Effect of acute and repeated restraint stress on glucose oxidation to CO2 in hippocampal and cerebral cortex slices

Contribution of the intra-hippocampal orexin system in the regulation of restraint stress response to pain-related behaviors in the formalin test

Stress-induced antinociception (SIA) is due to the activation of several neural pathways and neurotransmitters that often suppress pain perception. Studies have shown that the orexin neuropeptide system is essential in pain modulation. Therefore, this study aimed to investigate the role of orexinergic receptors in the hippocampal CA1 region in modulating SIA response during the formalin test as an animal model of inflammatory pain. The orexin-1 receptor (OX1r) antagonist, SB334867, at 1, 3, 10, and 30 nmol or TCS OX2 29 as an orexin-2 receptor (OX2r) antagonist at the same doses were microinjected into the CA1 region in rats. Five minutes later, rats were exposed to restraint stress (RS) for 3 h, and pain-related behaviors were monitored in 5-min blocks for the 60-min test period in the formalin test. Results showed that applying RS for 3 h reduced pain responses in the early and late phases of the formalin test. The main findings showed that intra-CA1 injection of orexin receptor antagonists reduced the antinociception caused by stress in both phases of the formalin test. In addition, the contribution of OX2r in mediating the antinociceptive effect of stress was more prominent than that of OX1r in the early phase of the formalin test. However, in the late phase, both receptors worked similarly. Accordingly, the orexin system and its two receptors in the CA1 region of the hippocampus regulate SIA response to this animal model of pain in formalin test.

Metabolic changes in the subtropical frog Boana pulchella during experimental cooling and recovery conditions

Frogs have developed biochemical and physiological adaptations to occupy diverse ecological niches on Earth successfully. Survival in frozen states is a fascinating strategy made possible by evolving adaptations to produce cryoprotectant solutes. The hylid frog Boana pulchella thrives in South American regions with cold climates, remaining active while enduring sporadic subzero temperatures during winter. The species' metabolic changes during subzero exposure remain unclear. Therefore, we exposed B. pulchella to cooling and recovery, assessing plasma and tissue metabolite changes. Cooling significantly reduced urea concentrations in plasma (P = 0.033), muscle (P = 0.001), heart (P = 0.009), and brain (P = 0.041) compared to acclimation. Liver glucose oxidation and glycogen synthesis were lower in cooling and recovery than in acclimation (P < 0.0001 and P = 0.0117, respectively). Muscle glycogen synthesis was lower in recovery than acclimation (P = 0.0249). These results demonstrate B. pulchella's physiological strategies during subzero exposure, likely reflecting species-specific evolutionary adaptations for brief subzero exposures that enable winter survival in its natural habitat.

Seasonal variations in the intermediate metabolism in South American tree-frog Boana pulchella

Seasonal metabolic changes can be observed in many anurans' species. In subtropical environments with environmental temperatures variations, the temperature is a factor that can influence the extent and intensity of activity in many anuran species. Nonetheless, some species of subtropical frogs may remain active throughout the year. Boana pulchella, a subtropical species, seems to be able to survive low temperatures and remain reproductively active even in the coldest months. Therefore, we hypothesized that B. pulchella presents seasonal changes in the energy metabolism to sustain activity during all year. This study evaluated the main energy substrate levels and metabolism of B. pulchella in plasma, liver and muscle of male individuals collected in winter, spring, summer and fall in the state of Rio Grande do Sul, Brazil. Our results showed that B. pulchella has a higher glycolytic oxidation rate in liver (P = 0.0152) and muscle (P = 0.0003) and higher glycogenesis from glucose in muscle (P = 0.0002) in summer, indicating the main energy substrates in this season is glucose. The higher muscle glycogen (P = 0.0008) and lower plasma glucose in fall (P = 0.0134) may indicate an anticipatory regulation for storing to the most thermally demanding cold period: winter. These results indicated seasonal differences in the main energy substrates, and these metabolic changes among seasons can be part of a metabolic adjustment allowing maintenance of reproductive activity all year in Boana pulchella species.

Differential glucose and beta-hydroxybutyrate metabolism confers an intrinsic neuroprotection to the immature brain in a rat model of neonatal hypoxia ischemia

Neonatal hypoxia ischemia (HI) is the main cause of newborn mortality and morbidity. Preclinical studies have shown that the immature rat brain is more resilient to HI injury, suggesting innate mechanisms of neuroprotection. During neonatal period brain metabolism experience changes that might greatly affect the outcome of HI injury. Therefore, the aim of the present study was to investigate how changes in brain metabolism interfere with HI outcome in different stages of CNS development. For this purpose, animals were divided into 6 groups: HIP3, HIP7 and HIP11 (HI performed at postnatal days 3, 7 and 11, respectively), and their respective shams. In vivo [¹⁸F]FDG micro positron emission tomography (microPET) imaging was performed 24 and 72 h after HI, as well as ex-vivo assessments of glucose and beta-hydroxybutyrate (BHB) oxidation. At adulthood behavioral tests and histology were performed. Behavioral and histological analysis showed greater impairments in HIP11 animals, while HIP3 rats were not affected. Changes in [¹⁸F]FDG metabolism were found only in the lesion area of HIP11, where a substantial hypometabolism was detected. Furthermore, [¹⁸F]FDG hypometabolism predicted impaired cognition and worst histological outcomes at adulthood. Finally, substrate oxidation assessments showed that glucose oxidation remained unaltered and higher level of BHB oxidation found in P3 animals, suggesting a more resilient metabolism. Overall, present results show [¹⁸F]FDG microPET predicts long-term injury outcome and suggests that higher BHB utilization is one of the mechanisms that confer the intrinsic neuroprotection to the immature brain and should be explored as a therapeutic target for treatment of HI.

Melissa officinalis L. hydro-alcoholic extract inhibits anxiety and depression through prevention of central oxidative stress and apoptosis

NEW FINDINGS

What is the central question of this study? How does an extract of Melissa officinalis L. ameliorate anxiety- and depressive-like behaviour of mice? What is the main finding and its importance? An extract of Melissa officinalis L. possessed anxiolytic and anti-depressant effects, which could mainly be mediated through its antioxidant and anti-apoptotic properties.

ABSTRACT

This study evaluated the effects of a hydro-alcoholic extract of Melissa officinalis (HAEMO) on anxiety- and depressive-like behaviours, oxidative stress and apoptosis markers in restraint stress-exposed mice. In order to induce a depression-like model, mice were subjected to restraint stress (3 h day-1 for 14 days) and received normal saline or HAEMO (50, 75 and 150 mg kg-1  day-1 ) for 14 days. The administered doses of HAEMO were designated based on the concentration of one of the main phenolic compounds present in the extract, rosmarinic acid (2.55 mg kg-1 at lowest dose); other phytochemical analyses including assays for antioxidant activity, total phenols and flavonoids were also carried out. The behavioural changes in an open field task, elevated plus maze, tail suspension and forced swimming tests were evaluated. Also, malondialdehyde (MDA) levels and enzyme activities of superoxide dismutase and glutathione peroxidase, and total antioxidant capacity were assessed in the prefrontal cortex and hippocampus. Moreover, levels of Bcl-2, Bax and caspase 3 in the brain as well as serum concentration of corticosterone were evaluated. HAEMO (75 and 150 mg kg-1 ) significantly reversed anxiety- and depressive-like behaviours. Also, HAEMO reduced MDA levels, enhanced enzymatic antioxidant activities and restored serum levels of corticosterone. An immunoblotting analysis also demonstrated that HAEMO decreased levels of pro-apoptotic markers and increased anti-apoptotic protein levels in the prefrontal cortex and hippocampus of restraint stress-exposed mice. Our findings suggested that HAEMO reduced inflammation and had anxiolytic and antidepressant effects in mice.

Effect of acute restraint stress in a polytrauma rat model

INTRODUCTION

A stressful environment may contribute to poor outcomes after TBI. The current study evaluates the impact of acute stress in a polytrauma rat model.

METHODS

Rats were stressed by a 45-minute immobilization period before instrumentation under ketamine (t1). Polytrauma was produced by blast overpressure and controlled hemorrhage (t2). Rats were euthanized immediately after a 3 h simulated Medevac-transport time (t3) or after 72 h post-trauma (t4). Corticosterone, ACTH, and ACTH receptor gene expression were measured at these time points. Physiological parameters were monitored throughout the study.

RESULTS

HR was higher in stressed compared to unstressed animals at t1. Corticosterone and ACTH levels were similar for all conditions at t1 and t2; ACTH and corticosterone became elevated in all groups at t3 and at t4, respectively. The ACTH receptor gene expression trended towards higher values at t4 for the stressed animals whether being injured or not. Survival after injury was 83% in both unstressed and stressed animals.

CONCLUSION

Overall, corticosterone was not significantly affected following acute stress in ketamine-anesthetized rats. Early mortality was primarily due to polytrauma and change in the animal's biochemical parameters appeared at t4 post trauma. The findings indicate that ketamine-anesthesia and/or surgery may have overshadowed the effect of the initial stress.

Akebia quinata Decaisne aqueous extract acts as a novel anti-fatigue agent in mice exposed to chronic restraint stress

ETHNOPHARMACOLOGICAL RELEVANCE

Akebia quinata Decaisne extract (AQE; Lardizabalaceae) is used in traditional herbal medicine for stress- and fatigue-related depression, improvement of fatigue, and mental relaxation.

AIM OF THE STUDY

To clarify the effects of AQE on stress-induced fatigue, we investigated the neuroprotective pharmacological effects of A. quinata Decaisne in mice exposed to chronic restraint stress.

MATERIALS AND METHODS

Seven-week old C57BL/6 mice chronically stressed by immobilization for 3 h daily for 15 d and non-stressed control mice underwent daily oral administration of AQE or distilled water. The open field, sucrose preference, and forced swimming behavioral tests were carried out once weekly, and immunohistochemical analyses of NeuN, brain-derived neurotrophic factor (BDNF), phosphorylated cAMP response element-binding (CREB) protein, and BDNF receptor tropomyosin receptor kinase B (TrkB) in striatum and hippocampus were performed at the end of the experimental period. Brain levels of serotonin, adrenaline, and noradrenaline as well as serum levels of corticosterone were measured.

RESULTS

Behavioral tests showed that treatment with AQE improved all lethargic behaviors examined. AQE significantly attenuated the elevated levels of adrenaline, noradrenaline, and serotonin in the brain and corticosterone, alanine transaminase, and aspartate transaminase levels in the serum. Histopathological analysis showed that AQE reduced liver injury and lateral ventricle size in restraint-stress mice via inhibition of neuronal cell death. Immunohistochemical analysis showed increased phosphorylation of CREB and expression of BDNF and its receptor TrkB in striatum and hippocampus. Chlorogenic acid, isochlorogenic acid A, and isochlorogenic acid C were identified as the primary components of AQE. All three agents increased expression of BDNF in SH-SY5Y cells and PC12 cells with H₂O₂-induced neuronal cell damage.

CONCLUSIONS

AQE may have a neuroprotective effect and ameliorate the effects of stress and fatigue-associated brain damage through mechanisms involving regulation of BDNF-TrkB signaling.

Isoflurane and the Analgesic Effect of Acupuncture and Electroacupuncture in an Animal Model of Neuropathic Pain

The present study aimed to determine whether isoflurane interferes with the analgesic effects of acupuncture (Ac) and electroacupuncture (EA), using a neuropathic pain (NP) rat model. In total, 140 male Wistar rats were used; isoflurane-induced nociceptive response was evaluated using the von Frey test, serum calcium-binding protein β (S100β) levels and nerve growth factor (NGF) levels in the left sciatic nerve. The NP model was induced by chronic constriction injury of the sciatic nerve at 14 days after surgery. Treatment was initiated after NP induction with or without isoflurane anesthesia (20 min/day/8 days). The von Frey test was performed at baseline, 14 days postoperatively, and immediately, 24 h, and 48 h after the last treatment. Results of the nociceptive test and three-way analysis of variance were analyzed by generalized estimating equations, the Bonferroni test, followed by Student-Newman-Keuls or Fisher's least significant difference tests for comparing biochemical parameters (significance defined as p ≤ 0.05). At baseline, no difference was noted in the nociceptive response threshold among all groups. Fourteen days after surgery, compared with other groups, NP groups showed a decreased pain threshold, confirming establishment of NP. Ac and EA enhanced the mechanical pain threshold immediately after the last session in the NP groups, without anesthesia. Isoflurane administration caused increased nociceptive threshold in all groups, and this effect persisted for 48 h after the last treatment. There was an interaction between the independent variables: pain, treatments, and anesthesia in serum S100β levels and NGF levels in the left sciatic nerve. Isoflurane enhanced the analgesic effects of Ac and EA and altered serum S100β and left sciatic nerve NGF levels in rats with NP.

Relevance of deprivation studies in understanding rapid eye movement sleep

Rapid eye movement sleep (REMS) is a unique phenomenon essential for maintaining normal physiological processes and is expressed at least in species higher in the evolution. The basic scaffold of the neuronal network responsible for REMS regulation is present in the brainstem, which may be directly or indirectly influenced by most other physiological processes. It is regulated by the neurons in the brainstem. Various manipulations including chemical, elec-trophysiological, lesion, stimulation, behavioral, ontogenic and deprivation studies have been designed to understand REMS genesis, maintenance, physiology and functional significance. Although each of these methods has its significance and limitations, deprivation studies have contributed significantly to the overall understanding of REMS. In this review, we discuss the advantages and limitations of various methods used for REMS deprivation (REMSD) to understand neural regulation and physiological significance of REMS. Among the deprivation strategies, the flowerpot method is by far the method of choice because it is simple and convenient, exploits physiological parameter (muscle atonia) for REMSD and allows conducting adequate controls to overcome experimental limitations as well as to rule out nonspecific effects. Notwithstanding, a major criticism that the flowerpot method faces is that of perceived stress experienced by the experimental animals. Nevertheless, we conclude that like most methods, particularly for in vivo behavioral studies, in spite of a few limitations, given the advantages described above, the flowerpot method is the best method of choice for REMSD studies.

Sex-specific effects of dehydroepiandrosterone (DHEA) on glucose metabolism in the CNS

DHEA is a neuroactive steroid, due to its modulatory actions on the central nervous system (CNS). DHEA is able to regulate neurogenesis, neurotransmitter receptors and neuronal excitability, function, survival and metabolism. The levels of DHEA decrease gradually with advancing age, and this decline has been associated with age related neuronal dysfunction and degeneration, suggesting a neuroprotective effect of endogenous DHEA. There are significant sex differences in the pathophysiology, epidemiology and clinical manifestations of many neurological diseases. The aim of this study was to determine whether DHEA can alter glucose metabolism in different structures of the CNS from male and female rats, and if this effect is sex-specific. The results showed that DHEA decreased glucose uptake in some structures (cerebral cortex and olfactory bulb) in males, but did not affect glucose uptake in females. When compared, glucose uptake in males was higher than females. DHEA enhanced the glucose oxidation in both males (cerebral cortex, olfactory bulb, hippocampus and hypothalamus) and females (cerebral cortex and olfactory bulb), in a sex-dependent manner. In males, DHEA did not affect synthesis of glycogen, however, glycogen content was increased in the cerebral cortex and olfactory bulb. DHEA modulates glucose metabolism in a tissue-, dose- and sex-dependent manner to increase glucose oxidation, which could explain the previously described neuroprotective role of this hormone in some neurodegenerative diseases.

Lactoferrin ameliorates corticosterone-related acute stress and hyperglycemia in rats

We aimed to assess the effects of lactoferrin (Lf) on glycemic regulatory responses under restraint stress (RS) in rats. Bovine Lf (bLf, 100 mg/kg) was intraperitoneally administered to rats before oral saline administration or oral glucose tolerance test (OGTT) following 60 min of RS load. In the case of oral saline administration, RS significantly raised plasma glucose, but bLf did not affect the level. Plasma glucose in OGTT showed an overall lower transition in the bLf group, and the levels at 30 and 180 min or the area under the curve (AUC) were significantly decreased. Although bLf suppressed an increase in plasma corticosterone during RS, the levels of plasma insulin, epinephrine and glucagon were not changed by the bLf treatment.

Unpredictable Chronic Stress Alters Adenosine Metabolism in Zebrafish Brain

Stress is considered a risk factor for several human disorders. Despite the broad knowledge of stress responses in mammals, data on the relationship between unpredictable chronic stress (UCS) and its effects on purinergic signaling are limited. ATP hydrolysis by ectonucleotidases is an important source of adenosine, and adenosine deaminase (ADA) contributes to the control of the nucleoside concentrations. Considering that some stress models could affect signaling systems, the objective of this study was to investigate whether UCS alters ectonucleotidase and ADA pathway in zebrafish brain. Additionally, we analyzed ATP metabolism as well as ada1, ada2.1, ada2.2, adaL, and adaasi gene expression in zebrafish brain. Our results have demonstrated that UCS did not alter ectonucleotidase and soluble ADA activities. However, ecto-ADA activity was significantly decreased (26.8%) in brain membranes of animals exposed to UCS when compared to the control group. Quantitative reverse transcription PCR (RT-PCR) analysis did not show significant changes on ADA gene expression after the UCS exposure. The brain ATP metabolism showed a marked increase in adenosine levels (ADO) in animals exposed to UCS. These data suggest an increase on extracellular adenosine levels in zebrafish brain. Since this nucleoside has neuromodulatory and anxiolytic effects, changes in adenosine levels could play a role in counteracting the stress, which could be related to a compensatory mechanism in order to restore the homeostasis.

Hypercaloric diet modulates effects of chronic stress: a behavioral and biometric study on rats

Obesity is a chronic disease that has been associated with chronic stress and hypercaloric diet (HD) consumption. Increased ingestion of food containing sugar and fat ingredients (comfort food) is proposed to "compensate" chronic stress effects. However, this eating habit may increase body fat depositions leading to obesity. This study evaluated behavioral/physiological parameters seeking to establish whether there is an association between the effects of HD intake and stress, and to test the hypothesis that the development of anxious behavior and obesity during chronic stress periods depends on the type of diet. Sixty-day-old male Wistar rats (n = 100) were divided into four groups: standard chow, hypercaloric diet, chronic stress/standard chow and chronic stress/hypercaloric diet. Chronic stress was induced by restraint stress exposure for 1 h/day, for 80 d. At the end of this period, rat behavior was evaluated using open-field and plus-maze tests. The results showed that HD alone increased weight gain and adipose deposition in subcutaneous and mesenteric areas. However, stress reduced weight gain and adipose tissue in these areas. HD also increased naso-anal length and concurrent stress prevented this. Behavioral data indicated that stress increased anxiety-like behaviors and comfort food reduced these anxiogenic effects; locomotor activity increased in rats fed with HD. Furthermore, HD decreased corticosterone levels and stress increased adrenal weight. The data indicate that when rats are given HD and experience chronic stress this association reduces the pro-obesogenic effects of HD, and decreases adrenocortical activity.

Effects of sciatic nerve transection on glucose uptake in the presence and absence of lactate in the frog dorsal root ganglia and spinal cord

Frogs have been used as an alternative model to study pain mechanisms because the simplicity of their nervous tissue and the phylogenetic aspect of this question. One of these models is the sciatic nerve transection (SNT), which mimics the clinical symptoms of “phantom limb”, a condition that arises in humans after amputation or transverse spinal lesions. In mammals, the SNT increases glucose metabolism in the central nervous system, and the lactate generated appears to serve as an energy source for nerve cells. An answerable question is whether there is elevated glucose uptake in the dorsal root ganglia (DRG) after peripheral axotomy. As glucose is the major energy substrate for frog nervous tissue, and these animals accumulate lactic acid under some conditions, bullfrogs Lithobates catesbeianus were used to demonstrate the effect of SNT on DRG and spinal cord 1-[14C] 2-deoxy-D-glucose (14C-2-DG) uptake in the presence and absence of lactate. We also investigated the effect of this condition on the formation of 14CO2 from 14C-glucose and 14C-L-lactate, and plasmatic glucose and lactate levels. The 3-O-[14C] methyl-D-glucose (14C-3-OMG) uptake was used to demonstrate the steady-state tissue/medium glucose distribution ratio under these conditions. Three days after SNT, 14C-2-DG uptake increased, but 14C-3-OMG uptake remained steady. The increase in 14C-2-DG uptake was lower when lactate was added to the incubation medium. No change was found in glucose and lactate oxidation after SNT, but lactate and glucose levels in the blood were reduced. Thus, our results showed that SNT increased the glucose metabolism in the frog DRG and spinal cord. The effect of lactate on this uptake suggests that glucose is used in glycolytic pathways after SNT.

A combination of plant-derived odors reduces corticosterone and oxidative indicators of stress

In this study, we measured typical stress markers in addition to oxidative status and reduced glutathione in erythrocytes, and plasma lipid peroxidation of restraint-stressed animals exposed to a combination of plant-derived odors (0.03% Z-3-hexen-1-ol, 0.03% E-2-hexenal, and 0.015% α-pinene in triethyl citrate). Male Wistar rats aged 6-7 weeks postnatal were exposed to vehicle (triethyl citrate, n = 12), plant-derived odors (n = 12), or 1% propionic acid odor (n = 12) under control or stress conditions, and blood samples were collected. Restraint stress increased plasma glucose and plasma corticosterone concentrations by approximately 10% (P < 0.01) and 125% (P < 0.001), respectively, in vehicle-exposed animals. Similar increases were observed in animals exposed to a 1% propionic acid odor, indicating the novelty of odor exposure does not alter stress responsiveness. There was also an increase of approximately 15% in both erythrocytic oxidative status (P < 0.001) and plasma lipid peroxidation (P < 0.05), and a decrease of approximately the same magnitude in reduced glutathione (P < 0.05) in restrained animals with vehicle exposure. There were no differences observed between control and stress treatment with plant-derived odor exposure in any of the measured parameters. It was concluded that exposure to plant-derived odors reduce corticosterone, glucose, and redox responses elicited by psychological stress.

Obesity and chronic stress are able to desynchronize the temporal pattern of serum levels of leptin and triglycerides

Disruption of the circadian system can lead to metabolic dysfunction as a response to environmental alterations. This study assessed the effects of the association between obesity and chronic stress on the temporal pattern of serum levels of adipogenic markers and corticosterone in rats. We evaluated weekly weight, delta weight, Lee index, and weight fractions of adipose tissue (mesenteric, MAT; subcutaneous, SAT; and pericardial, PAT) to control for hypercaloric diet-induced obesity model efficacy. Wistar rats were divided into four groups: standard chow (C), hypercaloric diet (HD), stress plus standard chow (S), and stress plus hypercaloric diet (SHD), and analyzed at three time points: ZT0, ZT12, and ZT18. Stressed animals were subjected to chronic stress for 1h per day, 5 days per week, during 80 days. The chronic exposure to a hypercaloric diet was an effective model for the induction of obesity and metabolic syndrome, increasing delta weight, Lee index, weight fractions of adipose tissue, and triglycerides and leptin levels. We confirmed the presence of a temporal pattern in the release of triglycerides, corticosterone, leptin, and adiponectin in naïve animals. Chronic stress reduced delta weight, MAT weight, and levels of triglycerides, total cholesterol, and leptin. There were interactions between chronic stress and obesity and serum total cholesterol levels, between time points and obesity and adiponectin and corticosterone levels, and between time points and chronic stress and serum leptin levels. In conclusion, both parameters were able to desynchronize the temporal pattern of leptin and triglyceride release, which could contribute to the development of metabolic diseases such as obesity and metabolic syndrome.

The activity of mate saponins (Ilex paraguariensis) in intra-abdominal and epididymal fat, and glucose oxidation in male Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Ilex paraguariensis A. St. Hilaire (mate) has traditionally been used in several South American countries to prepare tea-like beverages having stimulant effects on the CNS and appetite. In recent years, however, mate preparations have been recommended putatively as an appetite suppressant and slimming remedy. Moreover, studies carried out on either normal or diet-induced obese rats treated with mate extracts revealed anti-obesity and satiety effects, thus refuting ethnopharmacological data. In this work, the effect of mate on the intra-abdominal and epididymal fat, and glucose oxidation levels after oral administration in male Wistar rats, was studied using crude extract from leaves, unripe fruits, and a chemically well-defined purified saponin fraction (MSF).

MATERIAL AND METHODS

Saponin, polyphenol and methylxanthine contents in MSF were analyzed by HPLC-PDA and UPLC/Q-TOF-MS. Crude extracts from mate leaves (LAE) and unripe fruits (FHE) were assayed for comparison purposes. Male Wistar rats fed with standard diet and water ad libitum were used as the control group.

RESULTS

The fat weight and both liver and adipose glucose oxidation were reduced significantly by MSF (35, 90 and 60%, respectively), while LAE and FHE were less active. Also, a significant lowering of the blood triglycerides level was observed in rats treated with MSF and LAE. All creatinine, urea, and transaminase plasma levels remained unaffected no matter what mate preparation was considered. It is also worth pointing out that the glucose blood level was increased after treatment with FHE. This finding did not correlate either with the content of methylxanthines, polyphenols or saponins.

CONCLUSION

A reduction in both visceral fat weight and glucose oxidation of hepatic and adipose tissue in healthy rats fed with a standard diet could be ascribed to a purified mate saponin fraction from unripe fruits. These findings agree with former studies carried out with crude mate extracts and also suggest their potential use as an anti-obesity preparation. Nonetheless, further in vivo experiments are still required to corroborate its effect on human beings.

Cafeteria diet-induced obesity plus chronic stress alter serum leptin levels

Obesity is a disease that has become a serious public health issue worldwide, and chronic stressors, which are a problem for modern society, cause neuroendocrine changes with alterations in food intake. Obesity and chronic stress are associated with the development of cardiovascular diseases and metabolic disorders. In this study, a rat model was used to evaluate the effects of a hypercaloric diet plus chronic restraint stress on the serum leptin and lipids levels and on the weight of specific adipose tissue (mesenteric, MAT; subcutaneous, SAT and visceral, VAT). Wistar rats were divided into the following 4 groups: standard chow (C), hypercaloric diet (HD), stress plus standard chow (S), and stress plus hypercaloric diet (SHD). The animals in the stress groups were subjected to chronic stress (placed inside a 25 cm × 7 cm plastic tube for 1h per day, 5 days per week for 6 weeks). The following parameters were evaluated: the weight of the liver, adrenal glands and specific adipose tissue; the delta weight; the Lee index; and the serum levels of leptin, corticosterone, glucose, total cholesterol, and triglycerides. The hypercaloric diet induced obesity in rats, increasing the Lee index, weight, leptin, triglycerides, and cholesterol levels. The stress decreased weight gain even in animals fed a hypercaloric diet but did not prevent a significant increase in the Lee index. However, an interaction between the independent factors (hypercaloric diet and stress) was observed, which is demonstrated by the increased serum leptin levels in the animals exposed to both protocols.

The effect of dehydroepiandrosterone (DHEA) on renal function and metabolism in diabetic rats

Dehydroepiandrosterone (DHEA) is an endogenous steroid hormone involved in a number of biological actions in humans and rodents, but its effects on renal tissue have not yet been fully understood. The aim of this study is to assess the effect of DHEA treatment on diabetic rats, mainly in relation to renal function and metabolism. Diabetic rats were treated with subcutaneous injections of a 10mg/kg dose of DHEA diluted in oil. Plasma glucose and creatinine, in addition to urine creatinine, were quantified espectophotometrically. Glucose uptake and oxidation were quantified using radioactive glucose, the urinary Transforming Growth Factor β(1) (TGF-β(1)) was assessed by enzyme immunoassay, and the total glutathione in the renal tissue was also measured. The diabetic rats displayed higher levels of glycemia, and DHEA treatment reduced hyperglycemia. Plasmatic creatinine levels were higher in the diabetic rats treated with DHEA, while creatinine clearance was lower. Glucose uptake and oxidation were lower in the renal medulla of the diabetic rats treated with DHEA, and urinary TGF-β(1), as well as total gluthatione levels, were higher in the diabetic rats treated with DHEA. DHEA treatment was not beneficial to renal tissue, since it reduced the glomerular filtration rate and renal medulla metabolism, while increasing the urinary excretion of TGF-β(1) and the compensatory response by the glutathione system, probably due to a mechanism involving a pro-oxidant action or a pro-fibrotic effect of this androgen or its derivatives. In conclusion, this study reports that DHEA treatment may be harmful to renal tissue, but the mechanisms of this action have not yet been fully understood.

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.

Antioxidant enzymes are differently changed in experimental ischemic hippocampal CA1 region following repeated restraint stress

Restraint stress induces physiological changes in the brain. In the present study, we observed the effects of repeated stress on ischemic damage associated with oxidative stress in gerbils. Animals were placed into restrainers for 5h (between 09:30 h and 14:30 h) for 21 consecutive days prior to 5 min of transient cerebral ischemia. Experimental groups were divided into 4 groups; 1) sham-operated control-group (sham-group), 2) ischemia-operated control-group (ischemia-group), 3) sham-operated stress-group (stressed-sham-group), and 4) ischemia-operated stress-group (stressed-ischemia-group). Serum corticosterone level in the ischemia-group was highest (330% vs the sham-group) at 12h post-ischemia, and serum corticosterone levels in the stressed-ischemia-group were significantly lower than the ischemia-group. Locomotor activity in the ischemia-group was significantly increased (300% vs the sham-group) at 1 day post-ischemia; however, locomotor activity in the stressed-ischemia-group was less increased compared to the ischemia-group. A few NeuN (neuron-specific soluble nuclear antigen)-positive ((+)) cells were found in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) 4 days post-ischemia in the ischemia-group; however, in the stressed-ischemia-group at 4 days post-ischemia, 83.8% of NeuN(+) neurons were found. In addition, we found a few Fluro-Jade B (a marker for neuronal degeneration)(+) and TUNEL(+) cells in the stressed-ischemia-group at 4 days post-ischemia. In gliosis, glial fibrillary acidic protein(+) astrocytes in the stressed-ischemia-groups was similar to the ischemia-groups; however, ionized calcium-binding adapter molecule 1(+) microglia in the stressed-ischemia-groups were much less activated than the ischemia-groups. Among antioxidants, Cu,Zn-superoxide dismutase (SOD1) immunoreactivity in the SP was higher in the stressed-ischemia-groups than the ischemia-groups. Catalase immunoreactivity in the SP of the stressed-ischemia-groups was similar to the ischemia-groups. However, Mn-superoxide dismutase and glutathione peroxidase immunoreactivity were lower than the ischemia-groups. In brief, our results indicate that repeated restraint stress significantly attenuates ischemic neuronal damage and locomotor activity following ischemia. In addition, SOD1 among antioxidants significantly increases in the stressed-ischemia-groups.

Changes in corticosteroid hormone receptors in the ischemic gerbil hippocampal CA1 region following repeated restraint stress

Restraint stress produces physiological changes including suppression of long-term potentiation in the brain. We observed the effects of repeated stress on ischemic damage associated with corticosteroid hormone receptors in gerbils. Animals were placed into restrainers for 5 h (between 09:30 h and 14:30 h) for 21 consecutive days prior to induction of transient cerebral ischemia. The animals were divided into 4 groups; (1) sham-operated-control-group (sham-group), (2) ischemia-operated-control-group (ischemia-group), (3) sham-operated-stress-group (stressed-sham-group), and (4) ischemia-operated-stress-group (stressed-ischemia-group). We found that serum corticosterone level in the ischemia-group was highest (374% of the sham-group) 12 h after ischemia/reperfusion and its level in the stressed-ischemia-group was significantly lower than the ischemia-group. Locomotor activity in the ischemia-group was significantly increased (295% of the sham-group) at 1 day post-ischemia; however, the locomotor activity in the stressed-ischemia-group was less increased compared to the ischemia-group. Cresyl violet positive (CV(+)) cells were significantly decreased in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) of the 4 days post-ischemia-group, while 79.4% of CV(+) cells were detected in the CA1 of the stressed-ischemia-group. Also, a few NeuN (neuron-specific soluble nuclear antigen)(+) cells were detected in the SP of the 4 days post-ischemia-group; however, in the 4 days stressed-post-ischemia-group, 77.2% of NeuN(+) neurons were found in the SP. Glial fibrillary acidic protein(+) astrocytes in the CA1 in the stressed-ischemia-groups were similar to those in the ischemia-groups; however, ionized calcium-binding adapter molecule 1(+) microglia in the stressed-ischemia-groups were less activated compared to the ischemia-groups. Mineralocorticoid receptor (MCR) and glucocorticoid receptor (GR) immunoreactivity in the SP of the stressed-ischemia-group were higher than the ischemia-group; at 4 days post-ischemia, MCR and GR immunoreactivity were expressed in non-pyramidal cells. In brief, our results indicate that repeated restraint stress significantly increase levels of corticosteroid hormone receptors and attenuates neuronal damage in the ischemic hippocampal CA1 region.

Na+, K+ ATPase activity is reduced in amygdala of rats with chronic stress-induced anxiety-like behavior

In this study, we examined the effects of two chronic stress regimens upon anxiety-like behavior, Na(+), K(+)-ATPase activity and immunocontent, and oxidative stress parameters (antioxidant enzymes and reactive oxygen species production) in the amygdala. Male rats were subjected to chronic unpredictable and to chronic restraint stress for 40 days. Subsequently, anxiety-like behavior was examined. Both stressed groups presented increased anxiety-like behavior. Reduced amygdalal Na(+), K(+)-ATPase activity in the synaptic plasma membranes was also observed, without alterations in the amygdala immunocontent. In addition, when analyzing oxidative stress parameters, only superoxide dismutase activity was decreased in the amygdala of animals subjected to unpredictable stress. We conclude that both models of chronic stress lead to anxiety-like behavior and decreased amygdalal Na(+), K(+)-ATPase activity, which appears not to be related to oxidative imbalance. The relationship between this decreased activity and anxiety-like behavior remains to be studied.

Increased oxidative stress in submitochondrial particles into the brain of rats submitted to the chronic mild stress paradigm

Major depression is a common, serious and recurrent disorder, characterized by symptoms at the psychological, behavioral and physiological levels. Recent studies have suggested that reactive oxygen species (ROS) may play a role in the pathophysiology of bipolar disorder. The chronic mild stress (CMS) rat model has been used as an animal model of depression, since it induces some symptoms of a major depressive episode in humans (i.e. anhedonia). We investigated behavioral, physiological and neurochemical aspects of rats exposed for 40 days to CMS. Sweet food consumption, locomotor activity and body weight were assessed in stressed and control rats. We also investigated the potential involvement of ROS in the CMS model. Superoxide generation in submitochondrial particles from the rat hippocampus, prefrontal cortex and cortex was measured through superoxide-dependent oxidation of epinephrine to adrenochrome in a submitochondrial extract. We report that sweet food intake was reduced in rats subjected to CMS compared to controls. Further, CMS animals failed to gain body weight compared with non-stressed rats. Locomotor activity was not affected in stressed rats. An increase in superoxide production was detected in all brain structures analyzed. However, thiobarbituric acid reactive substances were increased only in cortex. In conclusion, these observations support the view that the CMS model of depression mimics alterations observed in depressed patients. The model affords a useful system in which to test the hypothesis that altered brain energy metabolism is associated with neuropsychiatric disorders.

Lactate metabolism in the muscle of the crab Chasmagnathus granulatus during hypoxia and post-hypoxia recovery

The present study showed that the lactate/glucose ratio in the hemolymph of Chasmagnathus granulatus maintained in normoxia (controls) was 4.9, suggesting that lactate is an important substrate for this crab. Periods of hypoxia are part of the biological cycle of this crab, and lactate is the main end product of anaerobiosis in this crab. Our hypothesis was that this lactate would be, therefore, used by gluconeogenic pathway or can be oxidized or excreted to the aquatic medium during hypoxia and post-hypoxia periods in C. granulatus. The concentrations of hemolymphatic lactate in animals in normoxia are high, and are used as an energy substrate. In hypoxia, muscle gluconeogenesis and excretion of lactate to the aquatic medium would contribute significantly in regulating the concentration of circulating lactate. Utilization of these pathways would serve the objective of maintaining the acid-base equilibrium of the organism. Muscle gluconeogenesis participates, during the recovery process, in metabolizing the lactate produced during the period of hypoxia. Lactate excretion to the external medium, was one of the strategies used to decrease the higher hemolymphatic lactate levels. However, oxidation of lactate in the muscle is not a main strategy used by this crab to metabolize lactate in the recovery periods.

Effect of chronic stress and L-carnitine on rat stomach

BACKGROUND AND AIM

L-Carnitine is an essential cofactor in the mitochondrial transfer of fatty acids, and it is also a scavenger of free radicals in mammalian tissues. The aim of the study was to determine the effect of L-carnitine on chronic restraint stress-induced gastric mucosal injury.

METHODS

Wistar rats were applied restraint stress (1 h/day) and L-carnitine (50 mg/kg) for 21 days. The lesion index, prostaglandin E(2) and mucus content, lipid peroxidation, superoxide dismutase, and catalase activity in gastric mucosa were evaluated.

RESULTS

Chronic restraint stress increased the lesion index, lipid peroxidation, and superoxide dismutase activity in gastric mucosa, and it decreased prostaglandin E(2) and mucus content. L-Carnitine treatment prevented the stress-induced increase in lesion index, lipid peroxidation and a stress-induced decline in prostaglandin E(2), and mucus content in gastric mucosa, but it increased catalase activity.

CONCLUSIONS

L-Carnitine prevents the occurrence of lesion by strengthening the gastric mucosal barrier and by reducing lipid peroxidation against the harmful effects of chronic restraint stress.

The effects of restraint stress on nociceptive responses induced by formalin injected in rat's TMJ

It has been reported that stress can alter nociception from superficial tissues, such as skin and subcutaneous region. However, the influence of stress on an experimental deep nociception model is not understood. In this study, the temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute and chronic restraint stress on nociceptive responses in rats. Animals were initially submitted to one session of acute restraint stress (1 h) or exposed to chronic stress (40 days-1 h/day). Then, animals were killed immediately to collect blood for hormonal determinations by radioimmunoassay, or submitted to the TMJ formalin test to evaluate nociception. Rats submitted to acute restraint presented a performance similar to unstressed controls in the TMJ formalin test, whereas chronically stressed rats showed an increase in nociceptive responses. After 40 days of restraint, morphine was injected i.p. (1, 5 mg/kg or saline). The stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. These findings suggest that repeated stress can produce hyperalgesia, which is, at least in part, due to alterations in the activity of opioid systems. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on orofacial pain.

Acute and repeated restraint stress influences cellular damage in rat hippocampal slices exposed to oxygen and glucose deprivation

Several studies have shown that high corticosteroid hormone levels increase neuronal vulnerability. Here we evaluate the consequences of in vivo acute or repeated restraint stress on cellular viability in rat hippocampal slices suffering an in vitro model of ischemia. Cellular injury was quantified by measuring lactate dehydrogenase (LDH) and neuron-specific enolase released into the medium. Acute stress did not affect cellular death when oxygen and glucose deprivation (OGD) was applied both immediately or 24h after restraint. The exposure to OGD, followed by reoxygenation, resulted in increased LDH in the medium. Repeated stress potentiated the effect of OGD both, on LDH and neuron-specific enolase released to the medium. There was no effect of repeated stress on the release of S100B, an astrocytic protein. Additionally, no effect of repeated stress was observed on glutamate uptake by the tissue. These results suggest that repeated stress increases the vulnerability of hippocampal cells to an in vitro model of ischemia, potentiating cellular damage, and that the cells damaged by the exposure to repeated stress+OGD are mostly neurons. The uptake of glutamate was not observed to participate in the mechanisms responsible for rendering the neurons more susceptible to ischemic damage after repeated stress.

Acute and chronic stress alter ecto-nucleotidase activities in synaptosomes from the rat hippocampus

Hyperactivity of the stress response has long been recognized as maladaptive. The hippocampus, a brain structure important in mediating this response, is known to be affected by chronic stress, a situation reported to induce changes in adenine nucleotide hydrolysis in the rat. The enzymes catalyzing the hydrolysis of ATP to adenosine in the synaptic cleft are thought to have a role in modulating and controlling synaptic transmission. This study aimed to investigate the effect of acute and repeated restraint stress on the ATP, ADP and AMP hydrolyses in rat hippocampal synaptosomes. Adult male Wistar rats were submitted to acute or repeated (15 and 40 days) stress, and ATPase-ADPase, and 5'nucleotidase activities were assayed in the hippocampal synaptosomal fraction. Acute stress induced increased hydrolyses of ATP (21%), ADP (21%) and AMP (40%). In contrast, ATP hydrolysis was increased by 20% in repeatedly stressed rats, without changes in the ADP or AMP hydrolysis. The same results were observed after 15 or 40 days of stress. Therefore, acute stress increases ATP diphosphohydrolase activity which, in association with 5'-nucleotidase, contributes to the elimination of ATP and provides extracellular adenosine. Interestingly, increased ecto-ATPase activity in response to chronic stress reveals an adaptation to this treatment.

Repeated Restraint Stress Induces Oxidative Damage in Rat Hippocampus

It has been shown that emotional stress may induce oxidative damage, and considerably change the balance between pro-oxidant and antioxidant factors in the brain. The aim of this study was to verify the effect of repeated restraint stress (RRS; 1 h/day during 40 days) on several parameters of oxidative stress in the hippocampus of adult Wistar rats. We evaluated the lipid peroxide levels (assessed by TBARS levels), the production of free radicals (evaluated by the DCF test), the total radical-trapping potential (TRAP) and the total antioxidant reactivity (TAR) levels, and antioxidant enzyme activities (SOD, GPx and CAT) in hippocampus of rats. The results showed that RRS induced an increase in TBARS levels and in GPx activity, while TAR was reduced. We concluded that RRS induces oxidative stress in the rat hippocampus, and that these alterations may contribute to the deleterious effects observed after prolonged stress.

Repeated Restraint Stress Reduces Opioid Receptor Binding in Different Rat CNS Structures

Different effects of exposure to acute or to repeated stress have been observed upon the nociceptive response in rats. In the present study, we repeatedly submitted Wistar rats to restraint for 40 days, a treatment known to induce an increase in the nociceptive response in the tail-flick test. Afterwards, the effect of repeated restraint stress on the density of opioid receptors in rat spinal cord, frontal cortex, and hippocampus was investigated. Results showed that repeatedly stressed rats displayed a significant decrease in opioid receptors density in all structures studied; cortex (141.3 +/- 5.7 for control and 103.3 +/- 15.9 for stressed rats), hippocampus (92.4 +/- 7.2 for control and 64.8 +/- 7.7 for stressed rats), and spinal cord (122.2 +/- 12.8 for control and 79.7 +/- 9.7 for stressed rats). These findings suggest opioid mediation of the altered responses observed in these repeatedly-stressed animals, although the participation of non-opioid mechanisms in this phenomenon cannot be ruled out.

Repeated restraint stress alters hippocampal glutamate uptake and release in the rat

Glutamatergic mechanisms are thought to be involved in stress-induced changes of brain function, especially in the hippocampus. We hypothesized that alterations caused by the hormonal changes associated with chronic and acute stress may affect glutamate uptake and release from hippocampal synaptosomes in Wistar rats. It was found that [3H]glutamate uptake and release by hippocampal nerve endings, when measured 24 h after 1 h of acute restraint, presented no significant difference. The exposure to repeated restraint stress for 40 days increased neuronal presynaptic [3H]glutamate uptake as well as basal and K+-stimulated glutamate release when measured 24 h after the last stress session. Chronic treatment also caused a significant decrease in [3H]glutamate binding to hippocampal membranes. We suggest that changes in the glutamatergic system are likely to take part in the mechanisms involved in nervous system plasticity following repeated stress exposure.

Effects of prenatal protein malnutrition and acute postnatal stress on granule cell genesis in the fascia dentata of neonatal and juvenile rats

Although postnatal genesis of granule cells in the hippocampal fascia dentata is known to be influenced by prenatal protein deprivation or by stress, the combined effects of prenatal protein malnutrition and stress on these cells are unknown. This study was designed to examine this combined effect. Well-nourished and prenatally malnourished pups on postnatal day 7 (P7) were stressed by maternal separation and reduction of body temperature and on postnatal day 30 (P30) by immobilization with restraint. Bromodeoxyuridine (BrDU) was injected at the time of stress, and 2 h later, the numbers of immunolabeled cells were quantified by standard stereological techniques. In comparison to controls, prenatally malnourished rats showed a significantly lower number of cells tagged in the fascia dentata on P7 (p < or =0.05), and a significantly higher number of cells (p < or =0.05) on P30. In both age groups, control rats exposed to acute stress showed a significantly decreased number of cells tagged in the fascia dentata (p < or =0.05). In contrast, neurogenesis in malnourished rats was not significantly affected by acute stress at either age. Thus, the pattern of neurogenesis in the fascia dentata and its response to stress has been fundamentally altered by prenatal protein deprivation.

Lipid peroxidation and total radical-trapping potential of the lungs of rats submitted to chronic and sub-chronic stress

Exposure to stress induces a cluster of physiological and behavioral changes in an effort to maintain the homeostasis of the organism. Long-term exposure to stress, however, has detrimental effects on several cell functions such as the impairment of antioxidant defenses leading to oxidative damage. Oxidative stress is a central feature of many diseases. The lungs are particularly susceptible to lesions by free radicals and pulmonary antioxidant defenses are extensively distributed and include both enzymatic and non-enzymatic systems. The aim of the present study was to determine lipid peroxidation and total radical-trapping potential (TRAP) changes in lungs of rats submitted to different models of chronic stress. Adult male Wistar rats weighing 180-230 g were submitted to different stressors (variable stress, N = 7) or repeated restraint stress for 15 (N = 10) or 40 days (N = 6) and compared to control groups (N = 10 each). Lipid peroxidation levels were assessed by thiobarbituric acid reactive substances (TBARS), and TRAP was measured by the decrease in luminescence using the 2-2'-azo-bis(2-amidinopropane)-luminol system. Chronic variable stress induced a 51% increase in oxidative stress in lungs (control group: 0.037 +/- 0.002; variable stress: 0.056 +/- 0.007, P < 0.01). No difference in TBARS was observed after chronic restraint stress, but a significant 57% increase in TRAP was presented by the group repeatedly restrained for 15 days (control group: 2.48 +/- 0.42; stressed: 3.65 +/- 0.16, P < 0.05). We conclude that different stressors induce different effects on the oxidative status of the organism.

Effect of drugs active at adenosine receptors upon chronic stress-induced hyperalgesia in rats

Hyperalgesia and altered activities of enzymes involved in nucleotide hydrolysis are observed after exposure to repeated restraint in rats. Here, we investigated the effect of an adenosine A(1) receptor agonist, N(6)-cyclopentyladenosine (CPA, 3.35 mg/kg, i.p.), adenosine A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 0.8 mg/kg, i.p.) as well the effect of an adenosine reuptake blocker, dipyridamole (5 mg/kg, i.p.), on nociception in chronically stressed and control rats. We repeatedly submitted rats to restraint for 40 days. Nociception was assessed with a tail-flick apparatus. The control group presented increased tail-flick latencies after administration of CPA and dipyridamole, but this effect was not observed in the stressed group. DPCPX by itself had no effect on nociception. The analgesic effect of CPA and dipyridamole observed in the control group was reverted by DPCPX. These results indicate the involvement of adenosine A(1) receptor in the antinociception observed in control animals and suggest that the pain signaling induced by chronic stress presents a different modulation involving the adenosinergic system.

Gender differences in oxidative stress in spinal cord of rats submitted to repeated restraint stress

Behavioral and neurochemical gender-specific effects have been observed following repeated stress. The aim of this study is to verify the effects of repeated restraint stress on free radical production (evaluated by DCF test), lipoperoxidation (evaluated by TBARS levels), and total antioxidant reactivity (TAR) in the spinal cord of male and female rats. Results demonstrate no effect on lipoperoxidation; chronic stress decreased TAR both in male and female spinal cord. In addition, gender differences were observed both in TAR and in the production of free radicals, both being increased in females. These results may be relevant to the gender-specific differences observed after exposure to repeated stress.

Long-lasting delayed hyperalgesia after chronic restraint stress in rats-effect of morphine administration

Different effects upon the nociceptive response have been observed with exposure to acute and chronic stress in rats. In the present study we repeatedly submitted rats to restraint for 40 days, inducing hyperalgesia using the tail-flick test. A new session of acute stress was applied at the end of 40 days period, and the chronically-stressed animals demonstrated analgesia after forced swimming, but not after restraint. The effect of stress interruption for 14 or 28 days on the nociceptive threshold was then investigated. The basal tail-flick latency remained decreased for at least 28 days (hyperalgesic effect). Following the periods of suspension, the animals were submitted to new session of acute restraint, and stress-induced analgesia was observed only after 28 days of stress interruption. Thus, the mechanisms involved in the long-lasting hyperalgesia presented in this study are not exactly the same as those responsible for the analgesia induced by acute stressors. After 40 days of chronic stress treatment, morphine was injected i.p. (1.0, 5.0 mg/kg or saline). The repeatedly stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. The tolerance of the response to morphine agrees with previous studies suggesting that chronic restraint stress could modify the activity of opioid systems.

Chronic stress effects on adenine nucleotide hydrolysis in the blood serum and brain structures of rats

We have previously observed that adenosine 5'-diphosphate (ADP) hydrolysis was decreased 25% in spinal cord synaptosomes of chronically stressed male rats, while no changes were observed in ATPase activity. In the present study, we investigated the effect of chronic stress on the hydrolysis of adenine nucleotides in two cerebral structures (frontal cortex and hypothalamus) and in the blood serum of male rats. Adult male Wistar rats were submitted to 1-h restraint stress/day for 45 days (chronic) and were sacrificed 24 h after the last session of stress. Adenosine 5'-triphosphate (ATP) or ADP hydrolysis was assayed in the synaptosomal fraction obtained from the frontal cortex and hypothalamus of control and chronically stressed animals. No effects on ADP or ATP hydrolysis were observed in any of the cerebral structures analyzed after chronic stress. On the other hand, reduced ADP hydrolysis was observed in the blood serum of chronic stressed rats. It is possible that the effects observed in the blood serum may represent an adaptation to chronic stress and may reflect different functions of nucleotides and/or enzymes in these tissues. It is possible that altered levels of ADPase activity in the serum may be a biochemical marker for chronic stress situations.