雌性布氏田鼠对不同共居时间雄性气味的识别与记忆

啮齿动物的社会识别包括对化学信号的辨别、学习和记忆。田鼠属动物雌雄成年个体共居一定时间后,可以利用气味信号来识别配偶。本研究将成年雌雄布氏田鼠配对饲养12 h、18 h、24 h,确认发生交配行为形成配对关系后,分开单独饲养6 h,取配偶雄鼠和陌生雄鼠巢垫物作为个体气味,在气味选择箱中观察雌鼠对配偶雄鼠和陌生雄鼠气味信号的探究和选择行为,从而探讨不同共居时间雌性布氏田鼠对配偶气味信号的识别与记忆的影响。研究结果表明:共居时间影响雌性布氏田鼠对配偶气味的识别与记忆;共居时间越长,雌鼠在气味探究和选择时间上对配偶气味偏好越明显;共居24 h 后,雌性布氏田鼠能够识别出配偶雄鼠的气味信号并形成记忆,这样的记忆维持时间至少是6 h。     

Impaired discrimination of and aversion to parasitized male odors by female oxytocin knockout mice

A major cost of social behavior is the increased risk of exposure to parasites, with animals utilizing social information to recognize and avoid infected conspecifics. In mice, females can discriminate between infected and uninfected males on the basis of social cues, displaying aversive responses to the odors of infected males. In the present study, using female mice whose gene for oxytocin (OT) has been selectively deleted (OT knockout mice (OTKO)), we show that at least one normal allele for OT is required for the mediation of the recognition and avoidance of parasitized males. Female wild type (OTWT) and heterozygous (OTHZ) mice distinguished between the odors of individual males infected with the louse, Polyplax serrata , and uninfected males while the KO mice did not. Exposure to the odors of infected males induced analgesia in OTWT and OTHZ females, with OTKO females displaying attenuated analgesia. OTWT and OTHZ females, but not the OTKO females, also distinguished between the odors of novel and familiar infected males and modulated their analgesic responses on the basis of prior familiarity. In an odor choice test, OTWT and OTHZ females displayed a marked initial choice for the odors of uninfected males, whereas the OTKO females showed no consistent choice. This impairment was specific to the odors of infected males. OTKO females displayed normal analgesic responses to another aversive social odor, that of a stressed male, and an aversive non-social odor, that of a cat. The OTKOs had normal non-social olfactory memory, but were impaired in their social odor memory. These findings indicate that a normal OT gene comprises an essential part of the central recognition mechanism whereby females can both reduce the transmission of parasites to themselves and select for parasite-free males.     

Alteration of mouse urinary odor by ingestion of the xenobiotic monoterpene citronellal

Body odors provide a rich source of sensory information for other animals. There is considerable evidence to suggest that short-term fluctuations in body odor can be caused by diet; however, few, if any, previous studies have demonstrated that specific compounds can directly mask or alter mouse urinary odor when ingested and thus alter another animal's behavior. To investigate whether the ingestion of citronellal, a monoterpene aldehyde that produces an intense aroma detected by both humans and mice, can alter mouse urinary odor, mice (C57BL6J) were trained in a Y maze to discriminate between the urinary odors of male donor mice that had ingested either citronellal in aqueous solution or a control solution. Trained mice could discriminate between urinary odors from the citronellal ingestion and control groups. A series of generalization tests revealed that citronellal ingestion directly altered mouse urinary odor. Moreover, trained mice that had successfully discriminated between urinary odors from donor mice of different ages failed to detect age-related changes in urine from male mice that had ingested 50 ppm of citronellal. This study is the first to show that ingestion of a xenobiotic can alter mouse urinary odor and confuse the behavioral responses of trained mice to age-related scents.     

Aversive Responses of Female Mice to the Odors of Parasitized Males: Neuromodulatory Mechanisms and Implications for Mate Choice

The detection and avoidance of parasitized conspecifics is proposed to have important consequences for the behavior of animals, especially as related to mate choice. A reduction in pain sensitivity (i.e. analgesia) is a major correlate of exposure to real or potential danger and threatening stimuli, facilitating the expression of various active (e.g. fleeing) and passive (e.g. immobilization) defense responses. The present study examined pain sensitivity (latency of a foot-lifting response to 50 ° C thermal surface) of female mice, Mus musculus, that were exposed to the urine and other odor secretions of male mice subclinically infected with the naturally occurring, enteric, sporozoan parasite, Eimeria vermiformis. A 30-min exposure to the odors of a parasitized male induced an analgesia in the female mice that was found to be mediated by the increased activity of endogenous opioid peptide systems. A brief 1-min exposure to the male odors induced a shorter duration and lower amplitude analgesia of a non-opioid (serotonergic) nature. Maximum analgesic responses were induced by the odors of pre-infective [5 days post-infection (PI)] and infective (day 10 PI) males, with significantly lower responses elicited by the odors of post-infective (day 17 PI) male mice. Exposure to the odors of unparasitized males had no significant effects on the pain sensitivity of female mice. These results indicate that female mice can distinguish between the odors of parasitized and non-parasitized male mice, and find the odors of parasitized males threatening and/or stressful. These odor-induced analgesic responses and their neurohormonal correlates may be part of an adaptive preparatory defense mechanism that facilitates the detection and avoidance of parasitized males by female mice and contributes to female mate choice.     

Primer effects by conspecific odors in house mice: a new perspective in the study of primer effects on reproductive activities

Half a century has passed since the first report of the influence of odors on mice. Odors are known to influence behavior (signaling effect) and affect the physiology (primer effect) of mice. This review focuses on summarizing the primer effects found so far in female and male mice. Odors from conspecifics of the opposite sex had the tendency to enhance reproductive activities, whereas odors from conspecifics of the same sex diminish them. Only 2,5-dimethylpyrazine, one of the odor components identified in group-housed females, has been reported to have a suppressive influence on both males and females by lowering reproductive activities. Studies showed progress from the discovery of phenomena to the identification of odor components that cause such changes in reproductive organs and related neuroendocrinological changes. Compared to studies on the mechanisms of primer effects in females, the mechanisms in males are not yet clarified, and detailed studies on effects on the reproductive organs are still in primitive stages especially for males. Hypotheses on the influence of changes in the concentration of testosterone, estrogen, and prolactin on spermatogenesis and sperm maturation after exposure to odors are discussed.     

The major histocompatibility complex and the chemosensory signalling of individuality in humans

The chemosensory identity of mice and rats is determined partly by polymorphic genes of the major histocompatibility complex (MHC). In inbred strains of mice, as well as in seminatural populations, MHC‐associated mating preferences selectively influence reproductive success, thus serving to promote heterozygocity in the MHC. In order to determine whether MHC‐associated chemosignals are present in humans, two studies were conducted. In a first study, olfactory identification of MHC‐associated chemosignals was conducted on 12 trained rats' responses to the urine odors of humans. In a second study, MHC‐associated olfactory cues in humans were analyzed by means of gas chromatography. The results indicate that the urine odors of humans are associated with the MHC and demonstrate that the profile of volatile components in the urine odors shows some association with the MHC. Furthermore, results show that a profile of some specific components, as well as a few ubiquitous volatiles, constitutes MHC‐associated odor signals in humans. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential Responses to Same and Opposite Sex Odors by Adult House Mice Are Associated with Anogenital Distance

Intrauterine position (IUP) of female and male fetuses in litter-bearing mammals can affect their physiology, morphology and behavior. The relationship between anogenital distance (AGD) and IUP was used as a bioassay for the degree of exposure of female and male fetuses to hormones in utero . Based on laboratory work in several rodent species, the following predictions were made for house mice ( Mus musculus domesticus ): (1) female mice should prefer odors from males with larger AGDs because such males are more aggressive, could protect more resources, and are better parents than males with smaller AGDs; (2) male mice should prefer odors from females with smaller AGDs because these females produce more offspring and are better parents than females with larger AGDs. We also tested the prediction that within sexes, mice should avoid odors from mice with larger AGDs because such mice are more aggressive. Responses to odors in traps were used to test these predictions for house mice living in outdoor enclosures using odor-baited traps. Both predictions were confirmed. Furthermore, mice of both sexes tended to avoid odor cues from individuals of the same sex that had larger AGDs, probably to decrease chances of an aggressive encounter that could result in injury.     

Maintaining accuracy at the expense of speed: stimulus similarity defines odor discrimination time in mice

Odor discrimination times and their dependence on stimulus similarity were evaluated to test temporal and spatial models of odor representation in mice. In a go/no-go operant conditioning paradigm, discrimination accuracy and time were determined for simple monomolecular odors and binary mixtures of odors. Mice discriminated simple odors with an accuracy exceeding 95%. Binary mixtures evoking highly overlapping spatiotemporal patterns of activity in the olfactory bulb were discriminated equally well. However, while discriminating simple odors in less than 200 ms, mice required 70-100 ms more time to discriminate highly similar binary mixtures. We conclude that odor discrimination in mice is fast and stimulus dependent. Thus, the underlying neuronal mechanisms act on a fast timescale, requiring only a brief epoch of odor-specific spatiotemporal representations to achieve rapid discrimination of dissimilar odors. The fine discrimination of highly similar stimuli, however, requires temporal integration of activity, suggesting a tradeoff between accuracy and speed.     

Fear-like behavioral responses in mice in different odorant environments: Trigeminal versus olfactory mediation under low doses

Odors can have repulsive effects on rodents based on two complementary adaptive behaviors: the avoidance of predator odors (potentially dangerous) and the avoidance of trigeminal stimulants (potentially noxious). The present study aimed to compare the behavioral effects on mice of odors according to their trigeminal properties and ecological significance. We used three different odors: 2,4,5-trimethylthiazoline (TMT: a fox feces odor frequently used to elicit fear-induced behaviors), toluene (a strong stimulant of the trigeminal system) and phenyl ethyl alcohol (PEA: a selective stimulant of the olfactory system). First, we checked preference and avoidance behaviors in mice with and without anosmia towards these odors to ensure their olfactory/trigeminal properties. Secondly, we used a standard test (open-field and elevated plus-maze) to assess the behaviors of mice when exposed to these odors. The results show that the anosmic and control mice both avoided TMT and toluene odors. In the open-field and the elevated plus-maze, mice exhibited "anxious" behaviors when exposed to TMT. Conversely, exposure to PEA induced "anxiolytic" effects confirmed by low blood corticosterone levels resulting from completion of the elevated plus-maze. Compared with TMT exposure, toluene exposure induced moderate "anxious" effects.     

Ontogeny of Ultrasonic and Locomotor Responses to Nest Odors in Rodents

SYNOPSIS. Rodents discriminate and prefer familiar odors earlyin life. Almost from birth young rats suckle in response tomaternal odor, but suckle less when nipples are cleaned withorganic solvents. In two-choice tests, young prefer familiarnest odors, whether naturally occurring or artificially presented,and can even be made to tolerate odors normally aversive orto avoid odors normally pleasant. Variations in maternal dietcan alter odor preferences of theyoung. Nest odors can affect vocalization of young rodents. In contrastto the consistent effects of cold temperature and handling inthe many rodents studied, nest odors may affect vocalizationdifferently in different species. For example, familiar odorsreduce calling in rats, but increase calling in pine voles.Nest odor also alters spontaneous activity in young rats, whichlocomoteless when maternal odor is present. In this paper I report that home nest odors enhanced locomotionin rodents of three species (pine voles, Microtus pinetorum;white-footed mice, Peromyscus leucopus; and wild house mice,Mus musculus), but that the age at which this pattern occurredand the relationships of nest odors to vocalizations differedamong the species.     

The acoustic startle reflex as a tool for assessment of odor environment effects on affective states in laboratory mice

Apart from self and conspecific odors, odors from other species also influence the affective states in laboratory mice (Mus musculus musculus) in their home cages and during experimental procedures, possibly inducing confusion and inconsistency in experimental data. Thus, it is important to detect the types of animal odors associated with housing, husbandry, and laboratory practice that can arouse different types of affective changes in mice. Here, we aimed to test the effectiveness of the acoustic startle reflex (ASR) in detecting changes in the affective states of laboratory mice due to animal-derived-odor as it has a non-zero baseline, and can be enhanced or attenuated by positive or negative affective shifts, respectively. We used ASR to examine the affective changes in mice that were induced by bedding odors and an alarm pheromone. The odor of bedding obtained from the mice’ home cages significantly attenuated the ASR, suggesting positive affective shifts in the test mice, whereas that from bedding obtained from rat cages significantly enhanced the ASR, suggesting negative affective shifts. No significant changes in ASR were observed in mice presented with the odor of bedding obtained from cages of unfamiliar conspecifics. In contrast, there was significant ASR enhancement in mice exposed to volatile components of alarm pheromones trapped in water, suggesting negative affective shifts. Thus, our findings show that ASR may be a valuable tool in assessing the effects of odors on the affective states in laboratory mice.     

Attraction thresholds and sex discrimination of urinary odorants in male and female aromatase knockout (ArKO) mice

We previously found that both male and female aromatase knockout (ArKO) mice, which cannot synthesize estrogens due to a targeted mutation of the aromatase gene, showed less investigation of volatile body odors from anesthetized conspecifics of both sexes in Y-maze tests. We now ask whether ArKO mice are in fact capable of discriminating between and/or responding to volatile odors. Using habituation/dishabituation tests, we found that gonadectomized ArKO and wild-type (WT) mice of both sexes, which were tested without any sex hormone replacement, reliably distinguished between undiluted volatile urinary odors of either adult males or estrous females versus deionized water as well as between these two urinary odors themselves. However, ArKO mice of both sexes were less motivated than WT controls to investigate same-sex odors when they were presented last in the sequence of stimuli. In a second experiment, we compared the ability of ArKO and WT mice to respond to decreasing concentrations of either male or female urinary odors. We found a clear-cut sex difference in urinary odor attraction thresholds among WT mice: WT males failed to respond to urine dilutions higher than 1:20 by volume, whereas WT females continued to respond to urine dilutions up to 1:80. Male ArKO mice resembled WT females in their ability to respond to lower concentrations of urinary odors, raising the possibility that the observed sex difference among WT mice in urine attraction thresholds results from the perinatal actions of estrogen in the male nervous system. Female ArKO mice failed to show significant dishabituation responses to two (1:20 and 1:80) dilutions of female urine, perhaps, again, because of a reduced motivation to investigate less salient, same-sex urinary odors. Previously observed deficits in the preference of ArKO male and female mice to approach volatile body odors from conspecifics of either sex cannot be attributed to an inability of ArKO subjects to discriminate these odors according to sex but instead may reflect a deficient motivation to approach same-sex odors, especially when their concentration is low.     

Vomeronasal organ ablation elicits chemosensory dysfunction and abnormal behavior in mice

This study aimed to examine whether the vomeronasal organ (VNO) is a prerequisite in mice to acquire essential information from various social odors and whether long-term VNO dysfunction can elicit behavioral and physiological changes in mice. We used binary choice tests and habituation–dishabituation tests to measure the abilities of male mice to recognize social odors. We found that males with the VNO ablation failed to show olfactory preferences between the odors of mate versus non-mate females, offspring versus non-offspring pups, or opposite-sex conspecifics versus predators (cats or rats), but were capable of discriminating between the two treatments in each of the paired odors, suggesting that male mice with VNO ablation might smell out the chemical differences of the two types of odors, but could not extract the biological information contained in the odors. Furthermore, prolonged VNO deficiency resulted in a reduction in crossing behavior in a light/dark box, the frequency of urine marking, and the time spent in the center in an open field. These results indicate that chronic VNO dysfunction led to anxiety-like or submissive behavior. In addition, males with VNO ablation had atrophic adrenal glands and hypertrophic preputial glands, suggesting that VNO dysfunction could damage the physiological conditions to buffer the stress and that pheromone perception deficiency might enhance self-odor production in mice.     

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

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

Paradoxical relationship between speed and accuracy in olfactory figure-background segregation

In natural settings, many stimuli impinge on our sensory organs simultaneously. Parsing these sensory stimuli into perceptual objects is a fundamental task faced by all sensory systems. Similar to other sensory modalities, increased odor backgrounds decrease the detectability of target odors by the olfactory system. The mechanisms by which background odors interfere with the detection and identification of target odors are unknown. Here we utilized the framework of the Drift Diffusion Model (DDM) to consider possible interference mechanisms in an odor detection task. We first considered pure effects of background odors on either signal or noise in the decision-making dynamics and showed that these produce different predictions about decision accuracy and speed. To test these predictions, we trained mice to detect target odors that are embedded in random background mixtures in a two-alternative choice task. In this task, the inter-trial interval was independent of behavioral reaction times to avoid motivating rapid responses. We found that increased backgrounds reduce mouse performance but paradoxically also decrease reaction times, suggesting that noise in the decision making process is increased by backgrounds. We further assessed the contributions of background effects on both noise and signal by fitting the DDM to the behavioral data. The models showed that background odors affect both the signal and the noise, but that the paradoxical relationship between trial difficulty and reaction time is caused by the added noise.     

Origin, functions and chemistry of H‐2 regulated odorants

Genes located within the major histocompatibility complex (MHC) of mice are responsible for individual differences in body odor (odortypes). In this review we suggest that the MHC genes themselves are responsible for odor differences among MHC‐congenic mice. Recent studies indicating that volatile carboxylic acids are at least in part responsible for the individual odors and what this finding implies about the pathway from gene to odorant are also reviewed. We suggest that odorants or their precursors are bound directly by MHC products and are released into serum and concentrated in urine. Finally, possible functions of MHC odortypes in mice are enumerated and important future research questions are raised. This revised version was published online in July 2006 with corrections to the Cover Date.     

The capacity of humans to identify components in complex odor-taste mixtures

Despite the fact that humans experience mixtures of odors and tastes each time they eat, little is known of their capacity to detect the individual components of foods. To investigate this capacity, 43 subjects were trained to identify three odors and three tastes and were required to indicate which of these could be identified in stimuli consisting of one to six components. Although the odor and taste components of most binary mixtures were identified, subjects encountered substantial difficulties with more complex mixtures with only two components being identified in the four- to six-component mixtures. In general, tastes were more easily identified than smells and were the only stimuli identified in the five- to six-component mixtures. Several mechanisms are proposed to account for the poor identification of components.     

Oxytocin and estrogen receptor alpha and beta knockout mice provide discriminably different odor cues in behavioral assays

Social behavior involves both the recognition and production of social cues. Mice with selective deletion (knockout) of either the gene for oxytocin (OT) or genes for the estrogen receptor (ER) -α or -β display impaired social recognition. In this study we demonstrate that these gene knockout mice also provide discriminably different social stimuli in behavioral assays. In an odor choice test, which is a measure of social interest and discrimination, outbred female Swiss-Webster mice discriminated the urine odors of male knockouts (KO: OTKO, αERKO, βERKO) from the odors of their wildtype littermates (WT: OTWT, αERWT, βERWT). Females showed marked initial choices of the urine odors of OTWT and βERWT males over those of OTKO and βERKO males, and αERKO males over αERWT males. The odors of OTKO and βERKO males also induced aversive, analgesic responses, with the odors of WTs having no significant effects. Odors of both the αERWT and αERKO males induced aversive, analgesic responses, with the odors of the WT inducing significantly greater analgesia. The odors of restraint stressed WT and KO males also elicited analgesia with, again, females displaying significantly greater responses to the odors of stressed OTKO and βERKO males than their WTs, and significantly lower analgesia to the odors of stressed αERKO than αERWT males. These findings show that the KO mice are discriminated from their WTs on the basis of odor and that the various KOs differ in the relative attractiveness/aversiveness of their odors. Therefore, in behavioral assays one causal route by which gene inactivation alters the social behavior of knockout mice may be mediated through the partners' modified responses to their odors.     

Gonadal control of male scent in the tarmarin Saguinus fuscicollis (Callitrichidae, Primates)

Spontaneous responses to the scent marks of male Saguinus fuscicolliswere tested in experiments where the subjects received a choicebetween scent of intact males and castrated males. Male tamarinsdiscriminated between the odors of intact and castrated males,both on the basis of fresh individual scent marks and on thebasis of marks from several donors pooled in methanol. Theirdiscriminatory response to pooled odors was more pronouncedthan that to individual odors. Females discriminated betweenintact and castrated male scents only on the basis of pooledsamples. This result shows that castration causes changes inthe odor of males. The difference in the response of the tamarinsto individual scent marks as compared to pooled samples is discussedin terms of quantitative changes caused by extraction and ofindividual recognition.     

Odor and affect: individual differences in the impact of odor on liking for places, things and people

This paper provides evidence of substantial individual differences in the affective importance of odors, and offers initial validation for an eight-item scale of the impact of odor (AIO) on liking for people, places, foods and cosmetic/health products. In study 1, 116 American college students and 336 Flemish Belgian college students completed the AIO along with other measures of reactions to odors and to commercial products designed to mask body odors. There were substantial individual differences in AIO scores, but means were similar for males and females, and for US and Belgian respondents. Higher AIO scores were associated with more odor-mediated memory, more attention to odors and more liking or disliking for odors as a function of their association with liked and disliked persons. AIO scores were not related to preference for toiletries with artificial scents, to use of products to mask natural body odors, or to disgust sensitivity. In study 2, AIO scores were strongly related to a measure of evaluative conditioning (a form of Pavlovian associative learning) in the laboratory, using liked and disliked odors as unconditioned stimuli and pictures of faces as conditioned stimuli.