Pyrazine analogues are active components of wolf urine that induce avoidance and freezing behaviours in mice

Pheromone of grouped female mice impairs genome stability in male mice through stress-mediated pathways

Population density is known to affect the health and survival of many species, and is especially important for social animals. In mice, living in crowded conditions results in the disruption of social interactions, chronic stress, and immune and reproductive suppression; however, the underlying mechanisms remain unclear. Here, we investigated the role of chemosignals in the regulation of mouse physiology and behavior in response to social crowding. The pheromone 2,5-dimethylpyrazine (2,5-DMP), which is released by female mice in crowded conditions, induced aversion, glucocorticoid elevation and, when chronic, resulted in reproductive and immune suppression. 2,5-DMP olfaction induced genome destabilization in bone marrow cells in a stress-dependent manner, providing a plausible mechanism for crowding-induced immune dysfunction. Interestingly, the genome-destabilizing effect of 2,5-DMP was comparable to a potent mouse stressor (immobilization), and both stressors led to correlated expression changes in genes regulating cellular stress response. Thus, our findings demonstrate that, in mice, the health effects of crowding may be explained at least in part by chemosignals and also propose a significant role of stress and genome destabilization in the emergence of crowding effects.

Repeated exposure to kairomone-containing coffee odor improves abnormal olfactory behaviors in heterozygous oxytocin receptor knock-in mice

The oxytocin receptor (OXTR) knockout mouse is a model of autism spectrum disorder, characterized by abnormalities in social and olfactory behaviors and learning. Previously, we demonstrated that OXTR plays a crucial role in regulating aversive olfactory behavior to butyric acid odor. In this study, we attempted to determine whether coffee aroma affects the abnormal olfactory behavior of OXTR-Venus knock-in heterozygous mice [heterozygous OXTR (±) mice] using a set of behavioral and molecular experiments. Four-week repeated exposures of heterozygous OXTR (±) mice to coffee odor, containing three kairomone alkylpyrazines, rescued the abnormal olfactory behaviors compared with non-exposed wild-type or heterozygous OXTR (±) mice. Increased Oxtr mRNA expression in the olfactory bulb and amygdala coincided with the rescue of abnormal olfactory behaviors. In addition, despite containing the kairomone compounds, both the wild-type and heterozygous OXTR (±) mice exhibited a preference for the coffee odor and exhibited no stress-like increase in the corticotropin-releasing hormone, instead of a kairomone-associated avoidance response. The repeated exposures to the coffee odor did not change oxytocin and estrogen synthetase/receptors as a regulator of the gonadotropic hormone. These data suggest that the rescue of abnormal olfactory behaviors in heterozygous OXTR (±) mice is due to the coffee odor exposure-induced OXTR expression.

Modeling the Orthosteric Binding Site of the G Protein-Coupled Odorant Receptor OR5K1

With approximately 400 encoding genes in humans, odorant receptors (ORs) are the largest subfamily of class A G protein-coupled receptors (GPCRs). Despite its high relevance and representation, the odorant-GPCRome is structurally poorly characterized: no experimental structures are available, and the low sequence identity of ORs to experimentally solved GPCRs is a significant challenge for their modeling. Moreover, the receptive range of most ORs is unknown. The odorant receptor OR5K1 was recently and comprehensively characterized in terms of cognate agonists. Here, we report two additional agonists and functional data of the most potent compound on two mutants, L104^3.32 and L255^6.51. Experimental data was used to guide the investigation of the binding modes of OR5K1 ligands into the orthosteric binding site using structural information from AI-driven modeling, as recently released in the AlphaFold Protein Structure Database, and from homology modeling. Induced-fit docking simulations were used to sample the binding site conformational space for ensemble docking. Mutagenesis data guided side chain residue sampling and model selection. We obtained models that could better rationalize the different activity of active (agonist) versus inactive molecules with respect to starting models and also capture differences in activity related to minor structural differences. Therefore, we provide a model refinement protocol that can be applied to model the orthosteric binding site of ORs as well as that of GPCRs with low sequence identity to available templates.

Semibiocatalytic Approach toward Regioisomerically Enriched Ethyl Dimethylpyrazines Important in Flavor Industries

Alkylpyrazines are important heterocyclic compounds used as flavorants in food and beverage industries. In this study, a regioselective semibiocatalytic process was developed to synthesize 2-ethyl-3,5-dimethylpyrazine (235-EDMP) over its 3-ethyl-2,5-dimethyl pyrazine (325-EDMP) isomer and vice versa. We initially explored how sterics could direct the coupling orientations between diamines and diketones to access 235- or 325-EDMP selectively. Also, the physical parameters of the reaction conditions were changed, such as reduced temperature, the order-of-addition of the reactants, and supplementation with chiral zeolites to template the orientation of the coupling partners to direct the reaction regiochemistry. Each reaction trial resulted in 50:50 mixtures of the EDMP isomers. An alternative approach was explored to control the regioselectivity of the reactions; α-hydroxy ketones replaced the diketones as the electrophilic coupling reactant used in previous trial experiments. The hydroxy ketone reactants were made biocatalytically with pyruvate decarboxylase. The coupling reaction between 2-hydroxypentan-3-one and propane-1,2-diamine resulted in the desired 235-EDMP at >70% (∼77 mg) relative to 325-EDMP in the mixture. The 3-hydroxypentan-2-one congener was biocatalyzed and reacted with propane-1,2-diamine as a proof of principle to synthesize 325-EDMP (∼60% relative abundance, ∼73 mg) over 235-EDMP. These results suggested a mechanism that was directed by the hydroxy ketone electrophilicity and the sterics at the diamine nucleophilic centers.

A multifunctional study of naturally occurring pyrazines in biological systems; formation mechanisms, metabolism, food applications and functional properties

Natural pyrazines, mainly methyl- or ethyl-substituted forms, are commonly applied as flavor ingredients in raw and roasted food. Meanwhile alkylpyrazines are used as food preservatives due to their effective antimicrobial action. These natural pyrazines are widely distributed in several biological systems such as plants, animals, and insects; each with respective physiological role. Besides, pyrazines are formed in food via thermal treatment and fermentation. This review presents the most comprehensive overview of pyrazines with correlation to their chemical structures and different applications with emphasis on their food applications. The major part deals with pyrazines generated in thermally treated food, reaction mechanisms highlighting factors and optimum conditions affecting their production. Additionally, the several metabolic reactions mediating for pyrazines metabolism in humans and excretion via the kidney are discussed and on context to their effects. Lastly, a review of the different techniques applied for pyrazines isolation, detection and quantitation is presented. The study provides future considerations and direction of research on this important dietary component and their applications. Pyrazines multifunctional chemistry is of value to the food sector, by presenting the best practices for their production whilst the detrimental effects are minimized.

Changes in gaseous concentration of alkylpyrazine analogs affect mouse avoidance behavior

We developed a rapid and accurate method for quantifying gaseous phase odorants using headspace solid-phase microextraction (HS-SPME) in conjunction with GC-MS and used our system to quantify alkylpyrazine analogs in the Y-maze. Rapid extraction of volatile compounds in the vapor phase achieved accurate quantitative analysis of gaseous alkylpyrazine analogs at several locations in the Y-maze. We also used a series of three SPME fibers to quantify changes in the concentration over time. We conducted a behavioral test of mice in response to these alkylpyrazines and identified a positive relationship between the rate of increase in gaseous concentration and the avoidance rate induced. Our results demonstrate that the Y-maze is a simple but reliable apparatus for behavioral studies of olfaction. The HS-SPME fast extraction method can quantify how gaseous concentrations of alkylpyrazines change over time, and the time-dependent increase of alkylpyrazine concentration is correlated with induction of aversive behavior in mice.

Differential expression of urinary volatile organic compounds by sex, male reproductive status, and pairing status in the maned wolf (Chrysocyon brachyurus)

The maned wolf (Chrysocyon brachyurus) is an induced ovulator. Though the mechanism of ovulation induction remains unknown, it is suspected to be urinary chemical signals excreted by males. This study assessed volatile organic compounds (VOCs) in weekly urine samples across 5 months from 13 maned wolves (6 intact males, 1 neutered male, 6 females) with the goal of identifying VOCs that are differentially expressed across sex, reproductive status, and pairing status. Solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) were used to extract and separate VOCs that were identified via spectral matching with authentic standards, with spectral libraries, or with new software that further matches molecular fragment structures with mass spectral peaks. Two VOCs were present across all 317 urine samples: 2,5-dimethyl pyrazine and 2-methyl-6-(1-propenyl)-pyrazine. Fifteen VOCs differed significantly (Adj. P < 0.001 and |log2 fold change| >2.0) between intact males and females. Using partial least squares-discriminant analysis, the compounds with the highest importance to the sex classification were delta-decalactone, delta-dodecalactone, and bis(prenyl) sulfide. Sixty-two VOCs differed between intact males and the neutered male. Important classifier compounds were 3-ethyl 2,5-dimethyl pyrazine, 2-methyl-6-(1-propenyl)-pyrazine, and tetrahydro-2-isopentyl-5-propyl furan. Several VOCs established as important here have been implicated in reproductive communication in other mammals. This study is the most robust examination of differential expression in the maned wolf thus far and provides the most comprehensive analysis of maned wolf urinary VOCs to date, increasing the sample size substantially over previous chemical communication studies in this species. New data analysis software allowed for the identification of compounds in the hormone-producing mevalonate pathway which were previously unreported in maned wolf urine. Several putative semiochemicals were identified as good candidates for behavioral bioassays to determine their role in maned wolf reproduction, and specifically in ovulation induction.

An evolutionary conserved olfactory receptor for foodborne and semiochemical alkylpyrazines

Molecular recognition is a fundamental principle in biological systems. The olfactory detection of both food and predators via ecological relevant odorant cues are abilities of eminent evolutionary significance for many species. Pyrazines are such volatile cues, some of which act as both human-centered key food odorants (KFOs) and semiochemicals. A pyrazine-selective odorant receptor has been elusive. Here we screened 2,3,5-trimethylpyrazine, a KFO and semiochemical, and 2,5-dihydro-2,4,5-trimethylthiazoline, an innate fear-associated non-KFO, against 616 human odorant receptor variants, in a cell-based luminescence assay. OR5K1 emerged as sole responding receptor. Tested against a comprehensive collection of 178 KFOs, we newly identified 18 pyrazines and (2R/2S)-4-methoxy-2,5-dimethylfuran-3(2H)-one as agonists. Notably, OR5K1 orthologs in mouse and domesticated species displayed a human-like, potency-ranked activation pattern of pyrazines, suggesting a domestication-led co-evolution of OR5K1 and its orthologs. In summary, OR5K1 is a specialized olfactory receptor across mammals for the detection of pyrazine-based key food odors and semiochemicals.

Volatile scent chemicals in the urine of the red fox, Vulpes vulpes

The red fox is a highly adaptable mammal that has established itself world-wide in many different environments. Contributing to its success is a social structure based on chemical signalling between individuals. Urine scent marking behaviour has long been known in foxes, but there has not been a recent study of the chemical composition of fox urine. We have used solid-phase microextraction and gas chromatography-mass spectrometry to analyze the urinary volatiles in 15 free-ranging wild foxes (2 female) living in farmlands and bush in Victoria, Australia. Foxes here are routinely culled as feral pests, and the urine was collected by bladder puncture soon after death. Compounds were identified from their mass spectra and Kovats retention indices. There were 53 possible endogenous scent compounds, 10 plant-derived compounds and 5 anthropogenic xenobiotics. Among the plant chemicals were several aromatic apocarotenoids previously found in greater abundance in the fox tail gland. They reflect the dietary consumption of carotenoids, essential for optimal health. One third of all the endogenous volatiles were sulfur compounds, a highly odiferous group which included thiols, methylsulfides and polysulfides. Five of the sulfur compounds (3-isopentenyl thiol, 1- and 2-phenylethyl methyl sulfide, octanethiol and benzyl methyl sulfide) have only been found in foxes, and four others (isopentyl methyl sulfide, 3-isopentenyl methyl sulfide, and 1- and 2-phenylethane thiol) only in some canid, mink and skunk species. This indicates that they are not normal mammalian metabolites and have evolved to serve a specific role. This role is for defence in musteloids and most likely for chemical communication in canids. The total production of sulfur compounds varied greatly between foxes (median 1.2, range 0.4–32.3 μg ‘acetophenone equivalents’/mg creatinine) as did the relative abundance of different chemical types. The urinary scent chemistry may represent a highly evolved system of semiochemicals for communication between foxes.

Avoidance behaviour in laboratory house mice (Musmusculus) and Norway rats (Rattus norvegicus) towards predator odours

Mus musculus and Rattus sp. are considered pest species because they reach high densities in urban areas, crop fields and food storage and productive systems such as breeding farms and orchards. Their control relies mainly on rodenticide application, but the effectiveness of this application is reduced due to behavioural responses and resistance. Novel methods are based on the use of chemical signals as odours that may be attractants, repellents or may reduce the reproductive success of pest species. The aim of this paper is to study the aversive effect of TMT, cat urine and cat body odour on predator-inexperienced Mus musculus and Rattus norvegicus under laboratory conditions. The experimental apparatus comprised three boxes connected by PVC pipes in a linear arrangement. In lateral boxes, odour sources or distilled water were introduced, while animals were placed in the central box at the beginning of the experiment. Rats showed freezing behaviour, reduced visits in the presence of TMT and cat fur. Mice reduced their visits with cat body and cat urine. This study provides evidence of the usefulness of using fear responses as a way to control rodent pests, which must be adapted to the environment and species to be applied.

The Grueneberg ganglion: signal transduction and coding in an olfactory and thermosensory organ involved in the detection of alarm pheromones and predator-secreted kairomones

In numerous mammalian species, the nose harbors several compartments populated by chemosensory cells. Among them, the Grueneberg ganglion (GG) located in the anterior nasal region comprises sensory neurons activated by given substances. In rodents, in which the GG has been best studied, these chemical cues mainly include heterocyclic compounds released by predators or by conspecifics. Since some of these substances evoke fear- or stress-associated responses, the GG is considered as a detector for alerting semiochemicals. In fact, certain behavioral and physiological reactions to alarm pheromones and predator-secreted kairomones are attenuated in the absence of a functional GG. Intriguingly, GG neurons are also stimulated by cool temperatures. Moreover, ambient temperatures modulate olfactory responsiveness in the GG, indicating that cross-talks exist between the transduction pathways mediating chemo- and thermosensory signaling in this organ. In this context, exploring the relevant molecular cascades has demonstrated that some chemosensory transduction elements are also crucial for thermosensory signaling in the GG. Finally, for further processing of sensory information, axons of GG neurons project to the olfactory bulb of the brain where they innervate distinct glomerular structures belonging to the enigmatic necklace glomeruli. In this review, the stimuli activating GG neurons as well as the underlying transduction pathways are summarized. Because these stimuli do not exclusively activate GG neurons but also other sensory cells, the biological relevance of the GG is discussed, with a special focus on the role of the GG in detecting alarm signals.

Quantifying defence cascade responses as indicators of pig affect and welfare using computer vision methods

Affective states are key determinants of animal welfare. Assessing such states under field conditions is thus an important goal in animal welfare science. The rapid Defence Cascade (DC) response (startle, freeze) to sudden unexpected stimuli is a potential indicator of animal affect; humans and rodents in negative affective states often show potentiated startle magnitude and freeze duration. To be a practical field welfare indicator, quick and easy measurement is necessary. Here we evaluate whether DC responses can be quantified in pigs using computer vision. 280 video clips of induced DC responses made by 12 pigs were analysed by eye to provide 'ground truth' measures of startle magnitude and freeze duration which were also estimated by (i) sparse feature tracking computer vision image analysis of 200 Hz video, (ii) load platform, (iii) Kinect depth camera, and (iv) Kinematic data. Image analysis data strongly predicted ground truth measures and were strongly positively correlated with these and all other estimates of DC responses. Characteristics of the DC-inducing stimulus, pig orientation relative to it, and 'relaxed-tense' pig behaviour prior to it moderated DC responses. Computer vision image analysis thus offers a practical approach to measuring pig DC responses, and potentially pig affect and welfare, under field conditions.

Electrophysiological Responses of Eighteen Species of Insects to Fire Ant Alarm Pheromone

Olfaction plays a dominant role in insect communication. Alarm pheromones, which alert other insects of the same species of impending danger, are a major class of releaser pheromones. The major components of alarm pheromones in red imported fire ants, honeybees and aphids have been identified as 2-ethyl-3,6-dimethylpyrazine (2E-3,6-DP), isopentyl acetate (IPA), and E-β-farnesene (EβF), respectively. In this study, electroantennography (EAG) responses to EDP (a mixture of 2-ethyl-3,6-dimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine), IPA and EβF were investigated in a wide range of insect species. Beside imported fire ants, the EDP (2-ethyl-3,6(5)-dimethylpyrazine) elicited significant EAG response from all other tested insects, including six ant species and one hybrid ant, honeybee, bagrada bug, lady beetle, housefly, small hive beetle, yellow fever mosquito, termite, bedbug, water hyacinth weevil, southern green stink bug and two aphid species. In contrast, IPA elicited significant EAG response only in the honeybee, red imported fire ant, an Aphaenogaster ant, and the water hyacinth weevil. The EβF only elicited EAG responses in two aphids, small hive beetle and housefly. The results clearly indicate that EDP can be detected by widespread insect species that did not coevolve with S. invicta and further suggested alkylpyrazine may activate multiple generally tuned olfactory receptors (ORs) across a wide number of insect species.

Etizolam attenuates the reduction in cutaneous temperature induced in mice by exposure to synthetic predator odor

Anxiety- and stress-related disorders can be debilitating psychiatric conditions in humans. To prevent or ameliorate these conditions, reliable animal models are needed to evaluate the effects of anxiolytic drugs. Previously, we found that a mixture of three pyrazine analogues (P-mix) that were present at high levels in wolf urine induced fear-related responses in mice, rats and deer. A change in cutaneous temperature was shown to be induced by acute stress simultaneously with changes in heart rate, arterial pressure and freezing behavior, raising the possibility that cutaneous temperature could be used as an index of stress. In the present study, using infrared thermography, we showed that exposure of mice to P-mix induced a decrease in cutaneous temperature. We then examined the dose-dependent effects of an anxiolytic drug, etizolam (0-20 mg/kg), on the temperature decrease. Pre-administration of etizolam (5 mg/kg or higher) inhibited the P-mix-induced decrease in cutaneous temperature. Exposure to P-mix induced Fos-immunoreactivity, a marker of neuronal excitation, at the mouse amygdala and hypothalamus, and etizolam (5 mg/kg) attenuated that immunoreactivity. The present results suggested that the measurement of cutaneous P-mix-induced temperature changes in mice could be used as an animal model for evaluating the effects of anxiolytic drugs.

Pyrazine analogues from wolf urine induced unlearned fear in rats

Urine excreted from the common grey wolf (Canis lupus) contains a kairomone, inducing fear-related behaviors in various mammals. Numerous fear-inducing substances activate neurons at the main and/or accessory olfactory bulb (AOB), medial and central amygdala, and hypothalamus. Our previous study showed that the mixture of pyrazine analogues (P-mix) contained in wolf urine induced avoidance and fear-related behaviors in laboratory mice and Hokkaido deer (Cervus nippon yesoensis), a species native to Japan. Exposure to wolf urine or P-mix induced expression of Fos, a marker of neuronal excitation, in the AOB of mice. In the present study, we explored the effects of P-mix on fear-related behaviors and Fos-expression in rats. Exposure to P-mix induced avoidance and immobilization in rats, while that to a mixture of i-amyl acetate, linalool and R(+)-limonene (O-mix), which generate floral and fruity odors, induced avoidance but not immobilization. P-mix but not O-mix increased Fos-immunoreactivity of the AOB, medial and central amygdala, and hypothalamus of rats. The present results suggest that P-mix odor induces unlearned fear-related behaviors in rats.

Characterizing the scent and chemical composition of Panthera leo marking fluid using solid-phase microextraction and multidimensional gas chromatography-mass spectrometry-olfactometry

Lions (Panthera leo) use chemical signaling to indicate health, reproductive status, and territorial ownership. To date, no study has reported on both scent and composition of marking fluid (MF) from P. leo. The objectives of this study were to: 1) develop a novel method for simultaneous chemical and scent identification of lion MF in its totality (urine + MF), 2) identify characteristic odorants responsible for the overall scent of MF as perceived by human panelists, and 3) compare the existing library of known odorous compounds characterized as eliciting behaviors in animals in order to understand potential functionality in lion behavior. Solid-phase microextraction and simultaneous chemical-sensory analyses with multidimensional gas-chromatography-mass spectrometry-olfactometry improved separating, isolating, and identifying mixed (MF, urine) compounds versus solvent-based extraction and chemical analyses. 2,5-Dimethylpyrazine, 4-methylphenol, and 3-methylcyclopentanone were isolated and identified as the compounds responsible for the characteristic odor of lion MF. Twenty-eight volatile organic compounds (VOCs) emitted from MF were identified, adding a new list of compounds previously unidentified in lion urine. New chemicals were identified in nine compound groups: ketones, aldehydes, amines, alcohols, aromatics, sulfur-containing compounds, phenyls, phenols, and volatile fatty acids. Twenty-three VOCs are known semiochemicals that are implicated in attraction, reproduction, and alarm-signaling behaviors in other species.

The scent of wolves: pyrazine analogs induce avoidance and vigilance behaviors in prey

The common gray wolf (Canis lupus) is an apex predator located at the top of the food chain in the Northern Hemisphere. It preys on rodents, rabbits, ungulates, and many other kinds of mammal. However, the behavioral evidence for, and the chemical basis of, the fear-inducing impact of wolf urine on prey are unclear. Recently, the pyrazine analogs 2, 6-dimethylpyrazine, 2, 3, 5-trimethylpyrazine and 3-ethyl-2, 5-dimethyl pyrazine were identified as kairomones in the urine of wolves. When mice were confronted with a mixture of purified pyrazine analogs, vigilance behaviors, including freezing and excitation of neurons at the accessory olfactory bulb, were markedly increased. Additionally, the odor of the pyrazine cocktail effectively suppressed the approach of deer to a feeding area, and for those close to the feeding area elicited fear-related behaviors such as the "tail-flag," "flight," and "jump" actions. In this review, we discuss the transfer of chemical information from wolf to prey through the novel kairomones identified in wolf urine and also compare the characteristics of wolf kairomones with other predator-produced kairomones that affect rodents.

The olfactory hole-board test in rats: a new paradigm to study aversion and preferences to odors

Odors of biological relevance (e.g., predator odors, sex odors) are known to effectively influence basic survival needs of rodents such as anti-predatory defensiveness and mating behaviors. Research focused on the effects of these odors on rats’ behavior mostly includes multi-trial paradigms where animals experience single odor exposures in subsequent, separated experimental sessions. In the present study, we introduce a modification of the olfactory hole-board test that allows studying the effects of different odors on rats’ behavior within single trials. First, we demonstrated that the corner holes of the hole-board were preferentially visited by rats. The placement of different odors under the corner holes changed this hole preference. We showed that holes with carnivore urine samples were avoided, while corner holes with female rat urine samples were preferred. Furthermore, corner holes with urine samples from a carnivore, herbivore, and omnivore were differentially visited indicating that rats can discriminate these odors. To test whether anxiolytic treatment specifically modulates the avoidance of carnivore urine holes, we treated rats with buspirone. Buspirone treatment completely abolished the avoidance of carnivore urine holes. Taken together, our findings indicate that the olfactory hole-board test is a valuable tool for measuring avoidance and preference responses to biologically relevant odors.

Are single odorous components of a predator sufficient to elicit defensive behaviors in prey species?

When exposed to the odor of a sympatric predator, prey animals typically display escape or defensive responses. These phenomena have been well-documented, especially in rodents, when exposed to the odor of a cat, ferret, or fox. As a result of these experiments new discussions center on the following questions: (1) is a single volatile compound such as a major or a minor mixture constituent in urine or feces, emitted by the predator sufficient to cause defensive reactions in a potential prey species or (2) is a whole array of odors required to elicit a response and (3) will the relative size or escapability of the prey as compared to the predator influence responsiveness. Most predator-prey studies on this topic have been performed in the laboratory or under semi-natural conditions. Field studies could help to find answers to these questions. Australian mammals are completely naïve toward the introduced placental carnivores. That offers ideal opportunities to analyze in the field the responses of potential prey species to unknown predator odors. During the last decades researchers have accumulated an enormous amount of data exploring the effects of eutherian predator odors on native marsupial mammals. In this review, we will give a survey about the development of olfactory research, chemical signals and their influence on the behavior and-in some cases-physiology of prey species. In addition, we report on the effects of predator odor experiments performed under natural conditions in Australia. When studying all these literature we learned that data gained under controlled laboratory conditions elucidate the role of individual odors on brain structures and ultimately on a comparatively narrow range behaviors. In contrast to single odors odor arrays mimic much more the situation prey animals are confronted to in nature. Therefore, a broad range of methodology-from chemistry to ecology including anatomy, physiology, and behavior-is needed to understand all the different (relevant) stimuli that govern and guide the interactions between a predator and its potential prey.

Identification of pyridine analogs as new predator-derived kairomones

In the wild, animals have developed survival strategies relying on their senses. The individual ability to identify threatening situations is crucial and leads to increase in the overall fitness of the species. Rodents, for example have developed in their nasal cavities specialized olfactory neurons implicated in the detection of volatile cues encoding for impending danger such as predator scents or alarm pheromones. In particular, the neurons of the Grueneberg ganglion (GG), an olfactory subsystem, are implicated in the detection of danger cues sharing a similar chemical signature, a heterocyclic sulfur- or nitrogen-containing motif. Here we used a “from the wild to the lab” approach to identify new molecules that are involuntarily emitted by predators and that initiate fear-related responses in the recipient animal, the putative prey. We collected urines from carnivores as sources of predator scents and first verified their impact on the blood pressure of the mice. With this approach, the urine of the mountain lion emerged as the most potent source of chemical stress. We then identified in this biological fluid, new volatile cues with characteristic GG-related fingerprints, in particular the methylated pyridine structures, 2,4-lutidine and its analogs. We finally verified their encoded danger quality and demonstrated their ability to mimic the effects of the predator urine on GG neurons, on mice blood pressure and in behavioral experiments. In summary, we were able to identify here, with the use of an integrative approach, new relevant molecules, the pyridine analogs, implicated in interspecies danger communication.

Avoidance learning: a review of theoretical models and recent developments

Avoidance is a key characteristic of adaptive and maladaptive fear. Here, we review past and contemporary theories of avoidance learning. Based on the theories, experimental findings and clinical observations reviewed, we distill key principles of how adaptive and maladaptive avoidance behavior is acquired and maintained. We highlight clinical implications of avoidance learning theories and describe intervention strategies that could reduce maladaptive avoidance and prevent its return. We end with a brief overview of recent developments and avenues for further research.

Fox urine exposure induces avoidance behavior in rats and activates the amygdalar olfactory cortex

Predator odors represent a group of biologically-relevant chemosignals called kairomones. Kairomones enable prey animals to recognize potential predatory threats in their environment and to initiate appropriate defensive responses. Although the behavioral repertoire of anti-predatory responses (e.g. avoidance, freezing, risk assessment) has been investigated extensively, our knowledge about the neural network mediating these innate fear responses is rather limited. In the present study, the GABAA agonist muscimol was bilaterally injected (2.6 nmol/0.3 μl) into the amygdalar olfactory cortex (AOC), a brain area that receives massive olfactory input from both olfactory systems and is strongly interconnected with the medial hypothalamic defense circuit. Temporary inactivation of the AOC substantially disrupted avoidance behavior of rats to fox urine that is strongly avoided under control conditions (saline injections). Taken together, these results demonstrate that the AOC is critically involved in fox urine-induced fear behavior. This suggests that the AOC is part of a brain fear circuit that mediates innate fear responses toward predatory odors.

Pyrazine analogs are active components of wolf urine that induce avoidance and fear-related behaviors in deer

Our previous studies indicated that a cocktail of pyrazine analogs, identified in wolf urine, induced avoidance and fear behaviors in mice. The effects of the pyrazine cocktail on Hokkaido deer (Cervus nippon yesoensis) were investigated in field bioassays at a deer park in Hokkaido, Japan. A set of feeding bioassay trials tested the effects of the pyrazine cocktail odor on the behavior of the deer located around a feeding area in August and September 2013. This odor effectively suppressed the approach of the deer to the feeding area. In addition, the pyrazine cocktail odor provoked fear-related behaviors, such as “tail-flag”, “flight” and “jump” actions, of the deer around the feeding area. This study is the first experimental demonstration that the pyrazine analogs in wolf urine have robust and continual fearful aversive effects on ungulates as well as mice. The pyrazine cocktail might be suitable for a chemical repellent that could limit damage to forests and agricultural crops by wild ungulates.

Integrated action of pheromone signals in promoting courtship behavior in male mice

The mammalian vomeronasal organ encodes pheromone information about gender, reproductive status, genetic background and individual differences. It remains unknown how pheromone information interacts to trigger innate behaviors. In this study, we identify vomeronasal receptors responsible for detecting female pheromones. A sub-group of V1re clade members recognizes gender-identifying cues in female urine. Multiple members of the V1rj clade are cognate receptors for urinary estrus signals, as well as for sulfated estrogen (SE) compounds. In both cases, the same cue activates multiple homologous receptors, suggesting redundancy in encoding female pheromone cues. Neither gender-specific cues nor SEs alone are sufficient to promote courtship behavior in male mice, whereas robust courtship behavior can be induced when the two cues are applied together. Thus, integrated action of different female cues is required in pheromone-triggered mating behavior. These results suggest a gating mechanism in the vomeronasal circuit in promoting specific innate behavior.DOI: http://dx.doi.org/10.7554/eLife.03025.001.

Similar rate of information transfer on stimulus intensity in accessory and main olfactory bulb output neurons

Recently, evidence has accumulated that the vomeronasal system cooperates with the main olfactory system to process volatile cues that regulate the animal's behavior. This is contradictory to the traditional view that the vomeronasal system is quite different from the main olfactory system in the time scale of information processing. Particularly, the firing rate of mitral/tufted cells in the accessory olfactory bulb (MTAOB) is known to be significantly lower than that of mitral cells in the main olfactory bulb (MCMOB). To address this question of whether the low-frequency firing in MTAOB carries less information than the high-frequency firing in MCMOB in the early stages of stimulation, we compared MTAOB and MCMOB for their firing mechanisms and information transfer characteristics. A model computation demonstrated that the inherent channel kinetics of MTAOB was responsible for their firing at a lower frequency than MCMOB. Nevertheless, our analysis suggested that MTAOB were comparable to MCMOB in both the amount and speed of information transfer about depolarizing current intensity immediately after current injection onset (<200ms). Our results support a hypothesis of simultaneous processing of common cues in both systems.