Urine from stressed rats increases immobility in receptor rats forced to swim: Role of 2-heptanone

CFA-treated mice induce hyperalgesia in healthy mice via an olfactory mechanism

BACKGROUND

Social interactions with subjects experiencing pain can increase nociceptive sensitivity in observers, even without direct physical contact. In previous experiments, extended indirect exposure to soiled bedding from mice with alcohol withdrawal-related hyperalgesia enhanced nociception in their conspecifics. This finding suggested that olfactory cues could be sufficient for nociceptive hypersensitivity in otherwise untreated animals (also known as "bystanders").

AIM

The current study addressed this possibility using an inflammation-based hyperalgesia model and long- and short-term exposure paradigms in C57BL/6J mice.

MATERIALS & METHOD

Adult male and female mice received intraplantar injection of complete Freund's adjuvant (CFA) and were used as stimulus animals to otherwise naïve same-sex bystander mice (BS). Another group of untreated mice (OLF) was simultaneously exposed to the bedding of the stimulus mice.

RESULTS

In the long-term, 15-day exposure paradigm, the presence of CFA mice or their bedding resulted in reduced von Frey threshold but not Hargreaves paw withdrawal latency in BS or OLF mice. In the short-term paradigm, 1-hr interaction with CFA conspecifics or 1-hr exposure to their bedding induced mechanical hypersensitivity in BS and OLF mice lasting for 3 hrs. Chemical ablation of the main olfactory epithelium prevented bedding-induced and stimulus mice-induced mechanical hypersensitivity. Gas chromatography-mass spectrometry (GC-MS) analysis of the volatile compounds in the bedding of experimental mice revealed that CFA-treated mice released an increased number of compounds indicative of disease states.

DISCUSSION AND CONCLUSION

These results demonstrate that CFA-induced inflammatory pain can modulate nociception in bystander mice via an olfactory mechanism involving dynamic changes in volatile compounds detectable in the rodent bedding.

SIGNIFICANCE

Social context can influence nociceptive sensitivity. Recent studies suggested involvement of olfaction in this influence. In agreement with this idea, the present study shows that the presence of mice with inflammatory pain produces nociceptive hypersensitivity in nearby conspecifics. This enhanced nociception occurs via olfactory cues present in the mouse bedding. Analysis of the bedding from mice with inflammatory pain identifies a number of compounds indicative of disease states. These findings demonstrate the importance of olfactory system in influencing pain states.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Anogenital scent-marking signals fertility in a captive female Alaotran gentle lemur

The Lake Alaotra gentle lemur (Hapalemur alaotrensis) is one of the 25 most endangered primates in the world and shows low success rate in captive breeding programmes. It is therefore vital to further understand its reproductive biology. We studied a captive troop consisting of five individuals hosted at Jersey Zoo during breeding and non-breeding periods over 1 year. We collected behavioural data (n = 318 h) using all occurrence of some behaviours and ad libitum sampling methods, as well as faecal (n = 54) and anogenital scent (n = 35) samples of the breeding female. We measured sex hormone levels using enzyme immunoassay technique and investigated the volatile component of odour signals using solid-phase microextraction and gas chromatography-mass spectrometry. We observed sexual and aggressive behaviours occasionally during the breeding period. Our regression analysis showed that only period significantly predicted rates of female anogenital scent-marking, whereby the female performed anogenital scent-marking more frequently during the breeding rather than the non-breeding period. In contrast, female hormone levels did not significantly explain variation in rates of neither male nor female olfactory, sexual and affiliative behaviours, suggesting that individuals' behaviour alone is not an effective indicator of the ovulation window. The volatile chemical profile of anogenital odour secretions changed over the study, with four compounds distinguishing the fertile window during the breeding period. In conclusion, our findings suggest that anogenital scent-marking may signal the reproductive status of captive female gentle lemurs.

Pre- and Postnatal Predator Cues Shape Offspring Anti-predatory Behavior Similarly in the Bank Vole

Prey animals can assess the risks predators present in different ways. For example, direct cues produced by predators can be used, but also signals produced by prey conspecifics that have engaged in non-lethal predator-prey interactions. These non-lethal interactions can thereby affect the physiology, behavior, and survival of prey individuals, and may affect offspring performance through maternal effects. We investigated how timing of exposure to predation-related cues during early development affects offspring behavior after weaning. Females in the laboratory were exposed during pregnancy or lactation to one of three odor treatments: (1) predator odor (PO) originating from their most common predator, the least weasel, (2) odor produced by predator-exposed conspecifics, which we call conspecific alarm cue (CAC), or (3) control odor (C). We monitored postnatal pup growth, and we quantified foraging and exploratory behaviors of 4-week-old pups following exposure of their mothers to each of the three odour treatments. Exposure to odors associated with predation risk during development affected the offspring behavior, but the timing of exposure, i.e., pre- vs. postnatally, had only a weak effect. The two non-control odors led to different behavioral changes: an attraction to CAC and an avoidance of PO. Additionally, pup growth was affected by an interaction between litter size and maternal treatment, again regardless of timing. Pups from the CAC maternal treatment grew faster in larger litters; pups from the PO maternal treatment tended to grow faster in smaller litters. Thus, in rodents, offspring growth and behavior are seemingly influenced differently by the type of predation risk perceived by their mothers.

2-Heptanone reduces inhibitory control of the amygdala over the prelimbic region in rats

Basolateral amygdala (BLA) nuclei and their reciprocal connections with prelimbic (PL) and infralimbic (IL) regions of the medial prefrontal cortex (mPFC) are involved in the regulation of fear. 2-Heptanone is released in urine in stressed rats, and the olfactory detection of this odor produces immediate avoidance and alarm reactions and modifies neuronal activity in limbic connections in non-stressed rats. If 2-heptanone acts as a danger signal, then long-lasting actions would be expected. The aim of the present study was to investigate whether the forced inhalation of 2-heptanone modifies the response capacity of the BLA-mPFC circuit in the long term (48 h). Single-unit extracellular recordings were obtained from the PL and IL during electrical stimulation of the BLA (square-wave pulses; 1 ms, 20 µA, 0.3 Hz, 110 stimuli over a total duration of 360 s) in three groups of Wistar rats: control group (no sensory stimulation), unpredictable auditory stimulation group, and 2-heptanone stimulation group. A brief-latency (1 ms), short-duration (5 ms) paucisynaptic response followed BLA stimulation and was unaffected by any sensorial stimulation. The paucisynaptic response was followed by a mostly inhibitory and long-lasting (>750 ms) afterdischarge in the control and auditory stimulation groups. In the 2-heptanone group, the inhibitory afterdischarge shifted to an excitatory afterdischarge after ∼250 ms in the PL and after ∼500 ms in the IL. Importantly, the rats that were included in this study were born in local housing facilities. Thus, these animals were never in contact with predators and instead in contact with only conspecifics. These results indicate that the forced inhalation of 2-heptanone is able to modify BLA-mPFC responsivity in the long term. 2-Heptanone decreases inhibitory control of the amygdala over mPFC activity. Disinhibition of the mPFC may lead to the adaptive expression of defensive behaviors, even in animals that are not in the presence of predators.

Bank vole alarm pheromone chemistry and effects in the field

Chemical communication plays an important role in mammalian life history decisions. Animals send and receive information based on body odour secretions. Odour cues provide important social information on identity, kinship, sex, group membership or genetic quality. Recent findings show, that rodents alarm their conspecifics with danger-dependent body odours after encountering a predator. In this study, we aim to identify the chemistry of alarm pheromones (AP) in the bank vole, a common boreal rodent. Furthermore, the vole foraging efficiency under perceived fear was measured in a set of field experiments in large outdoor enclosures. During the analysis of bank vole odour by gas chromatography–mass spectrometry, we identified that 1-octanol, 2-octanone, and one unknown compound as the most likely candidates to function as alarm signals. These compounds were independent of the vole’s sex. In a field experiment, voles were foraging less, i.e. they were more afraid in the AP odour foraging trays during the first day, as the odour was fresh, than in the second day. This verified the short lasting effect of volatile APs. Our results clarified the chemistry of alarming body odour compounds in mammals, and enhanced our understanding of the ecological role of AP and chemical communication in mammals.

The smell of hunger: Norway rats provision social partners based on odour cues of need

When individuals exchange helpful acts reciprocally, increasing the benefit of the receiver can enhance its propensity to return a favour, as pay-offs are typically correlated in iterated interactions. Therefore, reciprocally cooperating animals should consider the relative benefit for the receiver when deciding to help a conspecific. Norway rats (Rattus norvegicus) exchange food reciprocally and thereby take into account both the cost of helping and the potential benefit to the receiver. By using a variant of the sequential iterated prisoner’s dilemma paradigm, we show that rats may determine the need of another individual by olfactory cues alone. In an experimental food-exchange task, test subjects were provided with odour cues from hungry or satiated conspecifics located in a different room. Our results show that wild-type Norway rats provide help to a stooge quicker when they receive odour cues from a hungry rather than from a satiated conspecific. Using chemical analysis by gas chromatography-mass spectrometry (GC-MS), we identify seven volatile organic compounds that differ in their abundance between hungry and satiated rats. Combined, this “smell of hunger” can apparently serve as a reliable cue of need in reciprocal cooperation, which supports the hypothesis of honest signalling.

Rats provide more food to hungry fellow rats than to satiated ones. This study shows that a rat can assess the need of their partner using odor cues alone, and identifies the volatile organic compounds responsible for this "smell of hunger," a potential example of honest signalling.

Differential responses by urban brown rats (Rattus norvegicus) toward male or female-produced scents in sheltered and high-risk presentations

Wild rats (Rattus norvegicus) are among the most ubiquitous and consequential organisms in the urban environment. However, collecting data from city rats is difficult, and there has been little research to determine the influence, or valence, of rat scents on urban conspecifics. Using a mark-release-monitor protocol, we previously learned rats can be attracted to remote-sensing points when baited with mixed-bedding from male and female laboratory rats. It was thus essential that we disambiguate which scents were eliciting attraction (+ valence), inspection, a conditioned response whereby attraction may be followed by avoidance (–valence), or null-response (0 valence). We used radio-frequency identification tagging and scent-baited antennas to assess extended (>40 days) responses to either male or female scents against two risk presentations (near-shelter and exposed to predators). In response to male scents, rats (n = 8) visited both treatments (shelter, exposed) more than controls (0.2 visits/day treatment vs. 0.1/day; P < 0.05) indicating scents accounted for response more so than risk. Dwell-times, however, did not differ (1.2 s/visit treatment vs. 0.9 s/visit; P > 0.5). These outcomes are consistent with inspection (–valence). In response to female scents, rats (n = 7) increased visitation (5.02 visits/day vs. 0.1/day controls; P < 0.05), while dwell-times also increased 6.8 s/visit vs. 0.2 s/visit in both risk-settings. The latter is consistent with persistent attraction (+valence), but was also influenced by shelter, as runway visits (1.1 visits/day) were a magnitude more common than predator-exposed (0.1 visits/day). Further understanding and exploiting the mobility of city rats is necessary for improvements in basic and applied research, including city pathogen-surveillance and urban wildlife management.

An odorant receptor from Anopheles sinensis in China is sensitive to oviposition attractants

Background

Anopheles sinensis is an important vector for the spread of malaria in China. Olfactory-related behaviours, particularly oviposition site seeking, offer opportunities for disrupting the disease-transmission process.

Results

This is the first report of the identification and characterization of AsinOrco and AsinOR10 in An. sinensis. AsinOrco and AsinOR10 share 97.49% and 90.37% amino acid sequence identity, respectively, with related sequences in Anopheles gambiae. A functional analysis demonstrated that AsinOrco- and AsinOR10-coexpressing HEK293 cells were highly sensitive to 3-methylindole, but showed no significant differences in response to other test odorants when compared to DMSO.

Conclusions

AsinOrco was characterized as a new member of the Orco ortholog subfamily. AsinOR10, which appears to be a member of the OR2-10 subfamily, is directly involved in identification of oviposition sites. This finding will help to elucidate the molecular mechanisms underlying olfactory signaling in An. sinensis and provide many more molecular targets for eco-friendly pest control.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2501-4) contains supplementary material, which is available to authorized users.

Social modulation of fear: Facilitation vs buffering

Social behaviors largely constitute mutual exchanges of social cues and the responses to them. The adaptive response also requires proper interpretation of the current context. In fear behaviors, social signals have bidirectional effects-some cues elicit or enhance fear whereas other suppress or buffer it. Studies on the social facilitation and social buffering of fear provide evidence of competition between social cues of opposing meanings. Co-expression of opposing cues by the same animal may explain the contradicting outcomes from the interaction between naive and frightened conspecifics, which reflect the fine balance between fear facilitation and buffering. The neuronal mechanisms that determine that balance provide an exciting target for future studies to probe the brain circuits underlying social modulation of emotional behaviors.

Avoidance and contextual learning induced by a kairomone, a pheromone and a common odorant in female CD1 mice

Chemosignals mediate both intra- and inter-specific communication in most mammals. Pheromones elicit stereotyped reactions in conspecifics, whereas kairomones provoke a reaction in an allospecific animal. For instance, predator kairomones elicit anticipated defensive responses in preys. The aim of this work was to test the behavioral responses of female mice to two chemosignals: 2-heptanone (2-HP), a putative alarm pheromone, and 2,4,5-trimethylthiazoline (TMT), a fox-derived putative kairomone, widely used to investigate fear and anxiety in rodents. The banana-like odorant isoamyl acetate (IA), unlikely to act as a chemosignal, served as a control odorant. We first presented increasing amounts of these odorants in consecutive days, in a test box in which mice could explore or avoid them. Female mice avoided the highest amounts of all three compounds, with TMT and IA eliciting avoidance at lower amounts (3.8 pmol and 0.35 μmol, respectively) than 2-HP (35 μmol). All three compounds induced minimal effects in global locomotion and immobility in this set up. Further, mice detected 3.5 pmol of TMT and IA in a habituation–dishabituation test, so avoidance of IA started well beyond the detection threshold. Finally, both TMT and IA, but not 2-HP, induced conditioned place avoidance and increased immobility in the neutral compartment during a contextual memory test. These data suggest that intense odors can induce contextual learning irrespective of their putative biological significance. Our results support that synthetic predator-related compounds (like TMT) or other intense odorants are useful to investigate the neurobiological basis of emotional behaviors in rodents. Since intense odorants unlikely to act as chemosignals can elicit similar behavioral reactions than chemosignals, we stress the importance of using behavioral measures in combination with other physiological (e.g., hormonal levels) or neural measures (e.g., immediate early gene expression) to establish the ethological significance of odorants.

Morphological and physiological species-dependent characteristics of the rodent Grueneberg ganglion

In the mouse, the Grueneberg ganglion (GG) is an olfactory subsystem implicated both in chemo- and thermo-sensing. It is specifically involved in the recognition of volatile danger cues such as alarm pheromones and structurally-related predator scents. No evidence for these GG sensory functions has been reported yet in other rodent species. In this study, we used a combination of histological and physiological techniques to verify the presence of a GG and investigate its function in the rat, hamster, and gerbil comparing with the mouse. By scanning electron microscopy (SEM) and transmitted electron microscopy (TEM), we found isolated or groups of large GG cells of different shapes that in spite of their gross anatomical similarities, display important structural differences between species. We performed a comparative and morphological study focusing on the conserved olfactory features of these cells. We found fine ciliary processes, mostly wrapped in ensheating glial cells, in variable number of clusters deeply invaginated in the neuronal soma. Interestingly, the glial wrapping, the amount of microtubules and their distribution in the ciliary processes were different between rodents. Using immunohistochemistry, we were able to detect the expression of known GG proteins, such as the membrane guanylyl cyclase G and the cyclic nucleotide-gated channel A3. Both the expression and the subcellular localization of these signaling proteins were found to be species-dependent. Calcium imaging experiments on acute tissue slice preparations from rodent GG demonstrated that the chemo- and thermo-evoked neuronal responses were different between species. Thus, GG neurons from mice and rats displayed both chemo- and thermo-sensing, while hamsters and gerbils showed profound differences in their sensitivities. We suggest that the integrative comparison between the structural morphologies, the sensory properties, and the ethological contexts supports species-dependent GG features prompted by the environmental pressure.

Factors influencing behavior in the forced swim test

The forced swim test (FST) is a behavioral test in rodents which was developed in 1978 by Porsolt and colleagues as a model for predicting the clinical efficacy of antidepressant drugs. A modified version of the FST added the classification of active behaviors into swimming and climbing, in order to facilitate the differentiation between serotonergic and noradrenergic classes of antidepressant drugs. The FST is now widely used in basic research and the pharmaceutical screening of potential antidepressant treatments. It is also one of the most commonly used tests to assess depressive-like behavior in animal models. Despite the simplicity and sensitivity of the FST procedure, important differences even in baseline immobility rates have been reported between different groups, which complicate the comparison of results across studies. In spite of several methodological papers and reviews published on the FST, the need still exists for clarification of factors which can influence the procedure. While most recent reviews have focused on antidepressant effects observed with the FST, this one considers the methodological aspects of the procedure, aiming to summarize issues beyond antidepressant action in the FST. The previously published literature is analyzed for factors which are known to influence animal behavior in the FST. These include biological factors, such as strain, age, body weight, gender and individual differences between animals; influence of preconditioning before the FST: handling, social isolation or enriched environment, food manipulations, various kinds of stress, endocrine manipulations and surgery; schedule and routes of treatment, dosage and type of the drugs as well as experimental design and laboratory environmental effects. Consideration of these factors in planning experiments may result in more consistent FST results.

Mouse alarm pheromone shares structural similarity with predator scents

Sensing the chemical warnings present in the environment is essential for species survival. In mammals, this form of danger communication occurs via the release of natural predator scents that can involuntarily warn the prey or by the production of alarm pheromones by the stressed prey alerting its conspecifics. Although we previously identified the olfactory Grueneberg ganglion as the sensory organ through which mammalian alarm pheromones signal a threatening situation, the chemical nature of these cues remains elusive. We here identify, through chemical analysis in combination with a series of physiological and behavioral tests, the chemical structure of a mouse alarm pheromone. To successfully recognize the volatile cues that signal danger, we based our selection on their activation of the mouse olfactory Grueneberg ganglion and the concomitant display of innate fear reactions. Interestingly, we found that the chemical structure of the identified mouse alarm pheromone has similar features as the sulfur-containing volatiles that are released by predating carnivores. Our findings thus not only reveal a chemical Leitmotiv that underlies signaling of fear, but also point to a double role for the olfactory Grueneberg ganglion in intraspecies as well as interspecies communication of danger.

Neural mechanisms of alarm pheromone signaling

Alarm pheromones are important semiochemicals used by many animal species to alert conspecifics or other related species of impending danger. In this review, we describe recent developments in our understanding of the neural mechanisms underlying the ability of fruit flies, zebrafish and mice to mediate the detection of alarm pheromones. Specifically, alarm pheromones are detected in these species through specialized olfactory subsystems that are unique to the chemosensitive receptors, second messenger-signaling and physiology. Thus, the alarm pheromones appears to be detected by signaling mechanisms that are distinct from those seen in the canonical olfactory system.

2-Heptanone increases the firing rate of the basal amygdala: role of anterior olfactory epithelial organs

Wistar rats subjected to physical stress release a urine alarm pheromone (2-heptanone) that produces signs of anxiety and despair in receptor rats not subjected to physical stress. However, unknown are the effects of 2-heptanone on the firing rate of the basal amygdala, a structure that participates in the expression of fear, and the participation of anterior olfactory epithelial organs, namely the septal organ and vomeronasal organ (SO-VNO). We explored the effects of 2-heptanone applied near the nostrils on single-unit extracellular recordings from the basal amygdala in a sham-operated group and rats that underwent removal of the SO-VNO. The firing rate of basal amygdala neurons in the SO-VNO removal group was significantly higher than in the sham-operated group. In both groups, recordings were classified according to the responses to 2-heptanone (i.e., increased firing rate, decreased firing rate, and no response). SO-VNO removal was associated with an increased firing rate in the three types of neurons. A similar number of neurons increased their firing rate during and after 2-heptanone stimulation in both groups, but such an increase in firing rate was longer in the group of rats subjected to SO-VNO removal. The results indicate that the SO-VNO is not essential for the effect of 2-heptanone on the firing rate of basal amygdala neurons. SO-VNO ablation did not block but rather accentuated the response of amygdala neurons to 2-heptanone.

Intra-lateral septal infusions of folic acid alone or combined with various antidepressant drugs produce antidepressant-like actions in male Wistar rats forced to swim

Intra-cerebral administrations of folic acid produce antidepressant-like effects; either alone or combined with several antidepressant drugs. However, the specific limbic structures implied in the antidepressant-like actions of folic acid are un-known. Thus, intra-lateral septal infusions of folic acid (5.0 nmol, P<0.05; 10.0 nmol, P<0.05) or oral administrations of folic acid (50 mg/kg, P<0.05, p.o.; 75.0; mg/kg, P<0.05, p.o.) or systemic administrations of fluoxetine (20.0 mg/kg, P<0.05; 25.0 mg/kg, P<0.05) reduced immobility by increasing swimming behavior in the forced swimming test (FST) of male Wistar rats. Conversely, desipramine (10.0 mg/kg, P<0.05; 15.0 mg/kg, P<0.05) reduced immobility by increasing climbing behavior. Subthreshold doses of folic acid (2.5 nmol/intra-LSN) combined with subthreshold doses of folic acid (25.0 mg/kg, p.o., P<0.05) or with subthreshold doses of fluoxetine (15.0 mg/kg, P<0.05) and they produced antidepressant-like effects which were canceled by ketanserin. In conclusion, intra-lateral septal infusions of folic acid alone or combined with systemic doses of folic acid or fluoxetine reduced immobility in the FST. These antidepressant-like actions, probably, were due to modifications of the serotonergic system since swimming behavior was increased and these effects were canceled by ketanserin.

The folic acid combined with 17-β estradiol produces antidepressant-like actions in ovariectomized rats forced to swim

Folic acid or 17-β estradiol produces antidepressant effects, either alone or combined with several antidepressants. However, the antidepressant-like actions of folic acid combined with 17-β estradiol in the forced swimming test (FST) have not been tested before. Thus, in the present study, ovariectomized female rats received folic acid (5.0 nmol/i.c.v., P<0.05; 10.0 nmol/ i.c.v., P<0.05; or 50mg/kg, P<0.05, p.o.; 75.0; mg/kg, P<0.05, p.o.), or fluoxetine (20.0mg/kg, P<0.05; 25.0mg/kg, P<0.05) or 17-β estradiol (10.0 μg/rat, P<0.05; 20.0 μg/rat, P<0.05) and they displayed reduced immobility by increasing swimming behavior when they were tested in the FST. Combination of subthreshold doses of folic acid (2.5 nmol/i.c.v.; or 25.0mg/kg, p.o.) with subthreshold doses of 17-β estradiol (5.0 μg/rat, P<0.05) or with subthreshold doses of fluoxetine (15.0mg/kg, P<0.05) produced antidepressant-like actions. Ketanserin was used to evaluate the participation of the drugs used in the serotonergic pathway; ketanserin cancelled the antidepressant-like actions of the several combinations used. In conclusion, folic acid alone or combined with estradiol or fluoxetine in the FST reduced immobility in the FST. These antidepressant-like actions probably were due to modifications of the serotonergic system since swimming behavior was increased and these effects were cancelled by ketanserin.

Mouse urinary biomarkers provide signatures of maturation, diet, stress level, and diurnal rhythm

Body fluids such as urine potentially contain a wealth of information pertaining to age, sex, social and reproductive status, physiologic state, and genotype of the donor. To explore whether urine could encode information regarding environment, physiology, and development, we compared the volatile compositions of mouse urine using solid-phase microextraction and gas chromatography-mass spectrometry (SPME-GC/MS). Specifically, we identified volatile organic compounds (VOCs) in individual urine samples taken from inbred C57BL/6J-H-2(b) mice under several experimental conditions-maturation state, diet, stress, and diurnal rhythms, designed to mimic natural variations. Approximately 1000 peaks (i.e., variables) were identified per comparison and of these many were identified as potential differential biomarkers. Consistent with previous findings, we found groups of compounds that vary significantly and consistently rather than a single unique compound to provide a robust signature. We identified over 49 new predictive compounds, in addition to identifying several published compounds, for maturation state, diet, stress, and time-of-day. We found a considerable degree of overlap in the chemicals identified as (potential) biomarkers for each comparison. Chemometric methods indicate that the strong group-related patterns in VOCs provide sufficient information to identify several parameters of natural variations in this strain of mice including their maturation state, stress level, and diet.

Odorant reception in the malaria mosquito Anopheles gambiae

The mosquito Anopheles gambiae is the major vector of malaria in sub-Saharan Africa. It locates its human hosts primarily through olfaction, but little is known about the molecular basis of this process. Here we functionally characterize the Anopheles gambiae Odourant Receptor (AgOr) repertoire. We identify receptors that respond strongly to components of human odour and that may act in the process of human recognition. Some of these receptors are narrowly tuned, and some salient odourants elicit strong responses from only one or a few receptors, suggesting a central role for specific transmission channels in human host-seeking behavior. This analysis of the Anopheles gambiae receptors permits a comparison with the corresponding Drosophila melanogaster odourant receptor repertoire. We find that odourants are differentially encoded by the two species in ways consistent with their ecological needs. Our analysis of the Anopheles gambiae repertoire identifies receptors that may be useful targets for controlling the transmission of malaria.

From Pheromones to Behavior

In recent years, considerable progress has been achieved in the comprehension of the profound effects of pheromones on reproductive physiology and behavior. Pheromones have been classified as molecules released by individuals and responsible for the elicitation of specific behavioral expressions in members of the same species. These signaling molecules, often chemically unrelated, are contained in body fluids like urine, sweat, specialized exocrine glands, and mucous secretions of genitals. The standard view of pheromone sensing was based on the assumption that most mammals have two separated olfactory systems with different functional roles: the main olfactory system for recognizing conventional odorant molecules and the vomeronasal system specifically dedicated to the detection of pheromones. However, recent studies have reexamined this traditional interpretation showing that both the main olfactory and the vomeronasal systems are actively involved in pheromonal communication. The current knowledge on the behavioral, physiological, and molecular aspects of pheromone detection in mammals is discussed in this review.

Acute restraint stress produces behavioral despair in weanling rats in the forced swim test

Stressful experiences in the rat during early life increase the vulnerability to later signs of behavioral despair in adulthood, reflected in increased immobility in the forced swim test (FST). However, the possible immediate effects of stress in weanling rats have only been partially described. The present study tested whether a single session of mild restraint stress modifies immobility in the FST in 21-day-old Wistar rats. After evaluating any possible changes in locomotion using the open field test (OFT), the latency and total duration of immobility were assessed in a single FST session. Regardless of gender, mild restraint stress significantly reduced crossings in the OFT, shortened the latency to the first period of immobility, and increased immobility in the FST compared with a control group devoid of stress. We conclude that a single mild physical stress session, as early as postnatal day 21, produces signs of behavioral despair.

Social modeling of conditioned fear in mice by non-fearful conspecifics

Social interactions with conspecifics markedly alter the neuroendocrine, behavioral and emotional responses to stressful events. Some of these effects involve observational learning and result in lasting changes of fear-motivated behavior. While most evidence reveals increased fearfulness after observation of fearful demonstrators (models) in a number of species, a few reports from human and non-human primates indicate that observational learning can also attenuate some forms of fear. In the present study, we set out to determine the effects of social modeling and observational learning on fear conditioning in the mouse. Observers were pre-exposed to a novel context in the presence of fearful (F group) or non-fearful (NF group) demonstrators. Mice of the F group acquired control levels of conditioned fear. On the other hand, mice of the NF group exhibited profound and persistent reduction of fear. The decrease of fear in NF observers was most likely due to context-specific impairments of fear conditioning, as revealed by selective effects on long- but not short-term contextual fear memory, and normal fear conditioning in response to a novel context or cue. The effect was lasting, but constrained by the shock intensity. Attenuation of fear conditioning resulting from interactions with non-fearful conspecifics was largely, but not entirely, mediated by vicarious learning. These findings identify an important social buffering process serving to prevent a lasting induction of fear in response to isolated, moderately intense stressful events.

Desipramine or glutamate antagonists synergized the antidepressant-like actions of intra-nucleus accumbens infusions of minocycline in male Wistar rats

Minocycline produces antidepressant-like actions in male rats tested in the forced swimming test (FST) and synergizes with several glutamate receptor antagonists. However, the limbic regions implicated in the antidepressant-like actions of minocycline are unknown. The objective of the present study was to test the potential antidepressant activity of nucleus accumbens infusions of minocycline alone or combined with antidepressant drugs or with several glutamate receptor antagonists, using the time-sampling method in the FST. The results show that intra-NAcc infusions of minocycline reduced immobility (1.0 microg, P<0.05; 1.5 microg, P<0.05) by increasing climbing (1.0 microg, P<0.05; 1.5 microg, P<0.05) in the FST. Likewise, systemic injections of desipramine (P<0.05), fluoxetine (P<0.05) or several glutamate receptor antagonists: EMQMCM (P<0.05), MTEP (P<0.05) or dizocilpine (P<0.05) combined with intra-nucleus accumbens infusions of vehicle produced antidepressant-like actions. The subthreshold dose of intra-nucleus accumbens infusions of minocycline combined with systemic injections of subthreshold doses of desipramine (P<0.05) or EMQMCM (P<0.05) or MTEP (P<0.05) or dizocilpine (P<0.05) produced antidepressant-like actions. It is concluded that intra-NAcc infusions of minocycline alone or combined with systemic injections of desipramine or with systemic injections of several glutamate receptor antagonists produced antidepressant-like actions in the FST.

Stressors can affect immobility time and response to imipramine in the rat forced swim test

We subjected Wistar rats to the forced swim test (FST) to compare the effects of two doses of imipramine in physically stressed rats (P: unavoidable electric footshocks), emotionally stressed rats (E: odors), or non-stressed rats (C). Stress or control sessions lasted 35 days. Drug treatments began on day 21 and continued for the next 14 days. E rats were placed for 10 min, once per day for 35 days, in a small non-movement-restricting cage impregnated with urine collected from a P rat. E and P rats exhibited opposite changes in locomotion. After 21 days of stress sessions, P rats displayed the longest immobility times in the FST, followed by E rats. In the P group, on day 7 of treatment (day 28 of the study), imipramine (2.5 mg/kg) reduced immobility time to baseline values. In the E group, immobility time decreased only after 14 days of treatment with the low imipramine dose. The high dose of imipramine (5.0 mg/kg) reduced immobility time at day 7 of treatment in all groups. In conclusion, physical and emotional stress similarly increased immobility time in the FST, but emotional stress appears to be more resistant to imipramine treatment.

Grueneberg ganglion cells mediate alarm pheromone detection in mice

Alarm pheromones (APs) are widely used throughout the plant and animal kingdoms. Species such as fish, insects, and mammals signal danger to conspecifics by releasing volatile alarm molecules. Thus far, neither the chemicals, their bodily source, nor the sensory system involved in their detection have been isolated or identified in mammals. We found that APs are recognized by the Grueneberg ganglion (GG), a recently discovered olfactory subsystem. We showed with electron microscopy that GG neurons bear primary cilia, with cell bodies ensheathed by glial cells. APs evoked calcium responses in GG neurons in vitro and induced freezing behavior in vivo, which completely disappeared when the GG degenerated after axotomy. We conclude that mice detect APs through the activation of olfactory GG neurons.

Sex- and gonad-affecting scent compounds and 3 male pheromones in the rat

This study was aimed at identifying sex pheromones of the rat (Rattus norvegicus). We characterized the volatiles and semivolatiles of rat preputial gland and voided urine by using gas chromatography-mass spectrometry (GC-MS) and quantified them by their GC areas (abundances) and percentage of GC areas (relative abundances). Although all the compounds other than 4-heptanone and phenol detected were shared by males and females, the quantities for some of these sex-common compounds exhibited sexual dimorphism and decreased with gonadectomy. Thus, these compounds might be sex pheromones. Among them, squalene from preputial glands and 2-heptanone and 4-ethyl phenol from urine were 3 major compounds. They were richer in males and could be suppressed by castration. Adding any of the 3 compounds (at a concentration higher than its physiological level in male urine) to castrated male urine (CMU) increased the attractiveness of CMU to sex-naive females. Adding the 3 together (at the levels in normal male urine) to CMU significantly increased the attractiveness of CMU to females. However, such combination did not fully restore females' preference for urine from intact males, suggesting that some other trace compounds such as 4-heptanone and phenol might also play some roles in sex attractiveness. Thus, squalene, 2-heptanone, and 4-ethyl phenol were indeed male pheromone molecules in rats. Our study also indicates that E,E-beta-farnesene and E-alpha-farnesene, both richer in females than males, might be putative female pheromones.

Antidepressant-like actions of minocycline combined with several glutamate antagonists

This study tested the potential antidepressant activity of minocycline alone or combined with two traditional antidepressant drugs or several glutamate receptor antagonists, using the time sampling method in the forced swimming test. Results showed that: desipramine (10.0 mg/kg, P<0.05; 15.0 mg/kg, P<0.05), minocycline (60.0 mg/kg, P<0.05; 80.0 mg/kg, P<0.05) and EMQMCM (1.5 mg/kg, P<0.05; 2.0 mg/kg, P<0.05), reduced immobility by increasing climbing. Fluoxetine (20.0 mg/kg, P<0.05; 25.0 mg/kg, P<0.05) reduced immobility by increasing swimming. MTEP (5.0 mg/kg, P<0.05; 10.0 mg/kg, P<0.05) and dizolcipine (1.0 mg/kg, P<0.05; 1.5 mg/kg, P<0.05) reduced immobility by increasing swimming and climbing. Combination experiments showed that a subthreshold dose of minocycline (50.0 mg/kg) synergized the antidepressant-like actions of subthreshold doses of: desipramine (5.0 mg/kg; P<0.05), EMQMCM (0.6 mg/kg; P<0.05), MTEP (2.5 mg/kg; P<0.05) and dizolcipine (0.5 mg/kg; P<0.05). In conclusion, minocycline produced antidepressant-like actions in the FST and subthreshold dose of minocycline combined with subthreshold dose of desipramine and several glutamate receptor antagonists and produced antidepressant-like actions.