Estradiol increases Pet-1 and serotonin transporter mRNA in the midbrain raphe nuclei of ovariectomized rats

Binge Eating Risk During Midlife and the Menopausal Transition: Sensitivity to Ovarian Hormones as Potential Mechanisms of Risk

PURPOSE OF REVIEW

Recent research suggests that binge eating may be more prevalent among women in midlife than previously believed. The menopausal transition, an important developmental stage during midlife, is characterized by substantial fluctuations and eventual decreases in ovarian hormones that may contribute to increased risk. This narrative review summarizes findings from studies of binge eating during midlife and menopause and discusses the potential role of ovarian hormones in binge eating risk.

RECENT FINDINGS

Studies are few in number and findings are mixed, with only some studies showing increased binge eating during midlife and the menopausal transition. Sensitivity to ovarian hormones, potentially through gene x hormone interactions, may influence who experiences increased binge eating risk and could help explain mixed findings in the field. Future studies of hormone sensitivity and gene x hormone interactions are needed to further elucidate midlife and menopausal risk for binge eating in women.

Increase in serotonin transporter binding in patients with premenstrual dysphoric disorder across the menstrual cycle: a case-control longitudinal neuroreceptor ligand PET imaging study

BACKGROUND

Premenstrual dysphoric disorder (PMDD) disrupts the lives of millions of people each month. The timing of symptoms suggests that hormonal fluctuations play a role in the pathogenesis. Here, we tested whether a heightened sensitivity of the serotonin system to menstrual cycle phase underlies PMDD, assessing the relationship of serotonin transporter (5-HTT) changes with symptom severity across the menstrual cycle.

METHODS

In this longitudinal case-control study, we acquired 118 [¹¹C]DASB positron emission tomography scans measuring 5-HTT nondisplaceable binding potential (BP_ND) in 30 patients with PMDD and 29 controls during 2 menstrual cycle phases (periovulatory, premenstrual). The primary outcome was midbrain and prefrontal cortex 5-HTT BP_ND. We tested whether BP_ND changes correlated with depressed mood.

RESULTS

Linear mixed effects modeling (significant group × time × region interaction) showed a mean increase of 18% in midbrain 5-HTT BP_ND (mean [SD] periovulatory = 1.64 [0.40], premenstrual = 1.93 [0.40], delta = 0.29 [0.47]: t₂₉ = -3.43, p = .0002) in patients with PMDD, whereas controls displayed a mean 10% decrease in midbrain 5-HTT BP_ND (periovulatory = 1.65 [0.24] > premenstrual = 1.49 [0.41], delta = -0.17 [0.33]: t₂₈ = -2.73, p = .01). In patients, increased midbrain 5-HTT BP_ND correlated with depressive symptom severity (R² = 0.41, p < .0015) across the menstrual cycle.

CONCLUSIONS

These data suggest cycle-specific dynamics with increased central serotonergic uptake followed by extracellular serotonin loss underlying the premenstrual onset of depressed mood in patients with PMDD. These neurochemical findings argue for systematic testing of pre-symptom-onset dosing of selective serotonin reuptake inhibitors or nonpharmacological strategies to augment extracellular serotonin in people with PMDD.

Combined oral contraceptive use and risk for binge eating in women: Potential gene × hormone interactions

Extant animal and human data suggest endogenous ovarian hormones increase risk for binge eating in females, possibly via gene × hormone interactions and hormonally induced increases in genetic influences. Approximately 85 % of women will take combined oral contraceptives (COCs) that mimic the riskiest hormonal milieu for binge eating (i.e., post-ovulation when both estrogen and progesterone are present). The purpose of this narrative review is to synthesize findings of binge eating risk in COC users. Few studies have been conducted, but results suggest that COCs may increase risk for binge eating and related phenotypes (e.g., craving for sweets), particularly in genetically vulnerable women. Larger, more systematic human and animal studies of COCs and binge eating are needed. The goal of this work should be to advance personalized medicine by identifying the extent of COC risk as well as the role of gene × hormone interactions in susceptibility.

Long-Term Effects of Intrauterine Exposure to Antidepressants on Physical, Neurodevelopmental, and Psychiatric Outcomes: A Systematic Review

OBJECTIVE

Reviews on child outcomes following in utero antidepressant exposure have focused on short-term outcomes. However, several recent individual studies reported on adverse physical, neurodevelopmental, and psychiatric outcomes beyond infancy and early childhood. The objective of this systematic review was to establish the long-term effects of prenatal antidepressant exposure on physical, neurodevelopmental, and psychiatric outcomes in individuals aged 4 years and older.

DATA SOURCES

Embase, MEDLINE Ovid, Web of Science, Cochrane Central, and Google Scholar were systematically searched for all relevant articles, written in English and published prior to November 8, 2018, using terms describing antidepressants, pregnancy, and developmental outcomes.

STUDY SELECTION

All original research articles on long-term outcomes of prenatal antidepressant exposure were eligible for inclusion. After screening and removal of duplicates, a total of 34 studies were identified.

DATA EXTRACTION

Included articles were qualitatively analyzed to determine inconsistency, indirectness, imprecision, and study bias.

RESULTS

The identified studies demonstrated statistically significant associations between prenatal antidepressant exposure and a range of physical, neurodevelopmental, and psychiatric outcomes. Yet, the risk of confounding by indication was high. When controlling for confounders, 5 studies investigating physical outcomes (asthma, cancer, body mass index [BMI], epilepsy) found no association except conflicting outcomes for BMI. Eighteen studies examining neurodevelopmental outcomes (cognition, behavior, IQ, motor development, speech, language, and scholastic outcomes) found no consistent associations with antidepressant exposure after taking confounders into account. Eleven studies investigated psychiatric outcomes. After adjusting for confounders, prenatal antidepressant exposure was associated with affective disorders but not with childhood psychiatric outcomes (eg, autism spectrum disorders, attention-deficit/hyperactivity disorder).

CONCLUSIONS

Reported associations between in utero exposure to antidepressants and physical, neurodevelopmental, and psychiatric outcomes, in large part, seem to be driven by the underlying maternal disorder. When limiting confounding by indication, prenatal exposure to antidepressants was significantly associated only with offspring BMI and affective disorders.

Genetics of sex differences in neuroanatomy and function

Sex differences are observed at many distinct biologic levels, such as in the anatomy and functioning of the brain, behavior, and susceptibility to neuropsychiatric disorders. Previously, these differences were believed to entirely result from the secretion of gonadal hormones; however, recent research has demonstrated that differences are also the consequence of direct or nonhormonal effects of genes located on the sex chromosomes. This chapter reviews the four core genotype model that separates the effects of hormones and sex chromosomes and highlights a few genes that are believed to be partly responsible for sex dimorphism of the brain, in particular, the Sry gene. Genetics of the brain's neurochemistry is discussed and the susceptibility to certain neurologic and psychiatric disorders is reviewed. Lastly, we discuss the sex-specific genetic contribution in disorders of sexual development. The precise molecular mechanisms underlying these differences are currently not entirely known. An increased knowledge and understanding of the role of candidate genes will undeniably be of great aid in elucidating the molecular basis of sex-biased disorders and potentially allow for more sex-specific therapies.

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.

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.

Central regulation of energy metabolism by estrogens

BACKGROUND

Estrogenic actions in the brain prevent obesity. Better understanding of the underlying mechanisms may facilitate development of new obesity therapies.

SCOPE OF REVIEW

This review focuses on the critical brain regions that mediate effects of estrogens on food intake and/or energy expenditure, the molecular signals that are involved, and the functional interactions between brain estrogens and other signals modulating metabolism. Body weight regulation by estrogens in male brains will also be discussed.

MAJOR CONCLUSIONS

17β-estradiol acts in the brain to regulate energy homeostasis in both sexes. It can inhibit feeding and stimulate brown adipose tissue thermogenesis. A better understanding of the central actions of 17β-estradiol on energy balance would provide new insight for the development of therapies against obesity in both sexes.

Amitraz changes NE, DA and 5-HT biosynthesis and metabolism mediated by alterations in estradiol content in CNS of male rats

Amitraz is a formamidine insecticide/acaricide that alters different neurotransmitters levels, among other neurotoxic effects. Oral amitraz exposure (20, 50 and 80 mg/kg bw, 5 days) has been reported to increase serotonin (5-HT), norepinephrine (NE) and dopamine (DA) content and to decrease their metabolites and turnover rates in the male rat brain, particularly in the striatum, prefrontal cortex, and hippocampus. However, the mechanisms by which these alterations are produced are not completely understood. One possibility is that amitraz monoamine oxidase (MAO) inhibition could mediate these effects. Alternatively, it alters serum concentrations of sex steroids that regulate the enzymes responsible for these neurotransmitters synthesis and metabolism. Thus, alterations in sex steroids in the brain could also mediate the observed effects. To test these hypothesis regarding possible mechanisms, we treated male rats with 20, 50 and 80 mg/kg bw for 5 days and then isolated tissue from striatum, prefrontal cortex, and hippocampus. We then measured tissue levels of expression and/or activity of MAO, catechol-O-metyltransferase (COMT), dopamine-β-hydroxylase (DBH), tyrosine hydroxylase (TH) and tryptophan hydroxylase (TRH) as well as estradiol levels in these regions. Our results show that amitraz did not inhibit MAO activity at these doses, but altered MAO, COMT, DBH, TH and TRH gene expression, as well as TH and TRH activity and estradiol levels. The alteration of these enzymes was partially mediated by dysregulation of estradiol levels. Our present results provide new understanding of the mechanisms contributing to the harmful effects of amitraz.

The effects of high fat diet and estradiol on hypothalamic prepro-QRFP mRNA expression in female rats

Estradiol (E2) is a potent regulator of feeding behavior, body weight and adiposity in females. The hypothalamic neuropeptide, QRFP, is an orexigenic peptide that increases the consumption of high fat diet (HFD) in intact female rats. Therefore, the goal of the current series of studies was to elucidate the effects of E2 on the expression of hypothalamic QRFP and its receptors, QRFP-r1 and QRFP-r2, in female rats fed a HFD. Alterations in prepro-QRFP, QRFP-r1, and QRFP-r2 expression across the estrous cycle, following ovariectomy (OVX) and following estradiol benzoate (EB) treatment were assessed in the ventral medial nucleus of the hypothalamus/arcuate nucleus (VMH/ARC) and the lateral hypothalamus. In intact females, consumption of HFD increased prepro-QRFP and QRFP-r1 mRNA levels in the VMH/ARC during diestrus, a phase associated with increased food intake and low levels of E2. To assess the effects of diminished endogenous E2, rats were ovariectomized. HFD consumption and OVX increased prepro-QRFP mRNA in the VMH/ARC. Ovariectomized rats consuming HFD expressed the highest levels of QRFP. In the third experiment, all rats received EB replacement every 4days following OVX to examine the effects of E2 on QRFP expression. Prepro-QRFP, QRFP-r1 and QRFP-r2 mRNA were assessed prior to and following EB administration. EB replacement significantly reduced prepro-QRFP mRNA expression in the VMH/ARC. Overall these studies support a role for E2 in the regulation of prepro-QRFP mRNA in the VMH/ARC and suggest that E2's effects on food intake may be via a direct effect on the orexigenic peptide, QRFP.

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.

Interactive effects of hypoxia with estradiol-17β on tryptophan hydroxylase activity and serotonin levels in the Atlantic croaker hypothalamus

Hypoxia causes a marked decline in reproductive neuroendocrine function in Atlantic croaker due to decreases in the hypothalamic expression and activities of tryptophan hydroxylase (TPH, the rate limiting enzyme in serotonin synthesis) and aromatase. In the present study, the influence of the estrogen status on hypothalamic TPH and serotonin (5-HT) regulation by hypoxia (dissolved oxygen: 1.7 mg/L for 4 weeks) was investigated in croaker. Treatment in vivo with the aromatase inhibitor, ATD (1,4,6-androstatrien-3,17-dione), significantly decreased TPH activity, TPHs (TPH-1 and TPH-2) mRNAs expression, and 5-hydroxytryptophan (5-HTP, an immediate precursor of 5-HT) and 5-HT contents in croaker hypothalamus. Treatment with estradiol-17β partially restored hypothalamic TPH activity, TPHs mRNA expression, and 5-HTP and 5-HT contents in hypoxia-exposed fish. These results suggest that the hypoxia-induced inhibition of TPH and 5-HT synthesis is dependent on the estrogen status. To our knowledge, this is the first report of a role for estrogens in modulating neural TPH and 5-HT responses to hypoxia in aquatic vertebrates.

Mechanisms of pain modulation by sex hormones in migraine

A number of pain conditions, acute as well as chronic, are much more prevalent in women, such as temporomandibular disorder (TMD), irritable bowel syndrome, fibromyalgia, and migraine. The association of female sex steroids with these nociceptive conditions is well known, but the mechanisms of their effects on pain signaling are yet to be deciphered. We reviewed the mechanisms through which female sex steroids might influence the trigeminal nociceptive pathways with a focus on migraine. Sex steroid receptors are located in trigeminal circuits, providing the molecular substrate for direct effects. In addition to classical genomic effects, sex steroids exert rapid nongenomic actions to modulate nociceptive signaling. Although there are only a handful of studies that have directly addressed the effect of sex hormones in animal models of migraine, the putative mechanisms can be extrapolated from observations in animal models of other trigeminal pain disorders, like TMD. Sex hormones may regulate sensitization of trigeminal neurons by modulating expression of nociceptive mediator such as calcitonin gene-related peptide. Its expression is mostly positively regulated by estrogen, although a few studies also report an inverse relationship. Serotonin (5-Hydroxytryptamine [5-HT]) is a neurotransmitter implicated in migraine; its synthesis is enhanced in most parts of brain by estrogen, which increases expression of the rate-limiting enzyme tryptophan hydroxylase and decreases expression of the serotonin re-uptake transporter. Downstream signaling, including extracellular signal-regulated kinase activation, calcium-dependent mechanisms, and cAMP response element-binding activation, are thought to be the major signaling events affected by sex hormones. These findings need to be confirmed in migraine-specific animal models that may also provide clues to additional ion channels, neuropeptides, and intracellular signaling cascades that contribute to the increased prevalence of migraine in women.

GPR30 is necessary for estradiol-induced desensitization of 5-HT1A receptor signaling in the paraventricular nucleus of the rat hypothalamus

Estrogen therapy used in combination with selective serotonin reuptake inhibitor (SSRI) treatment improves SSRI efficacy for the treatment of mood disorders. Desensitization of serotonin 1A (5-HT(1A)) receptors, which takes one to two weeks to develop in animals, is necessary for SSRI therapeutic efficacy. Estradiol modifies 5-HT(1A) receptor signaling and induces a partial desensitization in the paraventricular nucleus (PVN) of the rat within two days, but the mechanisms underlying this effect are currently unknown. The purpose of this study was to identify the estrogen receptor necessary for estradiol-induced 5-HT(1A) receptor desensitization. We previously showed that estrogen receptor β is not necessary for 5-HT(1A) receptor desensitization and that selective activation of estrogen receptor GPR30 mimics the effects of estradiol in rat PVN. Here, we used a recombinant adenovirus containing GPR30 siRNAs to decrease GPR30 expression in the PVN. Reduction of GPR30 prevented estradiol-induced desensitization of 5-HT(1A) receptor as measured by hormonal responses to the selective 5-HT(1A) receptor agonist, (+)8-OH-DPAT. To determine the possible mechanisms underlying these effects, we investigated protein and mRNA levels of 5-HT(1A) receptor signaling components including 5-HT(1A) receptor, Gαz, and RGSz1. We found that two days of estradiol increased protein and mRNA expression of RGSz1, and decreased 5-HT(1A) receptor protein but increased 5-HT(1A) mRNA; GPR30 knockdown prevented the estradiol-induced changes in 5-HT(1A) receptor protein in the PVN. Taken together, these data demonstrate that GPR30 is necessary for estradiol-induced changes in the 5-HT(1A) receptor signaling pathway and desensitization of 5-HT(1A) receptor signaling.

Middle-aged female rats retain sensitivity to the anorexigenic effect of exogenous estradiol

It is well established that estradiol (E2) decreases food intake and body weight in young female rats. However, it is not clear if female rats retain responsiveness to the anorexigenic effect of E2 during middle age. Because middle-aged females exhibit reduced responsiveness to E2, manifesting as a delayed and attenuated luteinizing hormone surge, it is plausible that middle-aged rats are less responsive to the anorexigenic effect of E2. To test this we monitored food intake in ovariohysterectomized young and middle-aged rats following E2 treatment. E2 decreased food intake and body weight to a similar degree in both young and middle-aged rats. Next, we investigated whether genes that mediate the estrogenic inhibition of food intake are similarly responsive to E2 by measuring gene expression of the anorexigenic genes corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), the long form of the leptin receptor (Lepr) and serotonin 2C receptors (5HT2CR) and the orexigenic genes agouti-related peptide (AgRP), neuropeptide Y (NPY), prepromelanin-concentrating hormone (pMCH) and orexin in the hypothalamus of young and middle-aged OVX rats treated with E2. As expected, E2 increased expression of all anorexigenic genes while decreasing expression of all orexigenic genes in young rats. Although CRH, 5HT2CR, Lepr, AgRP, NPY and orexin were also sensitive to E2 treatment in middle-aged rats, POMC and pMCH expression were not influenced by E2 in middle-aged rats. These data demonstrate that young and middle-aged rats are similarly sensitive to the anorexigenic effect of E2 and that most, but not all feeding-related genes retain sensitivity to E2.

Estradiol increases the anorexia associated with increased 5-HT(2C) receptor activation in ovariectomized rats

Estradiol's inhibitory effect on food intake is mediated, in part, by its ability to increase the activity of meal-related signals, including serotonin (5-HT), which hastens satiation. The important role that postsynaptic 5-HT(2C) receptors play in mediating 5-HT's anorexigenic effect prompted us to investigate whether a regimen of acute estradiol treatment increases the anorexia associated with increased 5-HT(2C) receptor activation in ovariectomized (OVX) rats. We demonstrated that intraperitoneal and intracerebroventricular (i.c.v.) administration of low doses of the 5-HT(2C) receptor agonist meta-chlorophenylpiperazine (mCPP) decreased 1-h dark-phase food intake in estradiol-treated, but not oil-treated, OVX rats. During a longer feeding test, we demonstrated that i.c.v. administration of mCPP decreased 22-h food intake in oil-treated and, to a greater extent, estradiol-treated OVX rats. In a second study, we demonstrated that estradiol increased 5-HT(2C) receptor protein content in the caudal brainstem, but not hypothalamus, of OVX rats. We conclude that a physiologically-relevant regimen of acute estradiol treatment increases sensitivity to mCPP's anorexigenic effect. Our demonstration that this same regimen of estradiol treatment increases 5-HT(2C) receptor protein content in the caudal hindbrain of OVX rats provides a possible mechanism to explain our behavioral findings.

Estradiol acts in the medial preoptic area, arcuate nucleus, and dorsal raphe nucleus to reduce food intake in ovariectomized rats

Estradiol (E2) exerts an inhibitory effect on food intake in a variety of species. While compelling evidence indicates that central, rather than peripheral, estrogen receptors (ERs) mediate this effect, the exact brain regions involved have yet to be conclusively identified. In order to identify brain regions that are sufficient for E2's anorectic effect, food intake was monitored for 48 h following acute, unilateral, microinfusions of vehicle and two doses (0.25 and 2.5 μg) of a water-soluble form of E2 in multiple brain regions within the hypothalamus and midbrain of ovariectomized rats. Dose-related decreases in 24-h food intake were observed following E2 administration in the medial preoptic area (MPOA), arcuate nucleus (ARC), and dorsal raphe nucleus (DRN). Within the former two brain areas, the larger dose of E2 also decreased 4-h food intake. Food intake was not influenced, however, by similar E2 administration in the paraventricular nucleus, lateral hypothalamus, or ventromedial nucleus. These data suggest that E2-responsive neurons within the MPOA, ARC, and DRN participate in the estrogenic control of food intake and provide specific brain areas for future investigations of the cellular mechanism underlying estradiol's anorexigenic effect.

QRFP in female rats: effects on high fat food intake and hypothalamic gene expression across the estrous cycle

Pyroglutamylated arginine-phenylalanineamide peptide (QRFP) is a neuropeptide involved in feeding behavior. Central administration of QRFP selectively increases the intake of a high fat diet in male rats. QRFP administration also stimulates the hypothalamic-pituitary-gonadal axis via gonadotrophin-releasing hormone in male and female rats. Prepro-QRFP mRNA is expressed in localized regions of the mediobasal hypothalamus which are abundant in neurotransmitters, neuropeptides and receptor systems important for food intake regulation and reproductive behaviors. The current experiments were conducted to investigate the effects of centrally administered QRFP-26 on the intake of a high fat diet (HFD, 60%kcal from fat) in female rats and to investigate alterations in hypothalamic prepro-QRFP and its receptors, GPR130a and GPR103b, mRNA levels over the estrous cycle. In Experiment 1, female rats were administered QRFP-26 (intracerebroventricular; 0.3nmol, 0.5nmol, 1.0nmol) in rats consuming either a HFD or a low fat diet. All doses of QRFP-26 selectively increased the intake of the HFD in female rats. These data suggest that QRFP-26 regulates the intake of energy dense foods in female rats, which is similar to previous findings in male rats. In Experiment 2, hypothalamic levels of prepro-QRFP mRNA and its receptors were assessed during diestrus, proestrus, or estrus. The level of prepro-QRFP mRNA in the ventromedial/arcuate nucleus (VMH/ARC) of the hypothalamus was increased during proestrus, which suggests that endogenous estrogen levels regulate QRFP expression in the VMH/ARC. These data suggest that QRFP may play a role in coordinating feeding behaviors with reproductive function when energy demand is increased.

The ovarian hormone estradiol plays a crucial role in the control of food intake in females

Despite a strong male bias in both basic and clinical research, it is becoming increasingly accepted that the ovarian hormone estradiol plays an important role in the control of food intake in females. Estradiol's feeding inhibitory effect occurs in a variety of species, including women, but the underlying mechanism has been studied most extensively in rats and mice. Accordingly, much of the data reviewed here is derived from the rodent literature. Adult female rats display a robust decrease in food intake during estrus and ovariectomy promotes hyperphagia and weight gain, both of which can be prevented by a physiological regimen of estradiol treatment. Behavioral analyses have demonstrated that the feeding inhibitory effect of estradiol is mediated entirely by a decrease in meal size. In rats, estradiol appears to exert this action indirectly via interactions with peptide and neurotransmitter systems implicated in the direct control of meal size. Here, I summarize research examining the neurobiological mechanism underlying estradiol's anorexigenic effect. Central estrogen receptors (ERs) have been implicated and activation of one ER subtype in particular, ERα, appears both sufficient and necessary for the estrogenic control of food intake. Future studies are necessary to identify the critical brain areas and intracellular signaling pathways responsible for estradiol's anorexigenic effect. A clearer understanding of the estrogenic control of food intake is prerequisite to elucidating the biological factors that contribute to obesity and eating disorders, both of which are more prevalent in women, compared to men.

Altered ventilatory and thermoregulatory control in male and female adult Pet-1 null mice

The integrity of the serotonin (5-HT) system is essential to normal respiratory and thermoregulatory control. Male and female transgenic mice lacking central 5-HT neurons (Lmx1b(f/f/p) mice) show a 50% reduction in the hypercapnic ventilatory response and insufficient heat generation when cooled (Hodges and Richerson, 2008a; Hodges et al., 2008b). Lmx1b(f/f/p) mice also show reduced body temperatures (T(body)) and O(2) consumption [Formula: see text] , and breathe less at rest and during hypoxia and hypercapnia when measured below thermoneutrality (24 °C), suggesting a role for 5-HT neurons in integrating ventilatory, thermal and metabolic control. Here, the hypothesis that Pet-1 null mice, which retain 30% of central 5-HT neurons, will demonstrate similar deficits in temperature and ventilatory control was tested. Pet-1 null mice had fewer medullary tryptophan hydroxylase-immunoreactive (TPH(+)) neurons compared to wild type (WT) mice, particularly in the midline raphé. Female (but not male) Pet-1 null mice had lower baseline ventilation (V(E)), breathing frequency (f), [Formula: see text] and T(body) relative to female WT mice (P < 0.05). In addition, V(E) and [Formula: see text] were decreased in male and female Pet-1 null mice during hypoxia and hypercapnia (P < 0.05), but only male Pet-1 null mice showed a significant deficit in the hypercapnic ventilatory response when expressed as % of control (P < 0.05). Finally, male and female Pet-1 null mice showed significant decreases in T(body) when externally cooled to 4 °C. These data demonstrate that a moderate loss of 5-HT neurons leads to a modest attenuation of mechanisms defending body temperature, and that there are gender differences in the contributions of 5-HT neurons to ventilatory and thermoregulatory control.

Prenatal stress induces anxiety-like behavior together with the disruption of central serotonin neurons in mice

Most pregnant women are at risk of showing some emotional abnormality, since some biological functions such as hormonal systems may dramatically change in pregnancy. Some of them may be exposed to strong stress as hesitation of positive drug therapies because of worries regarding adverse effects on the embryo. A growing body of evidence suggests that prenatal stress increases the vulnerability to neuropsychiatric disorders, including depression and anxiety. However, the mechanisms involved are still unknown. To clarify the influence of exposure to prenatal stress on emotional development, we examined behavioral responses in offspring exposed to weak- or strong-prenatal restraint stress. We found that offspring that had been exposed to strong stress displayed anxiety-like behavior as determined by the elevated plus-maze test. It has been widely accepted that central serotonin (5-hydroxytryptamine; 5-HT) neurons play a critical role in emotional behaviors. Immunohistochemical studies showed that exposure to strong-prenatal restraint stress increased the expression of 5-HT-positive cells in the dorsal raphe nuclei in mice. Moreover, under these conditions, tryptophan hydroxylase-like immunoreactivities were also dramatically increased. In contrast, these behavioral and neurochemical abnormalities were not observed in offspring that had been exposed to weak-prenatal restraint stress. These findings indicate that exposure to excessive prenatal stress induces anxiety-like behavior together with disruption of the development of 5-HT neurons in mice.

Central effects of estradiol in the regulation of food intake, body weight, and adiposity

In recent years, obesity and its associated health disorders and costs have increased. Accumulation of adipose tissue, or fat, in the intra-abdominal adipose depot is associated with an increased risk of developing cardiovascular problems, type-2 diabetes mellitus, certain cancers, and other disorders like the metabolic syndrome. Males and females differ in terms of how and where their body fat is stored, in their hormonal secretions, and in their neural responses to signals regulating weight and body fat distribution. Men and post-menopausal women accumulate more fat in their intra-abdominal depots than pre-menopausal women, resulting in a greater risk of developing complications associated with obesity. The goal of this review is to discuss the current literature on sexual dimorphisms in body weight regulation, adipose tissue accrual and deposition.

Pet-1 is required across different stages of life to regulate serotonergic function

Transcriptional cascades are required for specification of 5-HT neurons and 5-HT modulated behaviors. Expression of several cascade factors extends across lifespan suggesting their control of behavior may not be temporally restricted to programming normal numbers of 5-HT neurons. We applied new mouse conditional targeting approaches to investigate ongoing requirements for Pet-1, a cascade factor required for the initiation of 5-HT synthesis but whose expression persists into adulthood. We found that Pet-1 was required after 5-HT neuron generation, for multiple steps in 5-HT neuron maturation including axonal innervation to the somatosensory cortex, firing properties, and 5-HT_1A and 5-HT_1B autoreceptor expression. Targeting Pet-1 in adult 5-HT neurons showed that it was still needed to preserve normal anxiety-related behaviors through direct autoregulated control of serotonergic gene expression. These findings show that Pet-1 is required across lifespan and therefore behavioral pathogenesis can result from both developmental and adult-onset alterations in serotonergic transcription.