Opioids and sexual behavior

From pathology to pleasure: Reframing mechanistic studies on same-sex sexual behavior in primates

Same-sex sexual behaviors (SSB) in primates have historically been studied as sexual perversions, evolutionary paradoxes, and hormone-driven pathologies. Researchers in recent decades have challenged these perspectives, yet some of the original biases still linger. In this paper, we examine how the study of endocrinological mechanisms in SSB has been influenced by the historical framework of pathology. Societal attitudes and cultural conceptions of human sexuality have led researchers to study SSB in primates as the outcome of "abnormal" processes of "feminization" or "masculinization" of sexual behavior. Here, we argue for a renewed attention to other areas of inquiry regarding the relationship between hormones and SSB, such as the role of pleasure. We briefly review how current knowledge on the neuroendocrinology of pleasure in nonhuman primates may relate to the expression of SSB and highlight oxytocin and dopamine as potentially fruitful areas for future research. We argue that future studies on SSB in primates would benefit from 1) acknowledging how the historical study of SSB as a pathology has shaped mechanistic studies and 2) studying SSB with the same holistic approach as is taken with different-sex sexual behavior (DSB).

Endorphins, Sexuality, and Reproduction

Beta-endorphin is secreted from the hypothalamus and pituitary in both mother and newborn. The placenta produces numerous pituitary hormones from the third month of pregnancy, one of which is βE. It has been suggested that βE has a role in the appetitive and precopulatory phase of sexual behavior in animals. An increase in endorphin levels during sexual activity in humans may contribute to attachment and bonding between partners, but contradictory reports in the literature question the association between sexuality and βE levels. The level of βE also increases during pregnancy, rises in early labor, peaks in late labor, and drops in the postpartum period. This fluctuation provides natural analgesia, raises the pain threshold, decreases the sensation of pain, or suppresses pain, and decreases fear levels during labor and birth. Beta-endorphin also protects the fetus from hypoxia during labor and birth and potential neural damage by aiding blood flow to the brain under hypoxic conditions. It has been suggested that a variety of pharmacologic and nonpharmacologic complementary therapies, when used in pregnancy, labor, and birth, activate the opioid receptors in the CNS and alter the sensation of pain during labor and birth, affect the mother-child attachment and affect sexual function. These studies report contradictory results that will be discussed in this chapter.

Endogenous Opioid Release After Orgasm in Man: A Combined PET/Functional MRI Study

The endogenous μ-opioid receptor (MOR) system plays a key role in the mammalian reward circuit. Human and animal experiments suggest the involvement of MORs in human sexual pleasure, yet this hypothesis currently lacks in vivo support. Methods: We used PET with the radioligand [¹¹C]carfentanil, which has high affinity for MORs, to quantify endogenous opioid release after orgasm in man. Participants were scanned once immediately after orgasm and once in a baseline state. Hemodynamic activity was measured with functional MRI during penile stimulation. Results: The PET data revealed significant opioid release in the hippocampus. Hemodynamic activity in the somatosensory and motor cortices and in the hippocampus and thalamus increased during penile stimulation, and thalamic activation was linearly dependent on self-reported sexual arousal. Conclusion: Our data show that endogenous opioidergic activation in the medial temporal lobe is centrally involved in sexual arousal, and this circuit may be implicated in orgasmic disorders.

Courses of Arginine-Vasopressin in the Systemic and Cavernous Blood through Different Stages of Sexual Arousal in Healthy Males and Patients with Erectile Dysfunction

To investigate the role of the peptide arginine-vasopressin (AVP) in controlling the function of penile erectile tissue, we determined the course of AVP through different stages of sexual arousal in both the systemic and cavernous blood of healthy males and patients presenting with ED. Twenty-five healthy males and 45 patients with ED were exposed to erotic stimulation to induce sexual arousal. Blood was withdrawn from the corpus cavernosum and a cubital vein during penile flaccidity, tumescence, rigid erection (attained only by the healthy individuals), and detumescence. AVP (ng/l plasma) was determined by means of a radioimmunoassay. Effects of AVP (0.1 to 100 nM) on isolated human CC were examined using a tissue bath system. AVP elicited contraction of isolated CC. In the healthy subjects, a decline in AVP levels (5.4 to 3 ng/l) was seen in the systemic blood when the flaccid penis became rigid. In the cavernous blood, no alterations were registered. In the group of ED patients, AVP in the systemic circulation did not display a transient decline. The drop in systemic AVP in healthy males during sexual stimulation might be a prerequisite to enable penile erection.

Flexibility of neural circuits regulating mating behaviors in mice and flies

Mating is essential for the reproduction of animal species. As mating behaviors are high-risk and energy-consuming processes, it is critical for animals to make adaptive mating decisions. This includes not only finding a suitable mate, but also adapting mating behaviors to the animal's needs and environmental conditions. Internal needs include physical states (e.g., hunger) and emotional states (e.g., fear), while external conditions include both social cues (e.g., the existence of predators or rivals) and non-social factors (e.g., food availability). With recent advances in behavioral neuroscience, we are now beginning to understand the neural basis of mating behaviors, particularly in genetic model organisms such as mice and flies. However, how internal and external factors are integrated by the nervous system to enable adaptive mating-related decision-making in a state- and context-dependent manner is less well understood. In this article, we review recent knowledge regarding the neural basis of flexible mating behaviors from studies of flies and mice. By contrasting the knowledge derived from these two evolutionarily distant model organisms, we discuss potential conserved and divergent neural mechanisms involved in the control of flexible mating behaviors in invertebrate and vertebrate brains.

“Death drive” scientifically reconsidered: Not a drive but a collection of trauma-induced auto-addictive diseases

Over the last 102 years, a lot of discussion was being held about the psychoanalytic conception of the “death drive,” but still with inconclusive results. In this paper, we start with a brief review of Freud’s conception, followed by a comprised overview of its subsequent support or criticisms. The core of our argument is a systematic review of current biochemical research about two proposed manifestations of the “death drive,” which could hopefully move the discussion to the realm of science. It was already established that drive satisfaction leads to the secretion of beta-endorphins, and research evidence also shows that the same biochemical mechanisms get activated in the case of masochism and the gambling disorder but only if they are preceded by chronic frustration of the essential drives. We conclude that the actual situation is more complex than Freud hypothesized, and that a fundamental revision of the psychoanalytic drive theory is necessary.

Behavioral, Neural, and Molecular Mechanisms of Conditioned Mate Preference: The Role of Opioids and First Experiences of Sexual Reward

Although mechanisms of mate preference are thought to be relatively hard-wired, experience with appetitive and consummatory sexual reward has been shown to condition preferences for partner related cues and even objects that predict sexual reward. Here, we reviewed evidence from laboratory species and humans on sexually conditioned place, partner, and ejaculatory preferences in males and females, as well as the neurochemical, molecular, and epigenetic mechanisms putatively responsible. From a comprehensive review of the available data, we concluded that opioid transmission at μ opioid receptors forms the basis of sexual pleasure and reward, which then sensitizes dopamine, oxytocin, and vasopressin systems responsible for attention, arousal, and bonding, leading to cortical activation that creates awareness of attraction and desire. First experiences with sexual reward states follow a pattern of sexual imprinting, during which partner- and/or object-related cues become crystallized by conditioning into idiosyncratic “types” that are found sexually attractive and arousing. These mechanisms tie reward and reproduction together, blending proximate and ultimate causality in the maintenance of variability within a species.

μ-opioid receptor availability is associated with sex drive in human males

The endogenous mu-opioid receptor (MOR) system modulates a multitude of social and reward-related functions, and exogenous opiates also influence sex drive in humans and animals. Sex drive shows substantial variation across humans, and it is possible that individual differences in MOR availability underlie interindividual of variation in human sex drive. We measured healthy male subjects’ (n = 52) brain’s MOR availability with positron emission tomography (PET) using an agonist radioligand, [¹¹C]carfentanil, that has high affinity for MORs. Sex drive was measured using self-reports of engaging in sexual behaviour (sex with partner and masturbating). Bayesian hierarchical regression analysis revealed that sex drive was positively associated with MOR availability in cortical and subcortical areas, notably in caudate nucleus, hippocampus, and cingulate cortices. These results were replicated in full-volume GLM analysis. These widespread effects are in line with high spatial autocorrelation in MOR expression in human brain. Complementary voxel-based morphometry analysis (n = 108) of anatomical MR images provided limited evidence for positive association between sex drive and cortical density in the midcingulate cortex. We conclude that endogenous MOR tone is associated with individual differences in sex drive in human males.

Sexual Receptivity Signal of Lordosis Posture and Intra-Sexual Competition in Women

Previous research has shown that women may use self-enhancement strategies to compete with one other. Lumbar curvature in women is considered to enhance a woman′s attractiveness, potentially due to its role in bipedal fetal load and sexual receptiveness. The current study investigated the role of lumbar curvature on women’s perceptions of sexual receptiveness as well as its role in women’s intrasexual competitiveness. Study 1 (N = 138) tested and confirmed that women’s intrasexual competition influences their perception of sexual receptivity of women as a function of lordosis posture depicted in a standing posture. Study 2 (N = 69) replicated these results and extended them to other postures, namely, the quadruped and supine positions. Study 3 (N = 106), using a two-alternative forced-choice task, revealed that other women perceive relatively larger arched-back postures as more threatening to their relationship and frequently as being more attractive. Collectively, this work suggests that women consider a lordotic posture in other women as a signal of sexual receptivity and perceive it as a threat to their relationship. This research provides robust support for the sexually receptivity hypothesis of lumbar curvature, questioning the alternative morphological vertebral wedging hypothesis.

Erectile Function and Sexual Behavior: A Review of the Role of Nitric Oxide in the Central Nervous System

Nitric oxide (NO), the neuromodulator/neurotransmitter formed from l-arginine by neuronal, endothelial and inducible NO synthases, is involved in numerous functions across the body, from the control of arterial blood pressure to penile erection, and at central level from energy homeostasis regulation to memory, learning and sexual behavior. The aim of this work is to review earlier studies showing that NO plays a role in erectile function and sexual behavior in the hypothalamus and its paraventricular nucleus and the medial preoptic area, and integrate these findings with those of recent studies on this matter. This revisitation shows that NO influences erectile function and sexual behavior in males and females by acting not only in the paraventricular nucleus and medial preoptic area but also in extrahypothalamic brain areas, often with different mechanisms. Most importantly, since these areas are strictly interconnected with the paraventricular nucleus and medial preoptic area, send to and receive neural projections from the spinal cord, in which sexual communication between brain and genital apparatus takes place, this review reveals that central NO participates in concert with neurotransmitters/neuropeptides to a neural circuit controlling both the consummatory (penile erection, copulation, lordosis) and appetitive components (sexual motivation, arousal, reward) of sexual behavior.

Oxytocin, Erectile Function and Sexual Behavior: Last Discoveries and Possible Advances

A continuously increasing amount of research shows that oxytocin is involved in numerous central functions. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered.

Study of copulatory behaviour in old male rabbits

<p>Male rabbit sexual behaviour consists of a single mount followed immediately by ejaculation. In young bucks this pattern changes gradually as they reach sexual satiety in a day and sexual exhaustion after several daily tests. Little is known about the characteristics of sexual behaviour in old rabbits (aged 48-54 mo) within a day and across daily tests leading to sexual exhaustion. By using sexually receptive(young) females, changed within a session to maximise copulation, we found that: a) the inter-ejaculatory interval increased between the first and last days of testing; b) test duration was 3.1 h on day 1 and 0.5 h on day 15; c) the “miss rate” (i.e., mounts not accompanied by ejaculation) significantly increased from the first to the last day of testing, regardless of when this occurred in each individual buck; d) the total number of ejaculations displayed in a session significantly decreased between the first and the last day of testing in all males; e) scent-marking (“chinning”) frequency significantly decreased after copulation to satiety, relative to that quantified at baseline, and was restored the following day. Compared with young bucks our results indicate quantitative, rather than qualitative, differences in sexual behaviour associated with age in rabbits. Specifically, on day 1 old bucks spent a shorter time engaged in copulation and displayed a lower number of ejaculations before reaching satiety than young males. In contrast, the interval between ejaculatory events and the “miss rate” increased across test days in both old and young rabbits. These results merit investigating the neuroendocrine mechanisms underlying the display of such an active sexual behaviour by old rabbit bucks.</p>

Exploring the Association Between the "Big Five" Personality Traits and Fatal Opioid Overdose: County-Level Empirical Analysis

BACKGROUND

Opioid-related deaths constitute a problem of pandemic proportions in the United States, with no clear solution in sight. Although addressing addiction-the heart of this problem-ought to remain a priority for health practitioners, examining the community-level psychological factors with a known impact on health behaviors may provide valuable insights for attenuating this health crisis by curbing risky behaviors before they evolve into addiction.

OBJECTIVE

The goal of this study is twofold: to demonstrate the relationship between community-level psychological traits and fatal opioid overdose both theoretically and empirically, and to provide a blueprint for using social media data to glean these psychological factors in a real-time, reliable, and scalable manner.

METHODS

We collected annual panel data from Twitter for 2891 counties in the United States between 2014-2016 and used a novel data mining technique to obtain average county-level "Big Five" psychological trait scores. We then performed interval regression, using a control function to alleviate omitted variable bias, to empirically test the relationship between county-level psychological traits and the prevalence of fatal opioid overdoses in each county.

RESULTS

After controlling for a wide range of community-level biopsychosocial factors related to health outcomes, we found that three of the operationalizations of the five psychological traits examined at the community level in the study were significantly associated with fatal opioid overdoses: extraversion (β=.308, P<.001), neuroticism (β=.248, P<.001), and conscientiousness (β=.229, P<.001).

CONCLUSIONS

Analyzing the psychological characteristics of a community can be a valuable tool in the local, state, and national fight against the opioid pandemic. Health providers and community health organizations can benefit from this research by evaluating the psychological profile of the communities they serve and assessing the projected risk of fatal opioid overdose based on the relationships our study predict when making decisions for the allocation of overdose-reversal medication and other vital resources.

Roles of β-Endorphin in Stress, Behavior, Neuroinflammation, and Brain Energy Metabolism

β-Endorphins are peptides that exert a wide variety of effects throughout the body. Produced through the cleavage pro-opiomelanocortin (POMC), β-endorphins are the primarily agonist of mu opioid receptors, which can be found throughout the body, brain, and cells of the immune system that regulate a diverse set of systems. As an agonist of the body's opioid receptors, β-endorphins are most noted for their potent analgesic effects, but they also have their involvement in reward-centric and homeostasis-restoring behaviors, among other effects. These effects have implicated the peptide in psychiatric and neurodegenerative disorders, making it a research target of interest. This review briefly summarizes the basics of endorphin function, goes over the behaviors and regulatory pathways it governs, and examines the variability of β-endorphin levels observed between normal and disease/disorder affected individuals.

Medicinal plants/herbal supplements as female aphrodisiacs: Does any evidence exist to support their inclusion or potential in the treatment of FSD?

ETHNOPHARMACOLOGICAL RELEVANCE

Female Sexual Dysfunction is a complex condition with biopsychosocial origins. Plants traditionally used as aphrodisiacs may be promising as routes to develop therapeutic options which are lacking.

AIM

To distinguish the plants commonly used in (AP) on the market in the United States, and to evaluate their ethnobotanical and clinical evidence as a basis for their inclusion.

METHODS

This study is a narrative review of 53 species commonly found in AP on the market in the United States. Most species listed have anecdotal use as aphrodisiacs throughout history; therefore, a systematic search was done for clinical evidence. The primary outcome assessed is the clinical efficacy of plants in the treatment of libido desire disorders.

RESULTS

There is little to no evidence from the literature to substantiate claims of plants currently on the market as AP for female libido desire disorders.

CONCLUSIONS

The biggest problem in the literature is the lack of botanical verification and consistency in material across studies. Any botanical, commercial or otherwise must be tested for chemical markers exhibited by individual species; however, if no markers exist, work must first be done to determine these. Appropriate analytical techniques for this would include high pressure liquid chromatography, and mass spectroscopy. It would also be sufficient to taxonomically authenticate species provided the plant material. Further research should aim to standardize plant material and extraction methods utilized in order to compare studies effectively and allow for reproducibility to draw conclusions. While clear interest into investigation the aphrodisiac potential of plants exists, a translatable in vivo animal model does not. Clinical trials rely on patient reported outcomes to determine efficacy but cost and length of such trials deem a necessity for development of an animal model to first screen botanicals. We suggest development of screening tools utilizing the evident neurobiological underpinnings of FSD as the first step. In general, studies of plants currently used as ingredients for AP are severely lacking, and even so the evidence that exists is weak.

Endocannabinoids mediate long-lasting behavioural and physiological changes in male rats induced by the repeated activation of the mesolimbic system by copulation to satiety

Sexually satiated male rats exhibit long-lasting physiological changes, suggestive of brain plasticity, the most conspicuous of which are a sexual behaviour inhibition and a generalised drug hypersensitivity. Copulation activates the mesolimbic circuit increasing dopamine (DA) release in the nucleus accumbens (NAcc) and, enhanced midbrain DA neuron activity promotes endocannabinoid (eCB) release in the ventral tegmental area (VTA). The objective of this work was to explore the possible participation of DA and/or eCB transmission in the induction of these two long-lasting phenomena. To this aim we analysed the effect of blocking DA or CB1 receptors during the process of copulation to exhaustion, on the expression 24 h later, of the sexual inhibitory state and the hypersensitivity to two different drugs: 8-OH-DPAT, a 5-HT_1A receptor agonist, and yohimbine, an α₂-adrenoceptor antagonist. Blockade of DA receptors failed to prevent these phenomena, while blockade of CB1 receptors interfered with the appearance of the sexual inhibition and the hypersensitivity to both drugs in the sexually satiated animals. Specific blockade of CB1 receptors in the VTA during copulation to satiety mimicked these results, suggesting that both eCB-mediated effects were exerted in this brain region. It is concluded that eCBs play a role in the induction of behavioural and physiological changes, triggered by copulation to satiety, by acting at the VTA, while increased NAcc DA levels appear not to contribute to the changes induced by intense copulation. Results pose sexual satiety as a useful model for the study of brain plasticity phenomena induced by natural rewards.

Differential disruption of conditioned ejaculatory preference in the male rat based on different sensory modalities by micro-infusions of naloxone to the medial preoptic area or ventral tegmental area

RATIONALE

Male rats trained to associate a neutral odor or rodent jacket on a female with their post-ejaculatory reward state display a preference to ejaculate with females bearing the odor or jacket. This conditioned ejaculatory preference (CEP) can be shifted by systemic administration of the opioid antagonist naloxone (NAL) during training, such that NAL-trained males distribute their ejaculations to females without the cue, relative to saline (SAL)-trained males.

OBJECTIVE

The present study examined two brain sites, the medial preoptic area (mPOA) or ventral tegmental area (VTA), where the opioid reward state might be induced.

METHODS

Sexually naïve Long-Evans males were implanted with bilateral guide cannula aimed at either site before they underwent multi-ejaculatory conditioning trials at 4-day intervals with sexually receptive females that bore either an almond odor or rodent tethering jacket. Infusions of NAL (1 μl/side) or SAL (1 μl/side) were made prior to each conditioning trial. All males were infused with SAL prior to a final open-field choice test with two sexually receptive females, one scented and the other unscented, or one jacketed and the other unjacketed.

RESULTS

Males previously conditioned with SAL in either region showed significant CEP. In contrast, prior infusions of NAL to the mPOA shifted the preference towards the unfamiliar female, whereas prior infusions to the VTA abolished CEP for the odor. Subsequent detection of Fos protein induced by the cue showed that, relative to SAL-treated males, prior experience with NAL in the mPOA suppressed Fos in both the mPOA and VTA, whereas prior experience with NAL in to the VTA suppressed Fos in the VTA alone.

CONCLUSIONS

Opioid antagonism in the mPOA produces a state of non-reward whereas in the VTA, it produces a state in which the odor does not acquire incentive properties.

Neuroanatomy and function of human sexual behavior: A neglected or unknown issue?

INTRODUCTION

Sexual desire, arousal, and orgasm are mediated by complex, yet still not fully understood, interactions of the somatic and autonomic nervous systems operating at the central and peripheral levels. Disruption of endocrine, neural, or vascular response, caused by aging, medical illness, neurological diseases, surgery, or drugs, can lead to sexual dysfunctions, thus significantly affecting patients' quality of life.

PURPOSE

This narrative review aims at characterizing the involvement of the central nervous system in human sexual behavior.

METHODS

A literature search was conducted using PubMed in its entirety up to June 2018, analyzing the studies dealing with the neurobiological and neurophysiological basis of human sexuality.

RESULTS

Sexual behavior is regulated by both subcortical structures, such as the hypothalamus, brainstem, and spinal cord, and several cortical brain areas acting as an orchestra to finely adjust this primitive, complex, and versatile behavior. At the central level, dopaminergic and serotonergic systems appear to play a significant role in various factors of sexual response, although adrenergic, cholinergic, and other neuropeptide transmitter systems may contribute as well.

CONCLUSIONS

Providing healthcare professionals with information concerning sexual behavior may overcome useless and sometimes dangerous barriers and improve patient management, since sexual well-being is considered one of the most important aspects of one's quality of life.

Effects of inactivation of the ventral tegmental area on prefronto-accumbens activity and sexual motivation in male rats

Sexual motivation requires the processing of sexual stimuli. The prefrontal cortex (PFC) and nucleus accumbens (NAcc) receive dopaminergic innervation from the ventral tegmental area (VTA). Both structures participate in processing stimuli, and their adequate functioning is modulated by dopamine and other neurotransmitters. This study was designed to determine the effect of inactivation of the VTA on sexual motivation, relative power (RP) and electroencephalographic (EEG) correlation of the PFC and NAcc in male rats. A total of 20 rats implanted with electrodes in the left medial prefrontal cortex (mPFC) and NAcc, and with bilateral cannulae in the VTA, were divided into two groups of 10 rats each, one injected with tetrodotoxin (TTX), the other with a vehicle solution (VEH). EEGs from the mPFC and NAcc were recorded during the awake-quiet state in the presence of either a receptive or non-receptive female. The TTX group showed a lower preference for the receptive female accompanied by a lower RP of the 8-13 and 14-30 Hz bands in the mPFC. Also, in the presence of the receptive female, the TTX group had a lower RP of the 8-13 Hz band in the NAcc, but a higher prefronto-accumbens correlation in the same band. These results provide evidence that VTA activity is necessary for the adequate functioning of the mPFC and NAcc and, therefore, also for the adequate processing of sexually-relevant stimuli that allows the induction and maintenance of sexual motivation in male rats.

The Influence of Endogenous Opioids on the Relationship between Testosterone and Romantic Bonding

The endogenous opioid system has received attention and extensive research for its effects on reward, pleasure, and pain. However, relative to other neurochemicals, such as oxytocin, vasopressin and dopamine, the function of opioids in regulating human attachment, sociosexuality, and other aspects of human sociality has not received much consideration. For example, nonapeptides (oxytocin and vasopressin) have been extensively studied in animals and humans for their possible roles in mother-offspring attachment, romantic attachment, fatherhood, and social cognition. Likewise, others have proposed models wherein oxytocin and vasopressin are moderators of the relationship between steroid hormones and human social behaviors. Recently, opioids have generated renewed interest in relation to social pain, and importantly, the brain opioid hypothesis of social attachment (BOTSA), which suggests that endogenous opioids are a key implementer in primate and human bonding, has received some support. Here we focus on romantic bonds by proposing that endogenous opioids are an important mechanism mediating reproductive trade-offs through their inhibitory effects on testosterone production.

Sexual Dysfunctions are Predicted by Childhood Sexual Abuse in Women with Opioid Use Disorder

BACKGROUND

Studies on sexual functioning of populations with substance use disorders (SUDs) are mostly conducted with male substance users. We have very limited information about the sexuality and related factors in women with opioid use disorder (OUD).

OBJECTIVES

We aimed to evaluate the relationship between childhood traumatic experiences (CTEs) and sexual dysfunctions (SDs) of women with OUD and to compare it with a sample of women who do not have SUD.

METHODS

Participants included 51 outpatient women with OUD who were on opioid maintenance treatment (OMT) with Buprenorphine/Naloxone and 48 women without SUD. Participants were evaluated by a semi-structured sociodemographic form, the Golombok-Rust Inventory of Sexual Satisfaction (GRISS), the Childhood Trauma Questionnaire (CTQ-28), the Beck Depression Inventory (BDI) and the State-Trait Anxiety Inventory (STAI).

RESULTS

In women with OUD; CTQ-28, BDI, STAI, and GRISS scores were significantly higher. In the partial correlation analysis, sexual abuse was found to be significantly correlated with nonsensuality, avoidance and total GRISS score. In stepwise regression model, sexual abuse was found to predict SDs together with depression.

CONCLUSIONS

CTE, SD, depression, and anxiety rates were higher in the women with OUD. Especially childhood sexual abuse was associated with SDs in this group. Sexual abuse was predicting SDs together with depression. Further investigation of different characteristics of women with SUD may give an opportunity to clinicians to have a better understanding for adaptable treatment strategies.

Endorphins, oxytocin, sexuality and romantic relationships: An understudied area

Endorphins are the body’s natural opioids that are created and released by the central nervous system, hypothalamus and pituitary gland. Endorphins have a reputation for pain reduction, enhancing excitement or satisfaction, boosting confidence, enabling control of emotions and generating feelings of euphoria, and are involved in the natural reward cycle. There is also evidence in the literature suggesting the role of endorphins in sexuality (including sexual function and sexual behaviours), as they may regulate the release of sex hormones, prolactin and growth hormone, which are involved in sexual function and love. Endogenous oxytocin is another intrinsic hormone whose role in inducing labour contractions, the delivery of the baby and stimulating lactation has been well studied. However, the potential impact of endorphins and oxytocin on sexuality and romantic relationships is not well understood. This article reviews the research on endorphins and endogenous oxytocin and how they relate to human sexuality and romantic relationships. Some animal studies report the effect of endorphin and oxytocin on sex hormones and mating behaviours, but these findings have not been supported by research into human behaviour, indicating many gaps in knowledge relating to the association between these hormones and human sexuality.

Rats selectively bred for showing divergent behavioral traits in response to stress or novelty or spontaneous yawning with a divergent frequency show similar changes in sexual behavior: the role of dopamine

Sexual behavior plays a fundamental role for reproduction in mammals and other animal species. It is characterized by an anticipatory and a consummatory phase, and several copulatory parameters have been identified in each phase, mainly in rats. Sexual behavior varies significantly across rats even when they are of the same strain and reared under identical conditions. This review shows that rats of the same strain selectively bred for showing a divergent behavioral trait when exposed to stress or novelty (i.e. Roman high and low avoidance rats, bred for their different avoidance response to the shuttle box, and high and low novelty exploration responders rats, bred for their different exploratory response to a novel environment) or a spontaneous behavior with divergent frequency (i.e. low and high yawning frequency rats, bred for their divergent yawning frequency) show similar differences in sexual behavior, mainly in copulatory pattern, but also in sexual motivation. As shown by behavioral pharmacology and intracerebral microdialysis experiments carried out mainly in Roman rats, these sexual differences may be due to a more robust dopaminergic tone present in the mesocorticolimbic dopaminergic system of one of the two sub-lines (e.g. high avoidance, high novelty exploration, and low yawning rat sub-lines). Thus, differences in genotype and/or in prenatal/postnatal environment lead not only to individual differences in temperament and environmental/emotional reactivity but also in sexual behavior. Because of the highly conserved mechanisms controlling reproduction in mammals, this may occur not only in rats but also in humans.

A case report of over-the-counter codeine dependence as consequence of self-medication for premature ejaculation

Over-the-counter (OTC) opioid abuse, including codeine, has been a growing problem around the world. Although the majority of the abusers use it for recreational purposes, many become dependent on it after having used it a medication for pain or cough. We present a case of codeine dependence where the initial prescribed use had been as a cough medication, but the subsequent abuse of it occurred the following self-medication for premature ejaculation. There is growing need for awareness among doctors and pharmacists of OTC abuse of opioids and for preventive interventions such as restricting supply, audit of pharmacies, training pharmacists, and counter staff and dispensing knowledge about proper use of opioid-containing medications to patients.

The mu (μ) and delta (δ) opioid receptors modulate boar sperm motility

Endogenous and exogenous opioids modulate reproductive functions in target cells via opioid receptors (μ, δ, and κ). Sperm motility is a metric of gamete functionality, and serves as a suitable parameter for in vitro drug-induced toxicity assays. This study identifies the presence and location of opioid receptors in pig spermatozoa as well as their functional response after in vitro challenge with known agonists (morphine [μ]; [D-Pen 2,5]-enkephanile [δ]; and U 50488 [κ]) and antagonists (naloxone [μ]; naltrindole [δ]; and nor-binaltrorphimine [κ]). Only the μ- and δ-opioid receptors were present in the boar sperm plasma membrane, overlying the acrosome, neck, and principal piece. Challenge experiments with agonists and antagonists identified both μ- and δ-opioid receptors as regulators of sperm kinematics, wherein μ maintains or increases sperm movement whereas δ decreases sperm motility over time. Mol. Reprod. Dev. 83: 724-734, 2016 © 2016 Wiley Periodicals, Inc.

Mating and social exposure induces an opioid-dependent conditioned place preference in male but not in female prairie voles (Microtus ochrogaster)

In rodents, sexual stimulation induces a positive affective state that is evaluated by the conditioned place preference (CPP) test. Opioids are released during sexual behavior and modulate the rewarding properties of this behavior. Prairie voles (Microtus ochrogaster) are a socially monogamous species, in which copulation with cohabitation for 6h induces a pair bond. However, the mating-induced reward state that could contribute to the establishment of the long-term pair bond has not been evaluated in this species. The present study aimed to determine whether one ejaculation or cohabitation with mating for 6h is rewarding for voles. We also evaluated whether this state is opioid dependent. Our results demonstrate that mating with one ejaculation and social cohabitation with mating for 6h induce a CPP in males, while exposure to a sexually receptive female without mating did not induce CPP. In the female vole, mating until one ejaculation, social cohabitation with mating, or exposure to a male without physical interaction for 6h did not induce CPP. To evaluate whether the rewarding state in males is opioid dependent, the antagonist naloxone was injected i.p. The administration of naloxone blocked the rewarding state induced by one ejaculation and by social cohabitation with mating. Our results demonstrate that in the prairie vole, on the basis of the CPP in the testing conditions used here, the stimulation received with one ejaculation and the mating conditions that lead to pair bonding formation may be rewarding for males, and this reward state is opioid dependent.

Neurogenesis in the olfactory bulb induced by paced mating in the female rat is opioid dependent

The possibility to control the rate of sexual stimulation that the female rat receives during a mating encounter (pacing) increases the number of newborn neurons that reach the granular layer of the accessory olfactory bulb (AOB). If females mate repeatedly, the increase in the number of neurons is observed in other regions of the AOB and in the main olfactory bulb (MOB). It has also been shown that paced mating induces a reward state mediated by opioids. There is also evidence that opioids modulate neurogenesis. In the present study, we evaluated whether the opioid receptor antagonist naloxone (NX) could reduce the increase in neurogenesis in the AOB induced by paced mating. Ovariectomized female rats were randomly divided in 5 different groups: 1) Control (not mated) treated with saline, 2) control (not mated) treated with naloxone, 3) females that mated without controlling the sexual interaction (no-pacing), 4) females injected with saline before pacing the sexual interaction and 5) females injected with NX before a paced mating session. We found, as previously described, that paced mating induced a higher number of new cells in the granular layer of the AOB. The administration of NX before paced mating, blocked the increase in the number of newborn cells and prevented these cells from differentiating into neurons. These data suggest that opioid peptides play a fundamental role in the neurogenesis induced by paced mating in female rats.

Do rats have orgasms?

BACKGROUND

Although humans experience orgasms with a degree of statistical regularity, they remain among the most enigmatic of sexual responses; difficult to define and even more difficult to study empirically. The question of whether animals experience orgasms is hampered by similar lack of definition and the additional necessity of making inferences from behavioral responses.

METHOD

Here we define three behavioral criteria, based on dimensions of the subjective experience of human orgasms described by Mah and Binik, to infer orgasm-like responses (OLRs) in other species: 1) physiological criteria that include pelvic floor and anal muscle contractions that stimulate seminal emission and/or ejaculation in the male, or that stimulate uterine and cervical contractions in the female; 2) short-term behavioral changes that reflect immediate awareness of a pleasurable hedonic reward state during copulation; and 3) long-term behavioral changes that depend on the reward state induced by the OLR, including sexual satiety, the strengthening of patterns of sexual arousal and desire in subsequent copulations, and the generation of conditioned place and partner preferences for contextual and partner-related cues associated with the reward state. We then examine whether physiological and behavioral data from observations of male and female rats during copulation, and in sexually-conditioned place- and partner-preference paradigms, are consistent with these criteria.

RESULTS

Both male and female rats display behavioral patterns consistent with OLRs.

CONCLUSIONS

The ability to infer OLRs in rats offers new possibilities to study the phenomenon in neurobiological and molecular detail, and to provide both comparative and translational perspectives that would be useful for both basic and clinical research.

The Female Sexual Response: Current Models, Neurobiological Underpinnings and Agents Currently Approved or Under Investigation for the Treatment of Hypoactive Sexual Desire Disorder

How a woman responds to sexual cues is highly dependent on a number of distinct, yet related, factors. Researchers have attempted to explain the female sexual response for decades, but no single model reigns supreme. Proper female sexual function relies on the interplay of somatic, psychosocial and neurobiological factors; misregulation of any of these components could result in sexual dysfunction. The most common sexual dysfunction disorder is hypoactive sexual desire disorder (HSDD). HSDD is a disorder affecting women across the world; a recent in-person diagnostic interview study conducted in the USA found that an estimated 7.4% of US women suffer from HSDD. Despite the disorder's prevalence, it is often overlooked as a formal diagnosis. In a survey of primary care physicians and obstetrics/gynaecology specialists, the number one reason for not assigning an HSDD diagnosis was the lack of a safe and effective therapy approved by the US Food and Drug Administration (FDA). This changed with the recent FDA approval of flibanserin (Addyi™) for the treatment of premenopausal women with acquired, generalized HSDD; there are still, however, no treatments approved outside the USA. HSDD is characterized by a marked decrease in sexual desire, an absence of motivation (also known as avolition) to engage in sexual activity, and the condition's hallmark symptom, marked patient distress. Research suggests that HSDD may arise from an imbalance of the excitatory and inhibitory neurobiological pathways that regulate the mammalian sexual response; top-down inhibition from the prefrontal cortex may be hyperactive, and/or bottom-up excitation to the limbic system may be hypoactive. Key neuromodulators for the excitatory pathways include norepinephrine, oxytocin, dopamine and melanocortins. Serotonin, opioids and endocannabinoids serve as key neuromodulators for the inhibitory pathways. Evolving treatment strategies have relied heavily on these crucial research findings, as many of the agents currently being investigated as treatment options for HSDD target and influence key players within these excitatory and inhibitory pathways, including various hormone therapies and centrally acting drugs, such as buspirone, bupropion and bremelanotide.

Orphanin FQ-ORL-1 regulation of reproduction and reproductive behavior in the female

Orphanin FQ (OFQ/N) and its receptor, opioid receptor-like receptor-1 (ORL-1), are expressed throughout steroid-responsive limbic and hypothalamic circuits that regulate female ovarian hormone feedback and reproductive behavior circuits. The arcuate nucleus of the hypothalamus (ARH) is a brain region that expresses OFQ/N and ORL-1 important for both sexual behavior and modulating estradiol feedback loops. Within the ARH, the activation of the OFQ/N-ORL-1 system facilitates sexual receptivity (lordosis) through the inhibition of β-endorphin neuronal activity. Estradiol initially activates ARH β-endorphin neurons to inhibit lordosis. Simultaneously, estradiol upregulates coexpression of OFQ/N and progesterone receptors and ORL-1 in ARH β-endorphin neurons. Ovarian hormones regulate pre- and postsynaptic coupling of ORL-1 to its G protein-coupled signaling pathways. When the steroid-primed rat is nonreceptive, estradiol acts pre- and postsynaptically to decrease the ability of the OFQ/N-ORL-1 system to inhibit ARH β-endorphin neurotransmission. Conversely, when sexually receptive, ORL-1 signaling is restored to inhibit β-endorphin neurotransmission. Although steroid signaling that facilitates lordosis converges to deactivate ARH β-endorphin neurons, estradiol-only facilitation of lordosis requires the activation of ORL-1, but estradiol+progesterone does not, indicating that multiple circuits mediate ovarian hormone signaling to deactivate ARH β-endorphin neurons. Research on the role of OFQ/N-ORL-1 in ovarian hormone feedback loops is just beginning. In the rat, OFQ/N may act to terminate gonadotropin-releasing hormone and luteinizing hormone release under positive and negative feedbacks. In the ewe, it appears to directly inhibit gonadotropin-releasing hormone release to mediate progesterone-negative feedback. As a whole, the localization and actions of OFQ/N-ORL-1 system indicate that it may mediate the actions of estradiol and progesterone to synchronize reproductive behavior and ovarian hormone feedback loops.

Sexual dysfunction improved in heroin-dependent men after methadone maintenance treatment in Tianjin, China

Objective

To investigate whether methadone maintenance treatment (MMT) is correlated with sexual dysfunction in heroin-dependent men and to determine the prevalence and risk factors of sexual dysfunction among men on MMT.

Methods

The study included a retrospective survey and a cross-sectional survey which contained interviews of 293 men who are currently engaged in MMT. The results of the two surveys were compared. For a subset of 43 participants, radioimmunoassay was additionally conducted using retrospective and prospective blood samples to test the levels of plasma testosterone and luteinizing hormone. Other study evaluations were the International Index of Erectile Function (IIEF-15), and Self-rating Depression Scale.

Results

Sexual dysfunction in all five IIEF-15 domains (erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction) was strongly associated with long-term use of heroin. A decrease in the severity of sexual dysfunction was associated with MMT initiation. Erectile dysfunction, lack of sexual desire, inability to orgasm, and lack of intercourse satisfaction were significantly correlated with increasing age of the participants. Methadone dose and duration of methadone treatment were not found to be associated with sexual dysfunction. The level of plasma testosterone significantly declined during methadone treatment, but results from multivariate analysis indicated low levels of testosterone were not the main cause of sexual dysfunction. No correlation between reported depression status and sexual function was found.

Conclusions

While high levels of sexual dysfunction were reported by heroin-dependent men in our study before and after MMT initiation, MMT appears to be correlated with improved sexual function in the population of the study.

Neural regulation of sexual function in men

Male sexual response is controlled by a series of neurally mediated phenomena regulating libido, motivation, arousal and genital responses such as penile erection and ejaculation. These neural events that occur in a hormonally defined milieu involve different neurophysiological, neurochemical, and neuropsychological parameters controlled by central mechanisms, spinal reflexes and peripheral nervous system. Epidemiologic studies have suggested the high prevalence of male sexual dysfunction worldwide with significant impact on the quality of life of patients suffering from this problem. The incidence of sexual dysfunction is particularly high among men with neurologic disorders. Sexual dysfunction in men, such as loss of sexual desire, erectile dysfunction (ED), changes in arousal, and disturbances in orgasm and ejaculation may involve organic causes, psychological problems, or both. Organic male sexual disorders include a wide variety of neurologic, vasculogenic, neurovascular or hormonal factors that interfere with libido, erection, ejaculation and orgasm. Neurogenic sexual dysfunction may result from a specific neurologic problem or it could be the presenting symptom of a developing neurologic disease. Neurologic ED could result from complications of chronic neurologic disorders, trauma, surgical injury or iatrogenic causes. These etiologic factors and the underlying pathophysiologic conditions could overlap, which should be considered when making a diagnosis and selecting a treatment. A detailed history of physical examination, neurologic disorders, as well as any past history of psychological and psychiatric disturbances, and a thorough neurological examination will provide better understanding of the underlying causes of neurogenic sexual dysfunction. In patients with spinal cord injury, the location of the lesion and the time of onset of injury should be determined. Therapeutic strategies against erectile dysfunction are initiated with the least invasive options using the phosphodiesterase inhibitors. When oral medication options are exhausted, intraurethral and intracavernosal therapies and ultimately vacuum constriction devices and penile implants are considered. Recent basic research has suggested the potential role of stem cell-based therapeutic strategies to protect penile neural integrity and reverse cavernosal neurodegeneration in experimental models. Further insight into the central, spinal and peripheral neural mechanisms of male sexual response may help precise diagnosis and better management of neurogenic sexual dysfunction in men.

The role of conditioning, learning and dopamine in sexual behavior: a narrative review of animal and human studies

Many theories of human sexual behavior assume that sexual stimuli obtain arousing properties through associative learning processes. It is widely accepted that classical conditioning contributes to the etiology of both normal and maladaptive human behaviors. Despite the hypothesized importance of basic learning processes in sexual behavior, research on classical conditioning of the sexual response in humans is scarce. In the present paper, animal studies and studies in humans on the role of pavlovian conditioning on sexual responses are reviewed. Animal research shows robust, direct effects of conditioning processes on partner- and place preference. On the contrast, the empirical research with humans in this area is limited and earlier studies within this field are plagued by methodological confounds. Although recent experimental demonstrations of human sexual conditioning are neither numerous nor robust, sexual arousal showed to be conditionable in both men and women. The present paper serves to highlight the major empirical findings and to renew the insight in how stimuli can acquire sexually arousing value. Hereby also related neurobiological processes in reward learning are discussed. Finally, the connections between animal and human research on the conditionability of sexual responses are discussed, and suggestions for future directions in human research are given.

Temporal and concentration-dependent effects of oestradiol on neural pathways mediating sexual receptivity

The acceptance of oestradiol signalling through receptors found in the cell membrane, as well as, the nucleus, has provided for a re-examination of the timing and location of the actions of oestradiol on neural circuits mediating sexual receptivity (lordosis). Oestradiol membrane signalling involves the transactivation of metabotrophic glutamate receptors (mGluRs) that transduce steroid information through protein kinase C signalling cascades producing rapid activation of lordosis-regulating circuits. It has been known for some time that oestradiol initially produces an inhibition of the medial preoptic nucleus. We have demonstrated that underlying this inhibition is oestradiol acting in the arcuate nucleus to induce β-endorphin release, which inhibits the medial preoptic nucleus through a μ-opioid receptor mechanism. This transient inhibition is relieved by either subsequent progesterone treatment or longer exposure to higher doses of oestradiol to facilitate lordosis behaviour. We review recent findings about oestradiol membrane signalling inducing dendritic spine formation in the arcuate nucleus that is critical for oestradiol induction of sexual receptivity. Moreover, we discuss the evidence that, in addition to oestrogen receptor α, several other putative membrane oestrogen receptors facilitate lordosis behaviour through regulation of the arcuate nucleus. These include the GRP30 and the STX activated Gq-mER. Finally, we report on the importance of GABA acting at GABAB receptors for oestradiol membrane signalling that regulates lordosis circuit activation and sexual receptivity.

Concurrent substance abuse is associated with sexual risk behavior among adults seeking treatment for prescription opioid dependence

BACKGROUND

Increasingly, new HIV infections among people who use drugs are attributed to sexual risk behavior. However, HIV prevention research targeting persons with opioid dependence continues to focus on drug injection practices. Moreover, despite the rising prevalence of prescription opioid dependence in the United States, little is known about HIV risk in this population.

METHODS

This study examined the prevalence of sexual risk behavior among patients with opioid dependence who primarily use prescription opioids for non-medical purposes. As part of a multi-site clinical trial, participants (N = 653) completed a baseline assessment that included the Risk Behavior Survey.

RESULTS

In the past month, 74% were sexually active. Of these, most had opposite sex partners (97.3%) and vaginal intercourse (97.1%); anal intercourse was uncommon (3.1%). The majority reported unprotected intercourse (76.5%), but few had multiple partners (11.3%). Unprotected intercourse was associated with history of other substance dependence (adjusted odds ratio [AOR] = 1.73), and having multiple partners was associated with concurrent cocaine use (AOR = 2.54). Injection drug use in the past month was rare (2.5%).

CONCLUSIONS

While the majority of sexually active participants engaged in unprotected intercourse, the proportion with multiple sex partners was low relative to other samples of persons who use illicit drugs. Among persons with non-medical prescription opioid dependence, those who concurrently use other substances may be at elevated risk for HIV infection. Comprehensive assessment of substance abuse history among individuals dependent upon prescription opioids is critical for identifying patients who may require additional clinical interventions to reduce HIV sexual risk behavior.

Neuropeptides and central control of sexual behaviour from the past to the present: a review

Of the numerous neuropeptides identified in the central nervous system, only a few are involved in the control of sexual behaviour. Among these, the most studied are oxytocin, adrenocorticotropin, α-melanocyte stimulating hormone and opioid peptides. While opioid peptides inhibit sexual performance, the others facilitate sexual behaviour in most of the species studied so far (rats, mice, monkeys and humans). However, evidence for a sexual role of gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin and galanin-like peptide, cholecystokinin, substance P, vasoactive intestinal peptide, vasopressin, angiotensin II, hypocretins/orexins and VGF-derived peptides are also available. Corticotropin releasing factor, neuropeptide Y, cholecystokinin, vasopressin and angiotensin II inhibit, while substance P, vasoactive intestinal peptide, hypocretins/orexins and some VGF-derived peptide facilitate sexual behaviour. Neuropeptides influence sexual behaviour by acting mainly in the hypothalamic nuclei (i.e., lateral hypothalamus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus), in the medial preoptic area and in the spinal cord. However, it is often unclear whether neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except in a few cases (e.g., opioid peptides and oxytocin). Unfortunately, scarce information has been added in the last 15 years on the neural mechanisms by which neuropeptides influence sexual behaviour, most studied neuropeptides apart. This may be due to a decreased interest of researchers on neuropeptides and sexual behaviour or on sexual behaviour in general. Such a decrease may be related to the discovery of orally effective, locally acting type V phosphodiesterase inhibitors for the therapy of erectile dysfunction.

Sex for fun: a synthesis of human and animal neurobiology

Sex is a fundamental pleasure, and crucial to the survival of our species. Though not many people would disagree with the proposition that sexual behaviour depends on the brain, the neuroscientific study of human sex is still relatively taboo and much remains to be discovered. On the contrary, excellent experimental animal models (mostly rat) are available that have uncovered major behavioural, neurochemical, and neuroanatomical characteristics of sexual behaviour. Restructuring sexual behaviour into broader terms reflecting behavioural states (wanting, liking, and inhibition) facilitates species comparison, revealing many similarities between animal and human sexual pleasure cycles, some of which can serve as potential avenues of new human sex research. In particular, behavioural and brain evidence clearly shows that motivational and consummatory phases are fundamentally distinct, and that genitally-induced sexual reward is a major factor in sexual learning mechanisms.

The role of motivation and reward neural systems in vocal communication in songbirds

Many vertebrates are highly motivated to communicate, suggesting that the consequences of communication may be rewarding. Past studies show that dopamine and opioids in the medial preoptic nucleus (mPOA) and ventral tegmental area (VTA) play distinct roles in motivation and reward. In songbirds, multiple lines of recent evidence indicate that the roles of dopamine and opioid activity in mPOA and VTA in male birdsong differ depending upon whether song is used to attract females (sexually-motivated) or is produced spontaneously (undirected). Evidence is reviewed supporting the hypotheses that (1) mPOA and VTA interact to influence the context in which a male sings, (2) distinct patterns of dopamine activity underlie the motivation to produce sexually-motivated and undirected song, (3) sexually-motivated communication is externally reinforced by opioids released as part of social interactions, and (4) undirected communication is facilitated and rewarded by immediate opioid release linked to the act of singing.

Opioid mediation of learned sexual behavior

Identifying the role of opioids in the mediation of learned sexual behaviors has been complicated by the use of differing methodologies in the investigations. In this review addressing multiple species, techniques, and pharmaceutical manipulations, several features of opioid mediation become apparent. Opioids are differentially involved in conditioned and unconditioned sexual behaviors. The timing of the delivery of a sexual reinforcer during conditioning trials, especially those using male subjects, acutely influences the role that opioids have in learning. Opioids may be particularly important in the maintenance of conditioned sexual behaviors during periods of non-reinforcement. This appears to be true both for probe trials and procedures designed explicitly to extinguish a sexual conditioned response. These features of opioid mediation of learning do not appear to be restricted to sexual conditioning paradigms. This suggests that, as for other aspects of sexual learning that despite distinctive features conform to underlying behavioral principles, the mediation of conditioned sexual behavior by opioids relies on processes common across reinforcement systems.

Who, what, where, when (and maybe even why)? How the experience of sexual reward connects sexual desire, preference, and performance

Although sexual behavior is controlled by hormonal and neurochemical actions in the brain, sexual experience induces a degree of plasticity that allows animals to form instrumental and Pavlovian associations that predict sexual outcomes, thereby directing the strength of sexual responding. This review describes how experience with sexual reward strengthens the development of sexual behavior and induces sexually-conditioned place and partner preferences in rats. In both male and female rats, early sexual experience with partners scented with a neutral or even noxious odor induces a preference for scented partners in subsequent choice tests. Those preferences can also be induced by injections of morphine or oxytocin paired with a male rat's first exposure to scented females, indicating that pharmacological activation of opioid or oxytocin receptors can "stand in" for the sexual reward-related neurochemical processes normally activated by sexual stimulation. Conversely, conditioned place or partner preferences can be blocked by the opioid receptor antagonist naloxone. A somatosensory cue (a rodent jacket) paired with sexual reward comes to elicit sexual arousal in male rats, such that paired rats with the jacket off show dramatic copulatory deficits. We propose that endogenous opioid activation forms the basis of sexual reward, which also sensitizes hypothalamic and mesolimbic dopamine systems in the presence of cues that predict sexual reward. Those systems act to focus attention on, and activate goal-directed behavior toward, reward-related stimuli. Thus, a critical period exists during an individual's early sexual experience that creates a "love map" or Gestalt of features, movements, feelings, and interpersonal interactions associated with sexual reward.