Chemosensory cues from the lacrimal and preputial glands stimulate production of IP3 in the vomeronasal organ and aggression in male mice

Biostimulation methods based on chemical communication improve semen quality in male breeder rabbits

Biostimulation aims to optimize reproductive parameters as part of animal management practices by modulating animal sensory systems. Chemical signals, mostly known as pheromones, have a great potential in this regard. This study was conducted to determine the influence of short-term male rabbit exposure to different biological secretions, potentially pheromone-mediated, on reproductive parameters of males. Four groups of 18 males each were exposed to A) doe urine, B) 2-phenoxyethanol, C) doe vaginal swab, and D) distilled water (control), three times over a 2.5h exposure window, just before semen collection. Semen volume, sperm concentration and motility, as well as subpopulation analysis of the spermatozoa were assessed for each condition. Additionally, testosterone levels in blood samples were monitored at five time points over the 2.5 h exposure window. We found a higher percentage of motile, progressive, fast progressive and mid-progressive spermatozoa in any of the three experimental groups compared to the control group. In contrast, the semen volume and the percentage of immotile and non-progressive spermatozoa was generally higher in the control group. We then identified a higher proportion of a subpopulation of fast and progressive spermatozoa in groups A, B, and C compared to group D. Our data indicates that sperm motility increases when animals are exposed to specific biological fluids potentially containing pheromones, and that an increase in sperm volume does not correlate with an increase in spermatozoa concentration, progressiveness, and speed. Finally, no differences in testosterone levels were found among comparisons, although males of groups A and C (exposed to natural female biological fluids) showed a tendency towards higher testosterone levels. In conclusion, our results indicate that rabbit sperm quality increases upon exposure to the biological secretions proposed, thereby supporting further investigation into their molecular identity. This exploration could eventually pave the way for implementing the use of pheromones in rabbit husbandry to enhance reproductive and productive parameters in farmed rabbits.

Non-targeted Metabolomics Analysis Reveals Distinct Metabolic Profiles Between Positive and Negative Emotional Tears of Humans: A Preliminary Study

Background Basal, reflex, and emotional tears differ in chemical components. It is not yet known whether chemical differences exist in tears of different emotions. We investigated the biochemical basis of emotional tears by performing non-targeted metabolomics analyses of positive and negative emotional tears of humans. Methods Samples of reflex, negative, and positive emotional tears were obtained from 12 healthy college participants (11 females and one male). Untargeted metabolomics was performed to identify metabolites in different types of tears. The differentially altered metabolites were screened and assessed using univariate and multivariate analyses. Results The orthogonal partial least squares discriminant analysis model showed that reflex, negative, and positive emotional tears were clearly separated. A total of 133 significantly differentially expressed metabolites of electrospray ionization source (ESI-) mode were identified between negative and positive emotional tears. The top 50 differentially expressed metabolites between negative and positive emotional tears were highly correlated. Pathway analysis revealed that secretion of negative emotional tears was associated with some synapses in the brain, regulation of a series of endocrine hormones, including the estrogen signaling pathway, and inflammation activities, while secretion of positive emotional tears was correlated with biotin and caffeine metabolism. Conclusions It is indicated that metabolic profiles of reflex, positive, and negative emotional tears of humans are distinct, and secretion of the tears involves distinct biological activities. Therefore, we present a chemical method for detecting human emotions, which may become a powerful tool for the diagnosis of mental diseases and the identification of fake tears.

Emotional expression in human odour

Recent work has demonstrated that human body odour alters with changing emotional state and that emotionally laden odours can affect the physiology and behaviour of people exposed to them. Here we review these discoveries, which we believe add to a growing recognition that the human sense of smell and its potential role in social interactions have been underappreciated. However, we also critically evaluate the current evidence, with a particular focus on methodology and the interpretation of emotional odour studies. We argue that while the evidence convincingly indicates that humans retain a capacity for olfactory communication of emotion, the extent to which this occurs in ordinary social interaction remains an open question. Future studies should place fewer restrictions on participant selection and lifestyle and adopt more realistic experimental designs. We also need to devote more consideration to underlying mechanisms and to recognise the constraints that these may place on effective communication. Finally, we outline some promising approaches to address these issues, and raise some broader theoretical questions that such approaches may help us to answer.

Blocking olfactory input alters aggression in male and female California mice (Peromyscus californicus)

Olfactory input into the brain can be disrupted by a variety of environmental factors, including exposure to pathogens or environmental contaminants. Olfactory cues are often eliminated in laboratory rats and mice through highly invasive procedures like olfactory bulbectomy, which may also disrupt accessory olfactory pathways and detection of non-volatile odors. In the present study, we tested whether inducing anosmia through intranasal infusion of zinc gluconate alters aggression in a monogamous, biparental rodent species, the California mouse (Peromyscus californicus). This less invasive method of manipulating olfaction selectively targets the olfactory epithelium and reduces the detection of volatile odors. Treatment with zinc gluconate extended the time required for male and female California mice to find hidden pieces of apple and reduced the amount of time spent investigating bedding that was soiled by unfamiliar males. Moreover, inhibition of olfaction with zinc gluconate reduced aggressiveness in both sexes as demonstrated by an increased attack latency in the resident-intruder test among same-sex dyads from the same treatment group. These results suggest that volatile olfactory cues are necessary for agonistic responses in both male and female California mice. Therefore, even in species with complex social systems that include territorial aggression and monogamy, volatile olfactory cues modulate agonistic behavior.

Exocrine scent marking: Coordinative role of arginine vasopressin in the systemic regulation of social signaling behaviors

Arginine vasopressin (AVP) is a neurohypophysial hormone that coordinatively regulates central socio-emotional behavior and peripheral control of antidiuretic fluid homeostasis. Most mammals, including rodents, utilize exocrine or urine-contained scent marking as a social signaling tool that facilitates social adaptation. The exocrine scent marking behavior is postulated to fine-tune sensory and cognitive abilities to recognize key social features via exocrine/urinary olfactory cues and subsequently control exocrine deposition or urinary marking through the mediation of osmotic fluid balance. AVP is implicated as a major player in controlling both recognition and signaling responses. This review provides constructive hypotheses on the coordinative processes of the AVP neurohypophysial circuits in the systemic regulations of fluid control and social-communicative behavior, via the expression of exocrine scent marking, and further emphasizes a potential role of AVP in a common mechanism underlying social communication in rodents.

Analysis of Social Process in Two Inbred Strains of Male Mice: A Predominance of Contact-Based Investigation in BALB/c Mice

Developing mouse models for social communication deficits requires a better understanding of the nature of social investigatory processes between mice. Mice use different investigatory strategies based on a possibility of contacts with social sources. A detailed investigation of contact distance revealed strain differences in behavioral strategy between two male inbred C57BL/6 (B6) and BALB/c (BALB) mouse strains. When direct physical contact with stimulus mice was restricted, BALB mice displayed lower social approaches than B6 mice, accompanied by heightened innate anxiety in an unfamiliar environment. However, both BALB and B6 mice expressed distinct object and social recognition in the habituation/dishabituation paradigm. When allowed direct contact with stimulus mice, both B6 and BALB mice showed approach and discrimination of strain differences in the stimulus mice. Furthermore, BALB mice discriminated individuals of the same strain among cagemates and showed a discrete aversion to the anogenital but not facial region of the stranger mice. This anogenital aversion disappeared when the stranger mice received a buspirone injection that reduced anxiety or when familiar cagemates were exposed. These strain differences in investigatory strategies illustrate that B6 mice are able to respond to and process social cues in a vicinity, which does not require physical contact with the source, while BALB mice predominantly process social cues by direct contact with the source. Although BALB mice exhibit marked anxiety and defensive responses to unfamiliarity, there is no evidence of any defect in sociability in BALB mice as a possible autism model.

Revisiting the revisit: added evidence for a social chemosignal in human emotional tears

In a study by Gelstein et al., we found that human emotional tears act as a social chemosignal. In the first of three different experiments in that study we observed that sniffing women’s emotional tears reduced the sexual attractiveness attributed by men to pictures of women’s faces. In a study partly titled “Chemosignaling effects of human tears revisited”, Gračanin et al. claim failed replication of this effect in a series of experiments, one they described as “exactly the same procedure” as Gelstein. Given that Gračanin et al. refused our extended offer to jointly replicate the experiment at our expense, we can merely comment on their effort. We find that Gračanin, who are not a chemosignaling laboratory, used methodology that falls short of standards typically applied in chemosignaling research. Thus, their experiments were profoundly different from Gelstein. Finally, we found that in reanalysing their raw data we could in fact replicate the effect from Gelstein. Thus, we conclude that the failed replication in Gračanin is neither a replication nor failed.

Progesterone impairs social recognition in male rats

The influence of progesterone in the brain and on the behavior of females is fairly well understood. However, less is known about the effect of progesterone in the male system. In male rats, receptors for progesterone are present in virtually all vasopressin (AVP) immunoreactive cells in the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). This colocalization functions to regulate AVP expression, as progesterone and/or progestin receptors (PR)s suppress AVP expression in these same extrahypothalamic regions in the brain. These data suggest that progesterone may influence AVP-dependent behavior. While AVP is implicated in numerous behavioral and physiological functions in rodents, AVP appears essential for social recognition of conspecifics. Therefore, we examined the effects of progesterone on social recognition. We report that progesterone plays an important role in modulating social recognition in the male brain, as progesterone treatment leads to a significant impairment of social recognition in male rats. Moreover, progesterone appears to act on PRs to impair social recognition, as progesterone impairment of social recognition is blocked by a PR antagonist, RU-486. Social recognition is also impaired by a specific progestin agonist, R5020. Interestingly, we show that progesterone does not interfere with either general memory or olfactory processes, suggesting that progesterone seems critically important to social recognition memory. These data provide strong evidence that physiological levels of progesterone can have an important impact on social behavior in male rats.

Extreme aggression in male squid induced by a β-MSP-like pheromone

Male-male aggression is widespread in the animal kingdom and subserves many functions related to the acquisition or retention of resources such as shelter, food, and mates. These functions have been studied widely in the context of sexual selection, yet the proximate mechanisms that trigger or strengthen aggression are not well known for many taxa. Various external sensory cues (visual, audio, chemical) acting alone or in combination stimulate the complex behavioral interactions of fighting behaviors. Here we report the discovery of a 10 kDa protein, termed Loligo β-microseminoprotein (Loligo β-MSP), that immediately and dramatically changes the behavior of male squid from calm swimming and schooling to extreme fighting, even in the absence of females. Females synthesize Loligo β-MSP in their reproductive exocrine glands and embed the protein in the outer tunic of egg capsules, which are deposited on the open sea floor. Males are attracted to the eggs visually, but upon touching them and contacting Loligo β-MSP, they immediately escalate into intense physical fighting with any nearby males. Loligo β-MSP is a distant member of the chordate β-microseminoprotein family found in mammalian reproductive secretions, suggesting that this gene family may have taxonomically widespread roles in sexual competition.

Regulation of adult neurogenesis by behavior and age in the accessory olfactory bulb

The vomeronasal system (VNS) participates in the detection and processing of pheromonal information related to social and sexual behaviors. Within the VNS, two different populations of sensory neurons, with a distinct pattern of distribution, line the epithelium of the vomeronasal organ (VNO) and give rise to segregated sensory projections to the accessory olfactory bulb (AOB). Apical sensory neurons in the VNO project to the anterior AOB (aAOB), while basal neurons project to the posterior AOB (pAOB). In the AOB, the largest population of neurons are inhibitory, the granule and periglomerular cells (GCs and PGs) and remarkably, these neurons are continuously born and functionally integrated in the adult brain, underscoring their role on olfactory function. Here we show that behaviors mediated by the VNS differentially regulate adult neurogenesis across the anterior-posterior axis of the AOB. We used immunohistochemical labeling of newly born cells under different behavioral conditions in mice. Using a resident-intruder aggression paradigm, we found that subordinate mice exhibited increased neurogenesis in the aAOB. In addition, in sexually naive adult females exposed to soiled bedding odorized by adult males, the number of newly born cells was significantly increased in the pAOB; however, neurogenesis was not affected in females exposed to female odors. In addition, we found that at two months of age adult neurogenesis was sexually dimorphic, with male mice exhibiting higher levels of newly born cells than females. Interestingly, adult neurogenesis was greatly reduced with age and this decrease correlated with a decrease in progenitor cells proliferation but not with an increase in cell death in the AOB. These results indicate that the physiological regulation of adult neurogenesis in the AOB by behaviors is both sex and age dependent and suggests an important role of newly born neurons in sex dependent behaviors mediated by the VNS.

The rodent accessory olfactory system

The accessory olfactory system contributes to the perception of chemical stimuli in the environment. This review summarizes the structure of the accessory olfactory system, the stimuli that activate it, and the responses elicited in the receptor cells and in the brain. The accessory olfactory system consists of a sensory organ, the vomeronasal organ, and its central projection areas: the accessory olfactory bulb, which is connected to the amygdala and hypothalamus, and also to the cortex. In the vomeronasal organ, several receptors-in contrast to the main olfactory receptors-are sensitive to volatile or nonvolatile molecules. In a similar manner to the main olfactory epithelium, the vomeronasal organ is sensitive to common odorants and pheromones. Each accessory olfactory bulb receives input from the ipsilateral vomeronasal organ, but its activity is modulated by centrifugal projections arising from other brain areas. The processing of vomeronasal stimuli in the amygdala involves contributions from the main olfactory system, and results in long-lasting responses that may be related to the activation of the hypothalamic-hypophyseal axis over a prolonged timeframe. Different brain areas receive inputs from both the main and the accessory olfactory systems, possibly merging the stimulation of the two sensory organs to originate a more complex and integrated chemosensory perception.

Identification of testosterone-dependent volatile compounds and proteins in the preputial gland of rat Rattus norvegicus

Preputial gland is one of the best known and most odour-producing organs in many non-primate mammals. It is generally believed that the development of this gland and functions are regulated by testosterone. To substantiate this point, the present study was aimed to evaluate the testosterone-dependent volatile compounds and proteins in the preputial gland of rat adopting castration and testosterone supplementation. The results revealed that four compounds, geranyl linalool isomer, oxirane, farnesol and lanosterol, are testosterone-dependent. Similarly, a low molecular mass protein with molecular weight 18kDa, supposed to be a pheromone carrier, also is shown to be testosterone-dependent. This study leads to the conclusion that testosterone-dependent compounds and sex-associated protein are present in the preputial gland of rat which may act as a sex pheromone and pheromone carrier, respectively.

Self-grooming induced by sexual chemical signals in male root voles (Microtus oeconomus Pallas)

Sniffing is one-way animals collect chemical signals, and many males self-groom when they encounter the odor of opposite-sex conspecifics. We tested the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles (Microtus oeconomus Pallas). Specifically, we investigated the sniffing pattern of male root voles in response to odors from the head, trunk, and tail areas of lactating and non-lactating females. The self-grooming behavior of males in response to female individual odorant stimuli was documented, and the relationship between self-grooming and sniffing of odors from the head, trunk, and tails areas were analyzed. Sniffing pattern results showed that males are most interested in odors from the head area, and more interested in odors from the tail as compared to the trunk area. Males displayed different sniffing and self-grooming behaviors when they were exposed to odors from lactating females as compared to non-lactating females. Males also spent more time sniffing and engaged in more sniffing behaviors in response to odors from the lactating females' tail area as compared to the same odors from non-lactating females. Similarly, males spent more time self-grooming and engaged in more self-grooming behaviors in the presence of individual odors from lactating females as compared to individual odors from non-lactating females. Partial correlation analyses revealed that the frequency of self-grooming was significantly correlated with the frequency of tail area sniffs. Results from this experiment suggest that sexual attractiveness of lactating females is stronger than that of non-lactating females. Furthermore, the partial correlation analysis demonstrated that self-grooming in males is induced by odors from the tail area of females. Collectively, these results support the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles. Self-grooming may also reflect the groomer's sexual motivation and facilitate sexual interactions.

Extracts from salivary glands stimulate aggression and inositol-1, 4, 5-triphosphate (IP3) production in the vomeronasal organ of mice

Mammals use chemical cues to coordinate social and reproductive behaviors. Chemical cues are detected by the VNO organ (VNO), which is a cartilage-encased elongated organ associated with the vomer bone in the rostral nasal cavity. The resident intruder paradigm was utilized to examine the ability of saliva and its feeder exocrine glands, the submaxillary, parotid, and sublingual glands to mediate aggression in mice. Saliva and extracts from submaxillary and parotid glands, but not extracts from sublingual glands of male CD-1 mice, induced a greater number of attacks and lower latencies to sniff and attack (p<0.05) and significantly increased IP(3) production (p<0.05) versus vehicle (PBS) in CD-1 male mice VNO. We further show that CD-1 male mouse saliva and submaxillary gland extract induced significantly more attacks and a lower latency to attack in lactating female CD-1 mice and produced significantly more inositol triphosphate (IP(3)), indicative of phospholipase C(beta) signaling which mediates pheromonal activity, in CD-1 female VNO compared to PBS. Castrated CD-1 male mouse saliva, and exocrine gland extracts induced significantly less IP(3) production in male VNO and less aggression by CD-1 males and lactating females compared to responses to normal CD-1 male mouse saliva and gland extracts. Thus, chemical cues present in saliva, submaxillary and parotid glands of CD-1 male mice are capable of stimulating aggression in male and female congenic mice which are correlated with significant production of IP(3) in the VNO. Additionally, these stimulations of aggression and IP(3) production are shown to be androgen-dependent.

Adaptive plasticity of mammalian sperm production in response to social experience

Sperm competition theory predicts that males should invest prudently in ejaculates according to levels of female promiscuity. Males may therefore be sensitive to cues in their social environment associated with sexual competition, and tailor investment in sperm production accordingly. We tested this idea experimentally for the first time, to our knowledge, in a mammal by comparing reproductive traits of male house mice (Mus musculus domesticus) that had experienced contrasting encounter regimes with potential sexual competitors. We found that daily sperm production and numbers of sperm in the caput epididymis were significantly higher in subjects that had experienced a high encounter rate of social cues from three other males compared to those that had experienced a low encounter rate of social cues from just one other male. Epididymal sperm counts were negatively correlated with the frequency of scent-marking behaviour across all males in our study, suggesting that investment in ejaculate production may be traded off against traits that function in gaining copulations, although there was no difference in overall levels of scent marking between treatment groups. We conclude that social experience-mediated phenotypic plasticity in mammalian spermatogenesis is likely to be adaptive under sperm competition, enabling males to balance the energetic costs and paternity-enhancing benefits of ejaculate production, and is a potentially widespread explanation for intraspecific variation in ejaculate expenditure.

Preputialectomised and intact adult male mice exhibit an elevated urinary ratio of oestradiol to creatinine in the presence of developing females, whilst promoting uterine and ovarian growth of these females

Exposure to novel adult males and their urine can hasten the onset of sexual maturity in female mice. Some evidence implicates chemosignals from males’ preputial glands, while other evidence suggests that male urinary steroids, especially 17β-oestradiol, contribute to this effect. The present experiment was designed to determine whether preputial gland removal would influence the capacity of males to accelerate female sexual development, and to measure male urinary oestradiol and testosterone in the presence or absence of these glands. Juvenile females aged 28 days were housed for two weeks in isolation or underneath two outbred males that had undergone preputialectomy or sham surgery. Urine samples were collected non-invasively from males that were isolated or exposed to females, then assayed for oestradiol, testosterone and creatinine. Combined uterine and ovarian mass from females sacrificed at 43 days of age was increased by exposure to males, regardless of whether or not these males had been preputialectomised. Male urinary creatinine was reduced by exposure to developing females. Creatinine-adjusted oestradiol and testosterone were significantly greater in female-exposed than in isolated males, in both preputialectomised and intact males. These data suggest that the preputials are not necessary for the capacity of males to hasten female uterine and ovarian growth. As exogenous oestrogens can promote uterine growth and other parameters of female reproductive maturation, oestradiol in males’ urine may contribute to earlier sexual maturity in male-exposed females.

Sex differences in expression and differential regulation by androgen and estrogen of two odorant-binding tear lipocalins in lacrimal glands of immature hamsters

In adults of several mammalian species, lacrimal glands (LG) have sex differences but there is no report of any sexual dimorphism in LG of immatures. In LG and tears of adult hamsters, we found female-specific expression of two closely related odorant-/pheromone-binding lipocalins, FLP (female lacrimal protein) and MSP (male-specific protein; initially identified in salivary glands of males). Although, both androgens and estrogens markedly repress FLP and MSP in LG of adults, the expression of these lipocalins in females is due to their incomplete repression by endogenous estrogens. Here we report a marked sexual dimorphism in the expression of FLP and MSP in LG and tears of 20-day-old immature hamsters. The age-dependant expression of these lipocalins and effect of neonatal-gonadectomy and sex hormone treatments on their expression in immatures was investigated. FLP and MSP are detectable in LG at 10-day age in both sexes of hamster but by 20-day age levels of both lipocalins show sex differences wherein FLP is several fold higher in males and MSP is obliterated in males. Thereafter, FLP declines in male LG and is obliterated by 36-day age, resulting in female-specific expression of both LG lipocalins as seen in adults. In LG of 20-day-old immatures, FLP and MSP are insensitive to repression by androgen and estrogen, respectively, which was unlike the androgen/estrogen-repressed regulation of both lipocalins in adult LG. The estrogenic repression of FLP and androgenic repression of MSP in LG of immature hamsters could be prevented by treatment with tamoxifen and flutamide, respectively. Our studies indicate that (i) presence of gonads in immatures can have significant effects on LG lipocalins resulting in their sexually dimorphic expression, (ii) in immatures, unlike adults, the repressive effects of estrogen and androgen on LG lipocalins are selective for FLP and MSP, respectively, and (iii) these repressions are likely to be mediated by sex hormone receptors.