Estradiol and progesterone influence the response of ventromedial hypothalamic neurons to tactile stimuli associated with female reproduction

Female Reproductive Behavior

Reproductive behavior is the behavior related to the production of offspring and includes all aspects from the establishment of mating systems, courtship, sexual behavior, and parturition to the care of young. In this chapter, I outline the hormonal regulation of the estrous cycle, followed by a description of the neural regulation of female sexual behavior. Ovarian hormones play an important role in the induction of ovulation and behavioral estrus, in which they interact closely with several neurotransmitters and neuropeptides to induce sexual behavior. This chapter discusses the latest research on the role of estrogen, progesterone, serotonin, dopamine, noradrenaline, oxytocin, and GABA in female mating behavior. In addition, the most relevant brain areas, such as the preoptic area and the ventromedial nucleus of the hypothalamus, in which these regulations take place, are discussed.

The neural basis of sex differences in sexual behavior: A quantitative meta-analysis

Sexuality as to its etymology presupposes the duality of sexes. Using quantitative neuroimaging meta-analyses, we demonstrate robust sex differences in the neural processing of sexual stimuli in thalamus, hypothalamus, and basal ganglia. In a narrative review, we show how these relate to the well-established sex differences on the behavioral level. More specifically, we describe the neural bases of known poor agreement between self-reported and genital measures of female sexual arousal, of previously proposed male proneness to affective sexual conditioning, as well as hints of unconscious activation of bonding mechanisms during sexual stimulation in women. In summary, our meta-analytic review demonstrates that neurofunctional sex differences during sexual stimulation can account for well-established sex differences in sexual behavior.

Enhanced male-evoked responses in the ventromedial hypothalamus of sexually receptive female mice

Social encounters often start with routine investigatory behaviors before developing into distinct outcomes, such as affiliative or aggressive actions. For example, a female mouse will initially engage in investigatory behavior with a male but will then show copulation or rejection, depending on her reproductive state. To promote adaptive social behavior, her brain must combine internal ovarian signals and external social stimuli, but little is known about how socially evoked neural activity is modulated across the reproductive cycle [1]. To investigate this, we performed single-unit recordings in the ventrolateral region of the ventromedial hypothalamus (VMHvl) in freely behaving, naturally cycling, female mice interacting with conspecifics of both genders. The VMHvl has been implicated in rodent sociosexual behavior [2, 3]: it has access to social sensory stimuli [4-8] and is involved in aggression and mating [9-11]. Furthermore, many VMHvl neurons express ovarian hormone receptors [12, 13], which play a central role in female sociosexual behavior [14-16]. We found that a large fraction of VMHvl neurons was activated in the presence of conspecifics with preference to male stimuli and that the activity of most VMHvl neurons was modulated throughout social interactions rather than in response to specific social events. Furthermore, neuronal responses to male, but not female, conspecifics in the VMHvl were enhanced during the sexually receptive state. Thus, male-evoked VMHvl responses are modulated by the reproductive state, and VMHvl neural activity could drive gender-specific and reproductive state-dependent sociosexual behavior.

Activation of hypothalamic gono-like neurons in female rats during estrus

In mammals, gonadal function is controlled by the activity of hypothalamic gonadotropin-releasing hormone neurons, which control the secretion of adenohypophyseal and gonadal hormones. However, there are a number of unanswered questions in relation to gonadal function. It is currently unknown how erotogenic stimulation of the genitals influences the subpopulation of hypothalamic medial preoptic area neurons, antidromically identified as projecting to the median eminence at different periods of the estrous cycle. Additionally, the distinctiveness of hypothalamic medial preoptic area neurons, with respect to methods of feedback control by exogenous hormones, is also unknown. In this study, spontaneous discharges from individual neurons encountered within the medial preoptic area, gono-like neurons, were recorded extracellularly using glass microelectrodes. To confirm the cellular and histochemical properties of the recording units, antidromic stimulation was performed using a side-by-side bipolar stimulating electrode placed into the median eminence, alongside microiontophoretic injections of the conventional tracer, horseradish peroxidase. In addition, further immunohistochemical analyses were performed. Results showed that elevated gono-neuron activity was accompanied by increased background activity and greater responses to erotogenic stimuli during estrus. Application of clitoral traction stimulation resulted in increased activation of the gono-like neurons. This neuronal activity was noticeably inhibited by β-estradiol administration. Immunohistochemical analyses revealed the presence of gonadotropin-releasing hormone-reactive protein in hypothalamic cells in which electrophysiological recordings were taken. Thus, medial preoptic area neurons represent the subset of hypothalamic gonadotropin-releasing hormone neurons described from brain slices in vitro, and might serve as a useful physiological model to form the basis of future in vivo studies.

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

Glutamate release in the ventromedial hypothalamus of the female rat during copulation: modulation by estradiol

Binding of glutamate or its ionotropic receptor agonists in the ventromedial hypothalamus (VMH) of female rats inhibits both appetitive and consummatory aspects of sexual behavior. Because vaginocervical stimulation activates glutamate neurons in the VMH, and administration of estradiol benzoate (EB) and progesterone (P) delays this effect, the present study examined the effects of hormonal priming on glutamate release within the VMH of female rats paired with sexually vigorous males. Ovariectomized, sexually experienced rats were implanted with guide cannula aimed at the ventrolateral VMH, through which microdialysis probes were inserted prior to testing. Females were assigned randomly to one of three hormone treatment conditions: EB+P, EB alone, or the oil vehicle. Testing was conducted over 5h, including a 120-min period of habituation to the testing chamber, a 60-min period of baseline sample collection, and a 120-min period during which a sexually vigorous male was introduced into the testing chamber. Dialysates were collected every 20min during the test and were analyzed for glutamate using HPLC. Females primed with oil had large and significant increases in glutamate release from baseline once the male was introduced to the chamber. Treatment with EB alone decreased glutamate release in response to male cues. Although treatment with EB+P did not differ significantly from EB alone, the degree of reduced glutamate release was less than with EB alone. These results indicate that priming with EB reduces glutamate transmission in the VMH in response to male cues. Taken together with our previous findings, estradiol blunts the activation of glutamate neurons in the VMH thus allowing female rats to copulate.

AMPA/kainate receptors in the ventromedial hypothalamus mediate the effects of glutamate on estrus termination in the rat

Infusions of glutamate or its selective receptor agonists to the VMH of ovariectomized (OVX) female rats primed with estradiol benzoate (EB) and progesterone (P) inhibit both appetitive and consummatory aspects of sexual behavior whereas selective glutamate receptor antagonists facilitate these measures in females primed with EB alone. Because vaginocervical stimulation (VCS) activates glutamate neurons in the VMH, and induces a faster termination of estros behavior, the present study examined the effects of the AMPA/kainate receptor antagonist DNQX on the induction of estrus termination by manual VCS. Ovx, sexually-experienced rats were primed with EB and P and subsequently received either 1 or 50 distributed VCSs, over the course of an hour, 12 h before a test with sexually vigorous males. Half of the females in each stimulus group received bilateral infusions of 1 μl/side of either DNQX (19.8 mmol/μl) or saline aimed at the VMH immediately prior to VCS or sham stimulation. Saline-infused females given VCS had lower lordosis quotients compared to females given sham stimulation. In contrast, females infused with DNQX prior to VCS displayed more appetitive behaviors and higher lordosis quotients and magnitudes compared to females infused with saline. These data indicate that activation of AMPA/kainate receptors in the VMH by increased glutamate transmission induced by VCS mediates estrus termination.

Context alters the ability of clitoral stimulation to induce a sexually-conditioned partner preference in the rat

We have shown previously that clitoral stimulation (CLS) of female rats induces significant conditioned place preference (CPP), indicating that it is rewarding. The present study asked whether CLS could induce a conditioned partner preference. In the first experiment, sexually naïve females received 10 alternating trials of CLS and No-CLS in the presence of a male rat behind a wire-mesh screen. For one group, CLS was made in the presence of the male scented with almond extract. On alternating trials, those females received sham CLS in the presence of an unscented male behind the screen. The order was reversed for the other group. After 5 trials in each condition, females were placed into an open field with two sexually vigorous males, one scented and the other unscented. Contrary to expectation, females displayed a preference for the male associated with sham CLS. The second experiment examined whether a partner preference could be conditioned by associating CLS with the almond odor alone. A new group of sexually naive females received the same CLS-odor, No-CLS-No Odor pairings as above, but with the odor presented on cotton gauze in the chamber. During the final open field test, those females selectively solicited the scented male. We conclude that CLS that induces CPP also induces conditioned partner preference. However, we propose that CLS in the presence of an inaccessible male created a sexual inhibitory state for female rats.

Clitoral stimulation induces conditioned place preference and Fos activation in the rat

The present study examined the ability of clitoral stimulation (CLS) to induce conditioned place preference (CPP) and Fos protein in the brain. Ovariectomized, hormone-primed Long-Evans rats were randomly assigned to receive either distributed CLS (1 stimulation every 5 s for 1 min prior to being placed in one distinctive side of a nonbiased CPP box for 2 min, after which the cycle of stimulation and CPP exposure were repeated for 4 more cycles, totaling 60 stimulations) or continuous CLS (1 stimulation per second for 1 min with 2 min in one side of the CPP box, repeated for 4 more cycles, totaling 300 stimulations). Two days later, females were placed into the other side of the CPP box without prior stimulation. CPP was tested after 5 sequential exposures each of CLS and no stimulation. Females given distributed stimulation developed a significant CPP whereas females given continuous stimulation did not. CLS induced Fos in hypothalamic and limbic structures, including the nucleus accumbens, piriform cortex, arcuate nucleus, and dorsomedial portion of the ventromedial hypothalamus, compared to no stimulation. However, distributed CLS induced more Fos in the medial preoptic area than continuous CLS or no stimulation. In contrast, continuous CLS induced more Fos in the posteroventral medial amygdala compared to no stimulation. These data indicate that CLS induces a reward state in the rat and a pattern of Fos activation in regions of the brain that process genitosensory input, incentive salience, and reward.

Vaginocervical stimulation induces Fos in glutamate neurons in the ventromedial hypothalamus: attenuation by estrogen and progesterone

Vaginocervical stimulation (VCS) induces the immediate-early gene product Fos in the ventromedial hypothalamus (VMH) of female rats. However, this induction is lower in ovariectomized rats that receive estradiol benzoate (EB) and progesterone (P) relative to an oil vehicle. We have observed that a substantial proportion of cells activated in the VMH by VCS stain for glutamate, and infusions of glutamate or its selective receptor agonists to the VMH inhibit both appetitive and consummatory sexual behaviors in females. This raises the possibility that VCS activates an inhibitory glutamate system in the VMH, and that ovarian steroids blunt the activation, although it is not known whether EB or P, alone or in combination, lead to this effect. The present experiment examined the ability of VCS to induce Fos in glutamate neurons in the VMH of ovariectomized rats under 4 hormonal regimens: oil, EB alone, P alone, or EB+P, following 1 or 50 distributed VCSs administered with a lubricated glass rod over the course of 1 h. Treatment with EB or P alone significantly reduced the number of glutamate neurons activated by 1 VCS, with P being more effective than EB. Treatment with EB+P also produced a significant reduction, but not to the extent of EB or P alone. Although EB and P work in synergy to activate sexual behavior in female rats, actions of EB or P alone are sufficient to blunt the ability of VCS to activate glutamate neurons in the VMH. It thus appears that ovarian steroids may "disinhibit" sexual responding, in part, by dampening the ability of VCS to activate glutamate neurons in the VMH. In turn, this may allow females to receive a sufficient number of intromissions for the activation of sexual reward and the facilitation of pregnancy.

Estradiol induces region-specific inhibition of ZENK but does not affect the behavioral preference for tutored song in adult female zebra finches

Female zebra finches display a preference for songs of males raised with tutors compared to those from males without tutors. To determine how this behavioral preference may be mediated by auditory perception sites, the social behavior network, and the dopamine reward system, and whether responses of these regions are affected by estradiol, females were treated with hormone or blank implants. An auditory choice test was conducted followed by exposure to tutored or untutored song or silence to examine induction of the immediate early gene, ZENK. Birds spent significantly more time near tutored than untutored song, regardless of estrogen treatment, and estradiol significantly decreased the density of ZENK immunoreactive neurons within the ventromedial hypothalamus. These results suggest that selective neural and behavioral responses can be induced by both high quality vocalizations and estradiol, although they are not necessarily correlated.

Estradiol-associated variation in responses of rostral medullary neurons to somatovisceral stimulation

The lordosis posture and cervix stimulation during copulation are important reproductive events involving complex neural circuitries that are under hormonal influence. An important component of this circuitry, neurons within the medullary reticular formation (MRF), was examined in the present study using electrophysiological techniques. Single unit extracellular recordings were performed in the MRF of 27 urethane-anesthetized female rats. Using bilateral electrical stimulation of the dorsal nerve of the clitoris as the search stimulus, a detailed examination of the somatovisceral convergent responses of 585 individual MRF neurons was made. A total of 7 different groups of cycling and ovariectomized/hormone-supplemented rats were examined and their neuronal response properties to mechanical stimulation of various pelvic organs (cervix pressure, vaginal distension, colon distension) compared. The results indicate the existence of complex response properties as well as several variations in MRF response characteristics that are hormone-dependent. Specifically, estradiol is associated with hyposensitivity to cervix pressure and hypersensitivity to stroking the face. These opposing effects of estradiol in the same subset of neurons likely relate to lordosis behavior which can be either disrupted or elicited, depending on the area being stimulated (upper versus lower parts of the body, respectively).

Co-localization of midbrain projections, progestin receptors, and mating-induced fos in the hypothalamic ventromedial nucleus of the female rat

In female rats, sexual behavior requires the convergence of ovarian hormone signals, namely estradiol and progesterone, and sensory cues from the male on a motor output pathway. Estrogen and progestin receptors (ER and PR) are found in neurons in the hypothalamic ventromedial nucleus (VMH), a brain region necessary for lordosis, the stereotypic female copulatory posture. A subset of VMH neurons sends axonal projections to the periaqueductal gray (PAG) to initiate a motor output relay, and some of these projection neurons express PR. Previous studies showed that VMH neurons are activated during mating, based on the expression of the immediate early gene Fos. Many of the activated neurons expressed ER; however, it is not known if such activated neurons co-express PR. Fluorogold, a retrograde tracer, was injected into the PAG of ovariectomized rats to label neurons projecting from the VMH. Hormone-treated animals then were mated, and their brains were immunohistochemically stained for PR and Fos. Of the Fos-positive neurons, 33% were double-labeled for PR, 19% were double-labeled with Fluorogold, and 5% were triple-labeled for Fos, PR, and the retrograde tracer. The majority of triple-labeled neurons were found in the rostral, rather than caudal, portion of the VMH. These results show that PR-containing neurons are engaged during sexual behavior, which suggests that these neurons are the loci of hormonal-sensory convergence and hormonal-motor integration.

Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus)

Females alter their mate choices as they transition through different reproductive stages; however, the proximal mechanisms for such behavioral fluctuation are unclear. In many taxa, as females transition through different reproductive stages, there is an associated change in hormone levels; therefore, we examined whether fluctuation in hormone levels serves as a proximal mechanism for within-individual variation in mate choice in female túngara frogs (Physalaemus pustulosus). We manipulated hormone levels of females by administering 0, 10, 100, 500 or 1,000 IU of human chorionic gonadotropin (HCG), which is a ligand for luteinizing hormone (LH) receptors and will therefore cause increased gonadal hormone production. Phonotaxis assays were conducted to measure three aspects of mate choice behavior before and after HCG administration; receptivity (response to a conspecific mate signal), permissiveness (response to a signal that is less attractive than conspecific signals) and discrimination (ability to discern signal differences). The probability of response to a conspecific and an artificial hybrid signal significantly increased at the highest HCG doses. The difference in mean response time between pre- and post-HCG tests was significantly different for both the receptivity and permissiveness tests among the five doses. Increased permissiveness, however, was not due to decreased discrimination because females could discriminate between calls even at the highest HCG doses. These hormonal manipulations caused the same behavioral pattern we reported in females as they transitioned through different reproductive stages (Lynch, K.S., Rand, A.S., Ryan, M.J., Wilczynski, W., 2005. Plasticity in female mate choice associated with changing reproductive states. Anim. Behav. 69, 689-699), suggesting that changes in hormone levels can influence the female's mate choice behavior.

Short term suppression of follicular recruitment and spontaneous ovulation in the cat using levonorgestrel versus a GnRH antagonist

Suppression and subsequent rebound of ovarian activity using a progestin (levonorgestrel; Norplant) versus a GnRH antagonist (antide) was assessed in the domestic cat via fecal estradiol and progesterone metabolite analyses. Following an initial dose-response trial, queens were assigned to one of four treatments: (1) antide, two 6 mg/kg injections 15 days apart (n = 8 cats); (2) levonorgestrel, six silastic rods (36 mg levonorgestrel/rod) implanted for 30 days (n = 8); (3) control injections (n = 5); and (4) control implants (n = 5). Steroid metabolites were quantified from daily fecal samples for 90 days before, 30 days during, and 90 days after treatment. Antide and levonorgestrel inhibited estrous cyclicity in contrast to continued cyclicity in controls. Cats already at estradiol baseline in antide (n = 7) and levonorgestrel (n = 4) groups remained inhibited during treatment. In females with elevated estradiol levels at treatment onset (Day 0), a normal estradiol surge was completed before concentrations declined to baseline (approximately Days 5-7) and remained suppressed throughout the remaining treatment period. Additionally, 56% of treatment animals exhibited at least one spontaneous ovulation during the pre-treatment period, but no female ovulated during treatment with levonorgestrel or antide. Antide-treated cats exhibited lower (P < 0.05) baseline estradiol concentrations during treatment compared to pre- and post-treatment. In contrast, levonorgestrel induced elevations in baseline estradiol following treatment compared to pre- and during treatment intervals. Control females showed no change (P > 0.05) in baseline estradiol throughout the study period. All levonorgestrel and antide cats returned to estrus after treatment withdrawal. Results demonstrate that: (1) both antide and levonorgestrel are effective for inducing short-term suppression of follicular recruitment and ovulation in the cat; (2) inhibition is reversible; and (3) GnRH antagonists and progestins differentially regulate basal estradiol secretion. This study also confirmed a relatively high incidence of spontaneous ovulation in the cat, a species generally considered to be an induced ovulator.

Gonadal hormone modulation of dendrites in the mammalian CNS

This review focuses on the effect of gonadal steroid hormones, androgen and estrogen, on dendrites in the adult rat central nervous system (CNS). Four hormone-responsive nuclei are considered: The spinal nucleus of the bulbocavernosus (SNB), the medial nucleus of the amygdala (MeA), the ventromedial nucleus of the hypothalamus (VMN), and the CA1 region of the dorsal hippocampus. Particular emphasis is placed on the mode of hormone action in each nucleus. In the SNB, VMN, and hippocampus, hormones appear to mediate their effects indirectly, via cells other than those that display morphological plasticity. In the MeA, estrogen and/or androgen appears to act primarily on those cells whose dendrites are modulated by the hormone. Importantly, increasing levels of gonadal hormones do not simply result in increases in dendritic parameters. In the VMN, high levels of estrogen associated with proestrus increase dendritic spine density in one subset of cells and reduce spine density in another subset. The pyramidal cells of dorsal CA1 also undergo phasic changes in dendritic spine and synapse density across the estrous cycle. The estrogen-induced excitatory synapses connect with preexisting axonal boutons that also form synapses with other CA1 cells, thereby increasing the divergence of excitatory afferents to dorsal CA1. These findings indicate that gonadal steroids have a profound impact on the morphology of dendrites and patterns of synaptic connectivity. Consequently, the experimental manipulation of hormone levels is a powerful tool to study structure-function relationships in the mammalian brain.

Co-regulation of female sexual behavior and pregnancy induction: an exploratory synthesis

This paper will review both new and old data that address the question of whether brain mechanisms involved in reproductive function act in a coordinated way to control female sexual behavior and the induction of pregnancy/pseudopregnancy (P/PSP) by vaginocervical stimulation. Although it is clear that female sexual behavior, including pacing behavior, is important for induction of P/PSP, there has been no concerted effort to examine whether or how common mechanisms may control both functions. Because initiation of P/PSP requires that the female receive vaginocervical stimulation, central mechanisms controlling P/PSP may be modulated by or interactive with those that control female sexual behavior. This paper presents a synthesis of the literature and recent data from our lab for the purpose of examining whether there are interactions between behavioral and neuroendocrine mechanisms which reciprocally influence both reproductive functions.

Hormonal-neural integration in the female rat ventromedial hypothalamus: triple labeling for estrogen receptor-alpha, retrograde tract tracing from the periaqueductal gray, and mating-induced Fos expression

The lordosis reflex, a stereotypic posture adopted by female rats during sexual behavior, requires the convergence of a hormonal signal, estrogen, with a descending neural pathway from the ventromedial hypothalamic nucleus (VMH). The VMH contains at least three lordosis-relevant neural populations: estrogen receptor-alpha immunoreactive (ERalpha-IR) neurons, VMH neurons that project to the periaqueductal gray (PAG), and neurons that are ERalpha-IR and project to the PAG. Expression of Fos, a marker for neuronal activation, is increased in the VMH after mating. However, it is unknown which, if any, of these lordosis-relevant populations is activated. The majority of ERalpha-IR and projection neurons were not colocalized. Of the Fos-positive neurons, 41% neither contained ERalpha nor projected to the PAG, and 35% contained ERalpha but did not project to the PAG. Only 25% of Fos-positive neurons projected to the PAG, including projection neurons that expressed ERalpha. Our results suggest that mating activates several distinct VMH neuron types. However, ERalpha-IR neurons are activated to a greater extent compared with the PAG-projecting neurons.

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.

Temporal relationships among uterine pituitary adenylate cyclase-activating polypeptide, decidual prolactin-related protein and progesterone receptor mRNAs expressions during decidualization and gestation in rats

Pituitary adenylate cyclase-activating peptide (PACAP), a novel compound with vasoactive intestinal polypeptide-like activity, was recently shown to be localized in the neuronal endings of the human uterus. The purpose of the present study was to assess the functional presence of PACAP mRNA in the decidual endometrium and its relationship to the expression levels of decidual prolactin-related protein (dPRP) and the progesterone receptor mRNAs during decidualization and pregnancy in Sprague-Dawley rats. PACAP was constitutively and temporally expressed in the decidual endometrium and gravid uterus. The time-dependent correlated expression levels of PACAP, dPRP and the progesterone receptor were induced by the neurogenic reproductive signals, i.e. the vagino-cervical/deciduogenic stimuli of decidualization and by the normal equivalent stimuli of mating/blastocyst implantation of gestation. Correlation among the mRNA expression levels of PACAP, dPRP and the progesterone receptor and the coordinated inhibitory actions of the anti-progesterone (RU-486) suggest that there is also correlated time-dependent steroid regulation of the mRNA levels of PACAP, dPRP and the progesterone receptor in the decidual and pregnant uteri. One possible functional meaning for the time-related localization of endometrial/uterine PACAP could be to facilitate endometrial blood flow and increase the availability of metabolic substrates to the developing deciduoma or embryo. The study demonstrates the potential importance of PACAP expression in the regulation of the maternal feto-placental component and suggests a prominent reproductive role for the neuropeptide in mammalian pregnancy.

Fos expression in female hamsters after various stimuli associated with mating

Detection of the expression of c-fos mRNA or its protein product, Fos, has been used to indicate differences in neuronal response to exogenous stimuli. Factors contributing to differences in Fos expression as a result of various stimuli associated with mating have been extensively studied in the female rat. Less is known about the factors that contribute to Fos expression in female hamsters. Female hamsters differ from female rats in several aspects of sexual behavior; therefore, it seems likely that Fos expression may also differ. The purpose of this study was to determine which factors associated with mating selectively affect Fos expression in the female hamster. Animals were ovariectomized, hormone treated, and then exposed to several behavioral conditions. Fos expression in several brain areas was then assessed via immunocytochemistry (ICC). As has been found by others, mating increases Fos immunoreactivity in a number of brain regions. Specifically, vaginal-cervical stimulation (VCS) was determined to be the salient factor contributing to Fos expression in the preoptic area (POA) and bed nucleus of the stria terminalis (BNST) of ovariectomized hormone primed female hamsters that received a mating interaction.

Progesterone, but not progesterone-independent activation of progestin receptors by a mating stimulus, rapidly decreases progestin receptor immunoreactivity in female rat brain

Recent studies suggest that progestin receptors may be activated in vivo by neurotransmitters in the absence of ligand. More specifically, vaginal-cervical stimulation (VCS) can influence sexual behavior by activating progestin receptors in the absence of progesterone. Another way to test if progestin receptors are influenced by particular stimuli is to examine progestin receptor immunostaining. We report that progestin receptor immunoreactivity is decreased in the forebrain of estradiol-primed ovariectomized (OVX) rats within 1 h after a subcutaneous injection of progesterone, a time by which rapid down-regulation of progestin receptors does not seem to have occurred. In estradiol-primed OVX rats, VCS also decreased progestin receptor immunoreactivity within 1 h in the medial preoptic area, but not in any other area examined. To determine if the decrease in immunoreactivity by VCS was due to adrenal secretions or by ligand-independent activation of progestin receptors, we repeated the experiment in estradiol-primed OVX/adrenalectomized rats. Prior removal of the adrenal glands blocked the rapid decrease in progestin receptor immunoreactivity, even though data from other experiments suggest that progestin receptors are activated by VCS at this time. These studies suggest the possibility that progestin receptors may be affected differentially by progesterone-dependent or by progesterone-independent pathways. This raises the possibility that activation of progestin receptors by these two distinct pathways may lead to different neuronal consequences.

Appetitive and consummatory sexual behaviors of female rats in bilevel chambers. II. Patterns of estrus termination following vaginocervical stimulation

Copulation with intromission or manual vaginocervical stimulation (VCS) shortens the duration that intact female rats maintain lordosis responding during estrus. The present study examined whether VCS could shorten the duration of both appetitive and consummatory measures of female sexual behavior, and whether these effects occur differentially in time and across different hormone priming intervals. Ovariectomized, sexually experienced female rats were administered subcutaneous injections of estradiol benzoate 48 h and progesterone 4 h, before receiving 50 manual VCSs with a lubricated glass rod distributed over 1 h. Control females received sham VCSs distributed over the same time. The females were then tested for sexual behavior in bilevel chambers with two sexually vigorous males (to one ejaculatory series or 10 min with each male, separated by 5 min) 12, 16, and 20 h after VCS. Prior to the final hormone treatment, different groups of females had been given the same hormone treatment either 28, 14, 7, or 4 days before. In females tested at 28- and 14-day hormone intervals, VCS induced both active and passive rejection responses at 12, 16, and 20 h. In contrast, females that received sham VCS displayed relatively normal sexual behavior at 12 h, although by 16 and 20 h these females displayed active and passive rejection. Females tested at 7- or 4-day intervals displayed normal levels of lordosis at all testing times, regardless of VCS treatment. These data indicate that VCS facilitates rejection responses that precede the decrease in lordosis responsiveness. However, the effects of VCS are dependent on the frequency of hormone priming, suggesting that hormone treatment may block some of the long-term inhibitory effects of VCS on female sexual behavior.

Effects of mating on c-fos expression in the brains of male macaques

The c-fos polyclonal anti-c-fos antibody was used to examine the effects of mating on Fos expression in brain neurons of 11 male macaques. Behavior tests were for 30 min, five males were unmated, four were mated, and two were social controls. Mated males were killed 60 min after ejaculation. Social controls were paired with females, but mating did not occur. Fos immunoreactive (Fos-ir) neuronal nuclei were counted in nine brain regions extending from the medial preoptic to the mammillary body area of all males. In contrast to previous reports on nonprimate laboratory species, overall there was as much Fos-ir in unmated as in mated males. Moreover, there was significantly less Fos expression in four brain regions (known to contain steroid receptors), namely, ventromedial hypothalamus, arcuate nucleus, lateral mammillary area, and bed nucleus of stria terminalis, of mated than of unmated males. There were no significant differences between mated and unmated males in the 5 other brain regions studied. These findings may reflect taxonomic differences between primates and nonprimates, or result from greater neural activation in feral animals maintained in a laboratory than in domesticated, inbred laboratory species. The simplest interpretation would be that neural activity in the male primate is turned off by mating in some brain sites but not in others.

Protein synthesis in the medial preoptic area is important for the mating-induced decrease in estrus duration in hamsters

Sexual receptivity in female hamsters potentially lasts for about 16 h. However, vaginal cervical stimulation (VCS) from a male during mating eventually reduces receptivity and can shorten the duration of behavioral estrus. The process by which this change in response to the male takes place is unknown. Recently, detection of the Fos protein has indicated that the medial preoptic area (POA) is one of the brain regions particularly responsive to VCS. Additionally, the POA may have an inhibitory effect on sexual receptivity. To determine if protein synthesis in the POA is required to initiate the VCS-induced decrease in estrus duration, a protein synthesis inhibitor (anisomycin, 0.50 microg) or a control substance (cholesterol) was applied bilaterally to the POA of steroid-primed ovariectomized female hamsters. Females were tested with a sexually active male at five time points following the initial test for sexual receptivity (hour 1, 2, 6, 12, and 24). Half of the females tested were allowed to receive VCS from a male, while half were fitted with vaginal masks to prevent penile intromission. Each group receiving VCS showed a significant decrease in lordosis duration evident between hour 2 and hour 6, except the group which received anisomycin in the POA. In this respect the POA anisomycin group was similar to animals which did not receive VCS. Hamsters with vaginal masks and the anisomycin/POA animals allowed to receive VCS exhibited their first decrease in lordosis duration between hour 6 and hour 12. These results indicate that protein synthesis is important for VCS-induced decrease in estrus duration in the POA.

Fos expression in the female rat brain during the proestrous prolactin surge and following mating

A prolactin (PRL) surge occurs in the female rat during proestrus in response to elevated estradiol levels. The elevated release of ovarian steroids on the day of proestrus is also associated with sexual receptivity. Mating triggers twice-daily PRL surges that supplant the proestrous PRL surge and are responsible for maintaining luteal function during the first half of pregnancy. In order to understand the neuronal mechanisms controlling the proestrous- and mating-induced PRL surges, we examined patterns of Fos expression by immunocytochemistry in specific brain regions as a measure of neuronal activity. Intact female rats were sacrificed at 09.00, 15.00, and 18.00 h on the day of proestrus and the day of diestrus. Brain tissues were also collected at 21.00 h on the day of proestrus from rats receiving intromissions or mounts from males or taken directly from their homecage. On the day of proestrus, the number of neurons expressing Fos in the medial preoptic area (mPOA), medial amygdaloid nucleus (mAMYG), and ventromedial nucleus of the hypothalamus (VMH) was few and was associated with low plasma PRL levels at 09.00 h; however, the number of Fos-positive cells in these brain regions significantly increased at 15.00 and 18.00 h when the proestrous PRL surge occurred. Mating during the evening of proestrus resulted in a dramatic increase in the number of Fos-positive cells in the mPOA, mAMYG, and VMH as well as in the arcuate nucleus (ARC). Nonmated animals in diestrus showed low and unchanged PRL levels and Fos expression in all the brain areas throughout the day. These results suggest that the mPOA, mAMYG, VMH and ARC may be important brain sites for the integration of stimuli associated with proestrous- and mating-induced PRL surges.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Hypothalamic dopamine D1 receptors are involved in the stimulation of prolactin secretion by high environmental temperature in the female sheep

Recent evidence suggests that dopamine, acting via its D1 receptors, may function as a neurotransmitter in intrahypothalamic pathways involved in the stimulation of prolactin secretion. Functional dopamine D1 receptors are present in the ventromedial hypothalamic nucleus (VMH) and we hypothesized that they might be part of a prolactin-stimulatory pathway activated by stress. We tested this hypothesis in a series of experiments on sheep involving two different forms of stressors, audiovisual (barking dog) and high environmental temperature. We attempted to block the stimulation of prolactin secretion by infusion into the VMH of an antagonist specific for the D1 receptor. Ovariectomised, oestradiol-implanted merino ewes were surgically implanted with bilateral guide tubes directed at the VMH. After a 180 min pretreatment period, the ewes either were or were not exposed to a stressor (30 min of barking dog or 120 min at 35 degrees C, 65% relative humidity). D1 receptor antagonist, SCH23390 or vehicle (0.9% saline) was infused into the VMH (1.7 microliters/h, 120 nmol/h) for 60 min prior to and during the stressor period. Blood was sampled every 15 min via jugular cannulae and the plasma was assayed for prolactin, cortisol and growth hormone (GH). Both stressors significantly increased prolactin concentrations over control levels. SCH23390 infusion significantly attenuated the prolactin response to high environmental temperature, but had no effect on the prolactin response to audiovisual stress. Cortisol concentrations were significantly increased by audiovisual stress only and were not affected by SCH23390. GH concentrations were not changed by either stressor or infusion. Drug infusion alone did not affect the concentration of the hormones. The data suggest that the VMH D1 receptors are involved in a prolactin stimulatory pathway in response to high environmental temperature. The inability of the D1 antagonist to affect the response to the barking dog indicates that this pathway is stress-specific, implying that there is more than one mechanism or pathway involved in the prolactin response to different stressors.

Estrogen reduces cholecystokinin-induced c-Fos expression in the rat brain

Recent reports have shown that estradiol increases the hypophagic effect of exogenous cholecystokinin-octapeptide (CCK). CCK is known to increase the expression of Fos, a marker of neuronal activation, in specific medullary and hypothalamic nuclei. The present experiment tested the hypothesis that as estradiol enhances that behavioral effects of CCK, there is a parallel amplification of CCK-induced Fos expression. Instead, estradiol pretreatment reduced the level of CCK-induced Fos expression in the nucleus of the solitary tract (NTS) and in the medial parvocellular region of the hypothalamic paraventricular nucleus (PVN). The number of Fos-containing cells in the supraoptic nucleus and other regions of the PVN were not affected by estradiol pretreatment. The results are consistent with the hypothesis that the NTS and/or the PVN may mediate the estrogen-induced increased sensitivity to peripheral inhibitory signals in the control of food intake.

Differential induction of Fos in the female rat brain following different amounts of vaginocervical stimulation: modulation by steroid hormones

Vaginocervical stimulation (VCS), produced either by copulation with intromission or by manual stimulation of vagina and cervix with a glass rod, induces neuroendocrine and behavioral responses that are critical for female reproduction in many species. We and others have shown that Fos mRNA and protein are induced within different estrogen-concentrating and -non-concentrating regions of the female rat brain following copulation with intromission and manual VCS. In the present study, we investigated the amount of distributed VCS required to induce Fos immunoreactivity within estrogen-concentrating regions of the medial preoptic area, lateral septum, bed nucleus of the stria terminalis, ventromedial hypothalamus, medial amygdala, and mesencephalic central gray, and whether estrogen and progesterone could alter the threshold or pattern of induction. Ovariectomized rats were administered estradiol benzoate (10 micrograms) 48 h and progesterone (500 micrograms) 4 h before receiving either 0, 1, 5, 10, 20, 30, 40, or 50 manual VCSs with a lubricated glass rod. Ovariectomized hormone control rats received injections of the sesame oil vehicle 48 and 4 h before VCS. All rats were sacrificed 75 min after the first VCS. Fos immunoreactivity was induced differentially by VCS within the different regions, and the hormones either augmented, inhibited, or had no effect on the induction. These data demonstrate that cells within different estrogen-concentrating regions of the female rat brain are differentially sensitive to VCS, and that steroid hormones can either increase or decrease the amount of Fos induced by different amounts of VCS. Different brain regions may participate in gating the sensory information of VCS into different behavioral and neuroendocrine events.

Fos immunoreactivity in the rat brain following consummatory elements of sexual behavior: a sex comparison

In the present study a comparison was made between the distribution of Fos immunoreactivity in the brain of female and male rats following successive elements of sexual behavior. The distribution of Fos immunoreactivity following either mounting, eight intromissions or one or two ejaculations was compared with that in control animals. In both females, Fos immunoreactivity was induced in the medial preoptic nucleus, posteromedial part of the bed nucleus of the stria terminalis, posterodorsal part of the medial amygdala, and the parvicellular part of the subparafascicular thalamic nucleus. In addition, Fos immunoreactivity in females was induced in the ventrolateral part and the most caudoventral part of the ventromedial nucleus of the hypothalamus and in the premammillary nucleus. Differences between females and males were detected in the phases of sexual activity that resulted in Fos immunoreactivity in these brain areas, allowing more insight in the nature of the sensory and hormonal stimuli leading to the induction of Fos immunoreactivity. The posteromedial bed nucleus of the stria terminalis appears to be involved in chemosensory investigation, while specific distinct subregions are only activated following ejaculation. In addition, the parvicellular subparafascicular nucleus and the lateral part of the posterodorsal medial amygdala appear to be involved in the integration of viscero-sensory input. The neural circuitries underlying sexual behavior in males and females appear to be similar in terms of integration of sensory information. In males the medial preoptic nucleus may be regarded as the brain area where the integration of sensory and hormonal stimulation leads to the onset of male sexual behavior, while in females the ventrolateral part of the ventromedial hypothalamic nucleus appears to have this function. In addition, Fos immunoreactivity was distributed in distinct clusters in subregions with various brain areas in males and females. This was observed especially in the posteromedial bed nucleus of the stria terminalis and posterodorsal medial amygdala, but also in the parvicellular subparafascicular nucleus, ventromedial hypothalamic nucleus and ventral premammillary nucleus. It appears that relatively small subunits within these nuclei seem to be concerned with the integration of sensory and hormonal information and may play a critical role in sexual behavior.

FOS expression in grafted gonadotropin-releasing hormone neurons in hypogonadal mouse: mating and steroid induction

We used FOS expression, widely accepted as a marker for neuronal activation, to evaluate physiologically induced activation of gonadotropin-releasing hormone (GnRH) neurons within intraventricular preoptic area grafts in hypogonadal (hpg) female mice. Hpg mice lack endogenous GnRH due to a mutated gene, but can respond to grafted GnRH neurons with reproductive development. The purpose of this study was to determine the degree to which the host brain regulates grafted GnRH neurons. FOS expression in grafted GnRH neurons was induced in progesterone-primed female mice paired with sexually active males. The degree of sexual activity did not affect the outcome, with 40.9 +/- 12.2% of the grafted GnRH cells expressing FOS when male partners performed intromissions, and 47.5 +/- 10.2% when they also ejaculated. There was little or no FOS expression in the grafts of unprimed hpg mice paired with sexually active males, in unpaired mice primed with progesterone or sequential estradiol benzoate and progesterone, or in controls. The pattern of FOS expression in the brains of the female hpg mice engaged in mating behavior was similar to that reported in other species, with moderate to high expression in the medial preoptic area, ventromedial nucleus, and medial amygdala in females paired with males that ejaculated. The present results support the hypothesis that host-derived activation of grafted GnRH neurons underlies aspects of reproductive responses seen in hpg mice with grafts, and further, that at least a portion of the host-graft connectivity is steroid sensitive.

Pattern of Fos and Jun expression in the female rat forebrain after sexual behavior

Previous studies indicated that sexual behavior in female rats primed with estradiol and progesterone induced expression of the immediate early gene (IEG) c-Fos in various brain areas rich in estradiol receptors, including the medial preoptic area (MPA), the medial amygdala (AMe), and the ventromedial nucleus of the hypothalamus (VMN), and to a lesser extent areas with low densities of estradiol receptors, such as the caudate nucleus, the dentate gyrus and the cingulate cortex. The goal of the present experiment was to compare this pattern of expression with the distribution of other IEG products within the Jun family. The results indicate that in non-mated animals, Jun-B, c-Jun and Jun-D were differentially present in several forebrain areas. As previously reported for c-Fos, there was little effect of estradiol and progesterone treatment on the brain expression of these Jun proteins. The most striking result was that sexual behavior stimulated expression of Jun-B and c-Jun, but not Jun-D, in areas containing high densities of estradiol receptors. Specifically, after sexual behavior the MPA and the bed nucleus of the stria terminalis co-expressed c-Fos, Jun-B, c-Jun. c-Fos was co-induced with Jun-B in the VMN, and with c-Jun in the AMe. In contrast, there was no detectable increase in Jun-B, c-Jun or Jun-D in either the caudate nucleus, dentate gyrus or cingulate cortex after sexual behavior, although these regions expressed weak to moderate levels of either Jun-B, c-Jun, or Jun-D basally.(ABSTRACT TRUNCATED AT 250 WORDS)