c-Fos proto-oncogene activity induced by mating in the preoptic area, hypothalamus and amygdala in the female rat: role of afferent input via the pelvic nerve

Serotonin neurons in mating female mice are activated by male ejaculation

Sexual stimulation triggers changes in female physiology and behavior, including sexual satiety and preparing the uterus for pregnancy. Serotonin (5-HT) is an important regulator of reproductive physiology and sexual receptivity, but the relationship between sexual stimulation and 5-HT neural activity in females is poorly understood. Here, we investigated dorsal raphe 5-HT neural activity in female mice during sexual behavior. We found that 5-HT neural activity in mating females peaked specifically upon male ejaculation and remained elevated above baseline until disengagement. Artificial intravaginal mechanical stimulation was sufficient to elicit increased 5-HT neural activity but the delivery of ejaculatory fluids was not. Distal penis expansion ("penile cupping") at ejaculation and forceful expulsion of ejaculatory fluid each provided sufficient mechanical stimulation to elicit 5-HT neuron activation. Our study identifies a female ejaculation-specific signal in a major neuromodulatory system and shows that intravaginal mechanosensory stimulation is necessary and sufficient to drive this signal.

Serotonin neurons in mating female mice are activated by male ejaculation

Sexual stimulation triggers changes in female physiology and behavior, including sexual satiety and preparing the uterus for pregnancy. Serotonin is an important regulator of reproductive physiology and sexual receptivity, but the relationship between sexual stimulation and serotonin neural activity in females is poorly understood. Here, we investigated dorsal raphe serotonin neural activity in females during sexual behavior. We found that serotonin neural activity in mating females peaked specifically upon male ejaculation, and remained elevated above baseline until disengagement. Artificial intravaginal mechanical stimulation was sufficient to elicit increased 5-HT neural activity but the delivery of ejaculatory fluids was not. Distal penis erectile enlargement ("penile cupping") at ejaculation and forceful expulsion of ejaculatory fluid each provided sufficient mechanical stimulation to elicit serotonin neuron activation. Our study identifies a female ejaculation-specific signal in a major neuromodulatory system and shows that intravaginal mechanosensory stimulation is necessary and sufficient to drive this signal.

Brain circuits activated by female sexual behavior evaluated by manganese enhanced magnetic resonance imaging

Magnetic resonance imaging (MRI) allows obtaining anatomical and functional information of the brain in the same subject at different times. Manganese-enhanced MRI (MEMRI) uses manganese ions to identify brain activity, although in high doses it might produce neurotoxic effects. Our aims were to identify a manganese dose that does not affect motivated behaviors such as sexual behavior, running wheel and the rotarod test. The second goal was to determine the optimal dose of chloride manganese (MnCl₂) that will allow us to evaluate activation of brain regions after females mated controlling (pacing) the sexual interaction. To achieve that, two experiments were performed. In experiment 1 we evaluated the effects of two doses of MnCl₂, 8 and 16 mg/kg. Subjects were injected with one of the doses of MnCl₂ 24 hours before the test on sessions 1, 5 and 10 and immediately thereafter scanned. Female sexual behavior, running wheel and the rotarod were evaluated once a week for 10 weeks. In experiment 2 we followed a similar procedure, but females paced the sexual interaction once a week for 10 weeks and were injected with one of the doses of MnCl₂ 24 hours before the test and immediately thereafter scanned on sessions 1, 5 and 10. The results of experiment 1 show that neither dose of MnCl₂ induces alterations on sexual behavior, running wheel and rotarod. Experiment 2 demonstrated that MEMRI allow us to detect activation of different brain regions after sexual behavior, including the olfactory bulb (OB), the bed nucleus of the stria terminalis (BNST), the amygdala (AMG), the medial preoptic area (MPOA), the ventromedial hypothalamus (VMH), the nucleus accumbens (NAcc), the striatum (STR) and the hippocampus (Hipp) allowing the identification of changes in brain circuits activated by sexual behavior. The socio sexual circuit showed a higher signal intensity on session 5 than the reward circuit and the control groups indicating that even with sexual experience the activation of the reward circuit requires the activation of the socio sexual circuit. Our study demonstrates that MEMRI can be used repeatedly in the same subject to evaluate the activation of brain circuits after motivated behaviors and how can this activation change with experience.

Neuronal activity in the sagittalis nucleus of the hypothalamus after ovarian steroid hormone manipulation and sexual behavior in female rat

During extended observation of estrogen receptor (ER) α-immunoreactive neurons in the hypothalamus, we previously identified a novel nucleus, the Sagittalis Nucleus of the Hypothalamus (SGN), in the interstitial area between the arcuate nucleus and the ventromedial hypothalamic nucleus. The SGN exhibits sexual dimorphism in its volume and cell count, and estrous cycle related variations in ERα-immunoreactivity. These characteristics of the SGN implicate the nucleus in sex-biased brain functions and behaviors. In this study, we examined involvement of the SGN in sexual arousal in female rats. Immunohistochemical staining of c-Fos, a marker of neuronal activity was performed after administration of an estrus-inducing dose of estrogen and progesterone in ovariectomized female rats. Analysis of microscopic images showed a significant increase in the number of c-Fos-expressing neurons in the SGN following hormonal manipulation. Moreover, neuronal activity in the region exhibited a further increase after each animal was coupled with a male and allowed to mate. These results suggest that the SGN plays an important role in sexual activity in female rat.

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.

Embryonic transcription factor expression in mice predicts medial amygdala neuronal identity and sex-specific responses to innate behavioral cues

The medial subnucleus of the amygdala (MeA) plays a central role in processing sensory cues required for innate behaviors. However, whether there is a link between developmental programs and the emergence of inborn behaviors remains unknown. Our previous studies revealed that the telencephalic preoptic area (POA) embryonic niche is a novel source of MeA destined progenitors. Here, we show that the POA is comprised of distinct progenitor pools complementarily marked by the transcription factors Dbx1 and Foxp2. As determined by molecular and electrophysiological criteria this embryonic parcellation predicts postnatal MeA inhibitory neuronal subtype identity. We further find that Dbx1-derived and Foxp2+ cells in the MeA are differentially activated in response to innate behavioral cues in a sex-specific manner. Thus, developmental transcription factor expression is predictive of MeA neuronal identity and sex-specific neuronal responses, providing a potential developmental logic for how innate behaviors could be processed by different MeA neuronal subtypes.

DOI:http://dx.doi.org/10.7554/eLife.21012.001

Within the brain, a set of interconnected structures called the limbic system is involved in emotion, motivation and memory. This system – and in particular a structure called the medial amygdala – also contributes to behavioral drives that help an animal to survive and reproduce. These include the drive to avoid predators, to defend territory, and to find a mate. Such behaviors are thought to be inborn or innate. This means that animals display them instinctively whenever specific triggers are present, without the need to learn them beforehand.

However, just as a computer must be programmed to perform specific tasks, these innate behavioral responses must also be programmed into the brain. Given that animals do not learn these behaviors, Lischinsky et al. reasoned that specific events during the development of the brain must provide the animal’s brain with the necessary instructions. To test this idea, they studied how the development of the medial amygdala in mouse embryos may give rise to differences in innate mating behavior seen between male and female mice.

The medial amygdala contains many subtypes of neurons, which show different responses to sex hormones such as estrogen and androgen. Lischinsky et al. show that two sets of cells give rise to some of the different neurons of the adult medial amygdala. One set of these precursor cells makes a protein called Dbx1 and the other makes a protein called Foxp2. These two sets of precursors generate medial amygdala neurons with different arrays of sex hormone receptors in male and female mice. Moreover, while the two sets of medial amygdala neurons are activated during aggressive encounters, they show different patterns of activation in male and female animals during mating.

These findings suggest that the development of Dbx1-derived and Foxp2+ neurons in the medial amygdala helps program innate reproductive and aggressive behaviors into the brain. The new findings also provide insights into why these behaviors differ in male and female mice. The next challenge is to identify the inputs and outputs of these two distinct subpopulations of medial amygdala neurons. This should make it possible to work out exactly how these populations of cells control innate behaviors in male and female animals.

DOI:http://dx.doi.org/10.7554/eLife.21012.002

BP101 Peptide Promotes Female Sexual Receptivity in the Rat

INTRODUCTION

Low sexual desire is a frequent sexual problem in women, with only one drug for the condition approved by the Food and Drug Administration.

AIM

To evaluate the ability of a novel synthetic peptide, BP101, to facilitate sexual behavior after intranasal administration or infusion into certain brain areas in female rats.

METHODS

Bilaterally ovariectomized female rats, primed with a suboptimal combination of estradiol benzoate (EB) and progesterone, were used as a model of low sexual motivation. Sexual behavior was tested with stud male rats after acute (experiment 1) or long-term (experiment 2) intranasal administration of BP101 or peptide infusion into the olfactory bulb, medial preoptic area, ventromedial hypothalamic nucleus, or ventral tegmental area (experiment 3).

MAIN OUTCOME MEASURES

Frequency of solicitations (SF), as an indicator of sexual motivation in female rats, and lordosis frequency and ratio, as measurements of female consummatory sexual behavior.

RESULTS

Acute intranasal BP101 administration moderately increased SF, with the highest tested dose of 300 μg/kg causing an 80% increase. Female rats receiving BP101 75 or 300 μg/kg daily on days 6 to 16 of the peptide administration displayed twofold higher SF compared with the placebo-treated animals, an increase comparable to optimally hormone-primed female rats. Infusion of BP101 1 and 5 μg per rat into the medial preoptic area, but not into the olfactory bulb, ventromedial hypothalamic nucleus, or ventral tegmental area, increased SF in female rats supplemented with EB 10 or 20 μg. The effect was relatively more pronounced in female rats receiving EB 10 μg (≈300%) compared with EB 20 μg (≈50%) with direct brain infusions.

CONCLUSION

BP101 displays a potent stimulatory effect on sexual motivation in the female rat, and the medial preoptic area seems to be the site of its action. BP101 is effective in female rats receiving different hormone supplementations, making the present data generalizable to pre- and postmenopausal women with hypoactive sexual desire. Andreev-Andrievskiy A, Lomonosov M, Popova A, et al. BP101 Peptide Promotes Female Sexual Receptivity in the Rat. J Sex Med 2017;14:336-346.

Methamphetamine and Ovarian Steroid Responsive Cells in the Posteriodorsal Medial Amygdala are Required for Methamphetamine-enhanced Proceptive Behaviors

Methamphetamine (Meth) is a psychomotor stimulant strongly associated with increases in sexual drive and impulse in both men and women. These changes in sexual motivation have a greater impact on women due to their likelihood of facing the greater burden of unplanned pregnancies, as well as increased risk for psychiatric co-morbidities such as depression. We have previously established a rodent model of Meth-induced increases in sexual motivation. Using this model, we have identified the posteriodorsal medial amygdala (MePD) via excitotoxic lesion studies as a necessary nucleus in Meth-facilitated female sexual motivation. While lesion studies give us insight into key nuclei that may be targets of Meth action, such an approach does not give insight into the identity of the specific MePD neurons or neural circuitry involved in Meth-induced increases in proceptive behaviors. Using the DAUN02 inactivation method, a recently established technique for removing behaviorally relevant cell populations, we present evidence that the ovarian steroid/Meth responsive cells in the MePD are necessary for Meth-induced facilitation of proceptive behaviors. These findings form the basis for future work that will allow for the classification of neuronal subtypes involved in the MePD’s modulation of proceptive behavior as well as a stronger understanding of the neurocircuitry of female sexual motivation.

Electroencephalographic coupling in the amygdala and prefrontal cortex in relation to the estrous cycle and duration of vaginocervical stimulation in the rat

The influence of the duration of vaginocervical stimulation (VCS) on the electroencephalographic activity (EEG) of medial amygdala (MeA) and prefrontal cortex (PFC) in rats during proestrus-estrus (P-E) and diestrus (D) was examined. Using a glass syringe plunger, a constant force of 300g was exerted against the cervix during 60s. Relative power (RP) and correlation of three EEG band frequencies were compared between the first and last 30s intervals of VCS. A higher RP of the 4-7Hz band and a lower RP of the fast frequencies were observed in the MeA and PFC in P-E females during the first 30s of VCS as compared to the last 30s. Only during P-E, a higher interamygdaline correlation in the 8-12Hz band and a lower correlation in the 13-21Hz band during the first 30s were observed. Similarly, a higher interamygdaline correlation in the 8-12Hz band was observed during the first 30s of VCS during P-E as compared to D. During the last 30s of VCS there was no difference between phases. The VCS evoked EEG changes in the MeA that varied between phases of the estrous cycle and depended on the duration of the stimulation. These effects could be associated with the quantification processes of VCS that has been proposed to occur in the amygdala. These findings show differential responsiveness of the MeA and PFC according to the amount of VCS received, and that the response varies according to the estrous cycle.

Repeated administration of estradiol promotes mechanisms of sexual excitation and inhibition: Glutamate signaling in the ventromedial hypothalamus attenuates excitation

Repeated administration of 10 μg of estradiol benzoate (EB) every 4 days to the ovariectomized (OVX) rat induces a behavioral sensitization of sexual behaviors. Repeated copulation or the receipt of vaginocervical stimulation (VCS) attenuates the sensitization of appetitive sexual behaviors, suggesting that VCS acts in opposition to the mechanisms that induce the sensitization. It is known that VCS accelerates the onset of estrous termination (characterized by a decrease in appetitive sexual behaviors, and an increase in defensive behaviors prior to the decline in lordosis), and glutamate transmission in the ventromedial hypothalamus (VMH), particularly via AMPA receptor signaling, is an important regulator of this effect. Thus, the current studies examined whether mechanisms of estrous termination are involved in the attenuated sensitization to EB that occurs with repeated copulation. In the first study, OVX rats received infusions of AMPA to the VMH on tests 2-4, and sexual behavior was measured on tests 1 and 5. Appetitive sexual behaviors were lower in females that received AMPA infusions in place of copulation compared to saline, suggesting that AMPA receptor activation by VCS may be playing a role in the attenuation of sensitization. In the second study, females that were not given the opportunity to copulate on tests 2-4 fell out of behavioral estrus faster than those that did, suggesting that both excitatory and inhibitory mechanisms of sexual behavior become sensitized with repeated administration of EB. Together these findings extend our hypothesis that repeated episodes of heat sensitize the activation of sexual behaviors to increase the probability of eventual fertilization.

Methamphetamine-enhanced female sexual motivation is dependent on dopamine and progesterone signaling in the medial amygdala

Methamphetamine (METH) is a psychomotor stimulant strongly associated with increases in sexual drive and impulsive sexual behaviors that often lead to unsafe sexual practices. In women METH users, such practices have been associated with increases in unplanned pregnancies and sexually transmitted diseases. Despite this significant heath concern, the neural mechanisms underlying this drug-sex association are not known. We previously established a rodent model of METH-facilitated female sexual behavior in which estradiol and progesterone interact with METH to increase motivational components of female behavior and neuronal activation in the posterodorsal medial amygdala (MePD) (Holder et al., 2010; Holder and Mong, 2010). The current study more directly examines the mechanisms underlying the drug-sex interaction. Here, we hypothesize that METH-induced increases in MePD dopamine signaling bridge the METH-hormone interaction. In support of this hypothesis, we found that excitotoxic lesions targeted to the MePD attenuated the METH-induced increases in proceptive behavior. Furthermore, infusion of a D1 agonist into the MePD increased proceptive behavior, while infusion of a D1 antagonist blocked the ability of METH to increase proceptive behaviors. Additionally, we found that METH-treatment increased progesterone receptor (PR) immunoreactivity in the MePD, suggesting an interaction between dopamine and progesterone signaling. Indeed, infusions of the PR antagonist, RU486, prevented METH-induced increases in sexual behavior. Thus, taken together, the current findings suggest that dopamine in the MePD modulates enhanced sexual motivation via an amplification of progesterone signaling and contributes to a better understanding of the neurobiology of drug-enhanced sexual behaviors.

Ascending SAG neurons control sexual receptivity of Drosophila females

Mating induces pronounced changes in female reproductive behavior, typically including a dramatic reduction in sexual receptivity. In Drosophila, postmating behavioral changes are triggered by sex peptide (SP), a male seminal fluid peptide that acts via a receptor (SPR) expressed in sensory neurons (SPSNs) of the female reproductive tract. Here, we identify second-order neurons that mediate the behavioral changes induced by SP. These SAG neurons receive synaptic input from SPSNs in the abdominal ganglion and project to the dorsal protocerebrum. Silencing SAG neurons renders virgin females unreceptive, whereas activating them increases the receptivity of females that have already mated. Physiological experiments demonstrate that SP downregulates the excitability of the SPSNs, and hence their input onto SAG neurons. These data thus provide a physiological correlate of mating status in the female central nervous system and a key entry point into the brain circuits that control sexual receptivity.

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.

Repeated paced mating promotes the arrival of more newborn neurons in the main and accessory olfactory bulbs of adult female rats

We have previously shown that the first-paced mating encounter increases the number of newborn cells in the granule cell layer (Gra; also known as internal cell layer, ICL) of the accessory olfactory bulb (AOB) in the adult female rat (Corona et al., 2011). In the present study we evaluated if repetition of the stimulus (paced mating) could increase the arrival of more newborn neurons in the olfactory bulb generated during the first session of paced sexual contact. Sexually naive female rats were bilaterally ovariectomized, hormonally supplemented with estradiol (E2) and progesterone (P) and randomly assigned to one of four groups: (1) without sexual contact, (2) one session of paced mating, (3) four sessions of paced mating, and (4) four sessions of non-paced mating. We also included a group of gonadally intact females. On the first day of the experiment, all females were i.p. injected with the marker of DNA synthesis bromodeoxyuridine and were killed 16 days later. Blood was collected at sacrifice to determine the plasma levels of E2 and P. The number of newborn neurons that arrived at the ICL of the AOB and the Gra of the main olfactory bulb (MOB) increased, relative to all other groups, only in the group that repeatedly mated under pacing conditions. No differences were found in E2 and P levels between supplemented groups indicating that our results are not influenced by changes in hormone concentrations. We suggest that repeated paced mating promotes the arrival of more newborn neurons in the AOB and MOB.

Somatic genital reflexes in rats with a nod to humans: anatomy, physiology, and the role of the social neuropeptides

Somatic genital reflexes such as ejaculation and vaginocervical contractions are produced through the striated muscles associated with the genitalia. The coordination of these reflexes is surprisingly complex and involves a number of lumbosacral spinal and supraspinal systems. The rat model has been proven to be an excellent source of information regarding these mechanisms, and many parallels to research in humans can be drawn. An understanding of the spinal systems involving the lumbosacral spinal cord, both efferent and afferent, has been generated through decades of research. Spinal and supraspinal mechanisms of descending excitation, through a spinal ejaculation generator in the lumbar spinal cord and thalamus, and descending inhibition, through the ventrolateral medulla, have been identified and characterized both anatomically and physiologically. In addition, delineation of the neural circuits whereby ascending genitosensory information regarding the regulation of somatic genital reflexes is relayed supraspinally has also been the topic of recent investigation. Lastly, the importance of the "social neuropeptides" oxytocin and vasopressin in the regulation of somatic genital reflexes, and associated sociosexual behaviors, is emerging. This work not only has implications for understanding how nervous systems generate sexual behavior but also provides treatment targets for sexual dysfunction in people.

Sex differences in the neural circuit that mediates female sexual receptivity

Female sexual behavior in rodents, typified by the lordosis posture, is hormone-dependent and sex-specific. Ovarian hormones control this behavior via receptors in the hypothalamic ventromedial nucleus (VMH). This review considers the sex differences in the morphology, neurochemistry and neural circuitry of the VMH to gain insights into the mechanisms that control lordosis. The VMH is larger in males compared with females, due to more synaptic connections. Another sex difference is the responsiveness to estradiol, with males exhibiting muted, and in some cases reverse, effects compared with females. The lack of lordosis in males may be explained by differences in synaptic organization or estrogen responsiveness, or both, in the VMH. However, given that damage to other brain regions unmasks lordosis behavior in males, a male-typical VMH is unlikely the main factor that prevents lordosis. In females, key questions remain regarding the mechanisms whereby ovarian hormones modulate VMH function to promote lordosis.

Noradrenergic nuclei that receive sensory input during mating and project to the ventromedial hypothalamus play a role in mating-induced pseudopregnancy in the female rat

In female rats, vaginal-cervical stimulation (VCS) received during mating induces bicircadian prolactin surges that are required for the maintenance of pregnancy or pseudopregnancy (PSP). The neural circuits that transmit VCS inputs to the brain have not been fully described, although mating stimulation is known to activate medullary noradrenergic cell groups that project to the forebrain. In response to VCS, these neurones release noradrenaline within the ventrolateral division of the ventromedial hypothalamus (VMHvl) and the posterodorsal medial amygdala (MePD), two forebrain sites that are implicated in the initiation of PSP. Noradrenaline receptor activation within the VMHvl is both necessary and sufficient for PSP induction, suggesting that noradrenaline acting within the VMHvl is particularly important in mediating the effects of VCS towards the establishment of PSP. We therefore investigated whether or not endogenous, VCS-induced noradrenaline release within the VMHvl is involved in PSP induction in the rat. Before the receipt of sufficient mating stimulation to induce PSP, a retrograde neurotoxin, dopamine-β-hydroxylase-saporin (DBH-SAP), was infused bilaterally into the either the VMHvl or the MePD to selectively destroy afferent noradrenergic nuclei in the brainstem. DBH-SAP infusions into the VMHvl lesioned mating-responsive noradrenergic neurones in A1 and A2 medullary nuclei and reduced the incidence of PSP by 50%. Infusions of DBH-SAP into the MePD had no effect on the subsequent induction of PSP. These results suggest that VCS is conveyed to mating-responsive forebrain areas by brainstem noradrenergic neurones, and that the activity of noradrenergic cells projecting to the VMHvl is involved in the induction of PSP.

Conditioned place preference for mating is preserved in rats with pelvic nerve transection

Female rats exhibit a conditioned place preference (CPP) for a context paired with mating. The present experiment tested the hypothesis that the activation of the pelvic nerve mediates the reinforcing effects of mating for female rats. Rats underwent bilateral pelvic nerve or sham transection and then received paced mating, nonpaced mating, or the control treatment during a CPP procedure. Pelvic nerve transection did not affect the CPP for paced or nonpaced mating. In tests of paced mating behavior, contact-return latencies following intromissions were significantly shorter in rats with pelvic nerve transection than they were in rats with sham transections. These results show that the pathway conveying the reinforcing effects of mating stimulation does not depend on the integrity of the pelvic nerve, but that activation of the pelvic nerve contributes to the display of paced mating behavior.

AMPA receptors in the medial amygdala are critical for establishing a neuroendocrine memory in the female rat

We sought to examine AMPA receptor (AMPAR) function in the medial posterodorsal amygdala (MePD), as glutamate neurotransmission is critical for the neural response to vaginal-cervical stimulation that initiates pregnancy or pseudopregnancy. Female rats were infused with the AMPAR antagonist CNQX or vehicle directly into the MePD via bilaterally implanted cannulae, then either returned to their homecage (HC), or received 15 mounts-without-intromissions (MO) or 15 intromissions (15I) from a male. Expression of the activity marker EGR-1 was used to determine the CNQX concentration which would prevent mating-induced activation of MePD neurons. Separate cannulated females received CNQX infusions into the MePD prior to receiving 15I, and the oestrous cycle length was monitored by daily vaginal lavages. Infusion of CNQX (500 nm) blocked mating-induced neural activation and lengthened the oestrous cycle, demonstrating AMPAR involvement in the formation of pseudopregnancy. To further explore this involvement, separate groups of 15I, MO and HC females were killed 90 min or 3 h after testing treatment. Brain sections were immunolabeled for AMPAR-subunit GluR1 phosphorylated at one of two sites (Serine-831 or Serine-845), or total GluR1 and GluR2, and immunofluorescence intensity was measured in the MePD, hippocampus and hypothalamus. A mating-induced increase in Serine-831 phosphorylation after 3 h was observed only in the MePD, whereas there was no effect on Serine-845 phosphorylation. Additionally, we observed a time-dependent increase in total GluR1 staining intensity. These results suggest an increased AMPAR function in the MePD after receipt of VCS, and a role for AMPAR in the neural response to VCS resulting in pseudopregnancy.

Artificial vaginocervical stimulation induces a conditioned place preference in female rats

Female rats express a conditioned place preference (CPP) for a context paired with mating. During a mating encounter, the female rat is exposed to several different types of stimuli, including, but not limited to, vaginocervical stimulation and social contact. The present experiment tested the hypothesis that two components of the mating interaction, vaginocervical stimulation or social contact, each induce a CPP in female rats. During conditioning rats received nonpaced mating, artificial vaginocervical stimulation, social interaction or a control treatment. Rats expressed a CPP for the context paired with nonpaced mating or artificial vaginocervical stimulation whereas social interaction and the control treatment did not induce a CPP. The present findings highlight the important role that vaginocervical stimulation plays in the reinforcing effects of mating in female rats.

Mating-induced neuroendocrine responses during pseudopregnancy in the female mouse

Pseudopregnancy (PSP) is a neuroendocrine reflex triggered by vaginocervical stimulation similar to the neuroendocrine response of early pregnancy and is characterised by short-term neural activity, resulting in long-term neuroendocrine responses that cause repeated release of pituitary prolactin (PRL) over many days. PSP is a useful model to study how somatosensory input is transduced in the brain into neuroendocrine responses, and has been extensively characterised in rats. With increasing use of mice as an experimental model, however, and to allow use of transgenic mice to investigate mechanisms of this sensory response, it is important to characterise the principal neuroendocrine response of pseudopregnancy in this species. The present study aimed to examine the induction and neuroendocrine responses of PSP in mice using vasectomised stud males, to investigate mating-induced changes in vaginal cytology, uterine growth, and PRL secretion, and to map certain aspects of somatosensory transduction by assessing the neural activity marker FOS. Unlike the induction of pseudopregnancy in rats, which can be induced simply by multiple intromissions from a male or artificial mechanical stimulation of the cervix, PSP induction in mice required the receipt of an ejaculation from a male. In mice that received PSP-inducible mating stimuli, FOS expression was observed in a slightly different range of brain regions than has been observed in rats, with increases in the bed nucleus of the stria terminalis, medial preoptic area, and ventromedial hypothalamus, but not in limbic areas examined. Moreover, PSP mice expressed a single diurnal PRL surge on day 6 of PSP. Thus, the data demonstrate important species differences in the neuroendocrine mechanisms activated in response to a mating stimulus in mice compared with rats. A clear understanding of the species-specific response will be required in interpreting research into the reproductive biology of this species.

Effects of surgical induction of endometriosis on response properties of preoptic area neurons in rats

Subfertility and severe pelvic pains are symptoms associated with endometriosis (ENDO), a common condition among women that is characterized by the growth of the uterine endometrium on the surface of organs within the pelvic region and abdominal cavity. The contribution of the CNS to symptoms associated with ENDO is not known. In the present study, the preoptic area (POA) of the hypothalamus was investigated, as this region of the forebrain is known to play an important role in the neuroendocrine control of the reproductive cycle, mating behavior, and antinociception. Female rats were either induced for ENDO by autotransplantation of uterine tissue (n=20) or uterine fat for surgical sham controls (n=11). Terminal extracellular electrophysiological recordings (urethane anesthesia) were conducted in the POA six weeks post-ENDO induction when the rats were in either the proestrus or metestrus stages of their estrous cycle. Significant differences were found between the ENDO versus SHAM groups of animals for the proportion of inhibitory responses as well as the percentage of neurons responding to stimulation of the abdominal branches of the vagus, which innervates portions of the female reproductive tract, including the ovaries. The endometriotic cysts were found to be significantly larger in proestrus rats (stage when hormones are elevated). These data demonstrate that the responses of POA neurons are influenced by the presence of endometriotic cysts in the abdominal cavity. Since the POA is known to be part of the neural circuitries that mediate nociception and fertility, any deviation from its normal activity under ENDO conditions could contribute to the constellation of symptoms that ensue.

Nucleus paragigantocellularis afferents in male and female rats: organization, gonadal steroid receptor expression, and activation during sexual behavior

The supraspinal regulation of genital reflexes is poorly understood. The brainstem nucleus paragigantocellularis (nPGi) of rats is a well-established source of tonic inhibition of genital reflexes. However, the organization, gonadal steroid receptor expression, and activity of nPGi afferents during sex have not been fully characterized in male and female rats. To delineate the anatomical and physiological organization of nPGi afferents, the retrograde tracer Fluoro-Gold (FG) was injected into the nPGi of sexually experienced male and female rats. Animals engaged in sexual behavior 1 hour before sacrifice. Cells containing FG, estrogen receptor-alpha (ER(alpha)), androgen receptor (AR), and the immediate-early gene product Fos were identified immunocytochemically. Retrograde labeling from the nPGi was prominent in the bed nucleus of the stria terminalis, paraventricular nucleus (PVN), posterior hypothalamus, precommissural nucleus, deep mesencephalic nucleus, and periaqueductal gray (PAG) of both sexes. Sex differences were observed in the caudal medial preoptic area (MPO), with significantly more FG+ cells observed in males, and in the PAG and inferior colliculus, where significantly more FG+ cells were observed in females. The majority of regions that contained FG+ cells also contained ER(alpha) or AR, indicating sensitivity to gonadal steroids. The proportions of FG+ cells that co-localized with sex-induced Fos was high in the PVN of both sexes and high in the MPO of males but low in the PAG of both sexes despite the large number of PAG-nPGi output neurons and Fos+ cells in both sexes. The characterization of these afferents will lead to a further understanding of the neural regulation of genital reflexes.

Receipt of vaginal-cervical stimulation modifies synapsin content in limbic areas of the female rat

Female rats require a sufficient amount and pattern of vaginal-cervical stimulation to initiate neuroendocrine changes required for the successful implantation of a fertilized ovum in the uterus. These changes are characterized by twice daily prolactin surges that last 10-12 days. Following a sterile mating, the endocrine changes are still observed, and are termed pseudopregnancy (PSP). The mating stimulation required to initiate these changes prior to pregnancy or PSP has a neural representation, which we have termed the intromission mnemonic. We sought to examine if the formation of the intromission mnemonic is accompanied by alterations in the number or density of synapses in limbic areas by immuno-labeling a pre-synaptic protein, synapsin. Groups of cycling female rats on proestrus day received either 15 or 5 intromissions or mounts-without intromissions from a vasectomized male; an additional time-matched control group was left in the home cage. All females were perfused after 90 min or 8 h. The brains were removed and sliced, and the amygdala and hippocampus immunostained for synapsin, then imaged by confocal microscopy. We found that 90 min after mating sufficient for PSP, the number of synapsin puncta (points of immunoreactivity equivalent to a synapse) was decreased and the intensity of the synapsin staining was increased in the posterodorsal medial amygdala (MePD). A similar reduction of puncta was observed in the CA1 region of the hippocampus, and an increase of intensity occurred in the basolateral amygdala. Spaced intromissions had no effect on synapsin expression anywhere examined. Intensity reductions unrelated to receipt of vaginal-cervical stimulation were observed in the hippocampus. None of these effects were observed after 8 h. Together, these results raise the possibility that synapses in the MePD may be pruned after mating stimulation, resulting in pathway-specific stabilization that contributes to the intromission mnemonic associated with the establishment of PSP.

Convergence of nociceptive information in the forebrain of female rats: reproductive organ response variations with stage of estrus

Neurons in the preoptic area (POA) of the hypothalamus and the bed nucleus of stria terminalis (BST) play an important role in the neuroendocrine control of the reproductive cycle, mating behaviors and nociception. Single unit extracellular recordings were performed in the POA and BST region of 20 urethane anesthetized female rats during either the proestrus (elevated levels of estrogen/progesterone) or metestrus (low circulating hormones) stage of the estrous cycle. A total of 118 neurons in the POA and 65 neurons in the BST responded to the search stimuli, bilateral electrical stimulation of the viscerocutaneous branch of the pelvic nerve and/or sensory branch of the pudendal nerve (i.e., dorsal nerve of clitoris). Most of the neurons responding to the electrical search stimuli received a high degree of somatovisceral convergence, including inputs from the abdominal branches of the vagus, cervix, vagina, colon and skin territories on the perineum and trunk. Mean neuronal response thresholds for vaginal and cervical stimulation but not colon distention were significantly higher for animals tested during proestrus. Also, there was a shift in POA and BST neuronal responsiveness towards more inhibition and less excitation during proestrus for a variety of somatovisceral inputs. These data demonstrate that the changes in hormonal status affect the properties of POA and BST neurons, which likely relates not only to the functional importance of these inputs for reproductive behaviors but also for nociceptive processing as well.

Functional internal complexity of amygdala: focus on gene activity mapping after behavioral training and drugs of abuse

The amygdala is a heterogeneous brain structure implicated in processing of emotions and storing the emotional aspects of memories. Gene activity markers such as c-Fos have been shown to reflect both neuronal activation and neuronal plasticity. Herein, we analyze the expression patterns of gene activity markers in the amygdala in response to either behavioral training or treatment with drugs of abuse and then we confront the results with data on other approaches to internal complexity of the amygdala. c-Fos has been the most often studied in the amygdala, showing specific expression patterns in response to various treatments, most probably reflecting functional specializations among amygdala subdivisions. In the basolateral amygdala, c-Fos expression appears to be consistent with the proposed role of this nucleus in a plasticity of the current stimulus-value associations. Within the medial part of the central amygdala, c-Fos correlates with acquisition of alimentary/gustatory behaviors. On the other hand, in the lateral subdivision of the central amygdala, c-Fos expression relates to attention and vigilance. In the medial amygdala, c-Fos appears to be evoked by emotional novelty of the experimental situation. The data on the other major subdivisions of the amygdala are scarce. In conclusion, the studies on the gene activity markers, confronted with other approaches involving neuroanatomy, physiology, and the lesion method, have revealed novel aspects of the amygdala, especially pointing to functional heterogeneity of this brain region that does not fit very well into contemporarily active debate on serial versus parallel information processing within the amygdala.

Expression of FOS, EGR-1, and ARC in the amygdala and hippocampus of female rats during formation of the intromission mnemonic of pseudopregnancy

Pseudopregnancy (PSP) in the female rat is a neuroendocrine condition that is induced by repeated and intermittent vaginocervical stimulation received during mating and involves the expression of bicircadian prolactin surges and cessation of normal estrous cyclicity for 10-12 days postmating. The temporal patterning and number of intromissions received by the female are critical for PSP initiation, and thus, short-term encoding of VCS occurs during transduction of intromissions into PSP. In this experiment, we characterized and compared the mating-induced neural activation patterns within amygdalar and hippocampal regions using expression of the immediate early genes FOS, EGR-1, and ARC. Cycling female rats mated on proestrus received 15 or 5 intromissions under paced or nonpaced mating conditions. High numbers of intromissions during nonpaced mating or low numbers received during paced mating are sufficient to induce PSP, while five nonpaced intromissions and mounts without intromission are insufficient. Here we demonstrate that the CA1 region of the hippocampus was selectively sensitive to PSP-sufficient but not PSP-insufficient mating stimulation by showing significant effects of paced mating for all three IEGs. Paced mating also stimulated the expression of ARC within the basolateral, cortical, and central nuclei of the amygdala. The posterodorsal medial amygdala also showed selective EGR-1 responses to PSP-sufficient mating stimulation. There was no effect of hemisphere on IEG expression. The postmating expression profiles of these IEGs provide evidence that limbic areas involved in encoding and consolidation of memory are involved in initiating the neuroendocrine memory of PSP.

Morphological sex differences and laterality in the prepubertal medial amygdala

The medial amygdala (MeA) is crucial in the expression of sex-specific social behaviors. In adult rats the regional volume of the MeA posterodorsal subnucleus (MeApd) is approximately 50% larger in males than in females. The MeApd is also sexually dimorphic in prepubertal rats. We have recently shown that the left MeApd is significantly larger in prepubertal males than females. In contrast with volumetric sex differences elsewhere in the brain, however, we found no sex difference in the number of left MeApd neurons. In the present study we investigated the cellular bases of the sex difference in MeApd regional volume by quantifying the volume occupied by dendrites, axons, synapses, or glia, and by measuring MeApd dendritic morphology in 26-29-day-old male and female rats. We find that the volume occupied by dendritic shafts and glia completely accounts for the sex difference in left MeApd regional volume. Dendritic length measurements in the left hemisphere confirm that males have greater overall dendritic length, which is due to greater branching rather than to longer dendrite segments. In the right hemisphere the pattern of sex differences was different: Males have more MeApd neurons than females, whereas the dendritic morphology of individual neurons is not sexually dimorphic. These results highlight the importance of evaluating laterality in the MeA and suggest that the left and right MeA could play different roles in neuroendocrine regulation and sexually dimorphic social behaviors.

Effects of pelvic, pudendal, or hypogastric nerve cuts on Fos induction in the rat brain following vaginocervical stimulation

In the female rat, genitosensory input is conveyed to the central nervous system predominantly through the pelvic, pudendal, and hypogastric nerves. The present study examined the relative contribution of those three nerves in the expression of Fos immunoreactivity within brain regions previously shown to be activated by vaginocervical stimulation (VCS). Bilateral transection of those nerves, or sham neurectomy, was conducted in separate groups of ovariectomized, sexually-experienced females. After recovery, females were primed with estrogen and progesterone and given either 50 manual VCSs with a lubricated glass rod over the course of 1 h. VCS increased the number of neurons expressing Fos immunoreactivity in the medial preoptic area, lateral septum, bed nucleus of the stria terminalis, ventromedial hypothalamus, and medial amygdala of sham neurectomized females. Transection of the pelvic nerve reduced Fos immunoreactivity in the medial preoptic area, bed nucleus of the stria terminalis, ventromedial hypothalamus, and medial amygdala, whereas transection of the pudendal nerve had no effect. In contrast, transection of the hypogastric nerve increased Fos immunoreactivity in the medial preoptic area and lateral septum, whereas transaction of the pelvic nerve increased Fos immunoreactivity in the lateral septum, following VCS. All females given VCS, except those with pelvic neurectomy, displayed a characteristic immobility during each application. These data confirm that the pelvic nerve is largely responsible for the neural and behavioral effects of VCS, and support a separate function for the hypogastric nerve.

Medullary noradrenergic neurons release norepinephrine in the medial amygdala in females in response to mating stimulation sufficient for pseudopregnancy

In the female rat, stimuli from the uterine cervix and vagina are carried to the brain areas involved in the mating-induced pseudopregnancy (PSP) response via the ventral noradrenergic bundle. Noradrenergic neurons projecting through this tract synapse in many forebrain areas including the amygdala, and neurons in the posterodorsal medial amygdala (MePD) are activated following mating. The goal of this experiment was to investigate whether norepinephrine (NE) is released into the MePD after mating using microdialysis and to determine the origin of this release. Ovariectomized estrogen- and progesterone-treated rats were implanted unilaterally with guide cannulae aimed at the MePD. Females were placed with males until they received 15 intromissions (15I), 5 intromissions (5I) or 15 mounts-without-intromission (MO). Dialysate samples collected every 20 min for 2 h before to 3 h after mating were analyzed for NE using HPLC with electrochemical detection. A significant increase in mean NE release in the MePD was seen at 80 min after mating onset in females receiving 15I, and no increase was seen in animals receiving 5I or MO. The time of peak NE release varied in 15I animals from 60 to 160 min after mating. Mean baseline levels of NE did not differ between groups. The retrograde tracer FluoroGold (FG), administered through the probe after cessation of dialysis sampling, was observed within identified noradrenergic cells primarily within the A1 and A2 cell groups. Infusion of anti-dopamine-beta-hydroxylase-saporin (DBH-SAP) into the MePD lesioned noradrenergic neurons located in the A1 and A2 cell groups. Because high levels of NE release occurred in the MePD only after the females received a number of intromissions sufficient to induce PSP, these results suggest that NE release within the MePD may be important for the establishment of PSP.

Coding for the initiation of pseudopregnancy by temporally patterned activation of amygdalar NMDA receptors

Female rats modulate the number and interval between the intromissions the female receives during mating. This patterned vaginocervical stimulation (VCS) is critical for triggering long-term changes in prolactin (PRL) secretion necessary for pregnancy or pseudopregnancy (P/PSP). Previous work has shown that NMDA receptor activation in the posterodorsal medial amygdala (MEApd) is required at the time of mating for VCS to induce the twice-daily PRL surges characteristic of P/PSP. The current studies examined whether patterned activation of glutamate receptors within the MEApd induces P/PSP. In anesthetized, cycling females, three 0.27 microg NMDA infusions given at 30 min intervals into the MEApd initiated P/PSP, whereas a single NMDA infusion of the same total dose (0.8 microg) had no effect. In conscious, freely behaving females, three infusions of an excitatory amino acid (EAA) mixture applied at the same interval were more effective in initiating P/PSP and nocturnal PRL surges than were single infusions at the same or higher concentrations. Infusion intervals of 5 and 60 min as well as continuous 1 h infusion did not induce P/PSP. Finally, a synergistic effect was observed between EAA and mating stimulation, because a subthreshold EAA infusion combined with subthreshold numbers of intromissions induced P/PSP. These results demonstrate that repeated, properly spaced, temporally discreet periods of glutamate receptor activation within the MEApd, which mimic mating stimulation, encode for P/PSP. Such findings suggest that single intromissions normally release individually subthreshold quanta of glutamate within the MEApd that summate to induce P/PSP.

Identification of neural circuits involved in female genital responses in the rat: a dual virus and anterograde tracing study

The spinal and peripheral innervation of the clitoris and vagina are fairly well understood. However, little is known regarding supraspinal control of these pelvic structures. The multisynaptic tracer pseudorabies virus (PRV) was used to map the brain neurons that innervate the clitoris and vagina. To delineate forebrain input on PRV-labeled cells, the anterograde tracer biotinylated dextran amine was injected in the medial preoptic area (MPO), ventromedial nucleus of the hypothalamus (VMN), or the midbrain periaqueductal gray (PAG) 10 days before viral injections. These brain regions have been intimately linked to various aspects of female reproductive behavior. After viral injections (4 days) in the vagina and clitoris, PRV-labeled cells were observed in the paraventricular nucleus (PVN), Barrington's nucleus, the A5 region, and the nucleus paragigantocellularis (nPGi). At 5 days postviral administration, additional PRV-labeled cells were observed within the preoptic region, VMN, PAG, and lateral hypothalamus. Anterograde labeling from the MPO terminated among PRV-positive cells primarily within the dorsal PVN of the hypothalamus, ventrolateral VMN (VMNvl), caudal PAG, and nPGi. Anterograde labeling from the VMN terminated among PRV-positive cells in the MPO and lateral/ventrolateral PAG. Anterograde labeling from the PAG terminated among PRV-positive cells in the PVN, ventral hypothalamus, and nPGi. Transynaptically labeled cells in the lateral hypothalamus, Barrington's nucleus, and ventromedial medulla received innervation from all three sources. These studies, together, identify several central nervous system (CNS) sites participating in the neural control of female sexual responses. They also provide the first data demonstrating a link between the MPO, VMNvl, and PAG and CNS regions innervating the clitoris and vagina, providing support that these areas play a major role in female genital responses.

The effects of mating stimulation on c-Fos immunoreactivity in the female hamster medial amygdala are region and context dependent

During mating in hamsters, both tactile and nontactile sensory stimulation experienced by the female affect sexual behavior and progestational neuroendocrine reflexes. To test the interactions of these types of mating stimulation, c-Fos immunohistochemistry measured brain cellular activity during sexual behavior under conditions that included combinations of tactile and nontactile mating stimulation. Test groups received: (1) mating stimulation from a male, females being either fully mated or mated while wearing a vaginal mask, or (2) experimenter applied manual vaginocervical stimulation (VCS)-with or without males present, or (3) handling similar to VCS but without insertions-with or without males present. Numbers of c-Fos immunoreactive cells were counted in specific subdivisions of the posterior medial amygdala (MeP) and ventromedial hypothalamus (VMH). The medial amygdala dorsal and ventral subdivisions responded differentially to components of mating stimulation. The posterodorsal Me (MePD) cellular activation was greatest during mating conditions that included VCS and/or males present. However, the posteroventral Me (MePV) was sensitive to male exposure and not to VCS. Also, MePV and VMH shell responses mirrored each other, both being primarily sensitive to male exposure. In separate tests, manual VCS induced pseudopregnancy, though the procedure was most effective with additional nontactile stimulation from males present. In summary, contextual cues provided by nontactile male stimulation enhance the effect of vaginocervical and other tactile stimulation on reproductive processes. Furthermore, c-Fos expression in the female hamster medial amygdala is region and context dependent.

Brain activation during vaginocervical self-stimulation and orgasm in women with complete spinal cord injury: fMRI evidence of mediation by the vagus nerves

Women diagnosed with complete spinal cord injury (SCI) at T10 or above report vaginal-cervical perceptual awareness. To test whether the Vagus nerves, which bypass the spinal cord, provide the afferent pathway for this response, we hypothesized that the Nucleus Tractus Solitarii (NTS) region of the medulla oblongata, to which the Vagus nerves project, is activated by vaginal-cervical self-stimulation (CSS) in such women, as visualized by functional magnetic resonance imaging (fMRI). Regional blood oxygen level-dependent (BOLD) signal intensity was imaged during CSS and other motor and sensory procedures, using statistical parametric mapping (SPM) analysis with head motion artifact correction. Physiatric examination and MRI established the location and extent of spinal cord injury. In order to demarcate the NTS, a gustatory stimulus and hand movement were used to activate the superior region of the NTS and the Nucleus Cuneatus adjacent to the inferior region of the NTS, respectively. Each of four women with interruption, or "complete" injury, of the spinal cord (ASIA criteria), and one woman with significant, but "incomplete" SCI, all at or above T10, showed activation of the inferior region of the NTS during CSS. Each woman showed analgesia, measured at the fingers, during CSS, confirming previous findings. Three women experienced orgasm during the CSS. The brain regions that showed activation during the orgasms included hypothalamic paraventricular nucleus, medial amygdala, anterior cingulate, frontal, parietal, and insular cortices, and cerebellum. We conclude that the Vagus nerves provide a spinal cord-bypass pathway for vaginal-cervical sensibility in women with complete spinal cord injury above the level of entry into spinal cord of the known genitospinal nerves.

Neural control of ejaculation

Ejaculation is the most reinforcing component of sexual behavior. However, the neural substrates mediating ejaculation and processing ejaculation-related signals remain poorly understood. We review the current understanding of central control of ejaculation. Specifically, the recent identification of a candidate spinothalamic pathway involved in relay of ejaculation-specific signals is discussed. In addition, the discovery of a neural population of lumbar interneurons playing an pivotal role in expression of ejaculation is reviewed.

Central regulation of ejaculation

Ejaculation is a reflex mediated by a spinal control center, referred to as a spinal ejaculation generator. This spinal ejaculation generator coordinates sympathetic, parasympathetic and motor outflow to induce the two phases of ejaculation, i.e., emission and expulsion. In addition, the spinal ejaculation generator integrates this outflow with inputs that are related to the summation of sexual activity prior to ejaculation that are required to trigger ejaculation. Recently, a group of spinothalamic neurons in the lumbar spinal cord (LSt cells) were demonstrated to comprise an integral part of the spinal ejaculation generator. Specifically, lesions of LSt cells completely ablate ejaculatory function. Moreover, LSt cells are activated following ejaculation, but not following other components of sexual behavior. Furthermore, based on their relationship with autonomic nuclei, motoneurons and genital sensory inputs, LSt cells are also in the ideal anatomical position to integrate sensory inputs and autonomic and motor outflow. Additionally, the spinal ejaculation generator is under inhibitory and excitatory influence of supraspinal sites, including the nucleus paragigantocellularis (nPGi), the paraventricular nucleus of the hypothalamus (PVN) and the medial preoptic area (MPOA). Finally, sensory information related to ejaculation is processed in the spinal cord and brain, possibly contributing to the rewarding properties of ejaculation. One candidate pathway for relay of ejaculation-related cues consists of LSt cells and their projections to the parvocellular subparafascicular thalamic nucleus. Moreover, neural activation specifically related to ejaculation is observed in the brain and may reflect of processing of ejaculation-related sensory cues.

Identification of neural pathways involved in genital reflexes in the female: a combined anterograde and retrograde tracing study

The medial preoptic area (MPOA) is important for reproductive behavior in females. However, the descending pathways mediating these responses to the spinal motor output are unknown. The MPOA does not directly innervate the spinal cord. Therefore, pathways mediating MPOA-induced changes in sexual behavior must relay in the brain. The nucleus paragigantocellularis (nPGi) projects heavily to spinal circuits involved in female sexual reflexes and is involved in the tonic inhibition of genital reflexes. However, the periaqueductal gray (PAG) is also important for female sexual behavior. The present study examined the hypothesis that the MPOA output relays through PAG and the nPGi before descending to the spinal cord. We used anterograde and retrograde tracing techniques to examine the descending pathways and relay sites from the MPOA to the spinal cord and the nPGi in the female rat. Injection of biotinylated dextran amine into the MPOA produced dense labeling in specific regions of the PAG and Barrington's nucleus; anterogradely labeled fibers terminated close to neurons retrogradely labeled from the spinal cord in the PAG, Barrington's nucleus, nPGi, lateral hypothalamus and paraventricular nucleus (PVN). Anterogradely labeled fibers and varicosities were also found close to neurons retrogradely labeled from the nPGi in the PAG, lateral hypothalamus and PVN. These results suggest that the major MPOA output relays in the PAG and nPGi before descending to innervate spinal circuits regulating female genital reflexes and that the MPOA plays a multifaceted role in female reproductive behavior through its modulation of PAG output systems.

Influence of sex, estrous cycle and motherhood on dendritic spine density in the rat medial amygdala revealed by the Golgi method

The medial nucleus of the amygdala (MeA), a sexually dimorphic area, contains estrogen and androgen receptors and has an integrative role in behavioral, vegetative and endocrine activities of rats. The density of dendritic spines along the first 40 microm of dendritic length was studied in neurons from the anterodorsal (MeAD), posterodorsal (MePD) and posteroventral (MePV) aspects of the MeA in males, in virgin females during the four phases of the estrous cycle and in multiparous females in diestrus. The single-section Golgi method was employed (N=48 observations per experimental group). In the three MeA subnuclei males showed more dendritic spines than virgin females (P<0.001), with the only exception being the MePD data of females in diestrus (P>0.05). In virgin females, whereas more dendritic spines were found in diestrus, a decline in these values was found during the proestrus, estrus and metaestrus in the MePD and MePV (P<0.05) but not in the MeAD (P>0.05). Compared with virgin females in diestrus, postpartum rats showed more spines in the MeAD (P<0.001) and fewer in the MePD (P<0.001) but no difference was found in the MePV (P>0.05). These data suggest that there are subregion-specific differences in the density of dendritic spines within the MeA and that they appear to be affected by sex, cyclic fluctuations in the levels of ovarian steroids and following pregnancy in rats. These findings may add to the understanding of the MeA neuronal plastic changes that affect the ongoing processing of sensory information and the organization of the neuroendocrine and behavioral basis of reproduction.

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.

Induction of pseudopregnancy using artificial VCS: importance of lordosis intensity and prestimulus estrous cycle length

In cycling female rats, vaginocervical stimulation (VCS) received naturally during mating or by artificial mechanical stimulation induces neuroendocrine and behavioral responses that are critical for reproduction, including bi-circadian prolactin surges which result in pregnancy or an 8-14-day diestrous period called pseudopregnancy (PSP). Following mating, the incidence of PSP is higher when females receive high (10) as opposed to low (3-5) numbers of intromissions. Therefore, a threshold level of VCS must be exceeded before hypothalamic changes required for PSP can occur. This study characterized the threshold curve for PSP induction for artificial VCS (VCS-a). Proestrous females were given 1, 2, 3, 4, or 8 VCS-a applied with a glass rod using 200 g of force for 2 s, with an 8-min interval between stimulations. The lordosis response (LR) to the stimulus was measured on a scale of increasing intensity from 0 to 3, and the occurrence of PSP was measured by daily vaginal lavage. In contrast to previous findings, VCS-a induced robust lordosis responses without concurrent flank and perineal stimulation. The frequency of PSP induction did not increase in females as a function of amounts of VCS-a. However, the occurrence of PSP was strongly tied to the maximum lordosis response (LR(max)) observed. PSP was observed only among multiply stimulated females that showed the highest LR(max) (3.0) to at least one of the stimulations. Multiply stimulated females that showed a LR(max) < 3.0 or females that received only one VCS-a never became PSP. PSP and a stronger LR(max) were more likely to occur in females that had 5-day compared to 4-day prestimulus estrous cycle lengths. We conclude that central mechanisms important for VCS-induced PSP and lordosis may be potentiated by estradiol's actions in estrogen-concentrating forebrain areas.

Afferent connections of the parvocellular subparafascicular thalamic nucleus in the rat: evidence for functional subdivisions

The parvocellular subparafascicular nucleus of the thalamus (SPFp) consists of separate subdivisions, i.e., a medial portion containing galanin-immunoreactive (-IR) axons and a lateral portion containing calcitonin gene related peptide (CGRP)-IR neurons and fibers. These subdivisions appear to have distinct functional roles. In particular, ejaculation-induced Fos expression is expressed in the medial SPFp. Hence, it was hypothesized that medial SPFp is involved in relay of copulation-related information. In contrast, lateral SPFp is involved in the processing of auditory and visual signals involved in fear-conditioned responses. Here we tested the hypothesis that medial and lateral subdivisions of SPFp receive different sets of afferents and that these differences contribute to the separate functional roles of the two subdivisions. Inputs to medial and lateral SPFp were identified following injections of FG restricted to either division in male rats. The medial SPFp receives unique inputs from lumbar spinothalamic cells and brain regions involved in processing of visceral stimuli, supporting the hypothesis that the medial SPFp is involved in the relay of genitosensory information critical for the expression of male sexual behavior. The afferents of the lateral SPFp include brain regions involved in processing of visual and auditory signals and support a role for this subdivision in relay of visual and auditory information. Thus, the two subdivisions of SPFp are anatomically and functionally distinctive.

Parvocellular subparafascicular thalamic nucleus in the rat: anatomical and functional compartmentalization

The parvocellular subparafascicular thalamic nucleus (SPFp) is located in the posterior thalamus, consists of horizontally oriented cells, and extends from rostromedial to caudolateral, fusing with the posterior intralaminar nucleus and the peripeduncular nucleus. The present study demonstrates a chemoarchitechtonic and functional parcellation of the rat SPFp. Analysis of the distributions of the neuropeptides galanin, calcitonin gene related peptide (CGRP), substance P, and calbindin revealed the existence of a medial and lateral subdivision within SPFp, and a possible intermediate subdivision. The medial subdivision contains a dense population of galanin-immunoreactive fibers, originating from galanin neurons in the lumbosacral spinal cord. In contrast, the lateral subdivision contains CGRP-positive fibers and neurons. The presence of substance P and calbindin immunoreactivity throughout the entire nucleus suggests that these are separate subdivisions of SPFp, rather than different subnuclei. The present study also investigated the functional association of the separate subdivisions of SPFp for male and female rat sexual behavior. In the medial subdivision, Fos-positive neurons were activated in males by display of ejaculation and in females by vaginocervical stimulation. Thus, Fos induction in medial SPFp appears to reflect processing of inputs related to those events. In contrast, sexual behavior did not induce Fos in the lateral SPFp. Taken together, the present results indicate the existence of separate subdivisions in SPFp that are involved in different behavioral functions. The medial SPFp may process inputs important for sexual behavior, whereas the lateral SPFp may be involved in convergence of auditory and nociceptive inputs important for conditioned fear responses.

Neuronal activation in the caudal brainstem associated with mating by voles

The expression of c-fos, a marker of neuronal activation, was examined in the gracile nucleus (GN) and nucleus of the solitary tract (NTS) after social interactions, including mating, between male and female prairie voles. In GN, mating, but not non-sexual interactions, induced similar significant increases in c-fos immunoreactivity in both males and females. The increased immunoreactivity was concentrated in medial and dorsal GN suggesting that expression was driven by stimulation of reproductive organs. In contrast, in NTS, mating-induced increases in c-fos expression occurred only in males. These results suggest that both GN and NTS comprise different functional components of mating circuitry and may contribute to pair bonding in monogamous voles.