Reciprocal connections between the medial preoptic area and the midbrain periaqueductal gray in rat: A WGA-HRP and PHA-L study

Distinct patterns of activity within columns of the periaqueductal gray are associated with functionally distinct birdsongs

Male songbirds produce female-directed songs in spring that convey a state of sexual motivation. Many songbirds also sing in fall flocks in affiliative/gregarious contexts in which song is linked to an intrinsic positive affective state. The periaqueductal gray (PAG) in mammals, which is organized into functional columns, integrates information from multiple brain regions and relays this information to vocal motor areas so that an animal emits a vocal signal reflective of its affective state. Here, we test the hypothesis that distinct columns in the songbird PAG play roles in the distinct affective states communicated by sexually motivated and gregarious song. We quantified the numbers of immediate early gene ZENK-positive cells in 16 PAG subregions in male European starlings (Sturnus vulgaris) after singing gregarious or sexually motivated song. Results suggest that distinct PAG columns in songbirds context-specifically regulate song, agonistic, and courtship behaviors. A second exploratory, functional tract-tracing study also demonstrated that inputs to the PAG from specific subregions of the medial preoptic nucleus may contribute to gregarious song and behaviors indicative of social dominance. Together, findings suggest that conserved PAG columns and inputs from the preoptic nucleus may play a role in context-specific vocal and other social behaviors.

Whole-brain monosynaptic inputs to lateral periaqueductal gray glutamatergic neurons in mice

OBJECTIVE

The lateral periaqueductal gray (LPAG), which mainly contains glutamatergic neurons, plays an important role in social responses, pain, and offensive and defensive behaviors. Currently, the whole-brain monosynaptic inputs to LPAG glutamatergic neurons are unknown. This study aims to explore the structural framework of the underlying neural mechanisms of LPAG glutamatergic neurons.

METHODS

This study used retrograde tracing systems based on the rabies virus, Cre-LoxP technology, and immunofluorescence analysis.

RESULTS

We found that 59 nuclei projected monosynaptic inputs to the LPAG glutamatergic neurons. In addition, seven hypothalamic nuclei, namely the lateral hypothalamic area (LH), lateral preoptic area (LPO), substantia innominata (SI), medial preoptic area, ventral pallidum, posterior hypothalamic area, and lateral globus pallidus, projected most densely to the LPAG glutamatergic neurons. Notably, we discovered through further immunofluorescence analysis that the inputs to the LPAG glutamatergic neurons were colocalized with several markers related to important neurological functions associated with physiological behaviors.

CONCLUSION

The LPAG glutamatergic neurons received dense projections from the hypothalamus, especially nuclei such as LH, LPO, and SI. The input neurons were colocalized with several markers of physiological behaviors, which show the pivotal role of glutamatergic neurons in the physiological behaviors regulation by LPAG.

Orchestration of innate and conditioned defensive actions by the periaqueductal gray

The midbrain periaqueductal gray (PAG) has been recognized for decades as having a central role in the control of a wide variety of defensive responses. Initial discoveries relied primarily on lesions, electrical stimulation and pharmacology. Recent developments in neural activity imaging and in methods to control activity with anatomical and genetic specificity have revealed additional streams of data informing our understanding of PAG function. Here, we discuss both classic and modern studies reporting on how PAG-centered circuits influence innate as well as learned defensive actions in rodents and humans. Though early discoveries emphasized the PAG's role in rapid induction of innate defensive actions, emerging new data indicate a prominent role for the PAG in more complex processes, including representing behavioral states and influencing fear learning and memory. This article is part of the Special Issue on "Fear, Anxiety and PTSD".

Induction of flight via midbrain projections to the cuneiform nucleus

The dorsal periaqueductal gray is a midbrain structure implicated in the control of defensive behaviors and the processing of painful stimuli. Electrical stimulation or optogenetic activation of excitatory neurons in dorsal periaqueductal gray results in freezing or flight behavior at low and high intensity, respectively. However, the output structures that mediate these defensive behaviors remain unconfirmed. Here we carried out a targeted classification of neuron types in dorsal periaqueductal gray using multiplex in situ sequencing and then applied cell-type and projection-specific optogenetic stimulation to identify projections from dorsal periaqueductal grey to the cuneiform nucleus that promoted goal-directed flight behavior. These data confirmed that descending outputs from dorsal periaqueductal gray serve as a trigger for directed escape behavior.

Neural activation associated with maternal and aversive interactions with pups in the Mongolian gerbil (Meriones unguiculatus)

According to approach-avoidance model, virgin female laboratory rats display maternal behaviour when the tendency to approach and interact with the pup is stronger than avoiding it. A positive neural mechanism that includes the medial preoptic area (mPOA)/bed nucleus of the stria terminalis (BNST) and a negative mechanism that involves the anterior hypothalamic nucleus (AHN)/ventromedial nucleus (VMN)/ periaqueductal grey (PAG) underlie to these behaviours. Unlike virgin rats, which avoid the pups, virgin females Mongolian gerbils (Meriones unguiculatus) can be immediately either maternal or aggressive with the pups. Furthermore, the Mongolian gerbil is monogamous and biparental species. Despite these difference, we hypothesised that maternal and aggressive interaction with the pups could activate mPOA/BNST and AHN/VMH/PAG, respectively, and that maternal response could be associated with high concentrations of estradiol (E₂). Twenty virgin maternal females and 20 aggressive toward the pups were selected. Ten maternal females interacted with the pups (MAT-pups) and 10 with candy (MAT-candy). Of the 20 aggressive females, 10 interacted with the pups (AGG-pups) and 10 with candy (AGG-candy). Immediately after the test, blood samples were taken to quantify E₂. The brains were dissected for c-Fos immunohistochemistry. MAT-pups females had significantly higher activation in mPOA/BNST than MAT-candy females, while AGG-pups showed significant activation in AHN/VMH/PAG compared with AGG-candy females. The maternal response was associated with high concentrations of E₂. These results suggested a positive and a negative mechanism in the regulation of maternal behaviour in the Mongolian gerbil, and that the immediate maternal response could be due to high E₂ concentrations.

Exploration driven by a medial preoptic circuit facilitates fear extinction in mice

Repetitive exposure to fear-associated targets is a typical treatment for patients with panic or post-traumatic stress disorder (PTSD). The success of exposure therapy depends on the active exploration of a fear-eliciting target despite an innate drive to avoid it. Here, we found that a circuit running from CaMKIIα-positive neurons of the medial preoptic area to the ventral periaqueductal gray (MPA-vPAG) facilitates the exploration of a fear-conditioned zone and subsequent fear extinction in mice. Activation or inhibition of this circuit did not induce preference/avoidance of a specific zone. Repeated entries into the fear-conditioned zone, induced by the motivation to chase a head-mounted object due to MPA-vPAG circuit photostimulation, facilitated fear extinction. Our results show how the brain forms extinction memory against avoidance of a fearful target and suggest a circuit-based mechanism of exposure therapy.

Thermoregulation and Sleep: Functional Interaction and Central Nervous Control

Each of the wake-sleep states is characterized by specific changes in autonomic activity and bodily functions. The goal of such changes is not always clear. During non-rapid eye movement (NREM) sleep, the autonomic outflow and the activity of the endocrine system, the respiratory system, the cardiovascular system, and the thermoregulatory system seem to be directed at increasing energy saving. During rapid eye movement (REM) sleep, the goal of the specific autonomic and regulatory changes is unclear, since a large instability of autonomic activity and cardiorespiratory function is observed in concomitance with thermoregulatory changes, which are apparently non-functional to thermal homeostasis. Reciprocally, the activation of thermoregulatory responses under thermal challenges interferes with sleep occurrence. Such a double-edged and reciprocal interaction between sleep and thermoregulation may be favored by the fact that the central network controlling sleep overlaps in several parts with the central network controlling thermoregulation. The understanding of the central mechanism behind the interaction between sleep and thermoregulation may help to understand the functionality of thermoregulatory sleep-related changes and, ultimately, the function(s) of sleep. © 2021 American Physiological Society. Compr Physiol 11:1591-1604, 2021.

Opioid use during pregnancy can impair maternal behavior and the Maternal Brain Network: A literature review

Opioid Use Disorder (OUD) is a global epidemic also affecting women of reproductive age. A standard form of pharmacological treatment for OUD is Opioid Maintenance Therapy (OMT) and buprenorphine has emerged as the preferred treatment for pregnant women with OUD relative to methadone. However, the consequences of BUP exposure on the developing Maternal Brain Network and mother-infant dyad are not well understood. The maternal-infant bond is dependent on the Maternal Brain Network, which is responsible for the dynamic transition from a "nulliparous brain" to a "maternal brain". The Maternal Brain Network consists of regions implicated in maternal care (e.g., medial preoptic area, nucleus accumbens, ventral pallidum, ventral tegmentum area) and maternal defense (e.g., periaqueductal gray). The endogenous opioid system modulates many of the neurochemical changes in these areas during the transition to motherhood. Thus, it is not surprising that exogenous opioid exposure during pregnancy can be disruptive to the Maternal Brain Network. Though less drastic than misused opioids, OMTs may not be without risk of disrupting the neural and molecular structures of the Maternal Brain Network. This review describes the Maternal Brain Network as a framework for understanding how pharmacological differences in exogenous opioid exposure can disrupt the onset and maintenance of the maternal brain and summarizes opioid and OMT (in particular buprenorphine) use in the context of pregnancy and maternal behavior. This review also highlights future directions for evaluating exogenous opioid effects on the Maternal Brain Network in the hopes of raising awareness for the impact of the opioid crisis not only on exposed infants, but also on mothers and subsequent mother-infant bonds.

A Scientometric Approach to Review the Role of the Medial Preoptic Area (MPOA) in Parental Behavior

Research investigating the neural substrates underpinning parental behaviour has recently gained momentum. Particularly, the hypothalamic medial preoptic area (MPOA) has been identified as a crucial region for parenting. The current study conducted a scientometric analysis of publications from 1 January 1972 to 19 January 2021 using CiteSpace software to determine trends in the scientific literature exploring the relationship between MPOA and parental behaviour. In total, 677 scientific papers were analysed, producing a network of 1509 nodes and 5498 links. Four major clusters were identified: “C-Fos Expression”, “Lactating Rat”, “Medial Preoptic Area Interaction” and “Parental Behavior”. Their content suggests an initial trend in which the properties of the MPOA in response to parental behavior were studied, followed by a growing attention towards the presence of a brain network, including the reward circuits, regulating such behavior. Furthermore, while attention was initially directed uniquely to maternal behavior, it has recently been extended to the understanding of paternal behaviors as well. Finally, although the majority of the studies were conducted on rodents, recent publications broaden the implications of previous documents to human parental behavior, giving insight into the mechanisms underlying postpartum depression. Potential directions in future works were also discussed.

Significance of medial preoptic area among the subcortical and cortical areas that are related to pain regulation in the rats with stress-induced hyperalgesia

Psychophysical stresses frequently increase sensitivity and response to pain, which is termed stress-induced hyperalgesia (SIH). However, the mechanism remains unknown. The subcortical areas such as medial preoptic area (MPO), dorsomedial nucleus of the hypothalamus (DMH), basolateral (BLA) and central nuclei of the amygdala (CeA), and the cortical areas such as insular (IC) and anterior cingulate cortices (ACC) play an important role in pain control via the descending pain modulatory system. In the present study we examined the expression of phosphorylated -cAMP-response element binding protein (pCREB) and the acetylation of histone H3 in these subcortical and cortical areas after repeated restraint stress to reveal changes in the subcortical and cortical areas that affect the function of descending pain modulatory system in the rats with SIH. The repeated restraint stress for 3 weeks induced a decrease in mechanical threshold in the rat hindpaw, an increase in the expression of pCREB in the MPO and an increase in the acetylation of histone H3 in the MPO, BLA and IC. The MPO was the only area that showed an increase in both the expression of pCREB and the acetylation of histone H3 among these examined areas after the repeated restraint stress. Furthermore, the number of pCREB-IR or acetylated histone H3-IR cells in the MPO was negatively correlated with the mechanical threshold. Together, our data represent the importance of the MPO among the subcortical and cortical areas that control descending pain modulatory system under the condition of SIH.

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.

Neural control of fasting-induced torpor in mice

Torpor is a peculiar mammalian behaviour, characterized by the active reduction of metabolic rate, followed by a drop in body temperature. To enter torpor, the activation of all thermogenic organs that could potentially defend body temperature must be prevented. Most of these organs, such as the brown adipose tissue, are controlled by the key thermoregulatory region of the Raphe Pallidus (RPa). Currently, it is not known which brain areas mediate the entrance into torpor. To identify these areas, the expression of the early gene c-Fos at torpor onset was assessed in different brain regions in mice injected with a retrograde tracer (Cholera Toxin subunit b, CTb) into the RPa region. The results show a network of hypothalamic neurons that are specifically activated at torpor onset and a direct torpor-specific projection from the Dorsomedial Hypothalamus to the RPa that could putatively mediate the suppression of thermogenesis during torpor.

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.

REM Sleep and Endothermy: Potential Sites and Mechanism of a Reciprocal Interference

Numerous data show a reciprocal interaction between REM sleep and thermoregulation. During REM sleep, the function of thermoregulation appears to be impaired; from the other hand, the tonic activation of thermogenesis, such as during cold exposure, suppresses REM sleep occurrence. Recently, both the central neural network controlling REM sleep and the central neural network controlling thermoregulation have been progressively unraveled. Thermoregulation was shown to be controlled by a central “core” circuit, responsible for the maintenance of body temperature, modulated by a set of accessory areas. REM sleep was suggested to be controlled by a group of hypothalamic neurons overlooking at the REM sleep generating circuits within the brainstem. The two networks overlap in a few areas, and in this review, we will suggest that in such overlap may reside the explanation of the reciprocal interaction between REM sleep and thermoregulation. Considering the peculiar modulation of thermoregulation by REM sleep the result of their coincidental evolution, REM sleep may therefore be seen as a period of transient heterothermy.

The initial fall in arterial pressure evoked by endotoxin is mediated by the ventrolateral periaqueductal gray

This study tested the hypothesis that the initial fall in arterial pressure evoked by lipopolysaccharide (LPS) is mediated by the ventrolateral column of the midbrain periaqueductal gray region (vlPAG). To test this hypothesis, the local anaesthetic lidocaine (2%; 0.1 μL, 0.2 μL or 1.0 μL), the delta opioid receptor antagonist naltrindole (2 nmol) or saline was microinjected into the vlPAG of isoflurane-anaesthetized rats bilaterally and LPS (1 mg/kg) or saline was administered intravenously 2 min later. Both lidocaine and naltrindole inhibited LPS-evoked hypotension significantly but did not affect arterial pressure in saline-treated control animals. Neither lidocaine nor naltrindole altered heart rate significantly in either LPS-treated or control animals. Microinjection of lidocaine or naltrindole into the dorsolateral PAG was ineffective. These data indicate that the vlPAG plays an important role in the initiation of endotoxic hypotension and further show that delta opioid receptors in the vlPAG participate in the response.

Alterations in the brainstem volume of patients with major depressive disorder and their relationship with antidepressant treatment

BACKGROUND

Morphologic changes of the brainstem in major depressive disorder (MDD) have rarely been reported in neuroimaging studies, even though, monoaminergic neurotransmitters are synthesized in several brainstem regions. We aimed to investigate volume changes in each region of the brainstem and their association with antidepressant use or the remission status of MDD.

METHODS

A total of 126 patients with MDD and 101 healthy controls underwent T1-weighted structural magnetic resonance imaging. We analyzed volumes of each brainstem region, including the medulla oblongata, pons, midbrain, and superior cerebellar peduncle, and the volume of the whole brainstem using the FreeSurfer.

RESULTS

The patients with MDD had significantly greater midbrain volumes (P=0.013) compared to healthy controls. In particular, drug-naïve patients with MDD had significantly greater brainstem volumes compared to healthy controls (P=0.007), while no significant findings were observed between the antidepressant treatment group and healthy controls. The remitted patient group had reduced pons (P=0.002) and midbrain (P=0.005) volumes compared to healthy controls, while the non-remitted MDD patient group had significantly greater midbrain volumes compared to the healthy controls (P=0.017).

LIMITATIONS

We could not distinguish gray versus white matter volumes changes in our analysis.

CONCLUSIONS

We observed that the midbrain is enlarged in patients with a current depressive episode, who are not undergoing antidepressant treatment. This volume then returns to normal after antidepressant treatment, and is even reduced, when the patient is in remission. Further studies are needed to confirm our observations.

Normal male sexual function: emphasis on orgasm and ejaculation

Orgasm and ejaculation are two separate physiological processes that are sometimes difficult to distinguish. Orgasm is an intense transient peak sensation of intense pleasure creating an altered state of consciousness associated with reported physical changes. Antegrade ejaculation is a complex physiological process that is composed of two phases (emission and expulsion), and is influenced by intricate neurological and hormonal pathways. Despite the many published research projects dealing with the physiology of orgasm and ejaculation, much about this topic is still unknown. Ejaculatory dysfunction is a common disorder, and currently has no definitive cure. Understanding the complex physiology of orgasm and ejaculation allows the development of therapeutic targets for ejaculatory dysfunction. In this article, we summarize the current literature on the physiology of orgasm and ejaculation, starting with a brief description of the anatomy of sex organs and the physiology of erection. Then, we describe the physiology of orgasm and ejaculation detailing the neuronal, neurochemical, and hormonal control of the ejaculation process.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

The OVLT initiates the fall in arterial pressure evoked by high dose lipopolysaccharide: evidence that dichotomous, dose-related mechanisms mediate endotoxic hypotension

This study tested the hypothesis that lipopolysaccharide (LPS) lowers arterial pressure through two different mechanisms depending on the dose. Previously, we found that a low hypotensive dose of LPS (1mg/kg) lowers arterial pressure by activating vagus nerve afferents. Here we report that hypotension evoked by high dose LPS (15mg/kg) can be prevented by injecting lidocaine into the OVLT but not by vagotomy or inactivation of the NTS. The hypotension produced by both LPS doses was correlated with elevated extracellular norepinephrine concentrations in the POA and prevented by blocking alpha-adrenergic receptors. Thus, initiation of endotoxic hypotension is dose-related, mechanistically.

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.

Predator odor stress alters corticotropin-releasing factor-1 receptor (CRF1R)-dependent behaviors in rats

Humans with stress-related anxiety disorders exhibit increases in arousal and alcohol drinking, as well as altered pain processing. Our lab has developed a predator odor stress model that produces reliable and lasting increases in alcohol drinking. Here, we utilize this predator odor stress model to examine stress-induced increases in arousal, nociceptive processing, and alcohol self-administration by rats, and also to determine the effects of corticotropin-releasing factor-1 receptors (CRF1Rs) in mediating these behavioral changes. In a series of separate experiments, rats were exposed to predator odor stress, then tested over subsequent days for thermal nociception in the Hargreaves test, acoustic startle reactivity, or operant alcohol self-administration. In each experiment, rats were systemically injected with R121919, a CRF1R antagonist, and/or vehicle. Predator odor stress increased thermal nociception (i.e., hyperalgesia) and acoustic startle reactivity. Systemic administration of R121919 reduced thermal nociception and hyperarousal in stressed rats but not unstressed controls, and reduced operant alcohol responding over days. Stressed rats exhibited increased sensitivity to the behavioral effects of R121919 in all three tests, suggesting up-regulation of brain CRF1Rs number and/or function in stressed rats. These results suggest that post-stress alcohol drinking may be driven by a high-nociception high-arousal state, and that brain CRF1R signaling mediates these stress effects.

Vocal-motor and auditory connectivity of the midbrain periaqueductal gray in a teleost fish

The midbrain periaqueductal gray (PAG) plays a central role in the descending control of vocalization across vertebrates. The PAG has also been implicated in auditory-vocal integration, although its precise role in such integration remains largely unexplored. Courtship and territorial interactions in plainfin midshipman fish depend on vocal communication, and the PAG is a central component of the midshipman vocal-motor system. We made focal neurobiotin injections into the midshipman PAG to both map its auditory-vocal circuitry and allow evolutionary comparisons with tetrapod vertebrates. These injections revealed an extensive bidirectional pattern of connectivity between the PAG and known sites in both the descending vocal-motor and the ascending auditory systems, including portions of the telencephalon, dorsal thalamus, hypothalamus, posterior tuberculum, midbrain, and hindbrain. Injections in the medial PAG produced dense label within hindbrain auditory nuclei, whereas those confined to the lateral PAG preferentially labeled hypothalamic and midbrain auditory areas. Thus, the teleost PAG may have functional subdivisions playing different roles in vocal-auditory integration. Together the results confirm several pathways previously identified by injections into known auditory or vocal areas and provide strong support for the hypothesis that the teleost PAG is centrally involved in auditory-vocal integration.

Neurophysiology of erection and ejaculation

INTRODUCTION

Penile erection and ejaculation are closely associated during sexual intercourse. Erection is a central psychoneuroendocrine and peripheral neuro-vasculo-tissular event, resulting in blood filling the sinusoidal spaces of the corpora cavernosa and corpus spongiosum. Ejaculation represents the climax of the sexual cycle and comprises emission (secretion of semen) and expulsion (propulsion of semen) phases.

AIM

This article provides an overview of the proposed neurophysiology of erection and ejaculation.

METHODS

Review of the literature.

MAIN OUTCOME MEASURES

Current data on the neurophysiology of erection and ejaculation.

RESULTS

In terms of peripheral innervation, the pelvic plexus represents a junction for efferent nerves to the structures involved in erection and ejaculation. At the spinal level, the spinal cord contains three sets of neurons (thoracolumbar sympathetic, sacral parasympathetic, and somatic) innervating the sexual organs involved in erection and ejaculation. The presence of cerebral descending pathways to spinal erection and ejaculation centers indicates that the brain has an excitatory or inhibitory effect on these processes. Brain structures that modulate spinal command of erection and ejaculation are part of a larger network that is dedicated to regulating sexual responses. Neurophysiological and pharmacological research has elucidated that dopamine and serotonin have central roles in modulating erection and ejaculation. Interestingly, erection is not a prerequisite for ejaculation, and each of these sexual responses can exist without the other.

CONCLUSION

Despite the association between erection and ejaculation during intercourse, these two processes can be considered distinct events from an anatomical, physiological, and pharmacological perspective.

Swim stress activates serotonergic and nonserotonergic neurons in specific subdivisions of the rat dorsal raphe nucleus in a temperature-dependent manner

Physical (exteroceptive) stimuli and emotional (interoceptive) stimuli are thought to influence stress-related physiologic and behavioral responses through different neural mechanisms. Previous studies have demonstrated that stress-induced activation of brainstem serotonergic systems is influenced by environmental factors such as temperature. In order to further investigate the effects of environmental influences on stress-induced activation of serotonergic systems, we exposed adult male Wistar rats to either home cage control conditions or a 15-min swim in water maintained at 19 °C, 25 °C, or 35 °C and conducted dual immunohistochemical staining for c-Fos, a marker of immediate-early nuclear activation, and tryptophan hydroxylase (TPH), a marker of serotonergic neurons. Changes in core body temperature were documented using biotelemetry. As expected, exposure to cold (19 °C) swim, relative to warm (35 °C) swim, increased c-Fos expression in the external lateral part of the parabrachial nucleus (LPBel), an important part of the spinoparabrachial pathway involved in sensation of cold, cutaneous stimuli, and in serotonergic neurons in the raphe pallidus nucleus (RPa), an important part of the efferent mechanisms controlling thermoregulatory warming responses. In addition, exposure to cold (19 °C) swim, relative to 35 °C swim, increased c-Fos expression in the dorsal raphe nucleus, ventrolateral part/periaqueductal gray (DRVL/VLPAG) and dorsal raphe nucleus, interfascicular part (DRI). Both of these subregions of the dorsal raphe nucleus (DR) have previously been implicated in thermoregulatory responses. Altogether, the data are consistent with the hypothesis that midbrain serotonergic neurons, possibly via activation of afferents to the DR by thermosensitive spinoparabrachial pathways, play a role in integration of physiologic and behavioral responses to interoceptive stress-related cues involved in forced swimming and exteroceptive cues related to cold ambient temperature.

c-Fos expression in neurons projecting from the preoptic and lateral hypothalamic areas to the ventrolateral periaqueductal gray in relation to sleep states

The ventrolateral division of the periaqueductal gray (vlPAG) and the adjacent deep mesencephalic reticular nucleus have been implicated in the control of sleep. The preoptic hypothalamus, which contains populations of sleep-active neurons, is an important source of afferents to the vlPAG. The perifornical lateral hypothalamus (LH) contains populations of wake-active neurons and also projects strongly to the vlPAG. We examined nonREM and REM sleep-dependent expression of c-Fos protein in preoptic-vlPAG and LH-vlPAG projection neurons identified by retrograde labeling with Fluorogold (FG). Separate groups of rats (n=5) were subjected to 3 h total sleep deprivation (TSD) followed by 1 h recovery sleep (RS), or to 3 h of selective REM sleep deprivation (RSD) followed by RS. A third group of rats (n=5) was subjected to TSD without opportunity for RS (awake group). In the median preoptic nucleus (MnPN), the percentage of FG+ neurons that were also Fos+ was higher in TSD-RS animals compared to both RSD-RS rats and awake rats. There were significant correlations between time spent in deep nonREM sleep during the 1 h prior to sacrifice across groups and the percentage of double-labeled cells in MnPN and ventrolateral preoptic area (VLPO). There were no significant correlations between percentage of double-labeled neurons and time spent in REM sleep for any of the preoptic nuclei examined. In the LH, percentage of double-labeled neurons was highest in awake rats, intermediate in TSD-RS rats and lowest in the RSD-RS group. These results suggest that neurons projecting from MnPN and VLPO to the vlPAG are activated during nonREM sleep and support the hypothesis that preoptic neurons provide inhibitory input to vlPAG during sleep. Suppression of excitatory input to the vlPAG from the LH during sleep may have a permissive effect on REM sleep generation.

Sex steroid-induced neuroplasticity and behavioral activation in birds

The brain of adult homeothermic vertebrates exhibits a higher degree of morphological neuroplasticity than previously thought, and this plasticity is especially prominent in birds. In particular, incorporation of new neurons is widespread throughout the adult avian forebrain, and the volumes of specific nuclei vary seasonally in a prominent manner. We review here work on steroid-dependent plasticity in birds, based on two cases: the medial preoptic nucleus (POM) of Japanese quail in relation to male sexual behavior, and nucleus HVC in canaries, which regulates song behavior. In male quail, POM volume changes seasonally, and in castrated subjects testosterone almost doubles POM volume within 2 weeks. Significant volume increases are, however, already observable after 1 day. Steroid receptor coactivator-1 is part of the mechanism mediating these effects. Increases in POM volume reflect changes in cell size or spacing and dendritic branching, but are not associated with an increase in neuron number. In contrast, seasonal changes in HVC volume reflect incorporation of newborn neurons in addition to changes in cell size and spacing. These are induced by treatments with exogenous testosterone or its metabolites. Expression of doublecortin, a microtubule-associated protein, is increased by testosterone in the HVC but not in the adjacent nidopallium, suggesting that neuron production in the subventricular zone, the birthplace of newborn neurons, is not affected. Together, these data illustrate the high degree of plasticity that extends into adulthood and is characteristic of avian brain structures. Many questions still remain concerning the regulation and specific function of this plasticity.

Differential involvement of the periaqueductal gray in multiple system atrophy

The periaqueductal gray (PAG) consists of distinct columns that participate in the integrated control of autonomic function. We sought to determine whether the PAG is affected in multiple system atrophy (MSA), a disorder characterized by prominent autonomic failure. Brains were obtained at autopsy from 13 MSA patients (10 M, 3 F, age 61±3 years) and 13 controls (8 M, 5 F, age 67±4 years). Transverse formalin-fixed 50 μm sections were obtained throughout the PAG and immunostained for the vesicular transporter 2 (VGLUT-2), nitric oxide synthase (NOS), or α-synuclein and co-stained with thionin. Some sections were processed for myelin or astrocyte staining. Stereological quantitation was performed separately in the ventrolateral, lateral, dorsolateral, and dorsomedial columns of the PAG. In MSA cases, there was a decrease in the total estimated number of VGLUT-2 immunoreactive neurons in the ventrolateral, lateral, and dorsomedial and to a lesser extent dorsolateral PAG compared to controls (ventrolateral PAG: 16,299±1612 vs. 27,906±2480 respectively, p<0.01; lateral PAG: 11,004±1401 vs. 16,078±1140 respectively, p<0.05; and dorsomedial PAG: 8847±1052 vs. 15,412±1097 respectively, p<0.001). The number of NOS immunoreactive neurons in the dorsolateral PAG was similar to controls. In all columns, the number of non-immunolabelled Nissl-stained cells was similar between groups. There was accumulation of glial cytoplasmic inclusions in all PAG columns in MSA. Our findings indicate involvement of the PAG columns in MSA, which may contribute to autonomic disturbances in this disorder.

Ventromedial and medial preoptic hypothalamic ibotenic acid lesions potentiate systemic morphine analgesia in female, but not male rats

Sex differences in systemic morphine analgesia occur with male rodents displaying significantly greater analgesic magnitudes and potencies than females. Neonatal androgenization, and to a lesser degree, adult ovariectomy enhance systemic morphine analgesia in female rats, implicating both organizational and activational effects of gonadal hormones. The neuroanatomical circuits sensitive to sex-related hormones by which females display a smaller opiate analgesic effect is not clear, but the ventromedial (VMH) and medial preoptic (MPOA) hypothalamic nuclei are critical in the monitoring of estradiol and other sex hormone levels. To assess the contribution of these nuclei to sex and adult gonadectomy differences in systemic morphine analgesia, intact male, intact female and adult ovariectomized (OVEX) female rats received bilateral saline (SAL) or ibotenic acid (IBO) microinjections into either the VMH or MPOA. Following surgeries, baseline tail-flick latencies over 120 minutes (min) were assessed over 4 days in all nine groups with intact females tested in the estrus phase of their cycle. All animals then received an ascending series of morphine (1.0, 2.5, 5.0, 7.5, 10.0mg/kg) injections 30min prior to the tail-flick test time course with 8-12 day inter-injection intervals between doses. Baseline latencies failed to differ between SAL-treated intact males and females, but were significantly higher in SAL-treated OVEX females. Both VMH IBO and MPOA IBO lesions increased baseline latencies in intact male and female rats, but not in OVEX females. SAL-treated intact males (ED(50)=4.0mg/kg) and SAL-treated OVEX females (ED(50)=3.5mg/kg) displayed significantly greater potencies of systemic morphine analgesia than SAL-treated intact females (ED(50)=6.3mg/kg), confirming previous gender and gonadectomy differences. Neither VMH IBO (ED(50)=3.7 mg/kg) nor MPOA IBO (ED(50)=4.1mg/kg) males differed from SAL-treated males in the potency of systemic morphine analgesia. In contrast, VMH IBO (ED(50)=4.1mg/kg) and MPOA IBO (ED(50)=3.5mg/kg) intact females displayed significantly greater potencies in systemic morphine analgesia than SAL-treated intact females. However, VMH IBO OVEX (ED(50)=3.5mg/kg) and MPOA IBO OVEX (ED(50)=3.9 mg/kg) failed to differ from SAL-treated OVEX females in the potency of systemic morphine analgesia. The magnitudes of systemic morphine analgesia as measured by Maximum Percentage Effect values displayed similar patterns, but lesser degrees, of effects. These data suggest that VMH and MPOA nuclei act to tonically inhibit endogenous pain-inhibitory circuits in the intact female, but not intact male brain, and that removal of circulating gonadal hormones by OVEX and/or excitotoxic destruction of these estrogen receptor accumulating nuclei disinhibit the female analgesic response to systemic morphine.

"Sex, drugs and the brain": the interaction between drugs of abuse and sexual behavior in the female rat

Preclinical and clinical research investigating female sexual motivation has lagged behind research on male sexual function. The present review summarizes recent advances in our understanding of the specific roles of various brain areas, as well as our understanding of the role of dopaminergic neurotransmission in sexual motivation of the female rat. A number of behavioral paradigms that can be used to thoroughly evaluate sexual behavior in the female rat are first discussed. Although traditional assessment of the reflexive, lordosis posture has been useful in understanding the neuroanatomical and neurochemical systems that contribute to copulatory behavior, the additional behavioral paradigms described in this review have helped us expand our understanding of appetitive and consumatory behavioral patterns that better assess sexual motivation - the equivalent of "desire" in humans. A summary of numerous lesion studies indicates that different areas of the brain, including forebrain and midbrain structures, work together to produce the complex repertoire of female sexual behavior. In addition, by investigating the effects of commonly addictive drugs, we are beginning to elucidate the role of dopaminergic neurotransmission in female sexual motivation. Consequently, research in this area may contribute to meaningful advances in the treatment of human female sexual dysfunction.

Topographical specificity of regulation of respiratory and renal sympathetic activity by the midbrain dorsolateral periaqueductal gray

The midbrain periaqueductal gray (PAG) mediates the physiological responses to a wide range of stressors. It consists of four longitudinal columns that have different anatomical connections and functional properties. Previous anatomical and behavioral studies have led to the hypothesis that the dorsolateral PAG, but not the adjacent lateral and dorsomedial subregions, is a key center that integrates the behavioral response to acute psychological threatening stimuli. In this study, we tested whether, consistent with this hypothesis, activation of neurons in the dorsolateral PAG evokes a pattern of cardiovascular and respiratory responses that is distinct from that evoked from surrounding regions. Arterial pressure, heart rate, renal sympathetic nerve activity (RSNA), and phrenic nerve activity (PNA) were recorded simultaneously in urethane-anesthetized rats. Microinjections of very small amounts of d,l-homocysteic acid (750 pmol in 15 nl) were made in sites throughout the dorsomedial, dorsolateral, and lateral PAG subregions. Increases in RSNA of similar magnitude accompanied by small to moderate increases in arterial pressure and heart rate were evoked from all three PAG subregions. In contrast, large increases in both PNA burst rate (respiratory rate) and overall respiratory activity were evoked only from a highly circumscribed region that corresponded closely to the dorsolateral PAG subregion at an intermediate to caudal level. Within this region, the evoked increases in RSNA and respiratory activity were highly correlated (r = 0.914, P < 0.001), suggesting the possibility that a common population of "command neurons" within the dorsolateral PAG may generate both sympathetic and respiratory responses from this region.

GABAA receptor signaling in caudal periaqueductal gray regulates maternal aggression and maternal care in mice

Maternal aggression (maternal defense) is exhibited by lactating females towards intruders and contributes to the protection of offspring. Enhancement of Gamma-Aminobutyric acid (GABA)(A) receptor signaling by benzodiazepines elevates maternal aggression, and we previously found indirect evidence (via c-Fos immunohistochemistry) that caudal periaqueductal gray (cPAG) and lateral septum (LS) could be sites where benzodiazepines increase aggression. We recently found that GABA(A) receptor signaling in LS modulates maternal aggression, and in this study, we tested the hypothesis that GABA(A) receptor signaling in cPAG also regulates this behavior. Site-directed injections to cPAG were made in lactating mice using the GABA(A) receptor antagonist, bicuculline (3-9 ng) or the GABA(A) receptor positive modulator, chlordiazepoxide (CDP), a benzodiazepine (2.5-20 microg). Maternal aggression, other maternal behaviors, and anxiety-like measures (using the light-dark box) were then examined. GABA(A) receptor positive modulator did not increase aggression, which could have resulted from a ceiling effect. However, 8 ng and 9 ng of bicuculline in cPAG significantly decreased maternal aggression without altering other maternal behaviors or light-dark box performance, suggesting some GABA(A) receptor signaling in cPAG is required for full maternal aggression expression. Additionally, 7 ng of bicuculline significantly increased licking/grooming of pups, and decreased the number of transitions between the light and dark compartments of the light-dark box without affecting aggression. Given these results indicating that antagonizing GABA(A) receptor in cPAG dose-dependently promotes offspring grooming behavior while impairing aggression, it is possible that the cPAG represents a key site for decision making (aggression versus other behaviors) in the lactating female.

Estrogen-induced sexual incentive motivation, proceptivity and receptivity depend on a functional estrogen receptor alpha in the ventromedial nucleus of the hypothalamus but not in the amygdala

The display of copulatory behaviors usually requires the presence of a mate and is, therefore, preceded by a search for and approach to a potential partner. The intensity of approach behaviors is determined by a process labeled sexual incentive motivation. Although it is known that female sexual motivation depends on estrogens, their site of action within the brain is unknown. In the present experiment, we obtained data relevant to this issue. An shRNA encoded within an adeno-associated viral (AAV) vector directed against the estrogen receptor alpha (ERalpha) gene (or containing a nonsense base sequence as a control treatment) was injected bilaterally into the ventromedial nucleus of the hypothalamus (VMN) or the posterodorsal amygdala (MePDA) of female rats. After an 80% reduction of the number of ERalpha in the VMN, sexual incentive motivation was absent after treatment with estradiol and progesterone. Proceptivity and receptivity were also much reduced, while the number of rejections was enhanced. Suppression of the ERalpha in the MePDA lacked these effects. Likewise, the inactive control AAV vector failed to modify any behavior. Thus, the ERalpha in the VMN, but not in the MePDA, is important for proceptivity and receptivity as well as for sexual incentive motivation. These results show that ERalpha in the VMN is crucial for the entire sequence of behavioral events from the processes leading to the establishment of sexual contact until the accomplishment of copulatory behaviors.

Involvement of NTS2 receptors in stress-induced analgesia

Stress activates multiple neural systems that suppress pain sensation. This adaptive phenomenon referred as stress-induced analgesia (SIA) is mediated by the activation of endogenous pain inhibitory systems. Both opioid and non-opioid forms of SIA have been elicited in rodents according to stressor parameters and duration. There is accumulating evidence that the endogenous neurotensin (NT) system plays an important role in SIA. Especially, NT-deficient mice were shown to exhibit reduced SIA following water avoidance or restraint stress. Since central NT produces naloxone-insensitive analgesic effects by acting on spinal and supraspinal NTS2 receptors, we hypothesized that NT might mediate non-opioid SIA through NTS2 activation. Here, we evaluated the influence of an opioid-independent severe stress produced by a cold-water swim for 3 min at 15 degrees C on rodent offspring's pain perception. Our results demonstrated that mice lacking NTS2 exhibit significantly reduced SIA following cold-water swim stress. Indeed, NTS2 knockout mice submitted to both acute (plantar test) and tonic (formalin test) pain stimuli show a greater sensitivity to pain in comparison to wild-type littermates. Accordingly, pretreatment with the NT receptor antagonist SR142948A results in a hyperalgesic response to stress induced by cold-water swim. Endogenous NT regulates hypothalamic-pituitary-adrenal axis activity in stress condition by increasing corticosterone plasma levels. Accordingly, the plasma levels of corticosterone measured by radioimmunoassay are significantly reduced in non-stressed and stressed NTS2-deficient mice in comparison with wild-type mice. To further investigate the site of action of NT in mediating SIA, we microinjected NTS2 agonists in lumbar spinal cord and quantified post-stress sensitivity to pain in rats using the plantar test. Exogenously administered NTS2 analogs, JMV-431, beta-lactotensin and NT69L markedly enhance the magnitude and duration of stress antinociception in both 25- and 60-day-old rats. In sum, by using genetic and pharmacological approaches, we demonstrated here that NTS2 receptors mediate non-opioid SIA. Our results also revealed that the release of endogenous NT in response to stress requires the presence of NTS2 to stimulate corticotropin-releasing factor (CRF)-induced elevation of plasma corticosterone, and that NTS2 receptors localized at the lumbar spinal cord participate to the disinhibition of descending pain control pathways. Therefore, these data highlight the significance of NTS2 as a novel target for the treatment of pain and stress-related disorders.

Adverse early life experience and social stress during adulthood interact to increase serotonin transporter mRNA expression

Anxiety disorders, depression and animal models of vulnerability to a depression-like syndrome have been associated with dysregulation of serotonergic systems in the brain. To evaluate the effects of early life experience, adverse experiences during adulthood, and potential interactions between these factors on serotonin transporter (slc6a4) mRNA expression, we investigated in rats the effects of maternal separation (180 min/day from days 2 to 14 of life; MS180), neonatal handing (15 min/day from days 2 to 14 of life; MS15), or normal animal facility rearing (AFR) control conditions with or without subsequent exposure to adult social defeat on slc6a4 mRNA expression in the dorsal raphe nucleus (DR) and caudal linear nucleus. At the level of specific subdivisions of the DR, there were no differences in slc6a4 mRNA expression between MS15 and AFR rats. Among rats exposed to a novel cage control condition, increased slc6a4 mRNA expression was observed in the dorsal part of the DR in MS180 rats, relative to AFR control rats. In contrast, MS180 rats exposed to social defeat as adults had increased slc6a4 mRNA expression throughout the DR compared to both MS15 and AFR controls. Social defeat increased slc6a4 mRNA expression, but only in MS180 rats and only in the "lateral wings" of the DR. Overall these data demonstrate that early life experience and stressful experience during adulthood interact to determine slc6a4 mRNA expression. These data support the hypothesis that early life experience and major stressful life events contribute to dysregulation of serotonergic systems in stress-related neuropsychiatric disorders.

Functional correlates of activity in neurons projecting from the lamina terminalis to the ventrolateral periaqueductal gray

The lamina terminalis (LT) consists of the organum vasculosum of the LT (OVLT), the median preoptic nucleus (MnPO) and the subfornical organ (SFO). All subdivisions of the LT project to the ventrolateral periaqueductal gray (vlPAG). The LT and the vlPAG are implicated in several homeostatic and behavioral functions, including body fluid homeostasis, thermoregulation and the regulation of sleep and waking. By combining visualization of c-Fos protein and retrograde neuroanatomical tracer we have examined the functional correlates of LT-vlPAG projection neurons. Rats were injected with retrograde tracer into the vlPAG and, following a 1-week recovery period, they were subjected to either hypertonic saline administration (0.5 M NaCl, 1 mL/100 g i.p.), 24-h water deprivation, isoproterenol administration (increases circulating angiotensin II; 50 microg/kg s.c.), heat exposure (39 degrees C for 60 min) or permitted 180 min spontaneous sleep. Retrogradely labeled neurons from the vlPAG and double-labelled neurons were then identified and quantified throughout the LT. OVLT-vlPAG projection neurons were most responsive to hypertonic saline and water deprivation. SFO-vlPAG projection neurons were most active following isoproterenol administration, and MnPO-vlPAG projection neurons displayed significantly more Fos immunostaining following water deprivation, heat exposure and sleep. These results support the existence of functional subdivisions of LT-vlPAG-projecting neurons, and indicate three patterns of activity that correspond to thermal and sleep wake regulation, osmotic or hormonal stimuli.

Dopaminergic projections to the medial preoptic area of postpartum rats

Dopamine receptor activity in the rodent medial preoptic area (mPOA) is crucial for the display of maternal behaviors, as well as numerous other physiological and behavioral functions. However, the origin of dopaminergic input to the mPOA has not been identified through neuroanatomical tracing. To accomplish this, the retrograde tracer Fluorogold was iontophoretically applied to the mPOA of postpartum laboratory rats, and dual-label immunocytochemistry for Fluorogold and tyrosine hydroxylase later performed to identify dopaminergic cells of the forebrain and midbrain projecting to the mPOA. Results indicate that the number of dopaminergic cells projecting to the mPOA is moderate ( approximately 90 cells to one hemisphere), and that these cells have an unexpectedly wide distribution. Even so, more than half of the dual-labeled cells were found in either what has been considered extensions of the A10 dopamine group (particularly the ventrocaudal posterior hypothalamus and adjacent medial supramammillary nucleus), or in the A10 group of the ventral tegmental area. The rostral hypothalamus and surrounding region also contained numerous dual-labeled cells, with the greatest number found within the mPOA itself (including in the anteroventral preoptic area and preoptic periventricular nucleus). Notably, dual-labeled cells were rare in the zona incerta (A13), a site previously suggested to provide dopaminergic input to the mPOA. This study is the first to use anatomical tracing to detail the dopaminergic projections to the mPOA in the laboratory rat, and indicates that much of this projection originates more caudally than previously suggested.

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.

Coexpression of the mu-opioid receptor splice variant MOR1C and the vesicular glutamate transporter 2 (VGLUT2) in rat central nervous system

It has been reported that mu-opioid agonists depress glutamate release in some neurons but the specific receptor subtype mediating this effect is unclear. The purpose of the present study was to examine whether a particular mu-opioid receptor (MOR) splice-variant, MOR(1C), is expressed in rat central nervous system (CNS) by terminals expressing the vesicular glutamate transporter2 (VGLUT2), a marker of glutamatergic neurons. Several MOR splice variants have been identified in mice and MOR(1C) appears mainly to be localized to fibers and terminals, from which most neurotransmitter release would be expected. In addition, VGLUT2 has been found in the CNS and antibodies to it are reliable markers for glutamatergic terminals. Using fluorescence immunohistochemistry and confocal microscopy to examine spatial relationships between MOR(1C) and VGLUT2, we found that MOR(1C) and VGLUT2 puncta were widely distributed throughout the rat CNS; moreover, many regions contained terminals that expressed both. Thus, it appears that coexpression of MOR(1C) and VGLUT2 is common in the rat CNS. We hypothesize that activation of MOR(1C) by mu-opioid agonists at some glutamatergic terminals may be a mechanism by which glutamate release is inhibited.

Sexual experience modulates neuronal activity in male Japanese quail

After an initial increase, repeated exposure to a particular stimulus or familiarity with an event results in lower immediate early gene expression levels in relevant brain structures. We predicted that similar effects would occur in Japanese quail after repeated sexual experience within brain areas involved in sexual behavior, namely, the medial preoptic nucleus (POM), the bed nucleus of stria terminalis (BST), and the nucleus taeniae of the amygdala (TnA), an avian homolog of medial amygdala. High experience subjects copulated with a female once on each of 16 consecutive days, whereas low experience subjects were allowed to copulate either once or twice. Control subjects were never exposed to a female. High experience subjects were faster to initiate sexual interaction, performed more cloacal contacts, and completed each cloacal contact faster than low experience subjects. Low experience subjects showed an increase in egr-1 (ZENK) expression, an immediate early gene product used as marker of neural activation in birds, in the areas of interest. In contrast, in high experience animals, egr-1 expression in the POM, BST, and the periaqueductal gray (PAG) was not different than the level of expression in unmated controls. These results show that experience modulates the level of immediate early gene expression in the case of sexual behavior. Our results also indicate that immediate early gene expression in specific brain areas is not necessarily related to behavioral output but depends on the behavioral history of the subjects.

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.

Inactivation of the periaqueductal gray attenuates antinociception elicited by stimulation of the rat medial preoptic area

The medial preoptic area (MPOA) is a sexually dimorphic structure that plays key roles in gonado-steroidal regulation and thermoregulation. The MPOA may be involved in sex-based differences in nociceptive processing and steroid hormones effect on pain thresholds. Consistent with this, there is evidence that MPOA can produce antinociception or hyperalgesia. MPOA stimulation inhibits spinal cord or trigeminal neuronal responses to noxious stimuli or produces analgesia, yet most of these studies utilized electrical stimulation which antidromically activates periaqueductal gray (PAG) and rostroventromedial medulla (RVM) neurons involved in descending modulation of nociception. Effects of selective activation of MPOA neurons on behavioral indices of antinociception and the site-specificity of such responses are unknown. To address these questions, we examined the influence of MPOA microinjections of d,l homocysteate (DLH) on hindlimb and tail nocifensive reflexes in lightly anesthetized rats. DLH, but not saline, microinjections into several MPOA subregions markedly increased withdrawal response latencies to noxious thermal stimuli. Antinociceptive effects of MPOA activation were abolished by microinjection of lidocaine into PAG. These results suggest that activation of MPOA neurons produces antinociception that is at least partly mediated by projections to PAG.