Diverse actions of ovarian steroids in the serotonin neural system

Insights on Molecular Mechanisms of Ovarian Development in Decapod Crustacea: Focus on Vitellogenesis-Stimulating Factors and Pathways

Vitellogenesis in crustaceans is an energy-consuming process. Though the underlying mechanisms of ovarian maturation in decapod Crustacea are still unclear, evidence indicates the process to be regulated by antagonistically-acting inhibitory and stimulating factors specifically originating from X-organ/sinus gland (XO/SG) complex. Among the reported neuromediators, neuropeptides belonging to the crustacean hyperglycemic hormone (CHH)-family have been studied extensively. The structure and dynamics of inhibitory action of vitellogenesis-inhibiting hormone (VIH) on vitellogenesis have been demonstrated in several species. Similarly, the stimulatory effects of other neuropeptides of the CHH-family on crustacean vitellogenesis have also been validated. Advancement in transcriptomic sequencing and comparative genome analysis has led to the discovery of a large number of neuromediators, peptides, and putative peptide receptors having pleiotropic and novel functions in decapod reproduction. Furthermore, differing research strategies have indicated that neurotransmitters and steroid hormones play an integrative role by stimulating neuropeptide secretion, thus demonstrating the complex intertwining of regulatory factors in reproduction. However, the molecular mechanisms by which the combinatorial effect of eyestalk hormones, neuromediators and other factors coordinate to regulate ovarian maturation remain elusive. These multifunctional substances are speculated to control ovarian maturation possibly via the autocrine/paracrine pathway by acting directly on the gonads or by indirectly exerting their stimulatory effects by triggering the release of a putative gonad stimulating factor from the thoracic ganglion. Acting through receptors, they possibly affect levels of cyclic nucleotides (cAMP and cGMP) and Ca²⁺ in target tissues leading to the regulation of vitellogenesis. The "stimulatory paradox" effect of eyestalk ablation on ovarian maturation continues to be exploited in commercial aquaculture operations, and is outweighed by the detrimental physiological effects of this procedure. In this regard, the development of efficient alternatives to eyestalk ablation based on scientific knowledge is a necessity. In this article, we focus principally on the signaling pathways of positive neuromediators and other factors regulating crustacean reproduction, providing an overview of their proposed receptor-mediated stimulatory mechanisms, intracellular signaling, and probable interaction with other hormonal signals. Finally, we provide insight into future research directions on crustacean reproduction as well as potential applications of such research to aquaculture technology development.

An Association of Serotonin with Pain Disorders and Its Modulation by Estrogens

Ovarian hormones play an important role in pain perception, and are responsible, at least in part, for the pain threshold differences between the sexes. Modulation of pain and its perception are mediated by neurochemical changes in several pathways, affecting both the central and peripheral nervous systems. One of the most studied neurotransmitters related to pain disorders is serotonin. Estrogen can modify serotonin synthesis and metabolism, promoting a general increase in its tonic effects. Studies evaluating the relationship between serotonin and disorders such as irritable bowel syndrome, fibromyalgia, migraine, and other types of headache suggest a clear impact of this neurotransmitter, thereby increasing the interest in serotonin as a possible future therapeutic target. This literature review describes the importance of substances such as serotonin and ovarian hormones in pain perception and illustrates the relationship between those two, and their direct influence on the presentation of the aforementioned pain-related conditions. Additionally, we review the pathways and receptors implicated in each disorder. Finally, the objective was to stimulate future pharmacological research to experimentally evaluate the potential of serotonin modulators and ovarian hormones as therapeutic agents to regulate pain in specific subpopulations.

Dysmenorrhea increased the risk of postpartum depression in Chinese Han parturients

Several studies have shown that dysmenorrhea increased the risk of depression. However, the association between dysmenorrhea and postpartum depression (PPD) is unclear. The purpose of this study is to evaluate the effects of dysmenorrhea on the development of PPD among Chinese women. A case-control study was performed on parturients who delivered from January 1, 2016, to December 31, 2016, at Bao an Maternal and Child Health Hospital in Shenzhen, China. The Edinburgh Postnatal Depression Scale (EPDS) was used to screen for maternal postpartum depression. Logistic regression models were used to examine the association between dysmenorrhea and the risk of PPD. A total of 360 women including 120 cases and 240 controls were enrolled. Our study showed that parturients with PPD had a higher percentage of dysmenorrhea than women without PPD (64.2% vs 47.9%, P = 0.004). In univariate analysis, we observed that dysmenorrhea increased the risk for PPD (OR = 1.95; 95% CI: 1.24-3.06; P = 0.004). In the fully adjusted model, dysmenorrhea was still significantly associated with an increased risk of PPD (OR = 2.45; 95% CI: 1.36-4.54; P = 0.003). Our data confirmed that dysmenorrhea may be a risk factor for PPD. Therefore, screening for postpartum depression should be considered in parturients with a history of dysmenorrhea.

Role of Estradiol in the Expression of Genes Involved in Serotonin Neurotransmission: Implications for Female Depression

BACKGROUND

In women, changes in estrogen levels may increase the incidence and/or symptomatology of depression and affect the response to antidepressant treatments. Estrogen therapy in females may provide some mood benefits as a single treatment or might augment clinical response to antidepressants that inhibit serotonin reuptake.

OBJECTIVE

We analyzed the mechanisms of estradiol action involved in the regulation of gene expression that modulates serotonin neurotransmission implicated in depression.

METHOD

Publications were identified by a literature search on PubMed.

RESULTS

The participation of estradiol in depression may include regulation of the expression of tryptophan hydroxylase-2, monoamine oxidase A and B, serotonin transporter and serotonin-1A receptor. This effect is mediated by estradiol binding to intracellular estrogen receptor that interacts with estrogen response elements in the promoter sequences of tryptophan hydroxylase-2, serotonin transporter and monoamine oxidase-B. In addition to directly binding deoxyribonucleic acid, estrogen receptor can tether to other transcription factors, including activator protein 1, specificity protein 1, CCAAT/enhancer binding protein β and nuclear factor kappa B to regulate gene promoters that lack estrogen response elements, such as monoamine oxidase-A and serotonin 1A receptor.

CONCLUSION

Estradiol increases tryptophan hydroxylase-2 and serotonin transporter expression and decreases the expression of serotonin 1A receptor and monoamine oxidase A and B through the interaction with its intracellular receptors. The understanding of molecular mechanisms of estradiol regulation on the protein expression that modulates serotonin neurotransmission will be helpful for the development of new and more effective treatment for women with depression.

Chromatin organization in the female mouse brain fluctuates across the oestrous cycle

Male and female brains differ significantly in both health and disease, and yet the female brain has been understudied. Sex-hormone fluctuations make the female brain particularly dynamic and are likely to confer female-specific risks for neuropsychiatric disorders. The molecular mechanisms underlying the dynamic nature of the female brain structure and function are unknown. Here we show that neuronal chromatin organization in the female ventral hippocampus of mouse fluctuates with the oestrous cycle. We find chromatin organizational changes associated with the transcriptional activity of genes important for neuronal function and behaviour. We link these chromatin dynamics to variation in anxiety-related behaviour and brain structure. Our findings implicate an immediate-early gene product, Egr1, as part of the mechanism mediating oestrous cycle-dependent chromatin and transcriptional changes. This study reveals extreme, sex-specific dynamism of the neuronal epigenome, and establishes a foundation for the development of sex-specific treatments for disorders such as anxiety and depression.

The molecular mechanisms underlying the dynamic nature of the female brain structure and function remain poorly understood. Here the authors characterise chromatin organization in the mouse female ventral hippocampus, finding it fluctuates with the oestrous cycle, and identify changes in chromatin organization associated with the transcription of genes important for neuronal function and behaviour.

Menstrual cycle-associated modulations in neuromuscular function and fatigability of the knee extensors in eumenorrheic women

Sex hormone concentrations of eumenorrheic women typically fluctuate across the menstrual cycle and can affect neural function such that estrogen has neuroexcitatory effects, and progesterone induces inhibition. However, the effects of these changes on corticospinal and intracortical circuitry and the motor performance of the knee extensors are unknown. The present two-part investigation aimed to 1) determine the measurement error of an exercise task, transcranial magnetic stimulation (TMS)-, and motor nerve stimulation (MNS)-derived responses in women ingesting a monophasic oral contraceptive pill (hormonally-constant) and 2) investigate whether these measures were modulated by menstrual cycle phase (MCP), by examining them before and after an intermittent isometric fatiguing task (60% of maximal voluntary contraction, MVC) with the knee extensors until task failure in eumenorrheic women on days 2, 14, and 21 of the menstrual cycle. The repeatability of neuromuscular measures at baseline and fatigability ranged between moderate and excellent in women taking the oral contraceptive pill. MVC was not affected by MCP ( P = 0.790). Voluntary activation (MNS and TMS) peaked on day 14 ( P = 0.007 and 0.008, respectively). Whereas corticospinal excitability was unchanged, short-interval intracortical inhibition was greatest on day 21 compared with days 14 and 2 ( P < 0.001). Additionally, time to task failure was longer on day 21 than on both days 14 and 2 (24 and 36%, respectively, P = 0.030). The observed changes were larger than the associated measurement errors. These data demonstrate that neuromuscular function and fatigability of the knee extensors vary across the menstrual cycle and may influence exercise performance involving locomotor muscles.

NEW & NOTEWORTHY The present two-part study first demonstrated the repeatability of transcranial magnetic stimulation- and electrical motor nerve stimulation-evoked variables in a hormonally constant female population. Subsequently, it was demonstrated that the eumenorrheic menstrual cycle affects neuromuscular function. Changing concentrations of neuroactive hormones corresponded to greater voluntary activation on day 14, greater intracortical inhibition on day 21, and lowest fatigability on day 21. These alterations of knee extensor neuromuscular function have implications for locomotor activities.

In vivo Hippocampal Serotonin Dynamics in Male and Female Mice: Determining Effects of Acute Escitalopram Using Fast Scan Cyclic Voltammetry

Depression is a highly prevalent psychiatric disorder, impacting females at a rate roughly twice that of males. This disparity has become the focus of many studies which are working to determine if there are environmental or biological underpinnings to depression pathology. The biology of depression is not well understood, but experts agree that a key neurotransmitter of interest is serotonin. Most research on basic serotonin neurochemistry, by us and others, has predominantly focused on male models. Thus, it is now critical to include female models to decipher possible fundamental differences between the sexes that may underlie this disorder. In this paper, we seek to determine any such differences using fast-scan cyclic voltammetry (FSCV) and fast-scan controlled adsorption voltammetry. These techniques allow us to probe the serotonergic system via measurement of evoked and ambient serotonin at carbon fiber microelectrodes (CFMs). Our data reveal no statistical differences, in the hippocampus, in female serotonin chemistry during the different stages of the estrous cycle compared to the mean female response. Furthermore, no difference was observed in evoked serotonin release and reuptake, nor ambient extracellular serotonin levels between male and female mice. We applied a previously developed mathematical model that fits our serotonin signals as a function of several synaptic processes that control the extracellular levels of this transmitter. We used the model to study potential system differences between males and females. One hypothesis brought fourth, that female mice exhibit tighter autoreceptor control of serotonin, is validated via literature and methiothepin challenge. We postulate that this tight regulation may act as a control mechanism against changes in the serotonin signal mediated by estrogen spikes. Importantly, this safety mechanism has no consequence for acutely administered escitalopram’s (ESCIT’s) ability to increase extracellular serotonin between the sexes. This work demonstrates little fundamental differences in in vivo hippocampal serotonin between the sexes, bar control mechanisms in female mice that can be observed under extraneous circumstances. We thus highlight the importance of considering sex as a biological factor in determining pharmacodynamics for personalized medical treatments that involve targeting serotonin receptors.

Serotonin-estrogen interactions: What can we learn from pregnancy?

We have reviewed the scientific literature related to four diseases in which to serotonin (5-HT) is involved in the etiology, herein named 5-HT-linked diseases, and whose prevalence is influenced by estrogenic status: depression, migraine, irritable bowel syndrome and eating disorders. These diseases all have in common a sex-dimorphic prevalence, with women more frequently affected than men. The co-occurrence between these 5-HT-linked diseases suggests that they have common physiopathological mechanisms. In most 5-HT-linked diseases (except for anorexia nervosa and irritable bowel syndrome), a decrease in the serotonergic tone is observed and estrogens are thought to contribute to the improvement of symptoms by stimulating the serotonergic system. Human pregnancy is characterized by a unique 5-HT and estrogen synthesis by the placenta. Pregnancy-specific disorders, such as hyperemesis gravidarum, gestational diabetes mellitus and pre-eclampsia, are associated with a hyperserotonergic state and decreased estrogen levels. Fetal programming of 5-HT-linked diseases is a complex phenomenon that involves notably fetal-sex differences, which suggest the implication of sex steroids. From a mechanistic point of view, we hypothesize that estrogens regulate the serotonergic system, resulting in a protective effect against 5-HT-linked diseases, but that, in turn, 5-HT affects estrogen synthesis in an attempt to retrieve homeostasis. These two processes (5-HT and estrogen biosynthesis) are crucial for successful pregnancy outcomes, and thus, a disruption of this 5-HT-estrogen relationship may explain pregnancy-specific pathologies or pregnancy complications associated with 5-HT-linked diseases.

Serotonin and motherhood: From molecules to mood

Emerging research points to a valuable role of the monoamine neurotransmitter, serotonin, in the display of maternal behaviors and reproduction-associated plasticity in the maternal brain. Serotonin is also implicated in the pathophysiology of numerous affective disorders and likely plays an important role in the pathophysiology of maternal mental illness. Therefore, the main goals of this review are to detail: (1) how the serotonin system of the female brain changes across pregnancy and postpartum; (2) the role of the central serotonergic system in maternal caregiving and maternal aggression; and (3) how the serotonin system and selective serotonin reuptake inhibitor medications (SSRIs) are involved in the treatment of maternal mental illness. Although there is much work to be done, studying the central serotonin system's multifaceted role in the maternal brain is vital to our understanding of the processes governing matrescence and the maintenance of motherhood.

The dynamic serotonin system of the maternal brain

Many pregnant and postpartum women worldwide suffer from high anxiety and/or depression, which can have detrimental effects on maternal and infant well-being. The first-line pharmacotherapies for prepartum and postpartum affective disorders continue to be the selective serotonin reuptake inhibitors (SSRIs), despite the lack of large well-controlled studies demonstrating their efficacy in reproducing women and the potential for fetal/neonatal exposure to the drugs. Prepartum or postpartum use of SSRIs or other drugs that modulate the brain's serotonin system is also troubling because very little is known about the typical, let alone the atypical, changes that occur in the female central serotonin system across reproduction. We do know from a handful of studies of women and female laboratory rodents that numerous aspects of the central serotonin system are naturally dynamic across reproduction and are also affected by pregnancy stress (a major predisposing factor for maternal psychopathology). Thus, it should not be assumed that the maternal central serotonin system being targeted by SSRIs is identical to non-parous females or males. More information about the normative and stress-derailed changes in the maternal central serotonin system is essential for understanding how serotonin is involved in the etiology of, and the best use of SSRIs for potentially treating, affective disorders in the pregnant and postpartum populations.

The Effects and Action Mechanisms of Phytoestrogens on Vasomotor Symptoms During Menopausal Transition: Thermoregulatory Mechanism

Background:

Phytoestrogens have recently been claimed to positively influence menopausal discomforts, including hot flashes. However, little is known about the influence of phytoestrogens on core body temperature during oestrogen fluctuation at menopause.

Objective:

Previously published findings showed that phytoestrogens could relieve menopausal complaints, thus, the present review was aimed at assessing the effects of phytoestrogens on thermoregulatory mechanism during menopausal transition.

Results:

The molecular mechanisms underlying hot flashes are complex. Oestrogen fluctuations cause hypothalamic thermoregulatory centre dysfunction, which leads to hot flashes during menopause. The phytoestrogens of interest, in relation to human health, include isoflavones, lignans, coumestans, and stilbenes, which are widely distributed in nature. The phytoestrogens are capable of reducing hot flashes via their oestrogen-like hormone actions. The potential effects of phytoestrogens on hot flashes and their molecular mechanisms of action on thermoregulatory centre are discussed in this review.

Conclusion:

The effects of phytoestrogens on these mechanisms may help explain their beneficial effects in alleviating hot flashes and other menopausal discomforts.

Association between aromatase in human brains and personality traits

Aromatase, an enzyme that converts androgens to estrogens, has been reported to be involved in several brain functions, including synaptic plasticity, neurogenesis, neuroprotection, and regulation of sexual and emotional behaviours in rodents, pathophysiology of Alzheimer's disease and autism spectrum disorders in humans. Aromatase has been reported to be involved in aggressive behaviours in genetically modified mice and in personality traits by genotyping studies on humans. However, no study has investigated the relationship between aromatase in living brains and personality traits including aggression. We performed a positron emission tomography (PET) study in 21 healthy subjects using ¹¹C-cetrozole, which has high selectivity and affinity for aromatase. Before performing PET scans, subjects answered the Buss-Perry Aggression Questionnaire and Temperament and Character Inventory to measure their aggression and personality traits, respectively. A strong accumulation of ¹¹C-cetrozole was detected in the thalamus, hypothalamus, amygdala, and medulla. Females showed associations between aromatase levels in subcortical regions, such as the amygdala and supraoptic nucleus of the hypothalamus, and personality traits such as aggression, novelty seeking, and self-transcendence. In contrast, males exhibited associations between aromatase levels in the cortices and harm avoidance, persistence, and self-transcendence. The association of aromatase levels in the thalamus with cooperativeness was common to both sexes. The present study suggests that there might exist associations between aromatase in the brain and personality traits. Some of these associations may differ between sexes, while others are likely common to both.

Do Progestin-Only Contraceptives Contribute to the Risk of Developing Depression as Implied by Beta-Arrestin 1 Levels in Leukocytes? A Pilot Study

We reported previously that reduction in beta-arrestin 1 (β-AR 1) protein levels in peripheral blood mononuclear leukocytes (PBMC) significantly correlated with the severity of depressive symptoms in reproductive women. In this pilot study, we used β-AR 1 protein levels in PBMC as a marker for developing depressive symptoms and the Hamilton Depression Rating Scale (HAM-D) scores to assess potential mood-related side effects of oral contraceptive use for routine birth control among women. We evaluated 29 women in this study. We enrolled the participants in three groups: Estrogen-progestin combination-oral contraceptives (COC, n = 10), progestin-only contraceptives (POC, n = 12), and non-hormonal or no contraceptives (NC, n = 7). We determined the β-AR 1 protein levels in PBMCs by enzyme-linked immunosorbent assay (ELISA). We found that women in the POC group had significantly higher HAM-D scores compared to those in the COC (p < 0.0004) and NC (p < 0.004). The levels of β-AR 1 protein were significantly attenuated in women in the POC group compared to women in the NC group (p = 0.03). Our findings suggest that the use of POC is a potential risk factor for developing depressive symptoms.

Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders

Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.

Steroid Hormones and Their Action in Women's Brains: The Importance of Hormonal Balance

Sex hormones significantly impact women's lives. Throughout the different stages of life, from menarche to menopause and all stages in between, women experience dramatic fluctuations in the levels of progesterone and estradiol, among other hormones. These fluctuations affect the body as a whole, including the central nervous system (CNS). In the CNS, sex hormones act via steroid receptors. They also have an effect on different neurotransmitters such as GABA, serotonin, dopamine, and glutamate. Additionally, studies show that sex hormones and their metabolites influence brain areas that regulate mood, behavior, and cognitive abilities. This review emphasizes the benefits a proper hormonal balance during the different stages of life has in the CNS. To achieve this goal, it is essential that hormone levels are evaluated considering a woman's age and ovulatory status, so that a correct diagnosis and treatment can be made. Knowledge of steroid hormone activity in the brain will give women and health providers an important tool for improving their health and well-being.

Heavy Chronic Ethanol Exposure From Adolescence to Adulthood Induces Cerebellar Neuronal Loss and Motor Function Damage in Female Rats

Over the last years, heavy ethanol consumption by teenagers/younger adults has increased considerably among females. However, few studies have addressed the long-term impact on brain structures’ morphology and function of chronic exposure to high ethanol doses from adolescence to adulthood in females. In line with this idea, in the current study we investigated whether heavy chronic ethanol exposure during adolescence to adulthood may induce motor impairments and morphological and cellular alterations in the cerebellum of female rats. Adolescent female Wistar rats (35 days old) were treated with distilled water or ethanol (6.5 g/kg/day, 22.5% w/v) during 55 days by gavage. At 90 days of age, motor function of animals was assessed using open field (OF), pole, beam walking and rotarod tests. Following completion of behavioral tests, morphological and immunohistochemical analyses of the cerebellum were performed. Chronic ethanol exposure impaired significantly motor performance of female rats, inducing spontaneous locomotor activity deficits, bradykinesia, incoordination and motor learning disruption. Moreover, histological analysis revealed that ethanol exposure induced atrophy and neuronal loss in the cerebellum. These findings indicate that heavy ethanol exposure during adolescence is associated with long-lasting cerebellar degeneration and motor impairments in female rats.

Serotonin-specific lesions of the dorsal raphe disrupt maternal aggression and caregiving in postpartum rats

The behavioral modifications associated with early motherhood, which include high aggression, caring for the young, and low anxiety, are all affected by acute pharmacological manipulation of serotonin signaling. However, the effects on all these behaviors of permanently disrupting serotonin signaling from one of its primary sources, the dorsal raphe nucleus (DR), have not been examined in detail. To address this, serotonin-specific lesions centered on the dorsomedial DR (DRdm; DR subregion strongly implicated in emotional behaviors) were induced at mid-pregnancy (day 15) or early postpartum (day 2) in rats using a saporin-conjugated neurotoxin targeting the serotonin transporter (Anti-SERT-SAP). Prepartum or postpartum Anti-SERT-SAP reduced DRdm serotonin immunoreactivity by ∼40-65%, and postpartum Anti-SERT-SAP also reduced it in the ventromedial and lateral wings of the DR, as well as in the median raphe. Serotonin-immunoreactive fibers were significantly reduced in the anterior hypothalamus, but not medial preoptic area, of lesioned dams. Pre- or postpartum lesions both greatly reduced maternal aggression, but while prepartum lesions did not affect later undisturbed maternal caregiving, the larger postpartum lesions prevented the postpartum decline in kyphotic nursing and reduced pup licking. Serotonin lesions did not affect pup retrieval, but the prepartum lesions temporarily increased maternal hovering over and licking the pups observed immediately after the disruptive retrieval tests. Dams' anxiety-like behaviors and litter weight gains were unaffected by the lesions. These findings suggest that DRdm serotonin projecting to the AH is particularly critical for maternal aggression, but that more widespread disruption of midbrain raphe serotonin is necessary to greatly impair maternal caregiving. Postpartum anxiety may rely more on other neurochemical systems or different midbrain serotonergic cell populations.

Tph2-/- female mice restore socio-sexual recognition through upregulating ERα and OTR genes in the amygdala

The central 5-hydroxytryptamine system impairs sociosexual behaviors and olfaction preferences in sexually naive mice. However, it remains unknown whether reproductive experiences impart an effect on the sexual olfactory preferences of female mice lacking central serotonin. Here, we aimed at examining such effects and the underlying mechanisms using Tph2 knockout female mice. Sexually naive Tph2^−/− female mice failed to recognize olfactory cues regarding sex, genetic relatedness, and social hierarchy despite exhibiting normal olfactory discrimination. However, reproduction-experienced Tph2^−/− female mice recovered sexual olfactory preferences, as did sexually naive Tph2^+/+ females. Meanwhile, both the estrogen receptor α and oxytocin receptor in the amygdala of reproduction-experienced Tph2^−/− females presented upregulated expression at the mRNA level and an upward tendency at the protein level vs. sexually naive Tph2^−/− females. Intracerebroventricular administration of a combination of estrogen receptor α and oxytocin receptor agonists, but not either agent alone, could restore the sexual olfactory preferences of sexually naive Tph2^−/− female mice to some degree. We speculate that estrogen receptor α and oxytocin receptor activation in the amygdala after reproductive experiences restores sexual olfactory recognition in Tph2^−/− female mice.

Brain Aromatase Modulates Serotonergic Neuron by Regulating Serotonin Levels in Zebrafish Embryos and Larvae

Teleost fish are known to express two isoforms of P450 aromatase, a key enzyme for estrogen synthesis. One of the isoforms, brain aromatase (AroB), cyp19a1b, is highly expressed during early development of zebrafish, thereby suggesting its role in brain development. On the other hand, early development of serotonergic neuron, one of the major monoamine neurons, is considered to play an important role in neurogenesis. Therefore, in this study, we investigated the role of AroB in development of serotonergic neuron by testing the effects of (1) estradiol (E₂) exposure and (2) morpholino (MO)-mediated AroB knockdown. When embryos were exposed to E₂, the effects were biphasic. The low dose of E₂ (0.005 µM) significantly increased serotonin (5-HT) positive area at 48 hour post-fertilization (hpf) detected by immunohistochemistry and relative mRNA levels of tryptophan hydroxylase isoforms (tph1a, tph1b, and tph2) at 96 hpf measured by semi-quantitative PCR. To test the effects on serotonin transmission, heart rate and thigmotaxis, an indicator of anxiety, were analyzed. The low dose also significantly increased heart rate at 48 hpf and decreased thigmotaxis. The high dose of E₂ (1 µM) exhibited opposite effects in all parameters. The effects of both low and high doses were reversed by addition of estrogen receptor (ER) blocker, ICI 182,780, thereby suggesting that the effects were mediated through ER. When AroB MO was injected to fertilized eggs, 5-HT-positive area was significantly decreased, while the significant decrease in relative tph mRNA levels was found only with tph2 but not with two other isoforms. AroB MO also decreased heart rate and increased thigmotaxis. All the effects were rescued by co-injection with AroB mRNA and by exposure to E₂. Taken together, this study demonstrates the role of brain aromatase in development of serotonergic neuron in zebrafish embryos and larvae, implying that brain-formed estrogen is an important factor to sustain early development of serotonergic neuron.

Premenstrual disorders

Premenstrual disorders include premenstrual syndrome, premenstrual dysphoric disorder, and premenstrual worsening of another medical condition. While the underlying causes of these conditions continue to be explored, an aberrant response to hormonal fluctuations that occurs with the natural menstrual cycle and serotonin deficits have both been implicated. A careful medical history and daily symptom monitoring across 2 menstrual cycles is important in establishing a diagnosis. Many treatments have been evaluated for the management of premenstrual disorders. The most efficacious treatments for premenstrual syndrome and premenstrual dysphoric disorder include serotonin reuptake inhibitors and contraceptives with shortened to no hormone-free interval. Women who do not respond to these and other interventions may benefit from gonadotropin-releasing hormone agonist treatment.

Fear extinction in an obsessive-compulsive disorder animal model: Influence of sex and estrous cycle

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition that affects men and women equally, but with a sexually dimorphic pattern of development. Reproductive cycle events can influence symptom severity of OCD in females, indicating that ovarian hormones or their interaction with distinct neurotransmitter systems may play a role in OCD pathophysiology. Clinical studies and animal models have confirmed the importance of the serotonergic (5-HT) system in the neurobiology and treatment of OCD. Accordingly, the non-selective 5-HT2c agonist, meta-chlorophenylpiperazine (mCPP), exacerbates symptoms in untreated OCD patients. In rodents, it evokes repetitive behaviors that engage brain areas that are homologous with those found to be dysfunctional in OCD patients. These regions, including the medial prefrontal and anterior cingulate cortices, are also involved in fear inhibition, which is impaired in OCD. Here, we treated rats with mCPP (0.5 and 3.0 mg/kg) to evaluate its influence on self-grooming behavior and assess potential fear extinction retention deficits, taking into account sex differences and females' estrous cycle. We found that mCPP exacerbated grooming in male and female rats, irrespective of the estrous cycle phase. Fear extinction retention, however, was impaired only in females. Moreover, females undergoing fear extinction training during the metestrus/diestrus phases of the estrous cycle were more sensitive to the impairments induced by mCPP. Our results indicate that mCPP can induce OCD-like symptoms, exacerbating self-grooming and impairing fear extinction. It suggests that changes in 5-HT signaling through 5-HT2c receptors may have an important role in the OCD pathophysiology and that the influence of gonadal hormones in OCD should be further investigated.

Ginkgo biloba Extract (GbE) Stimulates the Hypothalamic Serotonergic System and Attenuates Obesity in Ovariectomized Rats

Menopause is associated with increased risk to develop obesity but the mechanisms involved are not fully understood. We have shown that Ginkgo biloba extract (GbE) improved diet-induced obesity. Since GbE might be effective in the treatment of obesity related to menopause, avoiding the side effects of hormone replacement therapy, we investigated the effect of GbE on hypothalamic systems controlling energy homeostasis. Wistar rats were either ovariectomized (OVX) or Sham-operated. After 2 months, either 500 mg.kg^-1 of GbE or vehicle were administered daily by gavage for 14 days. A subset of animals received an intracerebroventricular (i.c.v.) injection of serotonin (300 μg) or vehicle and food intake was measured after 12 and 24 h. Another subset was submitted to in vivo microdialysis and 5-HT levels of the medial hypothalamus were measured by high performance liquid chromatography, before and up to 2 h after the administration of 500 mg.kg^-1 of GbE. Additional animals were used for quantification of 5-HT_1A, 5-HT_1B, 5-HT_2C, 5-HTT, and pro-opiomelanocortin hypothalamic protein levels by Western blotting. OVX increased food intake and body weight and adiposity while GbE attenuated these alterations. i.c.v. serotonin significantly reduced food intake in Sham, Sham + GbE, and OVX + GbE groups while it failed to do so in the OVX group. In the OVX rats, GbE stimulated 5-HT microdialysate levels while it reduced hypothalamic 5-HTT protein levels. The results indicate that GbE improved the ovariectomy-induced resistance to serotonin hypophagia, at least in part through stimulation of the hypothalamic serotonergic activity. Since body weight gain is one of the most important consequences of menopause, the stimulation of the serotonergic transmission by GbE may represent a potential alternative therapy for menopause-related obesity.

Interactive Effects of Dopamine Baseline Levels and Cycle Phase on Executive Functions: The Role of Progesterone

Estradiol and progesterone levels vary along the menstrual cycle and have multiple neuroactive effects, including on the dopaminergic system. Dopamine relates to executive functions in an “inverted U-shaped” manner and its levels are increased by estradiol. Accordingly, dopamine dependent changes in executive functions along the menstrual cycle have been previously studied in the pre-ovulatory phase, when estradiol levels peak. Specifically it has been demonstrated that working memory is enhanced during the pre-ovulatory phase in women with low dopamine baseline levels, but impaired in women with high dopamine baseline levels. However, the role of progesterone, which peaks in the luteal cycle phase, has not been taken into account previously. Therefore, the main goals of the present study were to extend these findings (i) to the luteal cycle phase and (ii) to other executive functions. Furthermore, the usefulness of the eye blink rate (EBR) as an indicator of dopamine baseline levels in menstrual cycle research was explored. 36 naturally cycling women were tested during three cycle phases (menses–low sex hormones; pre-ovulatory–high estradiol; luteal–high progesterone and estradiol). During each session, women performed a verbal N-back task, as measure of working memory, and a single trial version of the Stroop task, as measure of response inhibition and cognitive flexibility. Hormone levels were assessed from saliva samples and spontaneous eye blink rate was recorded during menses. In the N-back task, women were faster during the luteal phase the higher their progesterone levels, irrespective of their dopamine baseline levels. In the Stroop task, we found a dopamine-cycle interaction, which was also driven by the luteal phase and progesterone levels. For women with higher EBR performance decreased during the luteal phase, whereas for women with lower EBR performance improved during the luteal phase. These findings suggest an important role of progesterone in modulating dopamine-cycle interactions. Additionally, we identified the eye blink rate as a non-invasive indicator of baseline dopamine function in menstrual cycle research.

Testosterone levels in healthy men correlate negatively with serotonin 4 receptor binding

The serotonergic system integrates sex steroid information and plays a central role in mood and stress regulation, cognition, appetite and sleep. This interplay may be critical for likelihood of developing depressive episodes, at least in a subgroup of sensitive individuals. The serotonin 4 receptor (5-HT₄R) indexes central serotonergic tonus, which may be related to endogenous sex-steroid levels in the mentally healthy state even though this remains elusive. Here we evaluate if peripheral levels of estradiol and testosterone are associated with 5-HT₄R binding as imaged by [¹¹C]SB207145 positron emission tomography in a group of 41 healthy men. We estimated global 5-HT₄R binding using a latent variable model framework, which models shared correlation between 5-HT₄R across multiple brain regions (hippocampus, amygdala, posterior and anterior cingulate, thalamus, pallidostriatum and neocortex). We tested whether testosterone and estradiol predict global 5-HT₄R, adjusting for age. We found that testosterone, but not estradiol, correlated negatively with global 5-HT₄R levels (p=0.02) suggesting that men with high levels of testosterone have higher cerebral serotonergic tonus. Our findings corroborate the link between sex hormone levels and serotonin signalling. Future longitudinal studies in clinical relevant populations are needed to elucidate the potential importance of testosterone in the pathophysiology of e.g. major depression and its treatment.

Interaction between estradiol and 5-HT1A receptors in the median raphe nucleus on acquisition of aversive information and association to the context in ovariectomized rats

The median raphe nucleus (MRN) is related to stress resistance and defensive responses, a crucial source of serotonergic neurons that project to prosencephalic structures related to stress and anxiety. Estrogen receptors were identified in this mesencephalic structure. It is possible that the estrogen action is related to serotonin effect on somatodendritic 5-HT_1A receptors, inhibiting the function of serotonergic neurons and thus preventing of the stress effect and inducing anxiolysis. So, in order to evaluate these aspects, female Wistar rats were ovariectomized and 21 days later were given a direct microinjection of estradiol benzoate (EB) (1200 ng) into the MRN, preceded by microinjections of saline or WAY100.635 (100 ng), a 5-HT_1A receptor antagonist. Immediately after the two microinjections, the ovariectomized rats were conditioned with an aversive event (foot shock) session in a Skinner box. Twenty-four hours later, they were exposed to the same context in a test session for 5 min for behavioral assessment: freezing, rearing, locomotion, grooming, and autonomic responses (fecal boluses and micturition). EB microinjection in the MRN prior to the exposure of animals to the foot shocks in the conditioning session did not alter their behavior in this session, but neutralized the association of the aversive experience to the context: there was a decrease in the expression of freezing and an increased rearing activity in the test session. This effect was reversed by prior microinjection of WAY100.635. In conclusion, EB acted on serotonergic neurons in the MRN of the ovariectomized rats, impairing the association of the aversive experience to the context, by co-modulating the functionality of somatodendritic 5-HT_1A.

Effects of obesogenic diet and estradiol on dorsal raphe gene expression in old female macaques

The beneficial effects of bioidentical ovarian steroid hormone therapy (HT) during the perimenopause are gaining recognition. However, the positive effects of estrogen (E) plus or minus progesterone (P) administration to ovariectomized (Ovx) lab animals were recognized in multiple systems for years before clinical trials could adequately duplicate the results. Moreover, very large numbers of women are often needed to find statistically significant results in clinical trials of HT; and there are still opposing results being published, especially in neural and cardiovascular systems. One of the obvious differences between human and animal studies is diet. Laboratory animals are fed a diet that is low in fat and refined sugar, but high in micronutrients. In the US, a large portion of the population eats what is known as a "western style diet" or WSD that provides calories from 36% fat, 44% carbohydrates (includes 18.5% sugars) and 18% protein. Unfortunately, obesity and diabetes have reached epidemic proportions and the percentage of obese women in clinical trials may be overlooked. We questioned whether WSD and obesity could decrease the positive neural effects of estradiol (E) in the serotonin system of old macaques that were surgically menopausal. Old ovo-hysterectomized female monkeys were fed WSD for 2.5 years, and treated with placebo, Immediate E (ImE) or Delayed E (DE). Compared to old Ovx macaques on primate chow and treated with placebo or E, the WSD-fed monkeys exhibited greater individual variance and blunted responses to E-treatment in the expression of genes related to serotonin neurotransmission, CRH components in the midbrain, synapse assembly, DNA repair, protein folding, ubiquitylation, transport and neurodegeneration. For many of the genes examined, transcript abundance was lower in WSD-fed than chow-fed monkeys. In summary, an obesogenic diet for 2.5 years in old surgically menopausal macaques blunted or increased variability in E-induced gene expression in the dorsal raphe. These results suggest that with regard to function and viability in the dorsal raphe, HT may not be as beneficial for obese women as normal weight women.

Characterization of Induced Pluripotent Stem Cell-derived Human Serotonergic Neurons

In the brain, the serotonergic neurons located in the raphe nucleus are the unique resource of the neurotransmitter serotonin, which plays a pivotal role in the regulation of brain development and functions. Dysfunction of the serotonin system is present in many psychiatric disorders. Lack of in vitro functional human model limits the understanding of human central serotonergic system and its related diseases and clinical applications. Previously, we have developed a method generating human serotonergic neurons from induced pluripotent stem cells (iPSCs). In this study, we analyzed the features of these human iPSCs-derived serotonergic neurons both in vitro and in vivo. We found that these human serotonergic neurons are sensitive to the selective neurotoxin 5, 7-Dihydroxytryptamine (5,7-DHT) in vitro. After being transplanted into newborn mice, the cells not only expressed their typical molecular markers, but also showed the migration and projection to the host’s cerebellum, hindbrain and spinal cord. The data demonstrate that these human iPSCs-derived neurons exhibit the typical features as the serotonergic neurons in the brain, which provides a solid foundation for studying on human serotonin system and its related disorders.

5-HT6 Receptor Antagonist as an Adjunct Treatment Targeting Residual Symptoms in Patients With Schizophrenia: Unexpected Sex-Related Effects (Double-Blind Placebo-Controlled Trial)

BACKGROUND

Treating patients who experience residual psychotic symptoms during remission of schizophrenia remains one of the most challenging problems. The mechanisms underlying these symptoms differ from those of acute hallucinations and delusions. 5-HT6 receptor antagonists have been considered promising agents in treatment of residual psychotic symptoms and cognitive dysfunction. The aim of the study was to assess the efficacy of a selective 5-HT6 inhibitor Avisetron in the reduction of residual psychotic symptoms in patients with schizophrenia on stable antipsychotic therapy.

METHODS

Eighty clinically stable outpatient subjects with schizophrenia with residual psychotic symptoms were randomized in a double-blind manner to 6 weeks of Avisetron or placebo at 1:1 ratio. Subjects received 8 mg of Avisetron or placebo on top their stable antipsychotic treatment. Standard clinical scales and cognitive tests were used for endpoint assessment. The primary efficacy endpoint was the mean reduction of total Positive and Negative Syndrome Scale score after 6 weeks of treatment.

RESULTS

No significant differences in the primary and secondary endpoints were found between the groups. However, based on the subgroup analysis, the significant improvement of total Positive and Negative Syndrome Scale score and residual psychotic symptoms was observed in female patients.

CONCLUSIONS

It was a negative study with unexpected benefits of the drug only in females. We hypothesized that the role of patients' sex can impact the treatment response to serotonergic drugs in general. We suggest a possible synergistic interaction between estrogen and Avisetron by means of modulating the effect of estrogens on the serotonergic system. Future studies targeting the sex-related effects of serotonergic drugs are warranted.

Influence of nonylphenol and octylphenol exposure on 5-HT, 5-HT transporter, and 5-HT2A receptor

Nonylphenol (NP) and octylphenol (OP) are priority environmental contaminants that have a potential role as endocrine disruptors. They can be biomagnified in the food chain and pose an estrogenic health risk to human health. A 28-day oral toxicity study was performed to observe the impact of single and combined exposure to NP and OP on 5-HT transporter (SERT) as well as 5-HT_2A receptor. Results showed that the 5-HT levels in rat plasma increased with exposure to middle-dose and high-dose NP, to high-dose OP, and to low, middle, and high doses of combined NP and OP (P < 0.05), while the 5-HT levels in rat platelets increased when exposed to NP/OP or combined NP and OP of middle or high dose (P < 0.05). The expression levels of SERT in rat platelets decreased when exposed to high-dose NP/OP or high dose of combined NP and OP (P < 0.05). Meanwhile, the expression levels of 5-HT_2A in rat platelets decreased when exposed to high-dose NP/OP as well as combined NP and OP (P < 0.05). These findings suggested that exposure to NP and OP could influence the metabolic network of 5-hydroxytryptamine via transportation and receptor binding pathways.

Estrogen-dependent effects of 5-hydroxytryptophan on cortical spreading depression in rat: Modelling the serotonin-ovarian hormone interaction in migraine aura

Background Cortical spreading depression (CSD) is the likely culprit of the migraine aura. Migraine is sexually dimorphic and thought to be a "low 5-HT" condition. We sought to decipher the interrelation between serotonin, ovarian hormones and cortical excitability in a model of migraine aura. Methods Occipital KCl-induced CSDs were recorded for one hour at parieto-occipital and frontal levels in adult male (n = 16) and female rats (n = 64) one hour after intraperitoneal (i.p.) injection of 5-hydroxytryptophan (5-HTP) or NaCl. Sixty-five oophorectomized females were treated with estradiol- (E2) or cholesterol- (Chol) filled capsules. Two weeks later we recorded CSDs after 5-HTP/NaCl injections before or 20 hours after capsule removal. Results 5-HTP had no effect in males, but decreased CSD frequency in cycling females, significantly so during estrus, at parieto-occipital (-3.5CSD/h, p < 0.001) and frontal levels (-2.5CSD/h, p = 0.014). In oophorectomized rats, CSD susceptibility increased during E2 treatment at both recording sites (+5CSD/h, p = 0.001 and +3CSD/h, p < 0.01), but decreased promptly after E2 withdrawal (-4.7CSD/h, p < 0.001 and -1.7CSD/h, p = 0.094). The CSD inhibitory effect of 5-HTP was significant only in E2-treated rats (-3.4CSD/h, p = 0.006 and -1.8CSD/h, p = 0.029). Neither the estrous cycle phase, nor E2 or 5-HTP treatments significantly modified CSD propagation velocity. Conclusion 5-HTP decreases CSD occurrence in the presence of ovarian hormones, suggesting its potential efficacy in migraine with aura prophylaxis in females. Elevated E2 levels increase CSD susceptibility, while estrogen withdrawal decreases CSD. In a translational perspective, these findings may explain why migraine auras can appear during pregnancy and why menstrual-related migraine attacks are rarely associated with an aura.

Pharmacologically Induced Sex Hormone Fluctuation Effects on Resting-State Functional Connectivity in a Risk Model for Depression: A Randomized Trial

Women are at relatively greater lifetime risk for depression than men. This elevated risk in women is partly due to heightened risk during time periods characterized by marked fluctuations in sex hormones, including postpartum and perimenopausal periods. How sex hormone fluctuations contribute to heightened risk is not fully understood but may involve intrinsic functional connectivity. We induced a biphasic ovarian sex hormone fluctuation using the gonadotropin-releasing hormone agonist (GnRHa) goserelin to determine, with a randomized placebo-controlled design, intervention effects on or GnRHa-provoked depressive symptoms associations with change in resting-state functional connectivity (rs-FC) in 58 healthy women for six seeds (amygdala, hippocampus, anterior cingulate cortex, dorsal raphe, median raphe, and posterior cingulate cortex). GnRHa intervention did not significantly affect rs-FC in any seeds. Considering the GnRHa group only, the emergence of depressive symptoms following intervention was positively associated with amygdala-right temporal cortex and negatively associated with hippocampus-cingulate rs-FC. A test for mediation suggested that rs-FC changes in these networks marginally mediated the association between decrease in estradiol and increase in depressive symptoms in the GnRHa group (p=0.07). Our findings provide novel evidence-linking changes in rs-FC networks, the emergence of depressive symptoms and sex hormone fluctuations. Notably, we observed evidence that changes in rs-FC may represent a key neurobiological intermediary between molecular changes induced by hormone fluctuations and the emergence of depressive symptoms. Taken together, our findings indicate that sex hormone fluctuations may contribute to heightened risk for developing depressive symptoms by affecting intrinsic functional connectivity of key limbic brain structures.

How Studies of the Serotonin System in Macaque Models of Menopause Relate to Alzheimer's Disease1

Serotonin plays a key role in mood or affect, and dysfunction of the serotonin system has been linked to depression in humans and animal models. Depression appears prior to or coincident with overt symptoms of Alzheimer's disease (AD) in about 50% of patients, and some experts consider it a risk factor for the development of AD. In addition, AD is more prevalent in women, who also show increased incidence of depression. Indeed, it has been proposed that mechanisms underlying depression overlap the mechanisms thought to hasten AD. Women undergo ovarian failure and cessation of ovarian steroid production in middle age and the postmenopausal period correlates with an increase in the onset of depression and AD. This laboratory has examined the many actions of ovarian steroids in the serotonin system of non-human primates using a rhesus macaque model of surgical menopause with short or long-term estradiol (E) or estradiol plus progesterone (E+P) replacement therapy. In this mini-review, we present a brief synopsis of the relevant literature concerning AD, depression, and serotonin. We also present some of our data on serotonin neuron viability, the involvement of the caspase-independent pathway, and apoptosis-inducing factor in serotonin-neuron viability, as well as gene expression related to neurodegeneration and neuron viability in serotonin neurons from adult and aged surgical menopausal macaques. We show that ovarian steroids, particularly E, are crucial for serotonin neuron function and health. In the absence of E, serotonin neurons are endangered and deteriorating toward apoptosis. The possibility that this scenario may proceed or accompany AD in postmenopausal women seems likely.

Hippocampal serotonin-2A receptor-immunoreactive neurons density increases after testosterone therapy in the gonadectomized male mice

The change of steroid levels may also exert different modulatory effects on the number and class of serotonin receptors present in the plasma membrane. The effects of chronic treatment of testosterone for anxiety were examined and expression of 5-HT_2A serotonergic receptor, neuron, astrocyte, and dark neuron density in the hippocampus of gonadectomized male mice was determined. Thirty-six adult male NMRI mice were randomly divided into six groups: intact-no testosterone treatment (No T), gonadectomy (GDX)-No T, GDX-Vehicle, GDX-6.25 mg/kg testosterone (T), GDX-12.5 mg/kg T, and GDX-25 mg/kg T. Anxiety-related behavior was evaluated using elevated plus maze apparatus. The animals were anesthetized after 48 hours after behavioral testing, and decapitated and micron slices were prepared for immunohistochemical as well as histopathological assessment. Subcutaneous injection of testosterone (25 mg/kg) may induce anxiogenic-like behavior in male mice. In addition, immunohistochemical data reveal reduced expression of 5-HT_2A serotonergic receptor after gonadectomy in all areas of the hippocampus. However, treatment with testosterone could increase the mean number of dark neurons as well as immunoreactive neurons in CA1 and CA3 area, dose dependently. The density of 5-HT_2A receptor-immunoreactive neurons may play a crucial role in the induction of anxiety like behavior. As reduction in such receptor expression have shown to significantly enhance anxiety behaviors. However, replacement of testosterone dose dependently enhances the number of 5-HT_2A receptor-immunoreactive neurons and interestingly also reduced anxiety like behaviors.

17β-Estradiol augments antidepressant efficacy of escitalopram in ovariectomized rats: Neuroprotective and serotonin reuptake transporter modulatory effects

The prevalence or recurrence of depression is seriously increased in women during the transition to and after menopause. The chronic hypo-estrogenic state of menopause may reduce the response to antidepressants; however the influence of estrogen therapy on their efficacy is still controversial. This study aimed at investigating the effects of combining escitalopram with 17β-estradiol on depression and cognitive impairment induced by ovariectomy, an experimental model of human menopause. Young adult female Wistar rats were subjected to either sham operation or ovariectomy. Ovariectomized animals were treated chronically with escitalopram (10mg/kg/day, i.p) alone or with four doses of 17β-estradiol (40μg/kg, s.c) given prior to the behavioral tests. Co-administration of 17β-estradiol improved escitalopram-induced antidepressant effect in forced swimming test verified as more prominent decrease in the immobility time without opposing its memory enhancing effect in Morris water maze. 17β-estradiol augmented the modulatory effects of escitalopram on the hippocampal levels of brain-derived neurotrophic factor and serotonin reuptake transporter as well as tumor necrosis factor-alpha without altering its effects on the gene expressions of serotonin receptor 1A, estrogen receptors alpha and beta, or acetylcholinestearase content. This combined therapy afforded synergistic protective effects on the brain histopathological architecture, particularly, the hippocampus. The antidepressant effect of 17β-estradiol was abolished by pretreatment with estrogen receptor antagonist, tamoxifen (10mg/kg, p.o). In conclusion, 17β-estradiol-induced antidepressant effect was confined to intracellular estrogen receptors activation. Moreover, 17β-estradiol enhanced escitalopram's efficiency in ameliorating menopausal-like depression, via exerting synergistic neuroprotective and serotonin reuptake transporter modulatory effects, without impeding escitalopram-mediated cognitive improvement.

Neuroendocrine Underpinnings of Increased Risk for Posttraumatic Stress Disorder in Women

Women are particularly vulnerable to the effects of psychological trauma and the development of trauma-, stressor-, and anxiety-related mental illnesses such as posttraumatic stress disorder (PTSD). In the current chapter, we examine the female hormonal systems that interact with psychobiological stress response systems to elicit maladaptive behavior and mental disease states in traumatized female populations. In addition, we provide a contemporary translational example of a stress vulnerability genomic profile (coding for pituitary adenylate cyclase-activating polypeptide) that may underlie the specific susceptibilities observed in women. Translational scientific investigations such as those described herein may lead to the identification of risk and resilience factors for PTSD as well as enhanced clinical interventions for treating excessive fear and anxiety.

Estradiol Valerate and Remifemin ameliorate ovariectomy-induced decrease in a serotonin dorsal raphe-preoptic hypothalamus pathway in rats

Perimenopausal syndromes begin as ovarian function ceases and the most common symptoms are hot flushes. Data indicate that the projections of serotonin to hypothalamus may be involved in the mechanism of hot flushes. Therefore, the aim of this study is to investigate the potential role of the serotonin dorsal raphe-preoptic hypothalamus pathway for hot flushes in an animal model of menopause. We determined the changes in serotonin expression in the dorsal raphe (DR) and preoptic anterior hypothalamus (POAH) in ovariectomized rats. We also explored the therapeutical effects of estradiol valerate and Remifemin in this model. Eighty female Sprague-Dawley rats were randomly assigned to sham-operated (SHAM) group, ovariectomy (OVX) group with vehicle, ovariectomy with estradiol valerate treatment (OVX+E) group and ovariectomy with Remifemin (OVX+ICR) group. Serotonin expression was evaluated in the DR and POAH using immunofluorescence and quantified in the DR using an enzyme-linked immunosorbent assay (ELISA). Apoptosis was analyzed in the DR by TUNEL assay. The number of serotonin immunoreactive neurons and the level of serotonin expression in the DR decreased significantly following OVX compared to the SHAM group. No TUNEL-positive cells were detected in the DR in any group. In addition, following OVX, the number of serotonin-positive fibers decreased significantly in the ventromedial preoptic nucleus (VMPO), especially in the ventrolateral preoptic nucleus (VLPO). Treatment with either estradiol or Remifemin for 4 weeks countered the OVX-induced decreases in serotonin levels in both the DR and the hypothalamus, with levels in the treated rats similar to those in the SHAM group. A fluorescently labeled retrograde tracer was injected into the VLPO at the 4-week time point. A significantly lower percentage of serotonin with CTB double-labeled neurons in CTB-labeled neurons was demonstrated after ovariectomy, and both estradiol and Remifemin countered this OVX-induced decrease. We conclude that serotonin pathway is changed after ovariectomy, including the serotonin synthesis in DR and serotonin fibers in PO/AH, both E and Remifemin have an equivalent therapeutic effect on it.

5-HT1A receptors of the prelimbic cortex mediate the hormonal impact on learned fear expression in high-anxious female rats

Hormones highly influence female behaviors. However, research on this topic has not usually considered the variable hormonal status. The prelimbic cortex (PrL) is commonly engaged in fear learning. Connections from and to this region are known to be critical in regulating anxiety, in which serotonin (5-HT) plays a fundamental role, particularly through changes in 5-HT1A receptors functioning. Also, hormone fluctuations can greatly influence anxiety in humans and anxiety-related behavior in rodents, and this influence involves the functioning of 5-HT brain systems. The present investigation sought to determine whether fluctuations in ovarian hormones relative to the estrous cycle would influence the expression of learned fear in female rats previously selected as low- (LA) or high-anxious (HA). Furthermore, we investigate the role of the 5-HT system of the PrL, particularly the 5-HT1A receptors, as a possible modulator of estrous cycle influence on the expression of learned fear through intra-PrL microinjections of 5-HT itself or the full 5-HT1A agonist 8-OH-DPAT (8-hydroxy-2-(di-n-propylamine)tetralin). Behavioral changes were assessed using the fear-potentiated startle (FPS) procedure. The results showed that fear intensity is associated with hormonal decay, being more accentuated during the estrus phase. This increase in fear levels was found to be negatively correlated with the expression of potentiated startle. In rats prone to anxiety and tested during the proestrus and estrus phases, 5-HT mechanisms of the PrL seem to play a regulatory role in the expression of learned fear. These results were not replicated in the LA rats. Similar but less intense results were found regarding the early and late diestrus. Our data indicate that future studies on this subject need to take into account the dissociation between low- and high-responsive females to understand how hormones affect emotional behavior.

Go and NoGo: modulation of electrophysiological correlates by female sex steroid hormones

RATIONALE

The behavioral and electrophysiological responses in a Go/NoGo task are objective measures of executive functioning that may be impaired in clinical conditions. Prior to the wider application of Go/NoGo tasks in clinics, it is tempting to evaluate factors causing modulation of the responses.

OBJECTIVE

We aimed to evaluate the effect of different levels of female sex steroids on Go/NoGo task-related ERPs in healthy females.

METHODS

Thirty-four young healthy females performed an equiprobable (50/50) auditory Go/NoGo task. Amplitudes and latencies of N2 and P3 peaks from Fz, Cz, and Pz electrodes were evaluated. 17β-estradiol and progesterone levels in saliva samples were measured. Electrophysiological measures were correlated to 17β-estradiol and progesterone concentrations.

RESULTS

The diverse pattern of modulation of P3 latencies was shown: higher levels of 17β-estradiol contributed to Go-P3 latency prolongation, and higher levels of progesterone contributed to NoGo-P3 latency shortening. Higher levels of 17β-estradiol were associated with more negative frontal N2 amplitude in both conditions.

CONCLUSIONS

The relationship between electrophysiological correlates of executive functioning to individual hormonal levels points to a broader range of variation sources in healthy subjects which might mask or pronounce between-group differences in clinical studies.

Reproductive Steroid Regulation of Mood and Behavior

In this article, we examine evidence supporting the role of reproductive steroids in the regulation of mood and behavior in women and the nature of that role. In the first half of the article, we review evidence for the following: (i) the reproductive system is designed to regulate behavior; (ii) from the subcellular to cellular to circuit to behavior, reproductive steroids are powerful neuroregulators; (iii) affective disorders are disorders of behavioral state; and (iv) reproductive steroids affect virtually every system implicated in the pathophysiology of depression. In the second half of the article, we discuss the diagnosis of the three reproductive endocrine-related mood disorders (premenstrual dysphoric disorder, postpartum depression, and perimenopausal depression) and present evidence supporting the relevance of reproductive steroids to these conditions. Existing evidence suggests that changes in reproductive steroid levels during specific reproductive states (i.e., the premenstrual phase of the menstrual cycle, pregnancy, parturition, and the menopause transition) trigger affective dysregulation in susceptible women, thus suggesting the etiopathogenic relevance of these hormonal changes in reproductive mood disorders. Understanding the source of individual susceptibility is critical to both preventing the onset of illness and developing novel, individualized treatments for reproductive-related affective dysregulation. © 2016 American Physiological Society. Compr Physiol 6:1135-1160, 2016e.

Preclinical Abuse Potential Assessment of Flibanserin: Effects on Intracranial Self-Stimulation in Female and Male Rats

INTRODUCTION

Flibanserin is a serotonin receptor subtype 1A agonist and 2A antagonist that has been approved by the Food and Drug Administration for treating female sexual interest and arousal disorder. Little is known about the abuse potential of flibanserin.

AIM

To examine abuse-related effects of flibanserin in rats using an intracranial self-stimulation (ICSS) procedure previously used to evaluate the abuse potential of other drugs.

METHODS

Adult female and male Sprague-Dawley rats with electrodes implanted in the medial forebrain bundle were trained to press a lever for electrical brain stimulation under a "frequency-rate" ICSS procedure. In this procedure, increasing frequencies of brain stimulation maintain increasing rates of responding. Drugs of abuse typically increase (or "facilitate") ICSS rates and produce leftward and upward shifts in ICSS frequency-rate curves, whereas drugs that lack abuse potential typically do not alter or only decrease ICSS rates. Initial studies determined the potency and time course of effects on ICSS produced by acute flibanserin administration (1.0, 3.2 and 10.0 mg/kg). Subsequent studies determined the effects of flibanserin (3.2-18 mg/kg) before and after a regimen of repeated flibanserin administration (5.6 mg/kg/d for 5 days). Effects of the abused stimulant amphetamine (1.0 mg/kg) were examined as a positive control.

MAIN OUTCOME MEASURES

Flibanserin effects on ICSS frequency-rate curves in female and male rats were examined and compared with the effects of amphetamine.

RESULTS

Baseline ICSS frequency-rate curves were similar in female and male rats. Acute and repeated administrations of flibanserin produced only decreases in ICSS rates, and rate-decreasing effects of the highest flibanserin dose (10 mg/kg) were greater in female than in male rats. In contrast to flibanserin, amphetamine produced an abuse-related increase in ICSS rates that did not differ between female and male rats.

CONCLUSION

These results suggest that flibanserin has low abuse potential. In addition, this study suggests that female rats might be more sensitive than male rats to the rate-decreasing effects of high flibanserin doses.

5-HTTLPR and gender differences in affective disorders: A systematic review

BACKGROUND

Serotonin transporter-linked polymorphic region (5-HTTLPR) variants have been extensively studied in psychiatric disorders. Although gender effects have been reported, they have not been comprehensively reviewed. The aim of our study was to summarize literature findings on 5-HTTLPR and gender differences in affective disorders.

METHODS

A systematic search of PubMed, ISI Web of Knowledge, and PsycINFO databases was performed for dates until January 2015. The included articles (n=78) analyzed the association between 5-HTTLPR and affective spectrum disorders, taking into account gender. The quality of each study was assessed through STROBE and CONSORT.

RESULTS

5-HTTLPR modulation of affective disorders varied by gender. The S allele (or SS genotype) seemed to be differently associated with an increased risk of depression, depressive symptoms, anxiety traits and symptoms, and symptoms of internalizing behavior among women and an increased risk of aggressiveness, conduct disorder and symptom counts of externalizing behavior among men. Moreover, the presence of stressful life events reinforced the association. Interestingly, these differences seemed to begin with adolescence and were not consistent among the elderly, suggesting a plausible role of hormonal fluctuations.

LIMITATIONS

The review is limited by the small number of included papers, due to the paucity of information in the literature regarding 5-HTTLPR and gender.

CONCLUSIONS

5-HTTLPR variants may exert a differential modulation on a number of features depending on gender. Further studies are needed to more deeply investigate the effect of 5-HTTLPR×gender on the modulation of affective disorders.

Microbiome-Gut-Brain Axis: A Pathway for Improving Brainstem Serotonin Homeostasis and Successful Autoresuscitation in SIDS-A Novel Hypothesis

Sudden infant death syndrome (SIDS) continues to be a major public health issue. Following its major decline since the "Back to Sleep" campaign, the incidence of SIDS has plateaued, with an annual incidence of about 1,500 SIDS-related deaths in the United States and thousands more throughout the world. The etiology of SIDS, the major cause of postneonatal mortality in the western world, is still poorly understood. Although sleeping in prone position is a major risk factor, SIDS continues to occur even in the supine sleeping position. The triple-risk model of Filiano and Kinney emphasizes the interaction between a susceptible infant during a critical developmental period and stressor/s in the pathogenesis of SIDS. Recent evidence ranges from dysregulated autonomic control to findings of altered neurochemistry, especially the serotonergic system that plays an important role in brainstem cardiorespiratory/thermoregulatory centers. Brainstem serotonin (5-HT) and tryptophan hydroxylase-2 (TPH-2) levels have been shown to be lower in SIDS, supporting the evidence that defects in the medullary serotonergic system play a significant role in SIDS. Pathogenic bacteria and their enterotoxins have been associated with SIDS, although no direct evidence has been established. We present a new hypothesis that the infant's gut microbiome, and/or its metabolites, by its direct effects on the gut enterochromaffin cells, stimulates the afferent gut vagal endings by releasing serotonin (paracrine effect), optimizing autoresuscitation by modulating brainstem 5-HT levels through the microbiome-gut-brain axis, thus playing a significant role in SIDS during the critical period of gut flora development and vulnerability to SIDS. The shared similarities between various risk factors for SIDS and their relationship with the infant gut microbiome support our hypothesis. Comprehensive gut-microbiome studies are required to test our hypothesis.

Beta-Arrestin1 Levels in Mononuclear Leukocytes Support Depression Scores for Women with Premenstrual Dysphoric Disorder

Depression is very common in reproductive women particularly with premenstrual dysphoric disorder (PMDD), which is a severe form of premenstrual syndrome (PMS). Beta-arrestins were previously implicated in the pathophysiology, diagnosis and treatment for mood disorders. This study examined whether a measurement for beta-arrestin1 levels in peripheral blood mononuclear leukocytes (PBMC), could aid to distinguish between PMDD and PMS. Study participants (n = 25) were non-pregnant women between 18-42 years of age with the symptoms of PMS/PMDD, but not taking any antidepressants/therapy and at the luteal phase of menstruation. The levels of beta-arrestin1 protein in the PBMCs were determined by ELISA using human beta-arrestin1 kit. The beta-arrestin1 levels were compared with the Hamilton Depression Rating Scale scores among these women. The magnitude of the different parameters for Axis 1 mental disorders were significantly higher and beta arrestin1 protein levels in PBMCs were significantly lower in women with PMDD as compared to PMS women. The reduction in beta arrestin1 protein levels was significantly correlated with the severity of depressive symptoms. Beta-arrestin1 measurements in women may potentially serve for biochemical diagnostic purposes for PMDD and might be useful as evidence-based support for questionnaires.

Ovarian steroids regulate gene expression related to DNA repair and neurodegenerative diseases in serotonin neurons of macaques

Depression often accompanies the perimenopausal transition and it often precedes overt symptomology in common neurodegenerative diseases (NDDs, such as Alzheimer's, Parkinson's, Huntington, amyotrophic lateral sclerosis). Serotonin dysfunction is frequently found in the different etiologies of depression. We have shown that ovariectomized (Ovx) monkeys treated with estradiol (E) for 28 days supplemented with placebo or progesterone (P) on days 14-28 had reduced DNA fragmentation in serotonin neurons of the dorsal raphe nucleus, and long-term Ovx monkeys had fewer serotonin neurons than intact controls. We questioned the effect of E alone or E+P (estradiol supplemented with progesterone) on gene expression related to DNA repair, protein folding (chaperones), the ubiquitin-proteosome, axon transport and NDD-specific genes in serotonin neurons. Ovx macaques were treated with placebo, E or E+P (n=3 per group) for 1 month. Serotonin neurons were laser captured and subjected to microarray analysis and quantitative real-time PCR (qRT-PCR). Increases were confirmed with qRT-PCR in five genes that code for proteins involved in repair of strand breaks and nucleotide excision. NBN1, PCNA (proliferating nuclear antigen), GADD45A (DNA damage-inducible), RAD23A (DNA damage recognition) and GTF2H5 (gene transcription factor 2H5) significantly increased with E or E+P treatment (all analysis of variance (ANOVA), P<0.01). Chaperone genes HSP70 (heat-shock protein 70), HSP60 and HSP27 significantly increased with E or E+P treatment (all ANOVA, P<0.05). HSP90 showed a similar trend. Ubiquinase coding genes UBEA5, UBE2D3 and UBE3A (Parkin) increased with E or E+P (all ANOVA, P<0.003). Transport-related genes coding kinesin, dynein and dynactin increased with E or E+P treatment (all ANOVA, P<0.03). SCNA (α-synuclein) and ADAM10 (α-secretase) increased (both ANOVA, P<0.02) but PSEN1 (presenilin1) decreased (ANOVA, P<0.02) with treatment. APP decreased 10-fold with E or E+P administration. Newman-Keuls post hoc comparisons indicated variation in the response to E alone versus E+P across the different genes. In summary, E or E+P increased gene expression for DNA repair mechanisms in serotonin neurons, thereby rendering them less vulnerable to stress-induced DNA fragmentation. In addition, E or E+P regulated four genes encoding proteins that are often misfolded or malfunctioning in neuronal populations subserving overt NDD symptomology. The expression and regulation of these genes in serotonergic neurons invites speculation that they may mediate an underlying disease process in NDDs, which in turn may be ameliorated or delayed with timely hormone therapy in women.

The MAOA, COMT, MTHFR and ESR1 gene polymorphisms are associated with the risk of depression in menopausal women

OBJECTIVE

The aim of the study was assessment of a possible relationship between the polymorphisms of the candidate genes participating in the etiology of some neurological and psychiatric disorders and the risk of depression in perimenopausal and postmenopausal women.

METHODS

A total of 167 (54 perimenopausal and 113 postmenopausal) Caucasian women from western Poland, aged 42-67, were recruited as the patient group in the study because of depressive symptoms, and another 321 healthy women (102 perimenopausal and 219 postmenopausal) served as the controls. All study participants were evaluated for climacteric and depressive disorders according to the Kupperman index and Hamilton rating scale for depression (HRSD), respectively. The following candidate genes were selected for the study: 5HTR2A, 5HTR1B, 5HTR2C, TPH1, TPH2, MAOA, COMT, NET, GABRB1, ESR1, MTHFR, MTR and MTHFD1. In each group the frequencies of the polymorphisms were determined using PCR-RFLP analysis.

RESULTS

After correcting for Bonferroni multiple tests, we found associations between the MAOA c.1460C>T (SNP 1137070), COMT c.472G>A (SNP 4680), MTHFR c.677C>T (SNP 1801133) and ESR1 454(-351) A>G (SNP 9340799) polymorphisms to mild and moderate depressive symptoms in menopausal women. In the perimenopausal and postmenopausal women, genotype association of the MAOA c.1460 CT and c.1460 CT+TT (OR=1.83; pcorr=0.009 and OR=1.85; pcorr=0.003, resp.), and of the MTHFR c.677 TT and c.677 CT+TT (OR=3.52; pcorr=0.00009 and OR=2.06; pcorr=0.0006, resp.), as well as of the COMT c.472 GA and COMT c.472 GA+AA genotypes (OR=2.23; pcorr=0.03 and OR=2.17; pcorr=0.027, resp.) in the postmenopausal women revealed significantly higher frequencies of these variants in depressed female patients than in controls, whereas the ESR1 454(-351) AG and 454(-351) AG+GG genotypes were associated with lower risk of depression in postmenopausal women (OR=0.48; pcorr=0.012, and OR=0.52; pcorr=0.015, resp.).

CONCLUSIONS

Our study substantiates the involvement of the MAOA and MTHFR polymorphisms in climacteric depression and offers evidence that the COMT and ESR1 genes may also play a role in the susceptibility to depressive mood in postmenopausal women.

Ovarian steroids regulate gene expression in the dorsal raphe of old female macaques

With extended life spans in modern humans, menopause has become a significant risk factor for depression, anxiety, loss of cognitive functions, weight gain, metabolic disease, osteoporosis, cardiovascular disease, and neurodegenerative diseases. Clinical studies have found beneficial neural effects of ovarian steroid hormone therapy (HT) during the menopausal transition and data are emerging that it can be continued long term. To further understand molecular underpinnings of the clinical studies, we used quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to examine gene expression in the serotonergic dorsal raphe of old (>18 years) rhesus macaques, focusing on genes related to depression, cellular resilience, and neurodegenerative diseases. The animals were ovariectomized (Ovx, surgically menopausal) and subjected to either estradiol or estradiol plus progesterone HT, or to placebo, starting 2 months after Ovx and continuing for ∼ 4 years. Significant changes were observed in 36 of 48 genes examined that encode proteins supporting serotonin neurotransmission, synapse assembly, glutamate neurotransmission, DNA repair, chaperones, ubiquinases and transport motors, as well as genes encoding proteins that have potential to delay the onset of neuropathologies. The data reveal important gene targets for chronic HT that contribute to neural health. Alternatively, the loss of ovarian steroids may lead to loss of functions at the gene level that contribute to many of the observable neural deficits after menopause.

High-Dose Testosterone Treatment Increases Serotonin Transporter Binding in Transgender People

BACKGROUND

Women are two times more likely to be diagnosed with depression than men. Sex hormones modulating serotonergic transmission are proposed to partly underlie these epidemiologic findings. Here, we used the cross-sex steroid hormone treatment of transsexuals seeking sex reassignment as a model to investigate acute and chronic effects of testosterone and estradiol on serotonin reuptake transporter (SERT) binding in female-to-male and male-to-female transsexuals.

METHODS

Thirty-three transsexuals underwent [(11)C]DASB positron emission tomography before start of treatment, a subset of which underwent a second scan 4 weeks and a third scan 4 months after treatment start. SERT nondisplaceable binding potential was quantified in 12 regions of interest. Treatment effects were analyzed using linear mixed models. Changes of hormone plasma levels were correlated with changes in regional SERT nondisplaceable binding potential.

RESULTS

One and 4 months of androgen treatment in female-to-male transsexuals increased SERT binding in amygdala, caudate, putamen, and median raphe nucleus. SERT binding increases correlated with treatment-induced increases in testosterone levels, suggesting that testosterone increases SERT expression on the cell surface. Conversely, 4 months of antiandrogen and estrogen treatment in male-to-female transsexuals led to decreases in SERT binding in insula, anterior, and mid-cingulate cortex. Increases in estradiol levels correlated negatively with decreases in regional SERT binding, indicating a protective effect of estradiol against SERT loss.

CONCLUSIONS

Given the central role of the SERT in the treatment of depression and anxiety disorders, these findings may lead to new treatment modalities and expand our understanding of the mechanism of action of antidepressant treatment properties.

Role of Serotonin Transporter Changes in Depressive Responses to Sex-Steroid Hormone Manipulation: A Positron Emission Tomography Study

BACKGROUND

An adverse response to acute and pronounced changes in sex-hormone levels during, for example, the perimenopausal or postpartum period appears to heighten risk for major depression in women. The underlying risk mechanisms remain elusive but may include transiently compromised serotonergic brain signaling. Here, we modeled a biphasic ovarian sex hormone fluctuation using a gonadotropin-releasing hormone agonist (GnRHa) and evaluated if emergence of depressive symptoms was associated with change in cerebral serotonin transporter (SERT) binding following intervention.

METHODS

A double-blind, randomized, placebo-controlled study included 63 healthy female volunteers (mean age 24.3 ± 4.9 years) with regular menstrual cycles between 23 and 35 days. Participants were randomized to active (goserelin [GnRHa] 3.6 mg implant) or placebo intervention. Sixty women completed follow-up and entered the analyses. Primary outcome measures were changes from baseline in depressive symptoms assessed on the 17-item Hamilton Depression Rating Scale and SERT binding as imaged by [(11)C]DASB positron emission tomography. Outcome measures were acquired at baseline in the follicular phase (cycle day 6.6 ± 2.2) and at follow-up (16.2 ± 2.6 days after intervention start).

RESULTS

Sex hormone manipulation with GnRHa significantly triggered subclinical depressive symptoms within-group (p = .003) and relative to placebo (p = .02), which were positively associated with net decreases in estradiol levels (p = .02) from baseline within the GnRHa group. Depressive symptoms were associated with increases in neocortical SERT binding in the GnRHa group relative to placebo (p = .003).

CONCLUSIONS

Our data imply both serotonergic signaling and estradiol in the mechanisms by which sex-steroid hormone fluctuations provoke depressive symptoms and thus provide a rationale for future preventive strategies in high-risk groups.