Different Effects of Novel Stressors on Sympathoadrenal System Activation in Rats Exposed to Long-Term Immobilization

Stress and the "extended" autonomic system

This review updates three key concepts of autonomic neuroscience-stress, the autonomic nervous system (ANS), and homeostasis. Hans Selye popularized stress as a scientific idea. He defined stress variously as a stereotyped response pattern, a state that evokes this pattern, or a stimulus that evokes the state. According to the "homeostat" theory stress is a condition where a comparator senses a discrepancy between sensed afferent input and a response algorithm, the integrated error signal eliciting specific patterns of altered effector outflows. Scientific advances since Langley's definition of the ANS have incited the proposal here of the "extended autonomic system," or EAS, for three reasons. (1) Several neuroendocrine systems are bound inextricably to Langley's ANS. The first to be described, by Cannon in the early 1900s, involves the hormone adrenaline, the main effector chemical of the sympathetic adrenergic system. Other neuroendocrine systems are the hypothalamic-pituitary-adrenocortical system, the arginine vasopressin system, and the renin-angiotensin-aldosterone system. (2) An evolving body of research links the ANS complexly with inflammatory/immune systems, including vagal anti-inflammatory and catecholamine-related inflammasomal components. (3) A hierarchical network of brain centers (the central autonomic network, CAN) regulates ANS outflows. Embedded within the CAN is the central stress system conceptualized by Chrousos and Gold. According to the allostasis concept, homeostatic input-output curves can be altered in an anticipatory, feed-forward manner; and prolonged or inappropriate allostatic adjustments increase wear-and-tear (allostatic load), resulting in chronic, stress-related, multi-system disorders. This review concludes with sections on clinical and therapeutic implications of the updated concepts offered here.

Linking Stress, Catecholamine Autotoxicity, and Allostatic Load with Neurodegenerative Diseases: A Focused Review in Memory of Richard Kvetnansky

In this Focused Review, we provide an update about evolving concepts that may link chronic stress and catecholamine autotoxicity with neurodegenerative diseases such as Parkinson's disease. Richard Kvetnansky's contributions to the field of stress and catecholamine systems inspired some of the ideas presented here. We propose that coordination of catecholaminergic systems mediates adjustments maintaining health and that senescence-related disintegration of these systems leads to disorders of regulation and to neurodegenerative diseases such as Parkinson's disease. Chronically repeated episodes of stress-related catecholamine release and reuptake, with attendant increases in formation of the toxic dopamine metabolite 3,4-dihydroxyphenylacetaldehyde, might accelerate this process.

Modification of COMT-dependent pain sensitivity by psychological stress and sex

Catecholamine-O-methyltransferase (COMT) is a polymorphic gene whose variants affect enzymatic activity and pain sensitivity via adrenergic pathways. Although COMT represents one of the most studied genes in human pain genetics, findings regarding its association with pain phenotypes are not always replicated. Here, we investigated if interactions among functional COMT haplotypes, stress, and sex can modify the effect of COMT genetic variants on pain sensitivity. We tested these interactions in a cross-sectional study, including 2 cohorts, one of 2972 subjects tested for thermal pain sensitivity (Orofacial Pain: Prospective Evaluation and Risk Assessment) and one of 948 subjects with clinical acute pain after motor vehicle collision (post-motor vehicle collision). In both cohorts, the COMT high-pain sensitivity (HPS) haplotype showed robust interaction with stress and number of copies of the HPS haplotype was positively associated with pain sensitivity in nonstressed individuals, but not in stressed individuals. In the post-motor vehicle collision cohort, there was additional modification by sex: the HPS-stress interaction was apparent in males, but not in females. In summary, our findings indicate that stress and sex should be evaluated in association studies aiming to investigate the effect of COMT genetic variants on pain sensitivity.

Optimizing laboratory animal stress paradigms: The H-H* experimental design

Major advances in behavioral neuroscience have been facilitated by the development of consistent and highly reproducible experimental paradigms that have been widely adopted. In contrast, many different experimental approaches have been employed to expose laboratory mice and rats to acute versus chronic intermittent stress. An argument is advanced in this review that more consistent approaches to the design of chronic intermittent stress experiments would provide greater reproducibility of results across laboratories and greater reliability relating to various neural, endocrine, immune, genetic, and behavioral adaptations. As an example, the H-H* experimental design incorporates control, homotypic (H), and heterotypic (H*) groups and allows for comparisons across groups, where each animal is exposed to the same stressor, but that stressor has vastly different biological and behavioral effects depending upon each animal's prior stress history. Implementation of the H-H* experimental paradigm makes possible a delineation of transcriptional changes and neural, endocrine, and immune pathways that are activated in precisely defined stressor contexts.

Learning about stress: neural, endocrine and behavioral adaptations

In this review, nonassociative learning is advanced as an organizing principle to draw together findings from both sympathetic-adrenal medullary and hypothalamic-pituitary-adrenocortical (HPA) axis responses to chronic intermittent exposure to a variety of stressors. Studies of habituation, facilitation and sensitization of stress effector systems are reviewed and linked to an animal's prior experience with a given stressor, the intensity of the stressor and the appraisal by the animal of its ability to mobilize physiological systems to adapt to the stressor. Brain pathways that regulate physiological and behavioral responses to stress are discussed, especially in light of their regulation of nonassociative processes in chronic intermittent stress. These findings may have special relevance to various psychiatric diseases, including depression and post-traumatic stress disorder (PTSD).

Lipopolysaccharide induces catecholamine production in mesenteric adipose tissue of rats previously exposed to immobilization stress

Catecholamines (CAs) are mainly produced by sympathoadrenal system but their de novo production has been also observed in adipose tissue cells. The aim of this work was to investigate whether immune challenge induced by lipopolysaccharide (LPS) modulates biosynthesis of CAs in mesenteric adipose tissue (MWAT), as well as whether previous exposure to immobilization (IMO) stress could modulate this process. Sprague-Dawley rats were exposed to single (2 h) or repeated (2 h/7 days) IMO and afterwards injected with LPS (i.p., 100 μg/kg body weight) and sacrificed 3 h later. LPS did not alter CA biosynthesis in MWAT in control rats. Single and repeated IMO elevated CAs and expression of CA biosynthetic enzymes in MWAT, including adipocyte and stromal/vascular fractions (SVF). Repeated IMO followed by LPS treatment led to the up-regulation of CA-biosynthetic enzymes expression, elevation of CAs in SVF but depletion of norepinephrine and epinephrine in adipocyte fraction. Prior IMO caused a marked LPS-induced macrophage infiltration in MWAT as evaluated by F4/80 expression. A positive correlation between expression of tyrosine hydroxylase and F4/80 suggests macrophages as the main source of LPS-induced CA production in MWAT. Furthermore, prior exposure to the single or repeated IMO differently affected immune responses following LPS treatment by modulation of inflammatory cytokine expression. These data suggest that stress might be a significant modulator of immune response in MWAT via stimulation of the macrophage infiltration associated with cytokine response and de novo production of CAs.

Effect of Hemin on Brain Alterations and Neuroglobin Expression in Water Immersion Restraint Stressed Rats

In the brain, the heme oxygenase (HO) system has been reported to be very active and its modulation seems to play a crucial role in the pathophysiology of neurodegenerative disorders. Hemin as HO-1 inducer has been shown to attenuate neuronal injury so the goal of this study was to assess the effect of hemin therapy on the acute stress and how it would modulate neurological outcome. Thirty male albino rats were divided into three groups: control group and stressed group with six-hour water immersion restraint stress (WIRS) and stressed group, treated with hemin, in which each rat received a single intraperitoneal injection of hemin at a dose level of 50 mg/kg body weight at 12 hours before exposure to WIRS. Stress hormones, oxidative stress markers, malondialdehyde (MDA), and total antioxidant capacity (TAC) were measured and expressions of neuroglobin and S100B mRNA in brain tissue were assayed. Our results revealed that hemin significantly affects brain alterations induced by acute stress and this may be through increased expression of neuroglobin and through antioxidant effect. Hemin decreased blood-brain barrier damage as it significantly decreased the expression of S100B. These results suggest that hemin may be an effective therapy for being neuroprotective against acute stress.

Effect of a single and repeated stress exposure on gene expression of catecholamine biosynthetic enzymes in brainstem catecholaminergic cell groups in rats

Brainstem catecholaminergic neurons significantly participate in the regulation of neuroendocrine system activity, particularly during stressful conditions. However, so far the precise quantitative characterisation of basal and stress-induced changes in gene expression and protein levels of catecholaminergic biosynthetic enzymes in these neurons has been missing. Using a quantitative reverse transcription-polymerase chain reaction method, we investigated gene expression of catecholamine biosynthetic enzymes in brainstem noradrenergic and adrenergic cell groups in rats under resting conditions as well as in acutely and repeatedly stressed animals. For the first time, we described quantitative differences in basal levels of catecholamine biosynthetic enzyme mRNA in brainstem catecholaminergic ascending and descending projecting cell groups. Moreover, we found and defined some differences among catecholaminergic cell groups in the time-course of mRNA levels of catecholaminergic enzymes following a single and especially repeated immobilisation stress. The data obtained support the assumption that brainstem catecholaminergic cell groups represent a functionally differentiated system, which is highly (but specifically) activated in rats exposed to stress. Therefore, potential interventions for the treatment of stress-related diseases need to affect the activity of brainstem catecholaminergic neurons not uniformly but with some degree of selectivity.

Concepts of scientific integrative medicine applied to the physiology and pathophysiology of catecholamine systems

This review presents concepts of scientific integrative medicine and relates them to the physiology of catecholamine systems and to the pathophysiology of catecholamine-related disorders. The applications to catecholamine systems exemplify how scientific integrative medicine links systems biology with integrative physiology. Concepts of scientific integrative medicine include (i) negative feedback regulation, maintaining stability of the body's monitored variables; (ii) homeostats, which compare information about monitored variables with algorithms for responding; (iii) multiple effectors, enabling compensatory activation of alternative effectors and primitive specificity of stress response patterns; (iv) effector sharing, accounting for interactions among homeostats and phenomena such as hyperglycemia attending gastrointestinal bleeding and hyponatremia attending congestive heart failure; (v) stress, applying a definition as a state rather than as an environmental stimulus or stereotyped response; (vi) distress, using a noncircular definition that does not presume pathology; (vii) allostasis, corresponding to adaptive plasticity of feedback-regulated systems; and (viii) allostatic load, explaining chronic degenerative diseases in terms of effects of cumulative wear and tear. From computer models one can predict mathematically the effects of stress and allostatic load on the transition from wellness to symptomatic disease. The review describes acute and chronic clinical disorders involving catecholamine systems-especially Parkinson disease-and how these concepts relate to pathophysiology, early detection, and treatment and prevention strategies in the post-genome era.

Elevated corticosterone in the dorsal hindbrain increases plasma norepinephrine and neuropeptide Y, and recruits a vasopressin response to stress

Repeated stress and chronically elevated glucocorticoids cause exaggerated cardiovascular responses to novel stress, elevations in baseline blood pressure, and increased risk for cardiovascular disease. We hypothesized that elevated corticosterone (Cort) within the dorsal hindbrain (DHB) would: 1) enhance arterial pressure and neuroendocrine responses to novel and repeated restraint stress, 2) increase c-Fos expression in regions of the brain involved in sympathetic stimulation during stress, and 3) recruit a vasopressin-mediated blood pressure response to acute stress. Small pellets made of 10% Cort were implanted on the surface of the DHB in male Sprague-Dawley rats. Blood pressure was measured by radiotelemetry. Cort concentration was increased in the DHB in Cort-treated compared with Sham-treated rats (60 ± 15 vs. 14 ± 2 ng Cort/g of tissue, P < 0.05). DHB Cort significantly increased the integrated arterial pressure response to 60 min of restraint stress on days 6, 13, and 14 following pellet implantation (e.g., 731 ± 170 vs. 1,204 ± 68 mmHg/60 min in Sham- vs. Cort-treated rats, day 6, P < 0.05). Cort also increased baseline blood pressure by day 15 (99 ± 2 vs. 108 ± 3 mmHg for Sham- vs. Cort-treated rats, P < 0.05) and elevated baseline plasma norepinephrine and neuropeptide Y concentrations. Cort significantly enhanced stress-induced c-Fos expression in vasopressin-expressing neurons in the paraventricular nucleus of the hypothalamus, and blockade of peripheral vasopressin V1 receptors attenuated the effect of DHB Cort to enhance the blood pressure response to restraint. These data indicate that glucocorticoids act within the DHB to produce some of the adverse cardiovascular consequences of chronic stress, in part, by a peripheral vasopressin-dependent mechanism.

Differential effects of repeated immobilization stress in early vs. late postnatal period on stress-induced corticosterone response in adult rats

This study was performed in order to determine how immobilization stress in the early postnatal period or in the late postnatal period affects growth in the developing rat, and the response of the hypothalamus-pituitary-adrenocortical (HPA) axis in adult rats subjected to subsequent novel stresses. In addition, the effects of maternal deprivation (MD) within the same period of exposure to immobilization stress were also examined. We used two different types of immobilization stress and two different types of MD: immobilization stress for 30min per day from postnatal day 7 (P7) to P13 (IS-E group); immobilization stress for 30min from P15 to P21 (IS-L group); MD for 30min per day from P7 to P13 (MD-E group); and MD for 30min per day from P15 to P21 (MD-L group). The IS-E group showed a significant reduction in body weight that was maintained until at least P40 when compared with the control group. On the other hand, the IS-L group showed a significant reduction in body weight at only postnatal day (P) 20 when compared with the control group. Furthermore, the IS-E group showed a larger HPA response to novel stress than the IS-L and control groups in adulthood. The MD-E group showed a significant reduction in body weight that was maintained until at least P20 when compared with the control group, but did not show a larger HPA response to novel stress, except at T30 (30min after exposure to novel stress) than the control group in adulthood. The MD-L group did not show a significant reduction in body weight or increased HPA response when compared with control rats. These results suggest that repeated immobilization stress, but not MD, in the early postnatal period induces long-term effects on growth and HPA response to novel stress in adulthood.

Tyrosine hydroxylase phosphorylation in catecholaminergic brain regions: a marker of activation following acute hypotension and glucoprivation

The expression of c-Fos defines brain regions activated by the stressors hypotension and glucoprivation however, whether this identifies all brain sites involved is unknown. Furthermore, the neurochemicals that delineate these regions, or are utilized in them when responding to these stressors remain undefined. Conscious rats were subjected to hypotension, glucoprivation or vehicle for 30, 60 or 120 min and changes in the phosphorylation of serine residues 19, 31 and 40 in the biosynthetic enzyme, tyrosine hydroxylase (TH), the activity of TH and/or, the expression of c-Fos were determined, in up to ten brain regions simultaneously that contain catecholaminergic cell bodies and/or terminals: A1, A2, caudal C1, rostral C1, A6, A8/9, A10, nucleus accumbens, dorsal striatum and medial prefrontal cortex. Glucoprivation evoked phosphorylation changes in A1, caudal C1, rostral C1 and nucleus accumbens whereas hypotension evoked changes A1, caudal C1, rostral C1, A6, A8/9, A10 and medial prefrontal cortex 30 min post stimulus whereas few changes were evident at 60 min. Although increases in pSer19, indicative of depolarization, were seen in sites where c-Fos was evoked, phosphorylation changes were a sensitive measure of activation in A8/9 and A10 regions that did not express c-Fos and in the prefrontal cortex that contains only catecholaminergic terminals. Specific patterns of serine residue phosphorylation were detected, dependent upon the stimulus and brain region, suggesting activation of distinct signaling cascades. Hypotension evoked a reduction in phosphorylation in A1 suggestive of reduced kinase activity. TH activity was increased, indicating synthesis of TH, in regions where pSer31 alone was increased (prefrontal cortex) or in conjunction with pSer40 (caudal C1). Thus, changes in phosphorylation of serine residues in TH provide a highly sensitive measure of activity, cellular signaling and catecholamine utilization in catecholaminergic brain regions, in the short term, in response to hypotension and glucoprivation.

Modulation of the sodium-calcium exchanger in the rat kidney by different sequential stressors

Stress, if exaggerated, modulates a variety of metabolic pathways and results in development of serious health consequences. The cell membrane sodium-calcium exchanger (NCX) is a major calcium extrusion system and is also modulated by stress. It has been shown previously that mRNA, protein levels and activity of the type 1 NCX (NCX1) in the left ventricle of the rat heart are increased by stressors, such as immobilization or hypoxia. In this study we investigated whether exposure to a subsequent different stressor can affect gene expression, protein level and activity of the NCX1 in rat kidney compared to exposure to only one type of stressor. In these experiments, we used immobilization and cold as the model stressors.We found that cold exposure at 4 degrees C for 24 h, when applied after immobilization repeated seven times, completely abolished the immobilization-induced increase in NCX mRNA level and after 7 days cold exposure the increases in NCX1 protein and activity in rat kidney were also abolished. Permanently increased NCX1 expression can result in imbalance of cellular calcium homeostasis and thus contribute to kidney dysfunction. Based on our results, we conclude that exposure to a cold stressor can have a protective effect on the kidney in rats exposed previously to repeated immobilization stress. This might be explained by differential stimulation of sympathetic neural and adrenal medullary responses by these different stressors.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Repeated immobilization stress in the early postnatal period increases stress response in adult rats

Repeated immobilization stress tests in the early postnatal period were performed to determine the effects on the growth of developing rats as well as the response of the HPA axis to subsequent novel stress in adulthood. In addition, effects of maternal deprivation (MD) with the same period of the exposure to immobilization stress were also examined. We used 2 different types of immobilization stress and 2 different types of MD: immobilization stress for 30 min/day from postnatal day 7 (P7) to P13 (IS7-13 group); immobilization stress for 30 min on P7 (IS7 group); MD for 30 min/day from P7 to P13 (MD7-13 group); and MD for 30 min on P7 (MD7 group). Body weights were lower in the IS7-13 group than in the control group from P10 to P50, although body weight gain in the MD7-13 group was only transiently affected. Stress-induced corticosterone levels in the IS7-13 group were higher than in the control group and did not return to baseline levels until at least 120 min after the termination of stress, whereas temporal variations of stress-induced corticosterone levels did not differ between the IS, MD7-13, MD7, and control groups. Repeated immobilization stress in the early postnatal period induced long-term effects on the growth of developing rats and stress response of the HPA axis to the novel stress in adulthood, although a single immobilization stress, periodic MD, or a single MD had little effect.

Stress-induced catecholaminergic function: transcriptional and post-transcriptional control

This review summarizes knowledge on the effects of stress on two catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). Information is presented on differential responses of the enzymes to a variety of stressors as well as differential responses of the enzymes localized to the central nervous system vs. peripheral nervous system and tissues. Changes in mRNA and protein or activity are described, including species- and stressor-specific effects. While temporal changes in these parameters may differ for the particular stressor or enzyme, in general, maximal changes in mRNA and protein content occur at 6-8 and 24 h after stressor exposure, respectively. Elevation of TH and PNMT transcriptional activators prior to mRNA induction and nuclear run-on assays show that stress activates the genes encoding these enzymes. Yet, extents of induction of mRNA, protein and enzyme activity are often discordant depending on the stress, its duration and repetition of exposure. The extremes are concordant changes in mRNA and protein/activity vs. highly elevated mRNA with no change in protein/activity. Post-transcriptional and/or post-translational regulatory influences that may contribute to the complex effects of stress on TH, PNMT and the stress hormone epinephrine are explored.

Influence of prior experience with homotypic or heterotypic stressor on stress reactivity in catecholaminergic systems

Here we review how prior experience with stress alters the response to a subsequent homotypic or heterotypic stressor, focusing on the catecholaminergic systems in the adrenal medulla and the locus coeruleus (LC). The changes in response to homotypic stress differ depending on the stressor applied. With immobilization stress (IMO), transcriptional responses in the adrenal medulla to a single exposure are pronounced and several of the transcription factors and signaling kinases induced or activated are reviewed and compared to the longer term alterations with repeated stress, consistent with persistent activation of gene expression of catecholamine (CA) biosynthetic enzymes. In the LC, transcriptional and post-transcriptional activation of gene expression are shown to be important. Repeated IMO stress triggers further activation of a number of signalling pathways. Neither adrenal medulla nor LC display habituation to long term repeated stress. In contrast, gene expression for CA biosynthetic enzymes habituates to prolonged cold stress in the adrenal medulla and LC, but displays an exaggerated response with exposure to a novel or heterotypic stressor such as IMO. Some of the transcriptional pathways displaying sensitization are described.

Evolution of concepts of stress

This essay describes the evolution of stress as a medical scientific idea. Claude Bernard, Walter B. Cannon and Hans Selye provided key founding concepts for the current view. Bernard introduced the idea of the internal environment bathing cells - the milieu intérieur - maintained by continual compensatory changes of bodily functions. Cannon coined the word, "homeostasis," referring to a set of acceptable ranges of values for internal variables. Cannon taught that threats to homeostasis evoke activation of the sympathoadrenal system as a functional unit. Selye defined stress as a state characterized by a uniform response pattern, regardless of the particular stressor, that could lead to long-term pathologic changes. "Allostasis" was introduced as a concept in recognition that there is no single ideal set of steady-state conditions in life; instead, setpoints and other response criteria change continuously. Stress is now viewed neither as a perturbation nor a stereotyped response pattern but as a condition characterized by a perceived discrepancy between information about a monitored variable and criteria for eliciting patterned effector responses. Different stressors elicit different patterns of activation of the sympathetic nervous, adrenomedullary hormonal, hypothalamic-pituitary-adrenocortical and other effectors, closing negative feedback loops. This systems concept of stress yields predictions that observation or experimentation can test and that are applicable to normal physiology and to a variety of acute and chronic disorders.

Stress-induced changes in epinephrine expression in the adrenal medulla in vivo

Immobilization (IMMO) stress was used to examine how stress alters the stress hormone epinephrine (EPI) in the adrenal medulla in vivo. In rats subjected to IMMO for 30 or 120 min, adrenal corticosterone increased to the same extent. In contrast, EPI changed very little, suggesting that EPI synthesis replenishes adrenal pools and sustains circulating levels for the heightened alertness and physiological responses of the 'flight or fight' response. In part, stress activates EPI via the phenylethanolamine N-methyltransferase (PNMT) gene as single or repeated IMMO elevated PNMT mRNA. The rise in PNMT mRNA was preceded by induction of the PNMT gene activator, Egr-1, with increases in Egr-1 mRNA, protein, and protein-DNA binding complex apparent. IMMO also evoked changes in Sp1 mRNA, protein, and Sp1-DNA complex formation, although for chronic IMMO changes were not entirely coincident. In contrast, glucocorticoid receptor and AP-2 mRNA, protein, and protein-DNA complex were unaltered. Finally, IMMO stress elevated PNMT protein. However, with seven daily IMMOs for 120 min and delayed killing, protein stimulation did not attain the highly elevated levels expected based on mRNA changes. The latter may perhaps suggest initiation of adrenergic desensitization to prolonged and repeated IMMO stress and/or dissociation of transcriptional and post-transcriptional regulatory mechanisms.

Chronic activation of dorsal hindbrain corticosteroid receptors augments the arterial pressure response to acute stress

Augmented cardiovascular responses to acute stress can predict cardiovascular disease in humans. Chronic systemic increases in glucocorticoids produce enhanced cardiovascular responses to psychological stress; however, the site of action is unknown. Recent evidence indicates that glucocorticoids can act within the dorsal hindbrain to modulate cardiovascular function. Therefore, we tested the hypothesis that the endogenous glucocorticoid corticosterone can act in the dorsal hindbrain to enhance cardiovascular responses to restraint stress in conscious rats. Adrenal-intact animals with indwelling arterial catheters were treated for 4 or 6 days with 3- to 4-mg pellets of corticosterone or silastic (sham pellets) implanted on the dorsal hindbrain surface. Corticosterone pellets were also implanted either on the surface of the dura or subcutaneously to control for the systemic effects of corticosterone (systemic corticosterone). The integrated increase in arterial pressure during 1 hour of restraint stress was significantly (P<0.05) greater in dorsal hindbrain corticosterone (912+/-98 mm Hg per 60 minutes) relative to dorsal hindbrain sham (589+/-57 mm Hg per 60 minutes) or systemic corticosterone (592+/-122 mm Hg per 60 minutes) rats. The plasma glucose response after 10 minutes of stress was also significantly higher in dorsal hindbrain corticosterone-treated rats relative to both other groups. There were no significant between-group differences in the heart rate or corticosterone responses to stress. There were no differences in baseline values for any measured parameters. We conclude that corticosterone can act selectively in the dorsal hindbrain in rats with normal plasma corticosterone levels to augment the arterial pressure response to restraint stress.

Stress sensitivity in metastatic breast cancer: analysis of hypothalamic-pituitary-adrenal axis function

The normal diurnal cortisol cycle has a peak in the morning, decreasing rapidly over the day, with low levels during the night, then rising rapidly again to the morning peak. A pattern of flatter daytime slopes has been associated with more rapid cancer progression in both animals and humans. We studied the relationship between the daytime slopes and other daytime cortisol responses to both pharmacological and psychosocial challenges of hypothalamic-pituitary-adrenal (HPA) axis function as well as DHEA in a sample of 99 women with metastatic breast cancer, in hopes of elucidating the dysregulatory process. We found that the different components of HPA regulation: the daytime cortisol slope, the rise in cortisol from waking to 30 min later, and cortisol response to various challenges, including dexamethasone (DEX) suppression, corticotrophin releasing factor (CRF) activation, and the Trier Social Stress Task, were at best modestly associated. Escape from suppression stimulated by 1mg of DEX administered the night before was moderately but significantly associated with flatter daytime cortisol slopes (r=0.28 to .30 at different times of the post DEX administration day, all p<.01). Daytime cortisol slopes were also moderately but significant associated with the rise in cortisol from waking to 30 min after awakening (r=.29, p=.004, N=96), but not with waking cortisol level (r=-0.13, p=.19). However, we could not detect any association between daytime cortisol slope and activation of cortisol secretion by either CRF infusion or the Trier Social Stress Task. The CRF activation test (following 1.5mg of DEX to assure that the effect was due to exogenous CRF) produced ACTH levels that were correlated (r=0.66, p<.0001, N=74) with serum cortisol levels, indicating adrenal responsiveness to ACTH stimulation. Daytime cortisol slopes were significantly correlated with the slope of DHEA (r=.21, p=.04, N=95). Our general findings suggest that flatter daytime cortisol slopes among metastatic breast cancer patients may be related to disrupted feedback inhibition rather than hypersensitivity in response to stimulation.

Effects of stress on catecholamine stores in central and peripheral tissues of long-term socially isolated rats

Both the peripheral sympatho-adrenomedullary and central catecholaminergic systems are activated by various psycho-social and physical stressors. Catecholamine stores in the hypothalamus, hippocampus, adrenal glands, and heart auricles of long-term socially isolated (21 days) and control 3-month-old male Wistar rats, as well as their response to immobilization of all 4 limbs and head fixed for 2 h and cold stress (4 degrees C, 2 h), were studied. A simultaneous single isotope radioenzymatic assay based on the conversion of catecholamines to the corresponding O-methylated derivatives by catechol-O-methyl-transferase in the presence of S-adenosyl-l-(3H-methyl)-methionine was used. The O-methylated derivatives were oxidized to 3H-vanilline and the radioactivity measured. Social isolation produced depletion of hypothalamic norepinephrine (about 18%) and hippocampal dopamine (about 20%) stores and no changes in peripheral tissues. Immobilization decreased catecholamine stores (approximately 39%) in central and peripheral tissues of control animals. However, in socially isolated rats, these reductions were observed only in the hippocampus and peripheral tissues. Cold did not affect hypothalamic catecholamine stores but reduced hippocampal dopamine (about 20%) as well as norepinephrine stores in peripheral tissues both in control and socially isolated rats, while epinephrine levels were unchanged. Thus, immobilization was more efficient in reducing catecholamine stores in control and chronically isolated rats compared to cold stress. The differences in rearing conditions appear to influence the response of adult animals to additional stress. In addition, the influence of previous exposure to a stressor on catecholaminergic activity in the brainstem depends on both the particular catecholaminergic area studied and the properties of additional acute stress. Therefore, the sensitivity of the catecholaminergic system to habituation appears to be tissue-specific.

Identification of phenylethanolamine N-methyltransferase gene expression in stellate ganglia and its modulation by stress

Phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28) is the terminal enzyme of the catecholaminergic pathway converting noradrenaline to adrenaline. Although preferentially localized in adrenal medulla, evidence exists that PNMT activity and gene expression are also present in the rat heart, kidney, spleen, lung, skeletal muscle, thymus, retina and different parts of the brain. However, data concerning PNMT gene expression in sympathetic ganglia are still missing. In this study, our effort was focused on identification of PNMT mRNA and/or protein in stellate ganglia and, if present, testing the effect of stress on PNMT mRNA and protein levels in this type of ganglia. We identified both PNMT mRNA and protein in stellate ganglia of rats and mice, although in much smaller amounts compared with adrenal medulla. PNMT gene expression and protein levels were also increased after repeated stress exposure in stellate ganglia of rats and wild-type mice. Similarly to adrenal medulla, the immobilization-induced increase was probably regulated by glucocorticoids, as determined indirectly using corticotropin-releasing hormone knockout mice, where immobilization-induced increase of PNMT mRNA was suppressed. Thus, glucocorticoids might play an important role in regulation of PNMT gene expression in stellate ganglia under stress conditions.

Meconium passage in utero: mechanisms, consequences, and management

Meconium passage in newborn infants is a developmentally programmed event normally occurring within the first 24 to 48 hours after birth. Intrauterine meconium passage in near-term or term fetuses has been associated with fetomaternal stress factors and/or infection, whereas meconium passage in postterm pregnancies has been attributed to gastrointestinal maturation. Despite these clinical impressions, little information is available on the mechanism(s) underlying the normal meconium passage that occurs immediately after birth or during the intrauterine period of fetal development. Birth itself is a stressful process and it is possible that fetal stress-mediated biochemical events may regulate the meconium passage occurring either during labor or after birth. Aspiration of meconium during intrauterine life may result in or contribute to meconium aspiration syndrome (MAS), representing a continued leading cause of perinatal death. This article reviews aspects of meconium passage in utero, its consequences, and management.

Stressor Specificity and Effect of Prior Experience on Catecholamine Biosynthetic Enzyme PhenylethanolamineN-Methyltransferase

The specific activation of two components of the sympathoadrenal system (adrenomedullary and sympathoneural) by various stressors was recently described. The aim of this work was to investigate changes in catecholamine (CA) biosynthetic enzyme phenylethanolamine N-methyltransferase (PNMT) gene expression, protein level, and activity in the adrenal medulla of rats after a single or repeated exposure to various homotypic or novel heterotypic stressors. Immobilization for 2 h (IMO), cold 4 degrees C (COLD), administration of insulin 5I U (INS), or 2-deoxyglucose 500 mg/kg (2DG) were used as stressors. Plasma epinephrine (EPI) and norepinephrine (NE) levels clearly showed that these stressors specifically activate the aforementioned systems. A single exposure to IMO, COLD, INS, or 2DG induced increases in PNMT mRNA levels in the adrenal medulla. Besides PNMT mRNA, repeated exposure to IMO also elevated activity and protein levels of the enzyme; however, chronic cold exposure did not show PNMT changes compared to control animals at room temperature. PNMT gene expression was also investigated in rats adapted to repeated immobilization stress or to chronic cold exposure after a single exposure to various heterotypic novel stressors. Cold-adapted rats responded to heterotypic novel stressors (IMO, INS) by exaggerated responses of PNMT mRNA levels compared to responses in naive rats exposed to the same stressors at room temperature. Immobilization-adapted rats did not show exaggerated responses of PNMT mRNA after exposure to novel stressors. Therefore, observed differences in plasma CA and adrenomedullary mRNA levels suggest a specific regulation of CA release, synthesis, and gene expression of CA biosynthetic enzymes, which depends on the quality of the stressor. Exposure of adapted rats to novel stressors induces exaggerated responses, but this process also depends on the specificity of the stressor used. Different stressors regulate PNMT gene expression by specific mechanisms especially in chronically stressed rats. These mechanisms remain to be elucidated. It is the ability of the long-term stressed organism to respond differently to novel heterotypic stressors that we consider an important adaptive phenomenon of catecholaminergic systems in rats.