Influence of ovariectomy, estradiol and progesterone on the behavior of mice in an experimental model of depression

Astrocyte focal adhesion kinase reduces passive stress coping by inhibiting ciliary neurotrophic factor only in female mice

Astrocytes have been implicated in stress responses and produce ciliary neurotrophic factor (CNTF), which we have shown in the mouse medial amygdala (MeA) to promote passive stress coping response only in females. Pharmacological inhibition of focal adhesion kinase (FAK) upregulates CNTF expression. Here, we found that inducible knockout of FAK in astrocytes or systemic treatment with an FAK inhibitor increased passive coping behavior, i.e., immobility, in an acute forced swim stress test in female, but not male, mice. Strikingly, four weeks of chronic unpredictable stress (CUS) did not further increase passive coping in female astrocytic FAK knockout mice, whereas it exacerbated it in female wildtype mice and male mice of both genotypes. These data suggest that astrocyte FAK inhibition is required for chronic stress-induced passive coping in females. Indeed, CUS reduced phospho-FAK and increased CNTF in the female MeA. Progesterone treatment after ovariectomy activated amygdala FAK and alleviated ovariectomy-induced passive coping in wildtype, but not astrocytic FAK knockout females. This suggests that progesterone-mediated activation of FAK in astrocytes reduces female stress responses. Finally, astrocytic FAK knockout or FAK inhibitor treatment increased CNTF expression in the MeA of both sexes, although not in the hippocampus. As mentioned, MeA CNTF promotes stress responses only in females, which may explain the female-specific role of astrocytic FAK inhibition. Together, this study reveals a novel female-specific progesterone-astrocytic FAK pathway that counteracts CNTF-mediated stress responses and points to opportunities for developing treatments for stress-related disorders in women.

Estrogen, the Peripheral Immune System and Major Depression – A Reproductive Lifespan Perspective

Major depression is a significant medical issue impacting millions of individuals worldwide. Identifying factors contributing to its manifestation has been a subject of intense investigation for decades and several targets have emerged including sex hormones and the immune system. Indeed, an extensive body of literature has demonstrated that sex hormones play a critical role in modulating brain function and impacting mental health, especially among female organisms. Emerging findings also indicate an inflammatory etiology of major depression, revealing new opportunities to supplement, or even supersede, currently available pharmacological interventions in some patient populations. Given the established sex differences in immunity and the profound impact of fluctuations of sex hormone levels on the immune system within the female, interrogating how the endocrine, nervous, and immune systems converge to impact women’s mental health is warranted. Here, we review the impacts of endogenous estrogens as well as exogenously administered estrogen-containing therapies on affect and immunity and discuss these observations in the context of distinct reproductive milestones across the female lifespan. A theoretical framework and important considerations for additional study in regards to mental health and major depression are provided.

Estradiol attenuates chronic restraint stress-induced dendrite and dendritic spine loss and cofilin1 activation in ovariectomized mice

Ovarian hormone deprivation is associated with mood disorders, such as depression, and estradiol therapy is significantly more effective than placebos in treating major depression associated with menopause onset. However, the effect of estradiol on neuronal plasticity and its mechanisms remain to be further elucidated. In this study, behavioral assessments were used to examine the antidepressant effect of estradiol in ovariectomized (OVX) B6.Cg-TgN (Thy-YFP-H)-2Jrs transgenic mice on chronic restraint stress (CRS)-induced dendrite and dendritic spine loss; Yellow fluorescent protein (YFP) is characteristically expressed in excitatory neurons in transgenic mice, and its three-dimensional images were used to evaluate the effect of estradiol on the density of different types of dendritic spines. Quantification and distribution of cofilin1 and p-cofilin1 were determined by qPCR, Western blots, and immunohistochemistry, respectively. The results revealed that treatment with estradiol or clomipramine significantly improved depression-like behaviors. Estradiol treatment also significantly upregulated the dendritic density in all areas examined and increased the density of filopodia-type, thin-type and mushroom-type spines in the hippocampal CA1 and elevated the thin-type and mushroom-type spine density in the PFC. Consistent with these changes, estradiol treatment significantly increased the density of p-cofilin1 immunopositive dendritic spines. Thus, these data reveal a possible estradiol antidepressant mechanism, in that estradiol promoted the phosphorylation of cofilin1 and reduced the loss of dendrites and dendritic spines, which of these dendritic spines include not only immature spines such as filopodia-type, but also mature spines such as mushroom-type, and attenuated the depression-like behavior.

Long-term oral administration of a novel estrogen receptor beta agonist enhances memory and alleviates drug-induced vasodilation in young ovariectomized mice

Development of estrogen therapies targeting the β (ERβ) but not α (ERα) estrogen receptor is critically needed for the treatment of negative menopausal symptoms, as ERα activation increases health risks like cancer. Here, we determined the effects of long-term oral treatment with EGX358, a novel highly selective ERβ agonist, on memory, vasodilation, and affect in young ovariectomized mice. Mice were orally gavaged daily for 9 weeks with vehicle, 17β-estradiol (E₂), the ERβ agonist diarylpropionitrile (DPN), or EGX358 at doses that enhance memory when delivered acutely. Tail skin temperature was recorded as a proxy for vasodilation following injection of vehicle or senktide, a tachykinin receptor 3 agonist used to model hot flashes. Anxiety-like behavior was assessed in the open field (OF) and elevated plus maze (EPM), and depression-like behavior was measured in the tail suspension (TST) and forced swim tests (FST). Finally, memory was assessed in object recognition (OR) and object placement (OP) tasks. E₂, DPN, and EGX358 reduced senktide-mediated increases in tail skin temperature compared to vehicle. All three treatments also enhanced memory in the OR and OP tasks, whereas vehicle did not. Although E₂ increased time spent in the center of the OF, no other treatment effects were observed in the OF, EPM, TST, or FST. These data suggest that long-term ERβ activation can reduce hot flash-like symptoms and enhance spatial and object recognition memories in ovariectomized mice. Thus, the highly selective ERβ agonist EGX358 may be a promising avenue for reducing menopause-related hot flashes and memory dysfunction.

The antidepressant and anxiolytic effect of GPER on translocator protein (TSPO) via protein kinase a (PKA) signaling in menopausal female rats

Postmenopausal depression is mainly caused by the deprivation of ovarian hormones during menopausal transition, it is of great importance to study on the treatment that could effectively relieve symptoms of menopausal depression with fewer side effects. Activation of G-protein-coupled estrogen receptor (GPER) has long been reported to facilitate neuronal plasticity and improve cognition in animals. Meanwhile, it could participate in regulation of intracellular signaling pathways through the characteristic of GPER, ameliorate intracellular mitochondrial function and oxidative stress. However, the impact of GPER on regulating estrogen deprived-depressant and anxious behaviors is still largely unknown. Here we used the ovariectomized female rats to imitate the condition of menopause. Owing to the lateral ventricle administration of G-1 which specifically react with GPER receptor intracerebrally, Ovariectomized (OVX) female rats showed depressive- or anxiety-like phenotypes with attenuated mitochondrial function. In addition, G-1 facilitated PKA activation, which further accelerated TSPO phosphorylation and alleviated menopausal depression- and anxiety-like behaviors. Moreover, PKA inhibitor PKI could partially antagonized the anti-anxiety and anti-depression effects of G-1. Taken together, we concluded that GPER activation might exhibit antidepressant and anxiolytic effect by elevating TSPO phosphorylation via protein kinase A signaling and rescuing the redox status in menopausal female rats.

Effects of Vitamin D3 in Long-Term Ovariectomized Rats Subjected to Chronic Unpredictable Mild Stress: BDNF, NT-3, and NT-4 Implications

The purpose of this study was to explore the antidepressant-like effects of vitamin D₃ at different doses (1.0, 2.5, and 5.0 mg/kg sc) on a model of depression produced by chronic unpredictable mild stress (CUMS) for 28 days in long-term (3 months) ovariectomized (OVX) adult rats. Sucrose preference (SPT), forced swimming (FST) and open-field (OFT) tests were conducted to examine the depression-like state. Serum corticosterone/adrenocorticotrophic hormone (ACTH) levels and hippocampal brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3/NT-4 expressions by ELISA kits and/or western blotting were determined to assess the possible mechanisms of the vitamin D₃ effects on the depression-like profile in long-term OVX rats subjected to CUMS. The results showed that vitamin D₃ (5.0 mg/kg), as well as fluoxetine treatment, considerably reversed the depression-like state in the SPT and FST, decreased serum corticosterone/ACTH levels, and increased BDNF and NT-3/NT-4 levels in the hippocampus of long-term OVX rats compared to OVX rats with CUMS (p < 0.05). Thus, a high dose of vitamin D₃ (5.0 mg/kg sc) could improve the depression-like profile in long-term OVX adult female rats subjected to the CUMS procedure, which might be mediated by the regulation of BDNF and the NT-3/NT-4 signaling pathways in the hippocampus, as well as the corticosterone/ACTH levels of the blood serum.

Additive antidepressant-like effects of fasting with β-estradiol in mice

Our recent study has shown that acute fasting produces antidepressant‐like effects in male mice. However, there is little evidence regarding the antidepressant‐like effects of acute fasting in female mice. Moreover, it is not yet clear whether estrogen produces additive effects with acute fasting. Therefore, this study aims to investigate the antidepressant‐like effects of acute fasting plus estrogen treatment. In this study, the acute fasting produced antidepressant‐like effects in female mice and the antidepressant‐like effects of 9 hours fasting with those of β‐estradiol (E2) were additive. Activity of the cyclic adenosine monophosphate (cAMP) response element‐binding protein (CREB)‐brain‐derived neurotrophic factor (BDNF) pathway in the prefrontal cortex (PFC) and hippocampus (HP) was increased, as well as neurogenesis in the subgranular zone of the hippocampus. Serum ghrelin and estrogen were also increased by fasting plus E2. Furthermore, RNA‐seq analysis indicated that fasting and E2 co‐regulate similar gene expression pathways, underlying similar neurological functions. Taken together, these data suggest that E2 produces additive antidepressant‐like effects with fasting by activating the CREB‐BDNF pathway in the PFC and HP. Genome‐wide transcriptome mapping suggests that fasting may be used as an adjunct to estrogen replacement therapy for the treatment of depression associated with reduced estrogen function.

Pathophysiological mechanisms implicated in postpartum depression

This review aims to summarize the diverse proposed pathophysiological mechanisms contributing to postpartum depression, highlighting both clinical and basic science research findings. The risk factors for developing postpartum depression are discussed, which may provide insight into potential neurobiological underpinnings. The evidence supporting a role for neuroendocrine changes, neuroinflammation, neurotransmitter alterations, circuit dysfunction, and the involvement of genetics and epigenetics in the pathophysiology of postpartum depression are discussed. This review integrates clinical and preclinical findings and highlights the diversity in the patient population, in which numerous pathophysiological changes may contribute to this disorder. Finally, we attempt to integrate these findings to understand how diverse neurobiological changes may contribute to a common pathological phenotype. This review is meant to serve as a comprehensive resource reviewing the proposed pathophysiological mechanisms underlying postpartum depression.

Hormonal Regulation of Hippocampal Neurogenesis: Implications for Depression and Exercise

Adult hippocampal neurogenesis exists in all mammalian species, including humans, and although there has been considerable research investigating the function and regulation of neurogenesis, there remain many open questions surrounding the complexity of this phenomenon. This stems partially from the fact that neurogenesis is a multistage process that involves proliferation, differentiation, migration, survival, and eventual integration of new cells into the existing hippocampal circuitry, each of which can be independently influenced. The function of adult neurogenesis in the hippocampus is related to stress regulation, behavioral efficacy of antidepressants, long-term spatial memory, forgetting, and pattern separation. Steroid hormones influence the regulation of hippocampal neurogenesis, stress regulation, and cognition and differently in males and females. In this chapter, we will briefly tap into the complex network of steroid hormone modulation of neurogenesis in the hippocampus with specific emphasis on stress, testosterone, and estrogen. We examine the possible role of neurogenesis in the etiology of depression and influencing treatment by examining the influence of both pharmacological (selective serotonin reuptake inhibitors, tricyclic antidepressants) treatments and non-pharmacological (exercise) remedies.

Novel oestrogen receptor β-selective ligand reduces obesity and depressive-like behaviour in ovariectomized mice

Hormonal changes due to menopause can cause various health problems including weight gain and depressive symptoms. Multiple lines of evidence indicate that oestrogen receptors (ERs) play a major role in postmenopausal obesity and depression. However, little is known regarding the ER subtype-specific effects on obesity and depressive symptoms. To delineate potential effects of ERβ activation in postmenopausal women, we investigated the effects of a novel oestrogen receptor β-selective ligand (C-1) in ovariectomized mice. Uterine weight, depressive behaviour, and weight gain were examined in sham-operated control mice and ovariectomized mice administered placebo, C-1, or 17β-oestradiol (E2). Administration of C-1 or E2 reduced body weight gain and depressive-like behaviour in ovariectomized mice, as assessed by the forced swim test. In addition, administration of E2 to ovariectomized mice increased uterine weight, but administration of C-1 did not result in a significant increase in uterine weight. These results suggest that the selective activation of ERβ in ovariectomized mice may have protective effects against obesity and depressive-like behaviour without causing an increase in uterine weight. The present findings raise the possibility of the application of ERβ-ligands such as C-1 as a novel treatment for obesity and depression in postmenopausal women.

The interaction of dietary isoflavones and estradiol replacement on behavior and brain-derived neurotrophic factor in the ovariectomized rat

Phytoestrogens are plant derived, non-steroidal compounds naturally found in rodent chows that potentially have endocrine-disrupting effects. Isoflavones, the most common phytoestrogens, have a similar structure and molecular weight to 17β-estradiol (E2) and have the ability to bind and activate both isoforms of the estrogen receptor (ER). Most isoflavones have a higher affinity for ERβ, which is involved in sexually dimorphic behavioral regulation. The goal of this study was to examine the interaction of isoflavones and E2 presence in the OVX rat on anxiety- and depressive- like behavior and the related BDNF pathophysiology. E2 administration resulted in anxiogenic behaviors when isoflavones were present in the diet (p<0.05), but anxiolytic behaviors when isoflavones were not present (p<0.05). E2 resulted in antidepressive-like behaviors in animals fed an isoflavone-rich diet (p<0.05), with no effect when isoflavones were removed. Increased hippocampal BDNF expression was observed in animals fed an isoflavone-rich diet after E2 administration (p<0.05). BDNF expression in the amygdala and hypothalamus was increased after E2 treatment in animals fed an isoflavone-rich diet. Overall, these results demonstrate that the presence of dietary isoflavones can differentially regulate the effect of E2 replacement on behavior and BDNF expression.

Prepubertal Ovariectomy Exaggerates Adult Affective Behaviors and Alters the Hippocampal Transcriptome in a Genetic Rat Model of Depression

Major depressive disorder (MDD) is a debilitating illness that affects twice as many women than men postpuberty. This female bias is thought to be caused by greater heritability of MDD in women and increased vulnerability induced by female sex hormones. We tested this hypothesis by removing the ovaries from prepubertal Wistar Kyoto (WKY) more immobile (WMI) females, a genetic animal model of depression, and its genetically close control, the WKY less immobile (WLI). In adulthood, prepubertally ovariectomized (PrePubOVX) animals and their Sham-operated controls were tested for depression- and anxiety-like behaviors, using the routinely employed forced swim and open field tests, respectively, and RNA-sequencing was performed on their hippocampal RNA. Our results confirmed that the behavioral and hippocampal expression changes that occur after prepubertal ovariectomy are the consequences of an interaction between genetic predisposition to depressive behavior and ovarian hormone-regulated processes. Lack of ovarian hormones during and after puberty in the WLIs led to increased depression-like behavior. In WMIs, both depression- and anxiety-like behaviors worsened by prepubertal ovariectomy. The unbiased exploration of the hippocampal transcriptome identified sets of differentially expressed genes (DEGs) between the strains and treatment groups. The relatively small number of hippocampal DEGs resulting from the genetic differences between the strains confirmed the genetic relatedness of these strains. Nevertheless, the differences in DEGs between the strains in response to prepubertal ovariectomy identified different molecular processes, including the importance of glucocorticoid receptor-mediated mechanisms, that may be causative of the increased depression-like behavior in the presence or absence of genetic predisposition. This study contributes to the understanding of hormonal maturation-induced changes in affective behaviors and the hippocampal transcriptome as it relates to genetic predisposition to depression.

Antidepressant-like effects of YL-IPA08, a potent ligand for the translocator protein (18 kDa) in chronically stressed rats

The present study aimed to examine the molecular and cellular mechanisms underlying the antidepressant-like effect of YL-IPA08, a novel TSPO ligand designed and synthesized at our institute. We firstly used the chronic unpredictable stress (CUS) procedure of rats, a well validated stress-related animal model of depression, to further determine the antidepressant-like of YL-IPA08. And we found that YL-IPA08 caused significant suppression of inhibiting of locomotor activity, reducing the sucrose preference and increasing the latency to eat induced by CUS. In addition, YL-IPA08 treatment increased the levels of progesterone and allopregnanolone in the hippocampus and prefrontal cortex of post- CUS rats. Furthermore, long-term YL-IPA08 administration reversed dendritic shrinkage, down-regulation of neurotrophic signaling pathway within the hippocampus, as well as HPA dysfunctions simultaneously observed in the CUS rats. Collectively, the evidence presented above supports the notion that binding to TSPO and the subsequent synthesis of neurosteroid, maintenance of hippocampal morphologic and functional plasticity, and preventing HPA axis dysfunction, may account for the profound molecular and cellular mechanism underlying the antidepressant-like effect of YL-IPA08.

Improvement of neurological disorders in postmenopausal model rats by administration of royal jelly

OBJECTIVE

Royal jelly (RJ) from honeybees (Apis mellifera) has estrogenic activity. Estrogen deficiency after menopause leads to a high risk of memory impairment and depression as well as metabolic syndrome and osteoporosis. We here investigated the effect of RJ on memory impairment and depression-like behaviors in ovariectomized (OVX) rats.

METHODS

OVX rats were administered with RJ for 82 days. Hippocampus-dependent spatial memory and depression-like behaviors were assessed by the Morris water maze test and the forced swimming test, respectively. The weights of body, brain and uterus and the contents of protein and myelin galactolipids including galactosylceramide and sulfatide were measured.

RESULTS

Memory impairment and depression-like behaviors in OVX rats were recovered to the levels of sham-operated rats by RJ administration. Increased body weight and decreased uterine weight in OVX rats were recovered to the levels of sham-operated rats by 17β-estradiol (E2) administration but not by RJ administration. In contrast, brain weight was slightly increased by RJ administration but not by E2 administration. The contents of protein and myelin galactolipids were higher in the brains of RJ-administered OVX rats than in the brains of E2-administered OVX rats.

CONCLUSION

The results suggest that RJ has a beneficial effect on neurological symptoms of a menopausal disorder.

Review: Puberty as a time of remodeling the adult response to ovarian hormones

During pubertal development, an animal's response to stress changes and sexual differentiation of the brain and behavior continue. We discovered that particular stressors, such as shipping from suppliers or an immune challenge with lipopolysaccharide, during the prolonged pubertal period of female mice result in long-term changes in behavioral responsiveness of the brain to estradiol assessed in adulthood. All behaviors influenced by estradiol and/or progesterone that we have studied are compromised by a stressor during pubertal development. Depending on the behavior, immune challenge or shipping from suppliers during pubertal development decreases, eliminates, or even reverses the effects of estradiol. Shipping during this period causes changes in the number of estrogen receptor-immunoreactive cells in key brain areas suggesting one cellular mechanism for this remodeling of the brain's response to hormones. We suggest that particular adverse experiences in girls may cause long-term alterations in the brain's response to estradiol and/or progesterone via activation of the immune system. This in turn could lead to an alteration in any aspect of mental health that is influenced by estradiol.

17α-ethinyl estradiol attenuates depressive-like behavior through GABAA receptor activation/nitrergic pathway blockade in ovariectomized mice

OBJECTIVES

This study was performed to investigate the antidepressant-like effect of 17α-ethinyl estradiol (EE2) in ovariectomized (OVX) mice and the possible role of nitrergic and gamma aminobutyric acid (GABA)ergic pathways in this paradigm.

METHODS

Bilateral ovariectomy was performed in female mice, and different doses of EE2 were intraperitoneally injected either alone or combined with GABAA agonist, diazepam, GABAA antagonist, flumazenil, non-specific nitric oxide synthase (NOS) inhibitor, N(ω)-nitro-L-arginine methyl ester (L-NAME), specific nNOS inhibitor, 7-nitroindazole (7-NI), a nitric oxide (NO) precursor, L-arginine, and selective PDE5I, sildenafil. After locomotion assessment, immobility times were recorded in the forced swimming test (FST) and tail suspension test (TST). Moreover, hippocampal nitrite concentrations were measured in the examined groups.

RESULTS

Ten days after ovariectomy, a significant prolonged immobility times were observed. EE2 (0.3 and 1μg/kg and 0.03, 0.1, and 1mg/kg) caused antidepressant-like activity in OVX mice in FST and TST. Diazepam (1 and 5mg/kg), L-NAME (30mg/kg), and 7-NI (100mg/kg) significantly reduced the immobility times. Co-administration of minimal and sub-effective doses of EE2 and diazepam (0.3μg/kg and 0.5mg/kg, respectively) exerted a significant antidepressant-like effect. The same effect was observed in combination of minimal and sub-effective doses of EE2 and either L-NAME or 7-NI. Moreover, combination of minimal and sub-effective doses of EE2, diazepam either L-NAME, or 7-NI emphasized the significant robust antidepressant-like activity.

CONCLUSIONS

The study has demonstrated that lowest dose of EE2 exerts a significant antidepressant-like behavior. It is suggested that suppression of NO system, as well as GABAA activation, may be responsible for antidepressant-like activity of EE2 in OVX mice. Moreover, GABAA activation may inhibit nitrergic pathway.

EFFICACY OF ESTRADIOL IN PERIMENOPAUSAL DEPRESSION: SO MUCH PROMISE AND SO FEW ANSWERS

BACKGROUND

Controversy regarding the antidepressant efficacy of hormone replacement therapy (HRT) stems almost from its inception and reflects the same methodological inconsistencies that have compromised efforts to determine whether the perimenopause is accompanied by an increase in mood symptoms or depression. Methodologic differences of note (other than study design) include menopausal state (perimenopause vs. postmenopause), determination of state (earlier studies used age as a proxy measure), baseline symptomatology (asymptomatic vs. depressive symptoms vs. syndromic depression), route of hormone administration (transdermal vs. oral), and symptom or syndrome measure. Zweifel and O'Brien's 1997 meta-analysis included 26 studies of the effects of menopausal HRT on depressed mood and revealed an overall effect size of 0.68. This moderate to large effect size, showing lower ratings of depressed mood in treated patients compared with controls, implicated HRT as a potential treatment of or prophylactic for depression in menopausal women. Since this publication, multiple studies have aimed to discern the relationship between HRT and menopausal mood.

METHODS

The purpose of this systematic review is to examine the findings and quality of the evidence amassed since Zweifel and O'Brien's meta-analysis.

RESULTS

Of the 24 studies meeting criteria for review, only five RCTs examined depressed subjects, and only two of the study samples were solely perimenopausal.

CONCLUSIONS

One can generalize from the studies reviewed here only with great caution, but there is little evidence to support the use of estradiol to improve mood in nondepressed patients (not surprisingly) and some evidence to support the antidepressant efficacy of estradiol in perimenopausal but not postmenopausal women.

The role of reproductive hormones in postpartum depression

Despite decades of research aimed at identifying the causes of postpartum depression (PPD), PPD remains common, and the causes are poorly understood. Many have attributed the onset of PPD to the rapid perinatal change in reproductive hormones. Although a number of human and nonhuman animal studies support the role of reproductive hormones in PPD, several studies have failed to detect an association between hormone concentrations and PPD. The purpose of this review is to examine the hypothesis that fluctuations in reproductive hormone levels during pregnancy and the postpartum period trigger PPD in susceptible women. We discuss and integrate the literature on animal models of PPD and human studies of reproductive hormones and PPD. We also discuss alternative biological models of PPD to demonstrate the potential for multiple PPD phenotypes and to describe the complex interplay of changing reproductive hormones and alterations in thyroid function, immune function, hypothalamic-pituitary-adrenal (HPA) axis function, lactogenic hormones, and genetic expression that may contribute to affective dysfunction. There are 3 primary lines of inquiry that have addressed the role of reproductive hormones in PPD: nonhuman animal studies, correlational studies of postpartum hormone levels and mood symptoms, and hormone manipulation studies. Reproductive hormones influence virtually every biological system implicated in PPD, and a subgroup of women seem to be particularly sensitive to the effects of perinatal changes in hormone levels. We propose that these women constitute a "hormone-sensitive" PPD phenotype, which should be studied independent of other PPD phenotypes to identify underlying pathophysiology and develop novel treatment targets.

The Antidepressant-like Effects of Estrogen-mediated Ghrelin

Ghrelin, one of the brain-gut peptides, stimulates food-intake. Recently, ghrelin has also shown to play an important role in depression treatment. However, the mechanism of ghrelin's antidepressant-like actions is unknown. On the other hand, sex differences in depression, and the fluctuation of estrogens secretion have been proved to play a key role in depression. It has been reported that women have higher level of ghrelin expression, and ghrelin can stimulate estrogen secretion while estrogen acts as a positive feedback mechanism to up-regulate ghrelin level. Ghrelin may be a potential regulator of reproductive function, and estrogen may have additional effect in ghrelin's antidepressantlike actions. In this review, we summarize antidepressant-like effects of ghrelin and estrogen in basic and clinical studies, and provide new insight on ghrelin's effect in depression.

Ovariectomy results in variable changes in nociception, mood and depression in adult female rats

Decline in the ovarian hormones with menopause may influence somatosensory, cognitive, and affective processing. The present study investigated whether hormonal depletion alters the nociceptive, depressive-like and learning behaviors in experimental rats after ovariectomy (OVX), a common method to deplete animals of their gonadal hormones. OVX rats developed thermal hyperalgesia in proximal and distal tail that was established 2 weeks after OVX and lasted the 7 weeks of the experiment. A robust mechanical allodynia was also occurred at 5 weeks after OVX. In the 5^th week after OVX, dilute formalin (5%)-induced nociceptive responses (such as elevating and licking or biting) during the second phase were significantly increased as compared to intact and sham-OVX females. However, chronic constriction injury (CCI) of the sciatic nerve-induced mechanical allodynia did not differ as hormonal status (e.g. OVX and ovarian intact). Using formalin-induced conditioned place avoidance (F-CPA), which is believed to reflect the pain-related negative emotion, we further found that OVX significantly attenuated F-CPA scores but did not alter electric foot-shock-induced CPA (S-CPA). In the open field and forced swimming test, there was an increase in depressive-like behaviors in OVX rats. There was no detectable impairment of spatial performance by Morris water maze task in OVX rats up to 5 weeks after surgery. Estrogen replacement retrieved OVX-induced nociceptive hypersensitivity and depressive-like behaviors. This is the first study to investigate the impacts of ovarian removal on nociceptive perception, negative emotion, depressive-like behaviors and spatial learning in adult female rats in a uniform and standard way.

Enhancement of BDNF concentration and restoration of the hypothalamic-pituitary-adrenal axis accompany reduced depressive-like behaviour in stressed ovariectomised rats treated with either Tualang honey or estrogen

A possible interaction between glucocorticoids and estrogen-induced increases in brain-derived-neurotrophic factor (BDNF) expression in enhancing depressive-like behaviour has been documented. Here we evaluated the effects of Tualang honey, a phytoestrogen, and 17β-estradiol (E2) on the depressive-like behaviour, stress hormones, and BDNF concentration in stressed ovariectomised (OVX) rats. The animals were divided into six groups: (i) nonstressed sham-operated control, (ii) stressed sham-operated control, (iii) nonstressed OVX, (iv) stressed OVX, (v) stressed OVX treated with E2 (20 μg daily, sc), and (vi) stressed OVX treated with Tualang honey (0.2 g/kg body weight daily, orally). Two months after surgery, the animals were subjected to social instability stress procedure followed by forced swimming test. Struggling time, immobility time, and swimming time were scored. Serum adrenocorticotropic hormone (ACTH) and corticosterone levels, and the BDNF concentration were determined using commercially available ELISA kits. Stressed OVX rats displayed increased depressive-like behaviour with significantly increased serum ACTH and corticosterone levels, while the BDNF concentration was significantly decreased compared to other experimental groups. These changes were notably reversed by both E2 and Tualang honey. In conclusion, both Tualang honey and E2 mediate antidepressive-like effects in stressed OVX rats, possibly acting via restoration of hypothalamic-pituitary-adrenal axis and enhancement of the BDNF concentration.

Puberty and adolescence as a time of vulnerability to stressors that alter neurobehavioral processes

Puberty and adolescence are major life transitions during which an individual's physiology and behavior changes from that of a juvenile to that of an adult. Here we review studies documenting the effects of stressors during pubertal and adolescent development on the adult brain and behavior. The experience of complex or compound stressors during puberty/adolescence generally increases stress reactivity, increases anxiety and depression, and decreases cognitive performance in adulthood. These behavioral changes correlate with decreased hippocampal volumes and alterations in neural plasticity. Moreover, stressful experiences during puberty disrupt behavioral responses to gonadal hormones both in sexual performance and on cognition and emotionality. These behavioral changes correlate with altered estrogen receptor densities in some estrogen-concentrating brain areas, suggesting a remodeling of the brain's response to hormones. A hypothesis is presented that activation of the immune system results in chronic neuroinflammation that may mediate the alterations of hormone-modulated behaviors in adulthood.

Enduring influence of pubertal stressors on behavioral response to hormones in female mice

This article is part of a Special Issue "Puberty and Adolescence". The pubertal period is a time of change in an animal's response to stress, and it is a second period of sexual differentiation of the brain. Recently, it was discovered that particular stressors during the prolonged pubertal period of female mice result in enduring changes in behavioral responsiveness of the brain to estradiol and progesterone. Depending on the behavior, pubertal immune challenge or shipping from suppliers may decrease, eliminate, or even reverse the effects of estradiol. Pubertal immune challenge results in changes in the number of estrogen receptor-immunoreactive cells in key brain areas suggesting a cellular mechanism for this remodeling of the brain's response to hormones. A hypothesis is put forward that predicts that particular adverse experiences in girls may cause long-term alterations in the brain's response to estradiol and/or progesterone via activation of the immune system. This could lead to mood disorders or altered response to any behavior influenced by estradiol in humans.

Estradiol reduces depressive-like behavior through inhibiting nitric oxide/cyclic GMP pathway in ovariectomized mice

Estradiol decline has been associated with depressive-like behavior in female mice and NO has been suggested to play a major role in the pathogenesis of major depression. This study was conducted to investigate the antidepressant-like effects of acute estradiol administration in female ovariectomized (OVX) mice and the possible role of nitric oxide (NO)/cyclic GMP (cGMP) pathway. To this end, bilateral ovariectomy was performed in female mice and different doses of estradiol were injected alone or in combination with non-specific NO synthase (NOS) inhibitor (L-NAME), selective neural NOS (nNOS) inhibitor (7-NI), an NO precursor (L-arginine) or selective phosphodiesterase type 5 inhibitor (sildenafil). The duration of immobility was recorded in the forced swimming test (FST) to assess the depressive behavior. Moreover, hippocampal levels of NO were determined in select groups. 10 days following the procedure, OVX mice showed significantly prolonged immobility time in comparison with the sham group. Estradiol (3, 10, and 30 μg/kg, s.c.), when injected 1 h prior to FST, exerted antidepressant-like effects in OVX mice. Both L-NAME (30 mg/kg, i.p.), and 7-NI (50 mg/kg, i.p.) significantly reduced the immobility times of OVX mice. Administration of a sub-effective dose of L-NAME (10mg/kg), 15 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) had a robust antidepressant-like effect in OVX mice. Also a sub-effective dose of 7-NI (25 mg/kg), 30 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) showed antidepressant-like effect in OVX mice. Both the NO precursor L-arginine (750 mg/kg, i.p.) and the cGMP-specific phosphodiesterase type 5 inhibitor sildenafil (5 mg/kg, i.p.), 30 min before estradiol treatment, prevented the antidepressant-like effect of a potent dose of estradiol (10 μg/kg, s.c.) in OVX mice. The present findings suggest that suppression of the NO synthase/NO/cGMP pathway may be involved in the antidepressant-like effects of estradiol in OVX mice.

A pubertal immune challenge alters the antidepressant-like effects of chronic estradiol treatment in inbred and outbred adult female mice

Puberty is a period characterized by brain reorganization that contributes to the development of neural and behavioral responses to gonadal steroids. A single injection of the bacterial endotoxin, lipopolysaccharide (LPS), during the pubertal period decreases sexual receptivity in response to ovarian hormones in adulthood. Because chronic estradiol treatment alleviates depression-like symptoms in ovariectomized adult mice, we investigated the effect of pubertal LPS treatment on estradiol's antidepressant effects. We hypothesized that pubertal LPS treatment would decrease the antidepressant-like effect of estradiol in adult ovariectomized female mice, as it decreases other behavioral responses to ovarian hormones. As expected, chronic estradiol treatment decreased depression-like behavior, as measured by the duration of immobility, in saline-treated mice from two different strains, as well as in mice treated with LPS in adulthood. In contrast, in mice treated pubertally with LPS, estradiol strikingly increased the duration of immobility. No difference in body weight and in locomotion was found among the groups, suggesting that the differences in depression-like behavior were not due to differences in body weight or locomotor activity between LPS-treated and control mice. These results suggest that exposure to an immune challenge during the pubertal period alters the responsiveness of depression-like behavior to estradiol.

Antidepressive and anxiolytic activity of selective estrogen receptor modulators in ovariectomized mice submitted to chronic unpredictable stress

Estradiol has antidepressive and anxiolytic actions. However, its therapeutic use is limited by its peripheral effects. Selective estrogen receptor modulators may represent an alternative to estradiol for the treatment of depressive symptoms. Here we report that tamoxifen and raloxifene decrease immobility time in the forced swim test and increases the time spent in open arms in the elevated plus maze in ovariectomized mice submitted to chronic unpredictable stress.

Long-term ovariectomy modulates the antidepressant-like action of estrogens, but not of antidepressants

Controversial results related to effectiveness of estrogen replacement therapy (ERT) to alleviate depression are frequently reported. The discrepancies could be related to (a) time when ERT is initiated after the beginning of menopause and/or (b) type of estrogen used. Furthermore, estrogens modulate the antidepressant effect of different compounds; therefore, the effectiveness of antidepressant drugs could also depend on the menopausal status. The aim of the present study was to analyze whether the time after estrogen decline can influence antidepressant-like effects of two estrogens and/or two antidepressants. Thus, the antidepressant-like actions of 17β-estradiol (E(2)), 17α-ethynyl-estradiol (EE(2)), fluoxetine (FLX) and desipramine (DMI) were studied at different periods (1, 3 and 12 weeks) after ovariectomy (OVX), using the forced swimming test (FST). Results showed that OVX increased depressive-like behavior only 1 week after OVX. The antidepressant-like actions of E(2), but not those of EE(2), were cancelled 12 weeks after OVX. Conversely, antidepressant-like actions of FLX and DMI were observed at 1, 3 and 12 weeks after OVX. In conclusion, while the antidepressant-like effects of estrogens depended on the time at which treatment is initiated after OVX as well as on the estrogenic compound used, antidepressant-like effects of FLX and DMI were not blocked by OVX.

The antidepressant-like effects of the 3β-hydroxysteroid dehydrogenase inhibitor trilostane in mice is related to changes in neuroactive steroid and monoamine levels

In the present study, we analyzed the effects of a systemic treatment with the competitive 3β-hydroxysteroid dehydrogenase (3β-HSD) inhibitor trilostane on: (i) neurosteroid and monoamine levels in the brain, and (ii) the antidepressant activity of steroids and antidepressants in the forced swimming test (FST). 3β-HSD converts pregnenolone (PREG) into progesterone (PROG) or dehydroepiandrosterone (DHEA) into androstenedione. These neuroactive steroids are known to regulate neurotransmitters effects in the brain, particularly glutamate, γ-aminobutyric acid (GABA) and serotonin (5-HT), with consequences on mood and depression. We previously reported that trilostane showed antidepressant-like properties in the FST and concomitantly regulated plasma adrenocorticotropin (ACTH) and corticosterone levels, markers of the stress-induced hypothalamus-pituitary-adrenal (HPA) axis activation. We here observed that adrenalectomy/castration blocked the trilostane effect, outlining the importance of peripheral steroid levels. Trilostane (25 mg/kg) decreased hippocampus PROG contents and paradoxically increased circulating PROG levels. It also increased PREG levels in the hippocampus and frontal cortex. In the FST, a co-treatment with trilostane facilitated DHEAS (5-20 mg/kg) antidepressant activity, but showed only an additive, not facilitative, effect with PREGS (10-40 mg/kg), PROG (10-40 mg/kg) or allopregnanolone (ALLO, 1-8 mg/kg). Trilostane (25 mg/kg) treatment significantly increased 5-HT and (-)-norepinephrine (NE) turnovers in the hippocampus, an effect likely related to its antidepressant action. In co-administration studies, trilostane further decreased immobility following fluoxetine (30-60 mg/kg), sertraline (20-40 mg/kg) and imipramine (20-40 mg/kg), but not desipramine (20-40 mg/kg), treatments. A significant additive effect was observed for the selective 5-HT reuptake inhibitors (SSRI) at their highest dose. This study confirmed that a systemic administration of trilostane directly affected peripheral and brain levels in neuroactive steroids and monoamine turnover, resulting in antidepressant activity. The drug could be proposed as a co-treatment with SSRI. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Gonadal steroids and affective symptoms during in vitro fertilization: implication for reproductive mood disorders

Gonadal steroids (GSs) have been associated with the onset of a number of reproductive-related mood disorders in women, in which fluctuating or unstable hormonal levels are postulated to act as the trigger for the destabilization of mood. There is, however, rather limited direct clinical evidence that can link rapidly changing GS levels with the induction of mood symptoms. We aimed to study the effect of controlled and rapid GS fluctuations on mood in an in vivo model. Women undergoing in vitro fertilization (n=108) were assessed for depression and anxiety levels on 3 time points: during a low estradiol and progesterone baseline, during a gonadotropin stimulated estradiol-dominant phase, and after embryo transfer, during a progesterone-dominant low estrogen phase. Plasma levels for estrogen and progesterone were drawn on these time points. Symptoms of depression and anxiety significantly increased from baseline to the high estradiol levels but were not correlated with estrogen. The sharp drop from high estradiol levels at the estradiol-dominant phase to low levels at the progesterone-dominant phase was significantly correlated with rising depression scores. The rise in progesterone levels from low levels at the estradiol-dominant phase to high levels at the progesterone-dominant phase was significantly and inversely correlated with depression scores. This study suggests that the mechanism underlying the role of estrogen in reproductive-related mood disorders involves an abrupt and precipitous drop in its plasma level that can precipitate negative mood states. This finding has implications on the treatment of GS-related mood disorders.

Replacement of homologous mouse DNA sequence with pathogenic 6-base human CREB1 promoter sequence creates murine model of major depressive disorder

Major depressive disorder (MDD) is a leading cause of disability worldwide. Families with recurrent, early-onset MDD (RE-MDD), a severe, familial form of MDD, have provided an important resource for identifying and characterizing genetic variants that confer susceptibility to MDD and related disorders. Previous studies identified a rare, highly penetrant A(-115)G transition within the human CREB1 promoter that reduced promoter activity in vitro and was associated with depressive disorders in RE-MDD families. The development of an etiology-based recombinant animal model for MDD would facilitate the advancement of our limited understanding of the pathophysiology of MDD, as well as the development of improved treatments. Here we report the construction and initial characterization of a congenic mutant C57BL/6NTac mouse model that carries the human pathogenic sequence at the homologous position of the mouse Creb1 promoter. The recombinant strain exhibited decreases in reproductive capacity and pup survival that may be related to increased infant mortality observed in RE-MDD families; enlargement of the cerebral ventricles; reduced levels of CREB protein in the mouse cerebral cortex, as predicted from transfection experiments employing the pathogenic human CREB1 promoter; and alterations in two standardized behavioral tests, the forced swim and marble burying tests. These initial findings support the pathogenicity of the human A(-115)G promoter variant, and invite further characterization of this etiology-based recombinant animal model for MDD. Human promoter variants that have highly penetrant effects on disease expression provide an attractive opportunity for creating etiology-based mouse models of human diseases, with minimal disruption of the mouse genome.

Progesterone attenuates depressive behavior of younger and older adult C57/BL6, wildtype, and progesterone receptor knockout mice

Progesterone may have actions independent of intracellular progestin receptors (PRs) to influence depressive behavior. To investigate this, we examined effects of progesterone (P; 10mg/kg, SC) on the depressive behavior of mice in the forced swim test (FST). In Experiment 1, subjects were 4 to 6 months old, intact or ovariectomized (OVX) female and intact or gonadectomized (GDX) male, C57/BL6 mice. Progesterone reduced depressive behavior of young diestrous and OVX mice but male mice were impervious to effects of P. In Experiment 2, subjects were intact aged (20-28 months old) C57/BL6 female and male mice. Progesterone reduced depressive behavior of aged female and male C57/BL6 mice, albeit effects were greater among males. In Experiment 3, effects of P were examined in 4 to 6 months old, gonadally-intact, female and male mice that were wildtype or PR knockouts (PRKOs). Progesterone decreased depressive behavior of young adult, wildtype and PRKO mice, which showed greater immobility than did their wildtype counterparts. In Experiment 4, subjects were 18-24 months old wildtype or PRKO mice (Exp 4). Progesterone decreased immobility among wildtype and PRKO mice (which were not different in terms of their baseline depressive behavior). Together these data demonstrate that P decreases depressive behavior of young and older adult C57/BL6, wildtype and PRKO mice, which suggest that acute anti-depressant effects of P may occur independent of actions at "classic" PRs.

Estradiol effects on behavior and serum oxytocin are modified by social status and polymorphisms in the serotonin transporter gene in female rhesus monkeys

Despite the well-documented relation between estradiol (E2) and behavior, exposure to stressors may modify sensitivity to E2. The effects of E2 on behavior are, in part, likely related to their modulation of the serotonin (5HT) and oxytocin systems. The short allele (s-variant) polymorphism found in the promoter region of the SLC6A4 gene that encodes the 5HT transporter (5HTT) modulates responsivity to stressors. The current study used ovariectomized adult female rhesus monkeys to evaluate how exposure to the psychosocial stressor of social subordination and polymorphisms in the gene encoding 5HTT influence the behavioral effects of E2 and immunoreactive serum oxytocin. Dominant females had higher levels of oxytocin than subordinate animals even though E2 increased immunoreactive serum oxytocin in all females. E2 increased affiliative behaviors in all animals, with even more of these prosocial behaviors directed at dominant females. S-variant females, regardless of social status, were more aggressive toward more subordinate cage mates and these behaviors too were increased by E2. Subordinate s-variant females are most often involved in agonistic behavior, less affiliative behavior, and were less responsive to the anxiolytic action of E2. The results show that the short allele of the 5HTT gene synergizes with psychosocial stress exposure to affect the behavioral efficacy of E2 while confirming the actions of E2 for producing generalized behavioral arousal in females. Whether differences in the central action of 5HT and/or oxytocin are responsible for this effect requires further study.

Neuroactive steroids in affective disorders: target for novel antidepressant or anxiolytic drugs?

In the past decades considerable evidence has emerged that so-called neuroactive steroids do not only act as transcriptional factors in the regulation of gene expression but may also alter neuronal excitability through interactions with specific neurotransmitter receptors such as the GABA(A) receptor. In particular, 3α-reduced neuroactive steroids such as allopregnanolone or allotetrahydrodeoxycorticosterone have been shown to act as positive allosteric modulators of the GABA(A) receptor and to play an important role in the pathophysiology of depression and anxiety. During depression, the concentrations of 3α,5α-tetrahydroprogesterone and 3α,5β-tetrahydroprogesterone are decreased, while the levels of 3β,5α-tetrahydroprogesterone, a stereoisomer of 3α,5α-tetrahydroprogesterone, which may act as an antagonist for GABAergic steroids, are increased. Antidepressant drugs such as selective serotonin reuptake inhibitors (SSRIs) or mirtazapine apparently have an impact on key enzymes of neurosteroidogenesis and have been shown to normalize the disequilibrium of neuroactive steroids in depression by increasing 3α-reduced pregnane steroids and decreasing 3β,5α-tetrahydroprogesterone. Moreover, 3α-reduced neuroactive steroids have been demonstrated to possess antidepressant- and anxiolytic-like effects both in animal and human studies for themselves. In addition, the translacator protein (18 kDa) (TSPO), previously called peripheral benzodiazepine receptor, is the key element of the mitochondrial import machinery supplying the substrate cholesterol to the first steroidogenic enzyme (P450scc), which transforms cholesterol into pregnenolone, the precursor of all neurosteroids. TSPO ligands increase neurosteroidogenesis and are a target of novel anxiolytic drugs producing anxiolytic effects without causing the side effects normally associated with conventional benzodiazepines such as sedation or tolerance. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

The antidepressant-like effect of the 3β-hydroxysteroid dehydrogenase inhibitor trilostane involves a regulation of β-type estrogen receptors

RATIONALE

Trilostane is a competitive inhibitor of 3β-hydroxysteroid dehydrogenase (3β-HSD), which notably converts pregnenolone into progesterone or dehydroepiandrosterone into androstenedione. Trilostane shows antidepressant-like properties in the forced swimming test (FST). The compound, however, induced only moderate effects on neuroactive steroid levels that could be related to its behavioral efficacy.

METHODS

We compared the behavioral effect of trilostane with the other 3β-HSD inhibitor, cyanoketone, and analyzed the putative involvement of the β-type estrogen receptor (ERβ) in its antidepressant effect.

RESULTS

Trilostane reduced immobility in the FST significantly at 12.5 and 25 mg/kg subcutaneously (s.c.), whereas cyanoketone (0-100 mg/kg s.c.) was ineffective. The negative ER modulator fulvestrant (ICI 182780) dose-dependently blocked the effect of trilostane (25 mg/kg). Trilostane increased circulating estradiol levels in the 12.5-50 mg/kg dose-range, and this effect was unaffected by stress and not shared by cyanoketone (25 mg/kg). The trilostane (25 mg/kg) treatment increased the ERβ mRNA expression in adrenals (+100%) and centrally, in the hippocampus (+330%). Stress and cyanoketone failed to affect ERβ mRNA levels in periphery or in the brain.

CONCLUSIONS

These data demonstrate that the antidepressant-like potential of trilostane is not due to its 3β-HSD inhibiting activity, since it is not shared by cyanoketone, but rather to its estrogenic activity. The compound, which releases estradiol and up-regulates ERβ receptors, could be used as a therapeutic tool to allow an estrogenic facilitation of antidepressant efficacy.

Progesterone reduces depressive behavior of young ovariectomized, aged progestin receptor knockout, and aged wild type mice in the tail suspension test

Progestins may have effects to reduce depressive behavior, in part through actions of its metabolite, 5α-pregnan-3α-ol-20-one (3α,5α-THP) at GABA(A) receptors, rather than through intracellular progestin receptors. In this study, we examined the effects of progesterone (10 mg/kg, subcutaneous injection) versus vehicle control (propylene glycol) on the depressive behavior of young and aged mice in the tail suspension test. In Experiment 1, we first characterized progesterone's anti-depressant effects by utilizing young (4-6-month-old) intact or ovariectomized female, and intact or gonadectomized male, C57BL/6 mice. Young female mice showed more depressive behavior than the young male mice. Compared with vehicle administration, progesterone reduced depressive behavior of ovariectomized female, but not male or intact female mice. In Experiment 2, mice were aged (20-24-month-old) intact wild type or progestin receptor knockout mice. Progestin receptor knockout mice showed less depressive behavior than wild type mice. Administration of progesterone to wild type and progestin receptor knockout mice reduced depressive behavior. Together, these data suggest that progesterone can decrease depressive behavior of young adult ovariectomized female, aged wild type and progestin receptor knockout mice. Thus, progesterone's effect to reduce depressive behavior of aged mice may not require actions at the intracellular progestin receptors.

Antidepressant effects of estrogens: a basic approximation

The use of estrogenic compounds as antidepressants or as coadjuvants to facilitate the effect of antidepressants has reported controversial results, suggesting that many factors could influence their actions. This review analyzes, from a basic research perspective, the possible factors that may underlie the antidepressant action of estrogens alone or in combination. The possible mechanisms of action of estrogens alone and in combination with the selective serotonin reuptake inhibitor, fluoxetine, the selective noradrenaline reuptake inhibitor, desipramine, and the mixed serotonin/noradrenaline reuptake inhibitor, venlafaxine are reviewed, focusing on monoaminergic systems and estrogen receptors as main targets. The antidepressant effect of estrogens depends on the type of estrogen, treatment duration, doses, sex, time after ovariectomy, and age. Estrogens potentiate the antidepressant-like action of fluoxetine, venlafaxine, and desipramine and drastically shorten their latency of action. The antidepressant-like effect of estrogens alone or in combination with antidepressants seems to be mediated by monoaminergic and classic estrogen receptors, as WAY100635, an antagonist to the serotonin 1A receptor, idaxozan, an antagonist to alpha2 adrenergic receptors, and RU 58668, an estrogen receptor antagonist, blocked their antidepressant-like effect. In conclusion, estrogens produce antidepressant-like actions by themselves and importantly facilitate the action of clinically used antidepressants.

Estradiol reduces anxiety- and depression-like behavior of aged female mice

Beneficial effects of the ovarian steroid, 17beta-estradiol (E(2)), for affective behavior have been reported in young individuals, but less is known about the effects of E(2) among older individuals, and the capacity of older individuals to respond to E(2) following its decline. In the present study, the effects of acute E(2) administration to aged mice for anxiety-like and depression-like behaviors were investigated. Intact female C57BL/6 mice (N=18) that were approximately 24 months old were administered vehicle (sesame oil, n=9) or E(2) (10 microg, n=9) subcutaneously 1h prior to behavioral testing. Mice were tested for anxiety-like behavior (open field, elevated plus maze, mirror chamber, light-dark transition task, Vogel conflict task) and depression-like behavior (forced swim task). To assess the role of general motor behavior and coordination in these aged mice, performance in an activity monitor and rotarod task, and total entries made in tasks (open field, elevated plus maze, light-dark transition task) were determined. Mice administered E(2), compared to vehicle, demonstrated anti-anxiety behavior in the open field, mirror chamber, and light-dark transition task, and anti-depressive-like behavior in the forced swim task. E(2) also tended to have anti-anxiety effects in the elevated plus maze and Vogel task compared to vehicle administration, but these effects did not reach statistical significance. E(2) did not alter motor behavior and/or coordination in the activity monitor, open field, or rotarod tasks. Thus, an acute E(2) regimen produced specific anti-anxiety and anti-depressant effects, independent of effects on motor behavior, when administered to aged female C57BL/6 mice.

Adult female wildtype, but not oestrogen receptor beta knockout, mice have decreased depression-like behaviour during pro-oestrus and following administration of oestradiol or diarylpropionitrile

Studies in people and animal models suggest that depression is influenced by natural fluctuations in the levels of 17beta-oestradiol (E(2)), as well as administration of E(2)-based therapies, such as selective oestrogen receptor modulators (SERMs). Elucidating the effects and mechanisms of E(2) is important to improve future E(2)-based therapeutics. An important question is whether effects of E(2) or SERMs for mood regulation act at the alpha or beta isoform of the oestrogen receptor (ER) because some of the unwanted trophic effects of E(2)-based therapies may involve actions at ERalpha, rather than ERbeta. In the present study, whether there are sex differences in depression-like behaviour of adult mice (experiment 1), and the effects of natural fluctuations in E(2) (experiment 2), or administration of E(2) or a SERM that has higher affinity for ERbeta than for ERalpha (diarylpropionitrile; DPN) to ovariectomised (experiment 3) wildtype and ERbeta knockout (betaERKO) mice were investigated. Results of this study supported our hypotheses that: there would be sex differences favouring males for depression-like behaviour and endogenous increases in, or exogenous administration of, E(2) or administration of an ERbeta SERM would decrease depression-like behaviour in wildtype, but not betaERKO, mice. In experiment 1, adult male mice spent less time immobile in the forced swim test (i.e., showed less depression-like behaviour) compared with female mice. In experiment 2, pro-oestrous (higher circulating E(2) levels), compared with dioestrous (lower circulating E(2) levels), mice had reduced immobility in the forced swim test; this effect was not observed in betaERKO mice. In experiment 3, administration of E(2) or DPN to ovariectomised wildtype, but not betaERKO, mice decreased immobility compared with vehicle administration, these data suggest that ERbeta may be required for some of the anti-depressant-like effects of E(2).

The 3beta-hydroxysteroid dehydrogenase inhibitor trilostane shows antidepressant properties in mice

Changes in neuro(active)steroid levels are involved in depressive states and mood disorders. For instance, dehydroepiandrosterone or pregnenolone sulfate showed anti-stress and antidepressant activity in rodents and regulation of allopregnanolone levels appeared to be one of the consequence of an effective antidepressant therapy in patients. 4alpha,5-Epoxy-17beta-hydroxy-3-oxo-5alpha-androstane-2alpha-carbonitrile (trilostane) inhibits the activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) that, in particular, converts pregnenolone into progesterone. We examined whether systemic administration of trilostane affects the response to stress and depression. An acute treatment with trilostane (6.3-50mg/kg SC injected twice -16 and -2h before the measure) increased 3beta-HSD mRNA levels in the hippocampus and adrenals, but had little effect on protein levels. The trilostane treatment failed to affect open-field, locomotor or exploratory behaviors, but significantly reduced the immobility duration in the forced swimming test, measuring antidepressant-like activity, and increased the time spent in open arm in the elevated plus-maze, measuring anxiety response. The antidepressant-like effect of trilostane was effective after a repeated treatment (2.5-20mg/kgSC twice-a-day during 7 days) or in mice submitted to a restraint stress during 21 days and showing several behavioral and physiological parameters of depression (decreased body weight, increased adrenal glands weight and anhaedonia). Trilostane also reduced stress-induced increase in plasma corticosterone and ACTH levels, showing direct effect on HPA axis activity. These observations suggest that the 3beta-HSD inhibitor trilostane present antidepressant-like activity, putatively by regulating brain and peripheral levels of neuroactive steroids.

From menarche to menopause: exploring the underlying biology of depression in women experiencing hormonal changes

Epidemiologic data consistently report an elevated prevalence of major depressive disorder (MDD) in women. This increase begins during adolescence and continues through the menopausal transition. Population-based clinical studies report an increase in the incidence of MDD during perimenopause compared to either the premenopausal or postmenopausal period. Evidence suggests that fluctuations and decline of hormonal levels are correlated with this observed increase in risk for MDD. A strong predictor of depression in the perimenopausal period is a previous history of MDD. However, recent studies revealed an increased risk of new onset depression in perimenopausal women without a history of MDD. Additionally, recent reports have indicated that the presence of vasomotor symptoms may be associated with an increased the risk for MDD. The objective of this paper is to review evidence that would support our hypothesis that neurotransmitter systems are affected by changes in hormonal status over the course of a woman's life, leading to increase vulnerability to perimenopausal depression. Relevant data from nonclinical experiments will be discussed in the context of observed clinical evidence of the risk for MDD before, during, and after the menopausal transition. A testable hypothesis will be proposed to advance our understanding of hormonal effects on mood.

Neuroactive steroids and affective disorders

Neuroactive steroids modulate neurotransmission through modulation of specific neurotransmitter receptors such as gamma-aminobutyric acid type A (GABA(A)) receptors. Preclinical studies suggested that neuroactive steroids may modulate anxiety and depression-related behaviour and may contribute to the therapeutical effects of antidepressant drugs. Attenuations of such neuroactive steroids have been observed during major depression and in several anxiety disorders, suggesting a pathophysiological role in such psychiatric conditions. In panic disorder patients a dysequilibrium of neuroactive steroid composition has been observed, which may represent a counterregulatory mechanism against the occurrence of spontaneous panic attacks. Furthermore, alterations of 3alpha-reduced pregnane steroids during major depression were corrected by successful treatment with antidepressant drugs. However in contrast, non-pharmacological antidepressant treatment strategies did not affect neuroactive steroid composition. In addition, changes in neuroactive steroid concentrations after mirtazapine therapy occurred independently from the clinical response, thereby suggesting that changes in neuroactive steroid concentrations more likely reflect direct pharmacological effects of antidepressants rather than clinical improvement in general. Nevertheless, the effects of antidepressant pharmacotherapy on the composition of neuroactive steroids may contribute to the alleviation of certain depressive symptoms, such as amelioration of anxiety, inner tension or sleep disturbances. Moreover, first studies investigating the therapeutical effects of dehydroepiandrosterone revealed promising results in the treatment of major depression. In conclusion, neuroactive steroids are important endogenous modulators of depression and anxiety and may provide a basis for development of novel therapeutic agents in the treatment of affective disorders.

Progesterone's effects to reduce anxiety behavior of aged mice do not require actions via intracellular progestin receptors

RATIONALE

Aging is associated with reduced secretion of, and down-regulation of receptors for, progesterone (P); yet, P's effects when administered to younger and older animals have not been systematically investigated. Some of P's antianxiety effects may be due to its conversion to 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) and its subsequent actions as a positive modulator at GABAA receptor complexes (GBRs).

OBJECTIVES

We investigated whether P administration can decrease anxiety behavior of progestin receptor (PR) knockout (PRKO) or wild-type control mice.

METHODS

P (10 mg/kg) or vehicle (propylene glycol) were administered subcutaneously to intact, female or male wild-type or PRKO mice that were either 9-12 or 18-24 months of age. Behavior in tasks that assess spontaneous activity (activity monitor and roto-rod), free exploration of a novel environment (open field, elevated plus maze, and elevated zero maze), and conflict behavior (mirror chamber, dark-light transition, and punished drinking) were examined 1 h after injection.

RESULTS

P significantly decreased anxiety behavior of both PRKO and wild-type mice. P did not alter motor behavior but increased central entries in the open field, time in the open quadrants of the elevated zero maze, time in the mirrored chamber, time in the light compartment of the dark-light transition, and punished drinking in young and old mice. P-administered mice had higher levels of hippocampal 3alpha,5alpha-THP and GABA-stimulated chloride flux than did vehicle-administered PRKO or wild-type mice.

CONCLUSIONS

The effects of P to decrease anxiety behavior of younger and older mice do not require classic PRs and may involve actions of 3alpha,5alpha-THP at GBRs.