Sexual behavior and dendritic spine density of posterodorsal medial amygdala neurons in oxytocin knockout female mice

The bilevel chamber revealed differential involvement of vasopressin and oxytocin receptors in female mouse sexual behavior

Arginine vasopressin (AVP) and oxytocin (OT) are well-known as neuropeptides that regulate various social behaviors in mammals. However, little is known about their role in mouse female sexual behavior. Thus, we investigated the role of AVP (v1a and v1b) and OT receptors on female sexual behavior. First, we devised a new apparatus, the bilevel chamber, to accurately observe female mouse sexual behavior. This apparatus allowed for a more precisely measurement of lordosis as receptivity and rejection-like behavior (newly defined in this study), a reversed expression of proceptivity. To address our research question, we evaluated female sexual behavior in mice lacking v1a (aKO), v1b (bKO), both v1a and v1b (dKO), and OT (OTRKO) receptors. aKO females showed decreased rejection-like behavior but a normal level of lordosis, whereas bKO females showed almost no lordosis and no change in rejection-like behavior. In addition, dKO females showed normal lordosis levels, suggesting that the v1b receptor promotes lordosis, but not necessarily, while the v1a receptor latently suppresses it. In contrast, although OTRKO did not influence lordosis, it significantly increased rejection-like behavior. In summary, the present results demonstrated that the v1a receptor inhibits proceptivity and receptivity, whereas the v1b and OT receptors facilitate receptivity and proceptivity, respectively.

From Parental Behavior to Sexual Function: Recent Advances in Oxytocin Research

Purpose of Review

Oxytocin plays many diverse roles in physiological and behavioral processes, including social activity, parental nurturing, stress responses, and sexual function. In this narrative review, we provide an update on the most noteworthy recent findings in this fascinating field.

Recent Findings

The development of techniques such as serial two-photon tomography and fiber photometry have provided a window into oxytocin neuroanatomy and real-time neuronal activity during social interactions. fMRI and complementary mapping techniques offer new insights into oxytocin's influence on brain activity and connectivity. Indeed, oxytocin has recently been found to influence the acquisition of maternal care behaviors and to mediate the influence of social touch on brain development and social interaction. Additionally, oxytocin plays a crucial role in male sexual function, affecting erectile activity and ejaculation, while its role in females remains controversial. Recent studies also highlight oxytocin's interaction with other neuropeptides, such as melanin-concentrating hormone, serotonin, and arginine vasopressin, influencing social and affective behaviors. Finally, an update is provided on the status of clinical trials involving oxytocin as a therapeutic intervention.

Summary

The exploration of oxytocin's complexities and its interplay with other neuropeptides holds promise for targeted treatment in various health and disease contexts. Overall, these findings contribute to the discovery of new and specific pathways to allow therapeutic targeting of oxytocin to treat disorders.

Sexual incentive motivation, sexual behavior, and general arousal: Do rats and humans tell the same story?

Sexual incentive stimuli activate sexual motivation and heighten the level of general arousal. The sexual motive may induce the individual to approach the incentive, and eventually to initiate sexual acts. Both approach and the ensuing copulatory interaction further enhance general arousal. We present data from rodents and humans in support of these assertions. We then suggest that orgasm is experienced when the combined level of excitation surpasses a threshold. In order to analyze the neurobiological bases of sexual motivation, we employ the concept of a central motive state. We then discuss the mechanisms involved in the long- and short-term control of that state as well as those mediating the momentaneous actions of sexual incentive stimuli. This leads to an analysis of the neurobiology behind the interindividual differences in responsivity of the sexual central motive state. Knowledge is still fragmentary, and many contradictory observations have been made. Nevertheless, we conclude that the basic mechanisms of sexual motivation and the role of general arousal are similar in rodents and humans.

Oxytocin system driven by experiences modifies social recognition and neuron morphology in female BALB/c mice

The oxytocin (OT) system, affected by life experiences, modulates neuron morphology in a sex-specific manner, leading to sex differences in social interactions. To date, few studies have focused on the OT system and social interactions of female mice. In this study, we used maternal deprivation (MD) and its possible treatment, environmental enrichment (EE), to affect social recognition in female BALB/c mice. We checked neuron morphology, synaptic connections, oxytocinergic (OTergic) neurons in the hypothalamus paraventricular nucleus (PVH), and OT receptor (OTR) in the basolateral amygdala (BLA) and layer II/III of the prelimbic cortex (PL). Our results showed that MD induced social recognition impairments, increased OTR levels in the BLA, and, meanwhile, reduced OTergic neurons in the magnocellular region of the PVH (mPVH). Decreased Nissl bodies, increased cell nuclei, and increased dendrites of projection neurons paralleled the increased OTR levels in the BLA of MD mice. EE restored MD-induced the impairments of novel object recognition and sociability; this effect paralleled a decrease in cell density in the PL and an increase in OTergic neurons in the parvocellular regions of the PVH and synaptic connections in the BLA and layer II/III of the PL. Our findings indicate that early life stress such as MD impairs social recognition, and meanwhile, remodels neuron morphology region-specifically in the female brain, apparently in the BLA but slightly in the PL; and EE could partially restore the deficits induced by MD. The results provide new insights into sex differences in the prevalence of psychological development disorders.

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.

Oxytocin is indispensable for conspecific-odor preference and controls the initiation of female, but not male, sexual behavior in mice

Oxytocin (OT) has been demonstrated to be involved in various social behaviors in mammals. However, OT gene knockout (OTKO) mice can conceive and deliver successfully, though females cannot rear their pups because of lack of lactation. Here, we investigated the sociosexual behavior of both sexes in two experimental setups: olfactory preference for sexual partner's odor and direct social interaction in an enriched condition. In the preference test, mice were given a choice of two airborne odors derived from intact male and receptive female mice, or from intact or castrated male mice. Wild-type (WT) mice significantly preferred opposite-sex odors, whereas OTKO mice showed vigorous but equivalent exploration to all stimuli. In social interactions in the enriched condition, no difference in sexual behavior was found between WT and OTKO males. In contrast, WT female initiated sexual behavior at the second week test, while OTKO females required 4 weeks to receive successful mounts. Neuronal activation by odor stimulation was compared between WT and OTKO mice. The numbers of cFos-immunoreactive cells increased in the medial amygdala and the preoptic area after exposure to opposite-sex odors in WT mice, whereas the increase was suppressed in OTKO mice. We conclude that OT plays an important role in the regulation of olfactory-related social behavior in both male and female mice. The influence of OT was greater in female mice, especially during social interactions involving the acquisition of sexual experience.

Factors promoting vulnerability to dysregulated stress reactivity and stress-related disease

Effective coordination of the biological stress response is integral for the behavioural well-being of an organism. Stress reactivity is coordinated by an interplay of the neuroendocrine system and the sympathetic nervous system. The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in orchestrating the bodily responses to stress, and the activity of the axis can be modified by a wide range of experiential events. This review focuses on several factors that influence subsequent HPA axis reactivity. Some of these factors include early-life adversity, exposure to chronic stress, immune activation and traumatic brain injury. The central premise is that each of these experiences serves as a general vulnerability factor that accelerates future HPA axis reactivity in ways that make individuals more sensitive to stress challenges, therefore feeding forward into the exacerbation of ongoing (or greater susceptibility toward) future stress-related disease states, especially as they pertain to negative affect and overall brain health.

Effect of long-term treatment with classical neuroleptics on NPQ/spexin, kisspeptin and POMC mRNA expression in the male rat amygdala

Neuroleptics modulate the expression level of some regulatory neuropeptides in the brain. However, if these therapeutics influence the peptidergic circuits in the amygdala remains unclear. This study specifies the impact profile of the classical antipsychotic drugs on mRNA expression of the spexin/NPQ, kisspeptin-1 and POMC in the rat amygdala. Animals were treated with haloperidol and chlorpromazine for 28 days prior to transcript quantification via qPCR. Haloperidol and chlorpromazine induced a change in the expression of all neuropeptides analyzed. Both drugs led to the decrease of Kiss-1 expression, whereas in POMC and spexin/NPQ their up-regulation in the amygdala was detected. These modulating effects on may represent alternative, so far unknown mechanisms, of classical antipsychotic drugs triggering pharmacological responses.

Female sexual behavior in mice is controlled by kisspeptin neurons

Sexual behavior is essential for the survival of many species. In female rodents, mate preference and copulatory behavior depend on pheromones and are synchronized with ovulation to ensure reproductive success. The neural circuits driving this orchestration in the brain have, however, remained elusive. Here, we demonstrate that neurons controlling ovulation in the mammalian brain are at the core of a branching neural circuit governing both mate preference and copulatory behavior. We show that male odors detected in the vomeronasal organ activate kisspeptin neurons in female mice. Classical kisspeptin/Kiss1R signaling subsequently triggers olfactory-driven mate preference. In contrast, copulatory behavior is elicited by kisspeptin neurons in a parallel circuit independent of Kiss1R involving nitric oxide signaling. Consistent with this, we find that kisspeptin neurons impinge onto nitric oxide-synthesizing neurons in the ventromedial hypothalamus. Our data establish kisspeptin neurons as a central regulatory hub orchestrating sexual behavior in the female mouse brain.

Mate preference and copulatory behavior in female rodents are coordinated with the ovulation cycles of the animal. This study shows that hypothalamic kisspeptin neurons control both mate choice and copulation, and therefore, that sexual behavior and ovulation may be synchronized by the same neuropeptide.

The Impact of Oxytocin Gene Knockout on Sexual Behavior and Gene Expression Related to Neuroendocrine Systems in the Brain of Female Mice

Social relations are built and maintained from the interaction among individuals. The oxytocin (OT), vasopressin (VP), estrogen, dopamine, and their receptors are involved in the modulation of sexual behavior in females. This study aimed to analyze the impact of OT gene knockout (OTKO) on sexual behavior and the gene expression of oxytocin (OTR), estrogen alpha (ERα), estrogen beta (ERβ), vasopressin (V1aR), and dopamine (D2R) receptors in the olfactory bulb (OB), prefrontal cortex (PFC), hippocampus (HPC), and hypothalamus (HPT), as well as in the synthesis of VP in the HPT of female mice. Wild-type (WT) littermates were used for comparisons. The CDNAs were synthesized by polymerase chain reaction and the gene expression was calculated with the 2-ΔΔCt formula. Our results showed that the absence of OT caused an increase in the frequency and duration of non-receptive postures and a decrease in receptive postures in the OTKO. OTKO females showed a significant decrease in the gene expression of OTR in the HPC, V1aR in the HPT, and ERα and ERβ in the PFC. There was no significant difference in the gene expression of D2R of OTKO. However, OTKO showed an increased gene expression of V1aR in the HPC. There is no significant difference in VP mRNA synthesis in the HPT between OTKO and WT. Our findings demonstrate that the absence of OT leads to significant changes in the expression of the studied genes (OTR, ERα, ERβ, V1aR), and these changes may contribute to the decreased sexual behavior observed in OTKO females.

Oxytocin in learning and addiction: From early discoveries to the present

Oxytocin (OXT) has a plethora of effects on brain function. This review provides a historical overview of the development of research on OXT and drug addiction. By focusing on research that has emerged from our laboratories, we describe how early discoveries of the influence of OXT on learning and memory processes and the emerging conceptualization of addiction as 'pathological learning' have contributed to the demonstration that OXT effectively attenuates long-term neuroadaptation related to opiate and psychostimulant addiction. Through integrating earlier evidence with recent discoveries of the social/affiliative role of OXT, we propose that OXT may interfere with reward and addiction by influencing neurobiological processes involved in stress, learning and memory and social/affiliative behavior.