Effects Of Acute Immobilization Stress Research Articles

Ecdysterone prevents negative effect of acute immobilization stress on energy metabolism of rat liver mitochondria

Ecdysterone is a naturally occurring steroid hormone, which presents in arthropods and in a number of plants as an insect defence tool. There are many studies showing that application of ecdysterone can alter mitochondrial functions of mammalian cells, however it is not clear whether its effects are direct or mediated by activation of other cellular processes. In our study, we have shown how ecdysterone acts at the mitochondrial level in normal conditions and in certain pathology. We have demonstrated that application of immobilization stress to male rats causes uncoupling of mitochondrial oxidative phosphorylation, the preliminary application of ecdysterone prevents negative effect of immobilization stress on mitochondria. In-vitro experiments with isolated mitochondria have shown that ecdysterone can increase mitochondrial coupling and hyperpolarise mitochondria but without a noticeable effect on ADP/O ratio. Molecular docking experiments revealed that ecdysterone has high binding energy with mitochondrial FOF1 ATP synthase, but further biochemical analysis have not revealed either stimulatory or inhibitory effect of ecdysterone on FOF1 ATPase activity of the enzyme. Thus, ecdysterone can directly affect mitochondrial bioenergetics, though we assume that its preventive effect on mitochondria during immobilization stress is also coupled with the activation of some other cellular processes.

Stress-induced impairment of fear extinction recall is associated with changes in neuronal activity patterns in PVT

Treatment resistance of anxiety-related disorders often arises from an inappropriate fear expression, impairment in fear extinction, and spontaneous return of fear. Stress exposure is considered a high risk factor for neuropsychiatric disorders, but understanding of the long-term consequences of stress is limited, particularly when it comes to treatment outcome. Therefore, studying the consequences of acute stress would provide critical information on the role of stress in psychopathology. In the present study, we investigated the effect of acute immobilization stress on anxiety-like behavior and on conditioned fear memory. Our results demonstrate that prior stress exposure had no effect on anxiety-related behavior, fear acquisition, as well as fear extinction compared to non-stressed controls, but resulted in significantly higher rates of freezing during recall of extinction, indicating a consolidation failure. Further, immunohistochemical analysis of the expression of the immediate early gene c-Fos after recall of extinction revealed increased neuronal activity in the posterior paraventricular nucleus of the thalamus (PVT) in previously stressed animals compared to non-stressed controls. These results indicate, firstly, that acute stress affects long-term fear memory even after successful extinction training, and secondly, a strong involvement of the PVT in maladaptive fear responses induced by prior stress. Thus, stress-induced changes in PVT neuronal activity might be of importance for the pathophysiology of stress-sensitive anxiety-related psychiatric disorders, since exposure to an earlier acute stressor could counteract the success of therapy.

Sex Differences in the Effects of Sertraline and Stressors in Rats Previously Exposed to Restraint Stress

The serotonergic system in the brain plays a major role in mood and anxiety regulation when exposed to stress. The aim of the present study was to evaluate the effects of Sertraline administration in coping with stress using the behavioural paradigms of the acoustic startle reflex (ASR) and its prepulse inhibition (PPI) in both sexes. Wistar rats were divided into two groups: intact animals and exposed to restraint stress (RS) 3 times per day during 7 days, which were then subdivided into three other groups: injected with Sertraline (5 mg/kg/day) or the drug vehicle saline for 8 consecutive days, and non-injected. ASR and PPI values were analyzed along 4 sessions to determine behavioral changes. Upon it, we also determine the effects of acute immobilization stress analyzing physiological stress indicators in blood. Our data show sex differences in response to stress paradigms. RS affected more intensely males than females, disturbing the males’ growth and the long-term startle habituation that were not affected in females. PPI increased in the vehicle-injected animals when compared to baseline in both sexes, and Sertraline reversed more efficiently it in females. Moreover, despite both sexes exposed to stressful paradigms exhibited a significant increase in serum glutamic-oxaloacetic transaminase and lactate dehydrogenase enzymes when compared with intact controls, as well as leucopenia, some differences according to sex were found in the haemostatic response to stress. Notably, the repeated injections procedure disturbed the early response to stress, which Sertraline only attenuated in both sexes. Our data suggest that 8-day Sertraline administration is effective in reversing stress-induced changes in some physio-logical parameters, but insufficient to return immunological values to normality.

MORPHOLOGICAL CHANGES OF TESTIS TISSUES IN INBRED MALE WHITE RATS UNDER THE EFFECT OF ACUTE IMMOBILIZATION STRESS

The present work showed negative effect of acute immobilization stress on the morphology of the rats` testis. The study was conducted in 22 sexually mature male albino rats (per 11 animals in the experimental and control groups). The rats of the experimental group were subjected to three-hour acute immobilization stress. The animals of the experimental group had degenerative changes in the epithelium of the seminiferous tubules until the development of focal necrosis. Also, the rats, exposed to stress, revealed a statistically significant reduction in the diameter of the seminiferous tubules and germinal layer thickness.

The influences of reproductive status and acute stress on the levels of phosphorylated delta opioid receptor immunoreactivity in rat hippocampus

In the hippocampus, ovarian hormones and sex can alter the trafficking of delta opioid receptors (DORs) and the proportion of DORs that colocalize with the stress hormone, corticotropin releasing factor. Here, we assessed the effects of acute immobilization stress (AIS) and sex on the phosphorylation of DORs in the rat hippocampus. We first localized an antibody to phosphorylated DOR (pDOR) at the SER363 carboxy-terminal residue, and demonstrated its response to an opioid agonist. By light microscopy, pDOR-immunoreactivity (ir) was located predominantly in CA2/CA3a pyramidal cell apical dendrites and in interneurons in CA1-3 stratum oriens and the dentate hilus. By electron microscopy, pDOR-ir primarily was located in somata and dendrites, associated with endomembranes, or in dendritic spines. pDOR-ir was less frequently found in mossy fibers terminals. Quantitative light microscopy revealed a significant increase in pDOR-ir in the CA2/CA3a region of male rats 1h following an injection of the opioid agonist morphine (20mg/kg, I.P). To look at the effects of stress on pDOR, we compared pDOR-ir in males and cycling females after AIS. The level of pDOR-ir in stratum radiatum of CA2/CA3a was increased in control estrus (elevated estrogen and progesterone) females compared to proestrus and diestrus females and males. However, immediately following 30min of AIS, no significant differences in pDOR levels were seen across estrous cycle phase or sex. These findings suggest that hippocampal levels of phosphorylated DORs vary with estrous cycle phase and that acute stress may dampen the differential effects of hormones on DOR activation in females.

Effect of acute immobilization stress with or without a heme oxygenase inducer on testicular structure and function in male albino rats

Stress disturbs homeostasis and may induce various disorders. Immobilization stress (IS) induced due to reduced area provided for mobility results in the imbalance of oxidant and antioxidant status. Stress leads to male reproductive dysfunction in many species, including rodents and humans. Induction of heme oxygenase-1 (HO-1), the rate limiting enzyme in heme degradation, increases host antioxidant defenses. We elucidated the protective role of induction of HO-1 by hemin on testicular damage induced by acute IS. Male albino rats were immobilized for a period of 6 h. Hemin was given for 3 consecutive days (40 μmol/kg/day, s.c.), before subjecting the animals to acute IS. Upregulation of HO-1 following hemin administration was evidenced in our study by increasing carboxyhemoglobin (COHb) level. Histopathological evaluation confirmed that acute IS caused significant testicular tissue injury, which improves in groups pretreated with hemin. Acute IS also caused significant increases in serum catecholamines and corticosterone levels; however, it produced a significant decrease in testosterone level with non-significant changes in luteinizing hormone (LH) level. In addition, it was found that IS significantly increased testicular malondialdehyde (MDA) and decreased catalase activities. The HO-1 inducer (i.e., hemin) significantly decreased catecholamines and corticosterone levels, and increased testosterone and LH levels. Hemin also decreased testicular MDA and increased catalase activities significantly. Induction of HO-1 protects the testes through its antioxidant and anti-inflammatory effects. Thus, it represents a potential therapeutic option to protect testicular tissue from detrimental effects of IS.

TRACE ELEMENTS DISTRIBUTION IN THE BRAIN OF STRESSED RATS

Because of their ability to modulate the Gamma Aminobutyric Acid (GABA) a receptor complex, the principal aim of the current work is to assess two essential heavy metals: Iron (Fe) and zinc (Zn) by atomic absorption in different brain areas of stressed rat s. To do so, we investigated the effect of acute immobilization stress (single 1-hour session) on th e distribution and the densities of GABA A receptors as well as the concentrations of Zn and Fe in several rat brain regions of the stressed rats. Animals wer e randomly assigned to either control or stress condi tions and changes in specific binding of the GABA A receptor as labelled with T-Butylbicyclophosphonothionate (TBPS) (ligand useful for GABA A receptor) were assessed by in vitro quantitative autoradiogra phy with the aid of a computer-assisted image analy sis system whereas the assessment of Fe and Zn concentrations was done by atomic absorption spectrophotometry. Exposure to 1h immobilization stress led to a significant increase in [ 35 S]-TBPS binding site density in stressed rats compared to controls (30-40% increase in cortex, hypothalamus, hippocampus and substatntia nigra). In the other analyzed brain structures, specific binding of [ 35 S]-TBPS remained unchanged in stressed rats. The spectrophotometer a nalysis showed significant decrease in Zn levels in the whole forebrain structures as well as the mesenceph alon of stressed rats. The striking differences are noticed in hippocampus and mesencephalon. Furthermore, Fe endogenous concentrations display similar pattern following stress. The present study demonst rates that immobilization stress induces an increas e in GABA A receptors concomitant to a reduction of Zn and Fe c ontent in the stress sensitive rat brain structures . Besides supporting the alteration of the modulatory function occurring at the GABA A receptor level after stress, our data also reveal that the measured brai n concentrations of the investigated heavy metals r emain not sufficient to efficiently modulate the activity of with efficacy such complex receptor. This could explain the higher densities of GABA A receptors observed after acute stress.

Male and female stress in serotonin transporter knockout mice

Serotonin (5-HT) is an important modulator of many physiological, behavioural and developmental processes and it plays an important role in stress coping reactions. Anxiety disorders and depression are stress-related disorders and they are associated with malfunction of the serotonin system, in which the serotonin transporter (5-HTT) plays an important role. 5-Htt knockout (KO) mice represent an artificially hyperserotonergic environment, show an increased anxiety-like behaviour and seem to be a good model to investigate the role of the serotonin system concerning stress reactions and anxiety disorders. As synaptic vesicle proteins (SVPs) seem to be involved in stress reactions we studied the effect of acute immobilization stress on SVP expression in the 5-Htt KO mouse model as well as the expression of the two immediate early genes (IEGs) FBJ osteosarcoma oncogene (c-Fos) and fos-like antigen 2 (Fra-2). Based on gender- and genotype-dependent differences in corticosterone levels we looked for expression differences in the brain by performing a quantitative real time-PCR study using primer pairs specific for the SVPs Synaptotagmin (Syt) I, Syt IV and Syntaxin (Stx) 1a and for the IEGs c-Fos and Fra-2 in five different brain regions in 5-Htt KO and wildtype mice. We found mainly gender-dependent differences but less stress effects on the expression of SVPs. Regarding the expression of IEGs we found stress-, gender- and genotype-dependent differences mainly in hypothalamus.

Stress and neuro-hormonal control of food intake

Event Abstract Back to Event Stress and neuro-hormonal control of food intake Mohamed Najimi1*, Fatiha Chigr1, Fatima Rachidi1, Catherine Tardivel2 and Emmanuel Moyse2 1 Lab. Génie Biologique, Morocco 2 CRN2M, France Stressful events are related with many dysfunctions leading to homeostasis disruption. For example, exposure to stress has been argued to produce maladaptive behavioral states, and many of the brain regions associated with stressor responding also mediate these affected behaviors. The effect of stress has been sown to act via the activation of the hypothalamo-hypophyseo-adrenocorticotropin (HPA) axis. Furthermore, many neurochemical pathways seemed to respond or to be affected by stress. This especially evidenced for those involved in the control of food intake in that several stressful situations can lead to a pathogenesis of anorexia. In this study, we analyzed the effects of acute immobilization stress (IS) on the expression of two major neuropeptide regulators of food intake, in the hypothalamus and the dorsal vagal complex (DVC). The expression of the neuropeptide Y (NPY) and cocaine- and amphetamine- regulated transcript (CART) displayed generally significant increases in stressed rats compared to controls, although with differential patterns. Thus, they rapidly increase in hypothalamus at the end of the stress session, whereas in the DVC th expression rise significantly at 24h post-stress and decline afterwards; it remains significantly higher in stressed than in controls for NPY whereas CART was down-regulated after 48h post-stress. These post stress alterations have generally linked to the response of the HPA axis and its recovery after IS as has been suggested. These results will be discussed with reference to brain plasticity. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Poster Presentation Topic: Stress Citation: Najimi M, Chigr F, Rachidi F, Tardivel C and Moyse E (2009). Stress and neuro-hormonal control of food intake. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.144 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Nov 2009; Published Online: 25 Nov 2009. * Correspondence: Mohamed Najimi, Lab. Génie Biologique, Beni-Mellal, Morocco, mnajimi1@fstbm.ac.ma Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Mohamed Najimi Fatiha Chigr Fatima Rachidi Catherine Tardivel Emmanuel Moyse Google Mohamed Najimi Fatiha Chigr Fatima Rachidi Catherine Tardivel Emmanuel Moyse Google Scholar Mohamed Najimi Fatiha Chigr Fatima Rachidi Catherine Tardivel Emmanuel Moyse PubMed Mohamed Najimi Fatiha Chigr Fatima Rachidi Catherine Tardivel Emmanuel Moyse Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Stress-induced changes in sleep and associated neuronal activity in rat hippocampus and amygdala

Stress increases vulnerability to anxiety and depression. We have investigated the effect of acute immobilization stress in amygdalohippocampal circuits by measuring the electroencephalogram (EEG) in male Wistar rats during rapid eye movement (REM) sleep. Electrodes were implanted stereotaxically in the hippocampus (CA1 and CA3 subregions of the hippocampus) and the amygdala (lateral nucleus). Prior to the stress, two baseline recordings were taken. Twenty-four hours later rats were exposed once to acute immobilization stress (AIS) session for 2 h. After the release and on subsequent days, electrophysiological changes that occurred due to stress during REM sleep were analyzed by comparing them with baseline measurements. Our results suggest that acute immobilization stress induced significant increase in REM sleep in the first 24 h after the exposure. In addition to changes in the sleep patterns, we have observed increased theta oscillations in CA1 area of the hippocampus with decreased coherence at theta range (4–8 Hz) between hippocampus and amygdala. These results suggest that single exposure to aversive experience such as immobilization stress can lead to dynamic changes in neuronal activities with altered sleep morphology. The results obtained in the present study are comparable to those seen in human patients suffering from panic, and anxiety due to posttraumatic stress disorder (PTSD).

Investigation of the anticonvulsive effect of acute immobilization stress in anxious Balb/cByJ mice using GABAA-related mechanistic probes

A disordered regulation of neuroactive steroids release in response to acute stress could induce GABAergic dysfunctions underlying anxiety disorders. First, we conducted studies indicating that a short immobilization stress in anxious Balb/cByJ mice produced an anticonvulsive effect. Second, the effects of different positive allosteric modulators (etifoxine, progesterone, clonazepam, and allopregnanolone) of GABA A receptors were compared in a mouse model mimicking the disruption of the acute stress-induced neuroactive steroids release with finasteride (types I and II 5alpha-reductase inhibitor). The acute stress-induced anticonvulsive effect, expressed by the threshold dose of t-butylbicyclophosphorothionate-producing clonic seizures, was time-dependent. The extent of the enhancement of acute stress-induced anticonvulsive effect was lowered in the presence of finasteride. The same effect was observed with PK11195, which behaves as an antagonist of the peripheral benzodiazepine receptor in the dose range used in this study. Picrotoxin reduced the acute stress anticonvulsive effect, proving that this effect operates through the GABA A receptor. Contrary to progesterone (up to 30 mg/kg), etifoxine (50 mg/kg), allopregnanolone (10 mg/kg), and clonazepam (10 microg/kg) inhibited the finasteride effect in stressed animals. The effect of etifoxine was blocked in the presence of finasteride and picrotoxin combined in stressed animals. These findings support the hypothesis suggesting an involvement of neuroactive steroids in the anticonvulsive effect of restraint stress. The dual and complementary mechanisms of action of etifoxine (directly on the GABA A receptor and indirectly via the neuroactive steroids) may represent a therapeutic benefit in the treatment of various anxiety disorders with abnormal production of neuroactive steroids.

The effect of acute immobilization stress on the expression of synaptic proteins in serotonin transporter deficient mice

The effect of acute immobilization stress on the expression of synaptic proteins in serotonin transporter deficient mice

The effect of acute immobilization stress on the expression of synaptic proteins in serotonin transporter deficient mice

The effect of acute immobilization stress on the expression of synaptic proteins in serotonin transporter deficient mice

Relationship Between Interindividual Differences and Physiological Indexes of Acute Stress in Rats

We used in vivo microdialysis to examine interindividual differences in the effects of acute immobilization stress and diazepam treatment on monoamine turnover in the hippocampus of male rats as an index of stress. Immobilization significantly increased the concentrations of 3,4‐dihydroxyphenyl‐aceticacid (DOPAC), homovanillic acid (HVA), and 5‐hydroxyindoleacetic acid (5‐HIAA). This effect was attenuated by injection of diazepam, Interindividual differences in reactivity to stressors caused differential changes in different metabolic products of monoamines. In our study, stress‐induced changes in DOPAC levels were relatively great, and there was a similar change in the concentration of HVA. We conclude that at least 2 indexes of stress should be measured to take into account interindividual differences in the changes in stress indexes.

Acute immobilization stress induces clinical and neuroimmunological alterations in experimental murine cutaneous leishmaniasis.

The skin is an important component of the neuroendocrine-immune axis. Several studies have shown that stress exacerbates skin disorders, affecting the function of sebaceous glands, keratinocytes, epidermal Langerhans cells and other cells, having an impact on the pathogenesis of many immunologically associated skin diseases. In American cutaneous leishmaniasis, we have shown the importance of the epidermis as a regulatory site, with the key participation of Langerhans cells. To analyse the effect of acute immobilization stress on Langerhans cells, substance P (SP), calcitonin gene-related peptide (CGRP) and the natural course of infection in a murine model of cutaneous leishmaniasis. BALB/c mice, susceptible to Leishmania infection, were placed under acute stress by immobilization (confinement) for 2 or 8 h before inoculation with L. mexicana (MHOM/BZ/82/BEL21). An avidin-biotin immunoperoxidase technique was used for cell and neuropeptide identification. The stressed animals became more susceptible to the parasite infection, which was manifested by acceleration and exacerbation of the lesions. In addition, the stressed animals showed morphological alterations (spherical bodies and shortened dendrites) and decreased numbers of epidermal Langerhans cells, when compared with control L. mexicana-infected mice. Mice stressed for 8 h showed greater and antidromic immunoreactivity to CGRP and SP at the time of infection. Moreover, the single inoculation of parasites caused a decrease of CGRP innervation. Acute immobilization stress induces an immunosuppressive state that further favours Leishmania invasion in susceptible animals.

Role of adrenergic mechanisms in regulation of phagocytic cell functions in acute stress response

The effects of acute immobilization stress and its combination with β-adrenergic receptor blockade on some functions of phagocytic cells have been analyzed. β-Adrenergic mechanisms were shown to be involved in regulation of phagocytic cell functions in acute stress response.

Acute stress decreases serotonin transporter mRNA in the raphe pontis but not in other raphe nuclei of the rat

In addition to elevated corticosterone levels, stress produces structural changes and neuronal damage especially in the hippocampus. In this line it has been shown, that in rats single or repeated immobilisation markedly reduces brain-derived neurotrophic factor (BDNF) mRNA levels in the hippocampal formation. Since this neurotrophin also controls the efficacy of serotonergic neurotransmission, the aim of the current study was to investigate the effect of acute immobilization stress on the expression of serotonin transporter (SERT) mRNA in the raphe nuclei as a parameter of serotonergic innervation. We have examined the expression of SERT mRNA and of BDNF mRNA in rats upon acute immobilisation by quantitative in situ hybridisation with a 35S-labelled oligonucleotide probe. Elevated corticosterone levels in stressed animals confirmed as internal controls the effect of stress under our conditions. Acute stress led to a significant decrease of BDNF mRNA in the hippocampus and of SERT mRNA in the raphe pontis, but not in other raphe nuclei investigated. These data provide evidence for fast interactions between neurotrophins, corticosterone and serotonergic neurotransmission under stress conditions.

The effect of acute immobilization stress on the abundance of corticotropin-releasing factor receptor in lymphoid organs

We have previously found a dramatic increase of corticotropin-releasing factor receptor (CRF-R1) production in splenic neutrophils of male C57BL/6N mice after application of an immunological stimulus. We demonstrate here that immobilization, a predominantly psychological stress, exhibited a similar effect. Shortly after 90 min of immobilization, the number of splenic CRF-R1 + cells was transiently increased by nearly 8-fold, while it was reduced in thymus and unchanged in lymph nodes. The CRF-R1 + cells were detected by an affinity-purified polyclonal antibody directed against the N-terminus of CRF-R1, and identified as neutrophils, eosinophils or their immature precursors on the basis of their nuclear shapes, Wright–Giemsa staining and colocalization of CRF-R1 with the ER-MP58 antigen.

Acute Immobilization Stress Triggers Skin Mast Cell Degranulation via Corticotropin Releasing Hormone, Neurotensin, and Substance P: A Link to Neurogenic Skin Disorders

Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and are associated with increased numbers and activation of mast cells which release vasoactive, nociceptive, and proinflammatory mediators. Nontraumatic acute psychological stress by immobilization has been shown to induce mast cell degranulation in the rat dura and colon. Moreover, intradermal injection of corticotropin-releasing hormone (CRH) or its analogue urocortin (10−5–10−7 M) induced skin mast cell degranulation and increased vascular permeability. Here, we investigated the effect of acute immobilization stress on skin mast cell degranulation by light microscopy and electron microscopy. Immobilization for 30 min resulted (P < 0.05) in degranulation of 40.7 ± 9.1% of skin mast cells compared to 22.2 ± 7.3% in controls killed by CO2 or 17.8 ± 2.4% in controls killed by pentobarbital. Pretreatment intraperitoneally (ip) with antiserum to CRH for 60 min prior to stress reduced (P < 0.05) skin mast cell degranulation to 21.0 ± 3.3%. Pretreatment with the neurotensin (NT) receptor antagonist SR48692 reduced (P < 0.05) mast cell degranulation to 12.5 ± 3.4%, which was significantly (P < 0.05) below control levels. In animals treated neonatally with capsaicin to deplete their sensory neurons of their neuropeptides, such as substance P (SP), mast cell degranulation due to immobilization stress was reduced to about 15%. This is the first time that stress has been shown to trigger skin mast cell degranulation, an action not only dependent on CRH, but apparently also involving NT and SP. These findings may have implications for the pathophysiology and possible therapy of neuroinflammatory skin disorders such as atopic dermatitis, neurogenic pruritus, or psoriasis, which are induced or exacerbated by stress.

Brain angiotensin II modulates sympathoadrenal and hypothalamic pituitary adrenocortical activation during stress.

Angiotensin II (Ang II) type-1 (AT1) receptors are present in areas of the brain controlling autonomic nervous activity and the hypothalamic-pituitary-adrenal (HPA) axis, including CRH cells in the hypothalamic paraventricular nucleus (PVN). To determine whether brain AT1 receptors are involved in the activation of the HPA axis and sympathetic system during stress, we studied the effects of acute immobilization stress on plasma catecholamines, ACTH and corticosterone, and mRNA levels of CRH and CRH receptors (CRH-R) in the PVN in rats under central AT1 receptor blockade by the selective antagonist, Losartan. While basal levels of epinephrine, norepinephrine and dopamine in plasma were unaffected 30 min after i.c.v. injection of Losartan (10 microg), the increases after 5 and 20 min stress were blunted in Losartan treated rats (P < 0.05 for norepinephrine, and P < 0.01 for epinephrine and dopamine, vs controls). Basal or stress-stimulated plasma ACTH and corticosterone levels were unaffected by i.c.v. Losartan treatment. Using in situ hybridization studies, basal levels of CRH mRNA and CRH-R mRNA in the PVN were unchanged after i.c.v. Losartan. While Losartan had no effect on the increases in CRH-R mRNA levels 2 or 3 h after 1 h immobilization, it prevented the increases in CRH mRNA. The blunted plasma catecholamine responses after central AT1 receptor blockade indicate that endogenous Ang II in the brain is required for sympathoadrenal activation during immobilization stress. While Ang II appears not to be involved in the acute secretory response of the HPA axis, it may play a role in regulating CRH expression in the PVN.