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

Comparison of pain modulatory effect of the LPGi estragon receptor on inflammatory pain between pro-estrus and estrus phases and OVX rats

The present study has investigated whether circulating estrogen level variations in the pro-estrus and estrus phases of the intact rats and estrogen depletion in the ovariectomized animals (OVX) adjust the formalin-induced nociceptive behaviors. During the pro-estrus and estrus phases of rats' estrus cycle and in the OVX rats, 17β-estradiol and ICI 182,780 (estrogen receptor antagonist) were administered into the right paragigantocellularis lateralis (LPGi) nucleus. Then, the formalin-induced flexing and licking responses were recorded for 60 min. The findings of this study revealed that intra-LPGi administration of 17β-estradiol (0.8 μmol) reduced the formalin-induced flexing and licking duration in pro-estrus and estrus rats (P < 0.001), suggesting an analgesic effect. 17β-Estradiol injection into the LPGi nucleus of OVX rats increased the flexing duration (P < 0.05) while decreasing the licking duration (P < 0.05) of the formalin test. The pain modulatory effect of 17β-estradiol on the flexing response was reversed by ICI 182,780 (15 nmol) in the pro-estrus (P < 0.001) and estrus rats (P < 0.001) but not in the OVX rats. Also, pretreatment of LPGi nucleus with ICI 182,780 reversed the analgesic effect of 17β-estradiol on the licking response in the pro-estrus (P < 0.05), estrus (P < 0.001), and OVX rats (P < 0.001). These results suggest that the pain threshold in intact female rats is modulated independently of the estrus state. Still, the basal level of plasma estrogen and the activation of its receptors are necessary for pain modulation.

Emotion in action: When emotions meet motor circuits

The brain is a remarkably complex organ responsible for a wide range of functions, including the modulation of emotional states and movement. Neuronal circuits are believed to play a crucial role in integrating sensory, cognitive, and emotional information to ultimately guide motor behavior. Over the years, numerous studies employing diverse techniques such as electrophysiology, imaging, and optogenetics have revealed a complex network of neural circuits involved in the regulation of emotional or motor processes. Emotions can exert a substantial influence on motor performance, encompassing both everyday activities and pathological conditions. The aim of this review is to explore how emotional states can shape movements by connecting the neural circuits for emotional processing to motor neural circuits. We first provide a comprehensive overview of the impact of different emotional states on motor control in humans and rodents. In line with behavioral studies, we set out to identify emotion-related structures capable of modulating motor output, behaviorally and anatomically. Neuronal circuits involved in emotional processing are extensively connected to the motor system. These circuits can drive emotional behavior, essential for survival, but can also continuously shape ongoing movement. In summary, the investigation of the intricate relationship between emotion and movement offers valuable insights into human behavior, including opportunities to enhance performance, and holds promise for improving mental and physical health. This review integrates findings from multiple scientific approaches, including anatomical tracing, circuit-based dissection, and behavioral studies, conducted in both animal and human subjects. By incorporating these different methodologies, we aim to present a comprehensive overview of the current understanding of the emotional modulation of movement in both physiological and pathological conditions.

Conservation and dimorphism in androgen receptor distribution in Alston's singing mouse (Scotinomys teguina)

Because of their roles in courtship and intrasexual competition, sexual displays are often sexually dimorphic, but we know little about the mechanisms that produce such dimorphism. Among mammals, one example is the vocalization of Alston's singing mouse (Scotinomys teguina), which consists of a series of rapidly repeated, frequency-modulated notes. The rate and duration of songs is sexually dimorphic and androgen responsive. To understand the neuronal mechanisms underlying this sexual dimorphism, we map the sites of androgen sensitivity throughout the brain, focusing analysis along a pathway that spans from limbic structures to vocal motor regions. We find widespread expression of AR immunoreactivity (AR-ir) throughout limbic structures important for social behavior and vocalization, including the lateral septum, extended amygdala, preoptic area and hypothalamus. We also find extensive AR staining along previously documented vocal motor pathways, including the periaqueductal gray, parabrachial nucleus, and nucleus ambiguus, the last of which innervates intrinsic laryngeal muscles. Lastly, AR-ir is also evident in sensory areas such as the medial geniculate, inferior, and superior colliculi. A quantitative analysis revealed that males exhibited more AR-ir than females, a pattern that was most pronounced in the hypothalamus. Despite the elaboration of vocalization in singing mice, comparison with prior literature suggests that the broad pattern of AR-ir may be conserved across a wide range of rodents. Together these data identify brain nuclei well positioned to shape the sexually dimorphic vocalization of S. teguina and suggest that such androgen modulation of vocalization is evolutionary conserved among rodents.

Acute caffeine reverses the disruptive effects of chronic fluoxetine on the sexual behavior of female and male rats

RATIONALE

Sexual side effects of chronic treatment with selective serotonin reuptake inhibitors (SSRIs) in humans include anorgasmia and loss of sexual desire and/or arousal which interferes with treatment compliance. There are few options at present to reduce these effects. Because orgasm and desire are mediated in part by activation of sympathetic arousal, we asked whether the sympathomimetic effects of acute caffeine treatment could reverse these effects.

OBJECTIVE

The present study examined whether acute treatment with caffeine (CAF; 10 or 20 mg/kg, ip) versus vehicle could ameliorate the disruption of appetitive and consummatory measures of copulatory behavior produced by chronic fluoxetine (10 mg/kg, sc) in adult, sexually active female or male rats.

METHODS

Sexually experienced female or male rats received daily injections of FLU over a 24-day period and were tested for sexual behaviors five times at 4-day intervals during this period in bilevel pacing chambers. Females had been ovariectomized and given hormone replacement with estradiol benzoate and progesterone prior to each test. Males were left gonadally intact. Four days after the final FLU test, rats were randomly assigned to one of the three doses of CAF and received ip injections of CAF or the saline vehicle 60 min before testing.

RESULTS

Chronic FLU reduced solicitations and lordosis over time in females and reduced the number of ejaculations in males. Both doses of CAF restored solicitations and lordosis in females and ejaculations in males. On their own, both doses of CAF increased females' pacing behavior and the number of mounts and intromissions in the males.

CONCLUSIONS

Stimulation of sympathetic outflow by CAF may constitute a readily accessible on-demand treatment for the sexual side-effects of SSRIs.

Mapping Central Projection of Oxytocin Neurons in Unmated Mice Using Cre and Alkaline Phosphatase Reporter

Oxytocin, a neuropeptide and peptide hormone, is produced by neurons in the hypothalamus and released by the posterior pituitary to control breastfeeding and labor. Recent studies have revealed that oxytocin in the central nervous system is also involved in modulating social interaction. To understand the potential role and innervation pattern of oxytocin neurons before sexual interaction, here we used transgenic mice which have the Cre recombinase under the control of an endogenous oxytocin promoter and Cre-dependent human placental alkaline phosphatase (AP) reporter to label the oxytocin neurons in the naive mouse brain. Since AP is located on the membrane of oxytocin neurons, AP histochemistry staining enabled us to observe the fine axonal terminals and the innervation pattern of oxytocin neurons in the thick serial coronal brain slices. Here we show that the number of AP-labeled cells varies with staining reaction time and ranges from 30% of the oxytocin immune-positive cell count to slightly higher than the oxytocin immune-positive cell count. Using AP staining with extended reaction time, which may not label all oxytocin neurons, we confirmed many innervation targets of oxytocin neurons from the anterior olfactory nucleus, some cortex regions, the limbic system, the hypothalamus, and the hindbrain, while the cell bodies were exclusively located in the hypothalamus and the bed nucleus of the stria terminalis. Finally, we observe some individual variance at the olfactory area, isocortex, striatum, paraventricular nucleus of thalamus, locus coeruleus, and Barrington's nucleus.

Sexually differentiated and neuroanatomically specific co-expression of aromatase neurons and GAD67 in the male and female quail brain

Testosterone aromatization into estrogens in the preoptic area (POA) is critical for the activation of male sexual behavior in many vertebrates. Yet, the cellular mechanisms mediating actions of neuroestrogens on sexual behavior remain largely unknown. We investigated in male and female Japanese quail by dual-label fluorescent in situ hybridization (FISH) whether aromatase-positive (ARO) neurons express glutamic acid decarboxylase 67 (GAD67), the rate-limiting enzyme in GABA biosynthesis. ARO cells and ARO cells double labeled with GAD67 (ARO-GAD67) were counted at standardized locations in the medial preoptic nucleus (POM) and the medial bed nucleus of the stria terminalis (BST) to produce three-dimensional distribution maps. Overall, males had more ARO cells than females in POM and BST. The number of double-labeled ARO-GAD67 cells was also higher in males than in females and greatly varied as a function of the specific position in these nuclei. Significant sex differences were however present only in the most caudal part of POM. Although both ARO and GAD67 were expressed in the VMN, no colocalization between these markers was detected. Together, these data show that a high proportion of estrogen-synthesizing neurons in POM and BST are inhibitory and the colocalization of GAD67 with ARO exhibits a high degree of anatomical specificity as well as localized sex differences. The fact that many preoptic ARO neurons project to the periaqueductal gray in male quail suggests possible mechanisms through which locally produced estrogens could activate male sexual behavior.

Differential innervation of superficial versus deep laminae of the dorsal horn by bulbo-spinal serotonergic pathways in the rat

Convergent data showed that bulbo-spinal serotonergic projections exert complex modulatory influences on nociceptive signaling within the dorsal horn. These neurons are located in the B3 area which comprises the median raphe magnus (RMg) and the lateral paragigantocellular reticular (LPGi) nuclei. Because LPGi 5-HT neurons differ from RMg 5-HT neurons regarding both their respective electrophysiological properties and responses to noxious stimuli, we used anatomical approaches for further characterization of the respective spinal projections of LPGi versus RMg 5-HT neuron subgroups. Adult Sprague-Dawley rats were stereotaxically injected into the RMg or the LPGi with the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L). The precise location of injection sites and RMg vs LPGi spinal projections into the different dorsal horn laminae were visualized by PHA-L immunolabeling. Double immunofluorescent labeling of PHA-L and the serotonin transporter (5-HTT) allowed detection of serotonergic fibers among bulbo-spinal projections. Anterograde tracing showed that RMg neurons project preferentially into the deep laminae V-VI whereas LPGi neuron projections are confined to the superficial laminae I-II of the ipsilateral dorsal horn. All along the spinal cord, double-labeled PHA-L/5-HTT immunoreactive fibers, which represent only 5-15% of all PHA-L-immunoreactive projections, exhibit the same differential locations depending on their origin in the RMg versus the LPGi. The clear-cut distinction between dorsal horn laminae receiving bulbo-spinal serotonergic projections from the RMg versus the LPGi provides further anatomical support to the idea that the descending serotonergic pathways issued from these two bulbar nuclei might exert different modulatory influences on the spinal relay of pain signaling neuronal pathways.

Dynamics of progesterone and estrogen receptor alpha in the ventromedial hypothalamus

Cyclic fluctuations of estradiol and progesterone in females influence neuronal activity in the ventrolateral division of the ventromedial hypothalamic nucleus (VMNvl), through the activation of progesterone receptors (PRs) and estrogen receptors (ERs). The expression of ER and PR in the VMNvl is influenced by their cognate ligands and is a central upstream trigger in the pathway of VMNvl-dependent modulation of endocrine responses. By studying the role played by estradiol and progesterone in PR and ERa expression in the VMNvl along the estrous cycle and how the two receptors interact in the same neuron, we aim to evaluate the synergistic action of both ovarian hormones in the regulation of VMNvl activity. In animals at all phases of the estrous cycle, the number of VMN neurons expressing PR or ERa was estimated by stereological methods, and the percentage, and rostro-caudal distribution, of neurons simultaneously expressing both receptors was determined. The highest number of PR-immunoreactive neurons was seen at proestrus, and of ERa-immunoreactive neurons was seen at proestrus and metestrus. The ERa/PR co-localization is increased at caudal levels. Approximately half the neurons expressing PR co-express ERa, a proportion that stays constant along the estrous cycle. The percentage of ERa neurons co-expressing PR changes from 60% at proestrus to 40% at metestrus. Fluctuations in circulating ovarian hormone levels promote coordinated changes in PR and ERa expression and co-localization. This may be an important mechanism in the regulation of input relayed by the VMNvl, allowing a precise modulation of endocrine responses.

Effect of hyperprolactinemia on PRL-receptor expression and activation of Stat and Mapk cell signaling in the prostate of long-term sexually-active rats

The abnormal elevation of serum PRL, referred to as hyperprolactinemia (HyperPRL), produces alterations in several reproductive parameters of male rats such as penile erection or decreased tendency to reach ejaculation. Additionally, this situation produces a significant modification of prostate histology, as observed in the epithelial structure and alveolar area, which could reach a level of hyperplasia in the long-term. In this tissue, HyperPRL produces an increase in expression of PRL receptors and activation of the Stat3 signaling pathway that is correlated with the evolution of prostate pathologies. However, the impact of HyperPRL in long-term sexually active male rats is unknown. In this work, using constantly copulating Wistar male rats with induced HyperPRL, we analyzed the level of serum PRL, the effect on prostate PRL receptors, and activation of pStat3, pStat5 and Mapk signaling pathways. Two procedures to induce HyperPRL were employed, comprising daily IP administration or adenohypophysis transplant, and although neither affected the execution of sexual behavior, the serum PRL profile following successive ejaculations was affected. Messenger RNA expression of the short and long isoforms of the PRL receptor at the ventral prostate was affected in different ways depending on the procedure to induce HyperPRL. The ventral prostate did not show any modification in terms of activation of the pStat5 signaling pathway in subjects with daily administration of PRL, although this was significantly increased in ADH transplanted subjects in the second and fourth consecutive ejaculation. A similar profile was found for the pStat3 pathway which additionally showed a significant increase in the third and fourth ejaculation of daily-injected subjects. The Mapk signaling pathway did not show any modifications in subjects with daily administration of PRL, but showed a significant increase in the second and third ejaculations of subjects with ADH transplants. Thus, although sexual behavior was not modified, HyperPRL modified the expression of PRL receptors and the activation of signal pathways in the prostate tissue. Hence, it is probable that prostatic alterations precede the sexual behavioral deficits observed in subjects with HyperPRL.

Animal Models for the Study of Female Sexual Dysfunction

INTRODUCTION

Significant progress has been made in elucidating the physiological and pharmacological mechanisms of female sexual function through preclinical animal research. The continued development of animal models is vital for the understanding and treatment of the many diverse disorders that occur in women.

AIM

To provide an updated review of the experimental models evaluating female sexual function that may be useful for clinical translation.

METHODS

Review of English written, peer-reviewed literature, primarily from 2000 to 2012, that described studies on female sexual behavior related to motivation, arousal, physiological monitoring of genital function and urogenital pain.

MAIN OUTCOMES MEASURES

Analysis of supporting evidence for the suitability of the animal model to provide measurable indices related to desire, arousal, reward, orgasm, and pelvic pain.

RESULTS

The development of female animal models has provided important insights in the peripheral and central processes regulating sexual function. Behavioral models of sexual desire, motivation, and reward are well developed. Central arousal and orgasmic responses are less well understood, compared with the physiological changes associated with genital arousal. Models of nociception are useful for replicating symptoms and identifying the neurobiological pathways involved. While in some cases translation to women correlates with the findings in animals, the requirement of circulating hormones for sexual receptivity in rodents and the multifactorial nature of women's sexual function requires better designed studies and careful analysis. The current models have studied sexual dysfunction or pelvic pain in isolation; combining these aspects would help to elucidate interactions of the pathophysiology of pain and sexual dysfunction.

CONCLUSIONS

Basic research in animals has been vital for understanding the anatomy, neurobiology, and physiological mechanisms underlying sexual function and urogenital pain. These models are important for understanding the etiology of female sexual function and for future development of pharmacological treatments for sexual dysfunctions with or without pain. Marson L, Giamberardino MA, Costantini R, Czakanski P, and Wesselmann U. Animal models for the study of female sexual dysfunction. Sex Med Rev 2013;1:108-122.

Anandamide reduces the ejaculatory threshold of sexually sluggish male rats: possible relevance for human lifelong delayed ejaculation disorder

INTRODUCTION

The sexually sluggish (SLG) male rat has been proposed as an animal model for the study of lifelong delayed ejaculation, a sexual dysfunction for which no treatment is available. Low endocannabinoid anandamide (AEA) doses facilitate sexual behavior display in normal sexually active and in noncopulating male rats through the activation of CB1 receptors.

AIM

To establish whether low AEA doses reduced the ejaculatory threshold of SLG male rats by acting at CB1 receptors.

METHODS

SLG male rats were intraperitoneally injected with different doses of AEA (0.1-3.0 mg/kg), the CB1 receptor antagonist AM251 (0.1-3.0 mg/kg), or their vehicles and tested for copulatory behavior during 60 minutes. Animals receiving AEA effective doses were subjected to a second sexual behavior test, 7 days later under drug-free conditions. To determine the participation of CB1 receptors in AEA-induced actions, SLG rats were pretreated with AM251 prior to AEA.

MAIN OUTCOME MEASURES

The sexual parameters, intromission latency, number of mounts and intromissions, ejaculation latency, and interintromission interval.

RESULTS

All sexual behavior parameters of SLG rats were significantly increased when compared with normal sexually experienced animals. Low AEA doses (0.3 and 1 mg/kg) significantly lowered the ejaculatory threshold of SLG rats, reducing the number of pre-ejaculatory intromissions and ejaculation latency. IL, M number, and locomotor activity were unaffected by AEA. Facilitation of the ejaculatory response of SLG rats disappeared 7 days after AEA injection. AM251 lacked an effect on copulation of SLG rats but blocked the AEA-induced lowering of the ejaculatory threshold.

CONCLUSIONS

AEA appears to specifically target the ejaculatory threshold of SLG rats through the activation of CB1 receptors. This specificity along with the fact that AEA's effects are exerted acutely and at low doses makes this drug emerge as a promising treatment for the improvement of the ejaculatory response in men with primary delayed ejaculation.

Neural correlates underlying naloxone-induced amelioration of sexual behavior deterioration due to an alarm pheromone

Sexual behavior is suppressed by various types of stressors. We previously demonstrated that an alarm pheromone released by stressed male Wistar rats is a stressor to other rats, increases the number of mounts needed for ejaculation, and decreases the hit rate (described as the number of intromissions/sum of the mounts and intromissions). This deterioration in sexual behavior was ameliorated by pretreatment with the opioid receptor antagonist naloxone. However, the neural mechanism underlying this remains to be elucidated. Here, we examined Fos expression in 31 brain regions of pheromone-exposed rats and naloxone-pretreated pheromone-exposed rats 60 min after 10 intromissions. As previously reported, the alarm pheromone increased the number of mounts and decreased the hit rate. In addition, Fos expression was increases in the anterior medial division (BNSTam), anterior lateral division (BNSTal) and posterior division (BNSTp) of the bed nucleus of the stria terminalis, parvocellular part of the paraventricular nucleus of the hypothalamus, arcuate nucleus, dorsolateral and ventrolateral periaqueductal gray, and nucleus paragigantocellularis (nPGi). Fos expression was decreased in the magnocellular part of the paraventricular nucleus of the hypothalamus. Pretreatment with naloxone blocked the pheromone-induced changes in Fos expression in the magnocellular part of the paraventricular nucleus of the hypothalamus, ventrolateral periaqueductal gray, and nPGi. Based on these results, we hypothesize that the alarm pheromone deteriorated sexual behavior by activating the ventrolateral periaqueductal gray-nucleus paragigantocellularis cluster and suppressing the magnocellular part of the paraventricular nucleus of the hypothalamus (PVN) via the opioidergic pathway.

Connections of the magnocellular medial preoptic nucleus (MPN mag) in male Syrian hamsters. II. The efferents

The magnocellular medial preoptic nucleus (MPN mag) plays a critical role in the regulation of male copulatory behavior in the Syrian hamster. Our study of the afferents are consistent with the hypothesis that the MPN mag receives input from areas in the chemosensory pathway and nuclear groups that contain receptors for gonadal steroids (Wang and Swann, 2006). The goal of the present study is to identify targets of the MPN mag by describing the location of labeled fibers following an injection of biotinylated dextran amine (BDA) into the MPN mag. Our results indicate that targets of the MPN mag include: (1) brainstem nuclei implicated in regulating male mating behavior in other species, such as the periaqueductal gray, deep mesencephalic nucleus, retrorubral field, ventral tegmental area and lateral paragigantocellular nucleus and (2) steroid-concentrating nuclei in the septum, preoptic area and hypothalamus. The lack of projections from the MPN mag to its chemosensory afferents indicate that the connections of the MPN mag with the posterior medial bed nucleus of the stria terminalis, medial and anterior cortical nuclei of the amygdala are unidirectional, and that chemosensory information flows from the medial amygdala and bed nucleus of the stria terminalis (BST) to the MPN mag. The bidirectional nature of the connections between the MPN mag and steroid-concentrating nuclei suggest that the MPN mag may influence the function of a steroid-concentrating network that regulates behaviors. Together these results support the hypothesis that the MPN mag regulates male mating behavior by integrating chemosensory and hormonal signals and relaying this information to brainstem areas that control motor output.

Brain neuronal activation induced by flibanserin treatment in female rats

RATIONALE

Flibanserin, a 5-HT1A agonist and 5-HT2A antagonist, is developed for the treatment of hypoactive sexual desire disorder in women, and its efficacy has been evidenced in several clinical studies. Flibanserin prosexual effects have been also evidenced in preclinical animal models. However, the mechanism of action of flibanserin remains not fully understood.

OBJECTIVE

The aim of the present study was to examine brain neuronal activation in female rats treated with flibanserin, using single immunocytochemical labeling of Fos protein, a marker of neuronal activation, and co-localization of Fos and catecholaminergic marker.

METHOD

Six groups of female rats received either acute or chronic administrations of vehicle, flibanserin 15 mg/kg or flibanserin 45 mg/kg. The brains were collected and processed for immunocytochemical labeling.

RESULTS

Acute flibanserin increased levels of Fos immunoreactivity in the nucleus accumbens, arcuate hypothalamic nucleus, locus coeruleus, lateral paragigantocellular nucleus, and nucleus of the solitary tract. Chronic 22-day treatment with flibanserin increased Fos expression in the medial preoptic area and arcuate nucleus of the hypothalamus, ventral tegmental area, locus coeruleus, and lateral paragigantocellular nucleus. Both acute and chronic flibanserin increased the density of activated catecholaminergic neurons in the ventral tegmental area but not in the locus coeruleus.

CONCLUSION

Altogether, our results showed that flibanserin, at the dose known to enhance female sexual motivation, preferentially activated the brain regions belonging to the mesolimbic dopaminergic pathway and hypothalamic structures involved in the integration of sexual cues related to sexual motivation.

Estrogen dependent activation function of ERβ is essential for the sexual behavior of mouse females

We previously generated and characterized a genuine estrogen receptor (ER) β-null mouse line (named ERβ(ST)(L-/L-)) and showed that ERβ(ST)(L-/L-) mice were sterile, due to an ovulation impairment in females and to an unknown reason in males, as their reproductive organs and spermatozoid motility appeared normal. We report here an assessment of the sexual behavior of ERβ(ST)(L-/L-) null mice. We found that ERβ(ST)(L-/L-) males display mildly impaired sexual behavior and that ERβ(ST)(L-/L-) females are significantly less receptive and less attractive than wild-type (WT) females. Decreased attractivity is also exhibited by ERβAF2(0) but not by ERβAF1(0) mutant females (females devoid of either AF2 or AF1 activation function of ERβ). Interestingly, by using an odor preference test, we have determined that the low attractiveness of ERβ(ST)(L-/L-) and ERβAF2(0) females is related to a deficiency of a volatile chemosignal.

Noxious stimulation excites serotonergic neurons: a comparison between the lateral paragigantocellular reticular and the raphe magnus nuclei

The present study was designed to record electrophysiological responses to graded noxious thermal stimuli of serotonergic and nonserotonergic neurons in the lateral paragigantocellular reticular (LPGi) and the raphe magnus (RMg) nuclei in rats. All of the neurons recorded were juxtacellularly filled with neurobiotin and identified with double immunofluorescent labeling for both neurobiotin and serotonin. Under halothane anesthesia (0.75%), noxious thermal stimuli ⩾48°C activated almost all (88%) of the serotonergic neurons located within the LPGi (n=16). The increase in firing was clear (3.4±0.3spike/s: mean of responses above the population median) and sustained during the whole application of strong thermal noxious stimuli, with a high mean threshold (48.3±0.3°C) and large receptive fields. Recording of serotonergic neurons in the RMg (n=21) demonstrated that the proportion of strongly activated (>2spike/s) neurons (19% vs 59% for the LPGi) as well as the magnitude of the activation (2.1±0.4spike/s: mean of responses above the population median) to thermal noxious stimuli were significantly lower than in the LPGi (P<.05). Within the boundaries of both the LPGi and the RMg (B3 group), nonserotonergic neurons were also predominantly excited (75%) by noxious stimuli, and the resulting activation (7.9±1.2spike/s) was even greater than that of serotonergic neurons. Thermal noxious stimuli-induced activation of LPGi serotonergic cells probably plays a key role in serotonin-mediated modulations of cardiac baroreflex and transmission of nociceptive messages occurring under such intense noxious conditions.

Origins of arousal: roles for medullary reticular neurons

The existence of a primitive CNS function involved in the activation of all vertebrate behaviors, generalized arousal (GA), has been proposed. Here, we provide an overview of the neuroanatomical, neurophysiological and molecular properties of reticular neurons within the nucleus gigantocellularis (NGC) of the mammalian medulla, and propose that the properties of these neurons equip them to contribute powerfully to GA. We also explore the hypothesis that these neurons may have evolved from the Mauthner cell in the medulla of teleost fish, although NGC neurons have a wider range of action far beyond the specific escape network served by Mauthner cells. Understanding the neuronal circuits that control and regulate GA is central to understanding how motivated behaviors such as hunger, thirst and sexual behaviors arise.

Testostérone et contrôle central de l’érection

La testostérone orchestre l’organisation périnatale et l’activation adulte des structures nerveuses cérébrales et spinales impliquées dans l’expression du comportement sexuel mâle. Cette revue décrit brièvement les différents effets de la testostérone dans la régulation de la motivation sexuelle et de l’érection, et les modèles génétiques générés, jusqu’à présent, dans le but d’élucider ses mécanismes d’action centraux.

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.

Serotonergic lesions of the periaqueductal gray, a primary source of serotonin to the nucleus paragigantocellularis, facilitate sexual behavior in male rats

While selective serotonin reuptake inhibitors (SSRIs) are widely used to treat anxiety and depression, they also produce profound disruptions of sexual function including delayed orgasm/ejaculation. The nucleus paragigantocellularis (nPGi), a primary source of inhibition of ejaculation in male rats, contains receptors for serotonin (5-HT). The ventrolateral periaqueductal gray (vlPAG) provides serotonin to this region, thus providing an anatomical and neurochemical basis for serotonergic regulation of the nPGi. We hypothesize that 5-HT acting at the nPGi could underlie the SSRI-induced inhibition of ejaculation in rodents. To this end, we produced 5-HT lesions of the source of 5-HT to the nPGi (the vlPAG) and examined sexual behavior. Removing the source of 5-HT to the nPGi facilitated genital reflexes, but not other aspects of sexual behavior, consistent with our hypothesis. Namely, 5-HT lesions produced a significant increase in the mean number of ejaculations and a significant decrease in ejaculation latency as compared to sham lesioned animals, while latency to mating and the post-ejaculatory interval did not differ. These data suggest that the serotonergic vlPAG-nPGi pathway is an important regulatory mechanism for the inhibition of ejaculation in rats and supports the hypothesis that this circuit contributes to SSRI-induced inhibition of ejaculation.

Excitotoxic lesions of the nucleus paragigantocellularis facilitate male sexual behavior but attenuate female sexual behavior in rats

Little is known regarding the descending inhibitory control of genital reflexes such as ejaculation and vaginal contractions. The brainstem nucleus paragigantocellularis (nPGi) projects bilaterally to the lumbosacral motoneuron pools that innervate the genital musculature of both male and female rats. Electrolytic nPGi lesions facilitate ejaculation in males, leading to the hypothesis that the nPGi is the source of descending inhibition to genital reflexes. However, the function of the nPGi in female sexual behavior remains to be elucidated. To this end, male and female rats received bilateral excitotoxic fiber-sparing lesions of the nPGi, and sexual behavior and sexual behavior-induced Fos expression were examined. In males, nPGi lesions facilitated copulation, supporting the hypothesis that the nPGi, and not fibers-of-passage, is the source of descending inhibition of genital reflexes in male rats. nPGi lesions in males did not alter sexual behavior-induced Fos expression in any brain region examined. nPGi-lesioned females spent significantly less time mating with stimulus males and had significantly longer ejaculation-return latencies compared to baseline. These results did not significantly differ from control females, but this trend warranted further analysis of the reinforcing value of sexual behavior. Both lesioned and non-lesioned females formed a conditioned place preference (CPP) for artificial vaginocervical stimulation (aVCS). However, post-reinforcement, nPGi-lesioned females did not differ in the percentage of time spent in the non-reinforced chamber versus the reinforced chamber, suggesting a weakened CPP for aVCS. nPGi lesions in females reduced sexual behavior-induced Fos expression throughout the hypothalamus and amygdala. Taken together, these results suggest that while nPGi lesions in males facilitate copulation, such lesions in females attenuate several aspects of sexual behavior resulting in a reduction in the rewarding value of copulation that may be mediated by nPGi control of genital reflexes. This work has important implications for the understanding and treatment of sexual dysfunction in people including delayed/premature ejaculation, involuntary vaginal spasms, and pain during intercourse.

Rapid regulation of brain oestrogen synthesis: the behavioural roles of oestrogens and their fates

Besides their well-known genomic actions, oestrogens also exert effects through the activation of receptors associated with the plasma membrane that are too fast to be mediated by transcriptional activation (nongenomic effects). Although the existence of such rapid effects of oestrogens and their involvement in various biological processes are not in doubt, questions remain about the mechanisms responsible for the rapid modulations of oestrogen production that are required to sustain their nongenomic effects. Recent data indicate that the conversion of androgens into oestrogens in the brain by the enzyme aromatase can be rapidly modulated by conformational changes of the enzyme, thus providing a possible mechanism for rapid controls of the effects of oestrogens on male sexual behaviour. In this review, the data supporting this hypothesis are described. Subsequently, a few unanswered questions are discussed, such as the mechanism of oestrogen inactivation or the potential cellular sites of action of brain-derived oestrogens on male sexual behaviour.

The posteromedial cortical amygdala regulates copulatory behavior, but not sexual odor preference, in the male Syrian hamster (Mesocricetus auratus)

In rodent species, the expression of reproductive behavior relies heavily on the perception of social odors, as well as the presence of circulating steroid hormones. In the Syrian hamster, chemosensory and hormonal cues are processed within an interconnected network of ventral forebrain nuclei that regulates many aspects of social behavior. Within this network, the posteromedial cortical amygdala (PMCo) receives direct projections from the accessory olfactory bulbs and contains a dense population of steroid receptor-containing neurons. Consequently, the PMCo may be important for generating odor-guided aspects of reproductive behavior, yet little is known regarding the role of this nucleus in regulating these behaviors. Thus, the present study tested male hamsters with site-specific electrolytic lesions of the PMCo for their (a) sexual odor preference in a Y-maze apparatus, (b) sexual odor discrimination in a habituation-dishabituation task, and (c) copulatory behavior when paired with a sexually receptive female. PMCo-lesioned males preferred to investigate female odors over male odors and were able to discriminate between these odor sources. However, PMCo lesions were associated with several alterations in the male copulatory pattern. First, PMCo-lesioned males displayed increased investigation of the female's non-anogenital region, suggesting that the PMCo may be involved in directing appropriate chemosensory investigation during mating. Second, PMCo lesions altered the temporal pattern of the mating sequence, as PMCo-lesioned males took longer than Sham-lesioned males to reach sexual satiety, as indicated by the delayed expression of long intromissions. This delayed onset of satiety was associated with an increased number of ejaculations compared with Sham-lesioned males. Importantly, these data provide the first direct evidence for a functional role of the PMCo in regulating male reproductive behavior.