Comparative biochemical responses of rats to different stressful stimuli

Restraint or immobilization: a comparison of methodologies for restricting free movement in rodents and their potential impact on physiology and behavior

Restriction of free movement has historically been used as a model for inducing acute and chronic stress in laboratory animals. This paradigm is one of the most widely employed experimental procedures for basic research studies of stress-related disorders. It is easy to implement, and it rarely involves any physical harm to the animal. Many different restraint methods have been developed with variations in the apparatuses used and the degree of limitation of movement. Unfortunately, very few studies directly compare the differential impact of the distinct protocols. Additionally, restraint and immobilization terms are not differentiated and are sometimes used interchangeably in the literature. This review offers evidence of great physiological differences in the impact of distinct restraint procedures in rats and mice and emphasizes the need for a standardized language on this topic. Moreover, it illustrates the necessity of additional systematic studies that compare the effects of the distinct restraint methodologies, which would help to decide better which procedure should be used depending on the objectives of each particular study.

Prenatal development toxicity study of zinc oxide nanoparticles in rats

This study investigated the potential adverse effects of zinc oxide nanoparticles ([ZnO(SM20(+)) NPs] zinc oxide nanoparticles, positively charged, 20 nm) on pregnant dams and embryo-fetal development after maternal exposure over the period of gestational days 5-19 with Sprague-Dawley rats. ZnO(SM20(+)) NPs were administered to pregnant rats by gavage at 0, 100, 200, and 400 mg/kg/day. All dams were subjected to a cesarean section on gestational day 20, and all of the fetuses were examined for external, visceral, and skeletal alterations. Toxicity in the dams manifested as significantly decreased body weight after administration of 400 mg/kg/day NPs; reduced food consumption after administration of 200 and 400 mg/kg/day NPs; and decreased liver weight and increased adrenal glands weight after administration of 400 mg/kg/day NPs. However, no treatment-related difference in: number of corpora lutea; number of implantation sites; implantation rate (%); resorption; dead fetuses; litter size; fetal deaths and placental weights; and sex ratio were observed between the groups. On the other hand, significant decreases between treatment groups and controls were seen for fetal weights after administration of 400 mg/kg/day NPs. Morphological examinations of the fetuses demonstrated significant differences in incidences of abnormalities in the group administered 400mg/kg/day. Meanwhile, no significant difference was found in the Zn content of fetal tissue between the control and high-dose groups. These results showed that oral doses for the study with 15-days repeated of ZnO(SM20(+)) NPs were maternotoxic in the 200 mg/kg/day group, and embryotoxic in the 400 mg/kg/day group.

Effect of zinc oxide nanoparticles on dams and embryo-fetal development in rats

This study investigated the potential adverse effects of zinc oxide nanoparticles (ZnO^SM20[−] NPs; negatively charged, 20 nm) on pregnant dams and embryo–fetal development after maternal exposure over the period of gestational days 5–19 with Sprague Dawley rats. ZnO^SM20(−) NPs were administered to pregnant rats by gavage at 0 mg/kg/day, 100 mg/kg/day, 200 mg/kg/day, and 400 mg/kg/day. All dams were subjected to caesarean section on gestational day 20, and all the fetuses were examined for external, visceral, and skeletal alterations. Toxicity in the dams manifested as significantly decreased body weight at 400 mg/kg/day and decreased liver weight, and increased adrenal glands weight at 200 mg/kg/day and 400 mg/kg/day. However, no treatment-related difference in the number of corpora lutea, the number of implantation sites, the implantation rate (%), resorption, dead fetuses, litter size, fetal deaths, fetal and placental weights, and sex ratio were observed between the groups. Morphological examinations of the fetuses demonstrated no significant difference in the incidences of abnormalities between the groups. No significant difference was found in the Zn content of fetal tissue between the control and high-dose groups. These results showed that a 15-day repeated oral dose of ZnO^SM20(−) was minimally maternotoxic at dose of 200 mg/kg/day and 400 mg/kg/day.

Effects of melamine on pregnant dams and embryo-fetal development in rats

There are worldwide concerns regarding the potential adverse effect of melamine. This study investigated the potential effects of melamine on pregnant dams and embryo-fetal development in Sprague-Dawley rats following maternal exposure on gestational days (GD) 6-20. Melamine was administered to pregnant rats by gavage at doses of 0, 200, 400 and 800 mg kg⁻¹ per day (n = 8-10 for each group). All dams were subjected to a Caesarean section on GD 21 and their fetuses were examined for morphological abnormalities. With administration of melamine at 800 mg kg⁻¹ per day, maternal toxicity manifested as increased incidences of clinical signs and death, lower body weight gain and food intake, and increases in heart, adrenal gland and kidney weights. Histopathological examinations revealed an increase in incidences of congestion, tubular necrosis/degeneration, crystals, casts, inflammatory cells in tubules, tubular dilation and tubular hyaline droplets in the maternal kidneys, while fetal kidneys (one fetus/litter) did not show any histopathological changes. Developmental toxic effects included a decrease in fetal weight, an increase in the incidence of skeletal variations and a delay in fetal ossification. No treatment-related maternal or developmental effects were observed at doses ≤ 400 mg kg⁻¹ per day. These results show that 15-day repeated oral dosing of melamine is embryo-/fetotoxic at a maternotoxic dose, but not teratogenic in rats. The no-observed-adverse-effect level of melamine for pregnant dams and embryo-fetal development is considered to be 400 mg kg⁻¹ per day.

Stress-induced decreases in local cerebral glucose utilization in specific regions of the mouse brain

Background

Restraint stress in rodents has been reported to activate the hypothalamic-pituitary-adrenocortical (HPA) axis and to increase c-fos expression in regions that express components of the corticotropin-releasing factor (CRF) system. We have previously reported that acute central administration of CRF increased a measure of relative local cerebral glucose utilization (LCGU), a measure of neuronal activity in specific brain regions, and activated the HPA axis in mice. It was hypothesized that the involvement of the CRF system in the stress response would lead to similar changes in relative LCGU after restraint stress. In the present studies the effect of restraint stress on relative LCGU and on the HPA axis in C57BL/6N mice were examined.

Findings

Restraint stress activated the HPA axis in a restraint-duration dependent manner, but in contrast to the reported effects of CRF, significantly decreased relative LCGU in frontal cortical, thalamic, hippocampal and temporal dissected regions. These findings support evidence that stressors enforcing limited physical activity reduce relative LCGU, in contrast to high activity stressors such as swim stress.

Conclusions

In conclusion, the present studies do not support the hypothesis that stress-induced changes in relative LCGU are largely mediated by the CRF system. Further studies will help to delineate the role of the CRF system in the early phases of the relative LCGU response to stress and investigate the role of other neurotransmitter systems in this response.

Acute anxiogenic-like effects of selective serotonin reuptake inhibitors are attenuated by the benzodiazepine diazepam in BALB/c mice

Selective serotonin re-uptake inhibitors (SSRIs), which are used commonly to treat anxiety disorders, have characteristic anxiogenic effects following acute administration. Treatment with anxiolytic benzodiazepines (BZs) may reduce these effects, although little is known about potential drug interactions. Our study evaluated acute anxiogenic-like effects of SSRIs, alone and combined with a BZ. Adult male BALB/c mice received fluoxetine (3.0-30.0mg/kg, i.p.) or citalopram (3.0-30.0mg/kg, i.p.) alone or in combination with diazepam (0.3-10.0mg/kg, i.p.), after which they were evaluated with the light/dark and open-field tests for anxiogenesis/anxiolysis. In addition, release of the stress hormone corticosterone was assessed following combined SSRI/BZ administration. In the light/dark and open-field tests, acute SSRIs produced a behavioral profile consistent with anxiogenesis, while diazepam produced an anxiolytic-like profile. Pre-treatment with diazepam (0.3-10mg/kg) reversed the effects of an anxiogenic-like dose of an SSRI (18mg/kg fluoxetine, 30mg/kg citalopram) in both light/dark and open-field tests. Diazepam, fluoxetine or citalopram, and their combination all significantly increased plasma corticosterone levels to the same degree. These findings suggest that a BZ-type drug can attenuate acute anxiogenic-like effects of an SSRI via a mechanism independent of corticosterone regulation.

Effects of tert-butyl acetate on maternal toxicity and embryo-fetal development in Sprague-Dawley rats

This study investigated the potential adverse effects of tert-butyl acetate (TBAc) on maternal toxicity and embryo-fetal development after maternal exposure of pregnant rats from gestational days 6 through 19. TBAc was administered to pregnant rats by gavage at 0, 400, 800, and 1,600 mg/kg/day. All dams were subjected to a Caesarean section on day 20 of gestation, and their fetuses were examined for any morphological abnormalities. At 1,600 mg/kg, maternal toxicity manifested as increases in the incidence of clinical signs and death, lower body weight gain and food intake, increases in the weights of adrenal glands and liver, and a decrease in thymus weight. Developmental toxicity included a decrease in fetal weight, an increase in the incidence of skeletal variation, and a delay in fetal ossification. At 800 mg/kg, only a minimal developmental toxicity, including an increase in the incidence of skeletal variation and a delay in fetal ossification, were observed. In contrast, no adverse maternal or developmental effects were observed at 400 mg/kg. These results show that a 14-day repeated oral dose of TBAc is embryotoxic at a maternally toxic dose (i.e., 1,600 mg/kg/day) and is minimally embryotoxic at a nonmaternally toxic dose (i.e., 800 mg/kg/day) in rats. However, no evidence for the teratogenicity of TBAc was noted in rats. It is concluded that the developmental findings observed in the present study are secondary effects to maternal toxicity. Under these experimental conditions, the no-observed-adverse-effect level of TBAc is considered to be 800 mg/kg/day for dams and 400 mg/kg/day for embryo-fetal development.

Involvement of NK1 receptors in metabolic stress markers after the central administration of substance P

Substance P (SP) is involved in the pathophysiology of several psychiatric disorders and is considered a central stress neurotransmitter. Endogenous SP does not inhibit the initial extent of the HPA axis response to restraint stress, but reduces the duration of the stress suggesting that SP plays an important role in the transition between acute and chronic stress. Stress hormones can alter metabolic functions in white adipose tissue and liver. The HPA axis is the endocrine pathway that promotes lipolysis elevating free fatty acid levels (FFA) in blood, besides indirectly causing hyperglycemia. In the present study, changes in the blood levels of stress markers in the anxiogenic-like effects of SP, as evaluated on the elevated plus-maze (EPM), were studied in adult male rats. Serum corticosterone was used as the traditional stress marker, while the plasma FFA and glucose were used as alternative anxiety/stress markers. Our findings show: (a) elevated corticosterone levels, confirming the aversive situation induced by SP (behaviorally assessed in the EPM) and indicating SP as a "chemical" stressor; (b) elevated levels of FFA and glucose, indicators of stress-induced mobilization of energy substrates, confirming the stressor effect of SP; (c) FFA levels can be used as an accurate, sensitive and reliable index of acute stress situations, including in the anxiogenic-like effect of SP, with the FFA response being as good as corticosterone as a stress marker in this case; (d) NK1 receptors involvement in the underlying mechanisms of the behavioral and metabolic effects of SP. Finally, our study indicates that some of these physiological variables are positively related to the stressor intensity.

Subacute toxicity evaluation in rats exposed to concrete and hwangto building environments

This study examined the potential adverse effects of the subacute exposure of rats to concrete and hwangto building environments. Polycarbonate was used as a comparison. Groups of 10 male rats were exposed to polycarbonate, concrete, or hwangto cages for a 4-week period in summer or winter. During the study period, the clinical signs, mortality, skin temperature, body weight, food consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weights, and histopathology were examined. The concentration of total volatile organic compounds (VOCs), temperature, and relative humidity in the each cages were also measured. There were no exposure-related effects in any group of the study examined in the summer. The temperature, relative humidity, and the concentration of VOCs in the cages were similar in all groups. However, in the winter study, significant differences in several parameters were detected among the groups. In the concrete group, there was an increase in the clinical signs, a reduction in the body weight gain, food intake, and liver weight, an increase in the lung weight, and an increase in the histopathological alterations in the lung and thymus. Infrared thermal analysis showed that the skin temperature of the rats in the concrete group was lower than that in the polycarbonate group. However, in the hwangto group, there was a decrease in the clinical signs and an increase in the body weight, food intake, and the weights of the heart, lung, spleen, and epididymides. Overall, the 4-week exposure of the rats to the concrete building environment had adverse effects on the clinical signs, skin temperature, body weight, and some organs in the winter but not in the summer. On the other hand, the exposure of hwangto building environment did not have any exposure-related adverse effects on the general health parameters and skin temperature in rats.

A tryptic hydrolysate from bovine milk alphaS1-casein improves sleep in rats subjected to chronic mild stress

The putative effects of a tryptic bovine alphaS1-casein hydrolysate on stress-induced sleep disorders were investigated and their possible link with typical blood stress parameters such as plasma corticosterone concentrations and glycaemia was assessed. Rats were subjected to chronic stress in the form of environmental disturbances, while receiving an oral administration of the alphaS1-casein hydrolysate (CH). Chronic stress significantly reduced sleep duration in control rats during the first 2 days of the stress period, but stress-induced sleep disturbance was prevented in CH-treated rats. Indeed, CH administration allowed the maintenance of slow wave sleep (SWS) duration and even a slight increase in paradoxical sleep (PS) duration in treated rats. Results on plasma corticosterone concentrations and on glycemia values were inconclusive with respect to the implication of the HPA axis in this study. However, the protective effect of the alphaS1-casein hydrolysate on sleep during exposure to our chronic mild stress conditions may be mediated by modulation of the central adrenergic response.

Effects of prenatal maternal stress by repeated cold environment on behavioral and emotional development in the rat offspring

It has been reported that many types of stresses, which caused physiological and psychological alterations in dams as prenatal maternal stress, affected behavioral and emotional traits of their offspring. However, effects of environmental temperature changes, which induce various stress responses in both animals and humans, have not been assessed as prenatal maternal stress. Repeated cold stress (RCS) is a type of chronic cold stress in which environmental temperature changes rapidly and frequently several times within a day. In the present study, to investigate effects of chronic maternal stress by the RCS on behavioral and emotional development of the rat offspring (prenatal RCS rats), the RCS stress was loaded to pregnant rats between day 9 and 19 after fertilization. The prenatal RCS rats showed similar locomotor activity in an open field to control rats that were borne by non-stressed pregnant rats. On the other hand, the prenatal RCS rats showed significantly higher startle responses than the control rats in a light enhanced startle paradigm. However, treatment of diazepam decreased the startle responses in the prenatal RCS rats to the same degree as those in the control rats. The results indicated that prenatal RCS affected emotional development of the rat offspring, but not locomotor activity. Comparison of the present results with the previous studies suggests that there might be unknown common mechanisms among different prenatal maternal stresses that induce similar behavioral developmental alteration.

The effects of chronic mild stress on male Sprague-Dawley and Long Evans rats: I. Biochemical and physiological analyses

The chronic unpredictable mild stress (CMS) is a paradigm developed in animals to model the relatively minor and unanticipated irritants that lead to a state of anhedonia in some individuals. However, the effectiveness of CMS is sometimes difficult to establish, for which unique strain sensitivities has been attributed as one contributing factor. These considerations led us to design the present study, which was an investigation of the corticosterone response to CMS in two outbred rat strains--Sprague-Dawley and Long Evans. Animals were exposed to one of two conditions--control or CMS--for 3 weeks during which body weight and fecal count were regularly monitored. At the end of this period, blood was sampled at a variety of time intervals following induction of a brief restraint stressor. First, a significant effect of CMS on corticosterone levels was evident at time 0 (prior to the application of the acute restraint stressor) in both strains. Second, the typical quadratic pattern of stressor-elicited fluctuations in this measure was similar in both Sprague-Dawley and Long Evans rats, with consistently elevated levels for the first hour following exposure to the acute stressor; near baseline values were observed at 2 h. However, only in the Long Evans strain were CMS related values much less than that observed in the control group after restraint stress. Third, both strains showed a reduced weight gain in the CMS groups relative to control groups. Fourth, spleen and adrenal weights were similar across all groups. Fifth, fecal counts remained stable across weeks of treatment in all groups with the exception of the Long Evans rats exposed to CMS; in this group, average counts were systematically reduced over the treatment period. We conclude that a history of chronic stress significantly blunts corticosterone levels in Long Evans but not Sprague-Dawley rats following exposure to an acute stressor. Physiological indices however are less influenced by this experience, at least when the exposure is limited to 3 weeks.

Psychological stress, but not physical stress, causes increase in diazepam binding inhibitor (DBI) mRNA expression in mouse brains

Effects of conditioned emotional stimuli (CES), which induce psychological stress, on the expression of cerebral diazepam binding inhibitor (DBI) mRNA in mouse were examined using a communication box. Cerebral DBI mRNA expression significantly increased in a time-dependent manner after the application of CES. The maximal enhancement of DBI mRNA expression was observed 2 days after the application of CES, and this increase faded out over 7 days after the treatment. Flunitrazepam (1 mg/kg), an agonist for central benzodiazepine (BZD) receptors, completely abolished the CES-induced elevation of cerebral DBI contents and its mRNA expressions. These results indicate that cerebral DBI is enhanced by psychological stress, which is regulated by central BZD receptors.

A comparison of female and male rats' ETOH-induced ataxia and exploration following restraint or swim stress

Animal models of stress reactivity are often employed in developing treatments for humans. Many studies use shock stress, and most use male rats. These experiments compare female and male rats exposed to either restraint stress (RS) or ambient-temperature swim stress (SS), using two durations of each stressor and naive controls. The ataxic effects of a 0.6 g/kg i.p. dose of ethanol (ETOH) were measured. Females exhibited less ataxia than males following ETOH administration. There were no significant effects of stress on ETOH-induced ataxia. Exploration was also measured in an open-field test (OFT) both pre- and poststress. In the prestress OFT, females were more active than males. For the no-stress groups and the shorter-duration stress groups, exploration decreased between the first and second OFTs. However, the groups exposed to the longer-duration stress did not show this expected decrease in exploration. A key finding of this research is that while sex differences may be present at baseline, the sexes may react similarly to stress. These data extend knowledge on sex differences in stress, alcohol reactivity and exploratory behavior.

Physiological correlates of the forced swim test in rats

Rats were tested in the forced swim test to evaluate the effects of duration of exposure (0, 5, 15, or 25 min), and water temperature (0, 35, 30, 25, or 20 degrees C), on a variety of physiological measures. Serum corticosterone, glucose, lactate, phosphorus levels, and the anion gap (a measure of acid-base status) were increased significantly, whereas carbon dioxide and potassium levels were consistently decreased by testing, as was the potassium/phosphorus ratio; creatinine, triglycerides, and magnesium were not altered significantly in any study. Effects on prolactin, amylase, lipase, cholesterol, alkaline phosphatase, sodium, and chloride were inconsistent. Levels of serum corticosterone were increased at each duration of testing, and the increments were significantly higher than the previous duration. Corticosterone levels were also increased in proportion to decreasing water temperature, but the increments were not significantly different from the previous or following temperatures. Glucose levels were increased at every duration and at every water temperature with the exception of the coldest water temperature. Lactate and phosphorus levels and the anion gap were all increased, whereas carbon dioxide levels decreased after 5 min of immersion. Potassium levels did not decrease until some time after 5 min of testing. Immobility times were marginally correlated with corticosterone levels (r = -0.38) but were highly correlated with serum carbon dioxide (r = 0.59), potassium (r = 0.67), and phosphorus levels (r = -0.73); the correlation between immobility times and the ratio of potassium/phosphorus was 0.82. The potassium/phosphorus ratio accounted for 67% of the variance in immobility. These high correlations were interpreted in terms of acid-base changes associated with testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Stress and dexfenfluramine: effects on the immune response and energy balance in the rat

The effects of stress, dexfenfluramine (d-Fen), and a combination of both were investigated on ingestive behavior, body weight, and the humoral immune response in the rat. Three-hundred and 84 male Sprague-Dawley rats were split into four groups of 96 animals. In a balanced design, each group was submitted or not to repeated intense stress for 20 consecutive days. Animals were also treated with 5 mg/kg/day d-Fen (IP, 1 ml/kg) or an equal volume of placebo (saline) for 28 days. The humoral immune response of rats to sheep red blood cells (50% solution, 1 ml IP at day 0) was assessed from the antibody titer on days 4, 8, 12, 16, 20, and 28. Antibodies were assayed by direct hemagglutination and by the Coombs' test. Plasma corticosterone was also measured on days 0 and 12. The effects of stress and d-Fen on ingestive behavior and body weight were consistent with previously published results. In addition, rats treated with d-Fen had a significantly reduced body weight (-20 g) 5 weeks after the end of the treatment, whereas the loss in body weight induced by stress had totally disappeared. Stress did not decrease animals' immune response despite a massive corticosterone secretion on day 0, with a marked response lasting for at least 12 days. d-Fen reduced the corticosterone levels determined on day 12. Antibody production was slightly but significantly reduced in rats receiving d-Fen.(ABSTRACT TRUNCATED AT 250 WORDS)

Social stress and atherosclerosis in roosters

1. Socially stressed roosters fed either plain mash or an atherogenic diet had a greater incidence and severity of aortic atherogenesis than similarly fed non-stressed birds. 2. Results demonstrated a significant atherogenic effect of stress in chickens even in the absence of hyperlipidaemia. 3. Lack of appreciable differences in plasma lipids between stressed and non-stressed birds suggested that the atherogenic effects of stress may be attributable to neuroendocrine responses. 4. Levels of HDLc of plain mash groups were significantly higher than in the atherogenic fed groups. 5. Haemodynamic data showed no treatment-related differences.

The serum glucose response to acute stress is sensitive to the intensity of the stressor and to habituation

The reliability of serum glucose concentrations as an index of habituation to chronic stress was evaluated in adult male rats. The glucose response to immobilization was attenuated by six days of previous chronic exposure to the same stressor, the degree of reduction being related to the duration (15 min, 1 hr or 4 hr) of the daily exposure to immobilization. In another experiment, three groups of rats were exposed to one of three stressors (handling plus change of room, restraint in tubes, or immobilization by wood boards), 1 hr daily for 27 days. On day 28, when faced with the same acute stressor to which they were chronically exposed, the rats showed a consistent reduction in glucose response, regardless of the type of stressor used. In addition, in stress-naive rats serum glucose levels were related to the intensity of the stressor as assessed by three independent measures (food intake, body weight changes, and adrenal weight after chronic exposure to the stressor). These data indicate that, under appropriate conditions, glucose levels can be a good index of both the intensity of acute stress experienced by the rats and their habituation to repeated stress.

Effects of age on metabolic responses to acute and chronic stress

The effect of age on the capacity of an organism to mobilize glucose and free fatty acids during stress and to adapt these responses from an acute to a chronic stress situation is not known. The purpose of this study was to determine whether aging impaired the capacity to 1) raise glucose and free fatty acid levels and suppress insulin release in acute stress situations and 2) develop adaptation of these responses to exposure to chronic stress. Our results indicate that 6-mo-old rats (young) trained to escape electric shock (short-term modulation) showed greater acute stress-induced hyperglycemic, hypoinsulinemic, and lipolytic responses than untrained young rats. By contrast, in 22-mo-old rats (old), responses of trained and untrained animals were not different. In the chronic stress (long-term adaptation) experiments, it was found that 1) adaptation of stress-induced hyperglycemia occurred at a faster rate in young than in old animals; 2) in young but not in aged rats, a strong positive correlation was observed between adaptation of stress-induced hyperglycemia and hypoinsulinemia; and 3) in young rats, stress-induced lipolytic responses declined proportionately to the duration of chronic stress exposure, whereas by contrast in chronically stressed aged rats steady-state levels of free fatty acids were not raised during exposure to stress. Thus we conclude that 1) glucose intolerance may play a key role in the altered stress-induced metabolic responses of aged rats; 2) with age, there is a loss of plasticity in physiological adaptive response mechanisms associated with metabolic responses to stress.

Adaptation of plasma catecholamine and corticosterone responses to short-term repeated noise stress in rats

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in blood frequently sampled via a cardiac catheter from freely moving rats exposed to three successive trials of white-noise stimulation (10 min, 100 dBA) with an intertrial interval of 30 min. During the sampling period, behavioral activities of the rats were recorded. It was demonstrated that the first exposure to noise induced a specific temporal pattern of neuroendocrine changes: Plasma A and NA contents increased rapidly and peaked early after stimulus onset but their peak-latencies were different (1 and 5 min, respectively). Noise offset was followed by quick return to basal levels. The changes in plasma CS concentrations were considerably slower in onset and slower in decline. The second and third exposure to this type of stressor resulted in attenuated hormonal responses and a reduced decrement of the NA/A-ratio, concurrent with a gradually less intense behavioral reaction. This differential pattern of plasma NA, A and CS responses following repetitive exposure to identical stressors, referred to as adaptation, is discussed with regard to the biochemical changes at various levels of the neuroendocrine systems involved.

Dietary protein and carbohydrate effects on blood parameters related to stress in cat

Adult cats were adapted to hypoglucidic semi-purified diets containing casein or soya as the protein source to study the effects of a 2 hr immobilization period. Body weight of cats fed hypoglucidic diets was significantly decreased. The control casein group showed higher plasma dopamine-beta-hydroxylase activity but lower pyridoxal 5'-phosphate level than control soya group. Cats fed hypoglucidic casein diet, plasma glucose, insulin and pyridoxal 5'-phosphate levels were increased whereas cats fed hypoglucidic soya diet, pyridoxal 5'-phosphate levels were decreased and dopamine-beta-hydroxylase activity increased when data were compared to their respective control groups. A 2 hr immobilization period induced hyperglycemia in all groups whereas cats fed soya diets, plasma insulin level and dopamine-beta-hydroxylase activity were significantly increased and pyridoxal 5'-phosphate content significantly decreased. These results demonstrate that dietary casein and soya protein might be differentiated on a physiological basis and immobilization emphasized the biochemical disturbances observed between the groups thus suggesting a greater resistance to stress in casein groups than in soya groups.

Chronic exposure to random restraint stress retards the development of estrogen-induced pituitary prolactinoma in rats

The effects of stress on carcinogenesis have been equivocal. The present work examined the influence of an unpredictable pattern of chronic restraint stress on estradiol-induced pituitary hyperplasia in male Fischer 344 rats. The animals were grouped as follows: (1) control, (2) stressed, (3) estradiol (31 mg), subcutaneous implant for 40 days and (4) estradiol with stress, 1 h daily, randomly, for 40 days. The pituitaries increased markedly in mass in groups 3 and 4 compared to the first two groups. However, the gland weight in rats exposed to estradiol plus stress was significantly (P less than 0.04) reduced as compared to estradiol per se. Prolactin levels increased due to estradiol treatment and decreased following exposure to stress. Weights of adrenal glands increased as a result of estradiol treatment when compared to those in stressed or untreated animals. This adrenal hypertrophy correlated well with plasma corticosterone levels. The data demonstrate that chronic immobilization stress retarded estradiol-induced pituitary prolactinoma. Modulation of the immune response by stress-related factors may play a role in the inhibition of tumorigenesis.

Hyperglycemia and fight-flight behavior in nondiabetic and diabetic mice

Glycemic responses to a resident-intruder encounter and to the drawing of blood from the retro-orbital sinus were studied in diabetic and normal male Swiss Webster mice. The diabetes induced with streptozotocin was either borderline, overt, or severe. The resident-intruder encounter consisted of a brief exposure to another male mouse trained to be aggressive. The blood collected was not sufficient (3% blood volume) to cause significant volume depletion. Behavior during the resident-intruder encounter was videotaped and later quantified. Borderline diabetic, overtly diabetic and nondiabetic mice responded to both procedures with significant increases in plasma glucose. The glycemic response to the resident-intruder encounter in these groups was significantly greater than that to the bleeding trial. The severely diabetic mice did not experience increases in plasma glucose in either test. Fight-flight behavior of nondiabetic mice was significantly correlated with increases in plasma glucose. Total activity was negatively correlated with change in plasma glucose in the borderline diabetic mice. In overtly diabetic mice no relationship between either measure and glucose increases was observed. These results indicate that plasma glucose elevation in overtly and severely diabetic mice is not as specific to behavior as in nondiabetic mice.

Forced swimming alters vaginal estrous cycles, body composition, and steroid levels without disrupting lordosis behavior or fertility in rats

The purpose of the present studies was to examine how exercise affects reproductive physiology and behavior. In four separate experiments, exercise regimens of forced swimming or swimming plus running, were gradually increased in duration to a maximum of 2.5 hours. Vaginal cycles were monitored daily and after eight weeks animals were tested for sexual behavior, ability to breed, changes in body composition, circulating levels of estradiol, progesterone, and corticosterone. Total body lipids were lowered in animals that both ran and swam and parametrial fat pad weight was reduced in all exercising animals. Although exercise lowered circulating levels of ovarian steroids, elevated corticosterone levels and disrupted vaginal cycles, exercised animals exhibited normal sexual behavior and bred successfully. These data indicate that intense exercise can, under certain conditions, disrupt the mechanisms controlling vaginal cycles while the neuroendocrine mechanisms controlling sexual receptivity, ovulation, and fertility remain intact.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.

Corticosterone, free fatty acid and glucose responses of rats to footshock, fear, novel stimuli and instrumental reinforcement

Rats were subjected to sessions of footshock, fear stimuli and instrumental reinforcement to assess responses of blood corticosterone, free fatty acids (FFA) and glucose. The corticosterone response to fearful situations exhibited a stimulus generalization decrement, thus demonstrating a contribution of Pavlovian classical conditioning to the activity of the hypothalamo-pituitary-adrenal system. Corticosterone levels were shown to decrease during operant sessions with large water reinforcements, while FFA and glucose levels were increasing, thus dissociating these stress measures. FFA responses to intermittent, intense footshock were found to be quadratic; blood levels of FFA increased within 10 min, decreased by 40 min, and then showed the increase with 80-min long sessions previously reported in the literature. This pattern of response was not influenced by prior food deprivation or different methods of sampling blood. Blood levels of FFA increased generally to novel/fearful situations and instrumental reinforcement sessions, which were stimulus situations less stressful than the footshock sessions. Glucose increases occurred to footshock and instrumental reinforcement sessions under some conditions, depending more than corticosterone and FFA on prior food deprivation and blood sampling method.

Stress-induced consumption of ethanol by rats

Rats were maintained in a continuous choice situation for consumption of either 0.1% aqueous saccharin or 10% ethanol- 0.1% saccharin with daily tube position reversal and 24 hour fluid consumption measurement. After a stabilized baseline was achieved, groups were exposed to either no stress, or to an unpredictable schedule of isolation or immobilization stress for 14 days. During baseline and stress-exposure periods, the rats consumed predominantly the saccharin solution. Upon cessation of the stress exposures the isolation and immobilization groups markedly increased their consumption of the ethanol solution, reaching intakes as high as 9.1 g/kg/24 hours in 2-3 weeks. In addition, after 3 weeks of ethanol consumption, placement of saccharin in both tubes resulted in the stressed animals preferentially consuming from the tube that should have contained ethanol. The results suggest that unpredictable exposure to stressful stimuli can, upon cessation of exposure, induce an alcohol consummatory behavior in rats.