Stress induced changes in testis function

The mechanism through which chronic stress inhibits the hypothalamic-pituitary-testicular axis has been investigated. Chronic restraint stress decreases testosterone secretion, an effect that is associated with a decrease in plasma gonadotropin levels. In chronically stressed rats there was a decrease in hypothalamic luteinizing hormone-releasing hormone (LHRH) content and the response on plasma gonadotropins to LHRH administration was enhanced. Thus the inhibitory effect of chronic stress on plasma LH and FSH levels seems not to be due to a reduction in pituitary responsiveness to LHRH, but rather to a modification in LHRH secretion. It has been suggested that beta-endorphin might interfere with hypothalamic LHRH secretion during stress. Chronic immobilization did not modify hypothalamic beta-endorphin, while an increase in pituitary beta-endorphin secretion was observed. Since we cannot exclude that changes in beta-endorphin secreted by the pituitary or other opioids may play some role in the stress-induced decrease in LHRH secretion, the effect of naltrexone administration on plasma gonadotropin was studied in chronically stressed rats. Naltrexone treatment did not modify the decrease in plasma concentrations of LH or FSH. These findings suggest that the inhibitory effect of restraint on the testicular axis is exerted at hypothalamic level by some mechanism other than opioids.     

Effect of acute and chronic psychogenic stress on corticoadrenal and pituitary-thyroid hormones in male rats

The effects of acute and chronic stress on serum corticosterone and pituitary-thyroid hormones were studied in male Wistar rats. Acute noise activated both the pituitary-adrenal and pituitary-thyroid axes. Chronic noise did not modify the basal serum levels of either corticosterone or pituitary-thyroid hormones. A decreased corticosterone response to noise was observed in chronically stressed rats, but the pituitary-thyroid response was the same in control and chronically stressed rats, suggesting that the mechanisms which control the responsiveness of both axes to a repeated stimulus are dissociated.     

Catecholamines in steroid-dependent brain development

Sex-specific peculiarities of catecholamine (CA) content and turnover in neuroendocrine brain areas and their modification with neonatal steroids or prenatal stress (PS) in Wistar rats were studied. No changes in noradrenaline (NA) content and turnover rate were found in the preoptic area (POA), meanwhile dopamine (DA) turnover rates in the POA and mediobasal hypothalamus (MBH) were increased in neonatally androgenized 10-day-old females. Treatment of female neonates with various catecholestrogens increased hypothalamic NA content by 30–95% but only 4-hydroxyestradiol-17β induced anovulation. 6-Hydroxydopamine had no significant impact on hypothalamic CA content in neonates and did not prevent testosterone-induced persistent estrous. Maternal stress (restriction for 1 h a day, 15–21st days of pregnancy) resulted in a decrease of hypothalamic NA and blood plasma corticosterone response to acute stress in adult male offspring. Sex differences in CA content in the POA and MBH disappeared in 10-day-old prenatally stressed rats. Conclusions: (1) sexual brain differentiation needs co-operative actions of sex steroids and CA to be completed; and (2) early changes in CA content and turnover induced by PS or neonatal steroid exposure predetermine long-term alterations of the stress responsiveness, reproductive behaviour and neuroendocrine control of ovulation.     

Dissociation between adrenocorticotropin and corticosterone responses to restraint after previous chronic exposure to stress

The effect on emotional reactivity produced by a model for chronic stress in which different types of acute stresses were randomly combined for 29 days was studied in adult male rats. Chronically stressed rats showed a slight decrease in body weight gain and an increase in relative adrenal weight. Chronic stress did not modify defecation rate but reduced exploratory activity in the holeboard. Neither basal nor acute-stress induced levels of adrenocorticotropin (ACTH) were modified by previous chronic stress. Likewise, basal corticosterone levels were similar in both groups. However, corticosterone response to acute restraint stress was higher in chronically stressed than in control rats. The mechanisms underlying the dissociation between ACTH and corticosterone as well as its possible implications are discussed.     

Different alterations in the development of the noradrenergic innervation of the cerebellum and the brain stem produced by neonatal 6-hydroxydopa.

The administration of 6-hydroxydopa (6-OH-DOPA) to rats during their pre- or postnatal development, produced long-term modifications in the distribution of noradrenaline (NA) within the brain. In the cerebellum, the concentration of NA was increased in adult rats exposed to the drug between the day 16 of gestation and the day of birth. When injected 3 days after birth, the drug did not modify NA levels while treatment at 20 days produced a marked depletion of cerebellar NA. The concentration of NA in the brain stem showed a different pattern of response to 6-OH-DOPA. Prenatal administration elevated NA in this region and, in contrast to the response of the cerebellum, injections in the inmediate postnatal period also elevated the transmitter content. Treatment at 20 days after birth resulted in a marked depletion of NA levels in the adult brain stem. These results demonstrate the existence of temporal differences in the responses to neonatal 6-OH-DOPA in two structures innervated by noradrenergic pathways originated in neurons of the nucleus locus coeruleus.     

Chronic intermittent stress-induced alterations in the spermatogenesis and antioxidant status of the testis are irreversible in albino rat

The study was undertaken to find out whether or not chronic stress-induced alterations in spermatogenesis are accompanied by oxidative damage in the testis and reversibility of these effects. Adult male rats (n?=?10) were subjected to restraint for 1 h and later after a gap of 4 h to forced swimming exercise for 15 min daily for 60 days and controls (n?=?5) were maintained without disturbance. After treatment period, controls and 5 rats in stress group were killed and remaining rats in stress group were maintained without any treatment for 4 months and then autopsied to find out whether effects are reversible or not. The body and testicular weight, total sperm count, and mean number of type A spermatogonia, mid-pachytene spermatocytes, stage 7 spermatids, and elongated spermatids (cellular association in stage VII of spermatogenesis) showed a significant decrease whereas the abnormal sperm count and germ cell apoptosis were increased in stressed and recovery group rats compared to controls. Activities of testicular SOD, CAT, GPx, and GST were significantly decreased whereas MDA levels were significantly increased in stressed rats compared to controls. The SOD, GST, and CAT activities of recovery groups were significantly lower than controls, whereas MDA levels and GPx activity of these rats did not differ from controls. The results, for the first time, reveal that stress-induced loss of germ cells leading to decrease in sperm count may be due to oxidative damage caused by chronic stress and majority of these changes are not reversible.     

Delayed Increase of Brain Noradrenaline After Acute Footshock Stress in Rats

Several lines of evidence strongly suggest that accumulation of noradrenaline (NA) in the brain may underlie the hyperarousal symptoms experienced in post-traumatic stress disorder. In animal experiments, however, the effect of stress on NA content appears complex; acute stress reduces the level, while chronic stress tends to increase it. To explain this discrepancy, it is necessary to observe the long-term effects of acute stress on NA metabolism in the brain. In this study, rats were exposed to intermittent intense footshock stress for 1 h, and the brain NA content was measured for 7 days after the stress stimulus. Hypothalamic NA content was immediately reduced and recovered within 24 h. However, a significant NA increase was observed 7 days after the footshock. In the cerebral cortex and hippocampus, an increase in NA content was observed 1 day after the stress and lasted for at least 7 days. The fact that the content of 3-methoxy-4-hydroxyphenylglycol, a major NA metabolite, only transiently increased in all these regions possibly reflects NA release. These results indicate that increase in the brain NA content can be induced by acute stress, though its emergence is delayed. Importantly, this suggests that both acute and chronic stress may lead to NA accumulation under the same mechanism.     

Chronic Stress Increases Serotonin and Noradrenaline in Rat Brain and Sensitizes Their Responses to a Further Acute Stress

The effects of 1 h/day restraint in plastic tubes for 24 days on the levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan (TP), and noradrenaline (NA) in six regions of rat brain 20 h after the last restraint period were investigated. The levels of 5-HT, 5-HIAA, and NA but not TP increased in several regions. The effects of 1 h of immobilization on both control and chronically restrained rats were also studied. Immobilization per se did not alter brain 5-HT, 5-HIAA, and TP levels, but decreased NA in the pons plus medulla oblongata and hypothalamus. However, immobilization after chronic restraint decreased 5-HT, increased 5-HIAA, and decreased NA in most brain regions in comparison with values for the chronically restrained rats. We suggest that chronic restraint leads to compensatory increases of brain 5-HT and NA synthesis and sensitizes both monoaminergic systems to an additional acute stress. These changes may affect coping with stress demands.     

Stress‐induced multiple organ damage in rats is ameliorated by the antioxidant and anxiolytic effects of regular exercise

Our aim was to investigate the effects of moderate load, regular swimming exercise on stress‐induced anxiety, and associated oxidative organ injury. Male Sprague‐Dawley rats (n = 48) were either kept sedentary or submitted to swimming exercise for 8 weeks. Rats were then divided as non‐stressed, acute stress, and chronic stress groups. After acute or chronic stress (electric foot shocks) applications, rats were placed on a holeboard and the exploratory behavior was recorded to assess the anxiety. Rats were decapitated after the stress application. Acute and chronic stress induction led to increased serum cortisol levels as compared to non‐stressed groups. Plasma aspartate aminotransferase levels that were elevated in sedentary rats with both stress exposures were lower in trained rats. Malondialdehyde levels and myeloperoxidase activity were increased in the cardiac muscle, liver, stomach, and brain of the stressed rats with a concomitant reduction in the glutathione levels, while stress‐induced changes in malondialdehyde, myeloperoxidase, and glutathione levels were reversed in the trained animals. Exercise, which led to increased malondialdehyde and reduced glutathione levels in the skeletal muscle of the non‐stressed rats, also protected against stress‐induced oxidative damage. Regular exercise with its anxiolytic and antioxidant effects ameliorates stress‐induced oxidative organ damage by a neutrophil‐dependent mechanism. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of repeated stress and administration of phenobarbital on the lymphoid tissue and on protein metabolism in the lymphocytes of infant and adult rats

Further study of the response to chronic stress stimulation in the early postnatal phase showed that the i.p. injection of physiological saline (stress stimulation) induced lymphopenia, a 50% decrease in the incorporation of 3H-leucine into isolated lymphocytes and a decrease in the weight of the thymus in 7-day-old male rats. No such changes were observed in adult animals. If repeated doses of phenobarbital were administered to stressed young rats, however, lymphopenia did not occur and the rate of the incorporation of 3H-leucine into isolated lymphocytes was not different from the control value; the protein content of the lymphocytes was significantly raised, however. In adult animals, phenobarbital increased the rate of incorporation of 3H-leucine into the lymphocytes. The repeated administration of phenobarbital reduced the weight of the thymus in both young and adult animals, but a decrease in spleen weight was recorded only in the young animals. A single i.p. injection of ACTH or dexamethasone caused lymphopenia and slowed down the incorporation of 3H-leucine into the lymphocytes of both young and adult animals. The results show that the striking decrease observed in the rate of the liver metabolism of corticosterone in suckling young rats not injured by repeated stress stimulation is accompanied by significant changes in the lymphoid tissue.     

Chronic-intermittent cold stress in rats induces selective ovarian insulin resistance

In rat ovary chronic cold stress increases sympathetic nerve activity, modifies follicular development, and initiates a polycystic condition. To see whether there is a relationship between the previously described changes in follicular development and metabolic changes similar to those in women with polycystic ovary, we have studied the effect of chronic cold stress (4 degrees C for 3 h/day, Monday to Friday, for 4 wk) on insulin sensitivity and the effect of insulin on sympathetic ovarian activity. Although cold-stressed rats ate more than the controls, they did not gain more weight. Insulin sensitivity, determined by hyperinsulinemic-euglycemic clamp, was significantly increased in the stressed animals. Insulin in vitro increased the basal release of norepinephrine from the ovaries of control rats but not from those of stressed rats, suggesting a local neural resistance to insulin in stressed rats. The levels of mRNA and protein for IRS1 and SLC2A4 (also known as GLUT4), molecules involved in insulin signaling, decreased significantly in the ovaries but not in the muscle of stressed rats. This decrease was preferentially located in theca-interstitial cells compared with granulosa cells, indicating that theca cells (the only cells directly innervated by sympathetic nerves) are responsible for the ovarian insulin resistance found in stressed rats. These findings suggest that ovarian insulin resistance produced by chronic stress could be in part responsible for the development of the polycystic condition induced by stress.     

Effect of acute and chronic cholinesterase inhibition on biogenic amines in rat brain

The effects of five cholinesterase inhibitors on forebrain monoamine and their metabolite levels, and on forebrain and plasma cholinesterase (ChE) activity in rat were studied in acute and chronic conditions. Acute tetrahydroaminoacridine (THA) dosing caused lower brain (68%) and higher plasma (90%) ChE inhibition than the other drugs studied increased levels of brain dihydroxyphenylacetic acid (DOPAC) (236%), homovanillic acid (HVA) (197%) and 5-hydroxyindolaecetic acid (5-HIAA) (130%). Acute physostigmine (PHY) administration caused a 215% increase in brain DOPAC content. Despite high brain ChE inhibition induced by metrifonate (MTF), dichlorvos (DDVP) or naled no changes in brain noradrenaline (NA), dopamine (DA) or serotonin (5-HT) occurred due to treatment with the study drugs in the acute study. In the chronic 10-day study THA or PHY caused no substantial ChE inhibition in brain when measured 18 hours after the last dose, whereas MTF induced 74% ChE inhibition. Long-term treatment with THA or MTF caused no changes in monoamine levels, but PHY treatment resulted in slightly increased 5-HT values. These results suggest that MTF, DDVP and naled seem to act solely by cholinergic mechanisms. However, the central neuropharmacological mechanism of action of THA and PHY may involve changes in cholinergic as well as dopaminergic and serotoninergic systems.     

Significance of the reciprocal relationship of monoaminergic systems of the brain in the pharmacological compensation of 6-hydroxydopamine-induced behavior disorders in animals

The paper studied the methods of compensation of the abnormal emotional behaviour by means of pharmacological substances, which change the content of biogenic amines. The experiments made in the Wistar rats (n-54) whose frustration reaction was diminished by neonatal treatment of 6-OHDA. It was established that recovery of the disturbances in the frustration reaction in the animals with chronic brain system activity deprivation can be achieved not only by the activation of NA system (L-DOPA, DOPS) but also by deactivation of the 5-HT brain system activity (PCPA). These findings confirm suggestion about existence of reciprocal relationship between NA and 5-HT brain systems.     

Chronic stress decreases the expression of sympathetic markers in the pineal gland and increases plasma melatonin concentration in rats

Chronic stress affects brain areas involved in learning and emotional responses. Although most studies have concentrated on the effect of stress on limbic-related brain structures, in this study we investigated whether chronic stress might induce impairments in diencephalic structures associated with limbic components of the stress response. Specifically, we analyzed the effect of chronic immobilization stress on the expression of sympathetic markers in the rat epithalamic pineal gland by immunohistochemistry and western blot, whereas the plasma melatonin concentration was determined by radioimmunoassay. We found that chronic stress decreased the expression of three sympathetic markers in the pineal gland, tyrosine hydroxylase, the p75 neurotrophin receptor and alpha-tubulin, while the same treatment did not affect the expression of the non-specific sympathetic markers Erk1 and Erk2, and glyceraldehyde-3-phosphate dehydrogenase. Furthermore, these results were correlated with a significant increase in plasma melatonin concentration in stressed rats when compared with control animals. Our findings indicate that stress may impair pineal sympathetic inputs, leading to an abnormal melatonin release that may contribute to environmental maladaptation. In addition, we propose that the pineal gland is a target of glucocorticoid damage during stress.     

Effect of cross-fostering on catalepsy and the brain monoamine level in rat offspring prone to catalepsy and in the control strain

Duration of cataleptic reactions in male rats of Wistar and GC strains depended both on the genotype and on the type of rearing: it was longer in the GC rats than in the Wistar ones. In the GC males reared by Wistar foster mothers this parameter was smaller than in the control GC but higher than in Wistar rats. The NA content was significantly lower in the GC cortex, hypothalamus and striatum, and the level of serotonin and 5-HIAA was lower in cortex of the GC as compared with Wistar rats. The cross-fostering affected monoamine content in some brain structures. On the whole, serotonin, DA and NA systems of the GC rats proved to be more susceptible to stress caused by cross-fostering than those of the Wistar rats. The cross-fostering diminished interstrain differences in the NA level in cortex, striatum, and hypothalamus.     

Gonadotropin inhibition during chronic stress: role of the adrenal gland

The effect of adrenalectomy, metyrapone and dexamethasone treatments on gonadotropin response to chronic stress were studied. Adult male rats were submitted to chronic restraint (6 h daily over 4 days). At the end of the last stress period animals were decapitated and trunk blood was collected. Chronic restraint evoked a decrease in plasma LH and to a lesser degree in plasma FSH in the intact rat. Adrenalectomy did not prevent the LH reduction induced by stress and magnified the inhibitory effect of restraint on FSH secretion. Administration of the corticosterone synthesis blocker metyrapone increased the inhibitory effect of restraint on plasma LH and to a lesser degree on plasma FSH. Dexamethasone treatment did not significantly modify plasma gonadotropin levels in adrenalectomized unstressed rats, but this treatment totally blocked plasma LH and FSH reduction after chronic restraint. These results indicate that plasma LH and FSH reduction during chronic restraint is not due to the increase in glucocorticoid secretion, but seems to be mediated by the increase of the hypothalamic-pituitary components of the adrenal axis.     

Long-term ACTH induced diminished responsiveness of prolactin secretion to morphine

The effect of morphine on plasma prolactin level and on dopamine turnover in the median eminence was studied using adult male rats chronically treated with ACTH. It was found that the ACTH pretreatment caused a decrease in the effect of morphine on prolactin secretion and prevented the inhibitory effect of morphine on dopamine turnover measured in the median eminence. The prolonged ACTH administration did not influence the prolactin content of the pituitaries and the in vitro dopamine sensitivity of lactotroph cells. Acute dexamethasone injection did not change the morphine-caused prolactin release. These results suggest that chronic ACTH treatment (possibly via corticosterone hyperproduction) elicits an opiate-tolerance like state of tuberoinfundibular dopaminergic neurons.     

alpha2-Adrenoceptors control the release of noradrenaline but not neuropeptide Y from perivascular nerve terminals

Neuropeptide Y (NPY) and noradrenaline (NA) are co-transmitters at many sympathetic synapses, but it is not yet clear if their release is independently regulated. To address this question, we quantified the electrically evoked release of these co-transmitters from perivascular nerve terminals to the mesenteric circulation in control and drug-treated rats. 6-Hydroxydopamine reduced the tissue content and the electrically evoked release of ir-NPY and NA as well as the rise in perfusion pressure. A 0.001 mg/kg reserpine reduced the content of ir-NPY and NA, but did not modify their release nor altered the rise in perfusion pressure elicited by the electrical stimuli. However, 0.1mg/kg reserpine reduced both the content and release of NA but decreased only the content but not the release of ir-NPY; the rise in perfusion pressure was halved. Clonidine did not affect the release of ir-NPY while it lowered the outflow of NA, not altering the rise in perfusion pressure elicited by the electrical stimuli. Yohimbine, did not modify the release of ir-NPY but increased the NA outflow, it antagonized the clonidine effect. Therefore, presynaptic alpha2-adrenoceptors modulate the release of NA but not NPY, implying separate regulatory mechanisms.     

Changes in plasma oxidative state with age and their influence on contractions elicited by noradrenaline in the rat tail artery.

The present study analyzes the changes in plasma oxidative state with age and their influence on the contractions induced by noradrenaline (NA) in endothelium-denuded segments from the tail artery of 6- (young), 24- (old) and 30- (very old) month-old Sprague Dawley rats. The sensitivity (-log EC50) to NA increased with age, this increase being higher in old than in very old animals. Moreover, the maximum response (Emax) to NA did not change in old rats, whereas decreased in very old animals. We also found a progressive increase in the plasma oxidative state with age, measured as malondialdehyde (MDA) levels, that was accompanied by a decrease in the plasma antioxidative state, measured as glutathione peroxidase activity. In addition, MDA (0.5, 1 and 10 microM) potentiated the NA responses in 6-, 24- and 30-month-old rats, respectively, without affecting Emax. In young animals, catalase (1000 U/ml) or dimethylsulfoxide (7 mM), scavengers of hydrogen peroxide or hydroxyl radicals, respectively, did not modify either the contractions induced by NA in control situation or the potentiation of these responses caused by MDA. However, the superoxide anion scavenger, superoxide dismutase (SOD, 150 U/ml), completely reversed the increase in sensitivity to NA caused by MDA, without affecting NA responses in control situation. These results suggest that the increase in NA sensitivity with age could be due, at least in part, to the enhancement of plasma oxidative state during aging. In addition, in this alteration of the responses to NA caused by MDA, the generation of superoxide anions appears to be involved. This study supports the hypothesis that the enhancement of plasma oxidative state could play an important role in the increase of vascular resistance with age.     

Neurokinin A in the anterior pituitary of female rats: effects of ovariectomy and estradiol.

The effect of acute and chronic ovariectomy and the substitutive treatment with 17-beta estradiol and/or progesterone on anterior pituitary levels of neurokinin A (NKA) was studied in female rats. Acute ovariectomy did not result in significant changes of NKA in the anterior pituitary gland as compared with the levels in diestrous intact rats, but a single injection of 5 micrograms of estradiol in ovariectomized rats significantly decreased NKA levels in the anterior pituitary gland. Progesterone was without effect and did not modify the decrease of NKA in the anterior pituitary gland induced by estradiol. In rats examined 11 to 17 days after ovariectomy, NKA in the anterior pituitary gland was significantly higher than in diestrous intact rats. In the hypothalamus, ovariectomy resulted in decreased levels of NKA in the median eminence-arcuate nucleus. Estradiol significantly reduced NKA stores in the anterior pituitary gland but increased them in the whole hypothalamus and in the median eminence-arcuate nucleus. Thus, estradiol seems to be a powerful regulator of NKA stores in the adenohypophysis and also in the hypothalamus.