Amphetamine and stress responses in developmentally lead-exposed rats.

In this study, pregnant Wistar dams were exposed to 220 ppm of lead (Pb) in drinking water during gestation and lactation. The response to the locomotor-stimulating effects of 0.5 mg/kg of amphetamine (AMPH) was evaluated in 35-day-old male offspring. The results demonstrated that developmental Pb exposure induced no differences in the response to the drug, although an increase in locomotor activity induced by a single saline (SAL) injection was observed selectively in the Pb-exposed group. Considering evidence that suggests a relationship between increased locomotor activity and stress response, a time course analysis of corticosterone (CS) secretion and locomotor performance was carried out. Higher basal levels of CS and elevated stress-induced secretion of this hormone in response to the injection were observed in Pb-exposed rats compared to controls, a pattern that showed a time-related increase in locomotor activity. Habituation to SAL injections prior to testing restored both CS secretion and locomotor response to SAL to levels comparable to controls and did not modify AMPH locomotor response measured in these new experimental conditions. Additionally, we demonstrated that these behavioral/hormonal disruptions were no longer detectable later in adulthood. Collectively, these data suggest that the stimulant-locomotor effect of AMPH in Pb-exposed rats is independent of the arousal of the animal at the time of its administration. They also support a unique profile of integrated behavioral and hormonal hyperresponsiveness in 35-day-old low-level Pb-exposed rats evidenced as hyperlocomotion and altered secretion of CS in response to an environmental manipulation, an effect that was no longer present later in life.

Characterization and functional significance of glucocorticoid receptors in patients with major depression: modulation by antidepressant treatment.

Hyperactivity of the hypothalamic pituitary adrenal (HPA) axis in patients with major depression is one of the most consistent findings in biological psychiatry. Experimental data support the idea that glucocorticoid-mediated feedback via glucocorticoid receptors (GR) is impaired in major depression. The aim of the present work was to assess the putative changes in GR density of peripheral blood mononuclear cells (PBMCs) in a group of patients with major depression and to determine modulation of these GR sites by antidepressant treatment. In addition, susceptibility of PBMCs to glucocorticoid effects was also studied using a functional end-point analysis in vitro, such as cortisol inhibition of mitogen-induced lymphocyte proliferation. Cortisol levels were also measured before and after dexamethasone suppression test (DST). The results showed a decrease in GR density in depressed patients compared with healthy subjects, mainly in those patients that showed basal cortisol levels in the upper normal range and were refractory to DST. Regarding the functional significance of this variation, two representative groups emerged from our study: a) free-medication patients with GR function comparable to healthy controls, and b) patients showing diminished GR activity. These results suggest a lack of relationship between GR density and cortisol-induced inhibition of lymphocyte proliferation. Patients treated with different antidepressant drugs showed a marked increase in the number of GR sites per cell compared to non-treated. Interestingly, this increase was even higher than in normal subjects. Hence, restoration of GR density after an efficient antidepressant treatment could be an index of an effective modulatory action of drugs on GR expression and highlights the possibility that GR levels might be used as markers of a successful treatment.

Glucocorticoid and mineralocorticoid receptors are involved in the facilitation of anxiety-like response induced by restraint.

In previous studies, we have shown that male Wistar rats exposed to a single inescapable stressor session (15 min restraint) exhibited 24 h later an anxiogenic-like behavior in the elevated plus-maze (EPM), which was reversed by inhibition of corticosterone (CS) synthesis with metyrapone (75 mg/kg i.p.) 3 h before stress. Since CS binds to two central corticosteroid receptors, the mineralocorticoid (MR) and the glucocorticoid (GR) receptors, involvement of MR and GR in the modulation of anxiogenic responses was assessed in the EPM. Administration of the GR agonist dexamethasone (Dex, 1.25 microg/kg s.c.) to metyrapone-pretreated rats 1 h before restraint restored the anxiogenic-like response induced by the stressor. Removal of the adrenals also inhibited the anxiogenic-like effect, which was restored by either Dex (1.25 microg/kg s.c.), the MR agonist deoxycorticosterone (0.8 mg/kg s.c.) or CS, the common endogenous agonist of MR and GR (5 mg/kg s.c.) administered 1 h before stress. Intracerebroventricular infusion to intact animals 15 min before restraint of either a selective GR antagonist (A-GR, RU 38486, 100 ng/2 microl), a selective MR antagonist (A-MR, RU 28318, 100 ng/2 microl) or a combination of A-GR and A-MR (100 ng of each one/2 microl), abolished the stress-induced anxiogenic-like effect. The present findings indicate that both MR and GR are involved in the long-term CS modulation of the anxiety response induced by restraint. Both receptors mediate CS effects in an independent manner.

Metyrapone pretreatment prevents the behavioral and neurochemical sequelae induced by stress.

In the present study, we examined the effect of metyrapone, an inhibitor of corticosterone (CS) synthesis, on the behavioral and neurochemical sequelae induced by a brief restraint session. A 15-min stress period induced an anxiogenic-like behavior on the elevated plus-maze (EPM), which was reversed with metyrapone (75 mg/kg i.p.) injected 3 h prior to the stress event. It was further demonstrated that metyrapone pretreatment normalized the decrease in maximal chloride uptake following GABA stimulation observed in brain cortex tissue obtained from animals exposed to both restraint and the EPM. In addition, plasma CS levels were assessed both after restraint and following EPM exposure. Furthermore, the administration of both CS (2.5 mg/kg s.c. at a dose that mimics CS levels induced by restraint) or dexamethasone (DEXA, 1.25 microg/kg s.c) resulted in an anxiogenic response in the EPM comparable to that induced by restraint. Taken together, all these evidence suggest that CS released in response to stress seems to be associated with functional changes at the GABAergic supramolecular complex which could underlie the enhanced anxiety observed following the exposure to an aversive experience.

Chronic treatment with desipramine: effect on endocrine and behavioral responses induced by inescapable stress.

Inescapable shock (IS) exposure induces behavioral inactivity, related to behavioral alterations in subsequent tests (i.e. escape failure during shuttle box task). Previous studies have demonstrated that various antidepressant treatments administered either before or after IS exposure reversed these behavioral deficits. Recently, we demonstrated corticosterone (CS) involvement both in inactivity performance during IS and in the number of escape failures in a shuttle box task. In the present study, we analyzed the effects of chronic desipramine (DMI) treatment administered before or after IS exposure on the dynamics of changes in serum CS concentration after both IS and shuttle box task, to explore a possible relationship between the hormonal response and the reversion of the behavioral induced by DMI. DMI (10 mg/kg intraperitoneally i.p.) administered during 6 consecutive days before IS reduced release and inactivity induced by this aversive experience. Two days later, when these DMI-treated rats were submitted to a shuttle box task, a reduction in CS release and IS-induced escape failures were observed as compared with saline-treated rats. Besides, in animals without IS experience, the pretreatment with DMI did not modify either the pattern of CS secretion or the percentage of escape failures as compared with saline-injected rats. On the other hand, CS values of rats treated with DMI during 6 consecutive days after IS exposure recovered to resting controls levels within 60 min post-shuttle box task, exhibiting fewer escape failures; unlike saline-treated, IS-exposed rats, which retained persistently elevated levels of CS (during the post-task sampling interval) a showed a high percentage of escape failures. Thus, chronic DMI administration before IS attenuated CS secretion and prevented the onset and expression of behavioral deficits induced by uncontrollable stressors. However, when it was administered after IS, it induced an increased negative feedback sensitivity in coincidence with the reversion of the IS-induced behavioral deficits.

Prior exposure to a brief restraint session facilitates the occurrence of fear in response to a conflict situation: behavioral and neurochemical correlates.

The influence of two different stressors on the behavioral and neurochemical responses to a subsequent exposure to the elevated plus maze (EPM) was examined. Rats were submitted to either a 15-min restraint period or to a 15-min forced swimming test (FS) and one day later exposed to the EPM. Animals with early restraint exhibited a significant decrease in the percent time spent and in the number of entries on the open arms. In addition, restraint induced a reduction in the total number of entries. An identical behavior in the EPM was observed between unstressed rats and those exposed to a previous swimming experience. As a humoral index of stress, corticosterone (CS) secretion in response to each stressor was evaluated. A similar increase of CS release was observed following each aversive stimulus. Exposure to both restraint and EPM decreased the cortical chloride uptake following GABA stimulation. Similar values of chloride flux were obtained from animals submitted to either restraint but without subsequent exposure to the EPM, exposed only to the EPM, or without any manipulation (controls). These findings are discussed in terms of a facilitated behavioral and neurochemical response to a fearful situation following an early and brief restraint experience.

Corticosterone is involved in foot shock-induced inactivity in rats.

Inescapable shock (IS) exposure induces behavioral inactivity, related to behavioral alterations in subsequent tests (i.e., escape failure, and inactivity during shuttle box task). Metyrapone (150 mg/kg, IP), a corticosterone (CS) synthesis inhibitor, administered 3 h prior to IS reduced inactivity during this aversive experience. Forty-eight hours later, when these rats were submitted to a shuttle box task, a reduction in both escape failure and inactivity was observed. These effects were reversed by CS (20 mg/kg, SC) and dose dependent of the synthetic glucocorticoid dexamethasone, both administered 1 h before IS. When metyrapone was administered 3 h before the shuttle box task to IS-exposed animals, escape failures and inactivity were markedly reduced. This effect was subsequently reversed by CS. The dynamics of changes in serum CS concentrations after both IS and shuttle box task paralleled behavioral changes. Animals injected with metyrapone before IS, which displayed active behavior, showed serum CS levels stable at their basal levels after shock, and their secretion pattern was quite attenuated after the shuttle box task, whereas vehicle-, CS alone-, and metyrapone + CS-injected animals showed higher serum CS concentrations post-IS, which slowly decreased to their corresponding basal levels. CS secretion after the shuttle box task was similar for the three groups: it had the same magnitude as after IS, though the decrease was faster. In all groups, animals displayed passive behavior. These results indicate that glucocorticoids are involved in the onset and expression of passive behaviors induced by uncontrollable stressors. Therefore, it is possible to suggest a functional relationship between CS released by exposure to inescapable stressor and the behavioral strategies adopted by rats under this stressful condition.

Gangliosides attenuate stress-induced changes on body weight, motor activity and on the behavioral response to 5-methoxy-N,N-dimethyltryptamine.

The major goal of this study was to evaluate the influence of gangliosides (GANG) treatment on the onset of adaptive changes and the sequelae induced by stress exposure. With this purpose, the behavioral response to 5-methoxy-N,N-dimethyltryptamine (5-MeODMT, 5 mg/kg, IP) and motor activity were evaluated in rats previously submitted either to a single restraint session (2 h) or to a daily restraint event for 3 consecutive days, combined or not to GANG administration (30 mg/kg IP). GANG was always injected 2 h before stress exposure. In addition, differences in body weights were recorded throughout the experiments. A similar behavioral response after 5-MeODMT was observed between saline (SAL) and GANG unstressed rats. Exposure to one or three restraint sessions did not modify the behavioral response to 5-MeODMT, whereas the association of GANG and stress during 3 consecutive days enhanced forepaw treading and hindlimb abduction. SAL-treated animals submitted to a single or to three stressful stimuli showed reduced locomotion and rearing. The combination of GANG and stress for 3 days, but not after a unique association, reversed the decrease on motor activity induced by the aversive experience. The decrease of body weights produced by one or three stress sessions was recovered only in animals treated with GANG and stress for 3 days. These findings suggest that GANG may accelerate the onset of adaptive changes on 5-HT1 sites and attenuate certain sequelae induced by previous stress experience.

Corticosterone influences forced swim-induced immobility.

The effect of corticosterone (CS) synthesis inhibition with metyrapone-a blocker of the 11 beta-hydroxylase (150 mg/kg IP)-on immobility time during the forced swim test was recorded. Immobility time was measured during a 15-min forced swim (test). Twenty-four hours later rats were subjected to an additional 5 min forced swim (retest). In one experiment, metyrapone or vehicle was administered 3 h before the initial test, while CS (0, 5, 10, or 20 mg/kg SC) was administered 1 h prior to the initial test. Metyrapone significantly reduced immobility time during both test and retest. This effect was reverted in a dose-dependent fashion by CS. In a second experiment, animals exposed to the initial test 24 h before were injected with metyrapone or vehicle 3 h before the retest, while CS (0, 10, or 20 mg/kg SC) was administered 1 h prior the retest. Metyrapone, administered before the retest, reduced immobility time and CS partially reverted metyrapone effect. In another group of animals, serum CS concentrations were evaluated before and after test and retest. In vehicle groups, the high immobility time during test and retest was associated with high CS serum concentrations poststress. In animals receiving metyrapone prior to the initial test, the reduced immobility time was related to low levels of CS after the test and an attenuated secretion following the retest. Moreover, CS (20 mg/kg) and metyrapone+CS groups had high CS levels before the test, which remained high 2 h after the test, although after the retest, both groups showed a pattern of CS secretion similar to that observed in vehicle animals.(ABSTRACT TRUNCATED AT 250 WORDS)

ACTH accelerates the attenuation of alpha 2-adrenoceptors response in nucleus accumbens following chronic desipramine.

The inclusion of clonidine (CLO) induced a dose-dependent reduction of K(+)-evoked [3H] dopamine ([3H]DA) release in slices from rat nucleus accumbens. This inhibition was clearly attenuated in animals previously administered desipramine daily (DMI, 10 mg/kg i.p.) during 21 days, but not in rats submitted to a persistent treatment with DMI during 10 days. However, the coadministration of adrenocorticotrophic hormone (ACTH, 50 IU/kg s.c.) and DMI (10 mg/kg i.p.) for 10 days provoked a clear decrease in the inhibition produced by alpha 2-adrenoceptor stimulation, while ACTH alone had no effect. These results may indicate that ACTH accelerates the onset of DMI-induced adaptive changes on central alpha 2-adrenoceptor in the mesolimbic area.

Adrenocorticotropic hormone influences the development of adaptive changes in dopamine autoreceptors induced by chronic administration of desipramine.

The influence of adrenocorticotropic hormone (ACTH) in the adaptive changes on central dopamine (DA) autoreceptors following chronic administration of desipramine (DMI) has been examined in rats. Dopamine had an inhibitory effect on basal and K(+)-induced release of [3H]DA from slices of striatum and n. accumbens of rats treated chronically (10 days) with ACTH (50 IU/kg, s.c.), DMI (10 mg/kg, i.p.) or the combination of ACTH and DMI. In slices of n. accumbens, but not in slices of striatum of rats exposed to the combined treatment of ACTH and DMI, a significant decrease in the inhibitory effect of exogenous DA on stimulated release of [3H]DA was observed. Chronic administration of ACTH or DMI alone had no effect. The effect of the combined treatment with both agents, on the reactivity of these DA receptors was evaluated by means of apomorphine-induced hypoactivity. The administration of ACTH and DMI (5 mg/kg, i.p.) reduced the hypoactivity induced by apomorphine, as compared to hypoactivity in rats treated with ACTH or DMI alone. Experiments with ACTH4-10 revealed that the peptide modified biochemical and behavioural parameters of dopaminergic function, which may implicate a direct action of the peptide on the brain, rather than on the release of adrenal hormones. These findings suggest that ACTH accelerates the onset of DMI-induced adaptive changes on dopamine in the mesolimbic area. However, because the effect of ACTH4-10 on release of adrenocortical hormone was not investigated, the possibility cannot be disregarded that the effect of the peptide was secondary to an enhancement of release of adrenal hormone.

Opioid involvement in the adaptive change of 5-HT1 receptors induced by chronic restraint.

Rats immobilized for 2 h daily for 7 days showed an increased behavioral response (forepaw treading and hind-limb abduction) to 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) 24 h after the last stress session. An injection of naloxone before each stress session fully antagonized the increased behavioral reactivity to 5-MeODMT. Treatment with morphine or beta-endorphin associated with each immobilization session for 3 days produced a response to 5-MeODMT higher than that of animals subjected to immobilization only. Chronic immobilization for 7 days did not affect the shaking behavior induced by 5-hydroxytryptophan (5-HTP) 24 h after the last restraint session. These findings suggest that chronic stress may induce a selective adaptive change of the 5-HT1 site and activate an opioid mechanism that is most likely to be involved in the development of this adaptive change.

Effect of chronic variable stress on monoamine receptors: influence of imipramine administration.

Adult male rats were exposed to a series of unpredictable stressors, a paradigm considered to be a model of experimental depression, with or without concurrent administration of imipramine. One day after the last stress event of the chronic regime, binding of cortical beta-adrenoreceptors and the behavioral serotonin (5-HT) syndrome induced by 5-methoxy-N,N,dimethyltryptamine (5-MeODMT) were determined in all the experimental groups. Stressed rats showed an "up-regulation" of cortical beta-adrenergic sites, while similar values to control rats were observed when stressed animals were administered imipramine. Regarding the behavioral 5-HT syndrome, comparable behavioral scores were observed between controls and chronically stressed rats. The combination of chronic exposure to different stressors with imipramine treatment resulted in a significant increase of forepaw treading and Straub tail scores. The probable facilitation of behavioral deficits induced by this scheme of chronic stress and the recovery following concurrent administration of imipramine are discussed.

Chronic stress-induced changes in locus coeruleus neuronal activity.

Locus coeruleus (LC) activity was assessed in rats exposed to either acute or chronic stress. After one immobilization session, the number of spontaneously active LC neurons dramatically decreased. On the other hand, repeated restraint sessions enhanced noradrenergic (NA) transmission and the inhibitory effect of clonidine (CLON) was greater on these cells than in those of controls. These results bear on the adaptive changes in the NA system following acute or chronic stress.

Chronic stress attenuation of alpha 2-adrenoceptor reactivity is reversed by naltrexone.

Low doses of clonidine (50-100 micrograms/kg IP) evoke a clear dose-dependent hypoactivity response. Seven daily immobilization sessions prevented the motor activity decrease induced by clonidine. On the contrary, a single stress failed to modify clonidine response. Pretreatment with naltrexone (2 mg/kg IP) fully antagonized the attenuating effect induced by chronic stress on clonidine sedative action. These evidences suggest that chronic but not acute stress reduces the reactivity of alpha 2-adrenoceptors involved in clonidine-induced sedation. In addition, a regulatory mechanism of endogenous opioids seems to participate on alpha 2-adrenoceptors adaptative changes.

Stimulation of release of growth hormone from the anterior pituitary by alpha-melanocyte-stimulating hormone: a possible mechanism for induction of pseudopregnancy in the rat.

In hypophysectomized rats on day 1 of dioestrus, as well as on day 4 of pseudopregnancy, alpha-MSH (continuous infusion of 1 microgram/h) failed to maintain serum concentrations of progesterone. On the other hand, alpha-MSH did not modify the increase induced by ACTH (1 microgram/microliter as an infusion plus two additional daily injections of 30 micrograms/microliter), prolactin (200 micrograms/0.2 ml at 12-h intervals) or GH (300 micrograms/0.2 ml twice daily) on serum concentrations of progesterone in such rats. However, in intact rats alpha-MSH caused a significant rise in serum concentrations of GH on day 1 and day 2 of dioestrus. Continuous infusion of alpha-MSH produced an increase in serum concentrations of GH at 12.00 and 14.00 h on day 1 of dioestrus and at 07.00 h on day 2. It is therefore suggested that alpha-MSH may exert its effect by facilitating the secretion of GH, which in turn may induce the release of progesterone.

Influence of adrenocorticotrophic hormone on the behaviour in the swim test of rats treated chronically with desipramine.

Chronic desipramine (DMI) administration induced a dose-dependent reduction in the immobility time of the swim test in rats. A combined treatment of ACTH (50 iu kg-1 s.c.) and DMI (5 or 10 mg kg-1 i.p.) for 7 days potentiated the anti-immobility effect of DMI. ACTH 4-10, a fragment peptide with little corticotrophic activity, mimicked ACTH-induced potentiation. No stimulating effect on locomotor activity was observed following seven daily co-administrations of ACTH or ACTH 4-10 and DMI (10 mg kg-1). This behavioural evidence indicates that ACTH potentiation involves a central mechanism and demonstrates a functional interaction between ACTH and DMI at the behavioural level.

Evidence for the role of alpha-MSH in the induction of pseudopregnancy in the rat.

In a previous study we have demonstrated that cervical stimulation (CS) induces alpha-MSH release. The present experiments were undertaken to (1) examine the pattern of serum alpha-MSH during CS-induced pseudopregnancy (PSP) and (2) assess the possibility that alpha-MSH contributes to the induction and maintenance of PSP. Throughout PSP serum alpha-MSH fluctuated in a cyclic manner demonstrating two daily surges which occurred between 12.00 and 13.00 h (diurnal surge) and between 24.00 and 04.00 h (nocturnal surge). Chronic exposure of animals to alpha-MSH administered via minipumps (24 micrograms/day, starting on the morning of estrus), induced PSP as determined by deciduoma formation and persistence of a characteristic diestrous vaginal cytology. Furthermore, insertion of an alpha-MSH-containing minipump at diestrus 1 (D1) resulted in progesterone and prolactin (PRL) levels on the afternoon of diestrus 2 (D2) similar to those levels found on day 2 of PSP. Uterine weight was significantly decreased in alpha-MSH-treated rats and pseudopregnant rats as compared with cyclic D2 controls. alpha-MSH was found to release PRL indirectly, through stimulation of adrenal progesterone. This effect, however, necessitates the presence of the ovaries as a source of estradiol (EB) since it is demonstrable in intact and acutely ovariectomized rats, but not in chronically ovariectomized animals. EB treatment of chronically ovariectomized rats is capable of restoring the sequence. These results indicate that, as demonstrated for PRL, cervical stimulation initiates rhythmic daily surges of alpha-MSH secretion which are maintained through PSP.(ABSTRACT TRUNCATED AT 250 WORDS)