Social Chemosignals Research Articles

Olfactory bulb astrocytes link social transmission of stress to cognitive adaptation in male mice

Emotions and behavior can be affected by social chemosignals from conspecifics. For instance, olfactory signals from stressed individuals induce stress-like physiological and synaptic changes in naïve partners. Direct stress also alters cognition, but the impact of socially transmitted stress on memory processes is currently unknown. Here we show that exposure to chemosignals produced by stressed individuals is sufficient to impair memory retrieval in unstressed male mice. This requires astrocyte control of information in the olfactory bulb mediated by mitochondria-associated CB1 receptors (mtCB1). Targeted genetic manipulations, in vivo Ca2+ imaging and behavioral analyses reveal that mtCB1-dependent control of mitochondrial Ca2+ dynamics is necessary to process olfactory information from stressed partners and to define their cognitive consequences. Thus, olfactory bulb astrocytes provide a link between social odors and their behavioral meaning.

A chemical signal in human female tears lowers aggression in males.

Rodent tears contain social chemosignals with diverse effects, including blocking male aggression. Human tears also contain a chemosignal that lowers male testosterone, but its behavioral significance was unclear. Because reduced testosterone is associated with reduced aggression, we tested the hypothesis that human tears act like rodent tears to block male aggression. Using a standard behavioral paradigm, we found that sniffing emotional tears with no odor percept reduced human male aggression by 43.7%. To probe the peripheral brain substrates of this effect, we applied tears to 62 human olfactory receptors in vitro. We identified 4 receptors that responded in a dose-dependent manner to this stimulus. Finally, to probe the central brain substrates of this effect, we repeated the experiment concurrent with functional brain imaging. We found that sniffing tears increased functional connectivity between the neural substrates of olfaction and aggression, reducing overall levels of neural activity in the latter. Taken together, our results imply that like in rodents, a human tear-bound chemosignal lowers male aggression, a mechanism that likely relies on the structural and functional overlap in the brain substrates of olfaction and aggression. We suggest that tears are a mammalian-wide mechanism that provides a chemical blanket protecting against aggression.

Stimulus-Induced Theta-Band LFP Oscillations Format Neuronal Representations of Social Chemosignals in the Mouse Accessory Olfactory Bulb.

Social communication is crucial for the survival of many species. In most vertebrates, a dedicated chemosensory system, the vomeronasal system (VNS), evolved to process ethologically relevant chemosensory cues. The first central processing stage of the VNS is the accessory olfactory bulb (AOB), which sends information to downstream brain regions via AOB mitral cells (AMCs). Recent studies provided important insights about the functional properties of AMCs, but little is known about the principles that govern their coordinated activity. Here, we recorded local field potentials (LFPs) and single-unit activity in the AOB of adult male and female mice during presentation of natural stimuli. Our recordings reveal prominent LFP theta-band oscillatory episodes with a characteristic spatial pattern across the AOB. Throughout an experiment, the AOB network shows varying degrees of similarity to this pattern, in a manner that depends on the sensory stimulus. Analysis of LFP signal polarity and single-unit activity indicates that oscillatory episodes are generated locally within the AOB, likely representing a reciprocal interaction between AMCs and granule cells. Notably, spike times of many AMCs are constrained to the negative LFP oscillation phase in a manner that can drastically affect integration by downstream processing stages. Based on these observations, we propose that LFP oscillations may gate, bind, and organize outgoing signals from individual AOB neurons to downstream processing stages. Our findings suggest that, as in other neuronal systems and brain regions, population-level oscillations play a key role in organizing and enhancing transmission of socially relevant chemosensory information.SIGNIFICANCE STATEMENT The accessory olfactory bulb (AOB) is the first central stage of the vomeronasal system, a chemosensory system dedicated to processing cues from other organisms. Information from the AOB is conveyed to other brain regions via activity of its principal neurons, AOB mitral cells (AMCs). Here, we show that socially relevant sensory stimulation of the mouse vomeronasal system leads not only to changes in AMC activity, but also to distinct theta-band (∼5 Hz) oscillatory episodes in the local field potential. Notably AMCs favor the negative phase of these oscillatory events. Our findings suggest a novel mechanism for the temporal coordination of distributed patterns of neuronal activity, which can serve to efficiently activate downstream processing stages.

Affective and physiological responses to human body odors in social anxiety – a pilot study on the possible effects as catalyst for treatment

IntroductionUnderstanding the way chemistry influences human communication is important since the reaction to chemosignals has many implications for science and society.Numerous research points out that human beings are able to identify feelings of fear and happiness through smell. Such emotional information can lead to approach-avoidance behaviors or changes in affective state. Moreover, a heightened sensitivity to social odors has been shown in subjects with social anxiety symptoms. However, more detailed research on the connection between olfaction, affective psychiatric disorders and interpersonal social communication is required.POTION is an EU funded project within the Horizon2020 initiative that aims at understanding the nature of chemosignals in humans and their sphere of influence on social interaction. Whitin this project, we conducted a preliminary study showing that individuals with social anxiety symptoms benefited from mindfulness training especially when exposed to social chemosignals. A significant reduction in anxiety symptoms was achieved with both the happiness (t(25)=4.37, p=0.029) and the fear (t(25)=4.35, p=0.031) chemosignals. Moreover, individuals exposed to the happiness chemosignal exhibit highier vagal tone compared to subjects exposed to fear chemosignals (p = 0.026), indicating overall increased well-being.ObjectivesGiven the exploratory nature of the preliminary study, an hypothesis driven pilot-RCT with larger sample size and refined design has been conducted. The aim was to further explore the catalyst effect of body odor on anxiety reduction. Notably, if the odor groups (happiness, fear or neutral) differ with the control group (clean air) and if they differ between each other in the outcome measure.MethodsTo this end, 96 participants with social anxiety symptoms (women aged between 18 to 35) were randomly allocated to one exposure group (happiness, fear or neutral human body odor or clean air) and followed a mindfulness intervention while being exposed to the odor. Psychological outcomes were measured before and after the intervention through the State-Trait Anxiety Inventory. During the intervention participants’ skin conductance and heart rate was also measured.Analysis of variance will be performed to assess psychological outcome differences between and within groups, as well as interactions (GroupxTime).ResultsResults of the study will be available and presented at the time of the congress.ConclusionsThis study represents an advancement in the field mental health as it explores the potential impact of using human chemosignals in the clinical setting.Disclosure of InterestNone Declared

Female-Based Patterns and Social Function in Avian Chemical Communication.

Much of the growing interest in avian chemical signals has focused on the role of kin recognition or mate attraction, often with an emphasis on males, with uropygial gland secretions perhaps providing information about an individual's identity and quality. Yet, data collected to date suggest sexual dimorphism in uropygial glands and secretions are often emphasized in female, rather than in male birds. That is, when a sexual difference occurs (often during the breeding season only), it is the female that typically exhibits one of three patterns: (1) a larger uropygial gland, (2) a greater abundance of volatile or semi-volatile preen oil compounds and/or (3) greater diversity of preen oil compounds or associated microbes. These patterns fit a majority of birds studied to date (23 of 30 chemically dimorphic species exhibit a female emphasis). Multiple species that do not fit are confounded by a lack of data for seasonal effects or proper quantitative measures of chemical compounds. We propose several social functions for these secretions in female-based patterns, similar to those reported in mammals, but which are largely unstudied in birds. These include: (1) intersexual advertisement of female receptivity or quality, including priming effects on male physiology, (2) intrasexual competition, including scent marking and reproductive suppression or (3) parental behaviors, such as parent-offspring recognition and chemical protection of eggs and nestlings. Revisiting the gaps of chemical studies to quantify the existence of female social chemosignals and any fitness benefit(s) during breeding are potentially fruitful but overlooked areas of future research.

Paradoxically Sparse Chemosensory Tuning in Broadly Integrating External Granule Cells in the Mouse Accessory Olfactory Bulb.

The accessory olfactory bulb (AOB), the first neural circuit in the mouse accessory olfactory system, is critical for interpreting social chemosignals. Despite its importance, AOB information processing is poorly understood compared with the main olfactory bulb (MOB). Here, we sought to fill gaps in the understanding of AOB interneuron function. We used 2-photon GCaMP6f Ca2+ imaging in an ex vivo preparation to study chemosensory tuning in AOB external granule cells (EGCs), interneurons hypothesized to broadly inhibit activity in excitatory mitral cells (MCs). In ex vivo preparations from mice of both sexes, we measured MC and EGC tuning to natural chemosignal blends and monomolecular ligands, finding that EGC tuning was sparser, not broader, than upstream MCs. Simultaneous electrophysiological recording and Ca2+ imaging showed no differences in GCaMP6f-to-spiking relationships in these cell types during simulated sensory stimulation, suggesting that measured EGC sparseness was not due to cell type-dependent variability in GCaMP6f performance. Ex vivo patch-clamp recordings revealed that EGC subthreshold responsivity was far broader than indicated by GCaMP6f Ca2+ imaging, and that monomolecular ligands rarely elicited EGC spiking. These results indicate that EGCs are selectively engaged by chemosensory blends, suggesting different roles for EGCs than analogous interneurons in the MOB.SIGNIFICANCE STATEMENT The mouse accessory olfactory system (AOS) interprets social chemosignals, but we poorly understand AOS information processing. Here, we investigate the functional properties of external granule cells (EGCs), a major class of interneurons in the accessory olfactory bulb (AOB). We hypothesized that EGCs, which are densely innervated by excitatory mitral cells (MCs), would show broad chemosensory tuning, suggesting a role in divisive normalization. Using ex vivo GCaMP6f imaging, we found that EGCs were instead more sparsely tuned than MCs. This was not due to weaker GCaMP6f signaling in EGCs than in MCs. Instead, we found that many MC-activating chemosignals caused only subthreshold EGC responses. This indicates a different role for AOB EGCs compared with analogous cells in the main olfactory bulb.

Co-localization of two-color rAAV2-retro confirms the dispersion characteristics of efferent projections of mitral cells in mouse accessory olfactory bulb.

The accessory olfactory bulb (AOB), located at the posterior dorsal aspect of the main olfactory bulb (MOB), is the first brain relay of the accessory olfactory system (AOS), which can parallelly detect and process volatile and nonvolatile social chemosignals and mediate different sexual and social behaviors with the main olfactory system (MOS). However, due to its anatomical location and absence of specific markers, there is a lack of research on the internal and external neural circuits of the AOB. This issue was addressed by single-color labeling and fluorescent double labeling using retrograde rAAVs injected into the bed nucleus of the stria terminalis (BST), anterior cortical amygdalar area (ACo), medial amygdaloid nucleus (MeA), and posteromedial cortical amygdaloid area (PMCo) in mice. We demonstrated the effectiveness of this AOB projection neuron labeling method and showed that the mitral cells of the AOB exhibited efferent projection dispersion characteristics similar to those of the MOB. Moreover, there were significant differences in the number of neurons projected to different brain regions, which indicated that each mitral cell in the AOB could project to a different number of neurons in different cortices. These results provide a circuitry basis to help understand the mechanism by which pheromone information is encoded and decoded in the AOS.

Human chemosignals of disgust facilitate food judgment

Choosing food is not a trivial decision that people need to make daily, which is often subject to social influences. Here, we studied a human homolog of social transmission of food preference (STFP) as observed in rodents and other animals via chemosignals of body secretions. Human social chemosignals (sweat) produced during a disgust or neutral state among a group of donors were presented to participants undergoing a 2-alternative-forced-choice food healthiness judgment task during functional magnetic resonance imaging (fMRI). Response speed and two key signal detection indices—d’ (discrimination sensitivity) and β (response bias)—converged to indicate that social chemosignals of disgust facilitated food healthiness decisions, in contrast to primary disgust elicitors (disgust odors) that impaired the judgment. fMRI analyses (disgust vs. neutral sweat) revealed that the fusiform face area (FFA), amygdala, and orbitofrontal cortex (OFC) were engaged in processing social chemosignals of disgust during food judgment. Importantly, a double contrast of social signaling across modalities (olfactory vs. visual—facial expressions) indicated that the FFA and OFC exhibited preferential response to social chemosignals of disgust. Together, our findings provide initial evidence for human STFP, where social chemosignals are incorporated into food decisions by engaging social and emotional areas of the brain.

Empathic Cognitions Affected by Undetectable Social Chemosignals: An EEG Study on Visually Evoked Empathy for Pain in an Auditory and Chemosensory Context.

Reduction of mu activity within the EEG is an indicator of cognitive empathy and can be generated in response to visual depictions of others in pain. The current study tested whether this brain response can be modulated by an auditory and a chemosensory context. Participants observed pictures of painful and non-painful actions while pain associated and neutral exclamations were presented (Study 1, N = 30) or while chemosensory stimuli were presented via a constant flow olfactometer (Study 2, N = 22). Chemosensory stimuli were sampled on cotton pads while donors participated in a simulated job interview (stress condition) or cycled on a stationary bike (sport condition). Pure cotton was used as a control. The social chemosignals could not be detected as odors. Activity within the 8–13 Hz band at electrodes C3, C4 (mu activity) and electrodes O1, O2 (alpha-activity) was calculated using Fast-Fourier-Transformation (FFT). As expected, suppression of power in the 8–13 Hz band was stronger when painful as compared to non-painful actions were observed (Study 1, p = 0.020; Study 2, p = 0.005). In addition, as compared to the neutral auditory and chemosensory context, painful exclamations (Study 1, p = 0.039) and chemosensory stress signals (Study 2, p = 0.014) augmented mu-/alpha suppression also in response to non-painful pictures. The studies show that processing of social threat-related information is not dominated by visual information. Rather, cognitive appraisal related to empathy can be affected by painful exclamations and subthreshold chemosensory social information.

Altered responses to social chemosignals in autism spectrum disorder.

Autism spectrum disorder (ASD) is characterized by impaired social communication, often attributed to misreading of emotional cues. Why individuals with ASD misread emotions remains unclear. Given that terrestrial mammals rely on their sense of smell to read conspecific emotions, we hypothesized that misreading of emotional cues in ASD partially reflects altered social chemosignaling. We found no difference between typically developed (TD) and cognitively able adults with ASD at explicit detection and perception of social chemosignals. Nevertheless, TD and ASD participants dissociated in their responses to subliminal presentation of these same compounds: the undetected 'smell of fear' (skydiver sweat) increased physiological arousal and reduced explicit and implicit measures of trust in TD but acted opposite in ASD participants. Moreover, two different undetected synthetic putative social chemosignals increased or decreased arousal in TD but acted opposite in ASD participants. These results implicate social chemosignaling as a sensory substrate of social impairment in ASD.

Zebra Finch chicks recognise parental scent, and retain chemosensory knowledge of their genetic mother, even after egg cross-fostering

Mechanisms underlying parent-offspring recognition in birds have fascinated researchers for centuries. Yet, the possibility that chicks recognise parental odour at hatching has been completely overlooked, despite the fact that olfaction is one of the first sensory modalities to develop, and social chemosignals occur in avian taxa. Here we show that Zebra Finch chicks (Taeniopygia guttata) are capable of identifying parental odours at hatching. In our first experiment, chicks begged significantly longer in response to the odour of their genetic mother or father compared to the odour of a non-relative of the same sex and reproductive status. In a second experiment, we cross-fostered eggs and tested the response of hatchlings to the scent of genetic vs. foster parents. Chicks from cross-fostered eggs responded significantly more to the odour of their genetic mother than their foster mother, but exhibited no difference in response to genetic vs. foster fathers. This is the first evidence that embryonic altricial birds are capable of acquiring chemosensory knowledge of their parents during early development, and retain chemical familiarity with their genetic mother despite egg cross-fostering. Furthermore our data reveals that kin recognition in birds can develop without any association with a genetic parent at hatching.

Chemosensory anxiety signals prime defensive behavior in prepubertal girls

Chemosensory anxiety signals effectively prime motor responses related to withdrawal behavior, such as the startle reflex, in adult humans. As the reproductive status strongly affects the response to social chemosignals, the current study examined whether chemosensory anxiety signals would augment the startle response in prepubertal children as it does in adults.Using cotton pads, axillary sweat was collected from 28 men while waiting for an important oral examination (anxiety condition), and during ergometer training (sport control condition). Using a constant-flow olfactometer, sweat samples and pure cotton samples (cotton control) were presented to 10 prepubertal girls aged 9–13years (M=11.25, SD=1.25) for 3000ms during inhalation. White noise bursts of 102dB(A) served as startle probes, and startle responses were recorded via electromyography of the orbicularis oculi muscle.The girls showed larger startle amplitudes to probes presented in the context of chemosensory anxiety signals as compared to a context of sport control sweat (p<0.01) as well as cotton control (p<0.05). This effect was not attributable to differences in stimulus detection rates or stimulus hedonics.The results show that in prepubertal girls, similar to adults, chemosensory anxiety signals prime defensive motor behavior. This effect appears unrelated to the odorous quality of anxiety sweat, but seems to reflect a specific preparedness to respond to the underlying social alarm signal. Thus, chemosensory communication supporting individual harm protection is independent of the reproductive status in humans.

Interglomerular Connectivity within the Canonical and GC-D/Necklace Olfactory Subsystems.

The mammalian main olfactory system contains several subsystems that differ not only in the receptors they express and the glomerular targets they innervate within the main olfactory bulb (MOB), but also in the strategies they use to process odor information. The canonical main olfactory system employs a combinatorial coding strategy that represents odorant identity as a pattern of glomerular activity. By contrast, the "GC-D/necklace" olfactory subsystem—formed by olfactory sensory neurons expressing the receptor guanylyl cyclase GC-D and their target necklace glomeruli (NGs) encircling the caudal MOB—is critical for the detection of a small number of semiochemicals that promote the acquisition of food preferences. The formation of these socially-transmitted food preferences requires the animal to integrate information about two types of olfactory stimuli: these specialized social chemosignals and the food odors themselves. However, the neural mechanisms with which the GC-D/necklace subsystem processes this information are unclear. We used stimulus-induced increases in intrinsic fluorescence signals to map functional circuitry associated with NGs and canonical glomeruli (CGs) in the MOB. As expected, CG-associated activity spread laterally through both the glomerular and external plexiform layers associated with activated glomeruli. Activation of CGs or NGs resulted in activity spread between the two types of glomeruli; there was no evidence of preferential connectivity between individual necklace glomeruli. These results support previous anatomical findings that suggest the canonical and GC-D/necklace subsystems are functionally connected and may integrate general odor and semiochemical information in the MOB.

Oxytocin Effects on Chemosensory Function in a Clinical Setting—a Preliminary Study

Despite the large body of literature on the effects of oxytocin via the exchange of social chemo-signals, no previous study tested the effects of oxytocin stimulation during parturition on the mother’s chemical senses. Therefore, in the present study, we investigated the effects of oxytocin, administered via intramyometrial and intravenous injection, on general odor processing andgustatory functioning in women shortly after giving birth via Caesarean section. General olfactory and gustatory sensitivity, and subjectively perceived taste intensities and hedonic ratings, next to self-reported mood and nausea were assessed 1 day before the Caesarean section in 21 women and again a few hours after the oxytocin stimulations. We found no changes in general olfactory sensitivity, self-reported mood, or nausea between test sessions. However, following oxytocin, women rated the quality of sweet taste as significantly more positive and tended to exhibit higher gustatory sensitivity. Although this study was performed in a highly controlled clinical environment, we cannot rule out potential confounders related to parturition, and our interpretation on the specific effects of oxytocin therefore is limited. However, our findings agree with the literature reporting oxytocin effects on chemo-sensory functions. We speculate that an increased preference for sweet taste might be particularly relevant during the early post-partum and breastfeeding period, facilitating thenecessary nutrient supply to the newborn via the intake of calorie-rich carbohydrate food.

A social chemosignaling function for human handshaking.

Social chemosignaling is a part of human behavior, but how chemosignals transfer from one individual to another is unknown. In turn, humans greet each other with handshakes, but the functional antecedents of this behavior remain unclear. To ask whether handshakes are used to sample conspecific social chemosignals, we covertly filmed 271 subjects within a structured greeting event either with or without a handshake. We found that humans often sniff their own hands, and selectively increase this behavior after handshake. After handshakes within gender, subjects increased sniffing of their own right shaking hand by more than 100%. In contrast, after handshakes across gender, subjects increased sniffing of their own left non-shaking hand by more than 100%. Tainting participants with unnoticed odors significantly altered the effects, thus verifying their olfactory nature. Thus, handshaking may functionally serve active yet subliminal social chemosignaling, which likely plays a large role in ongoing human behavior.

Vomeronasal organ lesion disrupts social odor recognition, behaviors and fitness in golden hamsters.

Most studies support the viewpoint that the vomeronasal organ has a profound effect on conspecific odor recognition, scent marking and mating behavior in the golden hamster (Mesocricetus auratus). However, the role of the vomeronasal organ in social odor recognition, social interaction and fitness is not well understood. Therefore, we conducted a series of behavioral and physiological tests to examine the referred points in golden hamster. We found that male hamsters with vomeronasal organ lesion showed no preference between a predator odor (the anal gland secretion of the Siberian weasels (Mustela sibirica) and putative female pheromone components (myristic acid and palmitic acid), but were still able to discriminate between these 2 kinds of odors. In behavioral tests of anxiety, we found that vomeronasal organ removal causes female hamsters to spend much less time in center grids and to cross fewer center grids and males to make fewer crossings between light and dark boxes than sham-operated controls. This indicates that a chronic vomeronasal organ lesion induced anxious responses in females. In aggressive behavioral tests, we found that a chronic vomeronasal organ lesion decreased agonistic behavior in female hamsters but not in males. The pup growth and litter size show no differences between the 2 groups. All together, our data suggested that vomeronasal organ ablation disrupted the olfactory recognition of social chemosignals in males, and induced anxiety-like and aggressive behavior changes in females. However, a vomeronasal organ lesion did not affect the reproductive capacity and fitness of hamsters. Our studies may have important implications concerning the role of the vomeronasal organ in golden hamsters and also in rodents.

Differential processing of social chemosignals obtained from potential partners in regards to gender and sexual orientation

On an individual level, human body odors carry information about whether a person is an eligible mate. The current studies investigate if body odors also transmit information about individuals being potential partners in more general terms, namely in regards to gender and sexual orientation.In study 1, 14 gay and 14 heterosexual men were presented with body odors obtained from potential partners (gay male and heterosexual female body odors, respectively) and heterosexual male body odor as a control. In study 2, 14 lesbian and 14 heterosexual women were presented with lesbian female and heterosexual male body odors representing body odors of potential partners, and heterosexual female body odor as a control. Central nervous processing was analyzed using chemosensory event-related potentials and current source density analysis (64-channel EEG recording).Gay and heterosexual men responded with shorter P2 latencies to the body odors of their preferred sexual partners, and lesbian women responded with shorter P2 latencies to body odors of their preferred gender. In response to heterosexual male body odors, lesbian women displayed the most pronounced P3 amplitude, and distinct neuronal activation in medial frontal and parietal neocortical areas. A similar pattern of neuronal activation was observed in gay men when presented with heterosexual male body odor.Both the early processing advantage (P2) for desirable partners’ body odors as well as the enhanced evaluative processing (P3, CSD) of undesirable partners’ body odors suggest that human body odors indeed carry information about individuals being potential partners in terms of gender and sexual orientation.

Processing of Body Odor Signals by the Human Brain

Brain development in mammals has been proposed to be promoted by successful adaptations to the social complexity as well as to the social and non-social chemical environment. Therefore, the communication via chemosensory signals might have been and might still be a phylogenetically ancient communication channel transmitting evolutionary significant information. In humans, the neuronal underpinnings of the processing of social chemosignals have been investigated in relation to kin recognition, mate choice, the reproductive state and emotional contagion. These studies reveal that human chemosignals are probably not processed within olfactory brain areas but through neuronal relays responsible for the processing of social information. It is concluded that the processing of human social chemosignals resembles the processing of social signals originating from other modalities, except that human social chemosignals are usually communicated without the allocation of attentional resources, that is below the threshold of consciousness. Deviances in the processing of human social chemosignals might be related to the development and maintenance of mental disorders.

The vomeronasal organ is not involved in the perception of endogenous odors

Chemosensory-based communication is a vital signaling tool in most species, and evidence has recently emerged in support of the notion that humans also use social chemosignals (so-called pheromones) to communicate. An ongoing controversy does exist, however, concerning the receptor organ through which these chemicals are processed. There is a widespread belief that the vomeronasal organ (VNO) is responsible for processing social chemosignals in humans. Here we demonstrate that functional occlusion of the VNO does not change the percept of, sensitivity toward, or functional neuronal processing of a putative human pheromone. Perithreshold and suprathreshold perception of the endogenous chemical androstadienone (AND) were compared, as were positron emission tomography brain activations evoked by AND when the VNO was either occluded or left open. In addition, we compared sensitivity to AND in subjects with an identifiable VNO to those in whom no VNO could be detected. Thus we could examine the effects of the VNO at several different levels of processing. Occlusion or absence of the VNO did not affect either the perceptual measurements or the functional processing of the putative human pheromone, AND. These results provide strong evidence that the human VNO has no obvious function. Pheromonal communication in humans may be conveyed via the main olfactory system.

From preen secretions to plumage: the chemical trajectory of blue petrels' Halobaena caerulea social scent

Petrel seabirds heavily rely on their olfactory sense and are thus appropriate models for the study of avian chemical communication. The uropygial secretions of blue petrels Halobaena caerulea, for instance, have been shown to encapsulate elaborate sociochemical information including species, gender and identity. Yet, it is the plumage, and not preening secretions per se, which acts as the final substrate of avian scents. Importantly, the chemical relationship between secretions from the uropygial gland, located at the dorsal base of the tail, and plumage lipids has been considered in only a handful of studies which reported large qualitative differences. The emission process of avian scents, and the possible participation of the uropygial gland in particular, are therefore not elucidated. In the present study, we examine the early chemical trajectory of blue petrels' social chemosignals by comparing secretion and feather samples using Gas‐Chromatography Mass‐Spectrometry (GC/MS) and recently developed multivariate statistics. Our results indicate that (1) 85% of the feather lipids come from the uropygial secretions, (2) chemical differentiation between secretions and feather lipids includes qualitative and quantitative variations, which both have interesting implications for scent production, (3) the sociochemical information contained within the secretions (i.e. a sex‐specific signal and individual chemical signatures) are present in very conserved forms on the plumage. In the light of these results, it is apparent that the uropygial gland plays a critical role for chemical communication in petrels and possibly other avian groups.