Estradiol-induced desensitization of 5-HT1A receptor signaling in the paraventricular nucleus of the hypothalamus is independent of estrogen receptor-beta

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

The Hypothalamic-Pituitary-Adrenal Axis: Development, Programming Actions of Hormones, and Maternal-Fetal Interactions

The hypothalamic-pituitary-adrenal axis is a complex system of neuroendocrine pathways and feedback loops that function to maintain physiological homeostasis. Abnormal development of the hypothalamic-pituitary-adrenal (HPA) axis can further result in long-term alterations in neuropeptide and neurotransmitter synthesis in the central nervous system, as well as glucocorticoid hormone synthesis in the periphery. Together, these changes can potentially lead to a disruption in neuroendocrine, behavioral, autonomic, and metabolic functions in adulthood. In this review, we will discuss the regulation of the HPA axis and its development. We will also examine the maternal-fetal hypothalamic-pituitary-adrenal axis and disruption of the normal fetal environment which becomes a major risk factor for many neurodevelopmental pathologies in adulthood, such as major depressive disorder, anxiety, schizophrenia, and others.

Estrogen receptors modulate ectonucleotidases activity in hippocampal synaptosomes of male rats

Extracellular adenine nucleotides and nucleosides, such as adenosine-5'-triphosphate (ATP) and adenosine, are among least investigated signaling factors that participate in 17β-estradiol (E2)-mediated synaptic rearrangements in rodent hippocampus. Their levels in the extrasynaptic space are tightly controlled by ecto-nucleoside triphosphate diphosphohydrolases1-3 (NTPDase1-3)/ecto-5'-nucleotidase (eN) enzyme chain. Therefore, the aim of the present study was to get closer insight in the E2-induced decrease in NTPDase and eN activity in the hippocampal synaptic compartment of male rats and to identify estradiol receptors (ERs i.e. ERα, ERβ or GPER1) responsible for the observed effects of E2. In this study we show indiscriminate participation of estradiol receptor α (ERα), -β (ERβ) and G- protein coupled estrogen receptor 1 (GPER1) in the mediation of E2 actions in hippocampal synaptosomes of male rats. Synaptic NTPDase1-3 activities are modulated only through activation of ERβ, while activation of ERα, -β and/or non-classical GPER1 decreases synaptic eN activity. Since both ATP and adenosine function as neuromodulators in the hippocampal networks, influencing its function, profound knowledge of mechanisms by which ectonucleotidases are regulated/modulated is of great importance.

Sex differences in the hypothalamic-pituitary-adrenal axis' response to stress: an important role for gonadal hormones

The hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrine network that controls hormonal responses to internal and external challenges in an organism's environment, exhibits strikingly sex-biased activity. In adult female rodents, acute HPA function following a stressor is markedly greater than it is in males, and this difference has largely been attributed to modulation by the gonadal hormones testosterone and estradiol. These gonadal hormones are produced by the hypothalamic-pituitary-gonadal (HPG) axis and have been shown to determine sex differences in adult HPA function after acute stress via their activational and organizational effects. Although these actions of gonadal hormones are well supported, the possibility that sex chromosomes similarly influence HPA activity is unexplored. Moreover, questions remain regarding sex differences in the activity of the HPA axis following chronic stress and the underlying contributions of gonadal hormones and sex chromosomes. The present review examines what is currently known about sex differences in the neuroendocrine response to stress, as well as outstanding questions regarding this sex bias. Although it primarily focuses on the rodent literature, a brief discussion of sex differences in the human HPA axis is also included.

Characterization and gonadal hormone regulation of a sexually dimorphic corticotropin-releasing factor receptor 1 cell group

Corticotropin-releasing factor binds with high affinity to CRF receptor 1 (CRFR1) and is implicated in stress-related mood disorders such as anxiety and depression. Using a validated CRFR1-green fluorescent protein (GFP) reporter mouse, our laboratory recently discovered a nucleus of CRFR1 expressing cells that is prominent in the female rostral anteroventral periventricular nucleus (AVPV/PeN), but largely absent in males. This sex difference is present in the early postnatal period and remains dimorphic into adulthood. The present investigation sought to characterize the chemical composition and gonadal hormone regulation of these sexually dimorphic CRFR1 cells using immunohistochemical procedures. We report that CRFR1-GFP-ir cells within the female AVPV/PeN are largely distinct from other dimorphic cell populations (kisspeptin, tyrosine hydroxylase). However, CRFR1-GFP-ir cells within the AVPV/PeN highly co-express estrogen receptor alpha as well as glucocorticoid receptor. A single injection of testosterone propionate or estradiol benzoate on the day of birth completely eliminates the AVPV/PeN sex difference, whereas adult gonadectomy has no effect on CRFR1-GFP cell number. These results indicate that the AVPV/PeN CRFR1 is regulated by perinatal but not adult gonadal hormones. Finally, female AVPV/PeN CRFR1-GFP-ir cells are activated following an acute 30-min restraint stress, as assessed by co-localization of CRFR1-GFP cells with phosphorylated (p) CREB. CRFR1-GFP/pCREB cells were largely absent in the male AVPV/PeN. Together, these data indicate a stress and gonadal hormone responsive nucleus that is unique to females and may contribute to sex-specific stress responses.

The Paraventricular Nucleus of the Hypothalamus: Development, Function, and Human Diseases

The paraventricular nucleus of the hypothalamus (PVH), located in the ventral diencephalon adjacent to the third ventricle, is a highly conserved brain region present in species from zebrafish to humans. The PVH is composed of three main types of neurons, magnocellular, parvocellular, and long-projecting neurons, which play imperative roles in the regulation of energy balance and various endocrinological activities. In this review, we focus mainly on recent findings about the early development of the hypothalamus and the PVH, the functions of the PVH in the modulation of energy homeostasis and in the hypothalamus-pituitary system, and human diseases associated with the PVH, such as obesity, short stature, hypertension, and diabetes insipidus. Thus, the investigations of the PVH will benefit not only understanding of the development of the central nervous system but also the etiology of and therapy for human diseases.

Estradiol suppresses ingestive response evoked by activation of 5-HT1A receptors in the lateral hypothalamus of ovariectomized rats

The present study investigated the effects of estradiol (E2) on ingestive behavior after activation of 5-HT1A receptors in the lateral hypothalamus (LH) of female rats habituated to eat a wet mash diet. Ovariectomized rats treated with corn oil (OVX) or estradiol cypionate (OVX+E) received local injections into the LH of vehicle or an agonist of 5-HT1A receptors, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT; at a dose of 6 nmol). To determine the involvement of these receptors in food intake, some animals were pretreated with N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide maleate (WAY-100635, a 5-HT1A receptor full antagonist, at a dose of 0.37 nmol), followed by the injection of the agonist 8-OH-DPAT or its vehicle. The results showed that the injection of 8-OH-DPAT into the LH of OVX rats significantly increased food intake, and the duration and frequency of this behavior. The pretreatment with E2 suppressed the hyperphagic response induced by 8-OH-DPAT in OVX animals. The inhibition of 5-HT1A receptors after pretreatment with WAY-100635 blocked the hyperphagic effects evoked by 8-OH-DPAT in OVX. These results indicate that the activity of LH 5-HT1A receptors could be affected by blood E2 levels.

Marked sexual dimorphism in 5-HT1 receptors mediating pronociceptive effects of sumatriptan

Amongst the side effects of triptans, a substantial percentage of patients experience injection site pain and tenderness, the underlying mechanism of which is unknown. We found that the dose range from 10fg to 1000ng (intradermal) of sumatriptan induced a complex dose-dependent mechanical hyperalgesia in male rats, with distinct peaks, at 1pg and 10ng, but no hyperalgesia at 1ng. In contrast, in females, there was 1 broad peak. The highest dose (1000ng) did not produce hyperalgesia in either sex. We evaluated the receptors mediating sumatriptan hyperalgesia (1pg, 1 and 10ng). In males, the injection of an antagonist for the serotonin (5-HT) receptor subtype 1B (5-HT_1B), but not 5-HT_1D, markedly inhibited sumatriptan (1pg)-induced hyperalgesia, at 10ng a 5-HT_1D receptor antagonist completely eliminated hyperalgesia. In contrast, in females, the 5-HT_1D, but not 5-HT_1B, receptor antagonist completely blocked sumatriptan (1pg and 10ng) hyperalgesia and both 5-HT_1B and 5-HT_1D receptor antagonists attenuated hyperalgesia (1ng) in females, which is GPR30 estrogen receptor dependent. While selective 5-HT_1D or 5-HT_1B, agonists produce robust hyperalgesia in female and male rats, respectively, when co-injected the hyperalgesia induced in both sexes was attenuated. Mechanical hyperalgesia induced by sumatriptan (1pg and 10ng) is dependent on the G-protein α_i subunit and protein kinase A (PKA), in IB4-positive and negative nociceptors. Understanding the mechanisms responsible for the complex dose dependence for triptan hyperalgesia may provide useful information for the design of anti-migraine drugs with improved therapeutic profiles.

Estrogen Receptor Beta Selective Agonists as Agents to Treat Chemotherapeutic-Induced Neuropathic Pain

Chemotherapy-induced neuropathic pain (CINP) remains a major unmet medical need. Estrogen receptor beta (ERβ)-selective agonists represent a novel strategy for treating CINP because they are neuroprotective and may also have anticancer activity. We confirmed that ERβ-selective agonists have antiallodynic effects in the spinal nerve ligation model of neuropathic pain. We then showed that structurally diverse ERβ-selective agonists also relieved allodynia in CINP caused by taxol, oxaliplatin, and vincristine. These effects were receptor subtype specific and mediated by ERβ receptors as ERα-selective and nonselective estrogen agonists were inactive, a mixture of an ERβ and ERα agonist was inactive, and ERβ-selective antagonists blocked the effects of the ERβ-selective agonists. The efficacy and potency of ERβ-agonists was greater in male rats than females. To address the possibility that AC-186 might stimulate proliferation of cancers, rendering it unsuitable for treating CINP, we evaluated proliferative effects of AC-186 on prostate cancer cells and found it inhibited growth (LNCaP cells) or had no effect (PC3 cells) on these cells. Thus, ERβ-selective agonists exhibit potential for treating CINP.

The Interaction of PPARα and CYP7B1 with ERα, β Impacted the Occurrence and Development of Intrahepatic Cholestasis in Pregnant Rats

Intrahepatic cholestasis of pregnancy (ICP) is a disorder of bile acid (BA) synthesis, excretion, and metabolism, with systemic accumulation of BAs, which can lead to prematurity, fetal distress, and intrauterine death. Here, we investigate the expression of peroxisome proliferator-activated receptor alpha and cytochrome P450 oxysterol 7alpha-hydroxylase by exposing to 17α-ethynylestradiol with or without the estrogen receptor signaling pathway in pregnant rats with intrahepatic cholestasis. In vivo and in vitro evidences showed that estrogen receptor alpha (ERα) may be the key point of occurrence and development of intrahepatic cholestasis in pregnant rats. Besides, the abnormalities in genes could be reversed by ERα small interfering RNA. Our findings provide the ERα-centered hypothesis on the mechanisms of ICP. New perspectives are emerging for the treatment of estrogen-induced hepatic complication.

The functions of estrogen receptor beta in the female brain: A systematic review

Females have unique and additional risk factors for neurological disorders. Among classical estrogen receptors, estrogen receptor beta (ERβ) has been suggested as a therapeutic target. However, little is known about the role of ERβ in the female brain. Six electronic databases were searched for articles evaluating the role of ERβ in the female brain and the influence of age and menopause on ERβ function. After screening 3186 titles and abstracts, 49 articles were included in the review, all of which were animal studies. Of these, 19 focused on cellular signaling, 7 on neuroendocrine pathways, 8 on neurological disorders, 4 on neuroprotection and 19 on psychological and psychiatric outcomes (6 studies evaluated two or more outcomes). Our findings showed that ERβ phosphorylated and activated intracellular second messenger proteins and regulated protein expression of genes involved in neurological functions. It also promoted neurogenesis, modulated the neuroendocrine regulation of stress response, conferred neuroprotection against ischemia and inflammation, and reduced anxiety- and depression-like behaviors. Targeting ERβ may constitute a novel treatment for menopausal symptoms, including anxiety, depression, and neurological diseases. However, to establish potential therapeutic and preventive strategies targeting ERβ, future studies should be conducted in humans to further our understanding of the importance of ERβ in women's mental and cognitive health.

Contribution of estrogen receptor subtypes, ERα, ERβ, and GPER1 in rapid estradiol-mediated enhancement of hippocampal synaptic transmission in mice

Estradiol rapidly modulates hippocampal synaptic plasticity and synaptic transmission; however, the contribution of the various estrogen receptors to rapid changes in synaptic function is unclear. This study examined the effect of estrogen receptor selective agonists on hippocampal synaptic transmission in slices obtained from 3-5-month-old wild type (WT), estrogen receptor alpha (ERαKO), and beta (ERβKO) knockout female ovariectomized mice. Hippocampal slices were prepared 10-16 days following ovariectomy and extracellular excitatory postsynaptic field potentials were recorded from CA3-CA1 synaptic contacts before and following application of 17β-estradiol-3-benzoate (EB, 100 pM), the G-protein estrogen receptor 1 (GPER1) agonist G1 (100 nM), the ERα selective agonist propyl pyrazole triol (PPT, 100 nM), or the ERβ selective agonist diarylpropionitrile (DPN, 1 µM). Across all groups, EB and G1 increased the synaptic response to a similar extent. Furthermore, prior G1 application occluded the EB-mediated enhancement of the synaptic response and the GPER1 antagonist, G15 (100 nM), inhibited the enhancement of the synaptic response induced by EB application. We confirmed that the ERα and ERβ selective agonists (PPT and DPN) had effects on synaptic responses specific to animals that expressed the relevant receptor; however, PPT and DPN produced only a small increase in synaptic transmission relative to EB or the GPER1 agonist. We demonstrate that the increase in synaptic transmission is blocked by inhibition of extracellular signal-regulated kinase (ERK) activity. Furthermore, EB was able to increase ERK activity regardless of genotype. These results suggest that ERK activation and enhancement of synaptic transmission by EB involves multiple estrogen receptor subtypes.

Estrogens Suppress Spinal Endomorphin 2 Release in Female Rats in Phase with the Estrous Cycle

BACKGROUND/AIMS

Male and female rats differ in their ability to utilize spinal endomorphin 2 (EM2; the predominant mu-opioid receptor ligand in spinal cord) and in the mechanisms that underlie spinal EM2 analgesic responsiveness. We investigated the relevance of spinal estrogen receptors (ERs) to the in vivo regulation of spinal EM2 release.

METHODS

ER antagonists were administered directly to the lumbosacral spinal cord of male and female rats, intrathecal perfusate was collected, and resulting changes in EM2 release were quantified using a plate-based radioimmunoassay.

RESULTS

Intrathecal application of an antagonist of either estrogen receptor-α (ERα) or the ER GPR30 failed to alter spinal EM2 release. Strikingly, however, the concomitant blockade of ERα and GPR30 enhanced spinal EM2 release. This effect was sexually dimorphic, being absent in males. Furthermore, the magnitude of the enhancement of spinal EM2 release in females was dependent upon estrous cycle stage, suggesting a relationship with circulating levels of 17β-estradiol. The rapid onset of enhanced EM2 release following intrathecal application of ERα/GPR30 antagonists (within 30-40 min) suggests mediation via ERs in the plasma membrane, not the nucleus. Notably, both ovarian and spinally synthesized estrogens are essential for membrane ER regulation of spinal EM2 release.

CONCLUSION

These findings underscore the importance of estrogens for the regulation of spinal EM2 activity and, by extension, endogenous spinal EM2 antinociception in females. Components of the spinal estrogenic mechanism(s) that suppress EM2 release could represent novel drug targets for improving utilization of endogenous spinal EM2, and thereby pain management in women.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

GPER1 stimulation alters posttranslational modification of RGSz1 and induces desensitization of 5-HT1A receptor signaling in the rat hypothalamus

Hyperactivity of the hypothalamic-pituitary-adrenal axis is a consistent biological characteristic of depression, and response normalization coincides with clinical responsiveness to antidepressant medications. Desensitization of serotonin 1A receptor (5-HT1AR) signaling in the hypothalamic paraventricular nucleus of the hypothalamus (PVN) follows selective serotonin reuptake inhibitor (SSRI) antidepressant treatment and contributes to the antidepressant response. Estradiol alone produces a partial desensitization of 5-HT1AR signaling and synergizes with SSRIs to result in a complete and more rapid desensitization than with SSRIs alone as measured by a decrease in the oxytocin and adrenocorticotrophic hormone (ACTH) responses to 5-HT1AR stimulation. G protein-coupled estrogen receptor 1 (GPER1) is necessary for estradiol-induced desensitization of 5-HT1AR signaling, although the underlying mechanisms are still unclear. We now find that stimulation of GPER1 with the selective agonist G-1 and nonselective stimulation of estrogen receptors dramatically alter isoform expression of a key component of the 5-HT1AR signaling pathway, RGSz1, a GTPase-activating protein selective for Gαz, the Gα subunit necessary for 5-HT1AR-mediated hormone release. RGSz1 isoforms are differentially glycosylated, SUMOylated, and phosphorylated, and differentially distributed in subcellular organelles. High-molecular-weight RGSz1 is SUMOylated and glycosylated, localized to the detergent-resistant microdomain (DRM) of the cell membrane, and increased by estradiol and G-1 treatment. Because activated Gαz also localizes to the DRM, increased DRM-localized RGSz1 by estradiol and G-1 could reduce Gαz activity, functionally uncoupling 5-HT1AR signaling. Peripheral G-1 treatment produced a partial reduction in oxytocin and ACTH responses to 5-HT1AR stimulation similar to direct injections into the PVN. Together, these results identify GPER1 and RGSz1 as novel targets for the treatment of depression.

Estradiol accelerates the effects of fluoxetine on serotonin 1A receptor signaling

A major problem with current anti-depressant therapy is that it takes on average 6-7 weeks for remission. Since desensitization of serotonin (5-HT)1A receptor signaling contributes to the anti-depressive response, acceleration of the desensitization may reduce this delay in response to antidepressants. The purpose of the present study was to test the hypothesis that estradiol accelerates fluoxetine-induced desensitization of 5-HT1A receptor signaling in the paraventricular nucleus of the hypothalamus (PVN) of rats, via alterations in components of the 5-HT1A receptor signaling pathway. Ovariectomized rats were injected with estradiol and/or fluoxetine, then adrenocorticotropic hormone (ACTH) and oxytocin responses to a 5-HT1A receptor agonist (+)-8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT) were examined to assess the function of 5-HT1A receptors in the PVN. Treatment with estradiol for either 2 or 7 days or fluoxetine for 2 days produced at most a partial desensitization of 5-HT1A receptor signaling, whereas 7 days of fluoxetine produced full desensitization. Combined treatment with estradiol and fluoxetine for 2 days produced nearly a full desensitization, demonstrating an accelerated response compared to either treatment alone. With two days of combined treatments, estradiol prevented the fluoxetine-induced increase in 5-HT1A receptor protein, which could contribute to the more rapid desensitization. Furthermore, EB treatment for 2 days decreased the abundance of the 35 kD Gαz protein which could contribute to the desensitization response. We found two isoforms of Gαz proteins with molecular mass of 35 and 33 kD, which differentially distributed in the detergent resistant microdomain (DRM) and in Triton X-100 soluble membrane region, respectively. The 35 kD Gαz proteins in the DRM can be sumoylated by SUMO1. Stimulation of 5-HT1A receptors with 8-OH-DPAT increases the sumoylation of Gαz proteins and reduces the 33 kD Gαz proteins, suggesting that these responses may be related to the desensitization of 5-HT1A receptors. Treatment with estradiol for 2 days also reduced the levels of the G-protein coupled estrogen receptor GPR30, possibly limiting to the ability of estradiol to produce only a partial desensitization response. These data provide evidence that estradiol may be effective as a short-term adjuvant to SSRIs to accelerate the onset of therapeutic effects.

Post-synaptic density-95 (PSD-95) binding capacity of G-protein-coupled receptor 30 (GPR30), an estrogen receptor that can be identified in hippocampal dendritic spines

The estrogen 17β-estradiol (E2) modulates dendritic spine plasticity in the cornu ammonis 1 (CA1) region of the hippocampus, and GPR30 (G-protein coupled estrogen receptor 1 (GPER1)) is an estrogen-sensitive G-protein-coupled receptor (GPCR) that is expressed in the mammalian brain and in specific subregions that are responsive to E2, including the hippocampus. The subcellular localization of hippocampal GPR30, however, remains unclear. Here, we demonstrate that GPR30 immunoreactivity is detected in dendritic spines of rat CA1 hippocampal neurons in vivo and that GPR30 protein can be found in rat brain synaptosomes. GPR30 immunoreactivity is identified at the post-synaptic density (PSD) and in the adjacent peri-synaptic zone, and GPR30 can associate with the spine scaffolding protein PSD-95 both in vitro and in vivo. This PSD-95 binding capacity of GPR30 is specific and determined by the receptor C-terminal tail that is both necessary and sufficient for PSD-95 interaction. The interaction with PSD-95 functions to increase GPR30 protein levels residing at the plasma membrane surface. GPR30 associates with the N-terminal tandem pair of PDZ domains in PSD-95, suggesting that PSD-95 may be involved in clustering GPR30 with other receptors in the hippocampus. We demonstrate that GPR30 has the potential to associate with additional post-synaptic GPCRs, including the membrane progestin receptor, the corticotropin releasing hormone receptor, and the 5HT1a serotonin receptor. These data demonstrate that GPR30 is well positioned in the dendritic spine compartment to integrate E2 sensitivity directly onto multiple inputs on synaptic activity and might begin to provide a molecular explanation as to how E2 modulates dendritic spine plasticity.

Estradiol signaling in the regulation of reproduction and energy balance

Our knowledge of membrane estrogenic signaling mechanisms and their interactions that regulate physiology and behavior has grown rapidly over the past three decades. The discovery of novel membrane estrogen receptors and their signaling mechanisms has started to reveal the complex timing and interactions of these various signaling mechanisms with classical genomic steroid actions within the nervous system to regulate physiology and behavior. The activation of the various estrogenic signaling mechanisms is site specific and differs across the estrous cycle acting through both classical genomic mechanisms and rapid membrane-initiated signaling to coordinate reproductive behavior and physiology. This review focuses on our current understanding of estrogenic signaling mechanisms to promote: (1) sexual receptivity within the arcuate nucleus of the hypothalamus, (2) estrogen positive feedback that stimulates de novo neuroprogesterone synthesis to trigger the luteinizing hormone surge important for ovulation and estrous cyclicity, and (3) alterations in energy balance.

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.

Serotonergic effects on feeding, but not hypothalamus-pituitary-adrenal secretion, are altered in ovine pregnancy

In ovine pregnancy, as in human pregnancy, hypothalamus-pituitary-adrenal activity is chronically increased. These studies were designed to test the hypotheses that expression of serotonergic genes and responsiveness to serotonin are increased in pregnancy. We tested the stimulatory effect of an acute, intracerebroventricular injection of the serotonin reuptake inhibitor fluoxetine on plasma ACTH and cortisol in ewes during late pregnancy or postpartum. We also tested the effect of lower-dose, longer-term stimulation by intracerebroventricular infusion of fluoxetine in pregnant and nonpregnant ewes over 6 days. Overall, we found that the stimulatory effect of fluoxetine on ACTH and cortisol was not significantly different between late-gestation and nonpregnant ewes, although the effect of acute fluoxetine administration was inversely related to plasma progesterone concentrations. Also, there were no differences in hypothalamic expression of the glucocorticoid and mineralocorticoid receptors, corticotropin-releasing hormone, AVP, the serotonin reuptake transporter, or the serotonin [5-hydroxytryptamine (5-HT)] receptors 5-HT(1A) and 5-HT(2A) with pregnancy or fluoxetine treatment. However, chronic fluoxetine infusion reduced food intake in the nonpregnant, but not pregnant, ewes. Expression of proopiomelanocortin mRNA in the hypothalamus was reduced in pregnant compared with nonpregnant ewes. Our results indicate that pregnancy does not increase responsiveness of ACTH and cortisol to serotonergic stimulation but, rather, that progesterone reduces the ACTH response. In addition, we found a reduced ability of serotonin to inhibit feeding in the pregnant ewes, consistent with a reduction in anorexic mechanisms in the pregnant state.

The role of oxytocin in mating and pregnancy

The hormone oxytocin (OT) is released both centrally and peripherally during and after mating. Although research in humans suggests a central role in sexuality, the most reliable findings to date involve peripheral activation. This review will discuss these results and will particularly focus on understanding the most recent findings from fMRI data and the effects of exogenous peripheral OT administration. We will then consider hypotheses of the roles played by central and systemic OT release as well as their control and modulation in the female, summarizing recent findings from animal research. Finally, we will discuss the contribution of OT to the initiation of pregnancy in rodents. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Estradiol induces partial desensitization of serotonin 1A receptor signaling in the paraventricular nucleus of the hypothalamus and alters expression and interaction of RGSZ1 and Gαz

Hyperactivity of hypothalamic-pituitary mediated hormone responses, such as to stimulation with a serotonin 1A (5-HT(1A)) receptor agonist, are a feature of depression which are normalized with clinical improvement during drug therapy. We previously reported that SSRIs induce desensitization of 5-HT(1A) receptor signaling in the paraventricular nucleus of the hypothalamus (PVN) while estradiol benzoate (EB) produces a more rapid, partial desensitization. In the current study, time course and dose-response experiments demonstrated that two once daily doses of EB is the minimum needed to induce the desensitization response as indicated by 5-HT(1A) receptor-stimulated release of oxytocin and that 10 μg/kg/day EB produces the maximal response, a partial desensitization of approximately 40%. The effects of two once daily injections of 10 μg/kg/day EB on Gαz and RGSZ1 proteins were examined as components of the 5-HT(1A) receptor signaling system, which mediates the release of oxytocin and adrenocorticotropic hormone. RGSZ1 appears to be a major target for EB-mediated responses in the 5-HT(1A) receptor signaling system. A 55 kD membrane-associate RGSZ1 protein was greatly increased in the PVN and rest of the hypothalamus and moderately increased in the dorsal hippocampus and amygdala after EB treatment as well as after an acute dose of a 5-HT(1A) receptor agonist. These results suggest that EB is a candidate for adjuvant therapy with SSRIs to hasten the therapeutic response and that RGSZ1 is a major target of EB therapy which could be explored as a target for novel therapeutic approaches for the treatment of depression.