Neural and Hormonal Basis of Opposite-Sex Preference by Chemosensory Signals

Effects of postweaning cadmium exposure on socioemotional behaviors in adolescent male mice

Exposure to cadmium (Cd), a toxic heavy metal classified as an environmental endocrine disruptor, can exert significant toxicity in both animals and humans. However, the potential effects of Cd exposure on socioemotional behaviors are still poorly understood, as are the underlying mechanisms. In the present study, employing a series of behavioral tests as well as 16 S rRNA sequencing analysis, we investigated the long-term effects of Cd exposure on socioemotional behaviors and their associated mechanisms in mice based on the brain-gut interaction theory. The results showed that postweaning exposure to Cd reduced the ability to resist depression, decreased social interaction, subtly altered sexual preference, and changed the composition of the gut microbiota in male mice during adolescence. These findings provided direct evidence for the deleterious effects of exposure to Cd in the postweaning period on socioemotional behaviors later in adolescence, and suggested that these effects of Cd exposure may be linked to changes in the gut microbiota.

Activity of estrogen receptor β expressing neurons in the medial amygdala regulates preference toward receptive females in male mice

The processing of information regarding the sex and reproductive state of conspecific individuals is critical for successful reproduction and survival in males. Generally, male mice exhibit a preference toward the odor of sexually receptive (RF) over nonreceptive females (XF) or gonadally intact males (IM). Previous studies suggested the involvement of estrogen receptor beta (ERβ) expressed in the medial amygdala (MeA) in male preference toward RF. To further delineate the role played by ERβ in the MeA in the neuronal network regulating male preference, we developed a new ERβ-iCre mouse line using the CRISPR-Cas9 system. Fiber photometry Ca2+ imaging revealed that ERβ-expressing neurons in the postero-dorsal part of the MeA (MeApd-ERβ+ neurons) were more active during social investigation toward RF compared to copresented XF or IM mice in a preference test. Chemogenetic inhibition of MeApd-ERβ+ neuronal activity abolished a preference to RF in "RF vs. XF," but not "RF vs. IM," tests. Analysis with cre-dependent retrograde tracing viral vectors identified the principal part of the bed nucleus of stria terminalis (BNSTp) as a primary projection site of MeApd-ERβ+ neurons. Fiber photometry recording in the BNSTp during a preference test revealed that chemogenetic inhibition of MeApd-ERβ+ neurons abolished differential neuronal activity of BNSTp cells as well as a preference to RF against XF but not against IM mice. Collectively, these findings demonstrate for the first time that MeApd-ERβ+ neuronal activity is required for expression of receptivity-based preference (i.e., RF vs. XF) but not sex-based preference (i.e., RF vs. IM) in male mice.

Vomeronasal Receptors Associated with Circulating Estrogen Processing Chemosensory Cues in Semi-Aquatic Mammals

In numerous animals, one essential chemosensory organ that detects chemical signals is the vomeronasal organ (VNO), which is involved in species-specific behaviors, including social and sexual behaviors. The purpose of this study is to investigate the mechanism underlying the processing of chemosensory cues in semi-aquatic mammals using muskrats as the animal model. Muskrat (Ondatra zibethicus) has a sensitive VNO system that activates seasonal breeding behaviors through receiving specific substances, including pheromones and hormones. Vomeronasal organ receptor type 1 (V1R) and type 2 (V2R) and estrogen receptor α and β (ERα and ERβ) were found in sensory epithelial cells, non-sensory epithelial cells and lamina propria cells of the female muskrats' VNO. V2R and ERα mRNA levels in the VNO during the breeding period declined sharply, in comparison to those during the non-breeding period, while V1R and ERβ mRNA levels were detected reversely. Additionally, transcriptomic study in the VNO identified that differently expressed genes might be related to estrogen signal and metabolic pathways. These findings suggested that the seasonal structural and functional changes in the VNO of female muskrats with different reproductive status and estrogen was regulated through binding to ERα and ERβ in the female muskrats' VNO.

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.

Clomiphene citrate treatment during perinatal development alters adult partner preference, mating behaviour and androgen receptor and vasopressin in the male mandarin vole Microtus mandarinus

During development, many aspects of behaviour, including partner preferences and sexual behaviour, are "organized" by neural aromatization of androgen and oestrogen. This study aimed to analyse these processes in the mandarin vole (Microtus mandarinus); this is a novel mammalian model exhibiting strong monogamous pair bonds. Male pups were treated daily with a sesame oil only (MC) or the oestrogen receptor blocker-clomiphene citrate sesame oil mixture (MT) from prenatal day 14 to postnatal day 10. Female pups were treated daily with sesame oil only (FC). Partner preferences, sexual behaviour, and the expression of androgen receptor (AR) and arginine vasopressin (AVP) were examined when animals were 3 months old. The MT and FC groups exhibited male-directed partner preferences and feminized behaviour. AR-immunoreactive neurons (AR-IRs) in the medial preoptic area (mPOA), bed nucleus of stria terminalis (BNST), and medial amygdaloid nucleus (MeA) were reduced in MT males compared to MC males, and there was no significant difference in the number of AR-IRs between MT males and FC females. AVP-immunoreactive neurons (AVP-IRs) in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were reduced in MT males compared to MC males, and there were no significant differences in the number of AVP-IRs between MT males and FC females. The results indicate a significant role of hormone signalling in the development of male mate preference in the novel monogamous mammal model.

Mass Spectrometry Approaches Empowering Neuropeptide Discovery and Therapeutics

The discovery of insulin in the early 1900s ushered in the era of research related to peptides acting as hormones and neuromodulators, among other regulatory roles. These essential gene products are found in all organisms, from the most primitive to the most evolved, and carry important biologic information that coordinates complex physiology and behavior; their misregulation has been implicated in a variety of diseases. The evolutionary origins of at least 30 neuropeptide signaling systems have been traced to the common ancestor of protostomes and deuterostomes. With the use of relevant animal models and modern technologies, we can gain mechanistic insight into orthologous and paralogous endogenous peptides and translate that knowledge into medically relevant insights and new treatments. Groundbreaking advances in medicine and basic science influence how signaling peptides are defined today. The precise mechanistic pathways for over 100 endogenous peptides in mammals are now known and have laid the foundation for multiple drug development pipelines. Peptide biologics have become valuable drugs due to their unique specificity and biologic activity, lack of toxic metabolites, and minimal undesirable interactions. This review outlines modern technologies that enable neuropeptide discovery and characterization, and highlights lessons from nature made possible by neuropeptide research in relevant animal models that is being adopted by the pharmaceutical industry. We conclude with a brief overview of approaches/strategies for effective development of peptides as drugs. SIGNIFICANCE STATEMENT: Neuropeptides, an important class of cell-cell signaling molecules, are involved in maintaining a range of physiological functions. Since the discovery of insulin's activity, over 100 bioactive peptides and peptide analogs have been used as therapeutics. Because these are complex molecules not easily predicted from a genome and their activity can change with subtle chemical modifications, mass spectrometry (MS) has significantly empowered peptide discovery and characterization. This review highlights contributions of MS-based research towards the development of therapeutic peptides.

A Protocol for the Non-invasive Method of Ultrasound Separation During the Sociosexual Vocal-Non-contact Model in Rats

Ultrasonic vocalization (USV) is one of the measurable behavioral parameters of sociosexual interactions in rats. To precisely and accurately describe the neurobehavioral properties of USV and the potentially related specific emotional responsiveness of animals, we need to know which animals vocalize and what is their exact behavioral and physiological response. To this end, we modified the non-contact cage [non-contact erection model (NCE)] by adding a modification [vocalization-non-contact erection (VOC-NCE)] that makes it possible to assign emitted ultrasonic signals to a particular animal. Typically, the NCE cage consists of two compartments separated by perforated baffles. A male is placed in one section, and a receptive female is placed in the other section. This makes possible the accurate description of sexual parameters related to the cues controlled by the experimenter. In VOC-NCE, we completely separated the male USV from the female USV by three appropriately perforated baffles and located microphones combined with ultrasonic screening. We recorded emission in both typical bands, the so-called 22- and 50-kHz bands, with various subtypes, thus highlighting the utility of our protocol to investigate the sexual dimorphism of vocalization. Similar to the anticipatory model, we showed that emission can occur without acoustic feedback from concomitants during the VOC-NCE test. Therefore, we propose a relatively simple method for assigning individual vocalization. We discuss its usefulness and limitations in assessing vocal differentiation related to sexual parameters, adaptive changes during conditioning procedures, and further applications.

Sex-dependent features of social behavior differ between distinct laboratory mouse strains and their mixed offspring

The survival of individuals of gregarious species depends on their social interactions. In humans, atypical social behavior is a hallmark of several psychopathological conditions, many of which have sex-specific manifestations. Various laboratory mouse strains are used to reveal the mechanisms mediating typical and atypical social behavior in mammals. Here, we used three social discrimination tests to characterize social behavior in males and females of three widely used laboratory mouse strains (C57BL/6J, BALB/c, and ICR). We found marked sex- and strain-specific differences in the behavior exhibited by subjects, in a test-dependent manner. Interestingly, some characteristics were strain-dependent, while others were sex-dependent. We then crossbred C57BL/6J and BALB/c mice and found that offspring of such crossbreeding exhibit social behavior which differs from both parental strains and depends on the specific combination of parental strains. Thus, social behavior of laboratory mice is sex- and strain-specific and depends on both genetic and environmental factors.

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Social investigation behavior of laboratory mice is highly strain- and sex-specific

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Some behavioral aspects are either strain- or sex-specific, but not both

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Mixed offspring of distinct strains behave differently from both parental strains

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The behavior of mixed offspring depends on the specific combination of parents

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.