Expression Of Female Sexual Behavior Research Articles

The Glutamine-Glutamate Cycle Contributes to Behavioral Feminization in Female Rats.

Introduction In perinatal female rats, the glutamine (Gln)-glutamate cycle (GGC) constitutively supplies Gln to neurons of the ventral lateral ventromedial nucleus of the hypothalamus (vlVMH) to sustain glutamatergic synaptic transmission (GST). In contrast, male pups may use Gln only during periods of elevated neuronal activity. Perinatal disruption of the GGC has sex-specific effects on the GST and morphology of vlVMH neurons during adulthood. Since (vl)VMH neuronal activities regulate mating behavior expression, we hypothesize that maintaining a perinatal intact GGC may be essential for the sexual differentiation of reproductive behaviors. Methods Using perinatal rats of both sexes, we pharmacologically killed astrocytes or blocked the GGC and supplemented them with exogenous Gln. Mating behavior, an open-field test and protein levels of GGC enzymes were examined during adulthood. Results Killing astrocytes reduced mating behavior expression by 38-48% and 71-72% in male and female rats, respectively. Any blocker targeting the GGC consistently reduced female lordosis behavior by 52-73% and increased glutaminase protein levels in the hypothalamus, but blockers had no effect on the expression of or motivation for copulatory behavior in males. Exogenous Gln supplementation partly rescued the decline in Gln synthetase inhibitor-mediated sex behavior in females. Perinatal interruption of the GGC did not increase induced expression of female sexual behavior in hormone-primed castrated male rats or affect locomotion or anxiety-like behavior in either sex. Conclusion The intact GGC is necessary for behavioral feminization in female rats and may play little or no role in behavioral masculinization or defeminization in males.

Stress during pubertal development affects female sociosexual behavior in mice

Puberty is a crucial phase for the development of female sexual behavior. Growing evidence suggests that stress during this period may interfere with the development of sexual behavior. However, the neural circuits involved in this alteration remain elusive. Here, we demonstrated in mice that pubertal stress permanently disrupted sexual performance without affecting sexual preference. This was associated with a reduced expression and activation of neuronal nitric oxide synthase (nNOS) in the ventrolateral part of the ventromedial hypothalamus (VMHvl). Fiber photometry revealed that VMHvl nNOS neurons are strongly responsive to male olfactory cues with this activation being substantially reduced in pubertally stressed females. Finally, treatment with a NO donor partially restored sexual performance in pubertally stressed females. This study provides insights into the involvement of VMHvl nNOS in the processing of olfactory cues important for the expression of female sexual behavior. In addition, exposure to stress during puberty disrupts the integration of male olfactory cues leading to reduced sexual behavior.

Role for the membrane estrogen receptor alpha in the sexual differentiation of the brain.

Estrogens exert pleiotropic effects on multiple physiological and behavioral responses. Male and female sexual behavior in rodents constitutes some of the best-characterized responses activated by estrogens in adulthood and largely depend on ERα. Evidence exists that nucleus- and membrane-initiated estrogen signaling cooperate to orchestrate the activation of these behaviors both in short- and long-term. However, questions remain regarding the mechanism(s) and receptor(s) involved in the early brain programming during development to organize the circuits underlying sexually differentiated responses. Taking advantage of a mouse model harboring a mutation of the ERα palmitoylation site, which prevents membrane ERα signaling (mERα; ERα-C451A), this study investigated the role of mERα on the expression of male and female sexual behavior and neuronal populations that differ between sexes. The results revealed no genotype effect on the expression of female sexual behavior, while male sexual behavior was significantly reduced, but not abolished, in males homozygous for the mutation. Similarly, the number of kisspeptin- (Kp-ir) and calbindin-immunoreactive (Cb-ir) neurons in the anteroventral periventricular nucleus (AVPv) and the sexually dimorphic nucleus of the preoptic area (SDN-POA), respectively, were not different between genotypes in females. In contrast, homozygous males showed increased numbers of Kp-ir and decreased numbers of Cb-ir neurons compared to wild-types, thus leading to an intermediate phenotype between females and wild-type males. Importantly, females neonatally treated with estrogens exhibited the same neurochemical phenotype as their corresponding genotype among males. Together, these data provide evidence that mERα is involved in the perinatal programming of the male brain.

The Role of Estrogen Receptor β in the Dorsal Raphe Nucleus on the Expression of Female Sexual Behavior in C57BL/6J Mice.

17β-Estradiol (E2) regulates the expression of female sexual behavior by acting through estrogen receptor (ER) α and β. Previously, we have shown that ERβ knockout female mice maintain high level of lordosis expression on the day after behavioral estrus when wild-type mice show a clear decline of the behavior, suggesting ERβ may be involved in inhibitory regulation of lordosis. However, it is not identified yet in which brain region(s) ERβ may mediate an inhibitory action of E2. In this study, we have focused on the dorsal raphe nucleus (DRN) that expresses ERβ in higher density than ERα. We site specifically knocked down ERβ in the DRN in ovariectomized mice with virally mediated RNA interference method. All mice were tested weekly for a total of 3 weeks for their lordosis expression against a stud male in two consecutive days: day 1 with the hormonal condition mimicking the day of behavioral estrus, and day 2 under the hormonal condition mimicking the day after behavioral estrus. We found that the level of lordosis expression in ERβ knockdown (βERKD) mice was not different from that of control mice on day 1. However, βERKD mice continuously showed elevated levels of lordosis behavior on day 2 tests, whereas control mice showed a clear decline of the behavior on day 2. These results suggest that the expression of ERβ in the DRN may be involved in the inhibitory regulation of sexual behavior on the day after behavioral estrus in cycling female mice.

Doing Protein Kinase C: Membrane Estrogen Receptor Signaling in a Neural Circuit

Female sexual behavior has been an exquisitely valuable model for developing an understanding of mechanisms of steroid action on nerve cells (1,2). The report by Dewing et al. (3) in this issue continues this grand tradition by identifying a set of biochemical pathways that mediate intracellular signaling stemming from interactions of estradiol with membrane binding sites. The work is of note from two points of view. The first is the inclusion of these novel signaling pathways coupled to membrane estrogen receptors with the more conventional intracellular mechanisms of estrogen action on reproduction. The second is the incorporation of these findings into a functional neuronal circuit mediating reproduction. For those new to this field, the acceptance of multiple forms of the estrogen receptor and even the existence of membrane estrogen receptors seems commonplace. Lost in today’s calm sea are the stormy history of dogmatic fervor and the battles defending each fundamentalist view of how estrogen exerts its biological actions. Jensen’s reviews of this history (4,5) are very revealing, tracing the transitions from the early beliefs that estrogen had an enzymatic-like action to the discovery and defense of the existence of intracellular receptors. The acceptance of intracellular receptors for estrogen (and other steroids of course) led to other debates about activated and inactivated receptor states, including the relocation of receptors in these states to different subcellular compartments (e.g. Refs. 6 and 7). This acceptance of intracellular receptors grew largely from the development of methodological approaches to visualize the receptors themselves using labeling of specific receptor antibodies (4) or by autoradiographic means to see the incorporation of estrogen into cells (8,9). In contrast, the existence of membrane steroid receptors was not so fondly embraced. These receptors are much like the dark side of the moon in that despite the weight of decades of physiological evidence (10), the inability to see the receptors has contributed to continued skepticism (and mystery). The appeal of the scientific approach taken in the research leading to this report is that the authors have taken a set of molecular processes identified in individual hippocampal neurons (11) and applied them to solving a fundamental question within a hypothalamic circuit. The model from hippocampal neurons suggests that estradiol-17β binds to conventional estrogen receptors that have been inserted into the cell membrane. The estrogen receptors in turn couple (directly or indirectly) with metabotropic glutamate receptors (mGluR; in this case mGluR1a), triggering signaling cascades associated with the glutamate receptor. Dewing et al. (3) took a systematic approach to investigating the role of protein kinase C (PKC) mediating the effects of estradiol and glutamate. The signaling pathway studied came from a combination of previous research and from the authors’ microarray analysis of estradiol-induced proteins in the arcuate nucleus. The arcuate nucleus sends projections to the medial preoptic area, and this circuit is part of a clearly larger neural pathway known to regulate the expression of female sexual behavior (termed lordosis in rodents). The functional endpoints included lordosis itself as well as internalization of the μ-opioid receptor in medial preoptic neurons. The rationale for this latter measure comes from the authors’ previous work showing that opioid release in the medial preoptic area is a key synaptic event regulating the expression of lordosis (12). Thus, μ-opioid receptor internalization serves as a proxy for increased synaptic opioid release, which in turn is a proxy for neural activation necessary for lordosis (when lordosis itself was not measured). Indeed, the results of the study supported the proposed model. Administration of either estradiol or an mGluR1a agonist produced opioid receptor internalization. Blocking PKC antagonized the effect mediated by the stimulation of either receptor. Finally, PKC activation mimicked the effects of estradiol or mGluR1a on opioid receptor internalization or female sexual behavior. The linchpin in all of this is the demonstration that estrogen receptors co-immunoprecipitated with mGluR1 in membrane fractions from the arcuate nucleus. Two key developments in this field loom on the horizon. The first is of course the visualization of membrane estrogen receptors. Here, Jensen’s (5) lesson of alternative approaches derived from the identification of intracellular receptors will be applicable, because little progress has been made in this arena. The other development will be the molecular details of the nature of the membrane interactions between estrogen receptors and other protein partners. Like the basic research and clinical impact of such a simple discovery as a method to immunostain the estrogen receptor, a similar discovery for membrane estrogen receptors is eagerly awaited.

Role of experience in the neuroendocrine control of ewes' sexual behavior

We assessed the role of learning in the expression of female sexual behavior and evaluated the relative importance of age versus experience. Two studies were conducted with ovariectomized ewes submitted to steroid treatment that mimicked an estrus cycle. We compared behavioral (experiments 1 and 2), neurochemical (experiment 1), and endocrine (experiment 2) responses of sexually naive young and adult ewes versus sexually experienced adults when exposed to males. In a third study, we compared their performance in an instrumental learning test and the extent to which it was affected by stress. These experiments showed that proceptivity is affected both by age and sexual experience. In experiment 1 only experienced adults were proceptive and displayed an increase in hypothalamic norepinephrine. By the second estrus cycle (experiment 2) naive adults performed similarly to experienced adults but proceptive behavior was still inferior in young ewes. Receptivity was also different between groups but affected more by age than by sexual experience. All ewes mated during the first interaction with a male, although males' latency to ejaculation was shorter with experienced females than naive adults or naive young. Young ewes found food as readily as adults in experiment 3 but were more affected by stress. Together, these experiments show that both experience and age influence sexual activity and that sensitivity to stress may also be involved. This may contribute to the deficient reproductive performance that is often observed in young female mammals.

Electrolytic lesions to the ventromedial hypothalamus abolish receptivity in female whiptail lizards, Cnemidophorus uniparens

Lesions to the ventromedial hypothalamus (VMH) inhibit receptive sexual behavior in the whiptail lizard, Cnemidophorus uniparens, an all-female species. All lesions to the VMH that effectively abolished receptivity specifically damaged the dorsal lateral VMH, an area containing high concentrations of estrogen receptor in this species. These data further emphasize conservation of the VMH as a brain area critical to the expression of female sexual behavior in vertebrates.

Progestin Receptor Induction and Sexual Behavior by Estradiol Treatment in Male and Female Rats

Abstract Sex differences in the induction of cytosolic progestin receptors (CPR) by estrogen priming were correlated with the sex differences in behavioral responses. We evaluated the temporal relationship between CPR in several brain regions and pituitary and the time-course of 17beta-estradiol (E(2)) activation of female sexual behavior in gonadectomized male and female rats implanted with subcutaneous E(2) Silastic capsules for 6 h, 24 h and 48 h. Both CPR levels and mating behavior increase monotonically with the time of E(2) exposure. Induction of CPR was observed in the periventricular region of the preoptic area (PVPOA), arcuate nucleus (ARC), ventromedial nuclei (VMN) and pituitary in both sexes. A small induction of CPR was found in parietal cortex. The VMN in female rats showed a significant E(2)-induced CPR increase at all times of exposure, while in male rats this induction was only significant after 24 h. Significant sex differences in absolute CPR levels and E(2)-induced receptors were found in the following structures: VMN, 18 h after 6 h of E(2) treatment and after 24 h and 48 h of continuous E(2) exposure; PVPOA, only after 48 h of continuous E(2) exposure; ARC at 24 h and 48 h; and pituitary after all E(2) treatment. Mating behavior was tested under two conditions: E(2) alone (2 h after removal of E(2) capsules) and E(2)+progesterone (2 h after a progesterone injection given 10 min after concluding the first test). Receptivity was first observed after 24 h E(2) exposure in female rats, whereas in male rats a small response appeared only after 48 h of E(2) exposure. After progesterone priming, the time of E(2) exposure necessary for expression of female sexual behavior was reduced to 6 h in females and 24 h in males. The appearance of mating behavior appears to follow that of inducible CPR in the VMN in both sexes. In addition, the CPR levels associated with the first receptivity either by male rats (16.6 fmol/mg protein) or female rats (15.3 fmol/mg protein) are very similar suggesting the presence of a threshold level controlling the expression of feminine sexual behavior. It is likely that inhibitory neural input plays a role in determining the threshold level of E(2)-induced CPR, which is sufficient to trigger lordosis behavior.

Hormonal Activation of Female Sexual Behavior is Accompanied by Hypothalamic Norepinephrine Release

Abstract The present study employed the intracranial microdialysis technique to measure norepinephrine release in the ventrolateral dendritic fields of the ventromedial hypothalamus of freely-moving animals before and during ovarian steroid (estradiol and progesterone) activation of female sexual behavior (lordosis). One day after implantation of a dialysis probe, animals were injected with 3 mug of estradiol benzoate followed 44 h later by 200 mug of progesterone. Introduction of a male rat 4 h after progesterone treatment was correlated with dramatic increases in extracellular norepinephrine levels measured in dialysates of the ventrolateral ventromedial hypothalamus of female rats which displayed high levels of lordosis behavior. In contrast, female rats given the same steroid treatment but which did not show lordosis responses did not have elevated norepinephrine levels in their dialysates. Moreover, animals that received an estrogen antagonist concurrently with the estrogen treatment had neither an increase in ventromedial hypothalamic levels of norepinephrine during behavior testing nor did they display lordosis. These results indicate a close relationship among ovarian steroids, noradrenergic transmission in the ventromedial hypothalamus, and the expression of female sexual behavior.

Sexual orientation, proceptivity, and receptivity in the male rat as a function of neonatal hormonal manipulation

The influence of neonatal androgen on the potential to exhibit feminine sexual behavior was investigated. Male rats castrated on Day 0 but not those castrated on Day 4 or later showed hop/darting, ear wiggling, and lordotic behavior in response to treatment with estrogen and progesterone in adulthood at a frequency equal to that of females. Neonatal treatment with testosterone propionate (1 mg/rat for 4 days) abolished the capacity to show these behaviors. In subsequent experiments, involving castration of male rats at 0 or 4 hr after cesarean delivery, the effect of the postnatal surge of testicular secretions on the expression of female sexual behavior was investigated. No differences were seen in the frequency of hop/darting, ear wiggling, and receptivity between males castrated immedately or 4 hr after delivery. In a preference test where the experimental male could choose between an estrous female and a sexually active male, the neonatally castrated males preferred the company of a male when treated with estrogen and progesterone. The implantation of testosterone resulted in a preference for an estrous female. It was concluded that testicular secretions in the newborn male influence adult sexual orientation and suppress the ability to show proceptive and receptive behaviors.

Hormonal correlates of sexual behavior in the female musk shrew: The role of estradiol

Plasma levels of several steroid hormones in the female musk shrew, ( Suncus murinus), are reported along with experiments on the causational role steroids play in female sexual behavior. Gonadally intact females sampled directly after a brief (about 7 minutes on average) sexual interaction with a male had equivalent plasma levels of estradiol (E 2) but significantly higher plasma progesterone (P 4) levels than resting females. In Experiment 2, females that engaged in nonsexual activities with conspecifics other than gonadally intact males had plasma levels of E 2 and P 4 equivalent to those of females that engaged in sexual behavior with males. Taken together, the results of these two experiments suggest that the relatively higher levels of plasma P 4 noted in active musk shrews is not a response specific to sexual interactions with males. In Experiment 3, ovariectomized musk shrews were treated with E 2 implants. These tonically administered physiological doses of E 2 were not able to activate sexual behavior. However, two steroid-sensitive reproductive target tissues, the cervix and flank pad, were responsive to E 2 treatment. Supplemental injections of P 4 given to E 2 treated ovariectomized females were also ineffective in restoring sexual behavior. These results suggest that physiological doses of E 2 do not have direct effects on the expression of female sexual behavior in this mammalian species.

Cytoplasmic progestin receptors in female Guinea Pig brain and their relationship to refractoriness in expression of female sexual behavior

Summary Cytoplasmic progestin receptors were assayed in the hypothalamus-preoptic area-septum and midbrain of ovariectomized guinea pigs given sequential treatment with estradiol benzoate and progesterone. As little as 50 μg of progesterone injected 40 h after estradiol benzoate caused a failure to display lordosis in response to a second progesterone injection 24 h after the first. Both 50 μg and 500 μg of progesterone decreased the concentration of cytoplasmic progestin receptors 24 h later in hypothalamus-preoptic area-septum and midbrain in estrogen-primed, ovariectomized guinea pigs. Therefore, progesterone injections that caused behavioral refractoriness to further stimulation by progesterone also decreased the concentration of availabke cytoplasmic progestin receptors. When progesterone was administered concurrently with 1.6 μg of estradiol benzoate, 500 μg, but not 100 μg suppressed behavioral responsiveness to a second progesterone injection 40 h later. The high dose, but not the low dose, also decreased the concentration of available cytoplasmic progestin receptors 40 h later in both the hypothalamus-preoptic area-septum and midbrain. These findings are consistent with the notion that a decrease in brain progestin receptor concentration is one of the subcellular mechanisms involved in failure of a second dose of progesterone to facilitate lordosis behavior in estrogen-primed animals exposed to a first dose of progesterone 24–40 h earlier.

Noradrenergic transmission and female sexual behavior of guinea pigs

Treatment with the dopamine beta-hydroxylase (DBH) inhibitor U-14,624 (50, 100, or 150 mg/kg) blocked the induction of lordosis behavior by estradiol benzoate (EB) and progesterone (P) in overiectomized guinea pigs. After treatment with U-14,624 (100 mg/kg), norepinephrine (NE) content of medial basal hypothalamus, preoptic area and cortex was reduced (by 55%) and dopamine (DA) content of medial basal hypothalamus was increased (by 155%) during the period when females treated with EB and P normally display lordosis. Treatment with the NE receptor stimulator clonidine (1.0 mg/kg) restored lordosis behavior in females treated with EB, P, and U-14,624 (100 mg/kg), but the putative DA and serotonin (5-HT) receptor blockers pimozide (1.0 mg/kg) and methysergide (20.0 mg/kg) were ineffective in this respect. Thus, inhibition of lordosis after treatment with U-14,624 appeared to be attributable primarily to a reduction in NE neurotransmission, rather than to an increase in DA or 5-HT activity. Because clonidine induced lordosis in females treated with EB, P, and U-14,624, it seemed unlikely that the facilitatory effects of clonidine on lordosis were mediated by activation of presynaptic alpha-adrenergic receptors (i.e. inhibitory NE autoreceptors) rather than by postsynaptic alpha-receptors. In addition, pretreatment with the postsynaptic alpha-adrenergic antagonist phenoxybenzamine (20.0 mg/kg) blocked the facilitation of lordosis by clonidine (1.0 mg/kg) in females primed with EB alone and with EB plus P. Thus, the facilitatory effects of clonidine on lordosis appear to be mediated by activation of postsynaptic alpha-adrenergic (i.e. NE) receptors. The results of this study provide further evidence that NE neurotransmission facilitates the expression of female sexual behavior in guinea pigs.

Female Sexual Response

Recent studies suggest that hormones do play a role in the expression of female sexual behavior, and the inconsistency of findings between various groups does not mean that hormonal effects can be disregarded. Hormones may interact with other situational variables to sometimes enhance sexual behavior, and at other times suppress it. Sexual activity may itself trigger alterations in hormone levels, just as hormones may activate changes in behavior.