Male mice ultrasonic vocalizations enhance female sexual approach and hypothalamic kisspeptin neuron activity

Kisspeptin and neurokinin B: roles in reproductive health

Kisspeptin and neurokinin B (NKB) play a key role in several physiological processes including in puberty, adult reproductive function including the menstrual cycle, as well as mediating the symptoms of menopause. Infundibular kisspeptin neurons, which coexpress NKB, regulate the activity of gonadotropin-releasing hormone (GnRH) neurons and thus the physiological pulsatile secretion of GnRH from the hypothalamus. Outside of their hypothalamic reproductive roles, these peptides are implicated in several physiological functions including sexual behavior and attraction, placental function, and bone health. Over the last two decades, research findings have considerably enhanced our understanding of the physiological regulation of the hypothalamic-pituitary-gonadal (HPG) axis and identified potential therapeutic applications. For example, recognition of the role of kisspeptin as the natural inductor of ovulation has led to research investigating its use as a safer, more physiological trigger of oocyte maturation in in vitro fertilization (IVF) treatment. Moreover, the key role of NKB in the pathophysiology of menopausal hot flashes has led to the development of pharmacological antagonism of this pathway. Indeed, fezolinetant, a neurokinin 3 receptor antagonist, has recently received Food and Drug Administration (FDA) approval for clinical use to treat menopausal vasomotor symptoms. Here, we discuss the roles of kisspeptin and NKB in human physiology, including in the regulation of puberty, menstrual cyclicity, reproductive behavior, pregnancy, menopause, and bone homeostasis. We describe how perturbations of these key physiological processes can result in disease states and consider how kisspeptin and NKB could be exploited diagnostically as well as therapeutically to treat reproductive disorders.

Do rodents smell with sound?

Chemosensation via olfaction is a critical process underlying social interactions in many different species. Past studies of olfaction in mammals often have focused on its mechanisms in isolation from other systems, limiting the generalizability of findings from olfactory research to perceptual processes in other modalities. Studies of chemical communication, in particular, have progressed independently of research on vocal behavior and acoustic communication. Those bioacousticians who have considered how sound production and reception might interact with olfaction often portray odors as cues to the kinds of vocalizations that might be functionally useful. In the olfaction literature, vocalizations are rarely mentioned. Here, we propose that ultrasonic vocalizations may affect what rodents smell by altering the deposition of inhaled particles and that rodents coordinate active sniffing with sound production specifically to enhance reception of pheromones. In this scenario, rodent vocalizations may contribute to a unique mode of active olfactory sensing, in addition to whatever roles they serve as social signals. Consideration of this hypothesis highlights the perceptual advantages that parallel coordination of multiple sensorimotor processes may provide to individuals exploring novel situations and environments, especially those involving dynamic social interactions.

The Emerging Therapeutic Potential of Kisspeptin and Neurokinin B

Kisspeptin (KP) and neurokinin B (NKB) are neuropeptides that govern the reproductive endocrine axis through regulating hypothalamic gonadotropin-releasing hormone (GnRH) neuronal activity and pulsatile GnRH secretion. Their critical role in reproductive health was first identified after inactivating variants in genes encoding for KP or NKB signaling were shown to result in congenital hypogonadotropic hypogonadism and a failure of pubertal development. Over the past 2 decades since their discovery, a wealth of evidence from both basic and translational research has laid the foundation for potential therapeutic applications. Beyond KP's function in the hypothalamus, it is also expressed in the placenta, liver, pancreas, adipose tissue, bone, and limbic regions, giving rise to several avenues of research for use in the diagnosis and treatment of pregnancy, metabolic, liver, bone, and behavioral disorders. The role played by NKB in stimulating the hypothalamic thermoregulatory center to mediate menopausal hot flashes has led to the development of medications that antagonize its action as a novel nonsteroidal therapeutic agent for this indication. Furthermore, the ability of NKB antagonism to partially suppress (but not abolish) the reproductive endocrine axis has supported its potential use for the treatment of various reproductive disorders including polycystic ovary syndrome, uterine fibroids, and endometriosis. This review will provide a comprehensive up-to-date overview of the preclinical and clinical data that have paved the way for the development of diagnostic and therapeutic applications of KP and NKB.

Courtship behaviour reveals temporal regularity is a critical social cue in mouse communication

While animals navigating the real world face a barrage of sensory input, their brains evolved to perceptually compress multidimensional information by selectively extracting the features relevant for survival. Notably, communication signals supporting social interactions in several mammalian species consist of acoustically complex sequences of vocalisations. However, little is known about what information listeners extract from such time-varying sensory streams. Here, we utilise female mice's natural behavioural response to male courtship songs to identify the relevant acoustic dimensions used in their social decisions. We found that females were highly sensitive to disruptions of song temporal regularity and preferentially approached playbacks of intact over rhythmically irregular versions of male songs. In contrast, female behaviour was invariant to manipulations affecting the songs' sequential organisation or the spectro-temporal structure of individual syllables. The results reveal temporal regularity as a key acoustic cue extracted by mammalian listeners from complex vocal sequences during goal-directed social behaviour.

Attraction of female house mice to male ultrasonic courtship vocalizations depends on their social experience and estrous stage

Male house mice (Mus musculus) produce complex ultrasonic vocalizations (USVs), especially during courtship and mating. Playback experiments suggest that female attraction towards recordings of male USVs depends on their social experience, paternal exposure, and estrous stage. We conducted a playback experiment with wild-derived female house mice (M. musculus musculus) and compared their attraction to male USVs versus the same recording without USVs (background noise). We tested whether female attraction to USVs is influenced by the following factors: (1) social housing (two versus one female per cage); (2) neonatal paternal exposure (rearing females with versus without father); and (3) estrous stage. We found that females showed a significant attraction to male USVs but only when they were housed socially with another female. Individually housed females showed the opposite response. We found no evidence that pre-weaning exposure to a father influenced females' preferences, whereas estrous stage influenced females' attraction to male USVs: females not in estrus showed preferences towards male USVs, whereas estrous females did not. Finally, we found that individually housed females were more likely to be in sexually receptive estrous stages than those housed socially, and that attraction to male USVs was most pronounced amongst non-receptive females that were socially housed. Our findings indicate that the attraction of female mice to male USVs depends upon their social experience and estrous stage, though not paternal exposure. They contribute to the growing number of studies showing that social housing and estrous stage can influence the behavior of house mice and we show how such unreported variables can contribute to the replication crisis.

The Neurobiology of Love and Pair Bonding from Human and Animal Perspectives

Love is a powerful emotional experience that is rooted in ancient neurobiological processes shared with other species that pair bond. Considerable insights have been gained into the neural mechanisms driving the evolutionary antecedents of love by studies in animal models of pair bonding, particularly in monogamous species such as prairie voles (Microtus ochrogaster). Here, we provide an overview of the roles of oxytocin, dopamine, and vasopressin in regulating neural circuits responsible for generating bonds in animals and humans alike. We begin with the evolutionary origins of bonding in mother-infant relationships and then examine the neurobiological underpinnings of each stage of bonding. Oxytocin and dopamine interact to link the neural representation of partner stimuli with the social reward of courtship and mating to create a nurturing bond between individuals. Vasopressin facilitates mate-guarding behaviors, potentially related to the human experience of jealousy. We further discuss the psychological and physiological stress following partner separation and their adaptive function, as well as evidence of the positive health outcomes associated with being pair-bonded based on both animal and human studies.

Male scent but not courtship vocalizations induce estrus in wild female house mice

Exposure to males or male urinary scent can induce and accelerate the rate of female estrous cycling in house mice ("Whitten effect"), and this response has been replicated many times since its discovery over 60 years ago. Here, we tested whether exposing female mice to recordings of male courtship ultrasonic vocalizations (USVs) induces estrous cycling, and whether exposure to both male scent and USVs has a stronger effect than to either of these stimuli alone. We conducted our study with 60 wild-derived female house mice (Mus musculus musculus). After singly housing females for 14 days, we monitored estrous stages via vaginal cytology for two weeks while isolated from males or male stimuli. We continued monitoring estrus for two more weeks during experimental exposure to one of four different types of stimuli: (1) clean bedding and background noise playback (negative control); (2) recordings of male USVs (16 min per day) and clean bedding (male USV treatment); (3) soiled male bedding and background noise playback (male odor treatment; positive control); or (4) male USVs and soiled male bedding (male odor and USV treatment). Females were then paired with males to test whether any of the four treatments influenced female reproduction (especially latency to birth). We confirmed that exposure to male odor increased female cycling, as expected, but exposure to recordings of male USVs had no effect on estrus. Females exposed to both USVs and odor went through more cycles compared to controls, but did not differ significantly from exposure to male odor (and background noise). After pairing females with a male, females showing male odor-induced cycling produced their first litter sooner than controls, whereas USVs did not have such an effect. This is the first study to our knowledge to show that male odor induces estrus in wild house mice and to show functional effects on reproduction. Our results do not support the hypothesis that male vocalizations induce female estrus, although we suggest other approaches that could be used to further test this hypothesis.

Vocal signals with different social or non-social contexts in two wild rodent species (Mus caroli and Rattus losea)

The ultrasonic vocalizations (USVs) of rodents play a substantial role in the communication and interaction between individuals; exhibit a high degree of complexity; and are influenced by a multitude of developmental, environmental, and phylogenetic factors. The functions of USVs are mainly studied in laboratory mice or rats. However, the behavioral relevance of USVs in wild rodents is poorly studied. In this work, we systematically investigated the vocal repertoire of the wild mouse Mus caroli and wild rat Rattus losea in multiple social or non-social contexts, e.g., pup-isolation, juvenile-play, paired opposite-sex encounter, female-female interaction, social-exploring, or foot-shock treatment. Unlike the laboratory mice, M. caroli, whose USVs were recorded during pup-isolation and courtship behaviors, did not produce any vocal sounds during juvenile-play and female-female interactions. R. losea, similar to laboratory rats, emitted USVs in all test situations. We found higher peak frequencies of USVs in both these two wild rodent species than in laboratory animals. Moreover, the parameters and structures of USVs varied significantly across different social or non-social contexts even within each species, confirming the context-sensitivity and complexity of vocal signals in rodents. We also noted a striking difference in call types between these two species: no downward type occurred in M. caroli, but no upward type occurred in R. losea, thereby highlighting the interspecific difference of vocal signals among rodents. Thus, the present study presents behavioral foundations of the vocalization context in wild mice and wild rats, and contributes to revealing the behavioral significance of widely used USVs in rodents.

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.

Prelimbic cortex responds to male ultrasonic vocalizations in the presence of a male pheromone in female mice

Sensory signals are critical to perform adaptive social behavior. During copulation, male mice emit ultrasonic vocalizations (USVs). Our previous studies have shown that female mice exhibit approach behavior toward sound sources of male USVs and that, after being exposed to a male pheromone, exocrine gland-secreting peptide 1 (ESP1), female mice exhibited a preference toward a particular type of male USVs. These findings suggest that male USVs modulate female courtship behavior. However, it remains unclear which brain regions and what cell types of neurons are involved in neuronal processing of male USVs. To clarify this issue, immediate early gene analysis, behavioral analysis, and neurochemical analysis were performed. The in situ hybridization analysis of c-fos mRNA in multiple brain regions showed that neurons in the prelimbic cortex were responsive to presentation of male USVs in the presence of ESP1. Furthermore, this study found that activity of prelimbic cortex was correlated with the duration of female exploration behavior toward a sound source of the USVs. Finally, by using double immunohistochemistry, the present study showed that the prelimbic neurons responding to the presentation of male USVs were presumably excitatory glutamatergic neurons. These results suggest that the prelimbic cortex may facilitate female courtship behavior in response to male USVs.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

Gaining insights into the internal states of the rodent brain through vocal communications

Animals display various behaviors during social interactions. Social behaviors have been proposed to be driven by the internal states of the animals, reflecting their emotional or motivational states. However, the internal states that drive social behaviors are complex and difficult to interpret. Many animals, including mice, use vocalizations for communication in various social contexts. This review provides an overview of current understandings of mouse vocal communications, its underlying neural circuitry, and the potential to use vocal communications as a readout for the animal's internal states during social interactions.

Current Perspectives on Kisspeptins Role in Behaviour

The neuropeptide kisspeptin is now well-established as the master regulator of the mammalian reproductive axis. Beyond the hypothalamus, kisspeptin and its cognate receptor are also extensively distributed in extra-hypothalamic brain regions. An expanding pool of animal and human data demonstrates that kisspeptin sits within an extensive neuroanatomical and functional framework through which it can integrate a range of internal and external cues with appropriate neuroendocrine and behavioural responses. In keeping with this, recent studies reveal wide-reaching effects of kisspeptin on key behaviours such as olfactory-mediated partner preference, sexual motivation, copulatory behaviour, bonding, mood, and emotions. In this review, we provide a comprehensive update on the current animal and human literature highlighting the far-reaching behaviour and mood-altering roles of kisspeptin. A comprehensive understanding of this important area in kisspeptin biology is key to the escalating development of kisspeptin-based therapies for common reproductive and related psychological and psychosexual disorders.

Unexpected Interacting Effects of Physical (Radiation) and Chemical (Bisphenol A) Treatments on Male Reproductive Functions in Mice

For decades, numerous chemical pollutants have been described to interfere with endogenous hormone metabolism/signaling altering reproductive functions. Among these endocrine disrupting substances, Bisphenol A (BPA), a widely used compound, is known to negatively impact germ and somatic cells in the testis. Physical agents, such as ionizing radiation, were also described to perturb spermatogenesis. Despite the fact that we are constantly exposed to numerous environmental chemical and physical compounds, very few studies explore the impact of combined exposure to chemical and physical pollutants on reproductive health. The aim of this study was to describe the impact of fetal co-exposure to BPA and IR on testicular function in mice. We exposed pregnant mice to 10 µM BPA (corresponding to 0.5 mg/kg/day) in drinking water from 10.5 dpc until birth, and we irradiated mice with 0.2 Gy (γ-ray, RAD) at 12.5 days post-conception. Co-exposure to BPA and γ-ray induces DNA damage in fetal germ cells in an additive manner, leading to a long-lasting decrease in germ cell abundance. We also observed significant alteration of adult steroidogenesis by RAD exposure independently of the BPA exposure. This is illustrated by the downregulation of steroidogenic genes and the decrease of the number of adult Leydig cells. As a consequence, courtship behavior is modified, and male ultrasonic vocalizations associated with courtship decreased. In conclusion, this study provides evidence for the importance of broadening the concept of endocrine disruptors to include physical agents, leading to a reevaluation of risk management and regulatory decisions.

Testosterone Increases the Emission of Ultrasonic Vocalizations With Different Acoustic Characteristics in Mice

Testosterone masculinizes male sexual behavior through an organizational and activational effects. We previously reported that the emission of ultrasonic vocalizations (USVs) in male mice was dependent on the organizational effects of testosterone; females treated with testosterone in the perinatal and peripubertal periods, but not in adults, had increased USV emissions compared to males. Recently, it was revealed that male USVs have various acoustic characteristics and these variations were related to behavioral interactions with other mice. In this regard, the detailed acoustic characteristic changes induced by testosterone have not been fully elucidated. Here, we revealed that testosterone administered to female and male mice modulated the acoustic characteristics of USVs. There was no clear difference in acoustic characteristics between males and females. Call frequencies were higher in testosterone propionate (TP)-treated males and females compared to control males and females. When the calls were classified into nine types, there was also no distinctive difference between males and females, but TP increased the number of calls with a high frequency, and decreased the number of calls with a low frequency and short duration. The transition analysis by call type revealed that even though there was no statistically significant difference, TP-treated males and females had a similar pattern of transition to control males and females, respectively. Collectively, these results suggest that testosterone treatment can enhance the emission of USVs both in male and female, but the acoustic characteristics of TP-treated females were not the same as those of intact males.

Primed to vocalize: Wild-derived male house mice increase vocalization rate and diversity after a previous encounter with a female

Males in a wide variety of taxa, including insects, birds and mammals, produce vocalizations to attract females. Male house mice emit ultrasonic vocalizations (USVs), especially during courtship and mating, which are surprising complex. It is often suggested that male mice vocalize at higher rates after interacting with a female, but the evidence is mixed depending upon the strain of mice. We conducted a study with wild-derived house mice (Mus musculus musculus) to test whether male courtship vocalizations (i.e., vocalizations emitted in a sexual context) are influenced by a prior direct interaction with a female, and if so, determine how long the effect lasts. We allowed sexually naïve males to directly interact with a female for five minutes (sexual priming), and then we recorded males'vocalizations either 1, 10, 20, or 30 days later when presented with an unfamiliar female (separated by a perforated partition) and female scent. We automatically detected USVs and processed recordings using the Automatic Mouse Ultrasound Detector (A-MUD version 3.2), and we describe our improved version of this tool and tests of its performance. We measured vocalization rate and spectro-temporal features and we manually classified USVs into 15 types to investigate priming effects on vocal repertoire diversity and composition. After sexual priming, males emitted nearly three times as many USVs, they had a larger repertoire diversity, and their vocalizations had different spectro-temporal features (USV length, slope and variability in USV frequency) compared to unprimed controls. Unprimed control males had the most distinctive repertoire composition compared to the primed groups. Most of the effects were found when comparing unprimed to all primed males (treatment models), irrespective of the time since priming. Timepoint models showed that USV length increased 1 day after priming, that repertoire diversity increased 1 and 20 days after priming, and that the variability of USV frequencies was lower 20 and 30 days after priming. Our results show that wild-derived male mice increased the number and diversity of courtship vocalizations if they previously interacted with a female. Thus, the USVs of house mice are not only context-dependent, they depend upon previous social experience and perhaps the contexts of these experiences. The effect of sexual priming on male courtship vocalizations is likely mediated by neuro-endocrine-mechanisms, which may function to advertise males' sexual arousal and facilitate social recognition.

Sex differences in vocalizations to familiar or unfamiliar females in mice

Mice, both wild and laboratory strains, emit ultrasound to communicate. The sex differences between male to female (male-female) and female to female (female-female) ultrasonic vocalizations (USVs) have been discussed for decades. In the present study, we compared the number of USVs emitted to familiar and unfamiliar females by both males (male-female USVs) and females (female-female USVs). We found that females vocalized more to unfamiliar than to familiar females. By contrast, males exhibited more USVs to familiar partners. This sexually dimorphic behaviour suggests that mice change their vocal behaviour in response to the social context, and their perception of the context is based on social cognition and memory. In addition, because males vocalized more to familiar females, USVs appear to be not only a response to novel objects or individuals, but also a social response.

Testosterone regulates the emission of ultrasonic vocalizations and mounting behavior during different developmental periods in mice

Testosterone masculinizes male sexual behavior by providing organizational and activational effects during the perinatal and peripubertal periods and during adulthood, respectively. We revealed that the emission of ultrasonic vocalizations (USVs) and mounting behavior was regulated by different neural circuits. However, the detailed testosterone effects on these two behaviors have not been fully elucidated. Here, we evaluated the time-dependent effects of testosterone on USVs and mounting behavior in mice using a testosterone treatment model, in which females were treated with testosterone to assess the "gain-of-function" and a "loss-of-function" model. In the loss-of-function model, we used Ad4BP/SF-1^ΔFLC/- male mice, in which testosterone production was abolished in prenatal and postnatal stages, and Ad4BP/SF-1^ΔFLC/ΔFLC mice, in which testosterone production was markedly reduced only in prenatal stages. When testosterone was administered to female mice during the neonatal and peripubertal periods, but not during adulthood, USV emissions increased. Conversely, testosterone treatment in adult female mice increased the mounting behavior, but not USVs. In Ad4BP/SF-1^ΔFLC/- mice, USVs and mounting behavior was completely absent. Ad4BP/SF-1^ΔFLC/ΔFLC male mice displayed equivalent levels of USVs but less mounting behavior. Collectively, these results suggest that testosterone has dual regulatory roles in USV emissions and mounting behavior.

Physiological and Behavioral Responses to Vocalization Playback in Mice

In mice, the caller’s production of social vocalizations has been extensively studied but the effect of these vocalizations on the listener is less understood, with playback studies to date utilizing one vocalization category or listeners of one sex. This study examines how several categories of mouse vocalizations affect listeners of both sexes to better understand the communicative functions of these vocal categories. We examined physiological and behavioral responses of male and female CBA/CaJ mice to playback of four social vocalization categories: ultrasonic vocalizations (USVs), low-frequency harmonic calls, mid-frequency vocalizations, and noisy calls. Based on the conditions under which these calls are emitted, we hypothesized that playback of these vocal categories would have differential effects on the listeners. In females, playback of all four vocalization categories increased stress hormone levels (corticosterone), but only the non-USV categories increased corticosterone in males. The magnitude of corticosterone increase in non-USV trials was greater in females than in males. In open field tests, all four vocal categories decreased central ambulation in males and females, indicating an increase in anxiety-related behavior. Further, we found that the proportions of USVs emitted by subjects, but not their overall calling rates, were affected by playback of some vocal categories, suggesting that vocalization categories have different communication content. These results show that, even in the absence of behavioral and acoustic contextual features, each vocal category evokes physiological and behavioral responses in mice, with some differences in responses as a function of the listener’s sex and playback signal. These findings suggest that at least some of the vocal categories have distinct communicative functions.

Ultrasonic vocalizations in house mice depend upon genetic relatedness of mating partners and correlate with subsequent reproductive success

Background

Courtship vocalizations are used by males of many species to attract and influence the behavior of potential mating partners. Our aim here was to investigate the modulation and reproductive consequences of courtship ultrasonic vocalizations (USVs) in wild-derived house mice (Mus musculus musculus). The courtship USVs of male mice are surprisingly complex and are composed of a variety of different syllable types. Our specific aims were to test whether (1) the emission of courtship USVs depends upon the kinship of a potential mating partner, and (2) whether USV emission during courtship affects the pairs’ subsequent reproductive success.

Results

We experimentally presented males with an unfamiliar female that was either genetically related or unrelated, and we recorded USV emission, first while the sexes were separated by a perforated partition and then during direct interactions, after removing the partition. USVs were detected by the Automatic Mouse Ultrasound Detector (A-MUD) and manually classified into 15 syllable types. The mice were kept together to test whether and how courtship vocalizations predict their subsequent reproductive success. We found that the mice significantly increased their amount of vocalizations (vocal performance) and number of syllable types (vocal repertoire) after the partition was removed and they began interacting directly. We show that unrelated pairs emitted longer and more complex USVs compared to related pairs during direct interactions. Unrelated pairs also had a greater reproductive success compared to related pairs, and in addition we found a negative correlation between the mean length and amount of vocalizations with the latency to their first litter.

Conclusion

Our study provides evidence that house mice modulate the emission of courtship USVs depending upon the kinship of potential mating partners, and that courtship USVs correlate with reproductive success.

Male mice adjust courtship behavior in response to female multimodal signals

Multimodal signaling is nearly ubiquitous across animal taxa. While much research has focused on male signal production contributing to female mate-choice or preferences, females often give their own multimodal signals during intersexual communication events. Multimodal signal components are often classified based on whether they contain redundant information (e.g., the backup hypothesis) or non-redundant information (e.g., the multiple messages hypothesis) from the perspective of the receiver. We investigated the role of two different female vocalizations produced by the female house mouse (Mus musculus): the broadband, relatively low-frequency squeaks (broadband vocalizations or BBVs,), and the higher-frequency ultrasonic vocalizations (USVs). These female vocalizations may convey differently valenced information to the male receivers. We paired these vocalizations with and without female urine to examine the influence of combining information across multiple modalities. We found evidence that female urine and vocalizations act as non-redundant multimodal cues as males responded with different behaviors and vocalization rates depending on the female signal presented. Additionally, male mice responded with greater courtship effort to the multimodal combination of female USVs paired with female urine than any other signal combination. These results suggest that the olfactory information contained in female urine provides the context by which males can then evaluate potentially ambiguous female vocalizations.

Female C57BL/6 and BALB/c mice differently use the acoustic features of male ultrasonic vocalizations for social preferences

Male mice emit ultrasonic vocalizations (USVs) in response to the presence of female mice and their urine. Male USVs attract females, enhancing female reproductive functions, and are thus considered as the courtship song. Previous studies have shown that female mice exhibit disassortative social preferences for male USVs. However, it remains unclear what acoustic features female mice use for the development of these preferences. To address this, we examined social preferences of female C57BL/6 and BALB/c mice using the three-chamber preference test using recorded male USVs. To dissociate the peak frequencies of these USVs from their syllable structure, we digitally manipulated the peak frequencies accordingly. We found that female mice preferred USVs that were dissimilar to those of their own strain. We also observed that, while female C57BL/6 mice were sensitive to changes in the syllable structure and the peak frequency, female BALB/c mice were sensitive to differences in the syllable structure. Our results demonstrate that female C57BL/6 and BALB/c mice differently use the acoustic features such as the peak frequency and the syllable structure for exhibiting disassortative social preferences.

Effect of Sociosexual Experience and Aging on Number of Courtship Ultrasonic Vocalizations in Male Mice

Sexual behaviors are instinctually exhibited without prior training, but they are modulated by experience. One of the precopulatory behaviors in adult male mice, courtship ultrasonic vocalizations (USVs), has attracted considerable academic attention recently. Male mice emit ultrasounds as courtship behavior when encountering females. However, the modulatory effects of experience on USVs remain unclear. In the present study, we aimed to clarify the effects of sociosexual experience and aging on adult male vocalizations. First, we examined the effect of aging. The number of USVs decreased in an age-dependent manner. Following this, young adult male mice were co-housed for two weeks with normal female mice or ovariectomized (OVX) female mice, or housed without female mice, and the number of courtship USVs before and after co-housing were compared. In males housed with normal or OVX females, USVs increased significantly after co-housing. In contrast, males housed without females did not exhibit a significant increase of USVs. A facilitative effect of co-housing with female mice on vocalizations was also observed in aged males. In addition, females used as co-housing partners became pregnant, and the reproductive rate may be related to the vocal activity observed in the partnered males. These results indicate that sociosexual experience and aging affect vocalization activity, which may be related to courtship and/or reproductive function.

Medial Preoptic Area Modulates Courtship Ultrasonic Vocalization in Adult Male Mice

Adult male mice emit highly complex ultrasonic vocalizations (USVs) in response to female conspecifics. Such USVs, thought to facilitate courtship behaviors, are routinely measured as a behavioral index in mouse models of neurodevelopmental and psychiatric disorders such as autism. While the regulation of USVs by genetic factors has been extensively characterized, the neural mechanisms that control USV production remain largely unknown. Here, we report that optogenetic activation of the medial preoptic area (mPOA) elicited the production of USVs that were acoustically similar to courtship USVs in adult mice. Moreover, mPOA vesicular GABA transporter-positive (Vgat +) neurons were more effective at driving USV production than vesicular glutamate transporter 2-positive neurons. Furthermore, ablation of mPOA Vgat+ neurons resulted in altered spectral features and syllable usage of USVs in targeted males. Together, these results demonstrate that the mPOA plays a crucial role in modulating courtship USVs and this may serve as an entry point for future dissection of the neural circuitry underlying USV production.

Female mice exhibit both sexual and social partner preferences for vocalizing males

Acoustic signals are widely used as courtship signals in the animal kingdom. It has long been known that male mice emit ultrasonic vocalizations (USVs) in the presence of female mice or in response to female secretions. This observation led to the hypothesis that male USVs play a role in courtship behavior. Although previous studies showed that female mice have a social partner preference for vocalizing males, it is not known if they exhibit a sexual partner preference when given a choice. To address this issue, we examined the copulatory behaviors of female mice with either devocalized males (with or without the playback of the USVs) or sham-operated males in 2 different behavioral paradigms: the no-choice paradigm in the home cage of a male mouse (without choice of mating partners) or the mate-choice paradigm in a 3-chambered apparatus (with choice of mating partners). In the no-choice paradigm, female mice exhibited comparable sexual receptivity with sham-operated and devocalized males. In addition, we found that female mice showed more approach behavior towards devocalized males when male USVs were played back. In the mate-choice paradigm, female mice visited more frequently and stayed longer with sham-operated than devocalized males. Furthermore, we showed that female mice received more intromissions from sham-operated males than devocalized males. In summary, our results suggested that, although female mice can copulate equally with both devocalized and vocalizing males when given no choice of mating partner, female mice exhibit both sexual and social partner preferences for vocalizing males in the mate-choice paradigm.

Kisspeptin and the control of emotions, mood and reproductive behaviour

Reproduction is fundamental for the survival of all species and requires meticulous synchronisation of a diverse complement of neural, endocrine and related behaviours. The reproductive hormone kisspeptin (encoded by the KISS1/Kiss1 gene) is now a well-established orchestrator of reproductive hormones, acting upstream of gonadotrophin-releasing hormone (GnRH) at the apex of the hypothalamic–pituitary–gonadal (HPG) reproductive axis. Beyond the hypothalamus, kisspeptin is also expressed in limbic and paralimbic brain regions, which are areas of the neurobiological network implicated in sexual and emotional behaviours. We are now forming a more comprehensive appreciation of extra-hypothalamic kisspeptin signalling and the complex role of kisspeptin as an upstream mediator of reproductive behaviours, including olfactory-driven partner preference, copulatory behaviour, audition, mood and emotion. An increasing body of research from zebrafish to humans has implicated kisspeptin in the integration of reproductive hormones with an overall positive influence on these reproductive behaviours. In this review, we critically appraise the current literature regarding kisspeptin and its control of reproductive behaviour. Collectively, these data significantly enhance our understanding of the integration of reproductive hormones and behaviour and provide the foundation for kisspeptin-based therapies to treat related disorders of body and mind.

Intrinsic links among sex, emotion, and reproduction

Species survival is dependent on successful reproduction. This begins with a desire to mate, followed by selection of a partner, copulation and in monogamous mammals including humans, requires emotions and behaviours necessary to maintain partner bonds for the benefit of rearing young. Hormones are integral to all of these stages and not only mediate physiological and endocrine processes involved in reproduction, but also act as neuromodulators within limbic brain centres to facilitate the expression of innate emotions and behaviours required for reproduction. A significant body of work is unravelling the roles of several key hormones in the modulation of mood states and sexual behaviours; however, a full understanding of the integration of these intrinsic links among sexual and emotional brain circuits still eludes us. This review summarises the evidence to date and postulates future directions to identify potential psycho-neuroendocrine frameworks linking sexual and emotional brain processes with reproduction.

Mice modulate ultrasonic calling bouts according to sociosexual context

Mice produce various sounds within the ultrasonic range in social contexts. Although these sounds are often used as an index of sociability in biomedical research, their biological significance remains poorly understood. We previously showed that mice repeatedly produced calls in a sequence (i.e. calling bout), which can vary in their structure, such as Simple, Complex or Harmonics. In this study, we investigated the use of the three types of calling bouts in different sociosexual interactions, including both same- and opposite-sex contexts. In same-sex contexts, males typically produced a Simple calling bout, whereas females mostly produced a Complex one. By contrast, in the opposite-sex context, they produced all the three types of calling bouts, but the use of each calling type varied according to the progress and mode of sociosexual interaction (e.g. Harmonic calling bout was specifically produced during reproductive behaviour). These results indicate that mice change the structure of calling bout according to sociosexual contexts, suggesting the presence of multiple functional signals in their ultrasonic communication.

Neuronal activity in the sagittalis nucleus of the hypothalamus after ovarian steroid hormone manipulation and sexual behavior in female rat

During extended observation of estrogen receptor (ER) α-immunoreactive neurons in the hypothalamus, we previously identified a novel nucleus, the Sagittalis Nucleus of the Hypothalamus (SGN), in the interstitial area between the arcuate nucleus and the ventromedial hypothalamic nucleus. The SGN exhibits sexual dimorphism in its volume and cell count, and estrous cycle related variations in ERα-immunoreactivity. These characteristics of the SGN implicate the nucleus in sex-biased brain functions and behaviors. In this study, we examined involvement of the SGN in sexual arousal in female rats. Immunohistochemical staining of c-Fos, a marker of neuronal activity was performed after administration of an estrus-inducing dose of estrogen and progesterone in ovariectomized female rats. Analysis of microscopic images showed a significant increase in the number of c-Fos-expressing neurons in the SGN following hormonal manipulation. Moreover, neuronal activity in the region exhibited a further increase after each animal was coupled with a male and allowed to mate. These results suggest that the SGN plays an important role in sexual activity in female rat.