Selective activation of estrogen receptors α and β: Implications for depressive-like phenotypes in female mice exposed to chronic unpredictable stress

Prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in ovariectomized female rats

Stress is a major risk factor for several neuropsychiatric disorders in women, including postpartum depression. During the postpartum period, diminished ovarian hormone secretion increases susceptibility to developing depressive symptoms. Pleiotropic peptide hormones, like prolactin, are markedly released during lactation and suppress hypothalamic-pituitary-adrenal axis responses in women and acute stress-induced behavioral responses in female rodents. However, the effects of prolactin on chronic stress-induced maladaptive behaviors remain unclear. Here, we used chronic variable stress to induce maladaptive physiology in ovariectomized female rats and concurrently administered prolactin to assess its effects on several depression-relevant behavioral, endocrine, and neural characteristics. We found that chronic stress increased sucrose anhedonia and passive coping in saline-treated, but not prolactin-treated rats. Prolactin treatment did not alter stress-induced thigmotaxis, corticosterone (CORT) concentrations, hippocampal cell activation or survival. However, prolactin treatment reduced basal CORT concentrations and increased dopaminergic cells in the ventral tegmental area. Further, prolactin-treated rats had reduced microglial activation in the ventral hippocampus following chronic stress exposure. Together, these data suggest prolactin mitigates chronic stress-induced maladaptive behaviors and physiology in hypogonadal females. Moreover, these findings imply neuroendocrine-immune mechanisms by which peptide hormones confer stress resilience during periods of low ovarian hormone secretion.

Behavioural changes in young ovariectomized mice via GPR30-dependent serotonergic nervous system

Fluctuations in estradiol levels at each stage of life in women are considered one of the causes of mental diseases through their effects on the central nervous system. During menopause, a decrease in estradiol levels has been reported to affect the serotonin nervous system and induce depression-like and anxiety symptoms. However, the regulation of brain and behaviour during childhood and adolescence is poorly understood. Moreover, the role of oestrogen receptors α and β in the regulation of the serotonergic nervous system has been reported, but little is known about the involvement of G protein-coupled receptor 30. Therefore, in this study, we used an ovariectomized childhood mouse model to analyse behaviour and investigate the effects on the serotonin nervous system. We showed that ovariectomy surgery at 4 weeks of age, which is the weaning period, induced a decrease in spontaneous locomotor activity during the active period and a preference for novel mice over familiar mice in the three-chamber social test at 10 weeks of age. In addition, the administration of G-1, a protein-coupled receptor 30 agonist, to ovariectomized mice suppressed spontaneous locomotor activity and the preference for novel mice. Furthermore, we demonstrated that childhood ovariectomy induces increased tryptophan hydroxylase gene expression in the raphe nucleus and increased serotonin release in the amygdaloid nucleus, and administration of G-1 ameliorated these effects. Our study suggests that G protein-coupled receptor 30-mediated regulation of serotonin synthesis is involved in changes in activity and social-cognitive behaviour due to decreased estradiol levels during childhood.

Differential effects of perigestational consumption of sucrose-sweetened beverages on anxiety and depression-related behaviors in adult offspring: Sex disparity in a mouse model

Consumption of sucrose-sweetened drinks (SSDs) during pregnancy and breastfeeding can lead to various health and metabolism issues, but the potential impact on neurodevelopment and long-term effects remains unclear. This study aims to examine how maternal consumption of SSDs during gestation and lactation influences anxiety and depression-related behavior in adult offspring. Adult female CD-1 mice were randomly assigned to a control group (CG) or a sucrose group (SG) 2 weeks before gestation. The SG had 2 h of access to an SSD (15% w/w, 0.6 kcal/ml) for 2 weeks before mating, during pregnancy, and throughout lactation, totaling 8 weeks. Adult offspring were then evaluated for depressive-related behaviors and anxiety-related behaviors. Our findings reveal that perigestational consumption of SSDs does not lead to offspring presenting behaviors related to depression, but it does increase swimming behavior. However, maternal consumption of SSDs could impact the fighting response due to a diminished motivational component. In contrast, perigestational consumption of SSDs has apparent effects on anxiety-related behavior. Furthermore, female offspring appeared to be particularly vulnerable, exhibiting a higher anxiety index compared with controls. These findings indicate that females could be more vulnerable to the effects of maternal consumption of SSDs, being more susceptible to the presence of anxiety-related behaviors.

Supportive care of female hormones in brain health: what and how?

Female hormones, functioning as neuroactive steroids, are utilized beyond menopausal hormone therapy. The rapid onset of allopregnanolone analogs, such as brexanolone and zuranolone, in treating depression, and the effectiveness of megestrol acetate in addressing appetite and weight gain, prompted the Food and Drug Administration to authorize the use of progesterone for treating postpartum depression and cancer-related cachexia. Progesterone has also been found to alleviate neuropathic pain in animal studies. These off-label applications offer a promising option for patients with advanced cancer who often experience various mood disorders such as depression, persistent pain, social isolation, and physical complications like cachexia. These patients have shown low tolerance to opioids and mood-regulating medications. However, the potential risks and uncertainties associated with hormone therapy treatment modalities can be daunting for both patients and medical professionals. This review aims to offer a comprehensive understanding of the non-reproductive functions and mechanisms of female hormones in brain health.

ERβ activation improves nonylphenol-induced depression and neurotransmitter secretion disruption via the TPH2/5-HT pathway

The aim of this study is to investigate the role of estrogen receptor β (ERβ) in nonylphenol (NP) - induced depression - like behavior in rats and its impact on the regulation of the TPH2/5-HT pathway. In the in vitro experiment, rat basophilic leukaemia cells (RBL-2H3) cells were divided into the four groups: blank group, NP group (20 μM), ERβ agonist group (0.01 μM), and NP＋ERβ agonist group (20 μM＋0.01 μM). For the in vivo experiment, 72 adult male Sprague-Dawley rats were randomly divided into following six groups: the Control, NP (40 mg/kg) group, ERβ agonist (2 mg/kg, Diarylpropionitrile (DPN)) group, ERβ inhibitor (0.1 mg/kg, 4-(2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl) phenol (PHTPP)) group, NP+ERβ agonist (40 mg/kg NP ＋ 2 mg/kg DPN) group, and NP+ERβ inhibitor (40 mg/kg NP + 0.1 mg/kg PHTPP) group, with 12 rats in each group. Each rat in drug group were given NP by gavage and/or received a single intraperitoneal injection of DPN 2 mg/kg or PHTPP 0.1 mg/kg. Both in vivo and in vitro, NP group showed a decrease in the expression levels of ERβ, tryptophan hydroxylase (TPH1), and tryptophan hydroxylase-2 (TPH2) genes and proteins, and reduced levels of DA, NE, and 5-hydroxytryptophan (5-HT) neurotransmitters. RBL-2H3 cells showed signs of cell shrinkage, with rounded cells, increased suspension and more loosely arranged cells. The effectiveness of the ERβ agonist stimulation exhibited an increase exceeding 60% in RBL-2H3 cells. The application of ERβ agonist resulted in an alleviation the aforementioned alterations. ERβ agonist activated the TPH2/5-HT signaling pathways. Compared to the control group, the NP content in the brain tissue of the NP group was significantly increased. The latency to eat for the rats was longer and the amount of food consumed was lower, and the rats had prolonged immobility time in the behavioral experiment of rats. The expression levels of ERβ, TPH1, TPH2, 5-HT and 5-HITT proteins were decreased in the NP group, suggesting NP-induced depression-like behaviours as well as disturbances in the secretion of serum hormones and monoamine neurotransmitters. In the NP group, the midline raphe nucleus showed an elongated nucleus with a dark purplish-blue colour, nuclear atrophy, displacement and pale cytoplasm. ERβ might ameliorate NP-induced depression-like behaviors, and secretion disorders of serum hormones and monoamine neurotransmitters via activating TPH2/5-HT signaling pathways.

Estradiol regulates voltage-gated potassium currents in corticotropin-releasing hormone neurons

Corticotropin-releasing hormone (CRH) neurons are the primary neural population controlling the hypothalamic-pituitary-adrenal (HPA) axis and the secretion of adrenal stress hormones. Previous work has demonstrated that stress hormone secretion can be regulated by circulating levels of estradiol. However, the effect of estradiol on CRH neuron excitability is less clear. Here, we show that chronic estradiol replacement following ovariectomy increases two types of potassium channel currents in CRH neurons: fast inactivating voltage-gated A-type K+ channel currents (IA) and non-inactivating M-type K+ channel currents (IM). Despite the increase in K+ currents following estradiol replacement, there was no overall change in CRH neuron spiking excitability assessed with either frequency-current curves or current ramps. Together, these data reveal a complex picture whereby ovariectomy and estradiol replacement differentially modulate distinct aspects of CRH neuron and HPA axis function.

Estrogen receptors mediate the antidepressant effects of aerobic exercise: A possible new mechanism

Purpose

This study aimed to examine whether aerobic exercise exerts mood-modulating effects through an estrogen signaling mechanism.

Method

The experiment was divided into two parts. The first part is to compare the three modeling methods to obtain the most obvious method of depression-like phenotype for further study in the second part. The first part of ovariectomized rats (age, 13 weeks) was tested when rats were 14 or 22 weeks old or in the sixth week after 3 weeks of chronic restraint stress. The second part was to treat the animals with the most obvious depression-like phenotype in different ways, placebo treatment or estradiol (E2) replacement therapy was administered, aerobic training, or estrogen receptor antagonist treatment. The cognitive (Barnes maze and 3-chamber social tests), anxiety-like (open-field and elevated plus maze tests) and depression-like (sucrose preference and forced swim tests) behaviors of rats in both parts were analyzed to study the effects of estrogen depletion and aerobic exercise.

Results

Rats did not develop depressive symptoms immediately after ovariectomy, however, the symptoms became more pronounced with a gradual decrease in ovarian hormone levels. Compared with the placebo or control groups, the exercise and E2 groups showed improved performance in all behavioral test tasks, and the antidepressant effects of aerobic exercise were comparable to those of estrogen. Moreover, the estrogen receptor antagonist has markedly inhibited the antidepressant effects of aerobic exercise.

Conclusion

Estrogen receptors may mediate the antidepressant effects of aerobic exercise. In addition, an increasingly fragile ovarian hormonal environment may underlies chronic restraint stress-induced depression.

Chaigui granule exerts anti-depressant effects by regulating the synthesis of Estradiol and the downstream of CYP19A1-E2-ERKs signaling pathway in CUMS-induced depressed rats

Background: There is a significant gender difference in the prevalence of depression. Recent studies have shown that estrogen plays a crucial role in depression. Therefore, studying the specific mechanism of estrogen's role in depression can provide new ideas to address the treatment of depression. Chaigui granule has been shown to have exact antidepressant efficacy, and the contents of saikosaponin (a, b1, b2, d) and paeoniflorin in Chaigui granule are about 0.737% and 0.641%, respectively. Some studies have found that they can improve depression-induced decrease in testosterone (T) levels (∼36.99% decrease compared to control). However, whether Chaigui granule can exert antidepressant efficacy by regulating estrogen is still unclear. This study aimed to elucidate the regulation of estrogen levels by Chaigui granule and the underlying mechanism of its anti-depressant effect. Methods: Eighty-four male Sprague-Dawley (SD) rats were modeled using a chronic unpredictable mild stress (CUMS) procedure. The administration method was traditional oral gavage administration, and behavioral indicators were used to evaluate the anti-depressant effect of Chaigui granule. Enzyme-linked immunosorbent assay (ELISA) was adopted to assess the modulating impact of Chaigui granule on sex hormones. Then, reverse transcription-quantitative PCR (RT-qPCR), and Western blot (WB) techniques were employed to detect extracellular regulated protein kinases (ERK) signaling-related molecules downstream of estradiol in the hippocampus tissue. Results: The administration of Chaigui granule significantly alleviated the desperate behavior of CUMS-induced depressed rats. According to the results, we found that Chaigui granule could upregulate the level of estradiol (E2) in the serum (∼46.56% increase compared to model) and hippocampus (∼26.03% increase compared to model) of CUMS rats and increase the levels of CYP19A1 gene and protein, which was the key enzyme regulating the synthesis of T into E2 in the hippocampus. Chaigui granule was also found to have a significant back-regulatory effect on the gene and protein levels of ERβ, ERK1, and ERK2. Conclusion: Chaigui granule can increase the synthesis of E2 in the hippocampus of CUMS-induced depressed rats and further exert antidepressant effects by activating the CYP19A1-E2-ERKs signaling pathway.

Alleviation of cognitive deficits via upregulation of chondroitin sulfate biosynthesis by lignan sesamin in a mouse model of neuroinflammation

Lignans are plant-derived compounds that act as partial estrogen agonists. Chondroitin sulfate proteoglycans (CSPGs) represent one of the major components of the extracellular matrix (ECM). Here we aimed to understand the role of sesamin (SES), a major lignan compound, in the biosynthesis and degradation of CSPGs in the mouse hippocampus because CSPGs play a key role in the regulation of cognitive functions through the promotion of adult neurogenesis. The expression of the pro-inflammatory cytokine interleukin-1β was decreased by SES administration in the hippocampus of lipopolysaccharide (LPS)-treated mice, a model of neuroinflammation-induced cognitive deficits. The expression of genes related to biosynthesis and degradation of CSPGs in the hippocampus of LPS-treated mice was both increased and decreased by SES administration. Further, the diffuse ECM labeling of CSPGs by Wisteria floribunda agglutinin (WFA) in the hippocampus of LPS-treated mice was increased by SES administration. The densities of neural stem cells, late transit-amplifying cells, and newborn-granule cells in the hippocampus of LPS-treated mice were also increased by SES administration. Moreover, SES-induced alterations in gene expression, WFA labeling, and adult neurogenesis in LPS-treated mice were more evident in the dorsal hippocampus (center of cognition) than in the ventral hippocampus (center of emotion). Neither LPS nor SES administration affected locomotor activity, anxiety-like behavior, and depression-related behavior. However, impairments in contextual memory and sensorimotor gating in LPS-treated mice were recovered by SES administration. Our results show that SES can promote adult hippocampal neurogenesis through the upregulation of CSPGs, which may alleviate cognitive deficits induced by neuroinflammation.

Nuclear receptors modulate inflammasomes in the pathophysiology and treatment of major depressive disorder

Major depressive disorder (MDD) is highly prevalent and is a significant cause of mortality and morbidity worldwide. Currently, conventional pharmacological treatments for MDD produce temporary remission in < 50% of patients; therefore, there is an urgent need for a wider spectrum of novel antidepressants to target newly discovered underlying disease mechanisms. Accumulated evidence has shown that immune inflammation, particularly inflammasome activity, plays an important role in the pathophysiology of MDD. In this review, we summarize the evidence on nuclear receptors (NRs), such as glucocorticoid receptor, mineralocorticoid receptor, estrogen receptor, aryl hydrocarbon receptor, and peroxisome proliferator-activated receptor, in modulating the inflammasome activity and depression-associated behaviors. This review provides evidence from an endocrine perspective to understand the role of activated NRs in the pathophysiology of MDD, and to provide insight for the discovery of antidepressants with novel mechanisms for this devastating disorder.

Microglial-glucocorticoid receptor depletion alters the response of hippocampal microglia and neurons in a chronic unpredictable mild stress paradigm in female mice

Chronic psychological stress is one of the most important triggers and environmental risk factors for neuropsychiatric disorders. Chronic stress can influence all organs via the secretion of stress hormones, including glucocorticoids by the adrenal glands, which coordinate the stress response across the body. In the brain, glucocorticoid receptors (GR) are expressed by various cell types including microglia, which are its resident immune cells regulating stress-induced inflammatory processes. To study the roles of microglial GR under normal homeostatic conditions and following chronic stress, we generated a mouse model in which the GR gene is depleted in microglia specifically at adulthood to prevent developmental confounds. We first confirmed that microglia were depleted in GR in our model in males and females among the cingulate cortex and the hippocampus, both stress-sensitive brain regions. Then, cohorts of microglial-GR depleted and wild-type (WT) adult female mice were housed for 3 weeks in a standard or stressful condition, using a chronic unpredictable mild stress (CUMS) paradigm. CUMS induced stress-related behavior in both microglial-GR depleted and WT animals as demonstrated by a decrease of both saccharine preference and progressive ratio breakpoint. Nevertheless, the hippocampal microglial and neural mechanisms underlying the adaptation to stress occurred differently between the two genotypes. Upon CUMS exposure, microglial morphology was altered in the WT controls, without any apparent effect in microglial-GR depleted mice. Furthermore, in the standard environment condition, GR depleted-microglia showed increased expression of pro-inflammatory genes, and genes involved in microglial homeostatic functions (such as Trem2, Cx3cr1 and Mertk). On the contrary, in CUMS condition, GR depleted-microglia showed reduced expression levels of pro-inflammatory genes and increased neuroprotective as well as anti-inflammatory genes compared to WT-microglia. Moreover, in microglial-GR depleted mice, but not in WT mice, CUMS led to a significant reduction of CA1 long-term potentiation and paired-pulse ratio. Lastly, differences in adult hippocampal neurogenesis were observed between the genotypes during normal homeostatic conditions, with microglial-GR deficiency increasing the formation of newborn neurons in the dentate gyrus subgranular zone independently from stress exposure. Together, these findings indicate that, although the deletion of microglial GR did not prevent the animal's ability to respond to stress, it contributed to modulating hippocampal functions in both standard and stressful conditions, notably by shaping the microglial response to chronic stress.

Lipopolysaccharide-induced depression is associated with estrogen receptor-α/SIRT1/NF-κB signaling pathway in old female mice

The present study aims to investigate the influence of sex/age on depressive-like behaviors in lipopolysaccharide (LPS)-challenged mice model, and explore the underlying mechanisms. Tail suspension test and forced swimming test were used to evaluate the depressive-like behaviors. SIRT1 mRNA expression was assessed by PCR. Levels of 17β-estradiol (E2), SIRT1, NF-κB, tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β) and interleukin 6 (IL-6) were detected by enzyme linked immunosorbent assay (ELISA). In the behavior tests, under the same LPS stimulation, significant depressive-like behavior was observed in young male mice but not in young female mice, however, female mice were more likely to be depressed than male mice in the old age. Moreover, we found age-related depression difference existed only in female mice. In the experiments of mechanism exploration in old female mice, E2 improved LPS-induced depressive-like behavior, and simultaneously elevated SIRT1 levels and downregulated expressions of NF-κB and inflammatory cytokines in the hippocampus and frontal cortex. Interestingly, ERα inhibition, not ERβ inhibition, abolished E2's function. Additionally, SIRT1 antagonist also reversed E2's effects on depressive-like behavior and the expressions of NF-κB and inflammatory cytokines. These results suggested that E2 could protect the old female mice from depression via E2/ERα/SIRT1/NF-κB signaling pathway. In other words, LPS-induced depression was associated with ER-α/SIRT1/NF-κB signaling pathway in old female mice. By comparing the results of mechanism exploration in old male mice and old female mice and the different expression levels of E2, SIRT1, NF-κB and inflammatory cytokines in young female mice and old female mice, we speculate that the age or gender-related depression difference may be associated with the different activation levels of the ERα/SIRT1/NF-κB signaling pathway.

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.

Rapid Jetlag Resetting of Behavioral, Physiological, and Molecular Rhythms in Proestrous Female Mice

A gradual adaptation to a shifted light-dark (LD) cycle is a key element of the circadian clock system and believed to be controlled by the central circadian pacemaker, the suprachiasmatic nucleus (SCN). Endocrine factors have a strong influence on the regulation of the circadian clock network and alter acute photic responses of the SCN clock. In females, endocrine function depends on the stage of the ovarian cycle. So far, however, little is known about the effect of the estrous cycle on behavioral and molecular responses to shifts in the LD rhythm. Based on this, we investigated whether estrous state affects the kinetics of phase shift during jetlag in behavior, physiology, and molecular clock rhythms in the SCN and in peripheral tissues. Female mice exposed to an advanced LD phase at proestrous or metestrous showed different phase-shift kinetics, with proestrous females displaying accelerated adaptation in behavior and physiology. Constant darkness release experiments suggest that these fast phase shifts do not reflect resetting of the SCN pacemaker. Explant experiments on SCN, adrenal gland, and uterus confirmed this finding with proestrous females showing significantly faster clock phase shifts in peripheral tissues compared with the SCN. Together, these findings provide strong evidence for an accelerated adaptation of proestrous compared with metestrous females to new LD conditions that is accompanied by rapid behavioral, physiological, and molecular rhythm resetting. Not only do these findings open up a new avenue to understand the effect of estrous cycle on the clock network under changing environmental conditions but also imply a greater susceptibility in proestrous females.

Oxytocin has sex-specific effects on social behaviour and hypothalamic oxytocin immunoreactive cells but not hippocampal neurogenesis in adult rats

Oxytocin regulates social behaviours, pair bonding and hippocampal neurogenesis but most studies have used adult males. Our study investigated the effects of oxytocin on social investigation and adult hippocampal neurogenesis in male and female rats. Oxytocin has poor penetration of the blood-brain barrier, therefore we tested a nanoparticle drug, TRIOZAN™ (Ovensa Inc.), which permits greater blood-brain-barrier penetration. Adult male and female rats were injected daily (i.p.) for 10 days with either: oxytocin in PBS (0.5 or 1.0 mg/kg), oxytocin in TRIOZAN™ (0.5 or 1.0 mg/kg), or vehicle (PBS) and tested for social investigation. Oxytocin decreased body mass and increased social investigation and number of oxytocin-immunoreactive cells in the supraoptic nucleus (SON) of the hypothalamus in male rats only. In both sexes, oxytocin decreased the number of immature neurons (doublecortin+ cells) in the ventral hippocampus and reduced plasma 17β-estradiol levels in a dose- and delivery-dependent way. Oxytocin in TRIOZAN™ reduced "sedation" observed post-injection and increased certain central effects (oxytocin levels in the hypothalamus and neurogenesis in the ventral hippocampus) relative to oxytocin in PBS, indicating that the nanoparticle may be used as an alternative brain delivery system. We showed that oxytocin has sex-specific effects on social investigation, body mass, "sedation", and the oxytocin system. In contrast, similar effects were observed in both sexes in neurogenesis and plasma 17β-estradiol. Our work suggests that sex differences in oxytocin regulation of brain endpoints is region-specific (hypothalamus versus hippocampus) and that oxytocin does not promote social investigation in females.