Adaptation of female rats to stress: shift to male pattern by inhibition of corticosterone synthesis

Omeprazole affects the expression of serotonin-1A in the brain regions and alleviates anxiety in rat model of immobilization-induced stress

Omeprazole, a drug of choice for the management of gastric hyperacidity, influences serotonergic neurotransmission in brain regions and its long-term use is known to cause stress-related behavioral deficits including anxiety. Aim of the current study was to explore the effects of omeprazole treatment on immobilization-induced anxiety in rats, specifically on the role of serotonin (5-HT). In view of the role of serotonin-1A (5-HT1A) autoreceptor in the availability of 5-HT in brain regions, mRNA expression of this autoreceptor was performed in raphe nuclei. Similarly, because of the role of hippocampal 5-HT neurotransmission in anxiety-like disorders, expression of the 5-HT1A heteroreceptors was determined in this region. We found that the treatment with omeprazole reduces anxiety-like behavior in rats, increases the expression of 5-HT1A autoreceptor in the raphe and decreases the hippocampal expression of 5-HT1A heteroreceptor. This suggests a role of 5-HT1A receptor types in omeprazole-induced behavioral changes. It also indicates a potential role of omeprazole in the management of serotonergic disorders.

Corticosterone administration immediately after peripuberty stress exposure does not prevent protracted stress-induced behavioral alterations

Stress-related disorders are commonly associated with abnormalities in hypothalamic-pituitary-adrenal (HPA) axis activity. Preliminary studies with cortisol administration in the aftermath of trauma suggest that this HPA axis hormone can potentially prevent maladaptive behavioral and biological stress responses. However, the efficacy of glucocorticoid administration during the peripuberty period has not been tested yet, although this lifetime is a critical time window in brain development and is highly sensitive to the harmful effects of stress. To further examine the short and long-lasting impact of glucocorticoids treatment given during the post-peripubertal stress period, the present study utilized a rat model of peripubertal stress-induced psychopathology and animals were subjected to a battery of tests to assess anxiety-like behaviors, exploratory behavior and reactivity to novelty at late adolescence and sociability, anhedonia and stress coping behaviors at adulthood. All the experiments were performed in males and females to evaluate the potential behavioral sex differences. Overall, our results demonstrated that rats exposed to peripubertal stress show decreased sociability in adulthood without differences in anxiety and depression-like behaviors. Moreover, this study shows that the administration of corticosterone after stress exposure at peripuberty does not prevent stress-induced behavioral alterations. However, we observed that some stress-induced behavioural alterations and corticosterone responses are sex-specific. Thus, the data obtained highlight that delineating sex differences in stress-related studies may ultimately contribute to the development of effective therapeutic interventions for each sex.

Increased reactivity of the paraventricular nucleus of the hypothalamus and decreased threat responding in male rats following psilocin administration

Psychedelics have experienced renewed interest following positive clinical effects, however the neurobiological mechanisms underlying effects remain unclear. The paraventricular nucleus of the hypothalamus (PVN) plays an integral role in stress response, autonomic function, social behavior, and other affective processes. We investigated the effect of psilocin, the psychoactive metabolite of psilocybin, on PVN reactivity in Sprague Dawley rats. Psilocin increased stimulus-independent PVN activity as measured by c-Fos expression in male and female rats. Psilocin increased PVN reactivity to an aversive air-puff stimulus in males but not females. Reactivity was restored at 2- and 7-days post-injection with no group differences. Additionally, prior psilocin injection did not affect PVN reactivity following acute restraint stress. Experimental groups sub-classified by baseline threat responding indicate that increased male PVN reactivity is driven by active threat responders. These findings identify the PVN as a significant site of psychedelic drug action with implications for threat responding behavior.

Glucocorticoids, their uses, sexual dimorphisms, and diseases: new concepts, mechanisms, and discoveries

The normal stress response in humans is governed by the hypothalamic-pituitary-adrenal (HPA) axis through heightened mechanisms during stress, raising blood levels of the glucocorticoid hormone cortisol. Glucocorticoids are quintessential compounds that balance the proper functioning of numerous systems in the mammalian body. They are also generated synthetically and are the preeminent therapy for inflammatory diseases. They act by binding to the nuclear receptor transcription factor glucocorticoid receptor (GR), which has two main isoforms (GRα and GRβ). Our classical understanding of glucocorticoid signaling is from the GRα isoform, which binds the hormone, whereas GRβ has no known ligands. With glucocorticoids being involved in many physiological and cellular processes, even small disruptions in their release via the HPA axis, or changes in GR isoform expression, can have dire ramifications on health. Long-term chronic glucocorticoid therapy can lead to a glucocorticoid-resistant state, and we deliberate how this impacts disease treatment. Chronic glucocorticoid treatment can lead to noticeable side effects such as weight gain, adiposity, diabetes, and others that we discuss in detail. There are sexually dimorphic responses to glucocorticoids, and women tend to have a more hyperresponsive HPA axis than men. This review summarizes our understanding of glucocorticoids and critically analyzes the GR isoforms and their beneficial and deleterious mechanisms and the sexual differences that cause a dichotomy in responses. We also discuss the future of glucocorticoid therapy and propose a new concept of dual GR isoform agonist and postulate why activating both isoforms may prevent glucocorticoid resistance.

Restraint or immobilization: a comparison of methodologies for restricting free movement in rodents and their potential impact on physiology and behavior

Restriction of free movement has historically been used as a model for inducing acute and chronic stress in laboratory animals. This paradigm is one of the most widely employed experimental procedures for basic research studies of stress-related disorders. It is easy to implement, and it rarely involves any physical harm to the animal. Many different restraint methods have been developed with variations in the apparatuses used and the degree of limitation of movement. Unfortunately, very few studies directly compare the differential impact of the distinct protocols. Additionally, restraint and immobilization terms are not differentiated and are sometimes used interchangeably in the literature. This review offers evidence of great physiological differences in the impact of distinct restraint procedures in rats and mice and emphasizes the need for a standardized language on this topic. Moreover, it illustrates the necessity of additional systematic studies that compare the effects of the distinct restraint methodologies, which would help to decide better which procedure should be used depending on the objectives of each particular study.

Stress-related impairment of fear memory acquisition and disruption of risk assessment behavior in female but not in male mice

Stress encompasses reactions to stimuli that promote negative and positive effects on cognitive functions, such as learning and memory processes. Herein, we investigate the effect of restraint stress on learning, memory, anxiety levels and locomotor activity of male and female mice. We used the plus-maze discriminative avoidance task (PMDAT), a behavioral task based on the innate exploratory response of rodents to new environments. Moreover, this task is used to simultaneously evaluate learning, memory, anxiety-like behavior and locomotor activity. Male and female mice were tested after repeated daily restraint stress (4h/day for 3 days). The results showed stress-induced deficits on aversive memory retrieval only in female mice, suggesting a sexual dimorphism on memory acquisition. Furthermore, stressed females exhibited increased anxiety-like behavior and decreased exploratory behavior. Plasma corticosterone levels were similarly increased by restraint stress in both sexes, suggesting that the behavioral outcome was not related to hormonal secretion. Our findings corroborate previous studies, showing a sexually dimorphic effect of restraint stress on cognition. In addition, our study suggests that stress-related acquisition deficit may be the consequence of elevated emotional response in females.

Sex differences in serum glucocorticoid levels and heterophil:lymphocyte ratios in adult pekin ducks (Anas platyrhynchos domesticus)

It is becoming more common for poultry scientists to utilize direct and indirect measures of stress hormones to monitor bird welfare. However, it has been clear that our understanding of the avian hypothalamic-pituitaryadrenal axis (HPA) is insufficient as evidenced by the many conflicting reports regarding stress responses, such as transportation stress, in poultry. It has long been assumed that the poultry HPA functions similarly to that of mammals, but now we know that there are considerable differences in the avian HPA compared to mammals. Synthesis and release of glucocorticoids (GC) are stimulated by adrenocorticotropin hormone (ACTH); GC are synthesized from a common pathway that begins with cholesterol and pregnenolone. The synthesis of one of the glucocorticoids does not depend upon the synthesis of the other. The purpose of our study was to test the hypothesis that ACTH will stimulate both corticosterone and cortisol release in ducks. To test this hypothesis, we injected artificial ACTH (cosyntropin; 0.0625 mg/kg, 0.031 mg/kg, or 0.016 mg/kg or saline as control) intramuscularly into adult drakes and hens (N = 10/sex/dose). Both glucocorticoids (GC) were assayed in serum using previously verified ELISAs. Blood smears were also assessed for heterophil to lymphocyte ratios (HLR). Data were analyzed by repeated measures 3-way ANOVA with Fishers PLSD as an ad hoc test. We observed that both GC were secreted in significantly (p = 0.0002) different patterns in a dose-dependent manner compared to controls, and that there was a significant (p = 0.0001) sex difference in both GC compared to saline controls. Further, we observed that all doses of ACTH elicited a significant (p = 0.004) sex difference in the HLR response compared to controls, but no dose-dependent effects were noted. Our data suggest that ducks, at least, may utilize more than just corticosterone to maintain physiological homeostasis in response to stress. Further, the time course of the stressor to release GC and subsequent HLR response may be dependent upon sex. More detailed analyses of the HPA are necessary in all avian species to better understand stress responses as we utilize biological bases for welfare assessments and stress responses.

Sex differences in glucocorticoid responses to shipping stress in Pekin ducks

Some concerns have been raised recently about the assay of corticosterone vs. cortisol in poultry species. Thus, we tested the hypothesis that ducks secrete both glucocorticoids. First, we validated two commercially ELISA kits for the two glucocorticoids by first charcoal stripping duck serum in order to remove all steroid hormones. We ran serial dilutions of spiked, charcoal-stripped serum on kits of opposite glucocorticoid as well as a serial dilution using the respective ELISA buffer of the opposite assay kit. We found that the glucocorticoid standard curve in duck serum matched the respective curve in that kit's own buffer. However, when the opposite hormone was run in each kit in both duck serum or ELISA buffer, a near zero slope was obtained. Second, we further validated the presence of both glucocorticoids using mass spectrometry. Third, we tested the hypothesis that exogenous ACTH would stimulate the release of both corticosterone and cortisol. And, fourth, we tested the hypothesis that each glucocorticoid would have different serum levels in response to shipping stress. To test this hypothesis, we collected serum from 10 drakes and 10 hens from 2 flocks (N = 20 per time point per sex): 24 h prior to shipping, at shipping as ducks were walked off the truck, 24 h after shipping, and 1 wk after shipping. Data were analyzed by 2-way repeated measures ANOVA. Surprisingly, we also observed a sex difference in both glucocorticoid levels in that hens showed higher (P < 0.01) serum levels than did drakes at all-time points in response to either ACTH or transportation. Finally, no differences were observed in either glucocorticoid levels associated with shipping in either sex. The fact that both glucocorticoids are released in measurable amounts lends to the possibility that they may be differentially regulated, or at least there is a sex difference in the neural pathways associated with glucocorticoid release in ducks. Although corticosterone is the likely predominate glucocorticoid in ducks, serious attention should be given to the role of cortisol in poultry. Further consideration of sex, age, and timing of blood collection to stressor needs to be considered when assessing glucocorticoid levels in any avian species.

A review of sex differences in the mechanisms and drivers of overeating

Disordered eating is often associated with marked psychological and emotional distress, and severe adverse impact on quality of life. Several factors can influence eating behavior and drive food consumption in excess of energy requirements for homeostasis. It is well established that stress and negative affect contribute to the aetiology of eating disorders and weight gain, and there is substantial evidence suggesting sex differences in sub-clinical and clinical types of overeating. This review will examine how negative affect and stress shape eating behaviors, and how the relationship between the physiological, endocrine, and neural responses to stress and eating behaviors differs between men and women. We will examine several drivers of overeating and explore possible mechanisms underlying sex differences in eating behavior.

Glucocorticoids in the Physiological and Transcriptional Regulation of 5-HT1A Receptor and the Pathogenesis of Depression

There is growing increase in the global prevalence of depression, but treatment outcome of this highly disabling disease is not satisfactory. Many patients are not benefitted by the currently prescribed antidepressants-together with this partial remission is very common. Improving treatment strategies and developing better therapeutic agents for treating depression is therefore highly needed. Stress-related epigenetic changes play a critical role in the pathogenesis as well as treatment of depression. Stressful events activate hypothalamic-pituitary-adrenal axis to increase circulating levels of glucocorticoids (GCs), and a greater sensitivity to this fright and flight response increases risk of depression. A role of serotonin (5-hydroxytryptamine; 5-HT) in responses to stress and in the pathogenesis and treatment of depression is well established. Substantial evidence supports a critical role of 5-HT1A receptors in these effects of 5-HT. The present article targets stress-induced higher and sustained increases of GCs and mediated influences on the physiological as well transcriptional regulation of 5-HT1A receptors to evaluate their causal role in the pathogenesis of depression. It is suggested that synthetic compounds with antagonist activity for GC receptors and agonist activity for 5-HT1A receptors may prove better therapeutic agents for treating depression.

Effects of tianeptine on behavioural and neurochemical responses to immobilization stress

The novel antidepressant drug tianeptine had an antidepressant-like effect on a rat model of depression based on the deficit in open field activity observed on the day after 2 h immobilization. Thus, tianeptine (10 mg/kg ip) given 2 h after the end of the immobilization period led to the deficit being opposed. Similar results were obtained using rats previously given 10 mg/kg of the drug per day for 13 days and a final dose 2 h after the end of immobilization. Other workers have found that tianeptine attenuates stress-induced activation of the hypothalamo-pituitary-adrenal axis. Possible relationships between these findings are discussed together with the paradoxical co-existence of the antidepressant properties of tianeptine with its ability to decrease the availability of 5-HT to receptors.

Circulating leptin, cortisol and gender differences associated with anorexia or obesity in depression

Objectives: To assess the role of circulating cortisol and leptin in depression associated with anorexia or obesity.Methods: Two hundred and fifty depressed patients presenting to the outpatient clinic of a psychiatric hospital and 250 non-depressed healthy volunteers were included in the study. The subjects of both groups were sub-grouped based upon their gender and BMI. Serum cortisol and leptin were determined by using respective ELISA kits.Results: The number of depressed than non-depressed subjects was three-fold higher in obese BMI groups of both genders. There were more depressed than non-depressed subjects in the underweight male BMI groups and in the overweight female BMI groups. There was a BMI-related increase in serum leptin and a decrease in serum cortisol in both genders. Depression in underweight BMI groups of both genders was associated with a decrease in serum leptin and an increase in cortisol. Higher serum leptin in obese BMI group was associated with a decrease in serum cortisol.Conclusions: Obesity is a risk factor for depression. The shift from typical to atypical depression is due to an inhibitory effect of higher circulating leptin on HPA axis activity and subsequent decrease in the lipolytic effects of cortisol.

Affective Behavior Shows Sex Differences in Mid-adulthood Rats Following Postnatal Immune Stimulation

Mid-adulthood represents the critical window period usually associated with the development of age-related diseases. Despite several attempts to delineate the pathological mechanisms underlying postnatal immune challenge and altered brain functions, the role of sex-dependent changes in affective behaviors of middle-aged animals requires more attention. In this study, we sought to investigate behavioral and molecular response patterns at mid-adulthood linked to early-life immune activation. Using affective behavioral test batteries, we showed that lipopolysaccharide (LPS)-induced postnatal immune challenge caused anxiety-like behaviors in both male and female Wistar rats at mid-adulthood, whereas only female rats exhibited depression-like behaviors. Our data further demonstrated a significant increase in microglial complexity and increased levels of tumor necrosis factor (TNFα), nitric oxide (NOx), and lipid peroxidation in the prefrontal cortex of female rats compared to their male counterparts and phosphate-buffered saline (PBS) littermate controls. With these results, we established significant interaction between sex differences and LPS-induced alterations in behavior and associated oxidative and immunohistochemical changes. These findings may provide an insight to better understand the neuroimmunological mechanisms of sex-dependent brain pathological manifestations occurring at mid-adulthood.

Chronic inflammatory pain drives alcohol drinking in a sex-dependent manner for C57BL/6J mice

Sex differences in chronic pain and alcohol abuse are not well understood. The development of rodent models is imperative for investigating the underlying changes behind these pathological states. In the present study, we investigated whether hind paw treatment with the inflammatory agent Complete Freund's Adjuvant (CFA) could generate hyperalgesia and alter alcohol consumption in male and female C57BL/6J mice. CFA treatment led to greater nociceptive sensitivity for both sexes in the Hargreaves test, and increased alcohol drinking for males in a continuous-access two-bottle choice (CA2BC) paradigm. Regardless of treatment, female mice exhibited greater alcohol drinking than males. Following a 2-h terminal drinking session, CFA treatment failed to produce changes in alcohol drinking, blood ethanol concentration (BEC), and plasma corticosterone (CORT) for both sexes. Two-hour alcohol consumption and CORT was higher in females than males, regardless of CFA treatment. Taken together, these findings have established that male mice are more susceptible to escalations in alcohol drinking when undergoing pain, despite higher levels of total alcohol drinking and CORT in females. Furthermore, the exposure of CFA-treated C57BL/6J mice to the CA2BC drinking paradigm has proven to be a useful model for studying the relationship between chronic pain and alcohol abuse. Future applications of the CFA/CA2BC model should incorporate manipulations of stress signaling and other related biological systems to improve our mechanistic understanding of pain and alcohol interactions.

Circadian and Ultradian Variations in Corticosterone Level Influence Functioning of the Male Mouse Basolateral Amygdala

The hypothalamic-pituitary-adrenal axis involves timed signaling between the hypothalamus, pituitary, and adrenal glands and back to the brain, causing an inherently oscillating system. Corticosteroids such as corticosterone (CORT) are secreted in a circadian rhythm, characterized by low and high levels at the start of the inactive and active phases, respectively. The circadian rhythm overarches ultradian CORT pulses, with approximate 1-hour interpulse intervals. We examined the physiological relevance of pulsatile CORT exposure for neurons of the basolateral amygdala (BLA), an area important for fear learning. We first applied four pulses of equal, high CORT concentration and measured the frequency of miniature excitatory postsynaptic currents (mEPSCs) reflecting spontaneous glutamate signaling. BLA neurons responded differently to each pulse, showing "metaplasticity," extending earlier studies. Next, we mimicked the progression of the inactive and active phases by four CORT pulses of increasing and decreasing concentrations, respectively. CORT pulses of increasing concentration were necessary and sufficient to gradually increase baseline (between-pulse) mEPSC frequency during the mimicked inactive phase, whereas the opposite was seen with decreasing CORT levels during the mimicked active phase. To study the relevance of changed glutamate transmission on behavior, mice were tested in tone-cued fear conditioning during the active or inactive phase. Animals tested at the inactive compared with the active phase showed efficient fear learning; this was also observed when animals tested during the active phase were treated with the CORT synthesis blocker metyrapone. This suggests that natural CORT rhythms influence electrical activity in the BLA, possibly contributing to altered behavioral function.

Associations between gastrointestinal-tract function and the stress response after weaning in pigs

Psychosocial stress is a major factor driving gastrointestinal-tract (GIT) pathophysiology and disease susceptibility in both humans and animals. Young weaned pigs typically undergo psychosocial and environmental stressors associated with production practices, including separation from their dam, mixing and crowding stress, transport and changed temperature and air-quality parameters, all of which can have significant deleterious impacts not only on performance but also on GIT structure and function, and, therefore, pig health and welfare. Strategies addressing some of these issues are explored in the current review, as well as discussion pertaining to sexual dimorphism in young pigs linked to stressful experiences, with young female pigs seemingly adversely affected more than their male counterparts. However, mechanisms governing susceptibility to stress-induced GIT functionality and disease remain inadequately understood.

Sex-specific differences in corticosterone secretion, behavioral phenotypes and expression of TrkB.T1 and TrkB.FL receptor isoforms: Impact of systemic TrkB inhibition and combinatory stress exposure in adolescence

Stress exposure has been implicated in the development of mood disorders, although little is known about the lasting effects of repeated stress during the adolescent period on sex-specific differences in endocrine and plasticity-signaling responses in adulthood. Using a 10-day combinatory stress paradigm (postnatal day (PND) 26 to 35), we examined sex-specific impact of adolescent stress and inhibition of tyrosine-related kinase B (TrkB) receptor (ANA-12; 0.5 mg/kg, i.p.) on 1) adolescent blood corticosterone levels, 2) adult locomotion and anxiety-like behavior, and 3) region-specific differences in endogenous TrkB full-length (TrkB.FL) and truncated (TrkB.T1) receptor isoforms. Blood collected on days 1, 5 and 10 revealed elevated basal and stress-induced CORT secretion in females compared to males, while ANA-12 attenuated CORT elevations post stress in both sexes. As adults, all females exhibited higher locomotor and exploratory activity than males in the open field test and elevated plus maze, and differences were comparable in the forced swim within stress-naïve and stress groups. Biochemically, vehicle-treated males showed elevated TrkB.T1 and TrkB.FL compared to vehicle-treated females in the PFC, hippocampus and NAc, and levels were consistently attenuated by ANA-12 treatment in non-stress males. With regards to stress exposure, expression of both isoforms was strongly down-regulated in the NAc of males only and was associated with increased TrkB.T1 in the PFC. ANA-12 enhanced expression in females, independent of stress exposure, compared to vehicle-treated counterparts, expression being increased for TrkB.T1 versus TrkB.FL and magnitude of the changes being region-specific. In contrast, ANA-12 effects in stressed males were restricted to inhibition of both isoforms in the hippocampus. Together, our findings support that TrkB activation, contingent on stress exposure, differentially affects TrkB isoform regulation during adulthood. Sex-specific biochemical responses at delayed intervals following adolescent stress exposure further support the need to include the sex variable in animal models.

Adhesive blood microsampling systems for steroid measurement via LC-MS/MS in the rat

INTRODUCTION

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) allows for the direct analysis of multiple hormones in a single probe with minimal sample volume. Rodent-based animal studies strongly rely on microsampling, such as the dry blood spot (DBS) method. However, DBS suffers the drawback of hematocrit-dependence (non-volumetric). Hence, novel volumetric microsampling techniques were introduced recently, allowing sampling of fixed accurate volumes. We compared these methods for steroid analysis in the rat to improve inter-system comparability.

EXPERIMENTAL

We analyzed steroid levels in blood using the absorptive microsampling devices Whatman® 903 Protein Saver Cards, Noviplex™ Plasma Prep Cards and the Mitra™ Microsampling device and compared the obtained results to the respective EDTA plasma levels. Quantitative steroid analysis was performed via LC-MS/MS. For the determination of the plasma volume factor for each steroid, their levels in pooled blood samples from each human adults and rats (18weeks) were compared and the transferability of these factors was evaluated in a new set of juvenile (21days) and adult (18weeks) rats. Hematocrit was determined concomitantly.

RESULTS

Using these approaches, we were unable to apply one single volume factor for each steroid. Instead, plasma volume factors had to be adjusted for the recovery rate of each steroid and device individually. The tested microsampling systems did not allow the use of one single volume factor for adult and juvenile rats based on an unexpectedly strong hematocrit-dependency and other steroid specific (pre-analytic) factors.

DISCUSSION

Our study provides correction factors for LC-MS/MS steroid analysis of volumetric and non-volumetric microsampling systems in comparison to plasma. It argues for thorough analysis of chromatographic effects before the use of novel volumetric systems for steroid analysis.

Effects of the combination of metyrapone and oxazepam on cocaine-induced increases in corticosterone in the medial prefrontal cortex and nucleus accumbens

We have previously demonstrated that a combination of drugs (i.e., metyrapone and oxazepam) known to attenuate HPA-axis activity effectively decreases cocaine self-administration and cue reactivity in rats. However, we did not find changes in plasma corticosterone that matched the behavioral effects we observed, indicating that a different mechanism of action must be involved. Therefore, we hypothesized that the combination of metyrapone and oxazepam attenuates cocaine taking and seeking by decreasing cocaine-induced increases in corticosterone in the brain. Male rats were implanted with guide cannulae targeting the medial prefrontal cortex or nucleus accumbens. After the rats recovered from surgery, the microdialysis session was conducted. Rats were housed in the experimental chamber and the dialysis probes inserted into the guide cannulae the night before the session. The following day, dialysate samples were collected over a five-hour session. Baseline samples were collected for the first two hours, every 20min. Samples were then collected following administration of cocaine (15mg/kg, ip). Before injections of cocaine, rats were pretreated with either vehicle or the combination of metyrapone (50mg/kg, ip) and oxazepam (10mg/kg, ip). The administration of cocaine resulted in an increase in corticosterone in the medial prefrontal cortex following vehicle pretreatment, which was not observed in the nucleus accumbens. This cocaine-induced increase in corticosterone was attenuated by metyrapone/oxazepam. Reducing cocaine-induced increases in corticosterone in the medial prefrontal cortex might represent a novel mechanism through which the combination of metyrapone/oxazepam produces its behavioral effects.

Neurochemical and behavioral effects of Nigella sativa and Olea europaea oil in rats

OBJECTIVES

In the last few decades, therapeutic uses of medicinal compounds present in food as a normal constituent has risen substantially, largely because of their fewer side effects and adequate efficacy. This study is designed to investigate a role of brain serotonin (5-HT) and dopamine (DA) in the potential nootropic, anxiolytic, and other beneficial effects of Nigella sativa (NS) and Olea europaea (OE) oil in rat models.

METHODS

Animals were treated with NS and OE oil orally at doses of 0.1 ml/kg and 0.25 ml/kg for 5 weeks. Food intake and body weight change, anxiety-like effects in elevated plus maze and activity in a novel and familiar environment were monitored weekly. Effects on learning and memory after 5 weeks treatment were monitored using Morris water maze test. Neurochemical analysis was carried using HPLC-ECD method.

RESULTS

NS and OE oil administration enhanced learning and memory in Morris water maze test and the effects were greater in NS than OE oil-treated animals. Low dose of OE oil increased exploration in an open field, higher dose of OE oil and both doses of NS oil produced no consistent effect on open field exploration. Effects of both oils on anxiety-like behavior, food and water intake, and activity in activity box were either not consistent or did not occur. The treatment increased homovanillic acid (HVA). 5-HT levels increased in high dose of NS oil and low dose of OE oil-treated groups. Low dose NS oil decreased 5-HT.

DISCUSSION

The present study suggests that active components in NS and OE oil may prove useful in treating impaired cognition. OE oil may produce psychostimulant-like effect. Modulation of DA and serotonin neurotransmission seems important in the pharmacological effect of these oils.

Behavioral, hormonal and central serotonin modulating effects of injected leptin

Leptin is viewed as an important target for developing novel therapeutics for obesity, depression/anxiety and cognitive dysfunctions. The present study therefore concerns behavioral, hormonal and central serotonin modulating effects of systemically injected leptin. Pharmacological doses (100 and 500 μg/kg) of leptin injected systemically decreased 24h cumulative food intake and body weight in freely feeding rats and improved acquisition and retention of memory in Morris water maze test. Potential anxiety reducing, hormonal and serotonin modulating effects of the peptide hormone were determined in a separate experiment. Animals injected with 100 or 500 μg/kg leptin were tested for anxiety in an elevated plus maze test 1h later. A significant increase in the number of entries and time passed in open arm of the elevated plus maze in leptin injected animals suggested pronounced anxiety reducing effect. Moreover, circulating levels of leptin correlated significantly with anxiety reducing effects of the peptide hormone. Serum serotonin increased and ghrelin decreased in leptin injected animals and correlated, positively and negatively respectively, with circulating leptin. Corticosterone increased at low dose and levels were normal at higher dose. Serotonin metabolism in the hypothalamus and hippocampus decreased only at higher dose of leptin. The results support a role of leptin in the treatment of obesity, anxiety and cognitive dysfunctions. It is suggested that hormonal and serotonin modulating effects of leptin can alter treatment efficacy in particularly comorbid conditions.

Investigations into the involvement of leptin in responses to stress

Stress is defined as a state that can threaten homeostasis in an organism to initiate the adaptive process. Stress mediators, which include the classic neuroendocrine hormones and a number of neurotransmitters, cytokines, and growth factors, regulate both basal and threatened homeostasis to help control the stress. Severity of stress, as well as malfunctioning of stress pathways, may impair its controllability, leading to the pathogenesis of psychiatric illnesses including depression. Leptin was initially identified as an antiobesity hormone, acting as a negative feedback adiposity signal to control energy homeostasis by binding to its receptors in the hypothalamus. Accumulating evidence has expanded the function of leptin from the control of energy balance to the regulation of other physiological and psychological processes. The aim of this paper is to evaluate the potential role of leptin in stress controllability. To this end, studies on the role of leptin in stress-induced activation of the hypothalamus-pituitary-adrenocortical axis, feeding behavior, learned helplessness, and other depression models have been accumulated. The knowledge accumulated in this article may facilitate the development of alternative treatment strategies, beyond serotonin and noradrenaline reuptake inhibition, for psychiatric care and stress-related disorders.

Development of the HPA axis: where and when do sex differences manifest?

Sex differences in the response to stress contribute to sex differences in somatic, neurological, and psychiatric diseases. Despite a growing literature on the mechanisms that mediate sex differences in the stress response, the ontogeny of these differences has not been comprehensively reviewed. This review focuses on the development of the hypothalamic-pituitary-adrenal (HPA) axis, a key component of the body's response to stress, and examines the critical points of divergence during development between males and females. Insight gained from animal models and clinical studies are presented to fully illustrate the current state of knowledge regarding sex differences in response to stress over development. An appreciation for the developmental timelines of the components of the HPA axis will provide a foundation for future areas of study by highlighting both what is known and calling attention to areas in which sex differences in the development of the HPA axis have been understudied.

Effects of cocaine on the hypothalamic-pituitary-adrenal axis

INTRODUCTION

Cocaine hydrochloride is a psychoactive substance extracted from the leaves of plants called Erythroxylum coca. Cocaine is the second most commonly used drug in the world after cannabis; 20 % of cocaine users will become long-term cocaine-dependent patients. Different routes of administration may be recognized: smokable modality, intranasal and intravenous. Cocaine is a potent stimulant of the sympathetic nervous system and causes structural changes on the brain, heart, lung, liver and kidney. It has long been known that use of cocaine may produce alterations to the endocrine system. Research on behavioral and neuroendocrine effects of cocaine dates back several years ago and has increasingly focused on alterations of the hypothalamic-pituitary-adrenal (HPA) axis, which appears to be the chief target of cocaine effects.

STUDIES

Animal (mainly rats and monkeys) and human studies have clearly shown a close relation between cocaine consumption and overdrive of the HPA axis. Such activation is likely involved, though via a still undefined mechanism, in the behavioral and cardiovascular changes of drug abusers as well as in the reinforcement/relapse phenomena. Further studies of the pathophysiology of cocaine addicts will help to devise new therapeutic strategies for these patients.

Chronic scream sound exposure alters memory and monoamine levels in female rat brain

Chronic scream sound alters the cognitive performance of male rats and their brain monoamine levels, these stress-induced alterations are sexually dimorphic. To determine the effects of sound stress on female rats, we examined their serum corticosterone levels and their adrenal, splenic, and thymic weights, their cognitive performance and the levels of monoamine neurotransmitters and their metabolites in the brain. Adult female Sprague-Dawley rats, with and without exposure to scream sound (4h/day for 21 day) were tested for spatial learning and memory using a Morris water maze. Stress decreased serum corticosterone levels, as well as splenic and adrenal weight. It also impaired spatial memory but did not affect the learning ability. Monoamines and metabolites were measured in the prefrontal cortex (PFC), striatum, hypothalamus, and hippocampus. The dopamine (DA) levels in the PFC decreased but the homovanillic acid/DA ratio increased. The decreased DA and the increased 5-hydroxyindoleacetic acid (5-HIAA) levels were observed in the striatum. Only the 5-HIAA level increased in the hypothalamus. In the hippocampus, stress did not affect the levels of monoamines and metabolites. The results suggest that scream sound stress influences most physiologic parameters, memory, and the levels of monoamine neurotransmitter and their metabolites in female rats.

The extra-adrenal effects of metyrapone and oxazepam on ongoing cocaine self-administration

Investigation of the role of stress in cocaine addiction has yielded an efficacious combination of metyrapone and oxazepam, hypothesized to decrease relapse to cocaine use by reducing stress-induced craving. However, recent data suggest an extra-adrenal role for metyrapone in mediating stress- and addiction-related behaviors. The interactions between the physiological stress response and cocaine self-administration were characterized in rodents utilizing surgical adrenalectomy and pharmacological treatment. Male Wistar rats were trained to self-administer cocaine (0.25mg/kg/infusion) and food pellets under a concurrent alternating fixed-ratio schedule of reinforcement. Surgical removal of the adrenal glands resulted in a significant decrease in plasma corticosterone and a consequent increase in ACTH, as expected. However, adrenalectomy did not significantly affect ongoing cocaine self-administration. Pretreatment with metyrapone, oxazepam and their combinations in intact rats resulted in a significant decrease in cocaine-reinforced responses. These same pharmacological treatments were still effective in reducing cocaine- and food-reinforced responding in adrenalectomized rats. The results of these experiments demonstrate that adrenally-derived steroids are not necessary to maintain cocaine-reinforced responding in cocaine-experienced rats. These results also demonstrate that metyrapone may produce effects outside of the adrenal gland, presumably in the central nervous system, to affect cocaine-related behaviors.

Habituation of hypothalamic-pituitary-adrenocortical axis hormones to repeated homotypic stress and subsequent heterotypic stressor exposure in male and female rats

Understanding potential sex differences in repeated stress-induced hypothalamic-pituitary-adrenocortical (HPA) axis habituation could provide insight into the sex-biased prevalence of certain affective disorders such as anxiety and depression. Therefore in these studies, male and female rats were exposed to 30 min of either audiogenic or restraint stress daily for 10 days in order to determine whether sex regulates the extent to which HPA axis hormone release is attenuated upon repeated homotypic stressor presentation. In response to the initial exposure, both stressors robustly increased plasma concentrations of both adrenocorticotropic hormone (ACTH) and corticosterone (CORT) in both sexes. Acutely, females displayed higher ACTH and CORT concentrations following restraint stress, whereas males exhibited higher hormone concentrations following loud noise stress. HPA axis hormone responses to both stressors decreased incrementally over successive days of exposure to each respective stressor. Despite the differential effect of sex on acute hormone responses, the extent to which HPA axis hormone response was attenuated did not differ between male and female animals following either stressor. Furthermore, ACTH and CORT responses to a novel environment were not affected by prior exposure to stress of either modality in either male or female rats. These experiments demonstrate that despite the acute stress response, male and female rats exhibit similar habituation of HPA axis hormones upon repeated homotypic stressor presentations, and that exposure to repeated stress does not produce exaggerated HPA axis hormone responses to a novel environment in either female or male rats.

Sex differences in the neurobiology of drug addiction

Epidemiological data demonstrate that while women report lower rates of drug use than men, the number of current drug users and abusers who are women continues to increase. In addition women progress through the phases of addiction differently than men; women transition from casual drug use to addiction faster, are more reactive to stimuli that trigger relapse, and have higher rates of relapse then men. Sex differences in physiological and psychological responses to drugs of abuse are well documented and it is well established that estrogen effects on dopamine (DA) systems are largely responsible for these sex differences. However, the downstream mechanisms that result from interactions between estrogen and the effects of drugs of abuse on the DA system are just beginning to be explored. Here we review the basic neurocircuitry which underlies reward and addiction; highlighting the neuroadaptive changes that occur in the mesolimbic dopamine reward and anti-reward/stress pathways. We propose that sex differences in addiction are due to sex differences in the neural systems which mediate positive and negative reinforcement and that these differences are modulated by ovarian hormones. This forms a neurobehavioral basis for the search for the molecular and cellular underpinnings that uniquely guide motivational behaviors and make women more vulnerable to developing and sustaining addiction than men.

The combination of metyrapone and oxazepam for the treatment of cocaine and other drug addictions

Although scientists have been investigating the neurobiology of psychomotor stimulant reward for many decades, there is still no FDA-approved treatment for cocaine or methamphetamine abuse. Research in our laboratory has focused on the relationship between stress, the subsequent activation of the hypothalamic-pituitary-adrenal (HPA) axis, and psychomotor stimulant reinforcement for almost 30 years. This research has led to the development of a combination of low doses of the cortisol synthesis inhibitor, metyrapone, and the benzodiazepine, oxazepam, as a potential pharmacological treatment for cocaine and other substance use disorders. In fact, we have conducted a pilot clinical trial that demonstrated that this combination can reduce cocaine craving and cocaine use. Our initial hypothesis underlying this effect was that the combination of metyrapone and oxazepam reduced cocaine seeking and taking by decreasing activity within the HPA axis. Even so, doses of the metyrapone and oxazepam combination that consistently reduced cocaine taking and seeking did not reliably alter plasma corticosterone (or cortisol in the pilot clinical trial). Furthermore, subsequent research has demonstrated that this drug combination is effective in adrenalectomized rats, suggesting that these effects must be mediated above the level of the adrenal gland. Our evolving hypothesis is that the combination of metyrapone and oxazepam produces its effects by increasing the levels of neuroactive steroids, most notably tetrahydrodeoxycorticosterone, in the medial prefrontal cortex and amygdala. Additional research will be necessary to confirm this hypothesis and may lead to the development of improved and specific pharmacotherapies for the treatment of psychomotor stimulant use.

Inhibition of immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion by injected leptin in rats

Leptin, originally identified as an anti-obesity hormone, also has an important role in the regulation of mood and emotion. The present study was designed to monitor effects of injected leptin on immobilization stress-induced anorexia, behavioral deficits, and plasma corticosterone secretion in rats. Exposure to 2 h immobilization stress decreased food intake and body weight in saline-injected animals. Animals exposed to open field, elevated plus maze, and light-dark transition tests the day following immobilization exhibited anxiety-like behavior. Leptin injected at doses of 0.1 and 0.5 mg/kg also decreased food intake and body weight in unstressed animals and elicited anxiolytic effects at dose of 0.5 mg/kg, monitored on the following day. Immobilization-induced decreases in food intake, body weight, as well as stress-induced behavioral deficits in the open field, elevated plus maze, and light-dark transition test were reversed by exogenous leptin in a dose-dependent (0.1-0.5 mg/kg) manner. Acute exposure to 2 h immobilization produced a fourfold rise in plasma levels of corticosterone. Animals injected with leptin at a dose of 0.1 mg/kg, but not at dose of 0.5 mg/kg, exhibited a marginal increase in plasma corticosterone. Immobilization-induced increases of plasma corticosterone were reversed by leptin injected at doses of 0.1 or 0.5 mg/kg. The data suggest that exogenous leptin can reduce stress perception, resulting in an inhibition of stress effects on the activity of hypothalamic-pituitary-adrenal axis and behavior. The reported pharmacological effects of leptin represent an innovative approach for the treatment of stress-related disorders.

Corticosterone synthesis inhibitor metyrapone preserves changes in maternal behavior and neuroendocrine responses during immunological challenge in lactating rats

Lactation is associated with profound behavioral and physiological adaptations in the mother that support reproductive success. These include neuroendocrine adaptation to stress that reduces anxiety-related behavior and emotional responsiveness. However, the way in which endogenous glucocorticoids secreted during immunological challenge influence the neuroendocrine system and behavior of lactating rats is not well understood. To evaluate the effects of glucocorticoids on the neuroendocrine response to suckling, maternal behavior and maternal anxiolysis, lactating female rats were treated with vehicle or metyrapone prior to the administration of a saline solution or a lipopolysaccharide (LPS) solution. LPS treatment reduced oxytocin and prolactin secretion during suckling and affected a variety of maternal behaviors, such as increasing the latency of retrieval a new nest, decreasing the number of pups gathered to the nest, increasing the latency of retrieving the first pup and decreasing the percentage of time spent in the arched-nursing position. In addition, the LPS treatment increased the baseline and avoidance latencies in an elevated T-maze. Pretreatment with metyrapone counteracted effects produced by LPS, including hormonal and behavioral responses in lactating rats. Taken together, our results indicate that stress induced by LPS treatment attenuates the neuroendocrine response to suckling, followed by disruption of maternal behavior and maternal anxiolysis in lactating female rats. These changes may be due to corticosterone release, as evidenced by the reversal of behavioral and neuroendocrine responses after immunological challenge in lactating rats that had been pretreated with metyrapone.

Effects of the combination of metyrapone and oxazepam on intravenous nicotine self-administration in rats

RATIONALE

Despite increased education regarding its dangers, cigarette smoking remains a significant public health concern due to serious associated health consequences such as cancer and respiratory and cardiovascular diseases. Most smokers fail in their attempts to quit smoking, and current pharmacological interventions have relatively low levels of efficacy and are associated with significant adverse events. We have previously reported that combinations of metyrapone and oxazepam, administered at doses that were ineffective when delivered singly, resulted in dose-related decreases in cocaine self-administration in rats while not affecting food-maintained responding during the same sessions.

OBJECTIVES

The current study was designed to test the effects of the administration of a metyrapone:oxazepam combination on nicotine self-administration in rats.

METHODS

Several dose combinations of metyrapone (12.5, 25 or 50 mg/kg) and oxazepam (5 or 10 mg/kg) were tested in rats trained to intravenously (IV) self-administer nicotine (0.03 mg/kg/infusion) during 1-h self-administration sessions using both fixed-ratio and progressive-ratio (PR) schedules of reinforcement.

RESULTS

The administration of low doses of metyrapone and oxazepam in combination significantly decreased IV nicotine self-administration in rats. At the lowest doses of 12.5 mg/kg of metyrapone and 5 mg/kg of oxazepam, the drugs alone did not decrease IV nicotine self-administration, but the combination was effective. Varenicline was also tested using the fixed-ratio schedule, and reductions in nicotine intake were similar to those seen with the moderate dose of the combination.

CONCLUSIONS

The results of this study suggest a potential utility of the combination of metyrapone and oxazepam for smoking cessation in humans.

Raphe-Hippocampal Serotonin Neurotransmission In The Sex Related Differences of Adaptation to Stress: Focus on Serotonin-1A Receptor

Stress is the major predisposing and precipitating factor in the onset of depression which is the most significant mental health risk for women. Behavioral studies in animal models show that female sex though less affected by an acute stressor; exposure to repeated stressors induces coping deficits to impair adaptation in them. A decrease in the function of 5-hydroxytryptamine (5-HT; serotonin) in the hippocampus and an increased function of the 5-HT-1A receptor in the raphe nucleus coexist in depression. Pharmacological and neurochemical data are relevant that facilitation of serotonin neurotransmission via hippocampus due to desensitization of somatodendritic 5-HT1A receptors may lead to adaptation to stress. The present article reviews research on sex related differences of raphe-hippocampal serotonin neurotransmission to find a possible answer that may account for the sex differences of adaptation to stress reported in preclinical research and greater incidence of depression in women than men.

Effects of the combination of metyrapone and oxazepam on cocaine craving and cocaine taking: a double-blind, randomized, placebo-controlled pilot study

Although cocaine dependence affects an estimated 1.6 million people in the USA, there are currently no medications approved for the treatment of this disorder. Experiments performed in animal models have demonstrated that inhibitors of the stress response effectively reduce intravenous cocaine self-administration. This exploratory, double-blind, placebo-controlled study was designed to assess the safety and efficacy of combinations of the cortisol synthesis inhibitor metyrapone, and the benzodiazepine oxazepam, in 45 cocaine-dependent individuals. The subjects were randomized to a total daily dose of 500 mg metyrapone/20 mg oxazepam (low dose), a total daily dose of 1500 mg metyrapone/20 mg oxazepam (high dose), or placebo for 6 weeks of treatment. The outcome measures were a reduction in cocaine craving and associated cocaine use as determined by quantitative measurements of the cocaine metabolite benzoylecgonine (BE) in urine at all visits. Of the randomized subjects, 49% completed the study. The combination of metyrapone and oxazepam was well tolerated and tended to reduce cocaine craving and cocaine use, with significant reductions at several time points when controlling for baseline scores. These data suggest that further assessments of the ability of the metyrapone and oxazepam combination to support cocaine abstinence in cocaine-dependent subjects are warranted.

Behavioral deficits and exaggerated feedback control over raphe-hippocampal serotonin neurotransmission in restrained rats

Serotonin (5-hydroxytryptamine, 5-HT), acting via the hippocampus, is thought to be critical for the neuroadaptation that alleviates the adverse effects of stress on emotion and behavior. It was hypothesized that a decrease in raphe-hippocampal serotonin neurotransmission caused by exaggerated feedback inhibition of 5-HT synthesis and release significantly contributes to stress-induced behavioral deficits. Acute exposure to 2 h of restraint stress increased 5-HT metabolism in the cortex and raphe region but had no such effect in the hippocampus. Exposure to 2 h of restraint stress elicited anxiety-like behavior, which was monitored in the light-dark transition test the next day. Animals sacrificed 24 h after termination of the stress period exhibited a decrease in the concentration of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus but not in the cortex and raphe. 8-Hydroxy-2-di-n-propylaminotetralin (8-OH-DPAT) injected at doses of 0.125, 0.25 and 0.5 mg/kg decreased 5-HT metabolism in the raphe, cortex and hippocampus of restrained and unrestrained animals, and the decreases in the raphe and hippocampus, but not those in the cortex, were greater in restrained than unrestrained animals. Exaggerated feedback control over raphe-hippocampal serotonin neurotransmission may be involved in the inability of the organism to cope with increased stress and elicits behavioral depression.

From stress to postpartum mood and anxiety disorders: how chronic peripartum stress can impair maternal adaptations

The peripartum period, in all mammalian species, is characterised by numerous adaptations at neuroendocrine, molecular and behavioural levels that prepare the female for the challenges of motherhood. These changes have been well characterised and, while they are necessary to ensure the survival and nurturance of the offspring, there is growing belief that they are also required for maternal mental health. Thus, while increased calmness and attenuated stress responsivity are common characteristics of the peripartum period, it also represents a time of increased susceptibility to mood disorders. While a number of risk factors for these disorders are known, their underlying aetiology remains poorly understood, due at least in part to a lack of appropriate animal models. One translatable risk factor is stress exposure during the peripartum period. In the following review we first describe common peripartum adaptations and the impact postpartum mood disorders have on these. We then discuss the known consequences of peripartum stress exposure on such maternal adaptations that have been described in basic research.

Sex differences in cortisol response to corticotropin releasing hormone challenge over puberty: Pittsburgh Pediatric Neurobehavioral Studies

OBJECTIVE

Consistent sex differences in regulation of the hypothalamic pituitary adrenocortical (HPA) axis have been shown in animal models and emerge over puberty. However, parallel work in humans is lacking despite implications for elucidating the emergence of sex differences in depression over puberty. We investigated sex differences in HPA response to corticotropin releasing hormone (CRH) challenge over puberty in a carefully screened normative sample.

METHODS

Participants were 68 healthy children (41% girls), ages 6-16, with no personal or family history of psychiatric disorder. Pubertal maturation was determined by Tanner staging. Following 24h of adaptation, 9-10 plasma cortisol samples were collected over 30-40 min pre-infusion baseline, 1 μg/kg CRH infusion, and 90-180 min post-infusion recovery. Thirty-seven participants completed 2+ CRH challenges allowing inclusion of cross-sectional and longitudinal data in all analyses. The influence of gender and pubertal maturation on parameters of cortisol response to CRH challenge was investigated using nonlinear mixed model methodology.

RESULTS

Girls showed increasing total cortisol output following CRH challenge over puberty, while boys showed little change in total cortisol output over puberty. Increased cortisol output in girls was explained by slower reactivity and recovery rates leading to prolonged time to reach peak cortisol and delayed return to baseline over puberty. Girls also showed increasing baseline cortisol over puberty, while boys showed declining baseline over puberty.

CONCLUSION

Results reveal subtle normative sex differences in the influence of pubertal maturation on HPA regulation at the pituitary level. This normative shift may tip the balance towards stress response dysregulation in girls at high risk for depression, and may represent one potential mechanism underlying elevated rates of depression among pubescent girls.

Neuropeptide Y (NPY)-induced reductions in alcohol intake during continuous access and following alcohol deprivation are not altered by restraint stress in alcohol-preferring (P) rats

Administration of neuropeptide Y (NPY) reduces anxiety-like behavior and alcohol intake in alcohol-preferring rats. The present experiment examined whether the effects of NPY on alcohol drinking are modulated by stress exposure during continuous access or following ethanol deprivation. Female P rats underwent 6 weeks of continuous access to 15% v/v ethanol and water prior to intracerebroventricular (ICV) cannula implantation. Deprived rats underwent two cycles of 5 days of ethanol exposure followed by 2 days of ethanol deprivation, while non-deprived rats had uninterrupted access to ethanol. Stressed rats in both ethanol access groups were exposed to restraint stress for 1h 4-6h after ethanol was removed from the deprived group in both cycles. ICV infusions of 5.0 μg NPY or aCSF were administered 48 h following the deprivation/stress procedure, after which ethanol was returned. Rats showed increased ethanol intake following ethanol deprivation compared to non-deprived controls. Food and water intake were increased, while ethanol intake was decreased, in rats infused with NPY. Stress did not increase ethanol intake or alter the response to NPY. Although no stress effects were found, the present experiment replicates previous findings regarding the effectiveness of NPY in reducing ethanol consumption. Future studies aimed at determining the extent to which stress may affect relapse to ethanol drinking and response to NPY would benefit from implementing different stress paradigms and varying the pattern of ethanol access.

Metyrapone blunts stress-induced hyperthermia and increased locomotor activity independently of glucocorticoids and neurosteroids

Metyrapone, a cytochrome P(450) inhibitor used to inhibit corticosterone synthesis, triggers biological markers of stress and also reduces stress-induced anxiety-like behaviors. To address these controversial effects, 6 separate investigations were carried out. In a first set of investigations, abdominal temperature (T(abd)), spontaneous locomotor activity (A(S)) and electroencephalogram (EEG) were recorded in freely moving rats treated with either saline or 150 mg kg(-1) metyrapone. An increase in T(abd) and A(S) occurred in saline rats, while, metyrapone rats exhibited an immediate decrease, both variables returning to basal values 5h later. Concomitantly, the EEG spectral power increased in the gamma and beta 2 bands and decreased in the alpha frequency band, and the EMG spectral power increased. This finding suggests that metyrapone depressed stress-induced physiological response while arousing the animal. In a second step, restraint stress was applied 5h after injection. Metyrapone significantly blunted the stress-induced T(abd) and A(S) rise, without affecting the brain c-fos mRNA increase. Corticosterone (5 and 40 mg kg(-1)) injected concomitantly to metyrapone failed to reverse the observed metyrapone-induced effects in T(abd) and A(S). Finasteride (50 mg kg(-1)), which blocks neurosteroid production, was also unable to block these effects. In conclusion, metyrapone acutely reduced stress-induced physiological response in freely behaving rats independently from glucocorticoids and neurosteroids.

Social influences on morphine sensitization in adolescent females

We recently observed that social interactions influence morphine responsiveness in adolescent males. Given sex-related differences in both social interactions and responses to morphine, the present study examines social influences on morphine sensitization in adolescent female mice. Four experimental groups were examined: (1) morphine-treated mice (twice daily, 10-40 mg/kg, s.c.) housed physically and visually separated from saline-treated mice ('morphine only'), (2) morphine-treated mice housed together with saline-treated mice ('morphine cage-mates (of saline)'), (3) saline-treated mice housed together with morphine-treated mice ('saline cage-mates (of morphine)'), and (4) saline-treated mice housed physically and visually separated from morphine-treated mice ('saline only'). Following the treatment period, mice were tested individually for their locomotor response to 20 mg/kg morphine (s.c.). There were no significant differences in morphine-induced hyper-locomotion between saline only and saline cage-mates (of morphine) female adolescent mice. Notably, morphine only mice exhibited significantly greater morphine sensitization as compared to morphine cage-mates (of saline). Thus, this study demonstrates social influences on morphine sensitization in adolescent females. Drug use during early adolescence is a key predictor of later drug abuse and dependence during adulthood. Thus, understanding the specific vulnerabilities to drug use in this age group may represent a first step in helping develop more effective treatment programs.

Depression during pregnancy and postpartum: contribution of stress and ovarian hormones

Depression is the most common psychiatric disease among women, exhibiting a prevalence which is 2-3x higher than in men. The postpartum period is considered the time of greatest risk for women to develop major depression and postpartum depression affects approximately 15% of women. A dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis is the most prominent endocrine change seen in depression and normalization of the HPA axis is a major target of recent therapies. Females exhibit different stress sensitivities than males which might contribute to their increased vulnerability for depression. Maternal stress or depression during pregnancy and/or postpartum is particularly concerning as early developmental influences can affect the maturation of the offspring as well as the mental health of the mother. Despite the urgent need for more information on depression in females, especially during pregnancy and postpartum, most animal models of depression have utilized only males. Given the sex differences in incidence of depression and treatment, it is vitally important to create or validate animal models of depression in females. This review will focus on the association between stress, glucocorticoids and depression in humans, with a special focus on depression in women during pregnancy and postpartum and on animal models of postpartum depression and the consequences for the offspring.

Self-administered and passive cocaine infusions produce different effects on corticosterone concentrations in the medial prefrontal cortex (MPC) of rats

Although our lab, as well as several others, has demonstrated a role for corticosterone in cocaine self-administration, there are no studies of the central dynamics of this hormone over the course of a behavioral session when rats are self-administering cocaine or receiving passive injections. The assay of corticosterone in microdialysates collected during such sessions allows for determinations of changes in brain corticosterone during drug-taking behavior. By using the combination of microdialysis in terminal fields for the mesocorticolimbic dopaminergic system and the yoked-triad model, one can distinguish between the direct cocaine-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis from the activation of the HPA axis related to drug-taking. In these experiments, we measured corticosterone in microdialysis samples collected from probes aimed at the medial prefrontal cortex, nucleus accumbens and basolateral amygdala in rats self-administering cocaine and receiving identical, passive infusions of cocaine or saline. While corticosterone was increased in all three brain regions in rats receiving cocaine, medial prefrontal cortex corticosterone was increased significantly more in rats receiving non-contingent infusions of the drug compared to rats self-administering cocaine. The results of these experiments demonstrate that control over drug delivery can affect the influence of a hormonal input on the functional characteristics of specific anatomical projections of the central nervous system. These results also provide evidence of the role steroid hormones play in shaping the functional activity of the brain.

ROLE OF SEROTONIN-1A RECEPTORS IN RESTRAINT-INDUCED BEHAVIORAL DEFICITS AND ADAPTATION TO REPEATED RESTRAINT STRESS IN RATS

8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a selective 5-hydroxy-tryptamine (5-HT; serotonin)-1A agonist was used to evaluate the role 5-HT-1 A receptors in restraint-induced behavioral deficits and adaptation to repeated restraint stress in rats. Animals were injected with 8-OH-DPAT at a dose of 0.25 mg/kg 1 h before exposing to an episode of 2 h/day restraint stress daily for 5 days. Effects of drug administration and restraint stress on 24 h cumulative food intakes were monitored daily. Intensity of 8-OH-DPAT-induced serotonin syndrome was also monitored each day before submitting animals to the episode of stress. Exposure to the first episode of 2 h restraint stress resulted in a decrease in 24 h cumulative food intake and an attenuation of 8-OH-DPAT-induced serotonin syndrome monitored next day. The deficits attenuated following 2nd and 3rd 2 h/day restraint were not observed following the 4th and 5th 2 h/day restraint. The decreases of food intake following 1st and 2nd day restraint sessions were smaller in 8-OH-DPAT than saline-injected animals. Administration of 8-OH-DPAT on day 6 elicited comparable serotonin syndrome in unrestrained and repeatedly restrained groups. Brain 5-HT metabolism decreased in unrestrained but not repeatedly restrained animals. The results suggest that a decrease in serotonergic neurotransmission is involved in restraint-induced behavioral deficits while a normalization of serotonin neurotransmission due to desensitization of somatodendritic 5-HT-1A receptors may help cope with the stress demand to produce adaptation to stress.