Limited brain diffusion of the glucocorticoid receptor agonist RU28362 following i.c.v. administration: implications for i.c.v. drug delivery and glucocorticoid negative feedback in the hypothalamic-pituitary-adrenal axis

Sex-Dependent Mechanisms of Glucocorticoid Regulation of the Mouse Hypothalamic Corticotropin-Releasing Hormone Gene

To limit excessive glucocorticoid secretion following hypothalamic-pituitary-adrenal (HPA) axis stimulation, circulating glucocorticoids inhibit corticotropin-releasing hormone (CRH) expression in paraventricular nucleus (PVN) neurons. As HPA function differs between sexes and depends on circulating estradiol (E2) levels in females, we investigated sex/estrous stage-dependent glucocorticoid regulation of PVN Crh. Using NanoString nCounter technology, we first demonstrated that adrenalectomized (ADX'd) diestrous female (low E2), but not male or proestrous female (high E2), mice exhibited a robust decrease in PVN CRH mRNA following 2-day treatment with the glucocorticoid receptor (GR) agonist RU28362. Immunohistochemical analysis of PVN CRH neurons in Crh-IRES-Cre;Ai14 mice, where TdTomato fluorescence permanently tags CRH-expressing neurons, showed similarly abundant co-expression of GR-immunoreactivity in males, diestrous females, and proestrous females. However, we identified sex/estrous stage-related glucocorticoid regulation or expression of GR transcriptional coregulators. Out of 17 coregulator genes examined using nCounter multiplex analysis, mRNAs that were decreased by RU28362 in ADX'd mice in a sex/estrous stage-dependent fashion included: GR (males = diestrous females > proestrous females), signal transducer and activator of transcription 3 (STAT3) (males < diestrous = proestrous), and HDAC1 (males < diestrous > proestrous). Steroid receptor coactivator 3 (SRC-3), nuclear corepressor 1 (NCoR1), heterogeneous nuclear ribonucleoprotein U (hnrnpu), CREB binding protein (CBP) and CREB-regulated transcription coactivator 2 (CRTC2) mRNAs were lower in ADX'd diestrous and proestrous females versus males. Additionally, most PVN CRH neurons co-expressed methylated CpG binding protein 2 (MeCP2)-immunoreactivity in diestrous female and male Crh-IRES-Cre;Ai14 mice. Our findings collectively suggest that GR's sex-dependent regulation of PVN Crh may depend upon differences in the GR transcriptional machinery and an underlying influence of E2 levels in females.

Chronic early postnatal scream sound stress induces learning deficits and NMDA receptor changes in the hippocampus of adult mice

Chronic scream sounds during adulthood affect spatial learning and memory, both of which are sexually dimorphic. The long-term effects of chronic early postnatal scream sound stress (SSS) during postnatal days 1-21 (P1-P21) on spatial learning and memory in adult mice as well as whether or not these effects are sexually dimorphic are unknown. Therefore, the present study examines the performance of adult male and female mice in the Morris water maze following exposure to chronic early postnatal SSS. Hippocampal NR2A and NR2B levels as well as NR2A/NR2B subunit ratios were tested using immunohistochemistry. In the Morris water maze, stress males showed greater impairment in spatial learning and memory than background males; by contrast, stress and background females performed equally well. NR2B levels in CA1 and CA3 were upregulated, whereas NR2A/NR2B ratios were downregulated in stressed males, but not in females. These data suggest that chronic early postnatal SSS influences spatial learning and memory ability, levels of hippocampal NR2B, and NR2A/NR2B ratios in adult males. Moreover, chronic early stress-induced alterations exert long-lasting effects and appear to affect performance in a sex-specific manner.

A users guide to HPA axis research

Glucocorticoid hormones (cortisol and corticosterone - CORT) are the effector hormones of the hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine system. CORT is a systemic intercellular signal whose level predictably varies with time of day and dynamically increases with environmental and psychological stressors. This hormonal signal is utilized by virtually every cell and physiological system of the body to optimize performance according to circadian, environmental and physiological demands. Disturbances in normal HPA axis activity profiles are associated with a wide variety of physiological and mental health disorders. Despite numerous studies to date that have identified molecular, cellular and systems-level glucocorticoid actions, new glucocorticoid actions and clinical status associations continue to be revealed at a brisk pace in the scientific literature. However, the breadth of investigators working in this area poses distinct challenges in ensuring common practices across investigators, and a full appreciation for the complexity of a system that is often reduced to a single dependent measure. This Users Guide is intended to provide a fundamental overview of conceptual, technical and practical knowledge that will assist individuals who engage in and evaluate HPA axis research. We begin with examination of the anatomical and hormonal components of the HPA axis and their physiological range of operation. We then examine strategies and best practices for systematic manipulation and accurate measurement of HPA axis activity. We feature use of experimental methods that will assist with better understanding of CORT's physiological actions, especially as those actions impact subsequent brain function. This research approach is instrumental for determining the mechanisms by which alterations of HPA axis function may contribute to pathophysiology.

Absence of glucocorticoids augments stress-induced Mkp1 mRNA expression within the hypothalamic-pituitary-adrenal axis

Stress-induced activation of hypothalamic paraventricular nucleus (PVN) corticotropin-releasing hormone (CRH) neurons trigger CRH release and synthesis. Recent findings have suggested that this process depends on the intracellular activation (phosphorylation) of ERK1/2 within CRH neurons. We have recently shown that the presence of glucocorticoids constrains stress-stimulated phosphorylation of PVN ERK1/2. In some peripheral cell types, dephosphorylation of ERK has been shown to be promoted by direct glucocorticoid upregulation of the MAP kinase phosphatase 1 (Mkp1) gene. In this study, we tested the hypothesis that glucocorticoids regulate Mkp1 mRNA expression in the neural forebrain (medial prefrontal cortex, mPFC, and PVN) and endocrine tissue (anterior pituitary) by subjecting young adult male Sprague-Dawley rats to various glucocorticoid manipulations with or without acute psychological stress (restraint). Restraint led to a rapid increase in Mkp1 mRNA within the mPFC, PVN, and anterior pituitary, and this increase did not require glucocorticoid activity. In contrast to glucocorticoid upregulation of Mkp1 gene expression in the peripheral tissues, we found that the absence of glucocorticoids (as a result of adrenalectomy) augmented basal mPFC and stress-induced PVN and anterior pituitary Mkp1 gene expression. Taken together, this study indicates that the presence of glucocorticoids may constrain Mkp1 gene expression in the neural forebrain and endocrine tissues. This possible constraint may be an indirect consequence of the inhibitory influence of glucocorticoids on stress-induced activation of ERK1/2, a known upstream positive regulator of Mkp1 gene transcription.

Galanin-induced decreases in nucleus accumbens/striatum excitatory postsynaptic potentials and morphine conditioned place preference require both galanin receptor 1 and galanin receptor 2

The neuropeptide galanin has been shown to alter the rewarding properties of morphine. To identify potential cellular mechanisms that might be involved in the ability of galanin to modulate opiate reward, we measured excitatory postsynaptic potentials (EPSPs), using both field and whole-cell recordings from striatal brain slices extracted from wild-type mice and mice lacking specific galanin receptor (GalR) subtypes. We found that galanin decreased the amplitude of EPSPs in both the dorsal striatum and nucleus accumbens. We then performed recordings in slices from knockout mice lacking either the GalR1 or GalR2 gene, and found that the ability of galanin to decrease EPSP amplitude was absent from both mouse lines, suggesting that both receptor subtypes are required for this effect. In order to determine whether behavioral responses to opiates were dependent on the same receptor subtypes, we tested GalR1 and GalR2 knockout mice for morphine conditioned place preference (CPP). Morphine CPP was significantly attenuated in both GalR1 and GalR2 knockout mice. These data suggest that mesolimbic excitatory signaling is significantly modulated by galanin in a GalR1-dependent and GalR2-dependent manner, and that morphine CPP is dependent on the same receptor subtypes.

Tonic, but not phasic corticosterone, constrains stress activatedextracellular-regulated-kinase 1/ 2 immunoreactivity within the hypothalamic paraventricular nucleus

The negative-feedback actions of corticosterone (CORT) depend on both phasic and tonic CORT secretion patterns to regulate hypothalamic-pituitary-adrenal (HPA) axis activity. How these two different CORT secretion pattens influence specific intracellular signal transduction pathway activity within the cellular elements of the HPA axis has not been determined. For example, it is unknown whether CORT has suppressive actions over signal transduction events within medial parvocellular paraventricular nucleus (PVN) corticotrophin-releasing hormone (CRH) neurones, nor whether these suppressive actions are responsible for alterations in PVN transcriptional processes and neurohormone secretion associated with stress. The extracellular-regulated kinase (ERK) is a stress activated intracellular signalling molecule that is potentially subject to glucocorticoid negative-feedback regulation. We tested the ability of CORT to modulate levels of the active (phosphorylated) form of ERK (pERK1/2) in the PVN of rats. Acute psychological stress (restraint) produced a rapid increase in the number of PVN pERK1/2 immunopositive cells within CRH neurones. Absence of tonic CORT via adrenalectomy (ADX) produced no change in basal pERK1/2 cell counts but augmented the increased pERK1/2 cell counts elicited by acute restraint. Treatment of ADX rats with CORT in the drinking water normalised this enhanced pERK1/2 response to stress. By contrast, treatment of ADX rats with a phasic increase in CORT 1 h before restraint had no effect on pERK1/2 cell counts, despite substantially suppressing stress-induced PVN crh gene expression and adrenonocorticotrophic hormone secretion. This tonic CORT inhibition of stress-induced activation of ERK1/2 may involve both alteration of the activity of stress-dependent neural inputs to PVN CRH neurones and alteration within those neurones of stress-dependent intracellular signalling mechanisms associated with ERK activation.

Oxytocin reduces background anxiety in a fear-potentiated startle paradigm: peripheral vs central administration

Oxytocin is known to have anti-anxiety and anti-stress effects. Using a fear-potentiated startle paradigm in rats, we previously demonstrated that subcutaneously administered oxytocin suppressed acoustic startle following fear conditioning compared with startle before fear conditioning (termed background anxiety), but did not have an effect on cue-specific fear-potentiated startle. The findings suggest oxytocin reduces background anxiety, an anxious state not directly related to cue-specific fear, but sustained beyond the immediate threat. The goal of the present study was to compare the effects of centrally and peripherally administered oxytocin on background anxiety and cue-specific fear. Male rats were given oxytocin either subcutaneously (SC) or intracerebroventricularly (ICV) into the lateral ventricles before fear-potentiated startle testing. Oxytocin doses of 0.01 and 0.1 μg/kg SC reduced background anxiety. ICV administration of oxytocin at doses from 0.002 to 20 μg oxytocin had no effect on background anxiety or cue-specific fear-potentiated startle. The 20 μg ICV dose of oxytocin did reduce acoustic startle in non-fear conditioned rats. These studies indicate that oxytocin is potent and effective in reducing background anxiety when delivered peripherally, but not when delivered into the cerebroventricular system. Oxytocin given systemically may have anti-anxiety properties that are particularly germane to the hypervigilance and exaggerated startle typically seen in many anxiety and mental health disorder patients.

Estrogen receptor beta activation prevents glucocorticoid receptor-dependent effects of the central nucleus of the amygdala on behavior and neuroendocrine function

Neuropsychiatric disorders such as anxiety and depression have formidable economic and societal impacts. A dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis leading to elevated endogenous glucocorticoid levels is often associated with such disorders. Chronically high glucocorticoid levels may act upon the central nucleus of the amygdala (CeA) to alter normally adaptive responses into those that are maladaptive and detrimental. In addition to glucocorticoids, other steroid hormones such as estradiol and androgens can also modify hormonal and behavioral responses to threatening stimuli. In particular, estrogen receptor beta (ERbeta) agonists have been shown to be anxiolytic. Consequently, these experiments addressed the hypothesis that the selective stimulation of glucocorticoid receptor (GR) in the CeA would increase anxiety-like behaviors and HPA axis reactivity to stress, and further, that an ERbeta agonist could modulate these effects. Young adult female Sprague-Dawley rats were ovariectomized and bilaterally implanted via stereotaxic surgery with a wax pellet containing the selective GR agonist RU28362 or a blank pellet, to a region just dorsal to the CeA. Four days later, animals were administered the ERbeta agonist S-DPN or vehicle (with four daily sc injections). Anxiety-type behaviors were measured using the elevated plus maze (EPM). Central RU28362 implants caused significantly higher anxiety-type behaviors in the EPM and greater plasma CORT levels than controls given a blank central implant. Moreover, S-DPN treated animals, regardless of type of central implant, displayed significantly lower anxiety-type behaviors and post-EPM plasma CORT levels than vehicle treated controls or vehicle treated animals implanted with RU28362. These results indicate that selective activation of GR within the CeA is anxiogenic, and peripheral administration of an ERbeta agonist can overcome this effect. These data suggest that estradiol signaling via ERbeta prevents glucocorticoid-dependent effects of the CeA on behavior and neuroendocrine function.

Chronic blockade of hindbrain glucocorticoid receptors reduces blood pressure responses to novel stress and attenuates adaptation to repeated stress

Exogenous glucocorticoids act within the hindbrain to enhance the arterial pressure response to acute novel stress. Here we tested the hypothesis that endogenous glucocorticoids act at hindbrain glucocorticoid receptors (GR) to augment cardiovascular responses to restraint stress in a model of stress hyperreactivity, the borderline hypertensive rat (BHR). A 3- to 4-mg pellet of the GR antagonist mifepristone (Mif) was implanted over the dorsal hindbrain (DHB) in Wistar-Kyoto (WKY) and BHRs. Control pellets consisted of either sham DHB or subcutaneous Mif pellets. Rats were either subjected to repeated restraint stress (chronic stress) or only handled (acute stress) for 3-4 wk, then all rats were stressed on the final day of the experiment. BHR showed limited adaptation of the arterial pressure response to restraint, and DHB Mif significantly (P Collapse

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MESH Headings

• Adaptation, Physiological/physiology
• Animals
• Blood Pressure/physiology
• Body Weight/physiology
• Corticosterone/blood
• Disease Models, Animal
• Heart Rate/physiology
• Hormone Antagonists/pharmacology
• Hypertension/metabolism
• Hypertension/physiopathology
• Male
• Mifepristone/pharmacology
• Rats
• Rats, Inbred WKY
• Rats, Sprague-Dawley
• Receptors, Glucocorticoid/antagonists & inhibitors
• Receptors, Glucocorticoid/drug effects
• Receptors, Glucocorticoid/metabolism
• Rhombencephalon/metabolism
• Stress, Physiological/physiology

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Grants

• R01-HL-076807 NHLBI NIH HHS

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Affiliation(s)

Andrea G Bechtold Department of Medical Pharmacology, School of Medicine, University of California Davis, Davis, California, USA
Gina Patel
Guenther Hochhaus
Deborah A Scheuer

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Sex differences in plasma corticosterone release in undisturbed chickens (Gallus gallus) in response to arginine vasotocin and corticotropin releasing hormone

In birds, two neuropeptides, corticotropin releasing hormone (CRH) and arginine vasotocin (AVT), are major regulators of the hypothalamo-pituitary-adrenal axis (HPA) during the stress response. In birds, however, the relative efficacy of CRH and AVT to stimulate the HPA axis in males and females remains unknown. The purpose of this study was to determine the time course of CORT release following central CRH and AVT administration to male and female chickens. Chickens were fitted with a stainless steel cannula surgically implanted in the lateral ventricle and a catheter chronically inserted in the jugular vein. Birds were housed individually in cages behind a one-way glass partition and unnecessary noise was avoided during the sampling period. Each bird received a single 5.0microtracerebroventricular (ICV) injection of either saline (SAL), AVT (10 and 100pmol), or CRH (10 and 100pmol). Blood was sampled remotely every 15min for 2h and plasma CORT was determined by radioimmunoassay. There was a significant increase in plasma CORT concentration in males injected with 100pmol AVT beginning at 15min post-injection through 2h compared with SAL injected birds. In males, injection of 100pmol CRH was significantly more effective in releasing CORT compared to an equal molar concentration of AVT or SAL. In females, ICV injection of 100pmol AVT induced moderate increase in CORT levels. In contrast, 100pmol CRH significantly increased plasma CORT compared to SAL injected controls but the CORT response was nearly 50% less than that obtained in males.