The central role of corticotrophin-releasing factor (CRF-41) in psychological stress in rats

Characteristics of Functional Hyperthermia Detected in an Outpatient Clinic for Fever of Unknown Origin

Background: Functional hyperthermia (FH) is characterized by hyperthermia resulting from sympathetic hyperactivity rather than inflammation, and it is frequently overlooked by medical practitioners due to the absence of abnormalities in a medical examination. Although FH is an important differential diagnosis for fever of unknown origin (FUO), the literature on FUO cases in Japan lacks information on FH. In this study, we aimed to uncover the population of FH patients hidden in FUO cases. Methods: An outpatient clinic for FUO was established at Okayama University Hospital, and 132 patients were examined during the period from May 2019 to February 2022. Results: A diagnosis of FH was made in 31.1% of the FUO cases, and FH predominantly affected individuals in their third and fourth decades of life with a higher incidence in females (68.3%). The frequency of a history of psychiatric illness was higher in patients with FH than in patients with other febrile illnesses. Although the C-reactive protein (CRP) is generally negative in FH cases, some obese patients, with a body mass index ≥ 25 had slightly elevated levels of CRP but were diagnosed with FH. Conclusions: The results showed the importance of identifying FH when encountering patients with FUO without any organic etiology.

The Role of the Paraventricular-Coerulear Network on the Programming of Hypertension by Prenatal Undernutrition

A crucial etiological component in fetal programming is early nutrition. Indeed, early undernutrition may cause a chronic increase in blood pressure and cardiovascular diseases, including stroke and heart failure. In this regard, current evidence has sustained several pathological mechanisms involving changes in central and peripheral targets. In the present review, we summarize the neuroendocrine and neuroplastic modifications that underlie maladaptive mechanisms related to chronic hypertension programming after early undernutrition. First, we analyzed the role of glucocorticoids on the mechanism of long-term programming of hypertension. Secondly, we discussed the pathological plastic changes at the paraventricular nucleus of the hypothalamus that contribute to the development of chronic hypertension in animal models of prenatal undernutrition, dissecting the neural network that reciprocally communicates this nucleus with the locus coeruleus. Finally, we propose an integrated and updated view of the main neuroendocrine and central circuital alterations that support the occurrence of chronic increases of blood pressure in prenatally undernourished animals.

NLRP3 at the crossroads between immune/inflammatory responses and enteric neuroplastic remodelling in a mouse model of diet-induced obesity

BACKGROUND AND PURPOSE

Enteric neurogenic/inflammation contributes to bowel dysmotility in obesity. We examined the role of NLRP3 in colonic neuromuscular dysfunctions in mice with high-fat diet (HFD)-induced obesity.

EXPERIMENTAL APPROACH

Wild-type C57BL/6J and NLRP3-KO (Nlrp3^-/- ) mice were fed with HFD or standard diet for 8 weeks. The activation of inflammasome pathways in colonic tissues from obese mice was assessed. The role of NLRP3 in in vivo colonic transit and in vitro tachykininergic contractions and substance P distribution was evaluated. The effect of substance P on NLRP3 signalling was tested in cultured cells.

KEY RESULTS

HFD mice displayed increased body and epididymal fat weight, cholesterol levels, plasma resistin levels and plasma and colonic IL-1β levels, colonic inflammasome adaptor protein apoptosis-associated speck-like protein containing caspase-recruitment domain (ASC) and caspase-1 mRNA expression and ASC immunopositivity in macrophages. Colonic tachykininergic contractions were enhanced in HFD mice. HFD NLRP3^-/- mice developed lower increase in body and epididymal fat weight, cholesterol levels, systemic and bowel inflammation. In HFD Nlrp3^-/- mice, the functional alterations of tachykinergic pathways and faecal output were normalized. In THP-1 cells, substance P promoted IL-1β release. This effect was inhibited upon incubation with caspase-1 inhibitor or NK₁ antagonist and not observed in ASC^-/- cells.

CONCLUSION AND IMPLICATIONS

In obesity, NLRP3 regulates an interplay between the shaping of enteric immune/inflammatory responses and the activation of substance P/NK₁ pathways underlying the onset of colonic dysmotility. Identifying NLRP3 as a therapeutic target for the treatment of bowel symptoms related to obesity.

Molecular Basis for Hormone Recognition and Activation of Corticotropin-Releasing Factor Receptors

Corticotropin-releasing factor (CRF) and the three related peptides urocortins 1-3 (UCN1-UCN3) are endocrine hormones that control the stress responses by activating CRF1R and CRF2R, two members of class B G-protein-coupled receptors (GPCRs). Here, we present two cryoelectron microscopy (cryo-EM) structures of UCN1-bound CRF1R and CRF2R with the stimulatory G protein. In both structures, UCN1 adopts a single straight helix with its N terminus dipped into the receptor transmembrane bundle. Although the peptide-binding residues in CRF1R and CRF2R are different from other members of class B GPCRs, the residues involved in receptor activation and G protein coupling are conserved. In addition, both structures reveal bound cholesterol molecules to the receptor transmembrane helices. Our structures define the basis of ligand-binding specificity in the CRF receptor-hormone system, establish a common mechanism of class B GPCR activation and G protein coupling, and provide a paradigm for studying membrane protein-lipid interactions for class B GPCRs.

Early-life epigenetic changes along the corticotropin-releasing hormone (CRH) gene influence resilience or vulnerability to heat stress later in life

Stressful events in early life might lead to stress resilience or vulnerability, depending on an adjustable stress-response set-point, which can be altered during postnatal sensory development and involves epigenetic regulation of corticotropin-releasing hormone (CRH). During the critical developmental period of thermal-control establishment in 3-day-old chicks, heat stress was found to affect both body temperature and expression of CRH in the hypothalamic paraventricular nucleus. Both increased during heat challenge in vulnerable chicks, whereas they decreased in resilient chicks. Our aim was to elucidate the epigenetic mechanism underlying the regulation of stress resilience or vulnerability. Accordingly, DNA CpG methylation (5mC) and hydroxymethylation (5hmC) at the CRH intron, which we found to serve as a repressor element, displayed low 5mc% alongside high 5hmc% in resilient chicks, and high 5mc% with low 5hmc% in vulnerable ones. RE1-silencing transcription factor (REST), which has a binding site on this intron, bound abundantly during acute heat stress and was nearly absent during moderate stress, restricting repression by the repressor element, and thus activating CRH gene transcription. Furthermore, REST assembled into a protein complex with TET3, which bound directly to the CRH gene. Finally, the adjacent histone recruited the histone acetylation enzyme GCN5 to this complex, which increased H3K27ac during harsh, but not moderate heat conditioning. We conclude that an epigenetic mechanism involving both post-translational histone modification and DNA methylation in a regulatory segment of CRH is involved in determining a resilient or vulnerable response to stress later in life.

Corticotropin-Releasing Hormone Family and Their Receptors in the Cardiovascular System

The identification of corticotropin-releasing hormone (CRH) has led to the discovery of a growing family of ligands and receptors. CRH receptor 1 (CRHR1) and CRHR2 are mammalian G-protein coupled receptors (GPCRs) with high affinity for CRH and the CRH family of peptides. CRHR1 is predominantly expressed in the brain and plays a vital role in the hypothalamic-pituitary-adrenal (HPA) axis stress responses by secreting adrenal corticotropic hormone (ACTH). CRHR2 is predominantly expressed in the heart, and a CRHR2-specific ligand, urocortin 2 (UCN2), shows positive cardiac chronotropic and inotropic effects through 3´,5´-cyclic adenosine monophosphate (cAMP) signaling in response to CRHR2-mediated Gαs activation in mice and humans. Central administration of the CRH family of peptides increases mean arterial pressure through CRHR1 activation, whereas peripheral administration of the peptides decreases mean arterial pressure through CRHR2 activation. These observations have led to further investigations of CRHR2 as an important and unique GPCR in the physiological and pathological functioning of the cardiovascular (CV) system. Moreover, recent clinical trials demonstrate CRHR2 as a potentially therapeutic target in the treatment of heart failure. We present recent reviews of the role of CRHRs in basic CV physiology and in the pathophysiology of CV diseases.

Neuropeptide and steroid hormone mediators of neuroendocrine regulation

To maintain the health and well-being of all mammals, numerous aspects of physiology are controlled by neuroendocrine mechanisms. These mechanisms ultimately enable communication between neurones and glands throughout the body and are centrally mediated by neuropeptides and/or steroid hormones. A recent session at the International Workshop in Neuroendocrinology highlighted the essential roles of some of these neuropeptide and steroid hormone mediators in the neuroendocrine regulation of stress-, reproduction- and behaviour-related processes. Accordingly, the present review highlights topics presented in this session, including the role of the neuropeptides corticotrophin-releasing factor and gonadotrophin-releasing hormone in stress and reproductive physiology, respectively. Additionally, it details an important role for gonadal sex steroids in the development of behavioural sex preference.

Acute psychosocial stress in mid-aged male rats causes hyperthermia, cognitive decline, and increased deep sleep power, but does not alter deep sleep duration

Aging is associated with altered sleep architecture and worsened hippocampus-dependent cognition, highly prevalent clinical conditions that detract from quality of life for the elderly. Interestingly, exposure to psychosocial stress causes similar responses in young subjects, suggesting that age itself may act as a stressor. In prior work, we demonstrated that young animals show loss of deep sleep, deficits in cognition, and elevated body temperature after acute stress exposure, whereas aged animals are hyporesponsive on these measures. However, it is unclear if these age-altered stress responses occur in parallel over the course of aging. To address this, here we repeated the experiment in mid-aged animals. We hypothesized that mid-aged stress responses would be intermediate between those of young and aged subjects. Sixteen mid-aged (12 months) male F344 rats were implanted with EEG/EMG emitters to monitor sleep architecture and body temperature, and were trained on the Morris water maze for 3 days. On the fourth day, half of the subjects were restrained for 3 hours immediately before the water maze probe trial. Sleep architecture and body temperature were measured during the ensuing inactive period, and on the following day, endpoint measures were taken. Restrained mid-aged animals showed resistance to deep sleep loss, but demonstrated stress-induced water maze probe trial performance deficits as well as postrestraint hyperthermia. Taken in the context of prior work, these data suggest that age-related loss of sleep architecture stress sensitivity may precede both cognitive and body temperature-related stress insensitivity.

Amelioration of neurodegeneration and cognitive impairment by Lemon oil in experimental model of Stressed mice

Citrous lemon (Rutaceae) an Indian folk medicine has been used for the treatment of various pathological diseases viz., diabetes, cardiovascular, inflammation, hepatobiliary dysfunction and neurodegenerative disorder. Can lemon oil altered the memory of unstressed and stressed mice, a basic question for which the present work was put on trial. The present investigation was intended to assess the impact of Lemon oil on memory of unstressed and Stressed Swiss young Albino mice. Lemon oil (50 and 100 mg/kg o.r.) and donepezil (10 mg/kg) were guided for three weeks to different groups of stressed and unstressed mice. The nootropic movement was assessed utilizing elevated plus maze and Hebbs Williams Maze. Cerebrum acetylcholinesterase (AChE), plasmacorticosterone, decreased glutathione, lipid per oxidation alongside superoxide dismutase and catalase was surveyed as marker for disease. Histopathology was performed for estimation of drug effects. Acute immobilized stress was induce, lemon oil (100 mg/kg) and donepezil together indicated memory enhancing movement both in stressed and unstressed mice. Lemon oil significantly (p < 0.001) altered and lowered brain AChE activity both in stressed and unstressed mice. Scopolamine induced amnesia was also significantly altered and reversed both in stressed and unstressed mice by lemon oil at a dose of 50 and 100 mg/kg. Lemon oil (50 and 100 mg/kg) was further able to control the corticosterone level in plasma for stressed mice. Lemon oil significantly (p < 0.001) elevated the level of catalase, superoxide dismutase and reduced glutathione levels both in stressed and unstressed animals with respect to controlled group along with TBARS both in stressed and unstressed compared with control group. Hence it can be concluded that memory enhancing activity might be related to reduction in AChE and TBARS activity and by elevated GSH, SOD and catalase through decrease in raised plasma corticosterone levels.

Age Dependent Hypothalamic and Pituitary Responses to Novel Environment Stress or Lipopolysaccharide in Rats

Previously, we have shown that the transcription factor nuclear factor interleukin (NF-IL)6 can be used as an activation marker for inflammatory lipopolysaccharide (LPS)-induced and psychological novel environment stress (NES) in the rat brain. Here, we aimed to investigate age dependent changes of hypothalamic and pituitary responses to NES (cage switch) or LPS (100 μg/kg) in 2 and 24 months old rats. Animals were sacrificed at specific time points, blood and brains withdrawn and analyzed using immunohistochemistry, RT-PCR and bioassays. In the old rats, telemetric recording revealed that NES-induced hyperthermia was enhanced and prolonged compared to the young group. Plasma IL-6 levels remained unchanged and hypothalamic IL-6 mRNA expression was increased in the old rats. Interestingly, this response was accompanied by a significant upregulation of corticotropin-releasing hormone mRNA expression only in young rats after NES and overall higher plasma corticosterone levels in all aged animals. Immunohistochemical analysis revealed a significant upregulation of NF-IL6-positive cells in the pituitary after NES or LPS-injection. In another important brain structure implicated in immune-to-brain communication, namely, in the median eminence (ME), NF-IL6-immunoreactivity was increased in aged animals, while the young group showed just minor activation after LPS-stimulation. Interestingly, we found a higher amount of NF-IL6-CD68-positive cells in the posterior pituitary of old rats compared to the young counterparts. Moreover, aging affected the regulation of cytokine interaction in the anterior pituitary lobe. LPS-treatment significantly enhanced the secretion of the cytokines IL-6 and TNFα into supernatants of primary cell cultures of the anterior pituitary. Furthermore, in the young rats, incubation with IL-6 and IL-10 antibodies before LPS-stimulation led to a robust decrease of IL-6 production and an increase of TNFα production by the pituitary cells. In the old rats, this specific cytokine interaction could not be detected. Overall, the present results revealed strong differences in the activation patterns and pathways between old and young rats after both stressors. The prolonged hyperthermic and inflammatory response seen in aged animals seems to be linked to dysregulated pituitary cytokine interactions and brain cell activation (NF-IL6) in the hypothalamus-pituitary-adrenal axis.

Acute Pressor Response to Psychosocial Stress Is Dependent on Endothelium-Derived Endothelin-1

Background

Acute psychosocial stress provokes increases in circulating endothelin‐1 (ET‐1) levels in humans and animal models. However, key questions about the physiological function and cellular source of stress‐induced ET‐1 remain unanswered. We hypothesized that endothelium‐derived ET‐1 contributes to the acute pressor response to stress via activation of the endothelin A receptor.

Methods and Results

Adult male vascular endothelium‐specific ET‐1 knockout mice and control mice that were homozygous for the floxed allele were exposed to acute psychosocial stress in the form of cage switch stress (CSS), with blood pressure measured by telemetry. An acute pressor response was elicited by CSS in both genotypes; however, this response was significantly blunted in vascular endothelium‐specific ET‐1 knockout mice compared with control mice that were homozygous for the floxed allele. In mice pretreated for 3 days with the endothelin A antagonist, ABT‐627, or the dual endothelin A/B receptor antagonist, A‐182086, the pressor response to CSS was similar between genotypes. CSS significantly increased plasma ET‐1 levels in control mice that were homozygous for the floxed allele. CSS failed to elicit an increase in plasma ET‐1 in vascular endothelium‐specific ET‐1 knockout mice. Telemetry frequency domain analyses suggested similar autonomic responses to stress between genotypes, and isolated resistance arteries demonstrated similar sensitivity to α₁‐adrenergic receptor‐mediated vasoconstriction.

Conclusions

These findings specify that acute stress‐induced activation of endothelium‐derived ET‐1 and subsequent endothelin A receptor activation is a novel mediator of the blood pressure response to acute psychosocial stress.

Stress-induced hyperthermia and hypothermia

Stress affects core body temperature (T_c). Many kinds of stress induce transient, monophasic hyperthermia, which diminishes gradually if the stressor is terminated. Stronger stressors produce a longer-lasting effect. Repeated/chronic stress induces anticipatory hyperthermia, reduces diurnal changes in T_c, or slightly increases T_c throughout the day. Animals that are exposed to chronic stress or a cold environment exhibit an enhanced hyperthermic response to a novel stress. These changes persist for several days after cessation of stress exposure. In contrast, long-lasting inescapable stress sometimes induces hypothermia. In healthy humans, psychologic stress induces slight increases in T_c, which are within the normal range of T_c or just above it. Some individuals, however, develop extremely high T_c (up to 41°C) when they are exposed to emotional events or show persistent low-grade high T_c (37-38°C) during or after chronic stress situations. In addition to the nature of the stressor itself, such stress-induced thermal responses are modulated by sex, age, ambient temperature, cage mates, past stressful experiences and cold exposure, and coping. Stress-induced hyperthermia is driven by mechanisms distinct from infectious fever, which requires inflammatory mediators. However, both stress and infection activate the dorsomedial hypothalamus-rostral medullary raphe region-sympathetic nerve axis to increase T_c.

Effects of estrogen replacement on stress-induced cardiovascular responses via renin-angiotensin system in ovariectomized rats

The purpose of this study was to determine whether chronic estrogen replacement in ovariectomized rats inhibits the pressor response to psychological stress by attenuating the activation of the renin-angiotensin system. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, the rats were randomly assigned to be implanted subcutaneously with pellets containing either 17β-estradiol (E2) or placebo (Pla). After 4 wk of treatment, the rats underwent cage-switch stress and, in a separate experiment, a subset received an infusion of angiotensin II. The cage-switch stress rapidly elevated blood pressure (BP) and heart rate (HR) as measured by radiotelemetry in both groups. However, the BP and HR responses to the stress were significantly attenuated in the E2 group compared with the Pla group. An angiotensin II type 1 receptor blocker, losartan, given in drinking water, abolished the difference in the pressor response to stress between the two groups. Moreover, the stress-induced elevation in plasma renin activity and angiotensin II concentration was significant in the Pla group, but not in the E2 group. In addition, the expression of renin mRNA in the kidney was lower in the E2 group relative to the Pla group. Finally, we found that intravenous angiotensin II infusion increased BP and decreased HR to a similar degree in both groups. These results suggest that the inhibitory effects of estrogen on psychological stress-induced activation of the renin-angiotensin system could be at least partially responsible for the suppression of the pressor responses to psychological stress seen in estrogen-replaced ovariectomized rats.

The transcription factor nuclear factor interleukin 6 mediates pro- and anti-inflammatory responses during LPS-induced systemic inflammation in mice

The transcription factor nuclear factor interleukin 6 (NF-IL6) plays a pivotal role in neuroinflammation and, as we previously suggested, hypothalamus-pituitary-adrenal-axis-activation. Here, we investigated its contribution to immune-to-brain communication and brain controlled sickness symptoms during lipopolysaccharide (LPS)-induced (50 or 2500 μg/kg i.p.) systemic inflammation in NF-IL6-deficient (KO) or wildtype mice (WT). In WT LPS induced a dose-dependent febrile response and reduction of locomotor activity. While KO developed a normal fever after low-dose LPS-injection the febrile response was almost abolished 3-7 h after a high LPS-dose. High-dose LPS-stimulation was accompanied by decreased (8 h) followed by enhanced (24 h) inflammation in KO compared to WT e.g. hypothalamic mRNA-expression including microsomal prostaglandin E synthase, inducible nitric oxide synthase and further inflammatory mediators, neutrophil recruitment to the brain as well as plasma levels of inflammatory markers such as IL-6 and IL-10. Interestingly, KO showed reduced locomotor activity even under basal conditions, but enhanced locomotor activity to novel environment stress. Hypothalamic-pituitary-adrenal-axis-activity of KO was intact, but tryptophan-metabolizing enzymes were shifted to enhanced serotonin production and reuptake. Overall, we showed for the first time that NF-IL6 plays a dual role for sickness response and immune-to-brain communication: acting pro-inflammatory at 8h but anti-inflammatory at 24 h after onset of the inflammatory response reflecting active natural programming of inflammation. Moreover, reduced locomotor activity observed in KO might be due to altered tryptophan metabolism and serotonin reuptake suggesting some role for NF-IL6 as therapeutic target for depressive disorders.

Effects of corticotropin releasing factor (CRF) on sleep and temperature following predictable controllable and uncontrollable stress in mice

Corticotropin releasing factor (CRF) is a major mediator of central nervous system responses to stressors, including alterations in wakefulness and sleep. However, its role in mediating stress-induced alterations in sleep has not been fully delineated. In this study, we assessed the role of CRF and the non-specific CRF antagonist, astressin (AST), in regulating changes in sleep produced by signaled, escapable shock (SES) and signaled inescapable shock (SIS), two stressors that can increase or decrease sleep, respectively. Male BALB/cJ mice were surgically implanted with transmitters (DataSciences ETA10-F20) for recording EEG, activity and core body temperature by telemetry and a cannula for intracerebroventricular (ICV) microinjections. After baseline (Base) sleep recording, mice were presented tones (90 dB, 2 kHz) that started 5.0 s prior to and co-terminated with footshock (0.5 mA; 5.0 s maximum duration). SES mice (n = 9) always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. Yoked SIS mice (n = 9) were treated identically, but could not alter shock duration. Training with SES or SIS was conducted over 2 days to stabilize responses. Afterwards, the mice received saline, CRF [0.4 μg (0.42 mM) or AST (1.0 μg (1.4 mM)] prior to SES or SIS. Sleep was analyzed over 20 h post-stress recordings. After administration of saline, REM was significantly greater in SES mice than in SIS mice whereas after CRF or AST, REM was similar in both groups. Total 20 h NREM did not vary across condition or group. However, after administration of saline and CRF, NREM episode duration was significantly decreased, and NREM episode number significantly increased, in SIS mice compared to SES animals. SES and SIS mice showed similar stress induced hyperthermia (SIH) across all conditions. These data demonstrate that CRF can mediate stress-induced changes in sleep independently of SIH, an index of hypothalamic-pituitary-adrenal axis activation.

Psychogenic fever: how psychological stress affects body temperature in the clinical population

Psychogenic fever is a stress-related, psychosomatic disease especially seen in young women. Some patients develop extremely high core body temperature (Tc) (up to 41°C) when they are exposed to emotional events, whereas others show persistent low-grade high Tc (37-38°C) during situations of chronic stress. The mechanism for psychogenic fever is not yet fully understood. However, clinical case reports demonstrate that psychogenic fever is not attenuated by antipyretic drugs, but by psychotropic drugs that display anxiolytic and sedative properties, or by resolving patients' difficulties via natural means or psychotherapy. Animal studies have demonstrated that psychological stress increases Tc via mechanisms distinct from infectious fever (which requires proinflammatory mediators) and that the sympathetic nervous system, particularly β3-adrenoceptor-mediated non-shivering thermogenesis in brown adipose tissue, plays an important role in the development of psychological stress-induced hyperthermia. Acute psychological stress induces a transient, monophasic increase in Tc. In contrast, repeated stress induces anticipatory hyperthermia, reduces diurnal changes in Tc, or slightly increases Tc throughout the day. Chronically stressed animals also display an enhanced hyperthermic response to a novel stress, while past fearful experiences induce conditioned hyperthermia to the fear context. The high Tc that psychogenic fever patients develop may be a complex of these diverse kinds of hyperthermic responses.

Protracted effects of chronic stress on serotonin-dependent thermoregulation

Chronic stress is known to affect serotonin (5HT) neurotransmission in the brain and to alter body temperature. The body temperature is controlled in part, by the medial preoptic area (mPOA) of the hypothalamus. To investigate the effect of chronic stress on 5HT and how it affects body temperature regulation, we examined whether exposure to a chronic unpredictable stress (CUS) paradigm produces long-term alterations in thermoregulatory function of the mPOA through decreased 5HT neurotransmission. Adult male Sprague-Dawley rats underwent 21 d of CUS. Four days after the last stress exposure, basal body temperature in the home cage and body temperature in a cold room maintained at 10 °C were recorded. The CUS rats had significantly higher subcutaneous basal body temperature at 13:00 h compared to unstressed (NoStress) rats. Whereas the NoStress rats were able to significantly elevate body temperature from basal levels at 30 and 60 min of exposure to the cold room, the CUS rats showed a hypothermic response to the cold. Treatment during CUS with metyrapone, a corticosterone synthesis inhibitor, blocked stress-induced decrease in body temperature in response to the cold challenge. CUS also decreased 5HT transporter protein immunoreactivity in the mPOA and 5HT2A/C agonist injection into the mPOA after CUS exposure caused stressed rats to exhibit a sensitized hyperthermic response to cold. These results indicate that the CUS induced changes to the 5HTergic system alter mPOA function in thermoregulation. These findings help us to explain the mechanisms underlying chronic stress-induced disorders such as chronic fatigue syndrome wherein long lasting thermoregulatory deficits are observed.

Corticotropin-releasing factor (CRF) receptor-1 is involved in cardiac noradrenergic activity observed during naloxone-precipitated morphine withdrawal

BACKGROUND AND PURPOSE

The negative affective states of withdrawal involve the recruitment of brain and peripheral stress circuitry [noradrenergic activity, induction of the hypothalamic-pituitary-adrenocortical (HPA) axis and activation of heat shock proteins (Hsps)]. Corticotropin-releasing factor (CRF) pathways are important mediators in the negative symptoms of opioid withdrawal. We performed a series of experiments to characterize the role of the CRF₁ receptor in the response of stress systems to morphine withdrawal and its effect in the heart using genetically engineered mice lacking functional CRF₁ receptors.

EXPERIMENTAL APPROACH

Wild-type and CRF₁ receptor-knockout mice were treated with increasing doses of morphine. Precipitated withdrawal was induced by naloxone. Plasma adrenocorticotropic hormone (ACTH) and corticosterone levels, the expression of myocardial Hsp27, Hsp27 phosphorylated at Ser⁸², membrane (MB)- COMT, soluble (S)-COMT protein and NA turnover were evaluated by RIA, immunoblotting and HPLC.

KEY RESULTS

During morphine withdrawal we observed an enhancement of NA turnover in parallel with an increase in mean arterial blood pressure (MAP) and heart rate (HR) in wild-type mice. In addition, naloxone-precipitated morphine withdrawal induced an activation of HPA axis and Hsp27. The principal finding of the present study was that plasma ACTH and corticosterone levels, MB-COMT, S-COMT, NA turnover, and Hsp27 expression and activation observed during morphine withdrawal were significantly inhibited in the CRF₁ receptor-knockout mice.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that CRF/CRF₁ receptor activation may contribute to stress-induced cardiovascular dysfunction after naloxone-precipitated morphine withdrawal and suggest that CRF/CRF₁ receptor pathways could contribute to cardiovascular disease associated with opioid addiction.

Environmental enrichment in female rodents: considerations in the effects on behavior and biochemical markers

Environmental enrichment (EE) exposes laboratory animals to novelty and complexity through alterations in the physical and social environment, which lead to enhanced sensory, cognitive and physical stimulation. Housing rodents in an EE is a highly recommended practice by governing bodies regulating animal welfare due to a growing body of evidence suggesting its benefits on rodents' wellbeing and the more naturalistic environment that such housing conditions provide. However, most paradigms and hypotheses rely on information currently available from studies performed on male subjects and the information regarding the effects of EE on female rodents' behavior and physiology is limited. Given the variety of EE paradigms described, it is increasingly difficult to ascertain the benefits or possible consequences of enriched housing strategies in females, let alone aid at establishing standardized environments in rodents. This review evaluates the female rodent literature that has examined the outcome of EE on behavior and neurochemistry and aims at identifying key elements to be addressed by future studies. Specifically, results from cognitive behavioral tests as well as commonly used tests of emotionality will be discussed, while also evaluating their relation to changes in neurochemistry and hormones brought on by various EE paradigms. Lastly, the impact of maternal enrichment on both offspring and maternal behavior and physiology will be reviewed.

Conditioned fear is modulated by CRF mechanisms in the periaqueductal gray columns

The periaqueductal gray (PAG) columns have been implicated in controlling stress responses through corticotropin-releasing factor (CRF), which is a neuropeptide with a prominent role in the etiology of fear- and anxiety-related psychopathologies. Several studies have investigated the involvement of dorsal PAG (dPAG) CRF mechanisms in models of unconditioned fear. However, less is known about the role of this neurotransmission in the expression of conditioned fear memories in the dPAG and ventrolateral PAG (vlPAG) columns. We assessed the effects of ovine CRF (oCRF 0.25 and 1.0 μg/0.2 μL) locally administered into the dPAG and vlPAG on behavioral (fear-potentiated startle and freezing) and autonomic (arterial pressure and heart rate) responses in rats subjected to contextual fear conditioning. The lower dose injected into the columns promoted proaversive effects, enhanced contextual freezing, increased the blood pressure and heart rate and decreased tail temperature. The lower dose of oCRF into the vlPAG, but not into the dPAG, produced a pronounced enhancement of the fear-potentiated startle response. The results imply that the PAG is a heterogeneous structure that is involved in the coordination of distinct behaviors and autonomic control, suggest PAG involvement in the expression of contextual fear memory as well as implicate the CRF as an important modulator of the neural substrates of fear in the PAG.

The effect of long-term ovariectomy on midbrain stress systems in free ranging macaques

Communication between the serotonin system and the CRF system plays a pivotal role in the mediation of stress and stress reactivity. CRF appears to be inhibitory of serotonin neurotransmission through the CRF receptor type 1 (CRF-R1). Serotonin neurons also detect the urocortins, which are thought to be anxiolytic. Components of the CRF system in the serotonergic dorsal raphe region were examined in macaques that were ovary-intact or ovariectomized for 3 years living in a relatively natural environment. Female Japanese macaques (Macaca fuscata) were ovariectomized or tubal-ligated (n=5/group) and returned to their natal troop for 3 years. Quantitation of (1) CRF innervation of the serotonergic dorsal raphe, (2) CRF-Receptor type 1 (CRF-R1) in the dorsal raphe, (3) Urocortin 1 (UCN1) cells near the Edinger-Westfal nucleus and (4) UCN1 axons, was obtained with immunocytochemical staining and image analysis. There was no statistical difference in CRF axonal staining in the dorsal raphe, or in UCN1 axonal staining near the dorsal raphe. However, the average number of detectable UCN1 postive cells was significantly lower in the Ovx group than in the Intact group (p=0.003). Average CRF-R1 positive pixel number and positive cell number were significantly higher in the Ovx group than in the Intact group (p=0.005 and 0.02, respectivly). The higher expression of CRF-R1 and lower expression of UCN1 in the Ovx group indicates they may be more vulnerable to stress. The greater expression of CRF-R1 could cause a greater inhibition of serotonin upon a stress-induced increase in CRF as well.

Cage change influences serum corticosterone and anxiety-like behaviors in the mouse

Environmental variables and husbandry practices can influence physiology and alter behavior in mice. Our study evaluated the effects of cage change on serum corticosterone levels and anxiety-like behaviors in C57BL/6 male mice. We examined the effects of 3 different methods of performing cage transfer and of transferring mice to a clean or a dirty familiar cage microenvironment. The 3 different handling methods were forceps transfer, gentle transfer with gloved hands, and a passive transfer technique that did not involve active handling. Active handling methods and transfer to both clean and dirty cage microenvironments significantly increased serum corticosterone 15 min after cage change; however, at 60 min after cage change, levels were comparable to those of unmanipulated mice. Although the effects were transient, cage change altered anxiety-like behaviors in the open field when behavioral testing was performed on the same day. These results demonstrate that the timing of cage change can influence behavioral results, an effect that is an important consideration for rodent behavioral studies.

Effects of citalopram on serotonin and CRF systems in the midbrain of primates with differences in stress sensitivity

This chapter reviews the neurobiological effects of stress sensitivity and s-citalpram (CIT) treatment observed in our nonhuman primate model of functional hypothalamic amenorrhea (FHA). This type of infertility, also known as stress-induced amenorrhea, is exhibited by cynomolgus macaques. In small populations, some individuals are stress-sensitive (SS) and others are highly stress-resilient (HSR). The SS macaques have suboptimal secretion of estrogen and progesterone during normal menstrual cycles. SS monkeys also have decreased serotonin gene expression and increased CRF expression compared to HSR monkeys. Recently, we found that CIT treatment improved ovarian steroid secretion in SS monkeys, but had no effect in HSR monkeys. Examination of the serotonin system revealed that SS monkeys had significantly lower Fev (fifth Ewing variant, rodent Pet1), TPH2 (tryptophan hydroxylase 2), 5HT1A autoreceptor and SERT (serotonin reuptake transporter) expression in the dorsal raphe than SR monkeys. However, CIT did not alter the expression of either Fev, TPH2, SERT or 5HT1A mRNAs. In contrast, SS monkeys tended to have a higher density of CRF fiber innervation of the dorsal raphe than HSR monkeys, and CIT significantly decreased the CRF fiber density in SS animals. In addition, CIT increased CRF-R2 gene expression in the dorsal raphe. We speculate that in a 15-week time frame, the therapeutic effect of S-citalopram may be achieved through a mechanism involving extracellular serotonin inhibition of CRF and stimulation of CRF-R2, rather than alteration of serotonin-related gene expression.

Effects of corticotropin releasing factor (CRF) on sleep and body temperature following controllable footshock stress in mice

Rapid eye movement sleep (REM) is increased after controllable stress (modeled by escapable footshock, ES) and decreased after uncontrollable stress (modeled by inescapable footshock, IS). Decreases in REM after IS are exacerbated by corticotropin releasing factor (CRF) and attenuated by a CRF antagonist. In this study, we trained mice with ES following injections of CRF, astressin (AST), or saline (SAL) to determine whether CRF would alter REM after ES. Male BALB/cJ mice (n=7) were implanted for recording sleep, activity and body temperature via telemetry and with a guide cannula aimed into a lateral ventricle. After recovery from surgery, sleep following exposure to a novel chamber was recorded as a handling control (HC). The mice received one day of training with ES without injection followed by weekly training sessions in which they received counterbalanced intracerebroventricular (ICV) microinjections of either SAL or CRF (days 7 & 14) or SAL or AST (days 21 & 28) prior to ES. On each experimental day, sleep was recorded for 20 h. Compared to HC, the mice showed significantly increased REM when receiving either SAL or AST prior to ES whereas CRF prior to ES significantly reduced REM. Stress-induced hyperthermia had longer duration after ES compared to HC, and was not significantly altered by CRF or AST compared to SAL. The current results demonstrate that activity in the central CRF system is an important regulator of stress-induced alterations in REM.

Role of corticotrophin releasing hormone in cerebral infarction-related gastrointestinal barrier dysfunction

BACKGROUND

Corticotrophin releasing hormone (CRH) is believed to mediate stress-induced behaviors, implying a broader, integrative role for the hormone in the psychological stress response, and studies on CRH in physical stress are few. This study was undertaken to investigate whether CRH plays an important role in cerebral infarction-related gastrointestinal barrier dysfunction.

METHODS

Thirty male Wistar rats were randomly divided into a pseudo-operation group (group C, n=10), a cerebral infarction group (group I, n=10), and a cerebral infarction + ic α-helical-CRH (9-41) group (group Aic, n=10). Urine samples were collected to determine the levels of epinephrine, norepinephrine, cortisol, and sucrose. At 24 hours after establishment of the models, blood samples were taken to determine the activity of diamine oxidase (DAO) and the concentration of D-lactic acid (D-lac). The stomach was taken to determine gastric Guth score, and the hypothalamus was also taken to determine tissue CRH protein expression using Western blotting.

RESULTS

The hypothalamus CRH protein, the indicators of stress, the plasma DAO activity and plasma D-lac, urine sucrose exertion and gastric Guth score in group I were higher than those in groups Aic and C.

CONCLUSIONS

After cerebral infarction, CRH in the hypothalamus was increased, the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system were activated, gastrointestinal permeability was increased, and gastrointestinal barrier function was destroyed. CRH receptor antagonist alleviated the gastrointestinal barrier function.

Metyrapone blunts stress-induced hyperthermia and increased locomotor activity independently of glucocorticoids and neurosteroids

Metyrapone, a cytochrome P(450) inhibitor used to inhibit corticosterone synthesis, triggers biological markers of stress and also reduces stress-induced anxiety-like behaviors. To address these controversial effects, 6 separate investigations were carried out. In a first set of investigations, abdominal temperature (T(abd)), spontaneous locomotor activity (A(S)) and electroencephalogram (EEG) were recorded in freely moving rats treated with either saline or 150 mg kg(-1) metyrapone. An increase in T(abd) and A(S) occurred in saline rats, while, metyrapone rats exhibited an immediate decrease, both variables returning to basal values 5h later. Concomitantly, the EEG spectral power increased in the gamma and beta 2 bands and decreased in the alpha frequency band, and the EMG spectral power increased. This finding suggests that metyrapone depressed stress-induced physiological response while arousing the animal. In a second step, restraint stress was applied 5h after injection. Metyrapone significantly blunted the stress-induced T(abd) and A(S) rise, without affecting the brain c-fos mRNA increase. Corticosterone (5 and 40 mg kg(-1)) injected concomitantly to metyrapone failed to reverse the observed metyrapone-induced effects in T(abd) and A(S). Finasteride (50 mg kg(-1)), which blocks neurosteroid production, was also unable to block these effects. In conclusion, metyrapone acutely reduced stress-induced physiological response in freely behaving rats independently from glucocorticoids and neurosteroids.

Ovarian steroid regulation of the midbrain corticotropin releasing factor and urocortin systems in macaques

A significant number of postmenopausal women report increased anxiety and vulnerability to stress, which has been linked to decreased secretion of ovarian steroids. Communication between the serotonin system and the corticotropin releasing factor (CRF) system determines stress sensitivity or resilience. This study examines the effects of the ovarian steroids, estradiol (E) and progesterone (P) on the CRF system components that impact serotonin neurons in the midbrain of nonhuman primates. Ovariectomized rhesus macaques were treated with placebo, E alone for 1 month, or E supplemented with P for the last 2 weeks. Quantitative (q)RT-PCR and immunocytochemistry were employed. E±P treatment decreased CRF-R1 and increased CRF-R2 gene expression in hemi-midbrain blocks and in laser captured serotonin neurons. Also in hemi-midbrains, E treatment increased urocortin 1 (UCN1) and CRFBP gene expression, but supplemental P treatment reversed these effects. E±P decreased CRF fiber density in the dorsal, interfascicular and median raphe nuclei and decreased CRF-R1 immunostaining in the dorsal raphe. E increased CRF-R2 immunostaining in the dorsal and median raphe. E±P increased UCN1 immunostaining in the cell bodies and increased UCN1 fiber density in the caudal linear nucleus. Estrogen receptor beta (ERβ), but not ERα was detected in the nucleus of UCN1-positive neurons. While the mechanism of ovarian hormone regulation of the midbrain CRF system requires further investigation, these studies clearly demonstrate another pathway by which ovarian hormones may have positive effects on anxiety and mood regulation.

Effects of AVP V1a and CRH receptor antagonist on psychological stress responses to frustrating condition in sheep

Arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH) are released in the brain to regulate behavioral and physiological stress responses. To elucidate the respective roles of these peptides under certain stressors, we examined the effects of intracerebroventricular infusions of either AVP V1a receptor antagonist, [Pmp(1), Tyr (Me)(2)]- Arg(8)-Vasopressin (Pmp, Tyr-AVP) or CRH receptor antagonist, alpha-helical CRF 9-41 (alphahCRF) on stress responses induced by frustrating condition in sheep. Four ovariectomized Corriedale ewes were assigned to the experiment. In a "frustrating" condition (FC), food was withheld for 60 minutes from only the experimental ewe while this ewe was in the presence of the other ewes that were given food. As "non-frustrating" control condition (C), food was withheld for 60 minutes from all ewes, thereby controlling for the nonspecific effects of lack of food. FC induced a significant rise in the plasma cortisol concentration (p < 0.05) and increased the pawing number and rectal temperature compared with that in C (p < 0.1). The effects of either Pmp, Tyr-AVP or alphahCRF on these stress responses were analyzed. The rise in cortisol restored nearly to the control level by infusion of Pmp, Tyr-AVP or alphahCRF. The pawing number restored nearly to the control level by alphahCRF. The hyperthermia restored nearly to the control level by Pmp, Tyr-AVP. These data suggest that both endogenous CRH and AVP might be concerned with inducing physiological and behavioral stress responses to frustrating condition in sheep.

Metyrapone decreases locomotion acutely

Metyrapone is a glucocorticoid synthesis inhibitor known to induce a stress-like biological syndrome, but also to limit stress-related behaviours. Since stress is usually associated to an increased locomotion, the aim of the study was to determine whether metyrapone will increase, decrease or respect locomotion. Forty rats were placed in infrared actimeters to study spontaneous locomotion before and after injecting 150 mg kg(-1) of either metyrapone (n=20) or saline (n=20). Two hours after injection, half of each treatment group animals were tested in an open field to study test-evoked locomotion. Stress-induced analgesia was quantified using plantar test just before blood sampling. Immediately after injection, metyrapone decreased drastically horizontal and vertical locomotion. During the open field test, metyrapone-treated rats remained less active with slower movement execution than saline-treated rats. Metyrapone did not modify plantar test performances but blunted stress-induced corticosterone and ACTH increases. Mechanisms by which metyrapone induced these effects on locomotion are further discussed.

Neurobiology of stress-induced reproductive dysfunction in female macaques

It is now well accepted that stress can precipitate mental and physical illness. However, it is becoming clear that given the same stress, some individuals are very vulnerable and will succumb to illness while others are more resilient and cope effectively, rather than becoming ill. This difference between individuals is called stress sensitivity. Stress sensitivity of an individual appears to be influenced by genetically inherited factors, early life (even prenatal) stress, and by the presence or absence of factors that provide protection from stress. In comparison to other stress-related diseases, the concept of sensitivity versus resilience to stress-induced reproductive dysfunction has received relatively little attention. The studies presented herein were undertaken to begin to identify stable characteristics and the neural underpinnings of individuals with sensitivity to stress-induced reproductive dysfunction. Female cynomolgus macaques with normal menstrual cycles either stop ovulating (stress sensitive) or to continue to ovulate (stress resilient) upon exposure to a combined metabolic and psychosocial stress. However, even in the absence of stress, the stress-sensitive animals have lower secretion of the ovarian steroids, estrogen and progesterone, have higher heart rates, have lower serotonin function, have fewer serotonin neurons and lower expression of pivotal serotonin-related genes, have lower expression of 5HT2A and 2C genes in the hypothalamus, have higher gene expression of GAD67 and CRH in the hypothalamus, and have reduced gonadotropin-releasing hormone transport to the anterior pituitary. Altogether, the results suggest that the neurobiology of reproductive circuits in stress-sensitive individuals is compromised. We speculate that with the application of stress, the dysfunction of these neural systems becomes exacerbated and reproductive function ceases.

Ovarian steroid treatment decreases corticotropin-releasing hormone (CRH) mRNA and protein in the hypothalamic paraventricular nucleus of ovariectomized monkeys

Corticotropin-releasing hormone (CRH) gene and protein expression were examined in the paraventricular nucleus (PVN) of ovariectomized female macaques treated with placebo or hormone therapy (HT) consisting of either estrogen (E) for 28 days, or progesterone (P) for the last 14 of 28 days, or E for 28 days supplemented with P for the last 14 of 28 days using Silastic capsules implanted s.c. in the periscapular region (n=4/group). Perfusion fixed sections (25 microm) at five levels of the PVN (rostral to caudal at 250 microm intervals) were immunostained (ICC) with an antibody to human CRH or processed in an in situ hybridization (ISH) assay with a monkey specific CRH riboprobe. The immunostained CRH-positive area was quantified with a Marianas Stereology Workstation and Slidebook 4.2. There was a significant decrease in the immunological CRH signal with E, P, and E+P treatment as measured by total or average pixels and microns (analysis of variance (ANOVA), p<0.002; Student-Newman-Keul's post hoc test versus placebo control group, p<0.05). There was also a decrease in the number of detectable CRH neurons (ANOVA, p<0.03) with HT. The sections processed for ISH were exposed to autoradiographic films. The CRH mRNA signal was analyzed with NIH Image. The average optical density and positive pixel area of the CRH mRNA signal was significantly suppressed by ovarian HT (ANOVA p<0.002; Student-Newman-Keul's post hoc test versus placebo control group, p<0.05). In summary, 1 month of stable treatment with a moderate dose of E, P or E+P significantly reduced CRH mRNA and protein in the PVN of ovariectomized monkeys. These results suggest that this hormone treatment regimen may increase stress resilience in surgically menopausal primates.

Intracerebroventricular administration of corticotrophin-releasing hormone receptor antagonists produces different effects on hypothalamic pituitary adrenal responses to novel restraint depending on the stress history of the animal

Corticotrophin-releasing hormone (CRH) regulates acute stress-induced changes in neuroendocrine function and behaviour. However, little is known about CRH functions in animals that have prior experience with repeated stress. Repeatedly-stressed rats exhibit a habituated hypothalamic-pituitary-adrenal (HPA) response to a familiar, homotypic stressor but exhibit maintained or enhanced HPA responses to a novel, heterotypic stressor. We examined the effects of intracerebroventricular (i.c.v.) administration of two different nonselective CRH receptor antagonists, alpha-helical CRH(9-41) (ahCRH) or D-Phe CRH(12-41) (D-PheCRH), on HPA responses to acute restraint in rats previously exposed to repeated cold stress (i.e. facilitated responses). Antagonists were administered as single i.c.v. injections prior to restraint to provide a general index of CRH function in control versus repeatedly-stressed rats. CRH receptor blockade with either ahCRH or D-PheCRH produced different effects on HPA responses to novel restraint depending on whether the animal had been previously cold stressed or not. Interestingly, some agonist-type effects were observed but only in repeatedly-stressed rats. In summary, these results indicate that manipulations of the CRH receptor have different effects on HPA activity depending on the stress history of the animal.

Psychological stress-induced oxidative stress as a model of sub-healthy condition and the effect of TCM

Distress-mediated tissue oxidative stress was examined as a model of sub-healthy condition defined in traditional Chinese medicine theory. Mice were subjected to psychologically stressful conditions by whiskers removal. Under this condition, spontaneous locomotive activity was significantly enhanced in the dark (P < 0.05 versus the control mice in three different movements), and granulocytes/lymphocytes balance shifted to granulocytes. At the same time, peroxynitrite level in blood plasma increased to ∼180% from that of the control mice at 6 h after removal of the whiskers (P < 0.01), and was maintained even after 12 h. Both protein carbonyl formation and lipid peroxidation were significantly increased under this condition in brain, heart, liver and spleen at 6 h after removal of whiskers (P < 0.05 or P < 0.01), and these levels were maximized after 12 h (increased to 120–160%, P < 0.05 or P < 0.01). The oxidative tissue injuries observed at 12 h after the removal of the whiskers were effectively prevented by two traditional Chinese medicine formula: Shengmai San (SMS) and Ling Gui Zhu Gan Tang (LGZGT), when administered for 5 days before the removal of the whiskers. Therefore, this stress model is considered useful in assessing the preventive potential of antioxidants and antioxidant-based herbal mixtures in treating the pathophysiology associated with psychological or emotional distress.

Corticotropin releasing factor increases in brown adipose tissue thermogenesis and heart rate through dorsomedial hypothalamus and medullary raphe pallidus

Corticotropin releasing factor, acting at hypothalamic corticotropin releasing factor receptors, contributes to the neural signaling pathways mediating stress-related responses, as well as those involved in maintaining energy balance homeostasis. Sympathetically-regulated lipid metabolism and heat production in brown adipose tissue contributes to the non-shivering thermogenic component of stress-evoked hyperthermia and to energy expenditure aspects of body weight regulation. To identify potential central pathways through which hypothalamic corticotropin releasing factor influences brown adipose tissue thermogenesis, corticotropin releasing factor was microinjected into the lateral ventricle (i.c.v.) or into hypothalamic sites while recording sympathetic outflow to brown adipose tissue, brown adipose tissue temperature, expired CO2, heart rate and arterial pressure in urethane/chloralose-anesthetized, artificially-ventilated rats. I.c.v. corticotropin releasing factor or corticotropin releasing factor microinjection into the preoptic area or the dorsomedial hypothalamus, but not the paraventricular nucleus of the hypothalamus, elicited sustained increases in brown adipose tissue sympathetic nerve activity, brown adipose tissue temperature, expired CO2 and heart rate. These sympathetic responses to i.c.v. corticotropin releasing factor were eliminated by inhibition of neuronal activity in the dorsomedial hypothalamus or in the raphe pallidus, a putative site of sympathetic premotor neurons for brown adipose tissue, and were markedly reduced by microinjection of ionotropic glutamate receptor antagonists into the dorsomedial hypothalamus. The increases in brown adipose tissue sympathetic outflow, brown adipose tissue temperature and heart rate elicited from corticotropin releasing factor into the preoptic area were reversed by inhibition of neuronal discharge in dorsomedial hypothalamus. These data indicate that corticotropin releasing factor release within the preoptic area activates a sympathoexcitatory pathway to brown adipose tissue and to the heart, perhaps similar to that activated by increased prostaglandin production in the preoptic area, that includes neurons in the dorsomedial hypothalamus and in the raphe pallidus.

The therapeutic potential of CRF1 antagonists for anxiety

Preclinical studies suggest that the brain corticotropin-releasing factor (CRF) systems mediate anxiety-like behavioural and somatic responses through actions at the CRF1 receptor. CRF1 antagonists block the anxiogenic-like effects of CRF and stress in animal models. Cerebrospinal fluid levels of CRF are elevated in some anxiety disorders and normalise with effective treatment, further implicating CRF systems as a therapeutic target. Prototypical CRF1 antagonists are highly lipophilic, non-competitive antagonists of peptide ligands. Modification of the chemotype and the identification of novel pharmacophores are yielding more drug-like structures with increased hydrophilicity at physiological pHs. Newer compounds exhibit improved solubility, pharmacokinetic properties, potency and efficacy. Several clinical candidates have entered Phase I/II trials. However, unmet challenges await resolution during further discovery, clinical development and therapeutic application of CRF1 antagonists.

Role of angiotensin II and corticotropin-releasing hormone in hemodynamic responses to cocaine and stress

Cocaine produces characteristic behavioral and autonomic responses due to its unique pharmacological properties. Many of the autonomic responses resemble those to acute behavioral stress. Both cocaine and behavioral stress have been shown to evoke an increase in sympathetic nerve activity that is primarily responsible for the peripheral cardiovascular responses. We noted varying hemodynamic and sympathetic response patterns to cocaine administration and to acute behavioral stress in rats that correlate with the predisposition to develop both a sustained increase in arterial pressure and cardiomyopathies. Several lines of evidence suggest that the autonomic response patterns are dependent on the actions of central peptides including angiotensin II (Ang II) and corticotropin-releasing hormone (CRH). This is based on observations demonstrating that intracerebroventricular (icv) administration of receptor antagonists for Ang II or CRH attenuated the decrease in cardiac output (CO) and increase in vascular resistance noted in some animals after cocaine administration or startle. In contrast, icv Ang II enhances the cardiodepression associated with cocaine administration or startle. Based on this and other evidence, we propose that the autonomic response patterns to startle and to cocaine are closely related and dependent on central Ang II and CRH. Furthermore, we suggest that these central peptides may be responsible for varying predisposition to cardiovascular disease.

Sympathetic and angiotensin-dependent hypertension during cage-switch stress in mice

The goal of this study was to determine the dependence of the acute hypertensive response to a novel model of acute psychosocial stress on the sympathetic and renin-angiotensin systems. Baseline mean arterial pressure (MAP), heart rate (HR), and locomotor activity were measured with telemetry in mice for a 1-h period and averaged 98 ± 1 mmHg, 505 ± 3 beats/min, and 5 ± 1 counts, respectively. Stress was induced by placing a mouse into a cage previously occupied by a different male mouse, and this increased MAP, HR, and activity in the control group by 40 ± 2 mmHg, 204 ± 25 beats/min, and 68 ± 6 counts, respectively. Each variable gradually returned to baseline levels by 90 min after beginning cage switch. Pretreatment with terazosin (10 mg/kg ip) significantly reduced the initial increase in MAP to 12 ± 6 mmHg, whereas MAP for the last 45 min was superimposable on control values. Atenolol (10 mg/ml drinking water) had no effect to blunt the initial increase in MAP but had a growing effect from 10 min onward, decreasing MAP all the way to baseline by 60 min after starting cage switch. Captopril (2 mg/ml drinking water) treatment caused a very similar response. All three treatments significantly decreased the area under the blood pressure curve, and the blood pressure effect could not be attributed uniformly to effects on HR or activity. These data suggest that our novel model of psychosocial stress causes an initial α1-receptor-dependent increase in MAP. The later phase of the pressor response is blocked similarly by a β1-receptor antagonist and an ACE inhibitor, independent of HR, suggesting that the β1-dependent blood pressure effect is due, in large part, to the renin-angiotensin system.

Estrogen replacement suppresses stress-induced cardiovascular responses in ovariectomized rats

We assessed the hypothesis that chronic estrogen replacement in ovariectomized rats has the beneficial effect of suppressing stress-induced cardiovascular responses through endothelial nitric oxide synthase (eNOS). We employed a radiotelemetry system to measure blood pressure and heart rate (HR). Female Wistar rats aged 11 wk were ovariectomized and implanted with radiotelemetry devices. After 4 wk, the rats were assigned either to a placebo-treated group (Placebo; n = 6) or a group treated with 17β-estradiol (Estrogen; n = 8) subcutaneously implanted with either placebo- or 17β-estradiol (1.5 mg/60-day release) pellets under anesthesia. These rats underwent either of the two types of stress after 4 wk of estrogen or placebo treatment. Cage-switch stress and restraint stress rapidly and continuously elevated the mean arterial pressure (MAP) and HR both in the Placebo and Estrogen groups. However, the MAP and HR responses to cage-switch stress and the MAP but not HR response to restraint stress were attenuated significantly in the Estrogen group compared with the Placebo group. A NOS inhibitor, NG-nitro-l-arginine methyl ester, given in drinking water, reduced the difference in the pressor response to cage-switch between the Estrogen and Placebo groups. In addition, Western blot analysis showed that eNOS expression in the mesentery was increased in the Estrogen group compared with the Placebo group. Thus for the first time we showed that mesenteric eNOS overexpression could explain at least partly why chronic estrogen treatment suppressed the enhanced cardiovascular responses to psychological stress in the ovariectomized rat.

CRF1 receptor antagonist CP-154,526 reduces cardiovascular responses during acute psychological stress in rabbits

We examined the effect of CP-154,526 on cardiovascular changes elicited in conscious rabbits by stressful stimuli (loud sound, cage move, pinprick, formaldehyde vapour and air-jet stress). CP-154,526 substantially reduced pressor and heart rate responses to these stimuli (both vagally and sympathetically mediated), and reduced QT shortening during air-jet stress. Blocking of central CRF1 receptors attenuates cardiovascular responses to environmental stimuli, presumably by affecting brain centres that control cardiovascular functions.

Drug-induced neurobehavioral plasticity: the role of environmental context

Repeated administrations of addictive drugs produce long-lasting changes in brain and behavior. However, drug-induced neurobehavioral plasticity is not a mere function of the neuropharmacological actions of drugs, but the result of complex drug-environment interactions. In the present review we summarize results obtained in a series of studies using an animal model of drug-environment interaction, showing that environmental context and past drug history interact to modulate the effects of amphetamine, cocaine and morphine on behavior, gene expression and structural plasticity. These findings may help shed some light on the conditions necessary for addictive drugs to enduringly alter brain and behavior.

Hypertensive response to acute stress is attenuated in interleukin-6 knockout mice

This study tested the hypothesis that the inflammatory cytokine, interleukin-6, contributes to the hypertensive response to acute psychosocial stress, caused by switching male mice to a cage previously occupied by a different male mouse. Male C57BL6 (WT) and interleukin-6 (IL-6) knockout (KO) mice were implanted with biotelemetry devices to monitor mean arterial pressure, heart rate, and motor activity in the unrestrained state. Baseline mean arterial pressure was 98+/-1 and 103+/-1 for WT and IL-6 KO mice. Cage switch increased mean arterial pressure by 42+/-2 mm Hg in WT mice, but this was blunted significantly in KO mice (31+/-3 mm Hg peak increase). Area under the curve for the first 90 minutes also was significantly less. Heart rate and motor activity increased similarly, and there also were no differences in the increases in plasma renin activity or plasma norepinephrine concentration between WT and KO mice. Thus, the acute hypertensive response to psychosocial stress depends significantly on IL-6, and the effect appears to be specific for blood pressure rather than to a global impairment in the response to stress. However, because perfusion of the isolated mesenteric bed with phenylephrine and chronic infusion of angiotensin II caused similar responses in WT and IL-6 KO mice, it is clear that future studies are needed to determine to what extent the acute blood pressure effect of IL-6 is stress-specific.