Odors Of Estrous Females Research Articles

Why does castrated male odor attract sexually active male rats?–Attractivity induced by hypothalamus-pituitary-gonad axis block.

Sexually experienced male rats show an olfactory preference for estrous female odor compared to male odor. Notably, they also prefer castrated male over gonadally intact male odor. This study examined the role of elevated circulating gonadotropins and gonadotropin-releasing hormone (GnRH) induced by disinhibition of the hypothalamus-pituitary-gonad axis in the castration-induced attractiveness of male rats. Experiment I compared preference of sexually experienced males between odors of castrated males injected with a GnRH antagonist (Cast+Ant), castrated males injected with saline (Cast), and gonadally intact males (Sham). These olfactory preference tests revealed that probe males significantly preferred Cast over Sham and Cast+Ant odors but had no preference between Sham and Cast+Ant odors. Experiment II used hypophysectomy (HPx) to remove the gonadotropin source in place of pharmacologically antagonizing GnRH. Similarly, the probe males preferred Cast (high both GnRH and gonadotropins) over HPx (high GnRH but no gonadotropin) odors, but also preferred HPx than Sham (low both GnRH and gonadotropins) odors. We then examined the effects of exogenous gonadotropins, human chorionic gonadotropin (hCG) and equine chorionic gonadotropin (eCG), to reveal which gonadotropins critically affect on the attractiveness of HPx males. The olfactory preference tests revealed that injecting eCG, but not hCG, significantly increased the probe males` preference compared to HPx male odor, suggesting that the attractiveness is augmented via follicle stimulating hormone (FSH) receptor rather than luteinizing hormone receptor. These results indicate that sexually active male rats show olfactory preference for castrated male rats due to elevated GnRH and FSH blood levels produced by a lack of androgens.

Modulation of male mouse sociosexual and anxiety-like behaviors by vasopressin receptors

Although the involvement of two types of vasopressin (AVP) receptors, v1a and v1b, in neural regulation of social behavior is well documented in rodents, there is no report on combined actions of them in regulation of social behavior. In this study, we investigated behavioral differences between wild-type (WT) and v1a and v1b double knockout (dKO) mice. For this, we measured olfactory preference, sexual behavior with receptive females (four weekly tests) in an enriched large observation cage, and anxiety-like behaviors. No difference between WT and dKO mice was found in olfactory preferences for estrous female odor to male odor. Over all four mating tests, the number of mounts and pursuits after receptive females was significantly greater in dKO mice than in WT mice. In the elevated plus maze and the open field test, dKO mice showed lower anxiety-like behavior than WT mice. Finally, we measured approach behavior to several types of objects, figurines, and caged anestrous or estrous females placed in the open field apparatus. The only difference observed was that dKO mice spent longer in the vicinity of estrous females than did WT mice. These findings suggest that vasopressin receptors are involved in the regulation of sociosexual behavior, presumably partly mediated by emotional responses, in male mice.

Sexual experience reduces neuronal activity in the central part of the medial preoptic nucleus in male rats during sexual behavior

The medial preoptic area (MPN) plays an important role in the control of male sexual behavior. In rats, the central part of the MPN (MPNc) is sexually dimorphic and contains a sexually dimorphic nucleus composed of neurons expressing calbindin-D28 K (CALB-SDN). Although the functions of the MPNc are not well understood, surgical destruction of the MPNc adversely affects the performance of sexual behavior in sexually naive males, but not in sexually experienced males, supporting the notion that the MPNc changes functionally with sexual experience. In this study, we aimed to determine the effects of sexual experience on the neuronal activity of the MPNc and CALB-SDN. Sexual behavior in sexually inexperienced males that had no experience of ejaculation, and experienced males that had ejaculated once was observed. After they displayed sexual behavior, the brains were sampled, and immunohistochemical analysis of c-Fos, a neuronal activity marker, in the MPNc and CALB-SDN was performed. The numbers of c-Fos-immunopositive cells with or without calbindin-D28K-immunoreactivity increased significantly in the MPNc and CALB-SDN following ejaculation in both sexually inexperienced and experienced males, although the numbers did not change significantly with exposure to estrous female odors, the first mount, and the first intromission before and after the first ejaculation. We further found that the number of c-Fos-immunopositive and calbindin-D28K-immunonegative cells in the MPNc, but not in the CALB-SDN, was significantly smaller in sexually experienced males than in sexually inexperienced males. These results suggest that a population of MPNc neurons, which is located outside the CALB-SDN and do not express calbindin-D28 K, are activated during the first copulation and then silent after acquisition of sexual experience.

Sexual odor discrimination and physiological profiles in adult male rats after a neonatal, short term, reversible nasal obstruction.

The present study was designed to examine behavioral responses (interpreted as preferences) to olfactory cues (nest bedding odor and odors of estrous and anestrus females) in adult male rats after they had a short term reversible, bilateral, nasal obstruction (RbNO) as developing rat pups. These results were compared to behavior of control (untreated) and sham operated male littermates. Behavioral tests and physiological parameters were analyzed 90 days after recovery of nasal breathing. Experiments investigated the time spent in arms or the center of a maze of male rats in response to odors from the nest bedding or from adult females. There were no differences in responses between untreated, sham and RbNO adult male rats to fresh and nest bedding odors. RbNO males spent more time in the center of the maze when given a choice of estrus or anestrus female odors, or bedding odors from untreated or sham operated female rats. In contrast untreated and sham male rats preferred the odors of estrous females and of untreated or sham females. Plasma corticosterone levels in the males increased during the behavioral tests. Plasma testosterone levels were significantly lower in RbNO males compared to untreated males and did not increase during the behavioral tests compared to sham operated males. Males from all groups had similar preferences for the odor of bedding from adult RbNO females. Plasma levels of cholesterol and triglycerides were increased in RbNO adults. In conclusion, short term nasal obstruction in males while juvenile has long term consequences on hormones and behavioral preferences, thus potential partner selection when adult.

Either main or accessory olfactory system signaling can mediate the rewarding effects of estrous female chemosignals in sexually naive male mice.

A long-held view has been that interest of male mice in female body odors reflects an activation of reward circuits in the male brain following their detection by the vomeronasal organ (VNO) and processing via the accessory olfactory system. We found that adult, sexually naive male mice acquired a conditioned place preference (CPP) after repeatedly receiving estrous female urine on the nose and being placed in an initially nonpreferred chamber with soiled estrous bedding on the floor. CPP was not acquired in control mice that received saline on the nose before being placed in a nonpreferred chamber with clean bedding. Robust acquisition of a CPP using estrous female odors as the reward persisted in separate groups of mice in which VNO-accessory olfactory function was disrupted by bilateral lesioning of the accessory olfactory bulb (AOB) or in which main olfactory function was disrupted by zinc sulfate lesions of the main olfactory epithelium (MOE). By contrast, no CPP was acquired for estrous odors in males that received combined AOB and MOE lesions. Either the main or the accessory olfactory system suffices to mediate the rewarding effects of estrous female odors in the male mouse, even in the absence of prior mating experience. The main olfactory system is part of the circuitry that responds to chemosignals involved in motivated behavior, a role that may be particularly important for humans who lack a functional accessory olfactory system.

Olfactory preference in the male rat depends on multiple chemosensory inputs converging on the preoptic area

Both volatile and nonvolatile molecules are involved in chemosensory communication in rodents. Volatile odors from physically inaccessible estrous females induced increased numbers of c-Fos-positive cells in the preoptic area (POA) and in the cortical nucleus of the amygdala (CoA) of male rats. The numbers of c-Fos-positive cells in the medial nucleus of the amygdala (MeA) increased in response to the nonvolatile odors of bedding soiled with the excreta of estrous females. In an alternate choice paradigm, male rats carrying ibotenic acid lesions in either the MeA or the CoA—or a combination of both—distinguished the odors of estrous females from those of males, although the time spent sniffing the stimuli was diminished. Males with POA lesions showed complete loss of this capability. Males carrying either of the lesions did not detect differences between estrous and anestrous females or between intact and orchidectomized males. Lesions in the POA or MeA severely impaired male sexual behavior, whereas a CoA lesion had no effects. Thus, c-Fos-positive cells in the CoA might be involved in chemosensory transmission relevant to certain social contexts, but not in the execution of male sexual behavior. The POA is indispensable for both olfactory preferences and sexual behavior. The residual olfactory preference in males with MeA or CoA lesions or the combination of both could reflect an additional route for chemosensory transmission from the main olfactory bulb to the POA.

Behavioral characterization of non-copulating male rats with high spontaneous yawning frequency rate

An important number of Sprague-Dawley males selected by strict inbreeding process for their high spontaneous yawing frequency (HY) fail to copulate after repeated exposure to receptive females. These HY males that fail to mate are called non-copulators (HYNC). The causes of this behavioral deficit are still unknown. The aim of the present study was to make a detailed behavioral characterization of these animals by evaluating: their partner preference between a sexually receptive female as opposed to a sexually active male; their ability to detect food related odors and their preference for sexually relevant chemosensory cues between bedding from estrous females, bedding from sexually active males and clean bedding. We also evaluated whether these males had alterations in motor function using a rotarod or in their general reward system mediated by opioids by injecting them with 1 mg/kg of morphine to evaluate if they develop conditioned place preference (CPP). At the end of these behavioral tests, we measured their plasmatic levels of testosterone (T). Together, these results will contribute to elucidate the causes of their deficient copulatory performance. Both HYNC and HY copulators (HYC) males showed a clear preference for receptive females as opposed to sexually active males. As well, both groups of animals had a similar ability to detect food related odors. HYC males had a clear preference for estrous female odors as opposed to male or clean bedding, but HYNC males spend the same amount of time sniffing estrous, anestrous, male and clean bedding. In both, HYC and HYNC, morphine induced CPP suggesting that in these males the reward system is functional. No differences were found in motor coordination or in T levels between HY and HYNC males. The behavioral deficit in HYNC male rats cannot be explained by an alteration in: partner preference, food related odor recognition, motor coordination, general reward system, or differences in plasmatic levels of T. However, HYNC males present clear deficits in recognizing sexually relevant odors. These results could, at least in part, explain the deficient execution of copulatory pattern in HYNC males.

Masculinization induced by neonatal exposure to PGE 2 or estradiol alters c- fos induction by estrous odors in adult rats

Processing of relevant olfactory and pheromonal cues has long been known as an important process necessary for social and sexual behavior in rodents. Several nuclei that receive input from the vomeronasal projection pathway are involved in sexual behavior and show changes in immediate early gene expression after stimulation with a variety of sex-related stimuli. The nuclei in this pathway are sexually dimorphic due to the early patterning events induced by estradiol derived from testicular androgens, which developmentally defeminize and masculinize the brain and adult sexual behavior. Masculinization can be induced independently of estradiol via prostaglandin-E 2 (PGE 2), and therefore assessed separately from defeminization. Here we examined the effects of brain defeminization and masculinization on neuronal response to sex-related odors using Fos, the protein product of the immediate early gene c -fos, as an indicator of activity. Female rat pups treated with a cyclooxygenase-2 inhibitor, to reduce PGE 2, plus estradiol, estradiol alone, and PGE 2 alone were exposed to estrous female odor as adults and the resulting Fos expression was examined in the medial amygdala, preoptic area, and ventromedial nucleus of the hypothalamus. Defeminized and/or masculinized females all showed patterns of Fos activity similar to control males and significantly different from control females. These results suggest that early exposure to estradiol and PGE 2 do not affect olfaction in females, but switch the activity pattern of sex-related nuclei in females to resemble that of males following exposure to sexually-relevant cues.

Sexual incentive motivation, olfactory preference, and activation of the vomeronasal projection pathway by sexually relevant cues in non-copulating and naive male rats

There are some apparently healthy male rats that fail to mate after repeated testing with receptive females. We have previously shown that these “non-copulator (NC)” males show no partner preference for a receptive female when given the opportunity to physically interact with a sexually receptive female or a sexually active male. We also demonstrated that although NC males prefer odors from estrous females to odors from anestrous females, this preference is significantly reduced in comparison to the preference displayed by copulating (C) males. The aim of the present study was to evaluate in NC males sexual incentive motivation, that is, the approach behavior of male rats to either a sexually receptive female or a sexually active male in a test where the subjects can smell, hear, and see the stimulus animal but prevents their physical interaction. In addition, we determined whether NC rats have alterations in their ability to detect odors from conspecifics or odors related to food. In the detection of odors from conspecifics, we determined if these NC males are sexually attracted toward odors from receptive females or sexually active males. For food-related odors, we quantified the time it took the subjects to locate a hidden a piece of apple. Finally, using the induction of Fos-immunoreactivity (Fos-IR) as an index of neuronal activation, we compared the response of the vomeronasal projection pathway (VN pathway) of C and NC male rats exposed to estrous bedding. Males without sexual experience (WSE) were included in all experiments to determine the importance of previous heterosexual experience in the different behavioral tests and in the activity of the VN pathway. In the sexual incentive motivation test, we found that C and WSE male rats have a clear preference for estrous females over sexually active males, whereas NC male rats showed no preference. In odor tests, our results showed that C males had a clear preference for odors from estrous females as opposed to odors from sexually active males. Although NC and WSE male rats showed a preference for estrous female odors, this preference was significantly reduced compared to that shown by C males. No differences were found between WSE, C, and NC males in the detection of stimuli associated with food-related odors. A significant increase in Fos-IR was observed in the mitral cell layer of the accessory olfactory bulb in all groups when exposed to estrous bedding. However, only the C male rats exposed to estrous female bedding showed an increase Fos-IR in all structures of the VN pathway. An increase in Fos-IR was observed in the medial preoptic area (MPOA) of WSE males exposed to estrous bedding. No increases in Fos-IR were detected along the VN pathway in NC male rats. We proposed that NC male rats do not display sexual behavior due to a reduced sexual motivation that could be caused by alterations in the neuronal activity of the VN pathway during the processing of estrous odors.

Effect of prenatal androgen receptor antagonist or aromatase inhibitor on sexual behavior, partner preference and neuronal Fos responses to estrous female odors in the rat accessory olfactory system

Many socially relevant odors are detected in rodent species by the vomeronasal organ and subsequently processed by the accessory olfactory system (AOS). We previously found that gonadectomized male and female rats treated in adulthood with testosterone propionate (TP) showed equivalent Fos responses in the AOS to odors derived from estrous females. Likewise, in contrast with numerous other mammalian species, gonadectomized female rats show surprisingly high levels of male-typical mounting behavior in response to adult TP. We tested the hypothesis that prenatal testosterone (T) exposure, acting via androgen receptors (ARs) or via estrogen receptors, masculinizes the AOS in rats of both sexes. Pregnant dams were treated with either the AR blocker, Flutamide, the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), or nothing (control) to assess the role of prenatal androgen and estradiol receptor activation, respectively, in this masculinization. Beginning at birth, male and female offspring were injected subcutaneously (sc) every other day with either ATD (pre- and neonatal ATD group) or oil vehicle (Flutamide and control groups) until postnatal Day 12. Subjects were gonadectomized as adults, hormonally treated and tested for different behaviors before having their AOS Fos responses to estrous female odors assessed. Prenatal treatment with Flutamide (but not ATD) significantly decreased anogenital distance and severely impaired intromissive and ejaculatory behaviors in males tested after TP replacement without disrupting mounting capacity in either sex. Pre- and neonatal treatment with ATD (but not Flutamide) enhanced lordosis responsiveness in males tested after sc injections of estradiol and progesterone, whereas these perinatal treatments had no effect on any aspect of masculine coital performance in either sex. After TP treatment, male and female control subjects preferred to approach a tethered stimulus female as opposed to a male, and prenatal Flutamide or perinatal ATD treatments did not modify this pattern of partner preference. Neuronal Fos responses to estrous odors were (as in previous studies) identical in the AOS of gonadectomized TP-treated control males and females. Prenatal Flutamide or perinatal ATD treatments failed to disrupt consistently this profile of Fos responses to estrous odors in the AOS of rats of either sex. These behavioral and neuroanatomical findings raise the possibility that the similar level of male-typical responsiveness to social odors that occurs in male and female rats after adult TP treatment results from nonsteroid-hormone-dependent, species-specific factors that act perinatally in the brains of rats of both sexes.

Altered responses to female odors in parasitized male mice: neuromodulatory mechanisms and relations to female choice

There is accumulating evidence that females may preferentially select parasite-free or -resistant males. Minimal attention has, however, been paid to the mate preferences and responses of the parasitized male hosts themselves. Here, we considered the effects of parasitic infection on male host mate responses, the neuromodulatory correlates of these responses, and the relations of these responses to female mate choice. Using an odor “preference” test, we examined the effects of different stages of an acute, sub-clinical infection with the naturally occurring, enteric, single host, protozoan parasite, Eimeria vermiformis, on the responses of male mice, Mus musculus domesticus, to the odors of estrous females along with the responses of uninfected females to the parasitized males. At 4 days post-infection (non-infective, pre-patent stage) E. vermiformis-infected male mice showed a significantly decreased preference for the odors of estrous females, whereas at 10 days post-infection (infective, patent stage) infected males showed a significantly increased preference for the odors of estrous females. Parasitized males displayed no significant changes in their responses to the odors of non-estrous females, supporting effects on the reproductively related responses of the host. In parallel, estrous females displayed a reduced interest in the odors of infected males. Least interest was expressed in the odors of the patent, infective males, consistent with the avoidance of contagion. Using selective opioid peptide receptor agonists and antagonists we found evidence that enhanced kappa opioid peptide (e.g., dynorphin) activity was related to the decreased sexual interest of the pre-infective males, while augmented delta opioid peptide (e.g., enkephalin) activity was associated with the enhanced responses of the infective males to females. We further showed that acute kappa opiate administration reduced the responses of uninfected males to females and that uninfected females displayed modified responses to the odors of uninfected males subject to acute modifications of opioid activity. We suggest that these differential shifts in endogenous opioid activity in the parasitized males are associated with and, or related to alterations in neuro-immune and endocrine functions. These findings show that parasitic infection can have, depending on the stage of infection and associated neuromodulatory changes, either significant facilitatory or inhibitory effects on male host preferences for and responses to females.

Male preference for the odors of estrous female mice is reduced by the neurosteroid pregnenolone sulfate

The effects of the neurosteroid, pregnenolone sulfate (PS), on the responses of male mice to the odors of estrous female mice were examined in an odor preference test. Control untreated mice displayed a significant preference for the odors of an estrous female, spending more time in a Y-maze in the vicinity of the odors of an estrous than a non-estrous female. Administration of PS decreased male preference for the odors of estrous females, causing a significant dose-related (0.01 – 10 mg/kg) decrease in the amount of time spent in the proximity of the odors of the estrous female, while having significantly less of an effect on the responses to the non-estrous female odors. Neither pregnenolone nor sodium sulfate had any significant effects on the olfactory responses. The effects of PS were significantly reduced by peripheral administrations of the non-competitive N-methyl- d-aspartate (NMDA) receptor antagonist, MK-801, but were not significantly affected by either the GABA A antagonists, bicuculline and picrotoxin, or the benzodiazepine antagonist, Ro 15–1788. These results suggest that pregnenolone sulfate has inhibitory effects on olfactory mediated male sexual interest, preference, or ‘motivation’ that, in part, involve interactions with NMDA receptor mediated mechanisms.

Male preference for the odors of estrous female mice is enhanced by the neurosteroid 3α-hydroxy-4-pregnen-20-one (3αHP)

The effects of the centrally produced allylic neurosteroid, 3α-hydroxy-4-pregnen-20-one (3αHP), on the responses of male mice to the odors of estrous female mice were examined in an odor preference test. Control untreated mice displayed a significant preference for the odors of an estrous female, spending more time in a Y-maze in the vicinity of the odors of an estrous than a non-estrous female. Intracerebroventricular (i.c.v.) administrations of 3αHP enhanced male preference for the odors of estrous females, causing a significant dose-related (0.01–1.0 μg) increase in the amount of time spent in the proximity of the odors of the estrous female, while having no significant effect on the responses to the non-estrous female odors. These effects of 3αHP were stereospecific, with the stereoisomer, 3β-hydroxy-4-pregnen-20-one (3βHP), having no significant effects on odor preferences. The analgesic, morphine, also had no significant effects on the responses to female odors suggesting that the enhanced preference for estrous female odors were unlikely to be directly due to any analgesic effects of 3αHP. The effects of 3αHP were significantly reduced by peripheral administrations of the GABA A antagonists, bicuculline and picrotoxin, but were unaffected by either the benzodiazepine antagonist, Ro 15-1788, or the opiate antagonist, naloxone. These results suggest that the neurosteroid 3αHP has facilitatory effects on olfactory mediated male sexual interest or motivation that involve interactions with the GABA A receptor.

Sexual experience and preferences for odors of estrous females in staggerer mutant male mice

Staggerer mutant male mice generally do not mate and olfactory disabilities may be involved. Choice tests were used to determine the preference of C57BL/6 male mice with the staggerer mutation for urine and vaginal secretions from receptive and unreceptive females. The staggerer mutation does not prevent the olfactory discrimination between vaginal secretions of estrous and anestrous females. Male preferences for odors of receptive females are related to the presence of sexual experience.

Suppression of adult copulatory behaviors following LiCl-induced aversive contingencies in juvenile male rats.

Sexually immature juvenile male rats received an injection of .3 M (20 ml/kg) lithium chloride (LiCl) during each of 8-10 pairings (spaced at 2-3-day intervals) with an estrous female. Approximately seven weeks later, these males displayed fewer copulatory behaviors in pairings with estrous females than saline control rats. Noncontingent .3 M LiCl injections administered to juvenile males did not affect adult copulatory behaviors. Males that were either group or individually housed during the retention interval displayed comparable suppression, which suggests that copulatory suppression does not represent a generalized aversion to social interactions with another animal. Males housed during the retention interval in an environment that contained the odors of estrous females also displayed suppression comparable to that of males housed in the absence of such odors. This suggests that the associations that mediate copulatory suppression are not elicited solely by the odor cues of estrous females. These data demonstrate that LiCl-induced aversive contingencies in juvenile male rats subsequently suppress adult copulatory behaviors.

Effects of fluprazine hydrochloride on conspecific odor preferences in rats

The effect of Fluprazine Hydrochloride (DU 27716) on preference for conspecific male, estrous female and food odors was examined in male rats utilizing a two-compartment choice apparatus. Treatment with 8.0 mg/kg Fluprazine enhanced the preference of males for male odors but had no effect on preference for either estrous female or food odors. The drug-induced enhancement of male odor preference is consistant with the suggestion that Fluprazine interferes in some way with the processing of olfactory stimuli which normally precede offensive attack. The failure of the drug to alter the preference of males for estrous female odors suggests that the increased sniffing of estrous females noted during social testing may be secondary to other sources of conspecific stimulation or may reflect a highly transitory effect on olfactory processes. These results suggest that the suppressive effects of Fluprazine on intermale aggression and copulation are mediated by somewhat distinct mechanisms.

Responses of male rats to sex odors

A series of 4 experiments investigated the responses of Sprague-Dawley male rats to the odors from sexually receptive females. Having established that Sprague-Dawley male rats prefer the odors of estrous females and that the preferences are not a function of the female's movements or sounds (Experiment 1), the contribution of the various components of the males' copulatory pattern to the development of preferences was examined (Experiment 2). The results showed that sexually naive males fail to show a sex odor preference and that mounting experience is sufficient for the preferences to appear. Experiment 3 investigated the relationship between the presence or absence of the testes and the sex odor preferences; approximately 3 weeks following castration the preferences disappear. Experiment 4 examined whether neonatal testicular secretions are necessary if the male rat is to display a sex odor preference in adulthood. Following testosterone propionate administration and mounting experience, Day 1 castrates showed a sex odor preference.