Contribution of anal scent gland and urinary odorants to mate recognition in the ferret

Previous research [J. Neurosci. 21 (2001) 5832-5840] showed that ferrets of both sexes require olfactory signals to identify opposite-sex mating partners at a distance. The present experiments assessed the contributions of anal scent gland and urinary odorants to these preferences. Sexually experienced, ovohysterectomized female and castrated male ferrets were injected daily with estradiol benzoate and testosterone propionate, respectively. When tested in an airtight Y-maze, subjects of both sexes preferred to approach volatile odors emitted from opposite- versus same-sex stimulus ferrets that were anesthetized and placed in the goal boxes, regardless of whether the anal scent glands of stimulus ferrets had been surgically removed or left intact. Subjects of each sex showed an equal preference to approach volatile odors emitted from anesthetized opposite-sex ferrets that were scent-gland intact as opposed to descented. Female subjects preferred to approach volatile anal scent gland odorants, as well as urinary odorants from male, as opposed to female conspecifics. Male subjects preferred to approach volatile anal scents from females versus males; however, males showed no preference for female over male urinary odorants. Our results suggest that anal scent gland odorants are sufficient, but not required, for mate recognition in the ferret. Instead, a combination of body odorants including, but not restricted to, those derived from anal scent gland secretions apparently underlie olfactory sex discrimination and partner preference in this carnivore.     

Effect of sex steroids and coital experience on ferrets' preference for the smell,sight and sound of conspecifics

Previous research showed that ferrets of both sexes recognize potential opposite-sex mates on the basis of volatile body odors. We compared the ability of estrogen and androgen treatments to activate a preference in gonadectomized male and female ferrets for distal cues (volatile body odors alone or volatile odors+sight+sounds) from male versus female stimulus ferrets using an airtight Y-maze and a "stimulus proximity" or a "discrete trials" testing paradigm. Sexually naive, gonadectomized male and female ferrets that received either testosterone propionate (TP) or estradiol benzoate (EB) spent equal time in proximity to goal boxes that provided either volatile odors alone or odors+sight+sounds of male and female stimulus animals. After they received coital experience, male and female subjects (treated with either EB or TP) showed a significant preference for both types of opposite-sex stimuli. When discrete trials tests were given to these ferrets prior to receiving coital experience, EB-treated females preferred to approach odor only cues, as well as odors+sight+sounds of stimulus males, and this preference was further strengthened after coital experience. Sexually naive, TP-treated males preferred to approach volatile odor cues from stimulus females; however, these animals showed an equal preference for odors+sight+sounds of stimulus females and males. Again, after coital experience, males' preference for both sets of cues from stimulus females was significantly enhanced. Thus, in sexually naive ferrets, discrete trials, but not stimulus proximity tests, revealed a preference for distal cues (body odors with or without concurrent sight and sounds) from opposite-sex conspecifics in subjects of both sexes. Coital experience significantly enhanced these preferences for heterosexual distal cues under both testing paradigms.     

A lack of avoidance of flank gland secretions by male Syrian hamsters

It is commonly assumed that sexually dimorphic cutaneous glands are important in supporting inter-male aggression in rodents. Such an intimidation role has been hypothesized as the function of the hamsters' flank gland. Two experiments failed to find avoidance of male flank odors. In one, subordinate males entered and spent comparable amounts of time in clean areas and areas scented with the dominant's flank secretion. In the other study, males were found to respond differentially to flank odors obtained from the subject, a familiar and a novel male. Although the males seemed to have habituated to the odor of the familiar male, there was no suggestion of avoidance of any of these odors. It may be that the males' flank odor is relevant not to other males but to females.     

Olfactory preference and Fos expression in the accessory olfactory system of male rats with bilateral lesions of the medial preoptic area/anterior hypothalamus

In the present study we evaluated if a medial preoptic area/anterior hypothalamus lesion affects the olfactory preference toward soiled bedding from receptive females in comparison to bedding from anestrous females or clean bedding. In the second part of the study we evaluated the accessory olfactory system response to estrous bedding with Fos immunoreactivity to determine if the preoptic lesions modify the processing of sexually relevant olfactory cues. Before medial preoptic area/anterior hypothalamus lesions, male rats spent more time investigating estrous bedding as opposed to anestrous or clean bedding. After the lesion, subjects showed no preference between estrous and anestrous bedding; that is, males spent the same amount of time investigating both types of bedding. These two odors were investigated more than clean bedding. Increments in Fos immunoreactivity neurons were seen in structures of the accessory olfactory system after exposure to soiled estrous bedding [granular layer of the accessory olfactory bulb, anterior-dorsal medial amygdala, posterior-dorsal medial amygdala, bed nucleus of the stria terminalis]. These results suggest that bilateral destruction of the medial preoptic area/anterior hypothalamus modify male olfactory preference in such a way that subjects spend the same time smelling and investigating bedding from estrous and anestrous females. This change in olfactory preference is not associated with alterations in the processing of sexually relevant olfactory cues by the accessory olfactory system.     

Mapping of odor-related neuronal activity using a fluorescent derivative of glucose

Previously [S.K. Woodley, M.J. Baum, Differential activation of glomeruli in the ferret's main olfactory bulb by anal scent gland odors from males and females: an early step in mate identification, Eur. J. Neurosci. 20 (2004) 1025–1032], the receipt of intromission from a male activated glomeruli (indexed by Fos immunoreactivity in juxtaglomerular cells) in the main olfactory bulb (MOB) of estrous female ferrets which exceeded the activation seen after exposure to male anal scent gland odorants alone. We asked whether centrifugal inputs (e.g., from the locus coeruleus to the MOB) generated by the receipt of vaginal-cervical stimulation influence odor-induced MOB glomerular activation. We compared the activation of MOB glomeruli in estrous female ferrets which received a unilateral naris occlusion prior to exposure to: unscented air, volatile odorants from an anesthetized male, volatile + non-volatile odorants from direct physical contact with an anesthetized male, or mating stimulation. Little glomerular activation was observed in the MOB ipsilateral to an occluded naris, including females which received intromission. An equivalent distribution of activated glomeruli was observed in the ventral MOB of estrous females which either received mating stimulation or had direct physical contact with an anesthetized male. Considerably less glomerular activation occurred in females exposed only to volatile male odors. The MOB of female ferrets responded to body odorants from the opposite sex; however, there was no evidence that mating-induced centrifugal inputs directly activated MOB glomeruli or modified odor-induced glomerular activation.     

Photoperiod and gonadal hormones influence odor preferences of the male meadow vole, Microtus pennsylvanicus.

Male meadow voles housed in a long photoperiod (14 h light/day, LP) preferred female to male odors, whereas males maintained in a short photoperiod (10 h light/day, SP) did not display preferences for odors of either sex. These odor-preference patterns matched those of free-living males during spring and autumn, respectively. The preference of LP male voles for female over male odors was eliminated by gonadectomy and reinstated by treatment with testosterone. In SP males, although gonadectomy did not affect odor choices, a preference for female odors was induced by testosterone treatment. Treatment with estradiol did not alter odor preferences of LP or SP males. In conjunction with previous result, the present findings suggest that hormonal responsiveness of neural substrates that control odor preferences are sexually dimorphic and may reflect sex differences in reproductive strategies.     

Inactivation of the medial preoptic area/anterior hypothalamus by lidocaine reduces male sexual behavior and sexual incentive motivation in male rats

Permanent bilateral lesions of the medial preoptic area anterior hypothalamus (MPOA/AH) produce a drastic inhibition of male sexual behavior in all species studied to date. The present experiment was designed to evaluate if temporal inactivation of the MPOA/AH by infusions of lidocaine also inhibits sexual behavior in male rats. This would allow us to rule out the possibility that the behavioral effects observed after damage of the MPOA/AH could be associated with plastic changes induced by the lesion in other brain regions. We also evaluated sexual incentive motivation in males after the infusion of lidocaine in a test in which copulation is not possible but where males maintain approach behavior to the estrous females despite repeated testing. The percentage of animals displaying mounts, intromissions and ejaculation was significantly reduced while mount and intromission latency were prolonged after infusion of lidocaine. No changes were observed in sexual behavior after infusion of lidocaine in animals with cannulae outside the MPOA/AH suggesting that the inhibitory effects are specific to this brain region. Sexual incentive motivation was also affected by administration of lidocaine. Males consistently showed a clear preference for the sexually receptive female except when infused with lidocaine. After the infusion of the compound a significant reduction in the time spent in the incentive zone of the stimulus female was observed. These results support the hypothesis that neurons of the MPOA/AH are involved in the control of male sexual motivation.     

Development of sex differences in the response of spiny mouse pups to adult male odors

Using a three-choice preference test, olfactory-mediated investigatory activity in response to adult male urine odor was examined in a precocially active rodent, the spiny mouse (Acomys cahirinus) aged between 3-26 days. Temporally related sex differences were seen in the time spent in the presence of the odors of father's or unfamiliar adult male's urine, or distilled (control) water. Neither male nor female pups discriminated between odors from the father and strange adult males. After the first olfactory test, when the pups were aged between four and six days, male pups strongly preferred to stay in the vicinity of urine odors of adult males, whereas female pups avoided odors of adult males and remained in the enclosure with the control odor source. To our knowledge this is the first time that such a behavioral sex difference related to olfaction has been shown to occur in young rodent pups. We suggest that the sexually dimorphic response of the pups is associated with the development of later sex differences in behavior.     

Effect of bilateral accessory olfactory bulb lesions on volatile urinary odor discrimination and investigation as well as mating behavior in male mice

Previous research raises the possibility that urinary volatiles from estrous female mice activate mitral cells in the accessory olfactory bulb (AOB) of male mice following detection via the main olfactory epithelium as opposed to the vomeronasal organ. We asked whether bilateral lesions of the AOB would disrupt the ability of male mice to discriminate between urinary volatiles from mice of different sexes or endocrine states, or affect their interest in investigating these odors when they were presented sequentially in home-cage habituation/dishabituation tests. Males with either partial or complete bilateral lesions of the AOB resembled sham-operated control males in their ability to discriminate between ovariectomized and estrous female urinary volatiles as well as between male and estrous female urinary volatiles. However, males with either complete or partial AOB lesions spent significantly less time than sham-operated control males investigating urinary volatiles from estrous females, especially during tests when the alternative stimulus presented was male urine. Placement of AOB lesions failed to disrupt males' mating performance. Our results suggest that the incentive value of opposite-sex (female) volatile urinary odors which are initially detected by the main olfactory system is enhanced when they are further processed by the male's AOB.     

Fos expression induced by cocaine-conditioned cues in male and female rats

Previous studies have shown that female rats exhibit different patterns of drug seeking during multiple phases of cocaine addiction when compared with males. However, the underlying mechanisms for these sex differences remain largely unknown. Here, we used a cocaine self-administration/reinstatement model to examine neuronal activation, as determined by Fos expression, following cue-induced reinstatement of cocaine seeking in male and female rats. Fos expression revealed both similarities between sexes in some brain regions, as well as selective sexually dimorphic patterns. As compared to no cue control subjects, conditioned cues induced higher Fos expression in the Cg1 region of the anterior cingulate cortex, but lower expression in the nucleus accumbens in both males and females. Females exhibited higher Fos expression than males in multiple brain regions, including the agranular insular cortex, dorsal medial caudate-putamen, nucleus accumbens shell, ventral tegmental area, dorsal subiculum, and ventral CA1 and CA3 regions of the hippocampus. Notably, only Fos expression in the prelimbic cortex, nucleus accumbens shell, basolateral amygdala, and ventral subiculum correlated positively with lever responding in response to conditioned cues across males and females. These findings indicate that while sexually dimorphic Fos activation does occur, the relationship between cue-induced cocaine seeking and neuronal activation may be similar for males and females in key brain regions of the relapse circuit.     

Responses of male hamsters to the ear gland secretions of conspecifics

The behavioral responses of sexually experienced males toward anesthetized conspecifics were examined. Males directed more mounts and spent significantly more time investigating the ears and genital region of castrated males and diestrous females than intact males. Castrated males were treated in a similar manner to females, suggesting that the absence of an androgen-dependent factor(s) renders an animal more sexually attractive. Males were also administered paired preference tests in which they investigated the odors from the ear glands of diestrous females, castrated males, and intact males. Subjects spent significantly more time investigating the odors originating from ear glands of females and gonadectomized males than intact males. There was no significant difference in the amount of time males spent with the ears of castrated males and diestrous females. These experiments demonstrate that sexually experienced male hamsters can utilize odors associated with the ears to discriminate the gender of conspecifics.     

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 consistent 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.     

Attraction of beagles to conspecific urine, vaginal and anal sac secretion odors

Attraction of male and female Beagles to conspecific urine, vaginal and anal sac secretion odors was examined in four experiments. Males spent more relative time investigating female urine odors than odors of vaginal or anal sac secretions. Sexually experienced males, but not sexually inexperienced ones, spent more time investigating estrous than diestrous female urine and vaginal odors. Anal sac secretions from estrous bitches were not more attractive to males than those from diestrous bitches. Estrous females spent no more time than diestrous ones in the investigation of male anal sac secretion and urine odors. Male urine and anal sac secretions elicited little investigation from male conspecifics. Females spent more time investigating female urine odors than female anal sac or vaginal secretion odors, and exhibited a slight general preference for diestrous over estrous stimuli. A positive correlation between the odor investigation times of this study and investigation times of comparable animals to conspecifics in a social situation suggests odor preferences are relatively good indicators of social preferences, and vice versa, in this breed.     

The role of the medial preoptic area in appetitive and consummatory reproductive behaviors depends on sexual experience and odor volatility in male Syrian hamsters

In Syrian hamsters (Mesocricetus auratus), the expression of reproductive behavior requires the perception and discrimination of sexual odors. The behavioral response to these odors is mediated by a network of ventral forebrain nuclei, including the medial preoptic area (MPOA). The role of MPOA in male copulatory behavior has been well-studied, but less is known about the role of MPOA in appetitive aspects of male reproductive behavior. Furthermore, many previous studies that examined the role of MPOA in reproductive behavior have used large lesions that damaged other nuclei near MPOA or fibers of passage within MPOA, making it difficult to attribute post-lesion deficits in reproductive behavior to MPOA specifically. Thus, the current study used discrete, excitotoxic lesions of MPOA to test the role of this nucleus in opposite-sex odor preference and copulatory behavior in both sexually-naïve and sexually-experienced males. Lesions of MPOA eliminated preference for volatile, opposite-sex odors in sexually-naïve, but not sexually-experienced, males. When males were allowed to contact the sexual odors, however, preference for female odors remained intact. Surprisingly, lesions of MPOA caused severe copulatory deficits only in sexually-naïve males, suggesting previous reports of copulatory deficits following MPOA lesions in sexually-experienced males were not due to damage to MPOA itself. Together, these results demonstrate that the role of MPOA in appetitive and consummatory aspects of reproductive behavior varies with the volatility of the sexual odors and the sexual experience of the male.     

The role of the hippocampal system in social odor discrimination and scent-marking in female golden hamsters (Mesocricetus auratus)

Female golden hamsters (Mesocricetus auratus) received aspiration lesions of the parahippocampal region (PARA) or electrolytic lesions of the fimbria-fornix (FNX) and were tested for their (a) discrimination between odors of individual males in a habituation-discrimination task, (b) preference for male over female odors, and (c) scent-marking in response to conspecific odors. Both lesion groups habituated to repeated presentations of a male's odor. However, only FNX females discriminated between scents of individual males, whereas PARA females did not. Neither lesion eliminated female preferences for male odors. Females with FNX lesions showed decreased levels of scent marking, but those with PARA lesions had more subtle deficits. Thus, the PARA, but not the subcortical connections of the hippocampus, is critical for discrimination of the odors of individuals.     

Effects of consanguinity, exposure to pregnant females, and stimulation from young on male gerbils' responses to pups.

In three experiments investigating variables affecting responses of male Mongolian gerbils to conspecific young, we compared the behavior directed towards pups of natural fathers, virgin foster fathers, and sexually experienced foster fathers (Experiment 1); males either previously exposed or not exposed to pregnant females (Experiment 2); and males provided or not provided with extra opportunities to huddle over pups (Experiment 3). We found no difference in responses to pups among natural fathers, virgin foster fathers, and foster fathers that had fathered litters. On the other hand, both a week of exposure to a pregnant female and opportunity to huddle over pups for an extra 15 min/day had significant effects on males' subsequent responses to conspecific young. We speculate on the reasons why a male's response to pups might be affected by his exposure to a pregnant female and stimuli from pups, but not by the probability that the pups were his own offspring.     

Central tegmental field and sexual behavior in the male rat: effects of neurotoxic lesions

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a key structure in the control of male sexual behavior. This area has reciprocal connections with mesencephalic and brainstem structures including the central tegmental field (CTF). It has been suggested that the CTF receives somatosensory information generated in the genitals promoting activation of the MPOA/AH. In the present study we evaluated the effects of bilateral neurotoxic lesions of the CTF upon male rat sexual behavior. We also explored the effects of these lesions on sociosexual behaviors, partner preference, sexual incentive motivation and motor execution. Tests were performed before and after bilateral quinolinic acid infusions. The lesion was evaluated by quantifying neuronal nuclei (Neu-N) and by the presence of glial fibrillary acidic protein (GFAP) immunohistochemistries. A significant reduction in the percentage of animals displaying mounts, intromissions, and ejaculations was observed in the bilateral and misplaced lesion groups 1 week after the lesion. In the second week post-lesion, only animals with bilateral damage of the CTF showed a significant reduction in sexual behavior. In the third post-lesion test, the percentage of animals displaying sexual behavior returned to control levels. The frequency of pursuit and self-grooming was reduced, and genital exploration was increased after the lesion. Partner preference and sexual incentive motivation were not affected by the lesion suggesting that the CTF is not involved in the appetitive aspects of sexual behavior. Mount, intromission, and ejaculation latency were increased in animals with damage of the CTF and in animals with lesions outside this region. Motor execution was also affected in both groups, suggesting that alterations in latencies could be associated with damage not specific to the CTF.     

Olfactory discrimination and incentive value of non copulating and sexually sluggish male rats

Some apparently healthy male rats fail to copulate despite being tested on repeated occasions with receptive females and are called non copulating (NC) rats. NC rats sniff and lick the female genitals, and show normal erectile and ejaculatory functions and hormonal levels. Sexually sluggish (S) male rats take a long time to ejaculate or sometimes they don't achieve ejaculation when tested repeatedly with receptive females. The aim of the present study was to determine if NC and S males can discriminate sexually relevant olfactory cues such as urine from estrous or anestrous female and urine from sexually experienced males. We also tested odors like amyl acetate and mint using an olfactory discrimination test. In a second experiment we evaluated if a sexually receptive female has a preference for a copulating (C) male, for a NC male, or for a S male in a sexual incentive motivation test. This would let us determine if a NC and an S male are equally attractive than a C male to a sexually receptive female. The olfactory test revealed that C, NC and S males have the same ability to discriminate sexually relevant odors. As well, all males clearly discriminate non sexual odors like amyl acetate and mint suggesting that NC and S male rats do not have alterations in their olfactory system. With respect to the sexual incentive motivation test, females spend the same time in the incentive zone of the NC and C males. As well, females spent the same time in the incentive zone of S and C males. These results demonstrate that NC, S and C males are equally attractive to receptive females.