Search

Abstract Many studies have been made about the physio-logical effects of isolated chronic or acute stress. However, few studies have been made to assess the combination of both responses. The fish submitted to chronic stress may be subjected to an additional acute stressor. The aim of the present work was to evaluate the acute stress response in Nile tilapia Oreochromis niloticus (L.) previously subjected to chronic stress. For this, two experiments were performed. In the first experiment, the fish were subjected to chronic stress followed by an additional acute stress. In the second experiment, the fish were submitted only to an acute stress. The data showed that Nile tilapia fingerlings can adapt to chronic stress situations, and this decreases, but does not eliminate, their capacity to respond to an additional acute stressor. In both experiments, plasma cortisol levels reached a peak 1 h after administration of the acute stressor. In fish previously submitted to chronic stress, the highest concentration of plasma cortisol measured was 196 ng mL[sup –1]. This value was significantly different from the cortisol concentration obtained in the second experiment (267 ng mL[sup –1]) with non-chronically stressed fish. The data also suggest that the chronic stress response can provoke a reduction in performance and growth rates compared with non-stressed fish. [ABSTRACT FROM AUTHOR]

Long-chain polyunsaturated n-3 fatty acids (n-3 LCPUFAs) have hypolipidemic effects and modulate intermediary metabolism to prevent or reverse insulin resistance in a way that is not completely elucidated. Here, effects of these fatty acids on the lipid profile, phosphoenolpyruvate carboxykinase (PEPCK) activity, lipid synthesis from glucose in epididymal adipose tissue (Ep-AT) and liver were investigated. Male rats were fed a high-sucrose diet (SU diet), containing either sunflower oil or a mixture of sunflower and fish oil (SU-FO diet), and the control group was fed a standard diet. After 13 weeks, liver, adipose tissue and blood were harvested and analysed. The dietary n-3 LCPUFAs prevented sucrose-induced increase in adiposity and serum free fat acids, serum and hepatic triacylglycerol and insulin levels. Furthermore, these n-3 LCPUFAs decreased lipid synthesis from glucose and increased PEPCK activity in the Ep-AT of rats fed the SU-FO diet compared to those fed the SU diet, besides reducing lipid synthesis from glucose in hepatic tissue. Thus, the inclusion of n-3 LCPUFAs in the diet may be beneficial for the prevention or attenuation of dyslipidemia and insulin resistance, and for reducing the risk of related chronic diseases., (Copyright © 2013 John Wiley & Sons, Ltd.)

Increasing evidence indicates that physical exercise induces adaptations at the cellular, molecular, and systemic levels that positively affect the brain. Insulin plays important functional roles within the brain that are mediated by insulin-receptor (IR) signaling. In the hippocampus, insulin improves synaptic plasticity, memory formation, and learning via direct modulation of GABAergic and glutamatergic receptors. Separately, physical exercise and central insulin administration exert relevant roles in cognitive function. We here use CF1 mice to investigate (i) the effects of voluntary exercise on hippocampal insulin signaling and memory performance and (ii) whether central insulin administration alters the effects of exercise on hippocampal insulin signaling and memory performance. Adult mice performed 30 days of voluntary exercise on running wheel and afterward both, sedentary and exercised groups, received intracerebroventricular (icv) injection of saline or insulin (0.5-5 mU). Memory performance was assessed using the inhibitory avoidance and water maze tasks. Hippocampal tissue was measured for [U-(14)C] glucose oxidation and the immunocontent of insulin receptor/signaling (IR, pTyr, pAktser473). Additionally, the phosphorylation of the glutamate NMDA receptor NR2B subunit and the capacity of glutamate uptake were measured, and immunohistochemistry was used to determine glial reactivity. Exercise significantly increased insulin peripheral sensitivity, spatial learning, and hippocampal IR/pTyrIR/pAktser473 immunocontent. Glucose oxidation, glutamate uptake, and astrocyte number also increased relative to the sedentary group. In both memory tasks, 5 mU icv insulin produced amnesia but only in exercised animals. This amnesia was associated a rapid (15 min) and persistent (24 h) increase in hippocampal pNR2B immunocontent that paralleled the increase in glial reactivity. In conclusion, physical exercise thus increased hippocampal insulin signaling and improved water maze performance. Overstimulation of insulin signaling in exercised animals, however, via icv administration impaired behavioral performance. This effect was likely the result of aberrant phosphorylation of the NR2B subunit., (Copyright © 2010 Wiley-Liss, Inc.)

Stress affects learning and memory processes and sensitivity to stress greatly varies between individuals. We studied behavioral and neurobiological effects of unpredictable subchronic stress (USCS) in two behavioral extremes of mice from the same strain (CF1) selected by their exploratory behavior of the central arena of an open field. The top and bottom 25% explorers were classified as low exploratory (LE) and high exploratory (HE) mice, respectively. The open field task, the novel object recognition task (NOR), sucrose intake and tail suspension task were evaluated in LE and HE groups exposed to USCS for two weeks or control conditions. Also serum corticosterone and hippocampal BDNF and S100B levels were analyzed. Both stressed groups exhibited less exploratory activity when submitted to USCS, but their difference in exploratory behavior remained. This short stress protocol did not induce changes in sucrose intake or immobility in the tail suspension task. Also, LE mice exhibited impaired NOR performance after USCS, whereas HE mice changed their pattern of exploration towards less exploration of the familiar object. HE had lower corticosterone levels than LE mice, but corticosterone levels increased after stress only in HE mice. Hippocampal BDNF in LE was lower than in HE but decreased after USCS only in HE mice, whereas S100B levels were not different between groups and did not change with USCS. In conclusion, our results suggest that individual differences in exploratory behavior in rodents from the same strain influence cognitive and biochemical response to stress., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Background/aims: To evaluate the effects of neonatal handling on hydroelectrolytic balance in adult rats., Methods: The litters were divided into two groups: nonhandled and handled. The procedure consisted of handling the pups for 1 min/day in the first 10 days postnatally. When adults, animals had their body weight verified and were housed in individual metabolic cages. After a 24-hour period, urine samples were collected and the urinary and water intake volumes measured. Blood samples to determine osmolality, aldosterone, corticosterone, angiotensin II, creatinine, urea, sodium and potassium levels were collected. The kidneys were removed for histological assessment. Urinary osmolality, sodium, urea and creatinine were also measured and the creatinine clearance (CC) calculated., Results: No difference between groups was found in the body weight. Handled animals showed a reduction in the total kidney wet weight, water intake, urinary volume, CC, plasma angiotensin II, corticosterone and aldosterone when compared to the nonhandled and an increase in the urinary osmolality and sodium excretion fraction. No differences in serum potassium and no evidence of structural changes were demonstrated by histological analysis., Conclusion: Neonatal handling induced long-lasting effects decreasing renal function without evidence of kidney structural changes., ((c) 2009 S. Karger AG, Basel.)

Aim: The complete biological effects of chronic use of dehydroepiandrosterone (DHEA), reported as a weak androgen, are not completely understood. The aim of the present study is to evaluate the effects of chronic administration of DHEA on the spermatogenesis in rats., Methods: Male Wistar rats, 4 months old, were selected for the study. The animals were divided into two groups. Group 1 (n = 9) received placebo (saline solution) 0.5 ml/day and Group 2 (n = 15) received DHEA 5 mg/kg/day. Both the groups received the respective treatments 5 days a week during 10 months. At the end of the exposure, the rats were sacrificed and the testes removed, weighed and processed for histologic analysis. Spermatogenesis was evaluated as the mean number of seminiferous tubules with and without spermatids in maturation phase in their lumen, in five random fields on the same slide., Results: The median levels of serum total testosterone and dehydroepiandrosterone sulfate was measured in the two groups. Significant higher concentrations in total testosterone (2.06 +/- 0.4 vs. 0.80 +/- 0.2; p < 0.05) and DHEAS (222.1 +/- 41.5 vs. 2.0 +/- 0.3) were observed in the group treated with DHEA as compared to the control group. The mean weights of the right testes were 1.59 +/- 0.3 in group 1 and 1.58 +/- 0.2 g in group 2 (p > 0.05). These values for the left testes were 1.57 +/- 0.3 and 1.55 +/- 0.3 g, respectively (p > 0.05). The histologic analysis showed a mean of 13.5 +/- 1.5 and 12.8 +/- 1.8 seminiferous tubules per field in the groups 1 and 2, respectively (p > 0.05). The same analysis demonstrated that in the control group 0.06 +/- 0.1 of the tubules presented without spermatids in maturation phase and in the DHEA group this was observed in 0.22 +/- 1.2 of the tubules (p > 0.05)., Conclusion: Chronic administration of DHEA in the present dose did not show any detectable effect on the quantitative and qualitative analyses of spermatogenesis in rats.

The jundiá Rhamdia quelen (Quoy and Gaimard) is a teleost species from the Siluridae family and is an important species for aquaculture in temperate and subtropical climates. Gonad and blood tissue samples were taken from cultured jundiá females between 1998 and 1999. Plasma concentrations of 17beta-estradiol (E(2)), testosterone (T), 11-ketotestosterone (11-KT), 17-hydroxy-4-pregnene-3,20-dione (17-P), 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P), and 17,20beta,21-trihydroxy-4-pregnen-3-one (20beta-S) were measured by radioimmunoassay and potential correlations with the stage of oogenesis and sexual maturation examined. During the experimental period two spawning episodes were observed. Plasma concentrations of E(2) increased progressively during oocyte development, simultaneously with the appearance of yolk vesicles and increasing amounts of deposited yolk. In female jundiá, the T peak occurred in October and was coincident with the peak in gonadosomatic index. Two distinct peaks of progestogens were detected, corresponding to the two spawning episodes, suggesting that one or more of these steroids might act as the "maturational-inducing steroid" in jundiá. Unusually large amounts of 11-KT were also measured in the plasma of mature jundiá females. The identity of 11-KT was confirmed by thin-layer chromatography. Although the profiles of the other steroids are compatible with the roles proposed for the action of these hormones in other teleosts, the role of 11-KT, normally found only in males, is unknown., (Copyright 2001 Academic Press.)

Although an increased prevalence of hypertension is associated with insulin-dependent diabetes, little is known about the effect of streptozotocin (STZ) diabetes on arterial pressure (AP) regulation in rats. Changes in AP induced by STZ, as well as associated factors in blood pressure regulation such as baroreflex sensitivity, plasma renin activity (PRA), plasma glucose and insulin levels and endothelium participation, were studied in male Wistar rats weighing 287 +/- 10 g. The same seven conscious rats were used for all measurements before and after STZ diabetes. AP pulses were stored on a videotape recorder and processed by a data acquisition system. Baroreflex sensitivity was evaluated by measuring heart rate (HR) changes induced by AP variations produced by phenylephrine and sodium nitroprusside injection. The effect of inhibition of nitric oxide synthesis with NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.v. bolus plus infusion at 20 mg kg-1 h-1) on AP was evaluated in another set of rats (6 normal and 5 submitted to STZ treatment). STZ induced hyperglycemia (306 +/- 19 mg/dl), a reduction in mean arterial pressure (MAP, from 116 +/- 5 to 101 +/- 4 mmHg) and no changes in HR (320 +/- 10 vs 298 +/- 14 bpm). The tachycardic response to arterial pressure decreases was impaired (-2.29 +/- 0.5 vs -4.5 +/- 0.7 bpm/mmHg, in control) while the bradycardic response to arterial pressure increases was unchanged. Pressure responsiveness to phenylephrine was impaired after STZ (3.78 +/- 0.4 vs 6.73 +/- 0.8 mmHg microU-1 ml-1, in control).(ABSTRACT TRUNCATED AT 250 WORDS)