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PubMed1996

Biomechanical effects of stress shielding of the rabbit patellar tendon depend on the degree of stress reduction.

A rabbit model was used to discover whether the effects of stress shielding on the mechanical properties of the patellar tendon depend on the degree of stress reduction. Ninety mature female Japanese White rabbits were divided into three groups: completely stress-shielded partially stress-shielded and sham-operation and contralateral controls. In the experimental groups, tension applied to the patellar tendon was 0%, approximately 30%, and 100% of the normal tension, respectively, with a polyester artificial ligament. Tensile tests were carried out on patella-patellar tendon-tibia complexes harvested 1, 2, 3, 6, or 12 weeks after surgery. The tensile strength decreased in comparison with the sham-operation group to 50.2, 13.5, 9.7, and 20.7% in the completely stress-shielded group and to 75.2, 57.6, 59.6, 57.3, and 72.9% in the partially stress-shielded group. The tensile strength in the completely stress-shielded group was significantly less than that in the partially stress-shielded group at 1, 2, 3, and 6 weeks. The cross-sectional area of the patellar tendon significantly increased to 132, 206, 237, and 136% in the completely stress-shielded group and to 136, 170, 175, 155, and 127% in the partially stress-shielded group compared with the sham-operation group. The cross-sectional area of the completely stress-shielded tendon was significantly larger than that of the partially stress-shielded tendon at 1, 2, and 3 weeks. This study demonstrated that effects of stress shielding on the mechanical properties of the patellar tendon were dependent on the degree of stress shielding.

Animals↗

PubMed2001

Chronic unpredictable stress, but not chronic predictable stress, enhances the sensitivity to the behavioral effects of cocaine in rats.

RATIONALE: Chronic unpredictable stress, in which the type and timing of stress exposures are varied, alters protein levels in the mesolimbic DA system in a manner previously shown to be associated with enhanced behavioral responsiveness to cocaine. Chronic exposure to the same or predictable stress (restraint) does not. Thus, we examined the effects of chronic unpredictable and chronic predictable (restraint) stress on the locomotor activating and place conditioning effects to low cocaine doses. OBJECTIVE: To test whether chronic unpredictable stress enhances the sensitivity to the behavioral effects of cocaine. METHODS: Rats were exposed to 10 days of chronic unpredictable stress, of chronic predictable (restraint) stress, or were not stressed. One day following cessation of stress exposure, locomotor activity to cocaine (0 or 7.5 mg/kg) was assessed for 4 consecutive days and corticosterone levels on the last day were determined. In other experiments, the effects of the chronic stress procedures on cocaine (0.5 and 7.5 mg/kg) place conditioning using an unbiased procedure were assessed. RESULTS: Chronic unpredictable, but not chronic predictable, stress transiently increased the locomotor activating effects of cocaine and this was correlated positively with corticosterone levels. Chronic unpredictable, but not chronic predictable, stress also enhanced the place conditioning effects of cocaine: increased place preference was seen with the low dose and a pronounced place aversion occurred with the high dose. CONCLUSIONS: These data demonstrate that chronic unpredictable stress enhances the behavioral effects of cocaine, including its aversive effects, whereas chronic predictable stress (restraint) is without effect.

Animals↗

PubMed1987

Effects of sequential acute stress exposure on stress-induced pituitary luteinizing hormone and prolactin secretion.

The present study was carried out to determine the effects of repetitive acute stress exposure on pituitary secretion of both luteinizing hormone (LH) and prolactin (PRL). Adult male rats were exposed to sequential episodes of acute novel environment stress separated by intervals of either 60 or 120 minutes. Serial blood samples were obtained from animals before, during and after each stress episode via indwelling intra-cardiac cannulas. The imposition of 10 minute episodes of novel environment stress on an hourly basis eventually rendered the hypothalamic-hypophyseal LH axis refractory to the stimulatory effect of stress. If sequential stress was imposed at 120 minute intervals, LH release was significantly enhanced during each exposure. A different pattern of PRL release was observed during the same sequential stress schedule. After an initial increase in hormone release in response to the first hourly stress episode, PRL levels were unaltered during the second and third hourly stress exposures. Thereafter, plasma PRL levels showed a trend toward a progressive increase in release during each successive episode, and were significantly elevated above preceding baseline levels during the fourth and fifth hourly stress exposures. In rats exposed to stress every two hours, a significant increase in PRL levels occurred following the first, but not the second stress episode. Hormone release was again enhanced in response to the third exposure to novel environment. The present results demonstrate that the repetitive exposure to acute novel environment stress results in differential alterations in pituitary LH and PRL secretion over time, and that the timing of repeated episodes is an important determinant of continued responsiveness to stress, particularly with regard to LH release. These findings suggest that the LH and PRL hormonal responses to at least this specific stressor are mediated by independent neural mechanisms.

Animals↗

PubMed1994

Neonatal chronic stress induces subsensitivity to chronic stress in adult rats: II. Effects on estrous cycle in females.

The purpose of the present report was to determine the effect of exposure of females rats to the unpredictable chronic stress model and two models of predictable chronic stress (cold and handling), from day 2-15 of life, on the estrous cycle alterations caused by the unpredictable chronic stress in adulthood. Adult control and neonatally stressed rats were submitted to estrous cycle analysis for 8 days through microscopic observations of vaginal smears. They were then exposed to chronic aleatory stress, and vaginal smears were analyzed daily throughout the stress period (17 days) up to day 5 after completion of the treatment. It was found that this treatment caused constant diestrus in a majority of control females. Such diestrus started at day 5.75 +/- 0.96 of stress administration and was maintained up to day 20.0 +/- 0.49 (i.e., about 3 days after interruption of stress). This effect was prevented by the neonatal aleatory stress and the neonatal cold stress. Neonatal handling only attenuated the estrous cycle alterations; this group showed a period of diestrus no longer than 4 days during the 17-day exposure to stress. The increased resistance of neonatally stressed rats to the estrous cycle effects of chronic aleatory stress in adulthood supports the speculation that neonatal manipulation can increase resistance of rats to stress-induced reactions throughout life.

Animals↗

PubMed2003

Chronic cold stress sensitizes brain noradrenergic reactivity and noradrenergic facilitation of the HPA stress response in Wistar Kyoto rats.

Many psychiatric disorders, including depression, post-traumatic stress disorder and other anxiety disorders, result from an interaction between genetic factors and exposure to a sufficiently sensitizing environmental stressor. The inbred Wistar Kyoto (WKY) rat strain has been proposed as a model of stress vulnerability, exhibiting an exaggerated hypothalamic-pituitary-adrenal (HPA) response to stress and susceptibility to gastric ulceration. Previously, we showed that stress-activation of the brain noradrenergic system was deficient in WKY rats, and they lacked noradrenergic facilitation of the HPA response in the lateral bed nucleus of the stria terminalis (BSTL), compared to outbred Sprague-Dawley (SD) controls. Deficient modulatory function of the noradrenergic system may contribute to the stress susceptibility of WKY rats. Thus, we investigated the influence of a sensitizing stimulus, chronic intermittent cold exposure, on neuroendocrine and noradrenergic stress reactivity, and on noradrenergic facilitation of the HPA response in these two strains. Chronic cold exposure (7 days, 4 h/day, 4 degrees C) potentiated activation of the HPA axis by acute immobilization stress, assessed by measuring plasma adrenocorticotropic hormone (ACTH), in both strains, although to a greater extent in WKY rats, and enhanced stress-induced norepinephrine (NE) release in BSTL of WKY but not SD rats. We then compared the influence of chronic cold exposure on noradrenergic modulation of the HPA stress response in BSTL, by measuring changes in acute stress-induced elevation of plasma ACTH after microinjecting the alpha(1)-adrenoreceptor antagonist benoxathian into the BSTL. As shown previously, benoxathian attenuated stress-induced ACTH secretion in control SD but not control WKY rats. After chronic cold, the ACTH response to acute stress was attenuated by benoxathian administration into BSTL of both strains, such that the WKY response was not different from that of SD rats. Thus, chronic cold not only sensitized the release of NE in BSTL of WKY rats, but also restored noradrenergic facilitation of their already-elevated HPA response. Such functional sensitization of a previously-deficient facilitatory system may be one mechanism whereby exposure to repeated or severe stress may induce pathologic dysregulation of the stress response in susceptible individuals, resulting in psychiatric illness.

Adrenergic alpha-Antagonists↗

PubMed2003

The stress experience dependent long-term depression disassociated with stress effect on spatial memory task.

Behavioral stress can either block or facilitate memory and affect the induction of long-term potentiation (LTP) and long-term depression (LTD). However, the relevance of the stress experience-dependent long-term depression (SLTD) to spatial memory task is unknown. Here we have investigated the effects of acute and sub-acute elevated platform (EP) and foot shock (FS) stress on LTD induction in CA1 region of the hippocampus of anesthetized rats and spatial memory in Morris water maze. We found that LTD was facilitated by acute EP stress, but not by sub-acute EP stress that may be due to the fast adaptation of the animals to this naturalistic mild stress. However, FS stress, an inadaptable strong stress, facilitated LTD induction both in acute and sub-acute treatment. In addition, with the same stress protocols, acute EP stress impaired spatial memory but the sub-acute EP stressed animals performed the spatial memory task as well as the controls, may due to the same reason of adaptation. However, acute FS stress slightly impaired learning but sub-acute FS even enhanced memory retrieval. Our results showed that SLTD was disassociated with the effect of stress on memory task but might be related to stress experience-dependent form of aberrant memory.

Adaptation, Biological↗

PubMed2003

Randomized controlled evaluation of the effects of cognitive-behavioral stress management on cortisol responses to acute stress in healthy subjects.

Psychosocial stress is a potent activator of the hypothalamus-pituitary-adrenal (HPA) axis. While neuroendocrine stress responses are essential for the maintenance of homeostasis, evidence suggests that excessive activation of the HPA axis constitutes a risk for disease and psychopathology. The purpose of the present study was to assess the effect of cognitive-behavioral stress management training on endocrine stress responses and cognitive appraisal under acute psychosocial stress among healthy young subjects. Forty-eight healthy, non-smoking male students without acute or chronic medical or psychiatric disorder on self report were randomly assigned to receive group-based cognitive-behavioral stress management training either before or after a standardized psychosocial stress test (Trier Social Stress Test, TSST). Endocrine and psychological stress responses were assessed with salivary free cortisol response and cognitive appraisal processes to the TSST. In comparison with the control group, subjects in the treatment group showed an attenuated endocrine response (F (2.55/117.41) = 3.81; P = 0.02; effect size f(2) = 0.35) to the TSST. In addition, subjects in the SIT group had lower stress appraisal and higher control expectancies (F (2/45) = 6.56; P = 0.003, effect size f(2) = 0.29) compared to controls. Short group-based cognitive-behavioral stress management training reduces the neuroendocrine stress response to an acute stressor in healthy subjects. Therefore, stress management training may prove useful in preventing detrimental effects of stress-induced neuroendocrine activation

Adult↗

PubMed2003

The effect of vitamin E on stress-induced changes in visual evoked potentials (VEPs) in rats exposed to different experimental stress models.

PURPOSE: The aim of the study was to investigate the effects of vitamin E on stress-induced changes in visual evoked potentials (VEPs) and lipid peroxidation. METHODS: Eight experimental groups of 10 rats per group were formed. These consisted of the control group (C); the group treated with vitamin E (E); groups exposed to cold stress (CS), immobilization stress (IS) and both cold and immobilization stress (CIS), and groups exposed to equivalent stresses and treated with vitamin E (CSE, ISE, CISE). Vitamin E was injected intramuscularly in a dose of 30 mg/kg/day. RESULTS: Following chronic stress (15 days), plasma corticosterone concentrations in all experimental groups were significantly increased over those in C group. Vitamin E significantly decreased corticosterone levels in all stress groups compared with their respective control groups. Brain nitrite levels were significantly more elevated in all stress groups than in the C group. Vitamin E reduced retina and brain nitrite levels in all stress and E groups compared with their respective control groups. Vitamin E decreased glutathione peroxidase (GSH-Px) activity in retina and brain tissues in the CSE group, but increased it in the ISE group compared with their respective control groups. Lipid peroxidation was increased in brain and retina tissues in all stress groups as indicated by the significant increase in thiobarbituric acid-reactive substance (TBARS) levels with respect to the C group. Vitamin E produced a significant decrease in brain and retina TBARS levels in all stress groups with respect to their corresponding control groups. The mean latencies of P1, N1, P2, N2 and P3 components were significantly prolonged in all stress groups compared with the C group. CONCLUSION: Vitamin E returned the VEP latencies in the stress groups to control values. Our findings clearly indicated that vitamin E has the potential to prevent VEP changes caused by stress.

Animals↗

PubMed2002

Combined dipyridamole-exercise stress echocardiography for detection of myocardial ischemia in hemodialysis patients: an alternative to stress nuclear imaging.

BACKGROUND: Stress nuclear imaging is the noninvasive technique currently used to detect coronary artery disease (CAD) in dialysis patients. Stress echocardiography is recognized as an alternative to stress nuclear imaging for the general population. The aim of this study is to assess the diagnostic accuracy of stress echocardiography for detecting myocardial ischemia in hemodialysis patients. METHODS: Stress echocardiography and stress technetium-99m-tetrofosmin (Myoview; Amersham International Plc) imaging were performed simultaneously for 66 asymptomatic hemodialysis patients in a single session, using a combination of high-dose dipyridamole and symptom-limited exercise. Coronary angiography was performed in 44 patients with at least one abnormal noninvasive test result or who were considered high-risk despite normal noninvasive test results. RESULTS: Results for stress echocardiography were abnormal in 15 patients (22%); stress Myoview, in 14 patients (21%); and coronary angiography, in 12 patients (18%). The sensitivity of stress echocardiography for detecting myocardial ischemia (defined as stress Myoview defect) was 86%; specificity, 94%; positive predictive value, 80%; negative predictive value, 96%; and overall accuracy, 92%. The sensitivity of stress echocardiography for detecting CAD (defined as abnormal coronary angiography result) was 83%; specificity, 84%; positive predictive value, 67%; negative predictive value, 93%; and overall accuracy, 84%. Stress echocardiography and stress Myoview did not differ significantly in overall accuracy for detecting CAD (84% versus 91%; P = not significant). CONCLUSION: In hemodialysis patients, combined dipyridamole-exercise echocardiography is an accurate method to detect both myocardial ischemia and CAD and represents an alternative to stress nuclear imaging.

Adult↗

PubMedDate not supplied

Identification of peak stresses in cardiac prostheses. A comparison of two-dimensional versus three-dimensional principal stress analyses.

This study assessed the accuracy of using a two-dimensional principal stress analysis compared to a three-dimensional analysis in estimating peak turbulent stresses in complex three-dimensional flows associated with cardiac prostheses. Three-component, coincident laser Doppler anemometer measurements were obtained in steady flow downstream of three prosthetic valves: a St. Jude bileaflet, Bjork-Shiley monostrut tilting disc, and Starr-Edwards ball and cage. Two-dimensional and three-dimensional principal stress analyses were performed to identify local peak stresses. Valves with locally two-dimensional flows exhibited a 10-15% underestimation of the largest measured normal stresses compared to the three-dimensional principal stresses. In nearly all flows, measured shear stresses underestimated peak principal shear stresses by 10-100%. Differences between the two-dimensional and three-dimensional principal stress analysis were less than 10% in locally two-dimensional flows. In three-dimensional flows, the two-dimensional principal stresses typically underestimated three-dimensional values by nearly 20%. However, the agreement of the two-dimensional principal stress with the three-dimensional principal stresses was dependent upon the two velocity-components used in the two-dimensional analysis, and was observed to vary across the valve flow field because of flow structure variation. The use of a two-dimensional principal stress analysis with two-component velocity data obtained from measurements misaligned with the plane of maximum mean flow shear can underpredict maximum shear stresses by as much as 100%.

Heart Valve Prosthesis↗

PubMedDate not supplied

The role of stressors and psychosocial variables in the stress process: a study of chronic caregiver stress.

OBJECTIVE: An investigation was conducted 1) to examine the relative importance of stressor types (ie, daily hassles, caregiving-specific stressors, and life events) on the stress response, 2) to assess the stability of relationships between psychosocial variables and stress over a 6-month period, and 3) to explore how the nature and magnitude of the contributions made by stressors and psychosocial factors to the stress process varied according to the qualitative characteristics of the stress response (ie, anxiety, depression, and stress). METHODS: Fifty spousal caregivers of patients with dementia were recruited and asked to participate in a detailed psychosocial evaluation at 3-month intervals; the evaluation involved measurement of stressor frequency, psychosocial variables, and indices of the stress response (ie, anxiety, depression, and stress). RESULTS: The data revealed that the effects of stressors and psychosocial factors on the stress response were considerable (accounting for 49-63% of the variance in stress response measures). Furthermore, there was some evidence of stability in the effects of the stressor and mediator variables on the stress response. Specifically, the contributions of life events and caregiver difficulties were largely consistent at both 3 and 6 months, and the psychosocial factor of "reactive coping and self-appraisal" influenced all three stress response indices at both 3 and 6 months. CONCLUSIONS: There is some evidence of stability in the effects of stressors and psychosocial variables on the stress process over a 6-month period. However, it would also seem that the nature of the stress process differs according to the qualitative characteristics of the stress response.

Adaptation, Psychological↗

PubMed2004

Self-reported stress reactivity and psoriasis-related stress of Nordic psoriasis sufferers.

OBJECTIVES: The purpose of the study was to investigate the perceived influence of stress on psoriasis onset and disease severity in a large sample of psoriatics and to compare stress reactors and non-reactors with respect to psoriasis-related stress, disease severity, family history of psoriasis and sociodemographic factors. PATIENTS/METHODS: A total of 5795 members of the Nordic psoriasis associations and 702 patients recruited from Nordic dermatologists or university clinics were asked whether their first outbreak of psoriasis occurred during times of worry and stress. They were also asked to rate the degree to which their psoriasis was influenced by stress and to complete the Psoriasis Life Stress Index, the Psoriasis Disability Index and a number of additional questions concerning sociodemographic factors. RESULTS: Seventy-one per cent of the members and 66% of the patients reported that their psoriasis was exacerbated by stress, and 35% in both groups reported that the onset of their psoriasis occurred during a time of worry and stress. Stress reactors, scoring above the median on stress reactivity, reported greater disease severity, psoriasis-related stress and impairment of disease-related quality of life. They also reported more frequent use of tobacco, tranquillizers and antidepressants. More women than men were stress reactors, and stress reactors were more likely to have a family history of psoriasis. CONCLUSION: Our findings confirm and extend the results of previous studies and indicate that a subgroup of psoriatics may be more psychologically reactive to their disease and its influence on everyday life. Whether this group is also physiologically more reactive to psychosocial stress remains to be investigated.

Analysis of Variance↗

PubMed1988

[The method for stress assessment of workers (Part 1). Stress score by self-rating method].

In order to evaluate the grade of reaction to stressors, especially those on occupational life of workers, the following stress survey was conducted. Eighteen new items of occupational life stressors were proposed in addition to the social readjustment rating scale (S.R.R.S.) prepared by Holmes. Furthermore, two items, "own stress tolerance" and "own stress at present," were designed in addition to the foregoing 65 stressors. Marriage is given a score of 50 in reference-standard of stress strength. These 67 items of 1,630 workers were evaluated by the self-rating method ranging in score from 0 to 100. The results can be summarized as follows: 1. As for each item, we examined the average value of the total sample and analyzed them by sex, age, kind of occupation, position, and length of service. We named these stress scores and analyzed the ranking of 65 stress scores. The item with the highest score was "death of spouse (score 82.7)" and the item with the lowest one was "income increase (score 24.7)." The scores of 27 out of 65 items were higher than 50. Next, 65 items were classified into 4 groups, that is, individual life, family life, occupational life, and social life. 2. Scores of the newly designed items to examine the ability to adjust oneself to place of work were "own stress tolerance (score: 73.7)" and "own stress at present (48.8)," respectively. 3. We examined the difference by sex, age, kind of occupation, position, and length of service based on the average value of stress score by t-test and the following results were obtained. 1) Scores of those in the thirties were higher than those in the twenties. 2) Section heads and leaders were under greater stress than division heads. In the same way, the differences among the four groups were analyzed and the following results were observed. 1) The only significant difference was seen in the occupational life stress group. 2) In the occupational life stress group, the scores of those in the thirties, forties, and fifties were higher than those in the twenties. Section heads and leaders were under greater stress than the staff. Workers in service for more than 21 years had higher scores than workers in service for less than 10 years. 4. The practical uses of our stress survey are also discussed in this report.

Adult↗

PubMed1999

Carbohydrate intake improves cognitive performance of stress-prone individuals under controllable laboratory stress.

Cognitive performance has been found to decline after exposure to stress, particularly in stress-prone subjects. The present study investigated whether a carbohydrate-rich, protein-poor (CR/PP) diet, which may enhance cerebral serotonin function in stress-prone subjects due to increases in the available tryptophan, improves the performance of stress-prone subjects after exposure to acute laboratory stress. Twenty-two high-stress-prone (HS) subjects and twenty-one low-stress-prone (LS) subjects aged between 19 and 26 years performed a memory scanning task after controllable and uncontrollable stress, following either a CR/PP diet or a protein-rich, carbohydrate-poor (PR/CP) isoenergetic diet. Uncontrollable stress reduced feelings of control (F(1,38) 9.30; P = 0.004), whereas pulse rate and skin conductance increased after both stress tasks (F(1,38) 78.34; P = 0.0005 and F(1,37) 83.16; P = 0.0004). Diet, stress-proneness and stress-controllability interacted (F(1,36) 9.46; P = 0.004) in such a way that performance in HS subjects was better with the CR/PP diet than with the PR/CP diet, but only after controllable stress. As the CR/PP diet has been found to increase the plasma tryptophan:large neutral amino acids ratio, indicating an increased availability of cerebral tryptophan and, thus, higher serotonin levels, it appears that there may be an increased availability of brain serotonin in HS subjects after controllable laboratory stress.

Adult↗

PubMed1998

Prenatal stress enhances stress- and corticotropin-releasing factor-induced stimulation of hippocampal acetylcholine release in adult rats.

There is growing evidence that stressors occurring during pregnancy can impair biological and behavioral responses to stress in the adult offspring. For instance, prenatal stress enhances emotional reactivity, anxiety, and depressive-like behaviors associated with a prolonged stress-induced corticosterone secretion and a reduction in hippocampal corticosteroid receptors. Among the neurotransmitters involved in these hormonal and behavioral responses, acetylcholine may play a critical role. However, it is unknown whether prenatal stressful events also may influence the development of cholinergic systems. In the present study, hippocampal acetylcholine was measured, by in vivo microdialysis, in both male and female adult prenatally stressed rats, under basal conditions, after a mild stress (saline injection) or after intracerebroventricular administration of corticotropin-releasing factor (CRF; 0.1 nM). No difference in basal release of acetylcholine was observed between control and prenatally stressed rats of both genders. Mild stress was found to increase hippocampal acetylcholine release to a greater extent in prenatally stressed rats than in controls. In males, the CRF-induced increase in hippocampal acetylcholine release was larger in prenatally stressed rats, as compared with controls, during the first hour after the injection and in females during the third hour after the injection. These data indicate that prenatal stress has long-term effects on the development of forebrain cholinergic systems. The augmented increase in hippocampal acetylcholine release after the mild stress and CRF injection in prenatally stressed rats may be involved in some of the hormonal and behavioral abnormalities found in prenatally stressed rats.

Acetylcholine↗

PubMed1988

Plasma corticosterone levels during repeated presentation of two intensities of restraint stress: chronic stress and habituation.

This study measured plasma corticosterone levels in male rats during repeated daily presentations of two intensities of restraint stress. The corticosterone response to a stress session was defined as the change from pre-stress levels to levels after 60 minutes of restraint. With the relatively intense stress imposed by four limb prone restraint, the corticosterone response partially habituated over seven days due to increasing basal corticosterone levels. However, even on day 7, there was still a large corticosterone response. With the milder stress of immobilization in a tube, the corticosterone response did not habituate at all over 21 days of repeated stress despite rising basal levels. Stress levels of corticosterone did not show significant change over days in either of the two restraint groups. Further, rising basal corticosterone levels suggest that repeated restraint produced a chronic stress state in these rats which may vary in some qualitative way with stressor intensity. Control rats placed in the same room as the stressed rats during the two stresses initially had increased corticosterone levels that matched the levels achieved in the stressed rats. The responses in control rats for the intense stress did not habituate completely in 7 days, whereas those in the control rats for the mild stress habituated completely within 3 days. These data suggest intraspecific communication of the intensity of stress.

Animals↗

PubMed2001

Modulating effects of prenatal stress on hyperthermia induced in adult rat offspring by restraint or LPS-induced stress.

The present study was carried out to investigate the effects of prenatal stress on stress-induced hyperthermia in adult rats. Prenatal stress was administered daily for 3 days (embryonic days 15-17) by restraining pregnant rats in a small cage either for 30 or 240 min. After birth, foster mothers raised the pups. Offspring were tested at 9-10-weeks-old. Changes in body temperature and in the plasma concentrations of corticosterone, norepinephrine (NE), and epinephrine (Epi) induced by restraint or lipopolysaccharide (LPS)-induced stress were examined. By comparison with the prenatally nonstressed control group, the 240-min stress group showed a significantly lower hyperthermia in response to restraint stress but a higher fever after injection of LPS. The 30-min stress group showed similar alterations in these hyperthermic responses but did not reach significance. Both the restraint stress and the injection of LPS evoked greater increases in the plasma level of corticosterone in the 240-min stress group than in the control group. Although restraint stress induced significant increases in NE and Epi in the control and 30-min stress groups, the plasma levels of these catecholamines did not increase in the 240-min stress group. These results demonstrate for the first time that prenatal stress has opposite effects on the hyperthermic responses to restraint and LPS injection, suggesting that different mechanisms underlie the modulating effects of prenatal stress on the responses to the two types of stressors.

Animals↗

PubMed2000

Morphological changes in osteoblastic cells (MC3T3-E1) due to fluid shear stress: cellular damage by prolonged application of fluid shear stress.

We investigated the effect of fluid shear stress on both changes in morphology and in resting level of cytosolic concentrations of Ca2+ ([Ca2+]i) in MC3T3-E1 cells, osteoblast-like cells derived from the neonatal mouse calvaria. The cells were subjected to fluid shear stress at about 1.0 Pa. Morphological characteristics were compared between stressed and control cells by scanning electron microscopic examination, actin filament evaluation using phalloidin fluorescence and [Ca2+]i measurement using fura-2/AM. The stressed cells changed from a polygonal to a spindle shape after 1-hour exposure to fluid shear stress, whereas control cells remained polygonal, and the stressed cells exhibited an increase in the number of microvilli. The diameter in the long axis of the stressed cells was significantly larger than that of controls, and about half of the stressed cells were oriented nearly along the direction of the fluid shear stress. The arrangement of the actin filaments of the stressed cells changed to parallel, and was positioned along the long axis of the cell process. The resting level of [Ca2+]i in the stressed cells showed a peak at 1 hour after the application of the stress. A more prolonged stress period over 1 hour caused cell shrinkage, an irregularity on the cell surface, and a gradual decrease in the resting level of [Ca2+]i, suggesting that prolonged stress time may cause cellular damage.

3T3 Cells↗