Partner preference: Assessing the role of the female goat

For domestic ruminants, the male is thought to have the control over mate choice. The aim of this study was to assess the potential role the female goat plays in choosing a sexual partner. Approach frequency and proximity time to various social or sexual stimuli in a Y-maze apparatus were used as partner preference assessment parameters. Ovariectomized females were either induced into estrus (n = 8) or induced into anestrus (n = 8) and exposed to various goal stimuli — intact unfamiliar females (estrous and diestrous), intact males, and neutral (empty) in six separate trials. Total arm entries and time spent within one body length of the goal (proximity time — used to calculate preference scores) were recorded for subjects. With a male present, anestrous subjects had significantly more total arm entries than estrous subjects. Estrous subjects showed a significant preference for the male goal (M) versus the estrous female (ES), diestrous female (DS), and empty goals, respectively. Estrous subjects also showed a preference for the ES and DS goals when one goal was left empty. Anestrous subjects showed a preference for the goal containing ES, DS, and M compared to empty goals. They also showed a preference for ES vs. DS. The Y-maze is a tool that can be used to assess sexual and social partner preferences in female goats. The role the female plays in choosing a partner may be much greater than previously considered.     

Olfactory experience and the development of odor preference and vaginal marking in female Syrian hamsters

Rodent reproductive behavior relies heavily on odor processing, and evidence suggests that many odor-guided sexual behaviors are shaped by prior experience. We sought to determine if exposure to male odors during development is required for the adult expression of proceptive sexual behavior toward male odors in female Syrian hamsters. Exposure to male odors was restricted in na?ve subjects by removing all male siblings from the litter at three to five days of age. Control litters were also culled, but included equal numbers of male and female pups. As adults, na?ve females displayed investigatory preferences toward male odors in a Y-maze that were comparable to control females; this preference was observed whether contact with the odor stimuli was prevented of allowed. In contrast, na?ve females vaginal scent-marked equally toward male and female volatile odors, suggesting an inability to target behavior toward sexually relevant odors. However, na?ve females marked preferentially toward male odors when allowed to contact the odor stimuli. These results provide evidence for the experience-dependent development of vaginal marking behavior toward volatile components of sexual odors. Furthermore, they suggest that distinct mechanisms regulate the development of odor preferences and vaginal marking behavior in this species.     

Stimulus animal characteristics do not modulate the expression of partner preference by female rats

The stimulus animals used in tests of partner preference in female rats vary. To test the hypothesis that the alternative stimulus animal modulates the preference for an intact male, gonadectomized (GDX) female rats received estradiol benzoate plus progesterone or the oil vehicle and were tested for partner preference with either an intact male paired with a GDX hormone-primed female or an intact male paired with a GDX male. Rats were tested under conditions that limited physical contact (No Contact) or allowed sexual interaction (Contact). Stimulus animal condition was not a primary determinant of partner preference. In contrast, contact condition and hormone treatment modulated preference, as well as activity levels and the display of proceptive behaviors. Our findings demonstrate that the characteristics of the alternative stimulus animals tested here do not play a significant role in modulating partner preference in female rats.     

On the organization of partner preference behavior in female Wistar rats

The possible prenatal organizing effects of testosterone (T) on adult sexual partner preference, i.e., sexual orientation in female rats, were studied through prenatal exposure (days 11-22) of female fetuses to the antiandrogens flutamide (Sch 13521; 4'-nitro-3'-trifluoromethylisobutyranilide; 5 or 10 mg/day; Experiment 1) or anandron [RU 23908; 5,5-dimethyl-3-(4-nitro-3-(trifluoromethyl)phenyl)- 2,4-imidazolidinedione; 35 mg/kg/day; Experiment 2]. The neonatal organizing effects of T were further studied by giving T, dihydrotestosterone (DHT) or oil within 9 h after birth to female pups (Experiment 3). In adulthood sexual orientation was ascertained, after ovariectomy followed by hormone treatment, in an automated open field (AOF), with stimulus animals behind wire mesh, and in a 3-compartment box (3-CB), with stimulus animals tethered. When given the choice between an estrous female and a sexually active male in the AOF, flutamide females, as well as controls, preferred the male partner. After long-term T treatment and 3 weekly pair-tests with an estrous female, flutamide females as well as controls switched their preference to the estrous female partner. In anadron females similar results were obtained. Thus the prenatal antiandrogens had no significant effect on sexual orientation in female rats. This suggests that adult sexual orientation in female rats is not organized prenatally through endogenous T. The change in preference after sexual experience corroborates earlier findings from our laboratory. When given the choice between an estrous female and a sexually active male in the 3-CB (sexual interaction with incentives possible), neonatally DHTP-treated females preferred the male; neonatally TP- or oil-treated females showed no preference.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sexual preference in female rats during estrous cycle, pregnancy and lactation.

Choice of a male or female social contact was studied in intact female rats in a runway-choice apparatus during estrous cycle, pregnancy, and lactation. The male was chosen significantly more often during proestrus/estrus than during the diestrous days of the cycle. During pregnancy this preference in choice declined only to reappear gradually during the lactation period. The shifts in the level of motivation to seek out the male support previous studies and point to the significance of estrogen in producing the preference for the male.     

Effects of neonatal castration and testosterone treatment on sexual partner preference in the ferret

Groups of male and female ferrets were tested in a T maze to determine whether they preferred to approach and interact with a sexually active male or an estrous female. Control male and female ferrets gonadectomized (GX) on postnatal Day 35 and tested in adulthood while receiving no hormone or testosterone (T) displayed no significant preference. When given estradiol benzoate (EB), however, control males preferred stimulus females whereas control females preferred stimulus males. When tested in adulthood with EB treatment, males GX on postnatal Day 5 showed a significant reduction in their approach to stimulus females, although they did not switch their preference to stimulus males and thereby resemble control females. Female ferrets GX on postnatal Day 5 and given a high dosage of T over postnatal Days 5–20 showed a significant reduction in their approach to stimulus males, although they did not switch their preference to stimulus females, and thereby resemble control males. The results suggest that extended perinatal exposure of male ferrets to T is required for the development of a sociosexual preference for females.     

Early olfactory learning is influenced by sex in hamsters but not rats

The odor of cedar shavings repels infant and juvenile rats and hamsters reared in pine shavings when animals are tested in a two-choice situation. Housing male and female infants of either species in cedar shavings for 3 days before testing increases preference for both cedar odor and for a mixture of cedar and conspecific odors. Similar exposure of juvenile male and female rats and male hamsters, has little or no significant impact on odor preferences. However, housing female hamsters in cedar at either developmental stage equally influences odor preferences. The data imply that sex differences influence the development of early odor-guided behavior in hamsters but not rats. These species differences may have adaptive significance in that the birth of a litter produces a greater environmental change demanding a larger preference adjustment of solitary female hamsters than colonial female rats.     

The role of vaginal stimulation for the acquisition of conditioned place preference in female Syrian hamsters

This study investigated the importance of vaginal stimulation on conditioned place preference by sexual behavior in female Syrian hamsters. Hormonally primed female hamsters given vaginal masks and topical lidocaine prior to conditioning sessions were no different in their place preference conditioning compared to female controls with no vaginal mask or lidocaine. Control females not provided a sexually active male did not show any preference for either compartment of the conditioning apparatus. These results suggest that stimuli, in addition to vaginal stimulation, are effective in producing a place preference during the mating experience in female hamsters.     

Neonatal organization of adult partner preference behavior in male rats

Male rats were castrated or sham castrated shortly after birth. Castrated males were then injected every other day on days 0-10 with testosterone propionate (TP, 0.5 mg), dihydrotestosterone propionate (DHTP, 0.5 mg) or the oil vehicle (0.05 ml); sham-castrated males received oil injections. In adulthood, when substituted with DHT, DHT + E2, or T (silastic implants), sexual partner preference was measured in an automated open field (AOF), in which wire mesh prevented sexual interaction with incentives, and in a 3-compartment box (3-CB), in which sexual interaction with tethered incentives was possible. Choices were an estrous female and a nonestrous female or an estrous female and a sexually active male. In adulthood, following long-term treatment with DHT or DHT + E2, the males did not show any partner preference when sexual interaction with incentives was prevented. Following sexual experience with an estrous female these males preferred the estrous over the nonestrous female, although this change could also be due to long-term hormone treatment. In the 3-CB, a clearcut preference emerged for the estrous female over the nonestrous conspecific, although the neonatally DHTP- or oil-treated males scored lower than the neonatally TP-treated or control males. Six weeks after removal of the hormone implants, when tested in the 3-CB (estrous female vs. active male), the males showed no partner preference. Unexpectedly the control males showed a low preference for the active male. Three weeks T-treatment made all males show a preference for the estrous female (in 3-CB).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Female discrimination of male dominance by urine odor cues in hamsters

Female hamsters have been found to differentially respond to the odors of dominant as opposed to subordinate males. This study reexamined these responses in an olfactometer allowing the females to choose between urinary odors obtained from males differing in dominance status and clean air source. The behavior of the estrous females was consistent with previous research which indicated that such females exhibit a preference for stimuli obtained from dominant males. Contrary to previous findings in a two-choice apparatus, diestrous females failed to prefer the odors of subordinates. These females spent significantly more time in the area infused with unscented air. These data emphasize the importance of odor cues as they relate to male attractivity and possibly mate choice. They also underscore the need to allow animals to avoid conspecific odors in order to reduce the possibility of forcing animals into an unrealistic choice situation.     

The effects of sexual experience and estrus on male-seeking motivated behavior in the female rat

Ovariectomized (OVX) female rats were trained to traverse a straight alley and return to a goal box where they had previously encountered a male rat, a female rat or an empty goal box. The time required to run the alley was used as an index of the subjects' motivation to re-engage the goal box target. Subjects were tested in both estrus and non-estrus, first sexually naïve and then again after sexual experience. Female rats ran most quickly for a male target, most slowly for an empty goal box, and at intermediate speeds for a female target. Sexual experience tended to slow run times for all but male targets. Estrus enhanced approach behavior for males and an empty goal box, but tended to slow the approach toward females, both before and after sexual experience. This latter finding was further investigated in a second experiment in which sexually naïve OVX females were tested during estrus and non-estrus in a locomotor activity apparatus, a runway with an empty goal box, and an open field. Estrus produced no changes in spontaneous locomotion either in the activity box or the open field, but decreased run times in the alley and increased the number of center-square entries in the open-field. Thus, estrus produces increases in sexual motivation that selectively enhance exploratory, presumably male-seeking behavior, but not simple spontaneous locomotion.     

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.     

Development of attraction to estrous females in male dogs

In simultaneous choice tests male beagles were allowed to visit a caged female in estrus, or caged, spayed female not in estrus. Males were tested periodically from 1-3 to 22-24 months of age. The 3 subject groups were normal males (Group N), males castrated 4-7 days postpartum and injected with testosterone propionate (TP) until they were 3 months old (Group TPTC), and males castrated 4-7 days but given no hormone treatment, i.e., untreated castrates (Group UC). A statistically reliable preference for visiting the estrous rather than the nonestrous female first appeared in N males at 4-6 months, in TPTC males at 1-3 months, and in UC males at 10-12 months. In N males attraction to the estrous female (measured by time spent visiting her) increased progressively from 4-6 to 16-18 months. In the same period concentration of plasma testosterone rapidly increased, reached a peak at 10-12 months, and then declined. UC males exhibited no significant increase in attraction to the estrous female from 10-12 months (when a preference first appeared) to 22-24 months. They then received 10 injections of TP after which their visiting time to the estrous female was equal to that of N males. TPTC males exhibited a precocious preference for the estrous female at 1-3 months, while they were receiving TP, and there was no decrease in strength of attraction in the following 9 months during which time no hormone was administered. Between 10-12 and 13-15 months, still without exogenous androgen, visiting to the estrous female began to increase and continued to do so until 19-21 months.     

Olfactory, partner preference and Fos expression in the vomeronasal projection pathway of sexually sluggish male rats

Sexually sluggish (S) male rats take a long time to ejaculate or sometimes they don't achieve ejaculation when tested on repeated occasions with receptive females. In order to further understand what factors might contribute to the inconsistent display of sexual behavior in these animals and determine if S and non-copulating males have a different neurobiological profile, the present study was design to characterize sex-related behaviors of S male rats. We tested their preference to physically interact between a sexually receptive female and a sexually active male. We also tested whether S males have a preference to investigate soiled bedding from females in estrous, anestrous or clean bedding. We also evaluated if the serum hormonal levels of testosterone (T) and estradiol (E) are different between copulating (C) and S male rats. Finally, we compared the neuronal activity of the vomeronasal projection pathway of C and S male rats exposed to estrous bedding. The results indicate that S male rats increased the percentage of animals displaying mounts and intromissions after repeated testing with receptive females but no increased was observed in the percentage of animals displaying ejaculations (a total of nine tests were performed). Both C and S males had a clear preference to interact with a sexually receptive female. Both groups showed a clear preference for bedding from estrous females as opposed to anestrous or clean bedding. However, the time investigating the estrous bedding was significantly lower for the S in comparison to C rats. No differences in the serum levels of T and E were found. The structures of the vomeronasal projection pathway were equally activated by estrous bedding in C and S male rats. The results indicate that S male rats do not have hormonal alterations or deficient processing of sexually relevant olfactory cues. Although S males showed a reduced preference for estrous bedding, no changes in preference for a receptive female were observed.     

Homosexual and heterosexual partner preference in ovariectomized female rats: effects of testosterone, estradiol and mating experience

Ovariectomized female rats, longterm treated with estradiol benzoate (EB, 20 micrograms, 3 x/week) or testosterone propionate (TP, 0.4 mg, 3 X/week), were tested for homo- or heterosexual partner preference behavior with either tethered animals (sexually active male vs. estrous female) or animals behind a wire mesh. A preference score was calculated by subtracting the time spent in the vicinity of the stimulus female from the time spent in the vicinity of the stimulus male. Thus, a positive score indicates preference for the male (heterosexual preference), a negative score preference for the female (homosexual preference). Two weeks of EB treatment caused a clearcut preference for the male incentive. This heterosexual preference was significantly different from the indistinct preference of the TP-treated females. Sexual interaction with a freely moving active male (with or without a vaginal mask which prevented intromissions) did not alter the preference for the male of the EB-treated females. It did affect, however, the preference behavior of the TP-treated females significantly: it changed in the direction of the sexually active estrous incentive female, i.e., a homosexual preference. This change in preference could not be attributed to the experience of penile intromissions, it occurred despite the presence of a vaginal mask. Apparently, being mounted by a sexually active male had a negative reinforcing value in the TP-treated female rats and provoked a homosexual partner preference.     

Accessory olfactory neural Fos responses to a conditioned environment are blocked in male mice by vomeronasal organ removal

The ability of an anesthetized estrous female to induce a conditioned place preference (CPP) response was assessed in male mice from which the vomeronasal organ (VNO) had either been removed (VNOx) or left intact (VNOi) in an initial effort to assess the possible contribution of VNO-accessory olfactory inputs to the intrinsically rewarding properties of opposite-sex body odorants. Both VNOi and VNOx male mice acquired a CPP after repeated pairing of an initially non-preferred test chamber with an anesthetized estrous female mouse, suggesting that odorants detected by the main olfactory system and/or visual and tactile cues from the anesthetized estrous female can compensate for absent VNO inputs to establish a CPP. Subsequent exposure to this conditioning chamber alone caused significant increases in the number of Fos-immunoreactive cells in the mitral and granule cell layers of the accessory olfactory bulb as well as in the medial amygdala and ventral tegmental area of VNOi but not of VNOx males. These results suggest that activity in distal segments of the VNO-accessory olfactory pathway, in addition to the mesolimbic dopamine reward system, can be conditioned to respond to non-odor cues.     

Role of urine in coordinating reproduction in a desert rodent (Dipodomys merriami)

Detection of reproductive status from chemical signals in the urine of a desert rodent was examined. Intact and castrated male and estrous (induced) and nonestrous (ovariectomized) female Dipodomys merriami were tested for their preferences for various combinations of water and urine from intact males, estrous females, castrated males, and nonestrous females. Intact and castrated males were also tested for their responses to urine from females at different stages of the reproductive cycle: proestrus, estrus, and diestrus. Neither intact nor castrated males exhibited a preference for urine from females in any stage of the estrous cycle. Urine from intact males, however, was preferred by both intact males and estrous females. Urine from reproductively active males, rather than from estrous females, seems to contain information for coordinating reproduction in D. merriami.     

Mating preference and sexual reinforcement in female rats

Intact female rats chose between sexually active males and inactive males or females in a runway-choice apparatus. In either a discrete choice or continuous choice format, sexually receptive female rats demonstrated a preference for sexually active males over the other two incentive animals. No preference was demonstrated when females were sexually non-receptive. The results demonstrate that, for sexually receptive female rats, copulation can have reinforcing effects distinct from the reinforcing effects of more general social and exploratory factors.     

Individual recognition of female hamsters by males: role of chemical cues and of the olfactory and vomeronasal systems

Sexually satiated male hamsters preferred to investigate and to mount an anesthetized, estrous, novel female over a similarly presented female with which the male had become satiated (the Coolidge effect); likewise, such males preferred a novel female recently mated with another male over the familiar female but showed no preference between fresh and mated novel females. Thus the Coolidge effect is at least partly dependent on discrimination of a new female by chemical cues. Another experiment indicated that transfer of a male's own scent during mating is not involved in discrimination between familiar and novel females. Flank gland secretion of females were sufficient for individual discrimination by males, whereas head region scents and vaginal secretions were not sufficient. The presence of female's flank glands was not, however, necessary for such discrimination. Lesions of or removal of the vomeronasal organ did not disrupt the preferences of sexually satiated males for a novel female, but elimination of main olfactory system function by ZnSO4 treatment of the olfactory mucosa did abolish such preferences. Thus olfactory cues are sufficient for individual discrimination of novel females by sexually satiated male hamsters, and such recognition leads to increased sexual arousal. These processes are mediated by the main olfactory system but not the vomeronasal accessory-olfactory system.