In the ventral tegmental area, cyclic AMP mediates the actions of progesterone at dopamine type 1 receptors for lordosis of rats and hamsters

Cellular and molecular mechanisms of action of ovarian steroid hormones II: Regulation of sexual behavior in female rodents

Female sexual behaviors in rodents (lordosis and appetitive or "proceptive" behaviors) are induced through a genomic mechanism by the sequential actions of estradiol (E2) and progesterone (P), or E2 and testosterone (T) at their respective receptors. However, non-steroidal agents, such as gonadotropin-releasing hormone (GnRH), Prostaglandin E2 (PGE2), noradrenaline, dopamine, oxytocin, α-melanocyte stimulating hormone, nitric oxide, leptin, apelin, and others, facilitate different aspects of female sexual behavior through their cellular and intracellular effects at the membrane and genomic levels in ovariectomized rats primed with E2. These neurotransmitters often act as intermediaries of E2 and P (or T). The classical model of steroid hormone action through intracellular receptor binding has been complemented by an alternative scenario wherein the steroid functions as a transcription factor after binding the receptor protein to DNA. Another possible mechanism occurs through the activation of second messenger systems (cyclic AMP, cyclic GMP, calcium), which subsequently initiate phosphorylation events via diverse kinase systems (protein kinases A, G, or C). These kinases target the progesterone receptor (PR) or associated effector proteins that connect the PR to the trans-activation machinery. This may also happen to the androgen receptor (AR). In addition, other cellular mechanisms could be involved since the chemical structure of these non-steroidal agents causes a change in their lipophobicity that prevents them from penetrating the cell and exerting direct transcriptional effects; however, they can exert effects on different components of the cell membrane activating a cross-talk between the cell membrane and the regulation of the transcriptional mechanisms.

A Recent Update on the Role of Estrogen and Progesterone in Alzheimer's Disease

Alzheimer's disease (AD), one of the most prevalent neurodegenerative disease responsible for 60%-80% dementia cases globally. The disease is more prevalent among elder females. Female reproductive hormones are found to be essential for cellular activities in brain. The physiological role of neurotrophins and sex hormones in hippocampal region during neurogenesis and neuron differentiation was studied as well. In addition to triggering cellular pathways, estrogen and progesterone carry out a number of biological processes that lead to neuroprotection. They might have an impact on learning and memory. One of estrogen's modest antioxidant properties is its direct scavenging of free radicals. The neurotrophic effect of estrogen and progesterone can be explained by their ability to rise the expression of the brain-derived neurotrophic factor (BDNF) mRNA. Additionally, they have the ability to degrade beta-amyloid and stop inflammation, apoptotic neuronal cell death, and tau protein phosphorylation. To enhance their neuroprotective action, various cross-talking pathways in cells that are mediated by estrogen, progesterone, and BDNF receptors. This include signaling by mitogen-activated protein kinase/extracellular regulated kinase, phosphatidylinositol 3-kinase/protein kinase B, and phospholipase/protein kinase C. Clinical research to establish the significance of these substances are fragmented, despite publications claiming a lower prevalence of AD when medication is started before menopause. This review article emphasizes an update on the role of estrogen, and progesterone in AD.

Progesterone-Mediated Non-Classical Signaling

Progesterone is essential for pregnancy maintenance and menstrual cycle regulation. Hormone action has been primarily ascribed to the well-characterized classical signaling pathway involving ligand binding, activation of nuclear progesterone receptors (PRs), and subsequent activation of genes containing progesterone response elements (PREs). Recent studies have revealed progesterone actions via non-classical signaling pathways, often mediated by non-genomic signaling. Progesterone signaling, in conjunction with growth factor signaling, impacts on the function of growth factors and regulates important physiological actions such as cell growth and remodeling, as well as apoptosis. This review focuses on non-classical progesterone signaling pathways, both including and excluding PR, and highlights how research in this area will provide a better understanding of progesterone actions and may inform novel therapeutic strategies.

Regulation of object recognition and object placement by ovarian sex steroid hormones

The ovarian hormones 17β-estradiol (E2) and progesterone (P4) are potent modulators of hippocampal memory formation. Both hormones have been demonstrated to enhance hippocampal memory by regulating the cellular and molecular mechanisms thought to underlie memory formation. Behavioral neuroendocrinologists have increasingly used the object recognition and object placement (object location) tasks to investigate the role of E2 and P4 in regulating hippocampal memory formation in rodents. These one-trial learning tasks are ideal for studying acute effects of hormone treatments on different phases of memory because they can be administered during acquisition (pre-training), consolidation (post-training), or retrieval (pre-testing). This review synthesizes the rodent literature testing the effects of E2 and P4 on object recognition (OR) and object placement (OP), and the molecular mechanisms in the hippocampus supporting memory formation in these tasks. Some general trends emerge from the data. Among gonadally intact females, object memory tends to be best when E2 and P4 levels are elevated during the estrous cycle, pregnancy, and in middle age. In ovariectomized females, E2 given before or immediately after testing generally enhances OR and OP in young and middle-aged rats and mice, although effects are mixed in aged rodents. Effects of E2 treatment on OR and OP memory consolidation can be mediated by both classical estrogen receptors (ERα and ERβ), and depend on glutamate receptors (NMDA, mGluR1) and activation of numerous cell signaling cascades (e.g., ERK, PI3K/Akt, mTOR) and epigenetic processes (e.g., histone acetylation, DNA methylation). Acute P4 treatment given immediately after training also enhances OR and OP in young and middle-aged ovariectomized females by activating similar cell signaling pathways as E2 (e.g., ERK, mTOR). The few studies that have administered both hormones in combination suggest that treatment can enhance OR and OP, but that effects are highly dependent on factors such as dose and timing of administration. In addition to providing more detail on these general conclusions, this review will discuss directions for future avenues of research into the hormonal regulation of object memory.

Non-genomic mechanisms of progesterone action in the brain

Progesterone is a gonadal steroid hormone whose physiological effects extend well beyond the strict confines of reproductive function. In fact, progesterone can have important effects on a variety of tissues, including the bone, the heart and the brain. Mechanistically, progesterone has been thought to exert its effects through the progesterone receptor (PR), a member of the nuclear steroid hormone superfamily, and as such, acts through specific progesterone response elements (PRE) within the promoter region of target genes to regulate transcription of such genes. This has been often described as the “genomic” mechanism of progesterone action. However, just as progesterone has a diverse range of tissue targets, the mechanisms through which progesterone elicits its effects are equally diverse. For example, progesterone can activate alternative receptors, such as membrane-associated PRs (distinct from the classical PR), to elicit the activation of several signaling pathways that in turn, can influence cell function. Here, we review various non-nuclear (i.e., non-genomic) signaling mechanisms that progesterone can recruit to elicit its effects, focusing our discussion primarily on those signaling mechanisms by which progesterone influences cell viability in the brain.

Effects and Mechanisms of 3α,5α,-THP on Emotion, Motivation, and Reward Functions Involving Pregnane Xenobiotic Receptor

Progestogens [progesterone (P(4)) and its products] play fundamental roles in the development and/or function of the central nervous system during pregnancy. We, and others, have investigated the role of pregnane neurosteroids for a plethora of functional effects beyond their pro-gestational processes. Emerging findings regarding the effects, mechanisms, and sources of neurosteroids have challenged traditional dogma about steroid action. How the P(4) metabolite and neurosteroid, 3α-hydroxy-5α-pregnan-20-one (3α,5α-THP), influences cellular functions and behavioral processes involved in emotion/affect, motivation, and reward, is the focus of the present review. To further understand these processes, we have utilized an animal model assessing the effects, mechanisms, and sources of 3α,5α-THP. In the ventral tegmental area (VTA), 3α,5α-THP has actions to facilitate affective, and motivated, social behaviors through non-traditional targets, such as GABA, glutamate, and dopamine receptors. 3α,5α-THP levels in the midbrain VTA both facilitate, and/or are enhanced by, affective and social behavior. The pregnane xenobiotic receptor (PXR) mediates the production of, and/or metabolism to, various neurobiological factors. PXR is localized to the midbrain VTA of rats. The role of PXR to influence 3α,5α-THP production from central biosynthesis, and/or metabolism of peripheral P(4), in the VTA, as well as its role to facilitate, or be increased by, affective/social behaviors is under investigation. Investigating novel behavioral functions of 3α,5α-THP extends our knowledge of the neurobiology of progestogens, relevant for affective/social behaviors, and their connections to systems that regulate affect and motivated processes, such as those important for stress regulation and neuropsychiatric disorders (anxiety, depression, schizophrenia, drug dependence). Thus, further understanding of 3α,5α-THP's role and mechanisms to enhance affective and motivated processes is essential.

Novel substrates for, and sources of, progestogens for reproduction

Steroid hormones, such as progesterone, are typically considered to be primarily secreted by the gonads (albeit adrenals can also be a source) and to exert their actions through cognate intracellular progestin receptors (PRs). Through its actions in the midbrain ventral tegmental Area (VTA), progesterone mediates appetitive (exploratory, anxiety, social approach) and consummatory (social, sexual) aspects of rodents' mating behaviour. However, progesterone and its natural metabolites ('progestogens') are produced in the midbrain VTA independent of peripheral sources and midbrain VTA of adult rodents is devoid of intracellular PRs. One approach that we have used to understand the effects of progesterone and mechanisms in the VTA for mating is to manipulate the actions of progesterone in the VTA and to examine effects on lordosis (the posture female rodents assume for mating to occur). This review focuses on the effects and mechanisms of progestogens to influence reproduction and related processes. The actions of progesterone and its 5α-reduced metabolite and neurosteroid, 5α-pregnan-3α-ol-20-one (3α,5α-THP; allopregnanolone) in the midbrain VTA to facilitate mating are described. The findings that 3α,5α-THP biosynthesis in the midbrain occurs with mating are discussed. Evidence for the actions of 3α,5α-THP in the midbrain VTA via nontraditional steroid targets is summarised. The broader relevance of these actions of 3α,5α-THP for aspects of reproduction, beyond lordosis, is summarised. Finally, the potential role of the pregnane xenobiotic receptor in mediating 3α,5α-THP biosynthesis in the midbrain is introduced.

Selective behavioral responses to male song are affected by the dopamine agonist GBR-12909 in female European starlings (Sturnus vulgaris)

Female songbirds use attributes of male song to select mates. Different types of male song differ in incentive value (or the ability to attract females). Dopamine plays a role in incentive value and reward; however, little is known about its role in selective female behavioral responses to male courtship signals. We examined the effects of the indirect dopamine agonist (dopamine reuptake inhibitor) GBR-12909 on female songbird responses to male song stimuli. Female European starlings were played recordings of long starling song (presumed high incentive value), short starling song (presumed lower incentive value), or purple martin song (lowest incentive value). Vehicle-treated females investigated nest boxes playing starling song more than purple martin song. However, GBR-12909 disrupted preferential responses to the starling song stimuli. GBR-12909 also increased cFOS immunolabeling in the ventromedial nucleus of the hypothalamus (VMH) at the same dose that disrupted female selective responses to male starling song. The results suggest that dopamine receptors play an important role in female selective responses to biologically meaningful stimuli and that the VMH may be influenced by dopamine to alter female responses to male song.

Infusions of anti-sense oligonucleotides for DARPP-32 to the ventral tegmental area reduce effects of progesterone- and a dopamine type 1-like receptor agonist to facilitate lordosis

Manipulating dopamine and/or adenosine 3',5' monophosphate regulated phosphoprotein of 32 kDa (DARPP-32) can influence sexual behavior of rodents. The ventral tegmental area (VTA) is an important brain site for progestogens to facilitate sexual behavior of rodents. We hypothesized that, in the VTA, dopamine type 1-like receptor (D1)-mediated increases in progesterone (P4)-facilitated lordosis involve DARPP-32. To investigate this, ovariectomized hamsters and rats, primed with estradiol (E2; 10 microg), received infusions to the VTA of saline vehicle or sense or anti-sense oligonucleotides targeted against DARPP-32 (4 nM). Subjects were then administered P4 via subcutaneous injection (hamsters: 200 microg; rats: 0 or 100 microg). Hamsters and rats were pre-tested for lordosis 3.5 h post-P4 injections, and then infused with the D1 agonist SKF38393 (100 ng) or vehicle to the VTA, and re-tested for sexual behavior 30 min later. Anti-sense oligonucleotides targeted against DARPP-32, but not infusions of sense oligonucleotides, to the VTA blocked the ability of systemic P4 to enhance receptive behavior of hamsters and rats. Similarly, SKF38393-mediated increases in P4-facilitated sexual behaviors were blocked by DARPP-32 anti-sense oligonucleotides to the VTA. The same pattern of effects was not observed in rats that were primed with E2-alone. Together, these findings suggest that, in the midbrain VTA, P4's actions to facilitate sexual behavior of female rodents, involving D1 receptors, may require DARPP-32.

Activity of protein kinase C is important for 3alpha,5alpha-THP's actions at dopamine type 1-like and/or GABAA receptors in the ventral tegmental area for lordosis of rats

In the ventral tegmental area, progestogens facilitate sexual receptivity of rodents via actions at dopamine type 1-like and/or gamma-aminobutyric acid type A receptors and activation of downstream signal transduction molecules. In the present study, we investigated whether effects of progesterone's metabolite, 3alpha,5alpha-THP, to enhance lordosis via actions at these receptors in the ventral tegmental area requires phospholipase C-dependent protein kinase C. The objective of this study was to test the hypothesis that: if progestogens' actions through dopamine type 1-like and/or gamma-aminobutyric acid type A receptors in the ventral tegmental area for lordosis require protein kinase C, then inhibiting protein kinase C in the ventral tegmental area should reduce 3alpha,5alpha-THP-facilitated lordosis and its enhancement by dopamine type 1-like or gamma-aminobutyric acid type A receptor agonists. Ovariectomized, estradiol (E(2); 10 microg s.c. at h 0)-primed rats were tested for their baseline lordosis responses and then received a series of three infusions to the ventral tegmental area: first, bisindolylmaleimide (75 nM/side) or vehicle; second, SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle; third, 3alpha,5alpha-THP (100, 200 ng/side) or vehicle. Rats were pre-tested for lordosis and motor behavior and then tested for lordosis after each infusion and 10 and 60 min after the last infusion. Rats were tested for motor behavior following their last lordosis test. As has been previously demonstrated, 3alpha,5alpha-THP infusions to the ventral tegmental area increased lordosis and effects were further enhanced by infusions of SKF38393 and muscimol. Infusions of bisindolylmaleimide to the ventral tegmental area attenuated 3alpha,5alpha-THP-, SKF38393-, and/or muscimol-facilitated lordosis. Effects on lordosis were not solely due to changes in general motor behavior. Thus, 3alpha,5alpha-THP's actions in the ventral tegmental area through membrane receptors may require activity of protein kinase C.

In the ventral tegmental area, the membrane-mediated actions of progestins for lordosis of hormone-primed hamsters involve phospholipase C and protein kinase C

Progestin-facilitated lordosis of rodents is enhanced by activation of dopamine type 1 (D(1)) or GABA(A) receptors, their downstream G-proteins, and/or second messengers in the ventral tegmental area (VTA). We examined whether the ability of progestins to enhance lordosis via actions at D(1) and/or GABA(A) receptors is contingent upon activation of the second messenger phospholipase C (PLC) and its associated kinase, protein kinase C (PKC), in the VTA. If the actions of progestins through D(1) and GABA(A) receptors in the VTA are mediated through PLC and PKC, then inhibiting PLC formation (Experiment 1) or blocking PKC (Experiment 2) should reduce progestin-facilitated lordosis and its enhancement by D(1) (SKF38393) or GABA(A) (muscimol) receptor agonists. In Experiment 1, ovariectomised hamsters, primed with oestradiol (10 microg; h 0) + progesterone (100 microg; h 45), were pretested for lordosis and motor behaviour (h 48) and then infused with the PLC inhibitor, U73122 (400 nM/side), or vehicle. Thirty minutes later, hamsters were retested and then received infusions of SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle to the VTA. Hamsters were post-tested for lordosis and motor behaviour 30 min later. In Experiment 2, a similar protocol was utilised except that instead of the PLC inhibitor hamsters were infused with the PKC inhibitor, bisindolylmaleimide (75 nM/side). Systemic progesterone, SKF38393-, and muscimol-facilitated lordosis was attenuated by infusion of the PLC inhibitor, U73122, or the PKC inhibitor, bisindolylmaleimide, compared to vehicle to the VTA. Thus, the actions of progestins in the VTA to enhance lordosis through D(1) and/or GABA(A) may include downstream activity of PLC and PKC.

Lordosis facilitation by LHRH, PGE2 or db-cAMP requires activation of the kinase A signaling pathway in estrogen primed rats

Dose-response curves for lordosis and proceptive behaviors were obtained for luteinizing hormone releasing hormone (LHRH), prostaglandin E2 (PGE2) and dibutyryl cyclic AMP (db-cAMP), by infusing them in the right lateral ventricle (i.c.v.) of ovariectomized (OVX) estradiol benzoate (E2B; 2 microg) treated rats. Two dose levels, one producing the maximal effect and the other one producing a submaximal response (approximately ED50) were selected for testing the capacity of Rp-cAMPS, a kinase A blocker, to modify the behavioral response to the three compounds. I.c.v. injections of Rp-cAMPS, significantly depressed both lordosis and proceptive responses induced by LHRH, PGE2 and db-cAMP. The results show that these agents use the cAMP-kinase A signaling pathway to elicit their stimulating effect on estrous behavior in the rat.

In the ventral tegmental area, progestins' membrane-mediated actions for lordosis of hamsters and rats involve protein kinase A

Progestin-facilitated lordosis of hamsters and rats is enhanced by activation of dopamine type 1 (D1) or GABAA/benzodiazepine receptor complexes (GBRs) in the ventral tegmental area (VTA) and these effects involve G-proteins and second messengers, such as adenosine 3',5'-monophosphate (cAMP). We examined whether D1- and/or GBR-mediated increases in progestin-facilitated lordosis of female hamsters and rats involve the cAMP-dependent protein kinase, protein kinase A (PKA), in the VTA. In experiment 1, ovariectomized hamsters, primed with estradiol (E2; 10 microg at h 0) + progesterone (P; 100 microg at h 45), were first pre-tested for lordosis and motor behavior (h 48) and then infused with the PKA inhibitor, Rp-cAMP (100 ng/side), or vehicle. Thirty minutes later, hamsters were retested and then received infusions of the D1 agonist, SKF38393 (100 ng/side), the GBR agonist, muscimol (100 ng/side), or vehicle to the VTA. Hamsters were post-tested for lordosis and motor behavior 30 min later. In Experiment 2, ovariectomized rats, primed with E2 (10 microg at h 0), were first pre-tested for lordosis and then infused with Rp-cAMP (100 ng/side) or vehicle to the VTA at h 44. Immediately after testing, rats received infusions of SKF38393 (100 ng/side), muscimol (100 ng/side), or vehicle and were retested for lordosis. Rats were then infused with the neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 100 or 200 ng/side), or beta-cyclodextrin vehicle and were post-tested for lordosis and motor behavior 10 and 60 min later. The enhancing effects of progestins or progestins plus D1 or GBR activation on lordosis of E2-primed hamsters and rats were blocked by the PKA inhibitor, Rp-cAMP. Thus, in the VTA, progestins' membrane actions involving D1 or GBRs are mediated, in part, by PKA.