Convergent pathways for steroid hormone- and neurotransmitter-induced rat sexual behavior

Recent advances in women’s sexual function and dysfunction

Current reconceptualization of women's sexual response acknowledges that women have many reasons or incentives for engaging in sex over and beyond sexual desire. Normative changes in their sexuality across the life span, with reproductive events, and with duration of relationship are recognized. Psychophysiological and preliminary functional magnetic resonance imaging data clarify that women's subjective experience of arousal may correlate poorly with signals reflective of genital congestion and also correlate poorly with activation of areas of the brain involved in organizing the reflexive genital vasocongestion. These aspects have been incorporated into new models of sexual response. Definitions of women's sexual dysfunction have recently been revised and expanded in keeping with these concepts. Mental well-being and other psychological and biological factors modulating desire, arousability, and response are areas of active research. Current understanding of the pathophysiology of chronic pain can be applied to the chronic intermittent pain and allodynia of chronic dyspareunia.

Sexual-incentive motivation and paced sexual behavior in female rats after treatment with drugs modifying dopaminergic neurotransmission

The effects of the dopamine receptor agonist apomorphine, the dopamine releaser amphetamine, and the dopamine receptor antagonist cis(Z)-flupenthixol on sexual-incentive motivation and on paced-mating behavior were studied in female rats. Apomorphine, in the doses of 0.125 and 0.5 mg/kg, showed a tendency to reduce incentive motivation. Ambulatory activity was inhibited, evidenced both by diminished distance moved and reduced velocity of movement. Amphetamine (0.25 and 1 mg/kg) and flupenthixol (0.25 and 0.5 mg/kg) failed to modify incentive motivation while stimulating and reducing ambulatory activity, respectively. In the mating test, apomorphine enhanced the latency to enter the male's half and reduced the number of proceptive behaviors. However, these effects were associated with the appearance of stereotyped sniffing. Amphetamine increased the propensity to escape from the male after a mount without having other effects. Flupenthixol augmented the duration of the lordosis posture. Neither amphetamine nor flupenthixol affected sniffing. These data show that facilitated dopaminergic neurotransmission stimulates neither paced female sexual behavior nor sexual-incentive motivation. Dopamine receptor blockade has slight consequences. It is concluded that dopamine is not a transmitter of major importance for unconditioned female sexual motivation and behavior.

A contemporary understanding of progesterone receptor function

Following the discovery of coactivators for nuclear receptors and the identification of a significant number of progesterone receptor (PR) target genes, our understanding of PR action has extended from its normally recognized functions to a wide variety of seemingly unlinked biological processes. Recent advances in defining the action of PR coactivators has revealed important mechanisms involving multiple layers of regulation in PR-mediated transcription. In this review, we will discuss the current understanding of PR physiology and the molecular basis of coactivator function in PR signaling events.

Has dopamine a physiological role in the control of sexual behavior? A critical review of the evidence

The role of dopaminergic systems in the control of sexual behavior has been a subject of study for at least 40 years. Not surprisingly, reviews of the area have been published at variable intervals. However, the earlier reviews have been summaries of published research rather than a critical analysis of it. They have focused upon the conclusions presented in the original research papers rather than on evaluating the reliability and functional significance of the data reported to support these conclusions. During the last few years, important new knowledge concerning dopaminergic systems and their behavioral functions as well as the possible role of these systems in sexual behavior has been obtained. For the first time, it is now possible to integrate the data obtained in studies of sexual behavior into the wider context of general dopaminergic functions. To make this possible, we first present an analysis of the nature and organization of sexual behavior followed by a summary of current knowledge about the brain structures of crucial importance for this behavior. We then proceed with a description of the dopaminergic systems within or projecting to these structures. Whenever possible, we also try to include data on the electrophysiological actions of dopamine. Thereafter, we proceed with analyses of pharmacological data and release studies, both in males and in females. Consistently throughout this discussion, we make an effort to distinguish pharmacological effects on sexual behavior from a possible physiological role of dopamine. By pharmacological effects, we mean here drug-induced alterations in behavior that are not the result of the normal actions of synaptically released dopamine in the untreated animal. The conclusion of this endeavor is that pharmacological effects of dopaminergic drugs are variable in both males and females, independently of whether the drugs are administered systemically or intracerebrally. We conclude that the pharmacological data basically reinforce the notion that dopamine is important for motor functions and general arousal. These actions could, in fact, explain most of the effects seen on sexual behavior. Studies of dopamine release, in both males and females, have focused on the nucleus accumbens, a structure with at most a marginal importance for sexual behavior. Since accumbens dopamine release is associated with all kinds of events, aversive as well as appetitive, it can have no specific effect on sexual behavior but promotes arousal and activation of non-specific motor patterns. Preoptic and paraventricular nucleus release of dopamine may have some relationship to mechanisms of ejaculation or to the neuroendocrine consequences of sexual activity or they can be related to other autonomic processes associated with copulation. There is no compelling indication in existing experimental data that dopamine is of any particular importance for sexual motivation. There is experimental evidence showing that it is of no importance for sexual reward.

Progestin receptors: neuronal integrators of hormonal and environmental stimulation

Although it originally was believed that neuronal steroid hormone receptors require binding to cognate ligand for activation, more recent evidence suggests that the receptors can be activated indirectly by other compounds, such as neurotransmitters and growth factors, acting through their own membrane receptors and specific intracellular signaling pathways. For example, as is the case with facilitation of sexual behavior by progesterone, facilitation of sexual behavior by D(1)/D(5) dopamine receptor agonists is blocked by disruption of progestin receptors. Therefore, some dopamine agonists facilitate sexual behavior at least in part by a progestin receptor-dependent mechanism, as does progesterone. This "ligand-independent activation" of neuronal progestin receptors is not limited to dopamine agonists; a variety of other compounds, as well as mating stimulation, facilitate sexual receptivity by a progestin receptor-dependent process. Steroid hormone receptors also can be regulated by afferent input in another way. Various neurotransmitters upregulate or downregulate steroid hormone receptors in some neurons. This, in turn, presumably confers greater or decreased sensitivity to the particular factors that can activate the particular steroid receptor in those particular neurons. Therefore, steroid hormones are but one class of factors that can regulate and activate steroid hormone receptors. Some additional factors that activate steroid hormone receptors have been identified, as have some factors that can regulate concentrations of receptors. Relatively little is known at this time about the range of neurotransmitters, humoral factors, and intracellular signaling pathways that are involved.

Functional diversity of protein phosphatase-1, a cellular economizer and reset button

The protein serine/threonine phosphatase protein phosphatase-1 (PP1) is a ubiquitous eukaryotic enzyme that regulates a variety of cellular processes through the dephosphorylation of dozens of substrates. This multifunctionality of PP1 relies on its association with a host of function-specific targetting and substrate-specifying proteins. In this review we discuss how PP1 affects the biochemistry and physiology of eukaryotic cells. The picture of PP1 that emerges from this analysis is that of a "green" enzyme that promotes the rational use of energy, the recycling of protein factors, and a reversal of the cell to a basal and/or energy-conserving state. Thus PP1 promotes a shift to the more energy-efficient fuels when nutrients are abundant and stimulates the storage of energy in the form of glycogen. PP1 also enables the relaxation of actomyosin fibers, the return to basal patterns of protein synthesis, and the recycling of transcription and splicing factors. In addition, PP1 plays a key role in the recovery from stress but promotes apoptosis when cells are damaged beyond repair. Furthermore, PP1 downregulates ion pumps and transporters in various tissues and ion channels that are involved in the excitation of neurons. Finally, PP1 promotes the exit from mitosis and maintains cells in the G1 or G2 phases of the cell cycle.

Minireview: Neuronal steroid hormone receptors: they're not just for hormones anymore

The ovarian steroid hormones have numerous effects on the brain, many of which are mediated, at least in part, by interaction with intracellular steroid hormone receptors acting as regulators of transcription. These intracellular steroid hormone receptors have often been considered to be activated solely by cognate hormone. However, during the past decade, numerous studies have shown that the receptors can be activated by neurotransmitters and intracellular signaling systems, through a process that does not require hormone. Although most of these have been in vitro experiments, others have been in vivo. Evidence from a wide variety of tissues and cells suggests that steroid hormone receptors are transcription factors that can be activated by a wide variety of factors, only one of which is cognate hormone. Furthermore, ligand-independent activation of neural steroid hormone receptors, rather than being a pharmacological or in vitro curiosity, seems to be a process that occurs in the normal physiology of animals. Thinking of steroid hormone receptors only as ligand-activated proteins may constrain our thinking about the many factors that may activate the receptors and cause receptor-dependent changes in neural gene expression and neuroendocrine function.

Steroid receptor control of reproductive behavior

Steroid hormone receptors in the brain were thought to be only activated by steroid hormones. Once steroid binds to the receptor, it would act on DNA to regulate gene transcription. Recent data indicate that steroid receptor action is more complex. Steroid receptor activity in the brain is under the control of co-regulatory proteins, such as coactivators. It is the expression of these additional proteins that modulate the activity of steroid receptors. Furthermore, steroid receptors are not only activated by steroid, but can also be activated by neurotransmitters in the absence of steroid. For example, progestin receptors in rodent brain are sensitive to progesterone and to social cues in the environment. This review discusses these emerging mechanisms for steroid receptor control in developing and adult brain.

In the ventral tegmental area, G-proteins and cAMP mediate the neurosteroid 3alpha,5alpha-THP's actions at dopamine type 1 receptors for lordosis of rats

Progestins have multiple mechanisms of action in the central nervous system that are important for modulating lordosis of female rats. In the ventral tegmental area (VTA), progestins, such as the progesterone metabolite and neurosteroid 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), regulate lordosis via actions independent of intracellular progestin receptors. We hypothesized that if, in the VTA, dopamine type 1 receptors (D1), G-proteins, and adenosine 3',5'-monophosphate (cAMP) are downstream effectors of 3alpha,5alpha-THP's actions for lordosis, then pharmacological manipulations of these signaling molecules will produce changes in 3alpha,5alpha-THP-facilitated lordosis of estradiol (E2)-primed rats. VTA infusions of 3alpha,5alpha-THP (50 ng) or 3alpha,5alpha-THP and the D1 agonist SKF38393 (100 ng) increased lordosis of ovariectomized, E2 (10 microg)-primed rats, compared to vehicle. Both 3alpha,5alpha-THP- and 3alpha,5alpha-THP plus SKF38393-facilitated lordosis was reduced by VTA infusions of the G-protein inhibitor guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S; 50 microM), but not vehicle. Also, in the VTA, blocking D1 with SCH23390 (100 ng) decreased, or increasing cAMP with 8-bromo-cAMP (200 ng) enhanced, 3alpha,5alpha-THP-facilitated lordosis of E2-primed rats. Notably, SCH23390's inhibitory effects on 3alpha,5alpha-THP-facilitated lordosis were reversed by 8-bromo-cAMP. Thus, in the VTA, 3alpha,5alpha-THP's actions for lordosis may involve activation of D1 and initiation of the G-protein-mediated second messenger cAMP.

Dopamine Antagonists Do Not Block Conditioned Place Preference Induced by Paced Mating Behavior in Female Rats

The authors assessed the behavioral effects of dopamine (DA) receptor antagonists, Cis (Z) flupentixol and S(+)-raclopride L-tartrate, on conditioned place preference (CPP) induced by paced mating behavior. Ovariectomized female rats of the Wistar strain were used. The administration of amphetamine (1 mg/kg) induced a clear CPP that was completely blocked by the DA antagonists flupentixol (0.25 mg/kg) or raclopride (0.125 mg/kg). These doses had no effect on motor coordination. Female rats that mated in a pacing chamber developed a clear CPP. Neither flupentixol nor raclopride blocked the reward state induced by paced mating behavior. These results indicate that DA is not involved in the reward state induced by paced mating behavior in female rats.

Progesterone-dependent regulation of female reproductive activity by two distinct progesterone receptor isoforms

The steroid hormone, progesterone, is a central coordinator of all aspects of female reproductive activity. The physiological effects of progesterone are mediated by interaction of the hormone with specific intracellular progesterone receptors (PRs) that are expressed from a single gene as two protein isoforms and that are members of the nuclear receptor superfamily of transcription factors. Analysis of the structural and functional relationships of each isoform using in vitro systems has demonstrated that the PR-A and PR-B proteins have different transcription activation properties when liganded to progesterone. More recently, selective ablation of the PR-A and PR-B proteins in mice had facilitated examination of the contribution of the individual PR isoforms to the pleiotropic reproductive activities of progesterone. Analysis of the phenotypic consequences of these mutations on female reproductive function has provided proof of concept that the distinct transcriptional responses to PR-A and PR-B observed in cell-based transactivation assays are reflected in a distinct tissue-selective contribution of the individual isoforms to the reproductive activities of progesterone. In PR-A knock-out mice, in which the expression of the PR-A isoform is selectively ablated (PRAKO), the PR-B isoform functions in a tissue-specific manner to mediate a subset of the reproductive functions of PRs. Ablation of PR-A does not affect response of the mammary gland or thymus to progesterone but results in severe abnormalities in ovarian and uterine function leading to female infertility. More recent studies using PR-B knock-out (PRBKO) mice have shown that ablation of PR-B does not affect either ovarian, uterine or thymic responses to progesterone but results in reduced mammary ductal morphogenesis and alveologenesis during pregnancy. Thus, PR-A is both necessary and sufficient to elicit the progesterone-dependent reproductive responses necessary for female fertility, while the PR-B isoform is required to elicit normal proliferative and differentiative responses of the mammary gland to progesterone. This review will summarize our current understanding of the selective contribution of the two PR isoforms to progesterone action.

Pituitary adenylate cyclase-activating peptide: a pivotal modulator of steroid-induced reproductive behavior in female rodents

Pituitary adenylate cyclase-activating polypeptide (PACAP) regulates the secretion of GnRH into the hypothalamic hypophysial portal system and sensitizes the pituitary for release of hormones that trigger ovulation. Because reproductive behavior is synchronized with GnRH release, the present study was undertaken to determine whether PACAP in the ventromedial nucleus (VMN) plays a role in receptivity. To this end, we used rat and mouse reproductive behavioral models to determine the biological relationship between PACAP and steroid receptor function in females. We provide evidence for the requirement of PACAP in the VMN for progesterone (P)-dependent sexual behavior in estrogen (E)-primed females. We clarify the biological and molecular mechanisms of PACAP activity by showing 1) that inhibition of endogenous PACAP suppresses P receptor (PR)-dependent sexual behavior facilitated by the steroid P or D1-like agonist SKF38393 and 2) that PR, steroid receptor coactivators-1 and -2, and new protein synthesis are essential for ligand independent PACAP-facilitated behavior. These findings are consistent with convergence of PACAP-mediated cellular signals on PR for genomic activation and subsequent behavioral changes. Further, we show that steroids regulate both endogenous PACAP mRNA in the VMN and immunoreactive PACAP in the medial basal hypothalamus and cerebral spinal fluid for ligand-dependent, steroid receptor-dependent receptivity. The present findings delineate a novel, steroid-dependent mechanism within the female hypothalamus by which the neuropeptide PACAP acts as a feed-forward, paracrine, and/or autocrine factor for synchronization of behavior coordinate with hypothalamic control of ovulation.

Making sense of cross-talk between steroid hormone receptors and intracellular signaling pathways: who will have the last word?

In classical models of nuclear steroid hormone receptor function, ligand binds receptor, heat shock proteins dissociate, and receptor dimers enter or are withheld in the nucleus and interact with coregulatory molecules to mediate changes in gene expression. The footnotes, "receptors become phosphorylated" and "dynamic nucleo-cytoplasmic shuttling occurs" describe well-accepted, but less well-understood aspects of receptor action. Recently, the idea that several protein kinases are activated in response to steroid hormone binding to cognate cytoplasmic or membrane-associated receptors has become fashionable. However, the precise role of steroid hormone receptor phosphorylation and our understanding of which cytoplasmic kinases are activated and their functional significance remain elusive. This review provides an overview of the primary ways in which steroid hormone receptor and growth factor cross-talk occurs, using the human progesterone receptor (PR) as a model. The functional consequences of PR phosphorylation by protein kinases classically activated in response to peptide growth factors and novel extranuclear or nongenomic functions of PR as potential independent initiators of signal transduction pathways are discussed. Intracellular protein kinases are emerging as key mediators of steroid hormone receptor action. Cross-talk between steroid receptor- and growth factor-initiated signaling events may explain how gene subsets are coordinately regulated by mitogenic stimuli in hormonally responsive normal tissues, and is suspected to play a role in their cancer biology.

Isolation and identification of L-dopa decarboxylase as a protein that binds to and enhances transcriptional activity of the androgen receptor using the repressed transactivator yeast two-hybrid system

The AR (androgen receptor) is a ligand-regulated transcription factor, which belongs to the steroid receptor family and plays an essential role in growth and development of the prostate. Transcriptional activity of steroid receptors is modulated by interaction with co-regulator proteins and yeast two-hybrid analysis is commonly used to identify these steroid receptor-interacting proteins. However, a limitation of conventional two-hybrid systems for detecting AR protein partners has been that they only allow for analysis of the ligand- and DNA-binding domains of the receptor, as its NTD (N-terminal domain) possesses intrinsic transactivation activity. To identify AR N-terminus-interacting proteins, its NTD was used in the RTA (repressed transactivator) system, which is specifically designed for transactivator bait proteins and was shown to be suitable for two-hybrid analysis with the AR NTD. DDC (L-dopa decarboxylase) was detected multiple times as a novel AR-interacting protein, which was subsequently confirmed in vitro and in vivo. Furthermore, transient transfection of DDC in prostate cancer cells strongly enhanced ligand-dependent AR transcriptional activity, an effect that was antagonized using high concentrations of the anti-androgen bicalutamide. Glucocorticoid receptor activity was also strongly enhanced with DDC co-transfection, while oestrogen receptor activity was only mildly affected. Together, our data demonstrate that DDC interacts with AR to enhance steroid receptor transactivation, which may have important implications in prostate cancer progression.

Double oestrogen receptor alpha and beta knockout mice reveal differences in neural oestrogen-mediated progestin receptor induction and female sexual behaviour

To test the hypothesis that oestrogen receptor alpha (ERalpha) and ERbeta act together to mediate the actions of oestrogen in the ventromedial hypothalamus (VMH), we used mice with single or double knockout mutations of the ERalpha and ERbeta genes. Ovariectomized mice were implanted with 17beta-oestradiol and killed 5 days later. Oestradiol treatment promoted progestin receptor (PR)-immunoreactivity (-ir) in the VMH of all genotypes, but was maximal in brains of wild-type and ERbetaKO females. Analysis of specific VMH subregions revealed that PR-ir induction was limited to the caudal VMH in ERalphaKO and ERalphabetaKO mice. In the rostral VMH, oestradiol only induced PR-ir in wild-type and ERbetaKO mice, and the number of PR-ir neurones in this region was greater in ERbetaKO than wild-type females. Next, we tested the ability of a dopamine agonist and progesterone to facilitate sexual behaviour in females lacking functional ERalpha, ERbeta, or both receptors. Ovariectomized mice were implanted with oestradiol, and tested for sexual behaviour three times after administration of the dopamine agonist, apomorphine, followed by two tests concurrent with progesterone treatment and a final test with just apomorphine treatment. ERalphaKO and ERalphabetaKO females failed to display lordosis under any testing conditions, while ERbetaKO females exhibited lordosis behaviour equal to that of wild-type females. Our data show that a subpopulation of PR-ir neurones is induced by oestradiol in the caudal VMH of female mice lacking both ERalpha and ERbeta genes. We hypothesize that this action of oestradiol is either mediated by a novel ER or by the mutant portion of the AF2 subregion of the ERalpha gene present in ERalphaKO brain. However, despite the presence of PR in VMH, females lacking a functional ERalpha gene do not display sexual behaviour, via either ligand-dependent or -independent activation.

Early social stress in female guinea pigs induces a masculinization of adult behavior and corresponding changes in brain and neuroendocrine function

This study was undertaken to investigate, in guinea pigs, the effects of pre- and early postnatal social stress on the functioning of hormonal-, autonomic-, behavioral-, and limbic-brain systems. Dams had either lived in groups with a constant composition (i.e. stable social environment) or in groups with changing compositions, that means every 3 days two females were transferred from one group to another (i.e. unstable social environment). The subjects studied were female offspring of dams who had either lived in a stable social environment during pregnancy and lactation (i.e. control daughters, CF) or in an unstable social environment during this period of life (i.e. early stressed daughters, SF). After weaning, each five groups of CF and SF, consisting of two females each, were established. The spontaneous behavior of the females was recorded, blood samples were taken to determine cortisol, testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulfate and estrogen levels, the adrenals were prepared to determine tyrosinehydroxylase (TH) activities and the brains to investigate the distribution of sex hormone receptors. SF showed not only a behavioral and endocrine masculinization, but also an upregulation of androgen receptor and estrogen receptor-alpha in the medial preoptic area and the nucleus arcuatus of the hypothalamus, the nucleus paraventricularis of the thalamus, and the CA1 region of the hippocampus. These findings corresponded with distinctly elevated serum-concentrations of testosterone and increased activities of the adrenal TH. In conclusion, early social stress caused by an unstable social environment induces in female guinea pigs a permanent behavioral masculinization that is accompanied by changes in the endocrine and autonomic system as well as by changes in the distribution of sex hormone receptors in the limbic system.

Immunocytochemical detection of progesterone receptor in the female rabbit forebrain: distribution and regulation by oestradiol and progesterone

There is no information on the neuroanatomical distribution of the progesterone receptor (PR) in the rabbit. Therefore, we mapped the distribution of PR-immunoreactive cells in the forebrain of ovariectomized female rabbits. Vehicle-injected ovariectomized rabbits showed PR-immunoreactive cells only in the infundibular nucleus (IN) and nucleus X (lateral to the ventromedial hypothalamic nucleus). The injection of oestradiol benzoate (EB; 5 micro g/day for 5 days) increased the number of PR-immunoreactive cells in the IN and in three nuclei of the preoptic region (periventricular, medial, and principal). Abundant PR were also found in the paraventricular nucleus and nucleus X. Administration of progesterone (10 mg/day) for 3 days to EB-treated rabbits (a treatment that induces digging behaviour for the maternal nest and suppresses sexual receptivity and scent-marking) eliminated PR-immunoreactivity from all brain areas analysed except the IN. Thus, one-third of the number of cells seen in the ovariectomized + EB condition persisted in this region despite progesterone injections. Withdrawal of progesterone (and continuation of EB) for 5 (but not for 2) days (in a schedule similar to the one that induces straw-carrying and hair-pulling for the maternal nest) increased the number of PR-immunoreactive cells in all regions analysed. These results show that restricted regions of the female rabbit forebrain express abundant PR which are either: (i). up-regulated by oestradiol and down-regulated by progesterone; (ii). oestradiol-insensitive and down-regulated by progesterone; or (iii). insensitive to both oestradiol and progesterone.

Non-ligand activation of estrous behavior in rodents: cross-talk at the progesterone receptor

Estrous behavior in rodents is triggered by the binding of progesterone (P) to its intracellular receptor (PR). Non-steroidal agents (i.e., gonadotropin-releasing hormone, noradrenaline, dopamine and others), acting at the membrane, can facilitate estrous behavior in estrogen-primed rats. This action is mediated through the generation of second messengers (cyclic AMP, cyclic GMP, calcium) which, in turn, phosphorylate through diverse kinase systems (protein kinases A, G or C) either the PR or associated effector proteins linking the PR to the trans-activation machinery. P or its metabolites also activate cyclic AMP-signaling pathways by acting directly on the membrane or by modulating neurotransmitter release. Molecular processes resulting from second messenger signaling pathways and those from the progesterone-RP interaction synergize to elicit a full behavioral response.

Emerging concepts in the regulation of female sexual behavior

Recent advances in the field of steroid hormone action have significantly advanced our understanding of neuroendocrine regulation of sexual behavior in female rodents. The presumed classical steroid receptor-steroid hormone functional relationship has undergone significant modifications to integrate the wider context of cellular signaling mechanisms initiated by sensory and environmental stimuli and their transcriptional regulation of steroid hormone receptors in reproductive behavior. This effort has greatly been aided by recent studies identifying steroid hormone receptors as transcriptional mediators of a variety of ligands, whose functional flexibility is dependent upon their recruitment of coregulators, and the availability of gene knockout animal models. This review provides a framework for current concepts in the field of steroid hormone action in the context of their regulation of female sexual behavior.

Factors that mediate and modulate androgen action

Androgens mediate a wide range of processes during embryogenesis and in the adult. In mammals, although a number of steroids can be shown to exert androgenic effects using in vitro and in vivo assays, testosterone and its 5alpha reduced metabolite, 5alpha-dihydrotestosterone (DHT) are considered to represent the principal physiologic androgens. Furthermore, although the effects that androgens exert differ widely among different tissues and cell types, genetic and biochemical data suggest that these effects are mediated via the protein products of a single androgen receptor gene, which is encoded on the X-chromosome in mammals.

Influence of paradoxical sleep deprivation and cocaine on development of spontaneous penile reflexes in rats of different ages

Recent studies have established that paradoxical sleep deprivation (PSD) and cocaine administration induce genital reflexes (penile erection and ejaculation) in adult and old rats. To determine whether the same effects would induce spontaneous genital reflexes in rats of different ages (30-90 days old), we administered with cocaine (7 mg/kg) or saline to rats after a 4-day period of PSD, or at the equivalent time-point in control animals, and penile erection and ejaculation were then evaluated. In PSD rats administered cocaine, erection was observed from 30 days old to 90 days old, when both genital reflexes reached a peak. Animals submitted to PSD and saline injection showed erection from 60 to 90 days old. None of the control (saline and cocaine) groups of any age displayed these behaviors. The effects of PSD on steroid hormone levels showed that, although testosterone levels increased with age, PSD caused a marked decrease in testosterone at all ages evaluated. Progesterone and corticosterone levels were higher in PSD groups than in the respective control groups. These findings suggest that the interaction of PSD and cocaine probably enhances dopaminergic transmission in the brain and may accelerate the development of genital reflexes in male rats.

Mitogen-activated protein kinase regulates nuclear association of human progesterone receptors

Breast cancers often have increased MAPK activity; this pathway may drive breast cancer cell growth by targeting steroid hormone receptors. MAPK phosphorylates human progesterone receptors (PRs) on Ser294, thus regulating several aspects of PR activity. To study the role of PR Ser294 phosphorylation on subcellular distribution, we stably expressed wild-type (wt) or S294A (Ser294 to Ala) PR-B in several cell types. PRs phosphorylated on Ser294 were nuclear. Activation of MAPK induced Ser294 phosphorylation and rapid nuclear translocation of wt, but not S294A, PR-B; both receptors concentrated in the nucleus after progestin treatment. The MAPK kinase inhibitor, U0126, blocked epidermal growth factor but not progestin-induced Ser294 phosphorylation and translocation of wt PR, indicating a novel mechanism for nuclear localization. After progestin treatment, wt PR-B underwent ligand-dependent down-regulation, while S294A PR-B persisted in nuclei. Prolonged treatment with U0126 or the nuclear export inhibitor, leptomycin B, promoted nuclear accumulation of wt PR-B and blocked ligand-dependent PR down-regulation, suggesting that PR degradation occurs in the cytoplasm and requires MAPK-dependent nuclear export. Stabilization of PRs by leptomycin B also blocked PR transcriptional activity, indicating a link between nucleocytoplasmic shuttling, receptor stability, and function. These results support a regulatory role for MAPK in nuclear steroid hormone receptor subcellular localization and coupling to multiple PR functions.

Prepulse inhibition of acoustic startle in aromatase knock-out mice: effects of age and gender

Estrogen has been suggested to play a neuromodulatory and neuroprotective role on the brain dopamine system. We used aromatase knockout (ArKO) mice that lack a functional aromatase enzyme and are unable to convert testosterone into estrogen, and assessed prepulse inhibition of acoustic startle, locomotor hyperactivity to amphetamine treatment and rotarod performance. Mice were tested at either 1 month, 4-5 months or 12-18 months of age. In male, but not female ArKO mice, there was an age-related reduction of prepulse inhibition. The 12-18 months old male ArKO mice also showed significantly greater amphetamine-induced hyperactivity. Mice heterozygous for the mutation showed no deficits or were in-between wildtype mice and ArKO mice. We postulate that these data indicate a neuroprotective role of estrogen, particularly in male mice, on ageing of brain mechanisms involved in pre-pulse inhibition and locomotor activity regulation. It is likely that these brain mechanisms are or include dopaminergic activity.

Oestrogen and progestin responses in human endometrium

Our understanding of the mechanisms of the actions of oestrogens and progestins have evolved from the simple concept of nuclear receptor-mediated regulation of transcription to a highly sophisticated, finely tuned interplay between various coregulators, other signaling cascades and transcription factors. The net result of these complex regulatory mechanisms is a steroid-, cell-, or tissue-specific action of oestrogens and progestins, their antagonists or selective modulators of their receptors. In this review, we have attempted to shed some light on the regulation of the actions of oestrogens and progestins on the human endometrium.

Biogenic amines in the antennal lobes and the initiation and maintenance of foraging behavior in honey bees

Previous findings showed that high levels of octopamine and serotonin in the antennal lobes of adult worker honey bees are associated with foraging behavior, and octopamine treatment induces precocious foraging. To better characterize the relationship between amines and foraging behavior in honey bees, we performed a detailed correlative analysis of amine levels in the antennal lobes as a function of various aspects of foraging behavior. Flight activity was measured under controlled conditions in a large outdoor flight cage. Levels of octopamine in the antennal lobes were found to be elevated immediately subsequent to the onset of foraging, but they did not change as a consequence of preforaging orientation flight activity, diurnal pauses in foraging, or different amounts of foraging experience, suggesting that octopamine helps to trigger and maintain the foraging behavioral state. In contrast, levels of serotonin and dopamine did not show changes that would implicate them as either causal agents of foraging, or as neurochemical systems affected by the act of foraging. Serotonin treatment had no effect on the likelihood of foraging. These results provide further support for the hypothesis that an increase in octopamine levels in the antennal lobes plays a causal role in the initiation and maintenance of the behavioral state of foraging, and thus is involved in the regulation of division of labor in honey bees.

Estrogen receptor-alpha and neural circuits to the spinal cord during pregnancy

Estrogen receptor immunoreactivity and mRNAs are present in spinal cord neurons in locations that are associated with sensory and autonomic innervation of female reproductive organs. The present study was undertaken to examine the expression of estrogen receptor-alpha in the spinal cord during different stages of pregnancy and to determine whether estrogen receptor-alpha-expressing neurons are related to uterine afferent nerves bringing information to the spinal cord at parturition. Immunohistochemistry showed estrogen receptor-alpha-immunoreactive neurons in the dorsal one-half of the spinal cord, i.e., dorsal horn, dorsal intermediate gray areas (dorsal commissural nucleus), and around the central canal and sacral parasympathetic autonomic nucleus of the lumbosacral spinal cord. Neurons in these areas corresponded topographically to the distribution of central processes of visceral primary afferent neurons (e.g., containing calcitonin gene-related peptide and substance P) that innervate and activate second-order spinal cord neurons (evidenced by their expression of Fos) at parturition. Western blots showed that estrogen receptor-alpha increases in the spinal cord, with a peak at day 20 of gestation, followed by a slight decrease by 2 days postpartum. These studies show that estrogen receptor-alpha is expressed by neurons in autonomic and sensory areas of the lumbosacral spinal cord that have connections with the female reproductive system and that the level of estrogen receptor-alpha changes over the course of pregnancy, which may follow profiles of steroid hormones. Many of these neurons may be involved in processing information related to reproductive organ function, changes during pregnancy, and relays to other CNS centers.

A Drosophila dopamine 2-like receptor: Molecular characterization and identification of multiple alternatively spliced variants

Dopamine is an important neurotransmitter in the central nervous system of both Drosophila and mammals. Despite the evolutionary distance, functional parallels exist between the fly and mammalian dopaminergic systems, with both playing roles in modulating locomotor activity, sexual function, and the response to drugs of abuse. In mammals, dopamine exerts its effects through either dopamine 1-like (D1-like) or D2-like G protein-coupled receptors. Although pharmacologic data suggest the presence of both receptor subtypes in insects, only cDNAs encoding D1-like proteins have been isolated previously. Here we report the cloning and characterization of a newly discovered Drosophila dopamine receptor. Sequence analysis reveals that this putative protein shares highest homology with known mammalian dopamine 2-like receptors. Eight isoforms of the Drosophila D2-like receptor (DD2R) transcript have been identified, each the result of alternative splicing. The encoded heptahelical receptors range in size from 461 to 606 aa, with variability in the length and sequence of the third intracellular loop. Pharmacologic assessment of three DD2R isoforms, DD2R-606, DD2R-506, and DD2R-461, revealed that among the endogenous biogenic amines, dopamine is most potent at each receptor. As established for mammalian D2-like receptors, stimulation of the Drosophila homologs with dopamine triggers pertussis toxin-sensitive Gi/o-mediated signaling. The D2-like receptor agonist, bromocriptine, has nanomolar potency at DD2R-606, -506, and -461, whereas multiple D2-like receptor antagonists (as established with mammalian receptors) have markedly reduced if any affinity when assessed at the fly receptor isoforms. The isolation of cDNAs encoding Drosophila D2-like receptors extends the range of apparent parallels between the dopaminergic system in flies and mammals. Pharmacologic and genetic manipulation of the DD2Rs will provide the opportunity to better define the physiologic role of these proteins in vivo and further explore the utility of invertebrates as a model system for understanding dopaminergic function in higher organisms.

Juvenile hormone and octopamine in the regulation of division of labor in honey bee colonies

Forager honey bees have high circulating levels of juvenile hormone (JH) and high brain levels of octopamine, especially in the antennal lobes, and treatment with either of these compounds induces foraging. Experiments were performed to determine whether octopamine acts more proximally than JH to affect the initiation of foraging behavior. Bees treated with octopamine became foragers more rapidly than bees treated with the JH analog methoprene. Bees treated with methoprene showed an increase in antennal lobe levels of octopamine, especially after 12 days. Bees with no circulating JH (corpora allata glands removed) treated with octopamine became foragers in similar numbers to bees with intact corpora allata. These results suggest that JH affects the initiation of foraging at least in part by increasing brain levels of octopamine, but octopamine can act independently of JH. Effects of JH that are not related to octopamine also are possible, as bees treated with both octopamine and methoprene were more likely to become foragers than bees treated with only octopamine or methoprene.

Progestin receptor immunoreactivity within steroid-responsive vasopressin-immunoreactive cells in the male and female rat brain

Progestin receptor immunoreactivity is found in the same regions of the bed nucleus of stria terminalis (BST) and centromedial amygdala (CMA) as steroid-responsive vasopressin immunoreactive (AVP-ir) cells. To test whether AVP-ir cells express progestin receptors, brains of male rats were stained immunocytochemically for arginine vasopressin as well as progestin receptors. In BST and CMA, over 95% of AVP-ir cells contained progestin receptor immunoreactivity. In contrast, none of the AVP-ir cells in the suprachiasmatic, supraoptic and paraventricular nuclei expressed progestin receptor immunoreactivity. To study whether progestin receptor expression in AVP-ir cells in the BST and CMA is responsive to gonadal steroids, male and female rats were castrated and implanted with either empty capsules or capsules filled with testosterone or oestradiol, respectively. Ten days later, brains were processed for AVP and progestin receptor immunoreactivity. Although there was no effect of hormonal status on the percentage of colocalized cells, the level of progestin receptor immunoreactivity was higher in rats that received gonadal steroids than those that did not. The presence of progestin receptor immunoreactivity in steroid responsive AVP-ir cells, and the responsiveness of this expression to gonadal hormones, is consistent with the possibility that the effects of gonadal steroids on AVP-ir expression in the BST and CMA may be mediated at least in part by progestin receptors.

Olanzapine and progesterone have dose-dependent and additive effects to enhance lordosis and progestin concentrations of rats

There is evidence that actions of both progesterone (P) and its metabolite, 5alpha-pregnane-3alpha-ol-20-one (3alpha,5alpha-THP), are important for sexual behavior of estradiol (E(2))-primed rodents. Olanzapine, an atypical antipsychotic, dose-dependently increases 3alpha,5alpha-THP in the cortex of male rats. These experiments investigated the effects of olanzapine administration on female sexual behavior and progestin concentrations. In Experiment 1, ovariectomized (ovx) rats (N=128) were primed with estradiol benzoate (EB) at Hour 0 and were administered P (0, 50, 100, or 200 microg sc) at Hour 44 and olanzapine (0.0, 2.5, 5.0, or 10.0 mg/kg ip) at Hour 47. At Hour 48, rats were tested for sexual receptivity with a stimulus male. Administration of 10.0 mg/kg of olanzapine, irrespective of P, significantly increased the occurrence (lordosis quotients, LQs) and the intensity (lordosis ratings, LRs) of lordosis compared to all other dosages. Administration of 2.5 or 5.0 mg/kg of olanzapine, irrespective of P, increased LQs and LRs compared to vehicle administration. Olanzapine without P dose-dependently increased LQs and LRs. As expected, administration of P without olanzapine also dose-dependently increased LQs and LRs. In Experiment 2, ovx rats (N=44, n=4 per group) received EB (0 or 10 microg sc), P (0 or 200 microg sc), and/or olanzapine (0.0, 2.5, 5.0, or 10.0 mg/kg ip). The same pattern of effects seen for lordosis was observed on progestin concentrations. Whole brain and plasma P and 3alpha,5alpha-THP concentrations were increased with olanzapine or P dosing and were greatest with coadministration. Together, these data demonstrate that olanzapine and P have independent effects to increase lordosis, P, and 3alpha,5alpha-THP concentrations of adult rats and additive effects in combination, suggesting complimentary mechanisms of action.

Puberty and the maturation of the male brain and sexual behavior: recasting a behavioral potential

The pubertal transition from the juvenile to adult state requires significant changes in behavior to meet the demands for success and survival in adulthood. These behavioral changes during puberty must be mediated by changes in the structure and/or function of the central nervous system. Despite the profound consequences of puberty on an animal's behavioral repertoire, the mechanisms underlying pubertal maturation of the nervous system remain largely unknown. In this review, we provide a synthesis of neural development during puberty as it relates to maturation of male reproductive behavior. We first outline neuroendocrine events associated with puberty and review work from our laboratory that identifies pubertal changes in the neural substrate controlling male reproduction by comparing the neural responses of prepubertal and adult males to steroids and female chemosensory cues. We then raise the question of whether puberty is a sensitive period in which gonadal hormones influence the structural and functional organization of neural circuits underlying male reproductive behavior. The central thesis of this review is that the development of the nervous system during puberty alters the way in which the male responds to social stimuli, involving the restructuring of neural circuits that integrate steroidal and sensory information and ultimately mediate steroid-dependent social behaviors in adulthood.

A progestin antagonist blocks vaginocervical stimulation-induced fos expression in neurones containing progestin receptors in the rostral medial preoptic area

Vaginocervical stimulation (VCS) has a variety of effects on the brain, physiology and behaviour. Previous work demonstrated that a progestin antagonist blocked neuronal response to VCS (i.e. Fos expression) in the absence of progesterone in some neurones, and suggested that some of the effects of VCS on the brain are mediated by ligand-independent activation of progestin receptors (PRs). Although it had been reported previously that some of the cells in which VCS induces Fos expression also contain PRs, it had not been determined if a progestin antagonist blocked Fos expression in these particular neurones. The purpose of this experiment was to determine if a progestin antagonist decreases Fos expression specifically in cells that also express PRs in the preoptic area and ventromedial hypothalamus. As has been shown previously, VCS increased Fos-immunoreactive (ir) expression in the particular areas studied. In the rostral medial preoptic area, VCS increased Fos expression in cells that coexpressed PRs, as well as in cells that do not. However, in the caudal medial preoptic area, VCS only increased Fos expression in cells that did not coexpress PRs. Injection of the progestin antagonist, RU 486, decreased Fos expression in the rostral, but not caudal medial preoptic area, and it decreased Fos expression only in cells that coexpressed PR-ir. In contrast to a previous report, in the present study, the progestin antagonist did not inhibit VCS-induced Fos expression in the ventromedial hypothalamic area. The results of this experiment suggest that the progestin antagonist inhibits VCS-induced Fos expression in some neurones by blocking PRs, and they provide further support for the idea that VCS influences neuronal response in some cells by ligand-independent activation of PRs in those cells.

SKF-82958 is a subtype-selective estrogen receptor-alpha (ERalpha ) agonist that induces functional interactions between ERalpha and AP-1

The transcriptional activity of estrogen receptors (ERs) can be regulated by ligands as well as agents such as dopamine, which stimulate intracellular signaling pathways able to communicate with these receptors. We examined the ability of SKF-82958 (SKF), a previously characterized full dopamine D1 receptor agonist, to stimulate the transcriptional activity of ERalpha and ERbeta. Treatment of HeLa cells with SKF-82958 stimulated robust ERalpha-dependent transcription from an estrogen-response element-E1b-CAT reporter in the absence of estrogen, and this was accompanied by increased receptor phosphorylation. However, induction of ERbeta-directed gene expression under the same conditions was negligible. In our cell model, SKF treatment did not elevate cAMP levels nor enhance transcription from a cAMP-response element-linked reporter. Control studies revealed that SKF-82958, but not dopamine, competes with 17beta-estradiol for binding to ERalpha or ERbeta with comparable relative binding affinities. Therefore, SKF-82958 is an ERalpha-selective agonist. Transcriptional activation of ERalpha by SKF was more potent than expected from its relative binding activity, and further examination revealed that this synthetic compound induced expression of an AP-1 target gene in a tetradecanoylphorbol-13-acetate-response element (TRE)-dependent manner. A putative TRE site upstream of the estrogen-response element and the amino-terminal domain of the receptor contributed to, but were not required for, SKF-induced expression of an ERalpha-dependent reporter gene. Overexpression of the AP-1 protein c-Jun, but not c-Fos, strongly enhanced SKF-induced ERalpha target gene expression but only when the TRE was present. These studies provide information on the ability of a ligand that weakly stimulates ERalpha to yield strong stimulation of ERalpha-dependent gene expression through cross-talk with other intracellular signaling pathways producing a robust combinatorial response within the cell.

A dopamine antagonist blocks vaginocervical stimulation-induced neuronal responses in the rat forebrain

During mating in rats, the male provides vaginocervical stimulation (VCS) to the female via intromissions. VCS, provided manually, mimics many aspects of mating, including facilitation of lordosis, induction of sexual receptivity, abbreviation of the period of sexual receptivity, and induction of twice-daily prolactin surges, which result in pseudopregnancy. VCS also induces the expression of Fos, the protein product of the immediate early gene c-fos, which has been used as a marker for neurons that are responsive to mating stimuli. Because VCS induces the release of dopamine in the forebrain, as well as phosphorylation of DARPP-32, a phosphoprotein associated with activation of the D(1) subtype of dopamine receptor, we tested the hypothesis that VCS induces Fos expression by acting on the D(1) class of dopamine receptors. Injection of SCH 23390, an antagonist of the D(1) class of dopamine receptors, virtually eliminated VCS-induced Fos expression without affecting constitutive levels of Fos-Immunoreactivity (Fos-IR) in all brain areas in which VCS induced Fos expression. In a follow-up experiment, expression of a second immediate early protein, egr-1, was blocked as well, suggesting that these results are not specific to Fos. Therefore, the results are consistent with the idea that VCS induces dopamine release, causing activation of D(1) dopamine receptors, which in turn, results in neuronal response, as seen by both Fos and egr-1 expression.

Invited review: Estrogens effects on the brain: multiple sites and molecular mechanisms

Besides their well-established actions on reproductive functions, estrogens exert a variety of actions on many regions of the nervous system that influence higher cognitive function, pain mechanisms, fine motor skills, mood, and susceptibility to seizures; they also appear to have neuroprotective actions in relation to stroke damage and Alzheimer's disease. Estrogen actions are now recognized to occur via two different intracellular estrogen receptors, ER-alpha and ER-beta, that reside in the cell nuclei of some nerve cells, as well as by some less well-characterized mechanisms. In the hippocampus, such nerve cells are sparse in number and yet appear to exert a powerful influence on synapse formation by neurons that do not have high levels of nuclear estrogen receptors. However, we also find nonnuclear estrogen receptors outside of the cell nuclei in dendrites, presynaptic terminals, and glial cells, where estrogen receptors may couple to second messenger systems to regulate a variety of cellular events and signal to the nuclear via transcriptional regulators such as CREB. Sex differences exist in many of the actions of estrogens in the brain, and the process of sexual differentiation appears to affect many brain regions outside of the traditional brain areas involved in reproductive functions. Finally, the aging brain is responsive to actions of estrogens, which have neuroprotective effects both in vivo and in vitro. However, in an animal model, the actions of estrogens on the hippocampus appear to be somewhat attenuated with age. In the future, estrogen actions over puberty and in pregnancy and lactation should be further explored and should be studied in both the hypothalamus and the extrahypothalamic regions.

Evolutionary changes in dopaminergic modulation of courtship behavior in Cnemidophorus whiptail lizards

Preoptic dopamine release is integral to the display of copulatory behaviors in male mammals and birds. However, while the anatomical distributions of the dopamine synthesizing enzyme tyrosine hydroxylase are similar among vertebrates, evolutionary changes in the functional role of dopamine are poorly understood. In this study, we tested whether a dopamine D1 receptor agonist would facilitate the display of courtship and copulatory behaviors in two related Cnemidophorine lizards (Cnemidophorus inornatus and Cnemidophorus uniparens). Cnemidophorus lizards offer a unique system to study evolutionary changes in functionality because ancestral (e.g., C. inornatus) and descendant (e.g., C. uniparens) species can be studied in parallel. Cnemidophorus uniparens is an all-female, parthenogenetic species and is the triploid descendant of the sexual and diploid species C. inornatus. Here we report that in castrated male C. inornatus and ovariectomized C. uniparens a dopamine D1 agonist increased the proportion of individuals mounting and decreased the latency to mount. Moreover, there was a species difference in sensitivity to the agonist: Mounting was elicited at a lower dose in C. uniparens than in C. inornatus. One possible explanation for this heightened sensitivity in the triploid parthenogen is that, by virtue of the increased ploidy, the parthenogen has elevated levels of D1 receptor in limbic brain areas modulating courtship behavior.

The role of neurosteroids and non-genomic effects of progestins and androgens in mediating sexual receptivity of rodents

Progestins and androgens modulate sexual receptivity in rodents, in part through mechanisms independent of traditional intracellular steroid receptors. Progesterone (PROG) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) facilitates lordosis but has different actions in these brain areas. Primarily using lordosis in rodents as an in vivo experimental model, we have examined the effects that progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that PROG's actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alters lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with PROG's metabolism to, or the biosynthesis of, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG or allopregnanolone), the most effective endogenous GBR agonist, in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhances neurosteroid production, by infusions of an MBR agonist to the VTA enhances lordosis. 3alpha,5alpha-TH PROG is increased in the midbrain of mated>proestrous>diestrous rodents. These data suggest that in the VTA, PROG may facilitate lordosis following metabolism to and/or biosynthesis of 3alpha,5alpha-TH PROG, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents. The 3alpha-hydroxysteroid oxidoreduced metabolite of dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol), is important for termination of sexual receptivity in rodents and has these effects in the absence of functional intracellular androgens receptors. As well, altering GBR function in the hypothalamus can influence 3alpha-androstanediol's inhibition of sexual receptivity. Through actions in the hypothalamus that are independent of intracellular androgen receptors but involving GBRs, 3alpha-androstanediol inhibits lordosis. These findings suggest that the PROG metabolite and pregnane neurosteroid, 3alpha,5alpha-TH PROG, and the testosterone metabolite and androstane neurosteroid, 3alpha-androstanediol, can have proximate influences on lordosis that is via nonclassical actions at intracellular steroid receptors.

Early membrane estrogenic effects required for full expression of slower genomic actions in a nerve cell line

Interpretations of steroid hormone actions as slow, nuclear, transcriptional events have frequently been seen as competing against inferences of rapid membrane actions. We have discovered conditions where membrane-limited effects potentiate later transcriptional actions in a nerve cell line. Making use of a two-pulse hormonal schedule in a transfection system, early and brief administration of conjugated, membrane-limited estradiol was necessary but not sufficient for full transcriptional potency of the second estrogen pulse. Efficacy of the first pulse depended on intact signal transduction pathways. Surprisingly, the actions of both pulses were blocked by a classical estrogen receptor (ER) antagonist. Thus, two different modes of steroid hormone action can synergize.

Effects of neonatal polychlorinated biphenyl exposure on female sexual behavior

The effects of polychlorinated biphenyls (PCBs) on development and reproduction are well documented. However, very little is known about the effects of PCBs on sexual behavior. In this study, we examined the effects of two commercial PCB mixtures, Aroclor 1221 (A1221) and Aroclor 1254 (A1254), on the development of female sexual behavior and of the incertohypothalamic dopaminergic cells (A11 and A13) in Long-Evans rats. Neonatal exposure to A1254 significantly reduced sexual receptivity and reduced the female's latency to approach a male after an intromission. Neonatal treatment with A1221 did not affect female sexual behavior nor did treatment of adult females with A1221 or A1254. Since sexual behavior is affected by dopamine and since PCBs have been reported to alter dopamine content in the brain, we examined the effects of A1221 or A1254 on dopaminergic cells in the incertohypothalamic region of neonatally exposed rats. None of the treatments significantly affected the number of A11 or A13 neurons that were immunoreactive for tyrosine hydroxylase (TH) or the expression of Fos (i.e., the product of the immediate early gene c-fos) in these dopaminergic neurons. Therefore, the disruption of behavior induced by neonatal treatment with A1254 does not appear to be mediated by toxic effects of the mixture on incertohypothalamic dopaminergic systems.

Complexities of androgen action

Androgens mediate a wide range of processes during embryogenesis and in the adult. In mammals, the principal androgens are testosterone and its 5alpha-reduced metabolite, 5alpha-dihydrotestosterone (DHT). Although these androgenic hormones are diverse in character, it is believed that their effects are mediated via the protein products of a single androgen receptor gene encoded on the X-chromosome. A great deal of information has now accumulated pertaining to the mechanisms by which nuclear receptors, such as the androgen receptor, modulate the activity of responsive genes. The studies have demonstrated the participation of a number of ancillary proteins in modulating activation or repression by nuclear receptors. In addition to studies focused on the mechanisms of nuclear receptor function, additional work has illuminated the mechanism by which androgens are metabolized in selected tissues. This information provides a perspective on the number of levels of complexity by which differential gene regulation by androgens may occur in different tissues and in different cell types.

Oestradiol increases phosphorylation of a dopamine- and cyclic AMP-regulated phosphoprotein (DARPP-32) in female rat brain

Recent studies suggest that oestrogen and progestin receptors may be activated by the neurotransmitter dopamine, as well as by their respective ligands. Because intracerebroventricular infusion of D(1), but not D(2), dopaminergic receptor agonists increases oestrous behaviour in oestradiol-primed rats, we wanted to determine if treatment with oestradiol alters the activity of D(1) receptor-associated processes in steroid receptor-containing areas in female rat brain. One D(1) receptor-associated phosphoprotein that may be influenced by oestradiol is a dopamine- and cyclic AMP-regulated phosphoprotein, Mr = 32,000 (DARPP-32). Because DARPP-32 is phosphorylated in response to dopamine acting via a cAMP-dependent protein kinase, it provides a useful marker to examine where in the brain a particular stimulus might be altering the activity of D(1) receptor-containing neurones. To determine if oestradiol alters the phosphorylation of DARPP-32, we stained immunocytochemically brain sections of female rats treated with behaviourally relevant doses of oestradiol or oil vehicle with an antibody that detects only the threonine 34-phosphorylated form of DARPP-32. Behaviourally effective doses of oestradiol increase the phosphorylation of DARPP-32 within the medial preoptic nucleus, bed nucleus of the stria terminalis, paraventricular nucleus of the hypothalamus and the ventromedial nucleus of the hypothalamus, 48 h after treatment. These data suggest that oestradiol increases the activity of D(1) dopamine receptor-associated processes in oestrogen receptor-containing areas of female rat forebrain.

Ligand-independent activation of progestin receptors in sexual receptivity

Ovarian steroid hormones, estradiol and progesterone, regulate cellular functions in the central nervous system, resulting in the alterations in physiology and reproductive behavior. One means by which steroid hormones exert their neural effects on reproductive behavior is via their intracellular receptors functioning as ligand-dependent transcription factors. Studies from our laboratory in the past few years have shown that in addition to their cognate ligands, neurotransmitters like dopamine can activate intracellular steroid receptors in a ligand-independent manner. Using biochemical and molecular approaches we have demonstrated that the effects of neurotransmitter dopamine, on reproductive behavior in female rats and mice, occur by means of cross talk between membrane receptors for dopamine and intracellular progestin receptors (PRs). In this article, our studies on the integration of intracellular signaling pathways leading to the activation of PRs and its impact on modulation of reproductive behavior are summarized.

Sensory cues mediating mating-induced potentiation of sexual receptivity in female rats

Repeated mating of estradiol-primed female rats increases sexual receptivity. Two studies were conducted to determine the contribution of vaginal--cervical stimulation (VCS) to this increase. In the first study, female rats were repeatedly mated for 165 min. The vaginas of half of the females were covered with tape (masked) to prevent intromissions by the males. The remaining females were unmasked. Only females receiving intromissions (unmasked) showed a significant increase in sexual receptivity during repeated mating, suggesting that VCS from intromissions is necessary for repeated mating to increase sexual receptivity. In the second experiment, female rats received either experimentally administered VCS or control scapular stimulation administered with a plastic probe 1 h prior to testing for sexual receptivity. VCS applied in this manner significantly increased sexual receptivity. Together, these findings suggest that VCS from intromissions is one of the primary factors responsible for increases in sexual receptivity following repeated mating.

Analysis of steroid-induced genes in the rat preoptic area-anterior hypothalamus using a differential-display reverse transcriptase-polymerase chain reaction

Steroid hormones modulate a variety of physiological functions in the hypothalamus. We attempted to identify steroid-regulated genes in the rat preoptic area-anterior hypothalamus by comparing differentially expressed mRNAs. Adult female rats were ovariectomized and, 1 week later, a silastic capsule containing 17beta-oestradiol (180 microg/ml) was subcutaneously implanted. After 2 days, a single injection of progesterone (1 mg) was administered at 10.00 h and rats were killed at 17.00 h on the same day. Differential-display polymerase chain reaction followed by Northern blot analysis showed that 10 clones were differentially regulated. Using homology search in Genbank, three genes were identified as sodium, potassium-ATPase beta1, protein kinase C-binding Nell-homologue protein and evectin-1. Further characterization of 10 clones showed that the expression patterns were tissue-specific and differentially regulated during puberty. Among these, mRNAs for protein kinase C-binding Nell-homologue protein, evectin-1 and human CGI-118 protein-like gene were induced after vagina opening, and differentially expressed during the oestrous cycle. Taken together, several steroid-regulated genes identified in the present study may play an important role in regulating hypothalamic functions, including puberty and the oestrous cycle.

Progesterone receptors as neuroendocrine integrators

Intracellular progesterone receptors (PRs) are ligand-inducible transcription factors that mediate the majority of the effects of progesterone (P) on neuroendocrine functions. During the past decade, evidence has accumulated which suggest that PRs can also be activated independently of P, by signals propagated through membrane-bound receptors to the interior of cells. The activation of PRs by this type of "cross-talk" mechanism has been implicated in the physiological regulation of several important neuroendocrine processes, including estrous behavior and periovulatory hormone secretions. We review evidence that both ligand-dependent and ligand-independent activation of PRs occurs in central neurons and in anterior pituitary cells and that the convergence and summation of these signals at the PR serves to integrate neural and endocrine signals which direct several critically important neuroendocrine processes. An integrative function for PRs is reviewed in several physiological contexts, including the display of lordosis behavior in female rodents, the neurosecretion of gonadotropin-releasing hormone surges, secretion of preovulatory gonadotropin surges, and release of periovulatory follicle stimulating hormone surges. The weight of evidence indicates that cross talk at the intracellular PR is an essential component of the integrative mechanisms that direct each of these neuroendocrine events. The recurrence of PR's integrative actions in several different physiological contexts suggests that other intracellular steroid receptors similarly function as integrators of neural and endocrine signals in other neuroendocrine processes.

20-hydroxyecdysone causes increased aggressiveness in female American lobsters, Homarus americanus

Lobsters become transiently more aggressive before ecdysis. This aggressiveness accompanies an increase in hemolymph titers of 20-hydroxyecdysone (20-HE). Combats between intermolt female lobsters, injected with premolt levels of 20-HE, and larger, saline-injected opponents were videotaped. Aggressive, defensive, and avoidance behaviors were ranked according to aggressiveness in a Rank of Aggression hierarchy, which included opponent-directed and (nonopponent) redirected behaviors. Treated animals performed more and more highly aggressive behaviors than saline-injected controls. Opponents of treated animals performed fewer aggressive behaviors than saline-injected control opponents. Controls performed more defensive behaviors than treated animals, when redirected behaviors were considered. Differences in avoidance behaviors among the four types of combatants were not significant. The total aggressive content was the same in treated and control fights, but the interactions between combatants in the two fights were significantly different. Treated animals were equally as aggressive and defensive as their opponents; controls were relatively less aggressive and more defensive than their opponents. These results correlate with molt-cycle variations in behavior, 20-HE titers, and the effects of 20-HE and molt-differentiated hemolymph on the claw opener muscle. They suggest that 20-HE orchestrates intrinsic, cellular, and nuclear events that produce the molt-cycle transformations in agonistic behavior and aggressive state of lobsters.

Progesterone receptor and dopamine receptors are required in Delta 9-tetrahydrocannabinol modulation of sexual receptivity in female rats

Ovarian steroids, estrogen and progesterone, influence the sensitivity of certain neural processes to cannabinoid treatment by modulation of brain dopaminergic activity. We examined the effects of the active ingredient of cannabis, Delta(9)-tetrahydrocannabinol (THC), on sexual behavior in female rats and its influence on steroid hormone receptors and neurotransmitters in the facilitation of sexual receptivity. Our results revealed that the facilitatory effect of THC was inhibited by antagonists to both progesterone and dopamine D(1) receptors. To test further the idea that progesterone receptors (PR) and/or dopamine receptors (D(1)R) in the hypothalamus are required for THC-facilitated sexual behavior in rodents, antisense and sense oligonucleotides to PR and D(1)R were administered intracerebroventricularly (ICV) into the third cerebral ventricle of ovariectomized, estradiol benzoate-primed rats. Progesterone- and THC-facilitated sexual behavior was inhibited in animals treated with antisense oligonucleotides to PR or to D(1)R. Antagonists to cannabinoid receptor-1 subtype (CB(1)), but not to cannabinoid receptor-2 subtype (CB(2)) inhibited progesterone- and dopamine-facilitated sexual receptivity in female rats. Our studies indicate that THC acts on the CB(1) cannabinoid receptor to initiate a signal transduction response that requires both membrane dopamine and intracellular progesterone receptors for effective induction of sexual behavior.

Progesterone receptor and dopamine receptors are required in 9-tetrahydrocannabinol modulation of sexual receptivity in female rats

Ovarian steroids, estrogen and progesterone, influence the sensitivity of certain neural processes to cannabinoid treatment by modulation of brain dopaminergic activity. We examined the effects of the active ingredient of cannabis, Delta(9)-tetrahydrocannabinol (THC), on sexual behavior in female rats and its influence on steroid hormone receptors and neurotransmitters in the facilitation of sexual receptivity. Our results revealed that the facilitatory effect of THC was inhibited by antagonists to both progesterone and dopamine D(1) receptors. To test further the idea that progesterone receptors (PR) and/or dopamine receptors (D(1)R) in the hypothalamus are required for THC-facilitated sexual behavior in rodents, antisense and sense oligonucleotides to PR and D(1)R were administered intracerebroventricularly (ICV) into the third cerebral ventricle of ovariectomized, estradiol benzoate-primed rats. Progesterone- and THC-facilitated sexual behavior was inhibited in animals treated with antisense oligonucleotides to PR or to D(1)R. Antagonists to cannabinoid receptor-1 subtype (CB(1)), but not to cannabinoid receptor-2 subtype (CB(2)) inhibited progesterone- and dopamine-facilitated sexual receptivity in female rats. Our studies indicate that THC acts on the CB(1) cannabinoid receptor to initiate a signal transduction response that requires both membrane dopamine and intracellular progesterone receptors for effective induction of sexual behavior.