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

Investigation of Relaxin-3 Serum Levels in terms of Social Interaction, Communication, and Appetite as a Biomarker in Children with Autism

Objective

To investigate the possible relationship between relaxin-3 and autism spectrum disorder (ASD).

Methods

Serum relaxin-3 was measured in 80 children (50 children diagnosed with ASD and 30 controls). Symptom severity in the ASD group was evaluated by the Childhood Autism Rating Scale (CARS). Behavioral and nutritional problems in the groups were evaluated using the Abnormal Behavior Checklist (ABC) and the Childrenʼs Eating Behavior Questionnaire (CEBQ).

Results

Our findings showed that serum relaxin-3 levels were higher in children with ASD than in the controls. The listening response sub-scale score of the CARS scale was found to decrease as the level of relaxin-3 increased. However, as relaxin-3 levels increased in children with ASD, it was found that the speech problem sub-scale score on the ABC scale and the desire to drink score on the CEBQ scale increased, but the satiety responsiveness and food fussiness scores decreased.

Conclusion

This study the first to investigate serum levels of relaxin-3, which has a role in regulating social behavior and nutritional behavior in children with ASD.

The Role of the Periaqueductal Gray Matter in Lower Urinary Tract Function

The periaqueductal gray matter (PAG), as one of the mostly preserved evolutionary components of the brain, is an axial structure modulating various important functions of the organism, including autonomic, behavioral, pain, and micturition control. It has a critical role in urinary bladder physiology, with respect to storage and voiding of urine. The PAG has a columnar composition and has extensive connections with its cranially and caudally located components of the central nervous system (CNS). The PAG serves as the control tower of the detrusor and sphincter contractions. It serves as a bridge between the evolutionary higher decision-making brain centers and the lower centers responsible for reflexive micturition. Glutamatergic cells are the main operational neurons in the vlPAG, responsible for the reception and relay of the signals emerging from the bladder, to related brain centers. Functional imaging studies made it possible to clarify the activity of the PAG in voiding and filling phases of micturition, and its connections with various brain centers in living humans. The PAG may be affected in a wide spectrum of disorders, including multiple sclerosis (MS), migraine, stroke, Wernicke’s encephalopathy, and idiopathic normal pressure hydrocephalus, all of which may have voiding dysfunction or incontinence, in certain stages of the disease. This emphasizes the importance of this structure for the basic understanding of voiding and storage disorders and makes it a potential candidate for diagnostic and therapeutic interventions.

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.

Relaxin-3/RXFP3 networks: an emerging target for the treatment of depression and other neuropsychiatric diseases?

Animal and clinical studies of gene-environment interactions have helped elucidate the mechanisms involved in the pathophysiology of several mental illnesses including anxiety, depression, and schizophrenia; and have led to the discovery of improved treatments. The study of neuropeptides and their receptors is a parallel frontier of neuropsychopharmacology research and has revealed the involvement of several peptide systems in mental illnesses and identified novel targets for their treatment. Relaxin-3 is a newly discovered neuropeptide that binds, and activates the G-protein coupled receptor, RXFP3. Existing anatomical and functional evidence suggests relaxin-3 is an arousal transmitter which is highly responsive to environmental stimuli, particularly neurogenic stressors, and in turn modulates behavioral responses to these stressors and alters key neural processes, including hippocampal theta rhythm and associated learning and memory. Here, we review published experimental data on relaxin-3/RXFP3 systems in rodents, and attempt to highlight aspects that are relevant and/or potentially translatable to the etiology and treatment of major depression and anxiety. Evidence pertinent to autism spectrum and metabolism/eating disorders, or related psychiatric conditions, is also discussed. We also nominate some key experimental studies required to better establish the therapeutic potential of this intriguing neuromodulatory signaling system, including an examination of the impact of RXFP3 agonists and antagonists on the overall activity of distinct or common neural substrates and circuitry that are identified as dysfunctional in these debilitating brain diseases.

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.

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.

Cavernous hemangioma of the mesencephalon: tonsillouveal transaqueductal approach

OBJECTIVE

Recent advances in microsurgical techniques facilitate surgical resection of brainstem lesions that were previously considered inoperable. In this article we present, for the first time, the tonsillouveal transaqueductal approach to access a progressively symptomatic cavernoma within the depth of the tegmentum of the mesencephalon.

METHODS

A 52-year-old woman presented with a history of slowly progressive right-sided hemiparesis and ataxia. On magnetic resonance imaging, a relatively large cavernoma involving the tegmentum of the mesencephalon was shown. The sylvian aqueduct was patent and there was no secondary ventriculomegaly. The patient underwent surgery via a suboccipital craniotomy and C1 laminectomy. The right tonsillouveal and medullotonsillar spaces were opened to the level of the choroidal point of the posteroinferior cerebellar artery. The tela choroidea was incised from the foramen of Magendie to the telovelar junction. Looking through the aqueduct and at a point 5 mm superior to its inferior inlet, there was a small cherry-like blister protruding into the aqueductal anterior surface. This was used as an entry point to access the cavernoma. The space around the cavernoma was gently dissected and the cavernoma was circumferentially coagulated to shrink it in a concentric manner toward its center.

RESULTS

The total removal of the lesion was achieved and the histopathological findings were consistent with a cavernoma. As a result of noncommunicating hydrocephalus, the patient needed a ventriculoperitoneal shunt. The 1-year postoperative neurological examination was consistent with preoperative findings.

CONCLUSION

This report shows, for the first time, direct surgical removal of a cavernous hemangioma in the mesencephalic tegmentum via the aqueduct. This approach adds to contemporary microneurosurgery, respecting functional anatomy and minimizing neurological deficits.

Zaprinast, a phosphodiesterase type-5 inhibitor, alters paced mating behavior in female rats

Nitric oxide (NO) is the primary mediator of blood flow in female genital tissues and drugs that enhance the activity of nitric oxide, such as phosphodiesterase type-5 (PDE-5) inhibitors, increase vaginal blood flow in anesthetized rats. The goal of the present study was to test the effects of one PDE-5 inhibitor, zaprinast, on the display of sexual behaviors in gonadectomized, estrogen- and progesterone-treated female rats. Experiment 1 demonstrates that zaprinast alters paced mating behavior by lengthening the contact-return latency to ejaculation; there is a significant relationship between dose of zaprinast (range 1.5-6 mg/kg) and contact-return latency to ejaculation. Experiment 2 illustrates that zaprinast has no effect on preference for an intact male as measured in a No Contact partner preference test. Rats receiving zaprinast tend to exhibit reduced locomotor activity in both experiments. Collectively, these findings demonstrate that modulation of the NO-cGMP pathway using a PDE-5 inhibitor alters the display of paced mating behaviors in rats.

Clitoral sexual arousal: neuronal tracing study from the clitoris through the spinal tracts

PURPOSE

Although genital tactile stimulation is regarded as a precursor to sexual arousal and a recognized initiator of central nervous system arousal, specific afferent neural pathways transmit sensory stimuli of arousal, beginning at the epithelial level on the clitoris and following the course of arousal stimuli through the central nervous system. Limited knowledge exists of the pathway from the cutaneous receptors of nerves originating in the epithelial tissue of the clitoris and continuing to spinal cord afferents. Such information may contribute to an understanding of sexual arousal, particularly in female vertebrates. We further defined the neural pathways and mechanisms responsible for arousal originating in the epithelium of the clitoris as well as related neural pathways to the spinal cord in a murine model.

MATERIALS AND METHODS

We performed a comprehensive review of the published relevant clinical and histological material from human and nonhuman vertebrate studies. In 29 adult female C57B1/6 mice the distribution of pelvic nerves and vessels was mapped. Gross dissection of 4 female mice was facilitated by resin injection of the vascular system in 2. Neuronal tracing was performed in 25 mice that received clitoral injection of wheat germ agglutinin-horseradish peroxidase into the clitoris and were sacrificed after 72 to 96 hours. The spinal cord and periclitoral tissue were removed and fixed. Immunohistochemistry was performed.

RESULTS

Gross anatomy of the mouse clitoris showed that pudendal and hypogastric nerves have a major role in the innervation of the external genitalia. Neuronal tracing revealed that the greatest nerve density was noted in the L5/6 spinal cord. The distribution extended from S1 to L2 with no labeling seen in the L3 spinal cord. Wheat germ agglutinin-horseradish peroxidase labeling was seen caudal in levels S1 through L4 and rostral in L2.

CONCLUSIONS

Understanding the neuroanatomy of the clitoris using a murine model may provide a valuable tool for the study of sexual arousal disorders and the further understanding of sexual function related to neural pathologies and trauma.

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.

Organization of brain somatomotor-sympathetic circuits

Numerous physiological and emotionally motivated behaviors require concomitant activation of somatomotor and sympathetic efferents. Likewise, adaptive and maladaptive responses to stress are often characterized by simultaneous recruitment of these efferent systems. This review describes recent literature that outlines the organization of somatomotor-sympathetic circuitry in the rat. These circuits were delineated by employing recombinant pseudorabies (PRV) viral vectors as retrograde trans-synaptic tract tracers. In these studies PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized hindlimb muscle, while PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. Immunofluorescent methods were then used to determine the presence of putative dual-function neurons that were infected with both viral strains. These somatomotor-sympathetic neurons (SMSNs) were detected in a number of brain regions. However, the most prominent nodes in this circuitry included the paraventricular, dorsomedial, and lateral nuclei of the hypothalamus, ventrolateral periaqueductal grey and ventromedial medulla. Phenotypic studies revealed subsets of SMSNs to be capable of synthesizing serotonin, or to contain neuroactive peptides vasopressin, oxytocin, orexins, or melanin-concentrating hormone. Based on these data and the results of studies employing monosynaptic tracers a central somatomotor-sympathetic circuit is proposed. This circuitry is likely recruited in diverse situations, including stress responses, cold defense, exercise and sleep. Furthermore, activation of specific classes of SMSNs likely shapes distinct stress-coping strategies. Dysregulation in the organization and function of this circuit may also contribute to the expression of physical symptoms of affective disorders, such as major depression, anxiety and panic.

Penile erection and micturition events triggered by electrical stimulation of the mesopontine tegmental area

The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) play a crucial role in the regulation of rapid eye movement (REM) sleep. Because penile erection occurs during REM sleep, the involvement of the LDT in penile erection was examined in unanesthetized head-restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced the following three CSP pressure patterns: 1) a full erection pattern indistinguishable from the nonevoked or spontaneous erection, characterized by a slow increase in CSP pressure with additional sharp CSP peaks associated with BS muscle bursts, 2) a muscular pattern characterized by sharp CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, and 3) a mixed-type response characterized by high-frequency CSP pressure peaks followed by a full erection response. Full erections were evoked in and around the LDT, including more medially and ventrally. The sites for inducing mixed-type events were intermingled with the sites that triggered full erections in the anterior half of the LDT, whereas they were separated in the posterior half. The sites for muscular responses were lateral to the sites for full erections. Finally, a CSP pressure response identical to micturition was evoked in and around the Barrington's nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in the regulation of penile erection. Moreover, different anatomical areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.

Arousing Properties of the Vulvar Epithelium

PURPOSE

The initiation of genital tactile stimulation is regarded as a precursor to sexual arousal and perhaps in women it is the most easily recognized initiator of central nervous system arousal. Unfortunately little published material details the specific mechanisms preceding arousal, beginning at the epithelial level, which are the sensory precursors to arousal. Little is known about its cutaneous receptors, nerves and the other histochemical properties of this epithelial tissue that contribute to sexual arousal. Sexual sensitivity evaluations target female genital somatosensory pathways for cutaneous sensation by testing evoked potentials of nerves, hot/cold and vibratory sensory discrimination. The anatomical bases of these several sensibilities form a subject for future investigation. We reviewed the known influences and mechanisms responsible for the arousing properties of the epithelium in the female external genitalia as well neural pathways associated with sexual arousal originating from the vulvar epithelium.

MATERIALS AND METHODS

A comprehensive review was done of published, relevant clinical and histological material in human and nonhuman vertebrate studies.

RESULTS

Tactile stimulation of the vulvar epithelium initiates changes suggesting complex integrative mechanisms. Influences of skin temperature, hormonal environment, mechanical tissue compliance and inflammation as well as the large number of transmitters and neuropeptides involved in peripheral pathways serving female sexual arousal speak of a direct sensory role.

CONCLUSIONS

Genital epithelial cells may actively participate in sensory function to initiate sexual arousal by expressing receptors and releasing neurotransmitters in response to stimuli, resulting in epithelial-neuronal interactions.

Androgens regulate the sexually dimorphic production of co-contained galanin and cholecystokinin in lumbar laminae VII and X neurons

A population of rat lumbar laminae VII and X putative spinothalamic (STT) neurons that co-contain cholecystokinin-8 (CCK) and galanin (GAL) are sexually dimorphic. Males have a significantly greater number of these neurons, as well as having greater optical densities for both neuropeptides than females. Optical densities for GAL and CCK immunoreactivities in these lumbar neurons in rats that have the testicular feminization mutation (Tfm) are not significantly different from females; however, the number of these lumbar neurons in Tfm rats is significantly smaller than in females. These data suggest that androgens, as well as functional androgen receptors (that Tfm rats lack), are necessary for the establishment of these sexual dimorphisms. Functionally, these CCK- and GAL-containing neurons in the deep lumbar laminae may contribute to the establishment of known sex differences in the affective component of somatic and visceral nociception, as well as the sexually dimorphic nature of some pelvic diseases, e.g., irritable bowel syndrome or cystitis.

Rostral elements of sympatho-motor circuitry: a virally mediated transsynaptic tracing study

Numerous physiological and emotionally motivated behaviors, including locomotion, exercise, escape, and attack behaviors as well as passive coping responses, require concomitant activation of motor and sympathetic efferents. Such functional heterogeneity suggests the existence of dual function neurons that can simultaneously coordinate motor and sympathetic output. Because previous physiological investigations have implicated a number of mesencephalic and telencephalic regions in mediating these behaviors, we hypothesized the presence of dual function sympatho-motor neurons in these neural structures. To test this hypothesis, we used recombinant strains of the pseudorabies virus (PRV) for transsynaptic tract-tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, whereas PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. Although coinfected neurons were detected in a number of mesencephalic and telencephalic regions, >50% of such neurons were located within specific subdivisions of two general areas: the hypothalamus and periaqueductal gray. These subdivisions included the ventrolateral periaqueductal gray, dorsomedial hypothalamus, dorsolateral lateral hypothalamus, and ventral portion of the medial parvocellular subdivision of the paraventricular nucleus of the hypothalamus (PVN). A subset of the sympatho-motor neurons within the PVN also contained either arginine vasopressin or oxytocin. This sympatho-motor circuitry likely plays an important role in mediating different aspects of stress responses and emotionally motivated behaviors.

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.

Sympathetic genital responses induced by p-chloroamphetamine in anaesthetized female rats

In urethane-anesthetized female rats, a branch of the hypogastric nerve equivalent to the vas deferens nerve in males was shown anatomically and electrophysiologically to supply the uterine horns and we have consequently termed this the uterine nerve. Administration of p-chloroamphetamine i.v. elicited patterned bursting uterine nerve activity responses together with contractions of the uterine horns and musculature of the vaginal wall. These responses are qualitatively similar to ejaculatory responses observed following p-chloroamphetamine administration to anesthetized male rats and the urethrogenital reflex in females, suggesting they represent responses occurring during sexual processes. This response to p-chloroamphetamine was still present after complete transection of the spinal cord at T8. These data indicate that common neurophysiological and pharmacological mechanisms regulate genital reflexes at the lumbosacral spinal level in both the female and the male rat.

Olfactory inputs to hypothalamic neurons controlling reproduction and fertility

In order to gain insight into sensory processing modulating reproductive behavioral and endocrine changes, we have aimed at identifying afferent pathways to neurons synthesizing luteinizing hormone-releasing hormone (LHRH, also known as gonadotropin-releasing hormone [GnRH]), a key neurohormone of reproduction. Injection of conditional pseudorabies virus into the brain of an LHRH::CRE mouse line led to the identification of neuronal networks connected to LHRH neurons. Remarkably, and in contrast to established notions on the nature of LHRH neuronal inputs, our data identify major olfactory projection pathways originating from a discrete population of olfactory sensory neurons but fail to document any synaptic connectivity with the vomeronasal system. Accordingly, chemosensory modulation of LHRH neuronal activity and mating behavior are dramatically impaired in absence of olfactory function, while they appear unaffected in mouse mutants lacking vomeronasal signaling. Further visualization of afferents to LHRH neurons across the brain offers a unique opportunity to uncover complex polysynaptic circuits modulating reproduction and fertility.

Central nervous system control of ejaculation

An overview is given of the regions in the spinal cord that are active during ejaculation. Motoneurons involved are the preganglionic sympathetic motoneurons in the upper lumbar spinal cord and the motoneurons in the nucleus of Onuf, located in the upper sacral cord. The first group is involved in the so-called emission phase of ejaculation, the last group in the expulsion phase. Both groups receive afferents from premotor interneurons in the so-called intermediomedial cell groups located at about the same level as the motoneurons themselves. A concept is put forward in which these premotor cell groups represent the central spinal pattern generators for ejaculation, one for the emission phase and one for the expulsion phase. Clinical observations in patients suffering from transection of the spinal cord indicate that the ejaculation motoneurons as well as their spinal central pattern generators are under strong influence of descending pathways originating in supraspinal parts of the brain. The various pathways possibly involved in ejaculation control are reviewed. Finally, the results of the brain activation of a PET-scan study in human males, ejaculating after penile stimulation by their female partner are discussed. Especially the ventral tegmental area and the cerebellum seem to be activated during ejaculation, while the amygdala region is deactivated. Apparently, a general lack of fear is necessary for ejaculation to occur.

Afferent projections to the pontine micturition center in the cat

The pontine micturition center (PMC) or Barrington's nucleus controls micturition by way of its descending projections to the sacral spinal cord. However, little is known about the afferents to the PMC that control its function and may be responsible for dysfunction in patients with urge-incontinence and overactive bladder. In five female cats, wheatgerm agglutinin-conjugated horseradish peroxidase (WGA-HRP) injections were made in the PMC and adjoining dorsolateral pontine tegmentum. Retrogradely labeled neurons were found in a large area, including the medullary and pontine medial and lateral tegmental field; dorsomedial, lateral, and ventrolateral periaqueductal gray matter (PAG); posterior hypothalamus; medial preoptic area (MPO); bed nucleus of the stria terminalis; central nucleus of the amygdala; and infralimbic, prelimbic, and insular cortices. To verify whether these areas indeed project specifically to the PMC or perhaps only to adjacent structures in the pontine tegmentum, in 67 cats (3)H-leucine or WGA-HRP injections were made in each of these regions. Five cell groups appeared to have direct connections to the PMC, the ventromedial pontomedullary tegmental field, the ventrolateral and dorsomedial PAG, the MPO, and the posterior hypothalamus. The possible functions of these projections are discussed. These results indicate that all other parts of the brain that influence micturition have no direct connection with the PMC.

Lesions of the periaqueductal gray block the medial preoptic area-induced activation of the urethrogenital reflex in male rats

The medial preoptic area (MPOA) is important for male sexual behavior, including erections and ejaculation. Stimulation of the MPOA evokes urethrogenital reflex-like responses. However, the descending pathways mediating this response are unknown. We examined the effect of bilateral lesions of the periaqueductal gray (PAG) on the MPOA-induced response. Electrical stimulation of the MPOA was used to induce rhythmic motor patterns of the bulbospongiosus muscle, discrete regions of the PAG were lesioned and the response to MPOA stimulation re-examined. These studies demonstrate that the descending pathway mediating the MPOA-induced activation of the urethrogenital reflex-like responses travel through and may relay in the PAG.