Ether Stress Research Articles

Evidence that endogenous vasoactive intestinal peptide (VIP) is involved in the regulation of rat pituitary-adrenocortical function: in vivo studies with a VIP antagonist

The effect of a subcutaneous bolus injection of 2 μg |Ac, Tyr 1,D-Phe 2|-GRF(1–29) amide, a specific VIP antagonist (VIP-A), on the hypothalamo-pituitary-adrenocortical (HPA) axis were investigated in both normal and ether- or cold-stressed rats. Blood concentrations of ACTH, aldosterone (ALDO) and corticosterone (B) were measured by specific RIA 1, 2 or 4 h after VIP-A injection. VIP-A administration to normal rats strikingly lowered the plasma concentration of ALDO, without significantly affecting those of ACTH and B. Ether and cold stresses notably raised the blood levels of ACTH, ALDO and B, and these rises lasted unchanged until 4 h. VIP-A did not affect the response of HPA axis to ether stress, but provoked a marked depression of that to cold stress. In light of these findings the following conclusions can be drawn: (i) endogenous VIP does not regulate HPA-axis function under basal conditions, but it plays a pivotal role in the mechanisms involved in the activation of HPA axis induced by cold exposure; and (ii) endogenous VIP exerts a tonic stimulatory action on ALDO secretion, probably by acting directly on the adrenal zona glomerulosa.

Effects of hyperprolactinemia on plasma glucose and prolactin in rats exposed to ether stress

The present study was designed to characterize the effect of chronic hyperprolactinemia on plasma glucose and prolactin (PRL) during ether stress in male and female rats. Wistar rats of both sexes were divided into a hyperprolactinemic group (bearing pituitary grafts) and a control group (sham operated). They were exposed to ether during 10 min and had blood samples taken immediately before, and 5, 15, 40, and 70 min after ether exposure and assayed for glucose and PRL concentrations. Ether stress induced significant increase in plasma PRL of control rats at 5 min (male 171%, female 161%; P < 0.01), but only a mild PRL increase occured in grafted rats (male 66%, female 62%; P < 0.05). Control male rats sustained elevated plasma PRL longer than females. There was a marked elevation of glucose levels at 5 min ( P < 0.01) which peaked at 15 min in all groups. Grafted rats had glucose levels significantly above control at baseline (female 15%, P < 0.05) and at 40 min (male 25%, female 29%; P < 0.05). It is concluded that ether-induced PRL release produced a rapid and transient response, more intense in males than in females and which was impaired by previous hyperprolactinemia (pituitary grafts). There was an acute hyperglycemic response, plasma glucose being increased in grafted rats, supporting the hypothesis of a hyperglycemic effect of PRL.

Differential effect of amygdaloid lesions on CRF-41, ACTH and corticosterone responses following neural stimuli

The effect of amygdaloid (AMG) lesions on changes in median eminence (ME) CRF-41 and serum ACTH and corticosterone (CS) levels following neural stimuli were investigated in rats. In intact animals photic or acoustic stimuli caused CRF-41 depletion from the ME and a rise in serum ACTH and CS levels. In rats with medial or central AMG nuclei lesions, these responses were blocked. Basal AMG lesions were not effective. Also, all groups of animals responded normally to ether stress. These results indicate a differential effect of AMG nuclei on the hypothalamo-pituitary-adrenocortical (HPA) axis and demonstrate that the facilitatory effect of the AMG nuclei on the HP A axis responses involves the release of ME CRF-41, which stimulates ACTH and consequently CS secretion.

GABA A receptors mediate the changes produced by stress on GABA function and locomotor activity

(1) This study shows the effects of bicuculline pretreatment on the GABAergic system in certain areas of the rat brain after acute ether and cold stress. (2) The spontaneous locomotor activity was diminished by either ether stress or cold stress or bicuculline. (3) Acute ether stress enhanced GABA concentration in the hypothalamus (69%) and in the frontal cerebral cortex (26%). Bicuculline prevented the increase in GABA levels induced by ether stress in both areas. (4) Acute cold stress decreased GABA concentation in the corpus striatum (29%). Bicuculline prevented the decrease in GABA levels induced by cold stress. (5) It is concluded that there is a GABA A receptor involved in stress induced changes on endogenous GABA levels as well as on locomotor activity.

Serum prolactin response to ether stress in diabetic rats: opiate system contribution.

Diabetes in streptozotocin-treated rats is associated with alterations in various neuroendocrine systems, including endogenous opioids. These changes are suggested to be responsible for the significant reduction in serum prolactin (PRL) response to a brief restraint stress in diabetic male rats, as compared with normoglycemic controls. The present study examines serum PRL response to ether exposure in diabetic male rats. The animals' response to ether stress, which is known to be related to the opioid system, was examined twice in each rat: shortly after cannula insertion (Day 1), and seven days later. In order to evaluate the opiate system involvement, the experiment was repeated on Day 1 and 7 after surgery in a group of rats which were pretreated with naltrexone (Nalt), an opioid receptor antagonist. Opioid receptor sensitization was also performed by prior acute morphine administration on Day 7 after cannulation surgery. Following adaptation to the cannulation, no difference in serum PRL response to ether stress was found between diabetic and normoglycemic rats. However, on Day 1 after surgery, a significant difference was found between the diabetic and control groups: the normoglycemic (control) group exposed to ether responded to the surgical stress by augmented serum PRL levels. This response was not recorded in the diabetic rats. Opioid receptor blockade by Nalt administration 30 min before ether exposure eliminated this difference. Opioid receptor sensitization by morphine pretreatment facilitated PRL secretion in normoglycemic rats exposed to either, while no effect could be distinguished in the diabetic group. It is therefore concluded that the streptozotocin-induced diabetic rats do not differ from normoglycemic ones in their ability to respond to acute ether stress by itself. However, enhanced PRL secretion induced by ether exposure under additional surgical stress, or by presensitization of the opioid receptors by morphine, is prevented in diabetic rats, probably due to diminished opioid receptor response.

The habituation of brainstem catecholaminergic groups to chronically daily restraint stress is stress specific like that of the hypothalamo-pituitary-adrenal axis

It has previously been shown that immobilization and ether stress induce activation of the hypothalamo-pituitary-adrenal (HPA) axis and that this occurs subsequent to activation of brain stem catecholaminergic neurones. In the present study we have investigated whether the brain stem catecholaminergic (CA) neurons show habituation to chronic daily intermittent exposure to the same restraint stress comparable to that of the HPA axis. The level of activity of the brainstem CA groups was estimated by measurement in this tissue punches of content of 3,4-dihydroxyphenylacetic acid (DOPAC), a side metabolite of noradrenaline and adrenaline biosynthesis which has been shown to be a reliable index of the stress-induced activation of the CA groups. The level of activity of the HPA axis was determined by measurement of plasma corticosterone and adrenocorticotrophic hormone (ACTH) levels. The animals were submitted to a 15 min restraint stress daily. They were sacrified at the end of the stress session on day 3, 5 and 10. The ACTH response to the acute restraint stress whilst unchanged on day 3 was significantly decreased on day 5 (−54%) and day 10 (−70%) compared to the response in naive rats. The approximately twofold increase in DOPAC level induced by acute restraint stress in the so-called CA medullary group A1/C1 of naive rats was reduced in daily restraint rats on day 5 (−22%) and day 10 (−30%) but was unchanged on day 3. A small (−20%) decrease of the stress-induced DOPAC response in the A2/C2 CA group and locus coeruleus was also observed on day 10. In animals submitted to four daily sessions of restraint stress, the increase in ACTH response to a novel (ether) stress was not reduced but rather was enhanced by 30% as compared to the response obtained in naive rats. Similarly the DOPAC response in the A1/C1 group to an acute ether stress was enhanced by 25% in chronically stressed animals while the DOPAC response inthe A2/C2 group and the locus coeruleus were unchanged. Our present data indicate that brain stem CA group show habituation to chronic intermittent stress. Habituation of the A1/C1 group and habituation of HPA axis have similar time-courses and are similarly stress-specific. The latter results suggest that habituation observed in these experimental conditions is not due to intrinsic biochemical changes in the brain stem CA neurones but indirectly reflects decreased stimulatory inputs to the brain stem CA groups resulting from behavioural adaptation at higher brain centers.

The role of central corticoliberin in the ether stress-induced secretion of neurohypophyseal hormones and corticosterone in the rat

As corticotropin-releasing factor (CRF) and oxytocin (OXT) are released in response to various stressors and a role of CRF in stress-induced OXT secretion has been proposed by previous authors, the present experiments were scheduled to investigate the participation of the brain CRF system in the stress-evoked release of OXT, arginine-8-vasopressin (AVP) and corticosterone. CRF-antiserum (AS) was given into the lateral ventricle of the brain of Wistar male rats, and 24 h later, the injection was repeated 30 min prior to ether stress followed by decapitation in 5 min. Plasma OXT and AVP were measured by radioimmunoassay and corticosterone by fluorimetry. Ether stress increased the levels of corticosterone and OXT, but not that of AVP. CRF-AS alone did not change the secretion of these hormones. CRF-AS pretreatment blocked the corticosterone-releasing action of ether stress, whereas it exerted no influence on the stress-induced OXT secretion into the circulation. There was no effect of a combined application of CRF-AS and stress on the plasma AVP level. These results suggest that the central CRF system is involved in the ether stress-elicited corticosterone response, however CRF is unlikely to be connected with the regulation of OXT secretion under these experimental conditions.

The possible involvement of galanin in the modulation of the function of rat pituitary-adrenocortical axis under basal and stressful conditions.

The effect of a s.c. bolus injection of 2 micrograms galanin on the hypothalamo-pituitary-adrenocortical (HPA) axis were investigated in both normal and ether-stressed (2 min ether-vapor inhalation) or cold-stressed (20 min at 4 degrees C) rats. Blood concentrations of ACTH, aldosterone (ALDO) and corticosterone (B) were measured by specific RIA, 1, 2 or 4 h after galanin injection. Galanin administration to normal rats resulted in a marked rise in the blood levels of ACTH, ALDO and B at 1h and 2 h, the values returned to the baseline after 4 h. Ether and cold stresses notably raised the blood levels of ACTH, ALDO and B, and these rises lasted unchanged until 4 h. Galanin markedly potentiated ACTH and ALDO responses to ether stress at 1 and 2 h, but B response remained unchanged. ACTH response to cold stress was not affected by galanin; however, galanin magnified ALDO response to cold stress at 4 h, and enhanced at 1 h and depressed at 2 h that of B. In light of these findings the following conclusions can be drawn: (i) galanin exerts a stimulatory effect on HPA axis of rats under basal conditions; (ii) under our experimental conditions, ether stress exerts a stronger stimulation of HPA axis than cold stress; (iii) the galaninergic mechanisms involved in the stimulation of ACTH release do not interfere with ether stress-activated ones controlling ACTH secretion, and are probably similar to those underlying the effect of cold stress; (iv) steroidogenic capacity of adrenal cortex, at least in term of glucocorticoid hormones, is a rate-limiting step in the response of rat HPA axis to severe stresses; and (v) galanin exerts a direct secretory action of the rat adrenal gland, that can manifest itself only in the case of submaximally cold stress-stimulated HPA axis.

Effects of neuromedin U (NMU)-8 on the rat hypothalamo-pituitary-adrenal axis. Evidence of a direct effect of NMU-8 on the adrenal gland

A 6-day subcutaneous (s.c.) treatment of adult rats with NMU-8 ( 1.5 or 6 μg 100 g/day ) increased the average volume of zona fasciculata cells and decreased the number of zona reticularis cells in the adrenal cortex. The lower dose of NMU-8 did not change blood ACTH concentration and adrenal weight, but it notably enhanced serum corticosterone level and basal corticosterone output by adrenal slices. ACTH blood level increased after ether stress in both control and NMU-8-treated rats, but stress-evoked rise in serum corticosterone was observed only in control rats. The higher dose of NMU-8 increased the level of circulating ACTH: however, it decreased adrenal weight and had no effect on serum corticosterone concentration and basal corticosterone output by adrenal slices. NMU-8 ( 10 −10 10 −6 M ) did not affect basal and ACTH-stimulated corticosterone yield by isolated adrenocortical cells, nor did it change their cytosolic Ca 2+ concentration. NMU-8 (10 −8 M) markedly raised basal corticosterone secretion by adrenal slices (including cortex and medulla); higher concentrations of NMU-8 ( 10 −7 10 −6 M ) were ineffective on basal corticosterone secretion, but strongly inhibited the response to ACTH stimulation. On the ground of these findings it seems reasonable to suggest that NMU-8 exerts a biphasic effect on the function of the peripheral branch of the hypothalamo-pituitary-adrenal axis in rats: NMU-8 at low doses directly stimulates the function and growth of the adrenal cortex, while at high doses exerts a direct inhibitory action. Our data also indicate that the effects of NMU-8 on the adrenal cortex require the structural integrity of the gland, probably the presence of the zona medullaris.

The role of the medial prefrontal cortex (cingulate gyrus) in the regulation of hypothalamic-pituitary-adrenal responses to stress

In the studies reported here we have examined the role of the medial prefrontal cortex (MpFC) in regulating hypothalamic-pituitary-adrenal (HPA) activity under basal and stressful conditions. In preliminary studies we characterized corticosteroid receptor binding in the rat MpFC. The results revealed high-affinity (Kd approximately 1 nM) binding with a moderate capacity (42.9 +/- 3 fmol/mg) for 3H-aldosterone (with a 50-fold excess of cold RU28362; mineralocorticoid receptor) and high-affinity (Kd approximately 0.5-1.0 nM) binding with higher capacity (183.2 +/- 22 fmol/mg) for 3H-RU 28362 (glucocorticoid receptor). Lesions of the MpFC (cingulate gyrus) significantly increased plasma levels of both adrenocorticotropin (ACTH) and corticosterone (CORT) in response to a 20 min restraint stress. The same lesions had no effect on hormone levels following a 2.5 min exposure to ether. Implants of crystalline CORT into the same region of the MpFC produced a significant decrease in plasma levels of both ACTH and CORT with restraint stress, but again, there was no effect with ether stress. Neither MpFC lesions nor CORT implants had any consistent effect on A.M. or P.M. levels of plasma ACTH or CORT. Manipulations of MpFC function were not associated with changes in the clearance rate for CORT or in corticosteroid receptor densities in the pituitary, hypothalamus, hippocampus, or amygdala. Taken together, these findings suggest that MpFC is a target site for the negative-feedback effects of glucocorticoids on stress-induced HPA activity, and that this effect is dependent upon the nature of the stress.

Unusual effect of prolonged vasoactive intestinal peptide (VIP) administration on the adrenal growth and corticosterone secretion in the rat

VIP is widely distributed in the body, and among others is present within the hypothalamo-pituitary-adrenal axis. The aim of this study was to investigate the effect of prolonged VIP administration on the structure and function of the rat adrenal cortex. Adult female rats were treated for 7 or 14 days with VIP (1.5 μg/100 g/day). This treatment did not change adrenal weight and evoked only slight changes in the stereologic parameters of adrenal cortex (volume of adrenocortical zones, average cell volume and number of cells in the gland). On the contrary, basal plasma corticosterone levels were markedly lowered (44% and 26% of control values in 7- and 14-day experiments, respectively), an effect accompanied by a significant decrease in corticosterone output by adrenal slices. After stanardized ether stress, blood corticosterone concentration was similar in control and 14-day VIP-treated rats, while corticosterone secretion by adrenal quarters was higher in VIP-administered animals. Thus, prolonged VIP administration results in an unusual inhibition of corticosterone secretion in the rat, which is not coupled with a compensatory hypertrophy of the rat adrenal cortex. Such changes may depend on a modulatory action of VIP on the hypothalamo-pituitary-adrenal axis, and its possible mechanism is discussed.

Suppression of hypothalamic-pituitary-adrenal axis responsiveness to stress in a rat model of acute cholestasis.

Cholestatic patients undergoing surgery have increased mortality and demonstrate clinical features suggestive of adrenal insufficiency. To examine whether cholestasis influences the status of the hypothalamic-pituitary-adrenal axis, we evaluated rats with acute cholestasis caused by bile duct resection (BDR) and sham-operated and unoperated controls. Basal unstressed plasma concentrations of ACTH and corticosterone were similar in BDR and sham-operated and unoperated control rats. However, exposure of BDR rats to saturated ether vapor resulted in significantly less ACTH and corticosterone release in plasma than in the control animals. To understand the mechanism(s) of decreased HPA axis responsiveness to ether stress in cholestasis, we administered corticotropin-releasing factor (CRF) and measured hypothalamic content, mRNA levels and in vitro secretion of CRF and arginine vasopressin (AVP), the two principal secretagogues of ACTH. In BDR animals, ACTH responses to CRF were decreased and hypothalamic content of CRF and CRF mRNA expression in the paraventricular nucleus were decreased by 25 and 37%, respectively. Furthermore, CRF release from hypothalamic explants of BDR rats was 23% less than that of controls. In contrast to CRF, hypothalamic content of AVP was 35% higher, AVP mRNA in the paraventricular nucleus was increased by 6.6-fold, and hypothalamic explant release of AVP was 24% higher in BDR rats than in control animals. Pituitary ACTH contents were similar in BDR and sham resected rats, but higher than unoperated controls. These findings demonstrate that acute cholestasis in the rat is associated with suppression of hypothalamic-pituitary-adrenal axis responsiveness to stress and demonstrate a dissociation between mechanisms of ACTH regulation mediated by CRF and AVP.

Acetyl‐L‐Carnitine Effect on Pituitary and Plasma β‐Endorphin Responsiveness to Different Chronic Intermittent Stressors

The aims of the present study were: 1) to compare the effect of two different chronic intermittent stressors i.e. cold-swimming versus ether, on the pituitary opioidergic system; 2) to evaluate the response of pituitary and plasma beta-endorphin (beta-EP) to an acute stress in chronically stressed rats; and 3) to evaluate the effect of acetyl-l-carnitine treatment (10 mg/day/rat per os at night) on pituitary and plasma beta-EP changes induced by two different types of chronic stress. The stressors were applied twice a day for 10 days. Rats were killed either before, during or after the last swimming or ether stress session. beta-EP was measured by radioimmunoassay in anterior pituitary and in neurointermediate lobe extracts and in plasma. The following observations were made: 1) Chronic intermittent cold-swimming stress increased anterior pituitary contents and plasma beta-EP levels; 2) both chronic intermittent cold-swimming stress and ether stress caused an increase of neurointermediate lobe beta-EP contents; 3) as in control animals, rats exposed to chronic intermittent swimming stress reduced pituitary beta-EP contents and raised plasma beta-EP levels in response to the last acute swimming stress; 4) in contrast to control animals, rats exposed to chronic intermittent ether stress did not show any significant response of the pituitary-plasma opioidergic system to the last acute ether session; 5) the acetyl-l-carnitine treatment counteracted the changes evoked by chronic intermittent cold-swimming stress on the pituitary and plasma beta-EP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

ACTH secretion from isolated hypophysial anterior lobes of male and female newborn rats: effects of corticotrophin-releasing factor, arginine vasopressin and oxytocin alone or in combination.

ACTH release by the anterior pituitary lobes of 8-day-old newborn rats (males and females) in the presence of rat corticotrophin-releasing factor (rCRF), arginine vasopressin (AVP) and oxytocin, given alone or in association, was measured in vitro. Rat CRF and AVP induced a dose-dependent release of ACTH in both sexes, while oxytocin was unable to stimulate ACTH secretion except at the highest dose tested. No sex-related difference was noted for any of the responses. Oxytocin (1 nmol/l) potentiated the response to rCRF (0.20 nmol/l) by the anterior pituitary lobes of females but not by those of males. This oxytocin potentiation was abolished when female newborn rats were injected at birth with testosterone (1 mg). AVP (1 nmol/l) alone stimulated ACTH release from the anterior pituitary lobes of the newborn rats of both sexes and markedly potentiated the ACTH response to rCRF. Although no difference between the sexes was noted for basal levels of AVP and oxytocin in the hypothalamus, the neurointermediate lobe and the peripheral plasma, the present data on the sex-related effect of oxytocin on the newborn adenohypophysis could, in part, explain why ACTH release in response to ether stress was previously reported to be more lasting in females than in males on day 8 postpartum.

Increased plasma ACTH responses to stress in nonhandled compared with handled rats require basal levels of corticosterone and are associated with increased levels of ACTH secretagogues in the median eminence

Postnatal handling of rat pups is known to alter permanently hypothalamic-pituitary-adrenal (HPA) responses to a wide variety of stressors. As adults, handled (H) and nonhandled (NH) animals also differ in sensitivity to the delayed negative-feedback effects of glucocorticoids on stress-induced HPA activity. However, it is not understood how handling alters neuroendocrine responses to stressful stimuli, and how differences in feedback sensitivity might account for changes in HPA activity both during and following stress. In the present studies, plasma ACTH responses to both restraint and ether stress were significantly greater in NH compared with H animals. Administration of 100 micrograms/kg corticosterone (B) immediately prior to restraint stress significantly decreased subsequent plasma ACTH responses to restraint to the same extent in H and NH animals, suggesting that H and NH animals do not differ in glucocorticoid fast feedback. H and NH animals adrenalectomized (ADX) 5 d prior to testing did not differ in plasma ACTH responses to restraint stress, demonstrating that the differences between the groups are dependent upon the presence of circulating B. However, the handling effect was apparent in ADX animals provided with a low level of B replacement (approximately 5-6 micrograms/dl). B replacement significantly decreased plasma ACTH levels under both basal conditions and in response to restraint stress in H/ADX rats. In contrast, although B replacement also decreased basal ACTH levels in ADX/NH rats, there were no differences in plasma ACTH responses to restraint between NH/ADX and NH/ADX+B animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal facilitation of stress-induced adrenocorticotropin secretion by prior stress: evidence for increased central drive to the pituitary.

The adrenocortical system of the neonatal rat exhibits both normal pituitary (ACTH) and blunted adrenal corticosterone (B) responses to a variety of different stressors. It is established that although circulating levels of B are low during the first 2 weeks of life, efficient inhibition of ACTH secretion by B is observed in neonatal rats. We investigated the ability of the hypothalamo-pituitary unit to respond to two consecutive, 1 h apart, exposures to 3 min ether vapor (stress 1 and stress 2) and whether an exogenously provided B signal that mimicked the amount of B secreted after the first stress could impair stress-induced ACTH secretion. We also determined in vivo and in vitro whether previous stress could alter pituitary responses to CRF, arginine vasopressin (AVP), or a combination of both peptides. After stress 2, 10-day-old neonates showed similar or increased peak (5 min = control) ACTH secretion compared to stress 1, although the area under the curve over 60 min after stress was comparable between stresses 1 and 2. Stress-induced B secretion was significantly elevated (P < 0.05) 60 min after stress 1, and the mean area (n = 5 experiments) was 39.3 +/- 14 micrograms/dl.60 min. Exogenously injected B (0.1 mg/kg BW) instead of stress 1 was able to mimic the magnitude of the B signal observed after stress 1 (area = 56.4 micrograms/dl.60 min) and significantly reduced (56.4 +/- 18% of ether peak) the peak ACTH secretion seen after stress 2. Doses of 1 and 0.01 mg B/kg BW also reduced peak ACTH amplitude to 20.6 +/- 6.6% and 73.7 +/- 30% of the ether peak value, respectively. Previous exposure to ether stress did not affect the in vivo ACTH response to CRF (10 micrograms/kg) or AVP (5 micrograms/kg) measured 30 min after ip injection, but increased (P < 0.05) the response to CRF plus AVP treatment. When pituitaries from previously stressed 13-day-old pups were incubated in vitro, basal ACTH release was increased, and the ACTH response to CRF (1 and 10 nM), expressed as a percentage of the control value, was reduced. A similar observation was made when intact pituitaries were treated with CRF (0.1 nM) during the preincubation period.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of valproate in brain monoamines of juvenile rats after stress

Mitsikostas Dimos, Anastasia sfikakis, Zetta Papadopoulou-Daifoti and Dionisios Varonos. The Effects of Valproate in Brain Monoamines of Juvenile Rats after Stress. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 1993, 17(2): 295–310. 1. 1. Clinical data suggest that valproate (VPA) may be useful in prophylaxis of affective disorders, which show disturbances of the serotoninergic system. On the other hand, chronic stress has an adverce effect on affective disorders, those with disturbances of the serotonergic system, especially. 2. 2.In order to study the effects of VPA on brain monoamines and acute stress, 200 mgr VPA /Kgr was administered intraperitoneal (ip) to juvenile male rats; the control group was treated with NaCL 0.9% ip. After 30 min, all animals were evoked on predictable neurogenic or systemic stress (30 min foot shock, or 15 min ether stress, respectively), and 48 hours later, VPA or NaCL were administered ip again; 30 min afterwards, the rats were decapitated. Rats without stress were also sacrificed 30 min after VPA or NaCL administration. 3. 3. Measurements of brain monoamines noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT). and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), and 5-hydroxy- indoleacetic acid (5-HIAA), were done in Frontal Cortex (FC), Hypothalamus (HY) and Striatum (S), by High Performance Liquid Chromatography (HPLC). 4. 4. Compared with the control stress group the level of 5-HIAA in the FC was significantly increased (P<0.01) in VPA stress rats; in the HY and in S the increase of 5-HIAA was not significant. No remarkable differences were observed in NA, DA, 5-HT and DOPAC concentrations, in any of the brain regions. No changes in brain monoamine levels were found in non stress rats, either. 5. 5. The augmentation of 5-HIAA level after VPA administration and after stress, in correlation with the decrease of 5-HIAA that is observed in depression, support the hypothesis that VPA may be effective in affective disorders by influencing the serotoninergic system.

Effect of different chronic intermittent stressors and acetyl-l-carnitine on hypothalamic beta-endorphin and GnRH and on plasma testosterone levels in male rats.

Chronic stress affects the reproductive function by modifying the neuroendocrine homeostasis. The aim of the present study was to clarify the neuroendocrine and the gonadal changes following chronic intermittent stress in male rats and the action of a neuroactive drug, acetyl-l-carnitine (ALC). The effect of two different stressors, cold water swimming or ether, on central beta-endorphin (beta-EP) and GnRH contents, and on plasma testosterone levels was investigated. In addition, the response to an acute stress in chronically stressed rats, treated or untreated with ALC (10 mg/day/rat p.o.), was evaluated. The stressors were applied twice a day for 10 days, and rats were killed before, during and after the last stress session. Mediobasal hypothalamus (MBH) beta-EP and GnRH contents, and plasma testosterone levels were evaluated by radioimmunoassay. The following results were obtained: (1) both chronic swimming and ether stress caused a decrease in hypothalamic beta-EP contents; (2) MBH GnRH contents increased after chronic swimming stress but not after ether stress; (3) chronic swimming stress induced a twofold decrease in plasma testosterone levels, while no changes were observed after ether stress; (4) the treatment with ALC prevented the decrease in plasma testosterone levels after chronic swimming stress, and (5) acute stress in chronically stressed animals caused an increase in MBH-beta-EP. The present data showed that chronic swimming stress reduces the reproductive capacity and impairs the capacity to respond to the acute stress and that ALC modulates the hormonal changes to physical stress and prevents the antireproductive effect of chronic cold swimming.

Restoration by bromocriptine of glucocorticoid receptors and glucocorticoid negative feedback on prolactin secretion in estrogen-induced pituitary tumors.

We previously reported a reduction of glucocorticoid receptors (GCR) in diethylstilbestrol-induced pituitary tumors (DES-T) in rats. Presently, we found that bromocriptine (BROM) treatment increased the levels of GCR in DES-T, demonstrated by steroid binding assays and immunocytochemistry using a monoclonal antibody against the type II GCR. We also found that the high content of nuclear estradiol receptors in the adenomata and the elevated levels of PRL in serum of DES-T were significantly reduced after BROM treatment. In parallel studies, PRL secretion was measured after administration of ether stress. In controls, serum PRL markedly increased after ether and this effect was blunted by prior dexamethasone (DEX) administration, due to the steroid negative feedback on PRL secretion. In animals with DES-T, ether stress had no effect on serum PRL, and the inhibition by DEX was lost unless they received BROM, which restored the negative feedback of DEX on serum PRL. Although increases of PRL titers in pituitary tumors may be due to estrogenic stimulation of lactotroph proliferation and function, coupled to absent dopaminergic inhibition on these cells, other mechanisms are possible. In this respect, inefficient steroid negative feedback on PRL synthesis due to down-regulation of GCR may contribute to hyperprolactinemia. This mechanism is supported from the restoration of GCR and steroid negative feedback on serum PRL by treatment of tumor-bearing rats with BROM.

Adrenal response to acute stress in mammillary medial nuclei lesioned rats.

In view of the inhibitory influence of Mammillary Medial Nuclei, pars lateralis (MMN) on corticoadrenal activity, experiments were conducted in order to determine whether these nuclei are involved in the control of adrenal response to ether stress. In bilateral MMN lesioned rats, prestress plasma corticosterone concentration (C) is significantly higher than that in sham lesioned animals. Acute stress produced a significant C increase in both, sham and lesioned rats, being this increase lower in lesioned animals. After exposure to ether vapors. adrenal concentration of norepinephrine was similar in lesioned and control animals. Whereas, adrenal epinephrine concentration was significantly higher in lesioned rats than that found in the sham lesioned ones. This study demonstrates that the integrity of MMN is not essential for adrenal response to acute stress.