition of PChRs leads to the improvement in exercise capacity. However, it has not been established yet: 1) whether similar mechanisms take part in heart failure with preserved ejection fraction (HFpEF) and 2) which component of PChRs functionality (PChT vs. PChS) is responsible for the benefit seen after the acute experimental blockade. To answer those questions we enrolled 12 stable patients with HFpEF. All participants underwent an assessment of PChT (attenuation of minute ventilation in response to low-dose dopamine infusion), PChS (enhancement of minute ventilation in response to hypoxia) and a symptom-limited cardiopulmonary exercise test on cycle ergometer. All tests were placebo-controlled, double-blinded and performed in a randomized order. Under resting conditions and at normoxia dopamine attenuated minute ventilation and systemic vascular resistance (p = 0.03 for both). These changes were not seen with placebo. Dopamine also decreased ventilatory and mean arterial pressure responses to hypoxia (p < 0.05 for both). Inhibition of PChRs led to a decrease in V˙E/V˙CO₂ comparing to placebo (36 ± 3.6 vs. 34.3 ± 3.7, p = 0.04), with no effect on peak oxygen consumption. We found a significant relationship between PChT and the relative decrement of V˙E/V˙CO₂ on dopamine comparing to placebo (R = 0.76, p = 0.005). There was a trend for correlation between PChS (on placebo) and V˙E/V˙CO₂ during placebo infusion (R = 0.56, p = 0.059), but the relative improvement in V˙E/V˙CO₂ was not related to the change in PChS (dopamine vs. placebo). We did not find a significant relationship between PChT and PChS. In conclusion, inhibition of PChRs in HFpEF population improves ventilatory efficiency during exercise. Increased PChS is associated with worse (higher) V˙E/V˙CO₂, whereas PChT predicts an improvement in V˙E/V˙CO₂ after PChRs inhibition. This results may be meaningful for patient selection in further clinical trials involving PChRs modulation.

Characterization of Chicken α2A-Adrenoceptor: Molecular Cloning, Functional Analysis, and Its Involvement in Ovarian Follicular Development

Adrenoceptors are suggested to mediate the functions of norepinephrine (NE) and epinephrine (EPI) in the central nervous system (CNS) and peripheral tissues in vertebrates. Compared to mammals, the functionality and expression of adrenoceptors have not been well characterized in birds. Here, we reported the structure, expression, and functionality of chicken functional α_2A-adrenoceptor, named ADRA2A. The cloned chicken ADRA2A cDNA is 1335 bp in length, encoding the receptor with 444 amino acids (a.a.), which shows high amino acid sequence identity (63.4%) with its corresponding ortholog in humans. Using cell-based luciferase reporter assays and Western blot, we demonstrated that the ADRA2A could be activated by both NE and EPI through multiple signaling pathways, including MAPK/ERK signaling cascade. In addition, the mRNA expression of ADRA2A is found to be expressed abundantly in adult chicken tissues including thyroid, lung, ovary and adipose from the reported RNA-Seq data sets. Moreover, the mRNA expression of ADRA2A is also found to be highly expressed in the granulosa cells of 6–8 mm and F5 chicken ovarian follicles, which thus supports that ADRA2A signaling may play a role in ovarian follicular growth and differentiation. Taken together, our data provide the first proof that the α_2A-adrenoceptor is functional in birds involving avian ovarian follicular development.

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

The effect of amisulpride, olanzapine, quetiapine, and aripiprazole single administration on c-Fos expression in vasopressinergic and oxytocinergic neurons of the rat hypothalamic paraventricular nucleus

Antipsychotics, including amisulpride (AMI), quetiapine (QUE), aripiprazole (ARI), and olanzapine (OLA), are used to treat mental illnesses associated with psychotic symptoms. The effect of these drugs on c-Fos expression in vasopressinergic (AVP) and oxytocinergic (OXY) neurons was studied in the hypothalamic paraventricular nucleus (PVN) of rats. The presence of c-Fos in AVP and OXY perikarya was investigated in seven PVN cells segregations: the anterior (Ant), dorsal cup (Dc), wing-shaped (Wi), periventricular zone (Pe), circle-shaped core (Co) and shell of core (Sh), and the posterior (pPVN) after an acute treatment with AMI-20 mg/kg, QUE-15 mg/kg, ARI-10 mg/kg, and OLA-5 mg/kg/bw in rats. Ninety min after treatments, the animals were sacrificed by transcardial perfusion with fixative and the PVN area sliced into 35 μm thick coronal sections for immunohistochemistry. The c-Fos was processed by avidin-biotin-peroxidase complex intensified with nickel-enhanced 3,3'-diaminobenzidine tetrahydrochloride. Visualization of AVP- and OXY-synthesizing neurons was achieved by a fluorescent marker Alexa Flour 568. The c-Fos-AVP and c-Fos-OXY colocalizations were evaluated from c-Fos stained sections merged with AVP or OXY ones. AMI, QUE, ARI, and OLA, single administration distinctly increased the c-Fos expression in each of the PVN cells segregations. QUE induced the highest magnitude of activation of AVP and OXY neurons, while OLA and AMI had only moderate effects. Incontestable variabilities detected in c-Fos expression in PVN AVP and OXY neurons extend the knowledge of selected antipsychotics extra-striatal actions and may also be helpful in a presumption of their possible functional impact.

Activation of alpha-1 adrenergic receptors increases cytosolic calcium in neurones of the paraventricular nucleus of the hypothalamus

Norepinephrine (NE) activates adrenergic receptors (ARs) in the hypothalamic paraventricular nucleus (PVN) to increase excitatory currents, depolarise neurones and, ultimately, augment neuro-sympathetic and endocrine output. Such cellular events are known to potentiate intracellular calcium ([Ca²⁺ ]_i ); however, the role of NE with respect to modulating [Ca²⁺ ]_i in PVN neurones and the mechanisms by which this may occur remain unclear. We evaluated the effects of NE on [Ca²⁺ ]_i of acutely isolated PVN neurones using Fura-2 imaging. NE induced a slow increase in [Ca²⁺ ]_i compared to artificial cerebrospinal fluid vehicle. NE-induced Ca²⁺ elevations were mimicked by the α₁ -AR agonist phenylephrine (PE) but not by α₂ -AR agonist clonidine (CLON). NE and PE but not CLON also increased the overall number of neurones that increase [Ca²⁺ ]_i (ie, responders). Elimination of extracellular Ca²⁺ or intracellular endoplasmic reticulum Ca²⁺ stores abolished the increase in [Ca²⁺ ]_i and reduced responders. Blockade of voltage-dependent Ca²⁺ channels abolished the α₁ -AR induced increase in [Ca²⁺ ]_i and number of responders, as did inhibition of phospholipase C inhibitor, protein kinase C and inositol triphosphate receptors. Spontaneous phasic Ca²⁺ events, however, were not altered by NE, PE or CLON. Repeated K⁺ -induced membrane depolarisation produced repetitive [Ca²⁺ ]_i elevations. NE and PE increased baseline Ca²⁺ , whereas NE decreased the peak amplitude. CLON also decreased peak amplitude but did not affect baseline [Ca²⁺ ]_i . Taken together, these data suggest receptor-specific influence of α₁ and α₂ receptors on the various modes of calcium entry in PVN neurones. They further suggest Ca²⁺ increase via α₁ -ARs is co-dependent on extracellular Ca²⁺ influx and intracellular Ca²⁺ release, possibly via a phospholipase C inhibitor-mediated signalling cascade.

Stimulatory Effect of Intermittent Hypoxia on the Production of Corticosterone by Zona Fasciculata-Reticularis Cells in Rats

Hypoxia or intermittent hypoxia (IH) have known to alter both synthesis and secretion of hormones. However, the effect of IH on the production of adrenal cortical steroid hormones is still unclear. The aim of present study was to explore the mechanism involved in the effect of IH on the production of corticosterone by rat ZFR cells. Male rats were exposed at 12% O₂ and 88% N₂ (8 hours per day) for 1, 2, or 4 days. The ZFR cells were incubated at 37 °C for 1 hour with or without ACTH, 8-Br-cAMP, calcium ion channel blockers, or steroidogenic precursors. The concentration of plasma corticosterone was increased time-dependently by administration of IH hypoxia. The basal levels of corticosterone production in cells were higher in the IH groups than in normoxic group. IH resulted in a time-dependent increase of corticosterone production in response to ACTH, 8-Br-cAMP, progesterone and deoxycorticosterone. The production of pregnenolone in response to 25-OH-C and that of progesterone in response to pregnenolone in ZFR cells were enhanced by 4-day IH. These results suggest that IH in rats increases the secretion of corticosterone via a mechanism at least in part associated with the activation of cAMP pathway and steroidogenic enzymes.

Hypoxia-Inducible Factor-1α Mediates Increased Sympathoexcitation via Glutamatergic N-Methyl-d-Aspartate Receptors in the Paraventricular Nucleus of Rats With Chronic Heart Failure

BACKGROUND

Increased sympathetic outflow is a major contributor to the progression of chronic heart failure (CHF). Potentiation of glutamatergic tone has been causally related to the sympathoexcitation in CHF. Specifically, an increase in the N-methyl-d-aspartate-type 1 receptor (NMDA-NR₁) expression within the paraventricular nucleus (PVN) is critically linked to the increased sympathoexcitation during CHF. However, the molecular mechanism(s) for the upregulation of NMDA-NR₁ remains unexplored. We hypothesized that hypoxia via hypoxia-inducible factor 1α (HIF-1α) might contribute to the augmentation of the NMDA-NR₁-mediated sympathoexcitatory responses from the PVN in CHF.

METHODS AND RESULTS

Immunohistochemistry staining, mRNA, and protein for hypoxia-inducible factor 1α were upregulated within the PVN of left coronary artery-ligated CHF rats. In neuronal cell line (NG108-15) in vitro, hypoxia caused a significant increase in mRNA and protein for HIF-1α (2-fold) with the concomitant increase in NMDA-NR₁ mRNA, protein levels, and glutamate-induced Ca⁺ influx. Chromatin immunoprecipitation assay identified HIF-1α binding to NMDA-NR₁ promoter during hypoxia. Silencing of HIF-1α in NG108 cells leads to a significant decrease in expression of NMDA-NR₁, suggesting that expression of HIF-1α is necessary for the upregulation of NMDA-NR₁. Consistent with these observations, HIF-1α silencing within the PVN abrogated the increased basal sympathetic tone and sympathoexcitatory responses to microinjection of NMDA in the PVN of rats with CHF.

CONCLUSIONS

These results uncover a critical role for HIF-1 in the upregulation of NMDA-NR₁ to mediate sympathoexcitation in CHF. We conclude that subtle hypoxia within the PVN may act as a metabolic cue to modulate sympathoexcitation during CHF.

Effect of acute hypoxia on cognition: A systematic review and meta-regression analysis

A systematic meta-regression analysis of the effects of acute hypoxia on the performance of central executive and non-executive tasks, and the effects of the moderating variables, arterial partial pressure of oxygen (PaO₂) and hypobaric versus normobaric hypoxia, was undertaken. Studies were included if they were performed on healthy humans; within-subject design was used; data were reported giving the PaO₂ or that allowed the PaO₂ to be estimated (e.g. arterial oxygen saturation and/or altitude); and the duration of being in a hypoxic state prior to cognitive testing was ≤6days. Twenty-two experiments met the criteria for inclusion and demonstrated a moderate, negative mean effect size (g=-0.49, 95% CI -0.64 to -0.34, p<0.001). There were no significant differences between central executive and non-executive, perception/attention and short-term memory, tasks. Low (35-60mmHg) PaO₂ was the key predictor of cognitive performance (R²=0.45, p<0.001) and this was independent of whether the exposure was in hypobaric hypoxic or normobaric hypoxic conditions.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

Contribution of peripheral and central chemoreceptors to sympatho-excitation in heart failure

Chronic heart failure (CHF) is a major public health problem. Tonic hyper-activation of sympathetic neural outflow is commonly observed in patients with CHF. Importantly, sympatho-excitation in CHF exacerbates its progression and is strongly related to poor prognosis and high mortality risk. Increases in both peripheral and central chemoreflex drive are considered markers of the severity of CHF. The principal peripheral chemoreceptors are the carotid bodies (CBs) and alteration in their function has been described in CHF. Mainly, during CHF the CB chemosensitivity is enhanced leading to increases in ventilation and sympathetic outflow. In addition to peripheral control of breathing, central chemoreceptors (CCs) are considered a dominant mechanism in ventilatory regulation. Potentiation of the ventilatory and sympathetic drive in response to CC activation has been shown in patients with CHF as well as in animal models. Therefore, improving understanding of the contribution of the peripheral and central chemoreflexes to augmented sympathetic discharge in CHF could help in developing new therapeutic approaches intended to attenuate the progression of CHF. Accordingly, the main focus of this review is to discuss recent evidence that peripheral and central chemoreflex function are altered in CHF and that they contribute to autonomic imbalance and progression of CHF.

Infantile hemangiomas, retinopathy of prematurity and cancer: a common pathogenetic role of the β-adrenergic system

The serendipitous demonstration that the nonselective β-adrenergic receptor (β-AR) antagonist propranolol promotes the regression of infantile hemangiomas (IHs) aroused interest around the involvement of the β-adrenergic system in angiogenic processes. The efficacy of propranolol was related to the β2-AR blockade and the consequent inhibition of the production of vascular endothelial growth factor (VEGF), suggesting the hypothesis that propranolol could also be effective in treating retinopathy of prematurity (ROP), a retinal pathology characterized by VEGF-induced neoangiogenesis. Consequent to the encouraging animal studies, a pilot clinical trial showed that oral propranolol protects newborns from ROP progression, even though this treatment is not sufficiently safe. Further, animal studies clarified the role of β3-ARs in the development of ROP and, together with several preclinical studies demonstrating the key role of the β-adrenergic system in tumor progression, vascularization, and metastasis, prompted us to also investigate the participation of β3-ARs in tumor growth. The aim of this review is to gather the recent findings on the role of the β-adrenergic system in IHs, ROP, and cancer, highlighting the fact that these different pathologies, triggered by different pathogenic noxae, share common pathogenic mechanisms characterized by the presence of hypoxia-induced angiogenesis, which may be contrasted by targeting the β-adrenergic system. The mechanisms characterizing the pathogenesis of IHs, ROP, and cancer may also be active during the fetal-neonatal development, and a great contribution to the knowledge on the role of β-ARs in diseases characterized by chronic hypoxia may come from research focusing on the fetal and neonatal period.

Regulation of hypothalamic-pituitary-interrenal axis function in male smallmouth bass (Micropterus dolomieu) during parental care

Male smallmouth bass (Micropterus dolomieu) provide sole parental care until offspring reach independence, a period of several weeks. During the early parental care period when males are guarding fresh eggs (MG-FE), cortisol responsiveness is attenuated; the response is re-established when males reach the end of the parental care period and are guarding free-swimming fry (MG-FSF). It was hypothesized that attenuation of the cortisol response in male smallmouth bass during early parental care reflected modulation of hypothalamic-pituitary-interrenal (HPI) axis function. Male smallmouth bass were sampled at the beginning (MG-FE) and end of the parental care period (MG-FSF), before and/or 25 min after exposure to a standardized stressor consisting of 3 min of air exposure. Repeated sampling of stressed fish for analysis of plasma cortisol and adrenocorticotropic hormone (ACTH) levels was carried out. Males significantly elevated both plasma cortisol and ACTH levels when guarding free-swimming fry but not during early parental care. Control and stressed fish were terminally sampled for tissue mRNA abundance of preoptic area (POA) and hypothalamic corticotropin-releasing factor (CRF) as well as head kidney melanocortin 2 receptor (MC2R), steroidogenic acute regulatory protein (StAR) and cytochrome P450 side chain cleavage enzyme (P450scc). No significant differences in either hypothalamus CRF or head kidney P450scc mRNA abundance were found across parental care stages or in response to stress. However, POA CRF mRNA abundance and interrenal cell MC2R and StAR mRNA abundances failed to increase in response to stress in MG-FE. Thus, the attenuated cortisol response in males guarding fresh eggs may be explained by hypoactive HPI axis function in response to stress. The present is one of few studies, and the first teleost study, to address the mechanisms underlying resistance to stress during the reproductive/parental care period.

Putative role of HIF transcriptional activity in melanocytes and melanoma biology

Hypoxia-inducible factor-1α (HIF-1α) is a highly oxygen sensitive bHLH protein that is part of the heterodimeric HIF-1 transcription factor. Under hypoxic stress, HIF-1 activity is induced to control expression of multiple downstream target genes, including vascular endothelial growth factor (VEGF). The normal epidermis exists in a constant mild hypoxic microenvironment and constitutively expresses HIF-1α and HIF-2α. Expression of HIF-1α and/or HIF-2α has been suggested to correlate with the increased malignant potential of melanocytes, therefore, failures of melanoma therapies may be partially linked to high HIF activity. Notably, melanomas that have the V600E BRAF mutation exhibit increased HIF-1α expression. We have utilized a bioinformatics approach to identify putative hypoxia response elements (HREs) in a set of genes known to participate in the process of melanogenesis (includingTRPM1, SLC45A2, HRAS, C-KIT, PMEL and CRH). While some of the mechanistic links between these genes and the HIF pathway have been previously explored, others await further investigation. Although agents targeting HIF activity have been proposed as novel treatment modalities for melanoma, there are currently no clinical trials in progress to test their efficacy in melanoma.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

Neuronal control of breathing: sex and stress hormones

There is a growing public awareness that hormones can have a significant impact on most biological systems, including the control of breathing. This review will focus on the actions of two broad classes of hormones on the neuronal control of breathing: sex hormones and stress hormones. The majority of these hormones are steroids; a striking feature is that both groups are derived from cholesterol. Stress hormones also include many peptides which are produced primarily within the paraventricular nucleus of the hypothalamus (PVN) and secreted into the brain or into the circulatory system. In this article we will first review and discuss the role of sex hormones in respiratory control throughout life, emphasizing how natural fluctuations in hormones are reflected in ventilatory metrics and how disruption of their endogenous cycle can predispose to respiratory disease. These effects may be mediated directly by sex hormone receptors or indirectly by neurotransmitter systems. Next, we will discuss the origins of hypothalamic stress hormones and their relationship with the respiratory control system. This relationship is 2-fold: (i) via direct anatomical connections to brainstem respiratory control centers, and (ii) via steroid hormones released from the adrenal gland in response to signals from the pituitary gland. Finally, the impact of stress on the development of neural circuits involved in breathing is evaluated in animal models, and the consequences of early stress on respiratory health and disease is discussed.

Upregulation of PVN CRHR1 by gestational intermittent hypoxia selectively triggers a male-specific anxiogenic effect in rat offspring

We previously reported that gestational intermittent hypoxia (GIH) causes anxiety-like behavior in neonatal rats. Here, we showed that the anxiogenic effect was correlated with upregulation of corticotropin-releasing hormone receptor 1 (CRHR1) in the hypothalamic paraventricular nuclei (PVN) by GIH, and was selective to male offspring. The anxiety-like behavior was assessed by both the open field (OF) and elevated plus maze (EPM) tests. We demonstrated that GIH triggered anxiety-like behavior in male offspring, but not in female offspring or in the postpartum dams. Microinjection of antalarmin, a CRHR1-selective antagonist, into the PVN of the male offspring significantly increased the distance traveled and time spent in the central portion of the OF, and the time spent in the open arms in the EPM compared with controls. However, microinjection of the CRHR2 agonist, urocortin III, into the PVN did not affect anxiogenic behavior in the male offspring. These findings clearly demonstrate a gender-selective effect of GIH to increase anxiety-like behavior and this anxiogenic effect might be linked to embryogenically-driven upregulation of PVN CRHR1.

Cocaine use in the past year is associated with altitude of residence

OBJECTIVES

Recently, increased rates of suicide in US counties at higher altitudes have been noted. Because of the documented association between cocaine use and suicide, we hypothesized that there would be a correlation between incidence of cocaine use and altitude of residence.

METHODS

Cocaine use data were obtained from the Substate Substance Abuse Estimates from the 1999-2001 National Surveys on Drug Use and Health. Data related to the percentages of people 12 years or older who used cocaine in the past year. Average elevation for US counties was calculated using the Shuttle Radar Topography Mission elevation data set, and subject region elevation was calculated by averaging the weighted elevations of each region's relevant counties. The correlation between elevation of a substate region and incidence of cocaine use in that region was calculated using Pearson correlation coefficients.

RESULTS

A significant correlation exists between mean altitude of a substate region and incidence of cocaine use in that region (r = 0.34; P < 0.0001). Regression analysis controlling for age, sex, race, education level, income, unemployment, and population density was performed. Altitude remained a significant factor (P = 0.007), whereas male sex (P = 0.008) and possessing less than a college education (P < 0.0001) were also significant predictors of self-reported cocaine use in the past year. It is important to note that cocaine use was assessed in isolation of other drugs of abuse, an additional confounding variable.

CONCLUSIONS

This study demonstrates a significant correlation between altitude of substate region of residence and incidence of cocaine use. It is possible that stress response due to hypoxia is responsible; however, this requires further investigation. However, because other substance use was not assessed, specificity of this association is unknown. In addition, this correlation may help explain the increased rate of suicide in areas of higher elevation.

Roles of the locus coeruleus and adrenergic receptors in brain-mediated hypothalamic-pituitary-adrenal axis responses to intracerebroventricular alcohol

BACKGROUND

Alcohol activates the hypothalamic-pituitary-adrenal (HPA) axis through its actions in both the periphery and the central nervous system (CNS). The studies presented here were designed to test the CNS-specific noradrenergic mechanisms by which alcohol stimulates HPA activity in the male rat.

METHODS

We used an experimental paradigm in which a small, nontoxic amount (5 μl) of alcohol was slowly microinfused intracerebroventricularly (icv). Alcohol was administered icv to animals with lesions of the locus coeruleus (LC) or in animals pretreated with α- or β-adrenergic receptor antagonists. Hormonal HPA activation was determined by measuring secretion of the pituitary stress hormone adrenocorticotropin (ACTH). Neuronal activation was determined by quantification of the expression of the transcription factor c-fos (Fos).

RESULTS

As expected, icv alcohol stimulated ACTH secretion from the pituitary and Fos expression in the paraventricular nucleus of the hypothalamus (PVN). Bilateral electrolytic LC lesions blocked the ability of icv alcohol to stimulate ACTH secretion. Pretreatment with icv propranolol increased basal ACTH secretion levels, but icv alcohol did not increase this effect. Propranolol also blunted icv alcohol-induced PVN Fos expression. A low dose of phenoxybenzamine, an α-adrenergic receptor antagonist, did not affect the ability of icv alcohol to stimulate ACTH release. However, a higher dose of the drug was able to block the ACTH response to icv alcohol. Despite this, phenoxybenzamine did not inhibit alcohol-induced Fos expression. Icv pretreatment with corynanthine, a selective α-1 adrenergic receptor antagonist, modestly raised basal ACTH levels and blocked the icv alcohol-induced secretion of this hormone.

CONCLUSIONS

These results indicate that the LC and norepinephrine play important roles in HPA activation caused by icv alcohol administration, but that the specific adrenergic receptor subtypes involved in this phenomenon still need to be identified.

G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei--serpentine gateways to neuroendocrine homeostasis

G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in the mammalian genome. They are activated by a multitude of different ligands that elicit rapid intracellular responses to regulate cell function. Unsurprisingly, a large proportion of therapeutic agents target these receptors. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important mediators in homeostatic control. Many modulators of PVN/SON activity, including neurotransmitters and hormones act via GPCRs--in fact over 100 non-chemosensory GPCRs have been detected in either the PVN or SON. This review provides a comprehensive summary of the expression of GPCRs within the PVN/SON, including data from recent transcriptomic studies that potentially expand the repertoire of GPCRs that may have functional roles in these hypothalamic nuclei. We also present some aspects of the regulation and known roles of GPCRs in PVN/SON, which are likely complemented by the activity of 'orphan' GPCRs.

Tryptophan hydroxylase: a target for neuroendocrine disruption

Tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin (5-HT) synthesis, performs an essential role in the maintenance of serotonergic functions in the central nervous system (CNS), including regulation of the neuroendocrine system controlling reproduction. The results of recent studies in a teleost model of neuroendocrine disruption, Atlantic croaker, indicated that hypothalamic TPH is a major site of interference of hypothalamic-pituitary-gonadal function by environmental stressors. The effects of exposure to two different types of environmental stressors, low dissolved oxygen (hypoxia) and a polychlorinated biphenyl mixture (Aroclor 1254), on the stimulatory brain serotonergic system controlling reproductive neuroendocrine function in Atlantic croaker are reviewed. Exposure to both stressors produced decreases in TPH activity, which were accompanied by a fall in hypothalamic 5-HT and gonadotropin-releasing hormone (GnRH I) content in the preoptic-anterior hypothalamic area and were associated with reduction in luteinizing hormone (LH) secretion and gonadal development. Pharmacological restoration of hypothalamic 5-HT levels after exposure to both stressors also restored neuroendocrine and reproductive functions, indicating that the serotonergic system is an important site for hypoxia- and Aroclor 1254-induced inhibition of reproductive neuroendocrine functions. The mechanisms underlying downregulation of TPH activity by these stressors remain unclear but may involve alterations in hypothalamic antioxidant status. In support of this hypothesis, treatment with an antioxidant, vitamin E, was found to reverse the inhibitory effects of Aroclor 1254 on TPH activity. The results suggest that TPH is a major target for neuroendocrine disruption by diverse environmental stressors.

Chronic intermittent hypoxia induces NMDA receptor-dependent plasticity and suppresses nitric oxide signaling in the mouse hypothalamic paraventricular nucleus

Chronic intermittent hypoxia (CIH) is a concomitant of sleep apnea that produces a slowly developing chemosensory-dependent blood pressure elevation ascribed in part to NMDA receptor-dependent plasticity and reduced nitric oxide (NO) signaling in the carotid body. The hypothalamic paraventricular nucleus (PVN) is responsive to hypoxic stress and also contains neurons that express NMDA receptors and neuronal nitric oxide synthase (nNOS). We tested the hypothesis that extended (35 d) CIH results in a decrease in the surface/synaptic availability of the essential NMDA NR1 subunit in nNOS-containing neurons and NMDA-induced NO production in the PVN of mice. As compared with controls, the 35 d CIH-exposed mice showed a significant increase in blood pressure and an increased density of NR1 immunogold particles located in the cytoplasm of nNOS-containing dendrites. Neither of these between-group differences was seen after 14 d, even though there was already a reduction in the NR1 plasmalemmal density at this time point. Patch-clamp recording of PVN neurons in slices showed a significant reduction in NMDA currents after either 14 or 35 d exposure to CIH compared with sham controls. In contrast, NO production, as measured by the NO-sensitive fluorescent dye 4-amino-5-methylamino-2',7'-difluorofluorescein, was suppressed only in the 35 d CIH group. We conclude that CIH produces a reduction in the surface/synaptic targeting of NR1 in nNOS neurons and decreases NMDA receptor-mediated currents in the PVN before the emergence of hypertension, the development of which may be enabled by suppression of NO signaling in this brain region.

Modulation of cardiorespiratory function mediated by the paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) coordinates autonomic and neuroendocrine systems to maintain homeostasis and to respond to stress. Neuroanatomic and neurophysiologic experiments have provided insight into the mechanisms by which the PVN acts. The PVN projects directly to the spinal cord and brainstem and, specifically, to sites that control cardio-respiratory function: the intermediolateral cell columns and phrenic motor nuclei in the spinal cord and rostral ventrolateral medulla (RVLM) and the rostral nuclei in the ventral respiratory column (rVRC) in the brainstem. Activation of the PVN increases ventilation (both tidal volume and frequency) and blood pressure (both heart rate and sympathetic nerve activity). Excitatory and inhibitory neurotransmitters including glutamate and GABA converge in the PVN to influence its neuronal activity. However, a tonic GABAergic input to the PVN directly modulates excitatory outflow from the PVN. Further, even within the PVN, microinjection of GABA(A) receptor blockers increases glutamate release suggesting an indirect mechanism by which GABA control contributes to PVN functions. PVN activity alters blood pressure and ventilation during various stresses, such as maternal separation, chronic intermittent hypoxia (CIH), dehydration and hemorrhage. Among the several PVN neurotransmitters and neurohormones, vasopressin and oxytocin modulate ventilation and blood pressure. Here, we review our data indicating that increases in vasopressin and vasopressin type 1A (V(1A)) receptor signalling in the RVLM and rVRC are mechanisms increasing blood pressure and ventilation after exposure to CIH. That blockade of V(1A) receptors in the medulla normalizes baseline blood pressure as well as blunts PVN-evoked blood pressure and ventilatory responses in CIH-conditioned animals indicate the role of vasopressin in cardiorespiratory control. In summary, morphological and functional studies have found that the PVN integrates sensory input and projects to the sympathetic and respiratory control systems with descending projections to the medulla and spinal cord.

Increased vasopressin transmission from the paraventricular nucleus to the rostral medulla augments cardiorespiratory outflow in chronic intermittent hypoxia-conditioned rats

A co-morbidity of sleep apnoea is hypertension associated with elevated sympathetic nerve activity (SNA) which may result from conditioning to chronic intermittent hypoxia (CIH). Our hypothesis is that SNA depends on input to the rostral ventrolateral medulla (RVLM) from neurons in the paraventricular nucleus (PVN) that release arginine vasopressin (AVP) and specifically, that increased SNA evoked by CIH depends on this excitatory input. In two sets of neuroanatomical experiments, we determined if AVP neurons project from the PVN to the RVLM and if arginine vasopressin (V(1A)) receptor expression increases in the RVLM after CIH conditioning (8 h per day for 10 days). In the first set, cholera toxin beta subunit (CT-beta) was microinjected into the RVLM to retrogradely label the PVN neurons. Immunohistochemical staining demonstrated that 14.6% of CT-beta-labelled PVN neurons were double-labelled with AVP. In the second set, sections of the medulla were immunolabelled for V(1A) receptors, and the V(1A) receptor-expressing cell count was significantly greater in the RVLM (P < 0.01) and in the neighbouring rostral ventral respiratory column (rVRC) from CIH- than from room air (RA)-conditioned rats. In a series of physiological experiments, we determined if blocking V(1A) receptors in the medulla would normalize blood pressure in CIH-conditioned animals and attenuate its response to disinhibition of PVN. Blood pressure (BP), heart rate (HR), diaphragm (D(EMG)) and genioglossus muscle (GG(EMG)) activity were recorded in anaesthetized, ventilated and vagotomized rats. The PVN was disinhibited by microinjecting a GABA(A) receptor antagonist, bicuculline (BIC, 0.1 nmol), before and after blocking V(1A) receptors within the RVLM and rVRC with SR49059 (0.2 nmol). In RA-conditioned rats, disinhibition of the PVN increased BP, HR, minute D(EMG) and GG(EMG) activity and these increases were attenuated after blocking V(1A) receptors. In CIH-conditioned rats, a significantly greater dose of blocker (0.4 nmol) was required to blunt these physiological responses (P < 0.05). Further, this dose normalized the baseline BP. In summary, AVP released by a subset of PVN neurons modulates cardiorespiratory output via V(1A) receptors in the RVLM and rVRC, and increased SNA in CIH-conditioned animals depends on up-regulation of V(1A) receptors in the RVLM.

Corticotropin releasing factor influences aggression and monoamines: modulation of attacks and retreats

Salmonids establish social hierarchies as a result of aggressive social interactions. The establishment of dominant or subordinate status is strongly linked to neuroendocrine responses mediated through the stress axis. In this study, we tested the effects of introcerebroventricular (icv) corticotropin releasing factor (CRF) on the behavioral outcome, plasma cortisol and monoamine function in trout subjected to a socially aggressive encounter. Rainbow trout were treated with an icv injection of artificial cerebrospinal fluid (aCSF), 500 or 2000 ng ovine CRF, or not injected. Fish were allowed to interact with a similarly sized conspecific for 15 min. Following the behavioral interaction, plasma cortisol and central monoamine concentrations were analyzed. Trout treated with CRF were victorious in approximately 66% of the aggressive encounters against aCSF-treated opponents. Trout injected with CRF exhibited a reduction in the total number of attacks and decreased latency to attack. When trout were divided into winners and losers, only victorious CRF-treated fish exhibited a reduced latency to attack and fewer retreats. Social stress increased cortisol levels in both winners and losers of aggressive interaction. This effect was enhanced with the additional stress incurred from icv injection of aCSF. However, icv CRF in addition to social stress decreased plasma cortisol in both winners and losers. While aggression stimulated significant changes in serotonergic and dopaminergic activity, the magnitude and direction were dependent on limbic brain region, CRF dose, and outcome of social aggression. With broad effects on aggressive behavior, anxiety, stress responsiveness, and central monoaminergic activity, CRF plays an important role in modulating the behavioral components of social interaction.

Erythropoietin inhibits basal and stimulated corticotropin-releasing hormone release from the rat hypothalamus via a nontranscriptional mechanism

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

Maternal attenuation of hypothalamic paraventricular nucleus norepinephrine switches avoidance learning to preference learning in preweanling rat pups

Infant rats learn to prefer stimuli paired with pain, presumably due to the importance of learning to prefer the caregiver to receive protection and food. With maturity, a more 'adult-like' learning system emerges that includes the amygdala and avoidance/fear learning. The attachment and 'adult-like' systems appear to co-exist in older pups with maternal presence engaging the attachment system by lowering corticosterone (CORT). Specifically, odor-shock conditioning (11 odor-0.5 mA shock trials) in 12-day-old pups results in an odor aversion, although an odor preference is learned if the mother is present during conditioning. Here, we propose a mechanism to explain pups ability to 'switch' between the dual learning systems by exploring the effect of maternal presence on hypothalamic paraventricular nucleus (PVN) neural activity, norepinephrine (NE) levels and learning. Maternal presence attenuates both PVN neural activity and PVN NE levels during odor-shock conditioning. Intra-PVN NE receptor antagonist infusion blocked the odor aversion learning with maternal absence, while intra-PVN NE receptor agonist infusion permitted odor aversion learning with maternal presence. These data suggest maternal control over pup learning acts through attenuation of PVN NE to reduce the CORT required for pup odor aversion learning. Moreover, these data also represent pups' continued maternal dependence for nursing, while enabling aversion learning outside the nest to prepare for pups future independent living.

Effects of hypoxia on glucose, insulin, glucagon, and modulation by corticotropin-releasing factor receptor type 1 in the rat

To determine the influence of continuous hypoxia on body weight, food intake, hepatic glycogen, circulatory glucose, insulin, glucagon, leptin, and corticosterone, and the involvement of the corticotropin-releasing factor receptor type 1 (CRFR1) in modulation of these hormones, rats were exposed to a simulated altitude of 5 km (approximately 10.8% O2) in a hypobaric chamber for 1, 2, 5, 10, and 15 d. Potential involvement of CRFR1 was assessed through five daily sc injections of a CRFR1 antagonist (CP-154,526) prior to hypoxia. Results showed that the levels of body weight, food intake, blood glucose, and plasma insulin were significantly reduced; the content of hepatic glycogen initially and transiently declined, whereas the early plasma glucagon and leptin remarkably increased; plasma corticosterone was markedly increased throughout the hypoxic exposure of 1-15 d. Compared with hypoxia alone, CRFR1 antagonist pretreatment in the hypoxic groups prevented the rise in corticosterone, whereas the levels of body weight and food intake were unchanged. At the same time, the reduction in blood glucose was greater and the pancreatic glucose was increased, plasma insulin reverted toward control, and plasma glucagon decreased. In summary, prolonged hypoxia reduced body weight, food intake, blood glucose, and plasma insulin but transiently enhanced plasma glucagon and leptin. In conclusion, CRFR1 is potentially involved in the plasma insulin reduction and transient glucagon increase in hypoxic rats.

Neonatal maternal separation and enhancement of the hypoxic ventilatory response in rat: the role of GABAergic modulation within the paraventricular nucleus of the hypothalamus

Neonatal maternal separation (NMS) affects respiratory control development as adult male (but not female) rats previously subjected to NMS show a hypoxic ventilatory response 25% greater than controls. The paraventricular nucleus of the hypothalamus (PVN) is an important modulator of respiratory activity. In the present study, we hypothesized that in awake rats, altered GABAergic inhibition within the PVN contributes to the enhancement of hypoxic ventilatory response observed in rats previously subjected to NMS. During normoxia, the increase in minute ventilation following microinjection of bicuculline (1 mm) within the PVN is greater in NMS versus control rats. These data show that regulation of ventilatory activity related to tonic inhibition of the PVN is more important in NMS than control rats. Microinjection of GABA or muscimol (1 mM) attenuated the ventilatory response to hypoxia (12% O2) in NMS rats only. The higher efficiency of microinjections in NMS rats is supported by results from GABAA receptor autoradiography which revealed a 22% increase in GABAA receptor binding sites within the PVN of NMS rats versus controls. Despite this increase, however, NMS rats still show a larger hypoxic ventilatory response than controls, suggesting that within the PVN the larger number of GABAA receptors either compensate for (1) a deficient GABAergic modulation, (2) an increase in the efficacy of excitatory inputs converging onto this structure, or (3) both. Together, these results show that the life-long consequences of NMS are far reaching as they can compromise the development of vital homeostatic function in a way that may predispose to respiratory disorders.

Corticotropin-releasing factor receptor subtype 1 and somatostatin modulating hypoxia-caused downregulated mRNA of pituitary growth hormone and upregulated mRNA of hepatic insulin-like growth factor-I of rats

The study aims to examine the effects of restraint, cold, and in combination of hypoxia on pituitary GH mRNA and hepatic IGF-I mRNA and its protein in rats, and the potential involvement of corticotropin-releasing factor receptor subtype 1 (CRFR1) and SS in mediating the effects of continual hypoxia. Continual or intermittent hypoxia of 5 km (10.8% O2) was simulated in a hypobaric chamber. The mRNAs and peptides were determined using RT-PCR and Elisa or histochemistry. Continual hypoxia of 5 km markedly enhanced immunostaining pituitary GH and hepatic IGF-I for 1 and 2 days restoring afterward. The hypoxia for 5 days significantly reduced the pituitary GH mRNA and increased the hepatic IGF-I mRNA. Intermittent hypoxia of 5 km 4 h/day for 2 days, cold (4 degrees C) 4h/day for 2 days, and restraint 4 h/day for 2 days alone or in combination significantly enhanced immunostaining pituitary GH and hepatic IGF-I (except cold). The combined stresses had greater effects than single stresses alone. CRFR1 antagonist (CP154526) or SS antagonist (cysteamine) markedly blocked hypoxia-reduced pituitary GH mRNA and hypoxia-activated hepatic IGF-I mRNA, and further reduced hypoxia-reduced plasma IGF. In conclusion, hypoxia (continually or intermittently), restraint, cold alone or in combination modulate pituitary GH and hepatic IGF-I. The pituitary GH/GH mRNA and hepatic IGF-I/IGF-I mRNA, and plasma IGF-I are modified by hypoxia through SS and CRFR1 mediation.

Paraventricular nucleus, stress response, and cardiovascular disease

The paraventricular nucleus of the hypothalamus (PVN) is a complex effector structure that initiates endocrine and autonomic responses to stress. It receives inputs from visceral receptors, circulating hormones such as angiotensin II, and limbic circuits and contains neurons that release vasopressin, activate the adrenocortical axis, and activate preganglionic sympathetic or parasympathetic outflows. The neurochemical control of the different subgroups of PVN neurons is complex. The PVN has been implicated in the pathophysiology of congestive heart failure and the metabolic syndrome.

CRF-related peptides contribute to stress response and regulation of appetite in hypoxic rainbow trout

Hypoxia stress suppresses appetite in a variety of fish species, but the mechanisms mediating this response are not known. Therefore, given their anorexigenic and hypophysiotropic properties, we investigated the contribution of forebrain corticotropin-releasing factor (CRF) and urotensin I (UI) to the regulation of food intake and the hypothalamic-pituitary-interrenal (HPI) stress axis in hypoxic rainbow trout. Exposure to 50 and 35% O(2) saturation for 24 h decreased food intake by 28 and 48%, respectively. The 35% O(2) treatment also increased forebrain CRF and UI mRNA levels, plasma cortisol, and lactate. Exposure for 72 h to the same conditions resulted in similar reductions in food intake, increases in plasma cortisol proportional to the hypoxia severity, and increases in forebrain CRF and UI mRNA levels in the 50% O(2) treatment. Relative to saline-infused fish, chronic intracranial infusion of the CRF receptor antagonist alpha-helical CRF((9-41)) reduced the appetite-suppressing effects of 24-h exposure to 35% O(2) and blocked the hypoxia-induced increase in plasma cortisol. Finally, forebrain microdissection revealed that 50 and 35% O(2) exposure for 24 h specifically increases preoptic area CRF and UI mRNA levels in proportion to the severity of the hypoxic challenge and either has no effect or elicits small decreases in other forebrain regions. These results show that CRF-related peptides play a physiological role in regulating the HPI axis and in mediating at least a portion of the reduction in food intake under hypoxic conditions in rainbow trout and demonstrate that the response of forebrain CRF and UI neurons to this stressor is region specific.

CRF receptor type 1 mediates continual hypoxia-induced CRF peptide and CRF mRNA expression increase in hypothalamic PVN of rats

We demonstrated previously that hypoxia activated CRF and CRF mRNA in PVN, and CRF receptor 1 (CRFR1) mRNA in rat pituitary. The aim of the study is to test whether the hypoxia-activated CRF and CRF mRNA is associated with triggering CRFR1. Rats were exposed to hypobaric hypoxia at altitude of 2 and 5 km. CRF and CRF mRNA were assayed by immunostaining and in situ hybridization. CRFR1 mRNA was assayed by RT-PCR. Results showed that 5 km continual hypoxia increased CRF and CRF mRNA in PVN, CRFR1 mRNA in pituitary, and plasma corticosterone. The hypoxia-increased CRF, CRF mRNA, CRFR1 mRNA, and corticosterone were blocked by CRFR1 antagonist (CP-154,526), suggesting that CRFR1 in PVN and pituitary are responsible for the hypoxia-increased CRF and CRF mRNA in PVN.

Corticotropin-releasing factor receptor type 1 and 2 mRNA expression in the rat anterior pituitary is modulated by intermittent hypoxia, cold and restraint

We had previously demonstrated that continual-hypoxia stimulated corticotropin-releasing factor (CRF)mRNA in hypothalamus, and release of CRF, as well as enhancing plasma adrenocorticotropic-hormone and corticosterone of rats. The present study demonstrates using in situ autoradiography that CRF receptor 1 (CRFR1) and CRF receptor 2 (CRFR2) mRNA in the rat anterior pituitary is changed by intermittent hypoxia, cold, restraint, alone and in combination. Rats were exposed to intermittent hypoxia for 4 h/day during various periods in a hypobaric chamber. Hypoxia equivalent to an altitude of around 2 km (16.0% O2) or 5 km (10.8% O2) caused a biphasic change in both CRFR1 and R2 mRNA, there being an initial significant decline on day 1 and then an enhancement by day 2. The increase of both receptor subtypes mRNA was relatively well maintained up to 15 days in rats exposed to 2 km intermittently. CRFR2 mRNA in rats exposed to 5 km, after peaking at day 2 therefore declined and was not different to controls at 15 days. Five kilometer hypoxia markedly reduced body weight gain. The increased CRFR1 mRNA was also induced by restraint alone, hypoxia+restraint and hypoxia+cold but not by cold alone. The CRFR2 mRNA was significantly increased by all the stresses except for hypoxia+restraint. These results show that the acute response to intermittent hypoxia is a decrease in the CRF receptor mRNA whereas longer exposure to the three environmental stressors hypoxia, cold and restraint is needed to provoke an increase. This may have important consequences for adaptation to high altitude. The significant differences between the expression of CRFR1 mRNA and CRFR2 mRNA in response to the different stimuli might suggest that the two receptors in the pituitary play different roles in behavior.