Female Odors Research Articles

Differences in brain activity during olfactory testing of female body odors between young men with and without sexual experience

Olfactory testing was performed in two groups of young men aged 18–22 years with and without sexual experience. Multichannel EEG was recorded at rest and upon the presentation of 45 natural body odors of young women in different phases of the menstrual cycle. The odors were either intact or mixed with J’Adore L’Absolu perfume (Christian Dior) with or without a female pheromone. Changes in spectral power within narrow frequency ranges in response to olfactory stimulation were estimated by multivariate analysis of variance. It was found that background electrical activity of the brain in young men with regular sex life had lower spectral power in all frequency ranges. The EEG responses to the intact olfactory stimuli in all young men were associated with a decrease in spectral power in the majority of the frequency ranges and especially in the θ2 and high- and low-frequency α rhythms. Presentation of female odors masked with a perfume resulted in bidirectional EEG responses; i.e., the spectral power in the θ1 and β1 ranges increased or decreased depending on the sexual experience of men and the menstrual cycle phase of a female donor as compared with an intact odor. The comparison of the EEG responses to intact or perfume-masked odors showed that individual odor remains dominant.

The integrity of the nucleus of the lateral olfactory tract is essential for the normal functioning of the olfactory system

The nucleus of the lateral olfactory tract (nLOT) is a relatively small component of the cortical pallial amygdala, with peculiar neurogenic, neurochemical and connectivity patterns. Although it has been suggested that it might be involved in non-pheromonal olfactory-guided behaviors, particularly feeding, the functional implications of the nLOT have never been investigated. In view of this fact, we have tackled this subject by performing a series of behavioral tests and by quantifying biological and biochemical parameters in sexually naïve adult male rats that were submitted to bilateral excitotoxic lesions of the nLOT. nLOT-lesioned rats had severe olfactory deficits with inability to detect and discriminate between odors. Additionally, they did not display innate behavioral responses to biologically relevant chemosignals. Specifically, nLOT-lesioned rats did not show avoidance towards predator odors or aggressive behaviors towards intruders, and had severely impaired sexual behavior. In fact, nLOT lesions abolished preference for odors of receptive females, reduced chemoinvestigatory behavior and eliminated mounting behavior. nLOT-lesioned rats had normal circulating levels of testosterone, did not display anxiety- or depressive-like behaviors, and had unimpaired cognitive functions and fear acquisition and memory. Altogether, our results suggest that the nLOT integrity is required for the normal functioning of the olfactory system.

Chemosensory danger detection in the human brain: Body odor communicating aggression modulates limbic system activation

Although the sense of smell is involved in numerous survival functions, the processing of body odor emitted by dangerous individuals is far from understood. The aim of the study was to explore how human fight chemosignals communicating aggression can alter brain activation related to an attentional bias and danger detection. While the anterior cingulate cortex (ACC) was seen involved in processing threat-related emotional information, danger detection and error evaluation, it still remains unknown whether human chemosignals communicating aggression can potentially modulate this activation. In the fMRI experiment, healthy male and female normosmic odor recipients (n=18) completed a higher-order processing task (emotional Stroop task with the word categories anger, anxiety, happiness and neutral) while exposed to aggression and exercise chemosignals (collected from a different group of healthy male donors; n=16). Our results provide first evidence that aggression chemosignals induce a time-sensitive attentional bias in chemosensory danger detection and modulate limbic system activation. During exposure to aggression chemosignals compared to exercise chemosignals, functional imaging data indicates an enhancement of thalamus, hypothalamus and insula activation (p<.05, FWE-corrected). Together with the thalamus, the ACC was seen activated in response to threat-related words (p<.001). Chemosensory priming and habituation to body odor signals are discussed.

Male Psyllids Differentially Learn in the Context of Copulation.

In the Asian citrus psyllid, Diaphorina citri Kuwayama, stimulatory cuticular hydrocarbons act as sex pheromone attractants. Male psyllids locate aggregations of females using those olfactory cues, as well as vibrational communication on the plant surface. Although previous research has indicated that learning plays a role in modulating female reproductive behaviors in psyllids, it is unknown whether males similarly use learning to increase the likelihood of copulatory success. We used an olfactometer-based bio-assay to study the effects of experience on male response to female odor. First, we compared male attraction to female odor in virgin and previously mated males. Second, we tested the effect of several modes of experience with a novel odor, vanillin, to determine whether mating, feeding, or general environmental exposure elicited a learned response. We found that male attraction to female odor significantly increased after mating experience. In addition, we found that males learn about odor specifically in the context of mating, rather than feeding or general exposure. Electrophysiological measurements of antennal response to odorants confirmed that mating status did not affect the sensitivity of the peripheral nervous system to volatile stimuli implicating learning at the level of the central nervous system. These results suggest that male response to female odor is not an entirely innate behavior. Males may require mating experience with female conspecifics to develop attraction to those olfactory cues produced by the female and in association with the female’s habitat. This adaptive plasticity may allow males to detect females in an ever-changing environment and promote diversification and further specialization on different host genotypes.

The effect of social experience on olfactory preference in male mice

Since olfaction plays a primary role in rodent social interaction, the olfactory preference test (OPT) is one of the most widely used behavioural tests. However, behavioural tests require specific experimental design and can easily be affected by environmental factors. Here, we discuss the effect of social experience on male mouse behaviour in the OPT. In the present study, we assessed olfactory preference of male mice towards male or female soiled bedding. Each male mouse was allowed to investigate two Petri dishes containing soiled bedding for 5min. We used four groups of animals differing in terms of social experience before the OPT: naïve males (Naïve), sexually experienced males (SE), males that had experienced 24h of contact with females (FE), and males that had experienced a 15-min contact period with both male and female intruders. Our data indicate that sexually experienced males show a reproducible female smell preference (mean female sniffing (mean F)=71.56%±2.59%, mean male sniffing (meanM)=28.44%±2.59%, p<0.001). Naïve males exhibited no bedding preference at all (mean F=51.30%±2.79%, mean M=48.70%±2.79%). Males that experienced contact with females (FE) also showed no odour preference (mean F=44.13%±3.74%, mean M=55.87%±3.74%). Interaction with male and female intruders for 15min resulted in a significant shift of odour preference to female odour in 50% of the test groups (group #1: mean F=67.61%±2.58%, mean M=32.39%±2.58%, p<0.001, group #2: mean F=62.58%±3.75%, mean M=37.42%±3.75%, p<0.05, group #3: mean F=49.80%±2.34%, mean M=50.20%±2.34%, group #4: mean F=52.80%±3.42%, mean M=47.20%±3.42%). Thus, this interaction can hardly evoke reproducible results in subsequent OPTs. Of all experimental setups tested, only sexual experience provides a consistent outcome of the OPT.

Behavioral and neuronal responses of two mouse species, Mus musculus and Mus spicilegus, to con- and heterospecific olfactory signals

The behavioral and neuronal responses of the males of two closely related species of mice (Mus musculus wagneri, M. spicilegus) to the urine odors of estrus con- and heterospecific females were studied. In two-choice odor tests males significantly longer investigated odor of conspecific females in comparison with heterospecific ones. To investigate neuronal activation in the main and accessory olfactory bulbs (MOB and AOB), one of the methods of functional tomography – manganese-enhanced MRI ( ME-MRI) – was used. There was a significant increase in Mn2+ accumulation in the dorsal section of the posterior part of the MOB in male M. m. wagneri and M. spicilegus exposed to odor of conspecific females compared with the control group males (odor not exposed). There was a local significant increase in manganese accumulation in the dorsal region of the anterior part of the MOB in the case of the exposure of odor of a heterospecific female. The exposure of heptanone-2 to mice resulted not only in an increase in Mn2+ accumulation in certain zones, but also in a significant decrease in the accumulation of Mn2+ in the rest of the olfactory bulbs. A significant increase in the accumulation of MRI contrast in AOB was observed in males only in the case of female urine-conspecific odor exposure. The results support the previously stated assumption of a significant difference in chemical communication systems in two species of mice. A comparison of these results and results obtained previously demonstrated the absence of any differences in behavioral and neuronal responses to con- and heterospecific odors of the house mouse subspecies allopatric (M. m. wagneri) and sympatric (M. m. musculus) to M. spicilegus. This fact does not allow us to assume the effect of the mechanism of “reinforcement” in the process of evolution in the formation of precopulatory reproductive isolation between the sympatric species M. spicilegus and M. musculus.

Study of chemical communication based on urine in tree shrews Tupaia belangeri (Mammalia: Scandentia: Tupaiidae)

Chemical communication plays a key role in mammalian reproductive and social behaviour. The chemical constituents of urine are the main signal resource that can encode sex, quality and social status. In order to investigate the role of urine in the reproductive biology of Tupaia belangeri, the volatile components of urine were analysed by gas chromatography-mass spectrometry, and the behaviour of the tree shrew in response to urinary odour was investigated in a Y-maze test. The results show that hydrocarbons were the major components of urine in wild, acclimated and laboratory-breeding animals. The concentrations of the chemical components in urine from individuals in the wild population were higher than those in the acclimated and breeding animals. Tupaia belangeri showed significant differences in reactions of individuals and urinary odour. Males and females had different components in their urine. The stay duration of male tree shrews to the urinary odour of females in oestrus or lactating was significantly longer than that to the odour of pregnant females. The chemical components were different at different reproductive stages. Taken together, these results suggest that the odour of urine can encode female reproductive status and gender. Tupaia belangeri relies on these odours to recognise sex and choose a mate. Chemical communication based on signals in urine plays an important role in the reproduction of T. belangeri.

Chemical cues correlate with agonistic behaviour and female mate choice in the southern blue-ringed octopus,Hapalochlaena maculosa(Hoyle, 1883) (Cephalopoda: Octopodidae)

Chemoreception cues potentially influence intraspecific interactions of cephalopods, including mate choice. However, at present there is limited empirical evidence demonstrating whether cephalopods can use olfaction to identify the sex or identity of conspecifics. This study examined the responses of the southern blueringed octopus, Hapalochlaena maculosa (Hoyle, 1883), to conspecific odours during controlled laboratory trials. The ventilation rates in aquaria of 25 wild-sourced animals were measured during four treatments: baseline, sea water, sea water containing male conspecific odour and sea water containing female conspecific odour. When used as 'receivers' in trials, female H. maculosa significantly increased their ventilation rates in response to male odours, but not to female odours. However, female response decreased significantly with the receiver's size during female-odour treatments. The ventilation rates of male H. maculosa were statistically similar in all treatments. However, their ventilation rates showed a significant progressive increase over the observation period during male and female-odour treatments. Eighteen of these animals (nine females and nine males) were used in focal-animal trials 1 week after odour-cue experiments. Of these individuals, females were significantly more receptive to copulation attempts, and spent significantly more time per day in copulation, with males whose odours had elicited a weaker ventilation response in prior trials. These results suggest that female H. maculosa can use chemosensory cues to discriminate the sex, and possibly identity, of conspecifics and that this information might influence their mate choice. However, the mechanisms underlying these responses and subsequent copulatory access to females by males remain unknown.

Male tarantula spiders’ reactions to light and odours reveal their motor asymmetry

AbstractMany vertebrates present behavioural asymmetries (i.e. functional and/or structural specializations of left and right sides of the brain); however, evidence for arthropods is scarce. Some behavioural asymmetries can be correlated with morphology. A better understanding of behavioural asymmetries would be a crucial step to understand the evolution of brain asymmetries. Here, we investigated behavioural asymmetries of adult males of a mygalomorph Brachypelma albopilosum. First, as the time budgets of these active hunting spiders had not yet been documented, we established the temporal distribution of males’ motor activity to be able to test them when they were active. Their motor activity peaks during the night and again early morning (around 3 h and 10 h local time). Then, choice tests in a T‐maze assessed the effects of light and of odours separately. Our results revealed that male tarantulas’ activity increased when they perceived light or the odour of conspecific females. Latencies to enter into the T‐maze were shorter when a light cue was present and even shorter when odour cues (of prey or of conspecifics) were present. Choice between two identical cues (light or female odours) in a T‐maze revealed, for the first time, their right behavioural laterality. Surprisingly, no significant external morphological differences could be evidenced between left and right eyes, lengths of the first legs or densities of mechanoreceptors and chemoreceptors on the tarsi of males’ first legs to suggest perceptual asymmetry supporting this behavioural asymmetry. This is the first report concerning tarantulas’ behavioural laterality.

Conditioned odor aversion induces social anxiety towards females in wild-type and TrpC2 knockout male mice.

Female-emitted pheromonal inputs possess an intrinsic rewarding value for conspecific males, promoting approach and investigation of the potential mating partner. In mice these inputs are detected mainly by the vomeronasal organ (VNO) and the main olfactory epithelium (MOE). We investigated the role of VNO-mediated inputs in experience-dependent plasticity of reproductive responses. We applied a sex-specific conditioned odor aversion (COA) paradigm on adult, wild-type (WT) male mice and on male mice impaired in VNO-mediated signal transduction (TrpC2-/- ). We found that WT males, which underwent COA to female-soiled bedding, lost their innate preference to female odors and presented lower motivation to approach a sexually receptive female. COA also abolished the testosterone surge normally seen following exposure to female odors. Moreover, the conditioned males displayed impairments in copulatory behaviors, which lasted for several weeks. Surprisingly, these males also exhibited phobic behaviors towards receptive females, including freezing and fleeing responses. In contrast, WT males which underwent COA specifically to male pheromones showed no change in olfactory preference and only a marginally significant elevation in intermale aggression. Finally, we show that TrpC2-/- males were able to acquire aversion to female-soiled bedding and presented similar behavioral alterations following COA in their responses to female cues. Our results demonstrate that the intrinsic rewarding value of female pheromones can be overridden through associative olfactory learning, which occurs independently of VNO inputs, probably through MOE signaling.

Development of the main olfactory system and main olfactory epithelium-dependent male mating behavior are altered in Go-deficient mice

In mammals, initial detection of olfactory stimuli is mediated by sensory neurons in the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). The heterotrimeric GTP-binding protein Go is widely expressed in the MOE and VNO of mice. Early studies indicated that Go expression in VNO sensory neurons is critical for directing social and sexual behaviors in female mice [Oboti L, et al. (2014) BMC Biol 12:31]. However, the physiological functions of Go in the MOE have remained poorly defined. Here, we examined the role of Go in the MOE using mice lacking the α subunit of Go Development of the olfactory bulb (OB) was perturbed in mutant mice as a result of reduced neurogenesis and increased cell death. The balance between cell types of OB interneurons was altered in mutant mice, with an increase in the number of tyrosine hydroxylase-positive interneurons at the expense of calbindin-positive interneurons. Sexual behavior toward female mice and preference for female urine odors by olfactory sensory neurons in the MOE were abolished in mutant male mice. Our data suggest that Go signaling is essential for the structural and functional integrity of the MOE and for specification of OB interneurons, which in turn are required for the transmission of pheromone signals and the initiation of mating behavior with the opposite sex.

Dix ans de collaboration entre la France et le Japon - Etudes sur la reproduction chez les macaques japonais

Our research interests are focused on the evolution of mating systems in primates and we aim at providing a better understanding of the adaptive signification of reproductive processes in female primates, using a comparative approach. Our Franco-Japanese collaboration (2006 - present) allowed us to study sociality and reproduction in a Catarrhine species, the Japanese macaque (Macaca fuscata), and on different but complementary topics (reproductive energetics, reproductive strategies, sexual signaling). We first investigated the links between energetics (i.e. nutritional status, body composition) and reproductive outcomes and our studies in captive Japanese macaques showed that, even in captivity with relaxed energetic constraints (e.g. constant food availability), seasonal breeding entails relatively high energy costs and females with higher energy status could invest more in reproductive activities and could afford to reproduce more rapidly. We also investigated the information that male Japanese macaques received from females that might enable them to discern periods with higher probabilities of conception and we developed a research program on the extent to which Japanese macaques, in common with people, have evolved a system of multimodal sexual signaling. We focused on the cues and signals available to males to make their mating decisions, and we provided information on the potential role of female behavior, female skin color, odours and vocalizations as sexual signals. We suggested, in particular, that females advertized their pregnancy through changes in behavioral, visual, and potentially auditory signals, and that males use these signals to adjust their mating behaviors and avoid wasting energy on non-reproductive copulations. This holistic study, combining fieldwork and laboratory experiments, and using a multidisciplinary approach (behavioral observations (sexual interactions), digital photography (visual scoring of female sexual skin color), hormonal (fecal ovarian steroids) and chemical data (components of female vaginal secretions)) allowed us to assess how different signals may combine to influence patterns of primate mate choices.

Genetic Isolation of Hypothalamic Neurons that Regulate Context-Specific Male Social Behavior.

Nearly all animals engage in a complex assortment of social behaviors that are essential for the survival of the species. In mammals, these behaviors are regulated by sub-nuclei within the hypothalamus, but the specific cell types within these nuclei responsible for coordinating behavior in distinct contexts are only beginning to be resolved. Here, we identify a population of neurons in the ventral premammillary nucleus of the hypothalamus (PMV) that are strongly activated in male intruder mice in response to a larger resident male but that are not responsive to females. Using a combination of molecular and genetic approaches, we demonstrate that these PMV neurons regulate intruder-specific male social behavior and social novelty recognition in a manner dependent on synaptic release of the excitatory neurotransmitter glutamate. These data provide direct evidence for a unique population of neurons that regulate social behaviors in specific contexts.

De Novo Transcriptome Analysis of the Common New Zealand Stick Insect Clitarchus hookeri (Phasmatodea) Reveals Genes Involved in Olfaction, Digestion and Sexual Reproduction.

Phasmatodea, more commonly known as stick insects, have been poorly studied at the molecular level for several key traits, such as components of the sensory system and regulators of reproduction and development, impeding a deeper understanding of their functional biology. Here, we employ de novo transcriptome analysis to identify genes with primary functions related to female odour reception, digestion, and male sexual traits in the New Zealand common stick insect Clitarchus hookeri (White). The female olfactory gene repertoire revealed ten odorant binding proteins with three recently duplicated, 12 chemosensory proteins, 16 odorant receptors, and 17 ionotropic receptors. The majority of these olfactory genes were over-expressed in female antennae and have the inferred function of odorant reception. Others that were predominantly expressed in male terminalia (n = 3) and female midgut (n = 1) suggest they have a role in sexual reproduction and digestion, respectively. Over-represented transcripts in the midgut were enriched with digestive enzyme gene families. Clitarchus hookeri is likely to harbour nine members of an endogenous cellulase family (glycoside hydrolase family 9), two of which appear to be specific to the C. hookeri lineage. All of these cellulase sequences fall into four main phasmid clades and show gene duplication events occurred early in the diversification of Phasmatodea. In addition, C. hookeri genome is likely to express γ-proteobacteria pectinase transcripts that have recently been shown to be the result of horizontal transfer. We also predicted 711 male terminalia-enriched transcripts that are candidate accessory gland proteins, 28 of which were annotated to have molecular functions of peptidase activity and peptidase inhibitor activity, two groups being widely reported to regulate female reproduction through proteolytic cascades. Our study has yielded new insights into the genetic basis of odour detection, nutrient digestion, and male sexual traits in stick insects. The C. hookeri reference transcriptome, together with identified gene families, provides a comprehensive resource for studying the evolution of sensory perception, digestive systems, and reproductive success in phasmids.

Evidence for an audience effect in mice: male social partners alter the male vocal response to female cues.

Mice (Mus musculus) form large and dynamic social groups and emit ultrasonic vocalizations in a variety of social contexts. Surprisingly, these vocalizations have been studied almost exclusively in the context of cues from only one social partner, despite the observation that in many social species the presence of additional listeners changes the structure of communication signals. Here, we show that male vocal behavior elicited by female odor is affected by the presence of a male audience - with changes in vocalization count, acoustic structure and syllable complexity. We further show that single sensory cues are not sufficient to elicit this audience effect, indicating that multiple cues may be necessary for an audience to be apparent. Together, these experiments reveal that some features of mouse vocal behavior are only expressed in more complex social situations, and introduce a powerful new assay for measuring detection of the presence of social partners in mice.

Non-neural androgen receptor promotes androphilic odor preference in mice

In mice, male-typical preference for female olfactory cues results largely from sexually differentiated testosterone production. It is currently unclear on which cells and tissues testosterone acts to produce male-typical preference for female olfactory cues. To further address the site of androgen action on olfactory preference, we have developed a loxP-based transgenic mouse that overexpresses androgen receptors (AR) only when activated by Cre. We used this transgene to overexpress AR globally in all tissues using a CMV-Cre driver and a Nestin-Cre driver to overexpress AR selectively in neural tissue. We then examined olfactory preference in transgenic and wildtype (Wt) littermates by simultaneously exposing animals to female-soiled, male-soiled and clean bedding. Ubiquitous overexpression of AR in CMV-AR mice increased preference for male bedding, whereas neural-specific AR overexpression in Nestin-AR transgenic mice did not differ from wildtype siblings in olfactory preference. Neural activation of olfactory brain areas in response to female-soiled bedding was also evaluated in these mice by measuring FOS immunoreactivity. This revealed a decrease in neural activity along the accessory olfactory pathway that accompanied the decrease in preference for female odors in CMV-AR males, compared to both Nestin-AR and Wt male siblings. Together, results indicate that androgens act via non-neural AR to mediate olfactory preference and neural responses to olfactory stimuli, and further suggest that AR in non-neural tissues can promote androphilic odor preferences in male mice.

The impact of artificial fragrances on the assessment of mate quality cues in body odor

Cultural practices may either enhance or interfere with evolved preferences as predicted by culture–gene coevolution theory. Here, we investigated the impact of artificial fragrances on the assessment of biologically relevant information in human body odor. To do this, we examined cross-sensory consistency (across faces and odors) in the perception of masculinity and femininity in men and women, and how consistency is influenced by the use of artificial fragrance. Independent sets of same and opposite-sex participants rated odor samples (with and without a fragrance, n=239 raters), and photographs (n=130) of 20 men and 20 women. In female, but not male raters, judgments of masculinity/femininity of non-fragranced odor and faces were correlated. However, the correlation between female ratings of male facial and odor masculinity was not evident when assessing a fragranced body odor. Further analysis also indicated that differences in ratings of male odor masculinity between men with high and low levels of facial masculinity were not present in fragranced body odor samples. This effect was absent in ratings of female odors by both female and male raters, suggesting sex-specificity in the effects of fragrance on odor perception. Our findings suggest that women may be more attentive to these odor cues, and therefore also to disruption of this information through fragrance use. Our results show that cultural practices might both enhance and interfere with evolved preferences.

Chemosensory Communication of Gender Information: Masculinity Bias in Body Odor Perception and Femininity Bias Introduced by Chemosignals During Social Perception.

Human body odor is a source of important social information. In this study, we explore whether the sex of an individual can be established based on smelling axillary odor and whether exposure to male and female odors biases chemosensory and social perception. In a double-blind, pseudo-randomized application, 31 healthy normosmic heterosexual male and female raters were exposed to male and female chemosignals (odor samples of 27 heterosexual donors collected during a cardio workout) and a no odor sample. Recipients rated chemosensory samples on a masculinity-femininity scale and provided intensity, familiarity and pleasantness ratings. Additionally, the modulation of social perception (gender-neutral faces and personality attributes) and affective introspection (mood) by male and female chemosignals was assessed. Male and female axillary odors were rated as rather masculine, regardless of the sex of the donor. As opposed to the masculinity bias in the odor perception, a femininity bias modulating social perception appeared. A facilitated femininity detection in gender-neutral faces and personality attributes in male and female chemosignals appeared. No chemosensory effect on mood of the rater was observed. The results are discussed with regards to the use of male and female chemosignals in affective and social communication.

Sex odour preference in guppy (Poecilia wingei) males is influenced by the social environment

The social environment of animals, particularly in the early stages of life, can have great impact on species-specific and sex-specific behaviours. These changes can be irreversible and continue during the entire life. In the present study we asked the question whether the social environment of male Endler’s guppies,Poecilia wingei, housed in an all-male community could affect their preference response to female or male odour cues in a flow through Y-maze. After 30 days in an all-male group males were tested for their preference-avoidance responses to conspecific odours. The males were attracted to male-scented water but not to water scented by females. In simultaneous choice between male and female odours they demonstrated no significant preference. The males were attracted to male-scented water after they were kept for 48 h or 12 days with females. After the Y-maze tests the males’ were placed with two females and their courting behaviour were recorded. The males showed low frequencies of reproductive behaviours. In the all-male group the males had been courting each other. The results show that the social environment influence sexual odour preference and courting behaviour in guppy males.

DREADD-Induced Silencing of the Medial Olfactory Tubercle Disrupts the Preference of Female Mice for Opposite-Sex Chemosignals(1,2,3).

Attraction to opposite-sex pheromones during rodent courtship involves a pathway that includes inputs to the medial amygdala (Me) from the main and accessory olfactory bulbs, and projections from the Me to nuclei in the medial hypothalamus that control reproduction. However, the consideration of circuitry that attributes hedonic properties to opposite-sex odors has been lacking. The medial olfactory tubercle (mOT) has been implicated in the reinforcing effects of natural stimuli and drugs of abuse. We performed a tract-tracing study wherein estrous female mice that had received injections of the retrograde tracer, cholera toxin B, into the mOT were exposed to volatile odors from soiled bedding. Both the anterior Me and ventral tegmental area sent direct projections to the mOT, of which a significant subset was selectively activated (expressed Fos protein) by testes-intact male (but not female) volatile odors from soiled bedding. Next, the inhibitory DREADD (designer receptors exclusively activated by designer drugs) receptor hM4Di was bilaterally expressed in the mOT of female mice. Urinary preferences were then assessed after intraperitoneal injection of either saline or clozapine-N-oxide (CNO), which binds to the hM4Di receptor to hyperpolarize infected neurons. After receiving CNO, estrous females lost their preference for male over female urinary odors, whereas the ability to discriminate these odors remained intact. Male odor preference returned after vehicle treatment in counterbalanced tests. There were no deficits in locomotor activity or preference for food odors when subject mice received CNO injections prior to testing. The mOT appears to be a critical segment in the pheromone–reward pathway of female mice.