Clitoral stimulation induces conditioned place preference and Fos activation in the rat

The present study examined the ability of clitoral stimulation (CLS) to induce conditioned place preference (CPP) and Fos protein in the brain. Ovariectomized, hormone-primed Long-Evans rats were randomly assigned to receive either distributed CLS (1 stimulation every 5 s for 1 min prior to being placed in one distinctive side of a nonbiased CPP box for 2 min, after which the cycle of stimulation and CPP exposure were repeated for 4 more cycles, totaling 60 stimulations) or continuous CLS (1 stimulation per second for 1 min with 2 min in one side of the CPP box, repeated for 4 more cycles, totaling 300 stimulations). Two days later, females were placed into the other side of the CPP box without prior stimulation. CPP was tested after 5 sequential exposures each of CLS and no stimulation. Females given distributed stimulation developed a significant CPP whereas females given continuous stimulation did not. CLS induced Fos in hypothalamic and limbic structures, including the nucleus accumbens, piriform cortex, arcuate nucleus, and dorsomedial portion of the ventromedial hypothalamus, compared to no stimulation. However, distributed CLS induced more Fos in the medial preoptic area than continuous CLS or no stimulation. In contrast, continuous CLS induced more Fos in the posteroventral medial amygdala compared to no stimulation. These data indicate that CLS induces a reward state in the rat and a pattern of Fos activation in regions of the brain that process genitosensory input, incentive salience, and reward.     

Vaginocervical stimulation induces Fos in glutamate neurons in the ventromedial hypothalamus: Attenuation by estrogen and progesterone

Vaginocervical stimulation (VCS) induces the immediate-early gene product Fos in the ventromedial hypothalamus (VMH) of female rats. However, this induction is lower in ovariectomized rats that receive estradiol benzoate (EB) and progesterone (P) relative to an oil vehicle. We have observed that a substantial proportion of cells activated in the VMH by VCS stain for glutamate, and infusions of glutamate or its selective receptor agonists to the VMH inhibit both appetitive and consummatory sexual behaviors in females. This raises the possibility that VCS activates an inhibitory glutamate system in the VMH, and that ovarian steroids blunt the activation, although it is not known whether EB or P, alone or in combination, lead to this effect. The present experiment examined the ability of VCS to induce Fos in glutamate neurons in the VMH of ovariectomized rats under 4 hormonal regimens: oil, EB alone, P alone, or EB + P, following 1 or 50 distributed VCSs administered with a lubricated glass rod over the course of 1 h. Treatment with EB or P alone significantly reduced the number of glutamate neurons activated by 1 VCS, with P being more effective than EB. Treatment with EB + P also produced a significant reduction, but not to the extent of EB or P alone. Although EB and P work in synergy to activate sexual behavior in female rats, actions of EB or P alone are sufficient to blunt the ability of VCS to activate glutamate neurons in the VMH. It thus appears that ovarian steroids may “disinhibit” sexual responding, in part, by dampening the ability of VCS to activate glutamate neurons in the VMH. In turn, this may allow females to receive a sufficient number of intromissions for the activation of sexual reward and the facilitation of pregnancy.     

Estrogen treatment during development alters adult partner preference and reproductive behavior in female laboratory rats

There is broad acceptance for the idea that during development estradiol ‘organizes’ many aspects of reproductive behavior including partner preferences in the laboratory rat. With respect to partner preference, this idea is drawn from studies where estrogen action was in someway blocked, either through aromatase or estrogen receptor inhibition, during development in male rats. The lack of estrogens neonatally results in a decrease in the male rat's preference for females. In this study, the effect of early postnatal estradiol treatment on the partner preferences of female rats was examined as a further test of the hypothesis that male-typical partner preference is dependent upon early exposure to estrogens. Our principal finding was that increased postnatal estradiol exposure during development affected partner preference in the expected direction, and this effect was seen under several adult hormonal and behavioral testing conditions. Female rats that received exogenous estradiol during development spent more time with an estrous female and less time with a sexually active male than did cholesterol treated females. The estradiol treatment also disrupted normal female sexual behavior, receptivity, and proceptivity.     

Sex-specific effects of gonadal steroids on conspecific odor preference in the rat

Effects of gonadal steroids on conspecific odor preference for either (1) sexually active male or active female, (2) sexually active or gonadectomized (gdx) males, (3) sexually active or gdx females, and (4) gdx males or gdx females were determined in male and female rats in a three-chamber apparatus. For the first test, gdx females were made sexually active by treatments with estradiol benzoate (EB) and progesterone (P), and sexually active males were selected by prior screening. Sexually active males and females preferred opposite-sex odor over same-sex odor. Odor of sexually active opposite-sex conspecifics was preferred over that of inactive ones. Immediately after the completion of the first test, sexually active males were gdx and females were left without hormonal treatment. Second and third tests were carried out 2 and 5 weeks after the first test. In the second test, gdx males preferred odor of sexually active males rather than that of receptive females (male-directed preference); in the third test, both males and females showed no preference when tested with four stimulus pairs. The final tests were carried out in gdx males with EB and P, and gdx females with 2-week exposure to testosterone (T). Males with EB and P showed a male-directed preference again, whereas T-treated females kept their own female preference. Injection of EB alone to gdx males did not induce any preference. The present study clearly demonstrated sex difference in conspecific odor preference. Although both male and female preferences depend on their circulating sex steroids, the direction of male preference is more susceptible to their hormonal states, compared to that of females.     

Female preference of the gobiid fish Eviota abax in relation to elongation of the first dorsal spine in males

The significance of elongation of the first and second spines of the first dorsal fin in male Eviota abax (Gobiidae) was examined in relation to female preference. Reproductive behavior occurred in three phases: male approach to female home, male leading female to nest, and male entering nest. During each phase, the female either accompanied the male or departed. The ratio of positive female mating responses to males before the elongated male dorsal spines were clipped and thereafter was compared in an aquarium. Females preferred male elongated spines in the first phase of courtship, but not in the second phase . Because females may be more exposed to predators during the second phase, owing to conspicuous male courtship, their greater receptivity to elongated dorsal spines in the first phase may decrease predation pressures during subsequent phases of courtship. Electronic Publication     

Effects of testosterone in the VMN on copulation,partner preference,and vocalizations in male rats

The present study tested whether testosterone propionate (TP) implanted in the ventromedial nucleus (VMN) of the hypothalamus could initiate performance, motivational, or sociosexual components of sexual behavior in castrated male rats. Twenty-seven intact male Long Evans rats were pretested for copulation, partner preference, and 50-kHz vocalization and were subsequently castrated. Approximately 3 weeks after castration, males were retested to confirm that these behaviors had declined, and groups were assigned. Groups 1 and 2 were implanted with bilateral stainless steel cannulae directed at the VMN that were either filled with TP (TVMN group) or remained empty (Blank group). A third group (TSC) was implanted subcutaneously with two 10-mm Silastic capsules filled with testosterone. Restoration of behavior was measured for 2 weeks after implants. We found that copulation and 50-kHz vocalization were not restored by TP in the VMN alone. However, partner preference returned to preoperative levels in both the TVMN and TSC groups, indicating that TP in the VMN was sufficient to restore sexual motivation. Following behavioral testing, prostate glands and seminal vesicles were weighed and confirmed that TP did not leak into the periphery in the TVMN group. Immunostaining for androgen receptors also verified that TP spread was confined to the immediate area surrounding the cannula tip. These results suggest that androgen activation at the VMN is sufficient to induce the motivational components of male sexual behavior, whereas activation of other brain sites is required for copulation and ultrasonic vocalization.     

Artificial vaginocervical stimulation induces a conditioned place preference in female rats

Female rats express a conditioned place preference (CPP) for a context paired with mating. During a mating encounter, the female rat is exposed to several different types of stimuli, including, but not limited to, vaginocervical stimulation and social contact. The present experiment tested the hypothesis that two components of the mating interaction, vaginocervical stimulation or social contact, each induce a CPP in female rats. During conditioning rats received nonpaced mating, artificial vaginocervical stimulation, social interaction or a control treatment. Rats expressed a CPP for the context paired with nonpaced mating or artificial vaginocervical stimulation whereas social interaction and the control treatment did not induce a CPP. The present findings highlight the important role that vaginocervical stimulation plays in the reinforcing effects of mating in female rats.     

Time spent close to a sexual partner as a measure of female mate preference in a sex-role-reversed population of the blenny<Emphasis Type="Italic"> Salaria pavo</Emphasis> (Risso) (Pisces: Blenniidae)

In most species females do not exhibit conspicuous sexual behaviours and female mate preferences are often measured by means of the time spent close to males. In spite of its widespread use, in only a few studies has this measure been validated as a reliable indicator of female mate preference. Sex-role-reversed species offer a better opportunity to test female preferences, as females usually court males. We tested in a sex-role-reversed population of the blenny Salaria pavo (Risso) if the time spent by females close to males related to the number of courtship displays directed towards males, and whether these measures of female preference reliably predicted matings. Females were simultaneously presented with two males behind a glass partition and the time spent close to each male was measured. We then allowed females to have access to the males' compartments and measured the courtship behaviours performed by females towards each male and recorded with which of the males females spawned. Females spent more time close to the male that subsequently received more courtship displays, and the preferred male had a more developed head crest. However, both measures of female preference failed to predict matings. Females were often attacked by males and probably had, in some occasions, to spawn with the less preferred male. Females that spawned with the previously preferred male had more swollen bellies than females that spawned with the less preferred male, suggesting a male preference towards more ripe females. These results validate the use of "time spent close to a sexual partner" as a measure of female preference in S. pavo. We argue that matings may not always reliably indicate mate preferences, particularly in the less choosy sex.Communicated by R. Serrão Santos     

Hormonal and experiential control of female-male mounting in the female rat

Mounting behavior in the female rat has been studied extensively in same-sex interactions, but not in the heterosexual dyad. The present study examined the display of female mounting of castrated noncopulating male rats (FMM). Ovariectomized (OVX) sexually naive female rats (N = 80) were given either estrogen (E) + progesterone (P), E + oil (O), P + O, or O + O treatment for five tests with castrated male rats. FMMs were observed in both the E + P and E + O females. The influence of the ovarian cycle on FMM was also investigated. Vaginal smears from sexually naive females (N = 16) were taken daily for 12 days immediately after testing with castrated males. FMM frequency was greatest during Proestrus. Finally, OVX females (N = 30) treated with E + P were given either 0, 1, 10 multi-ejaculatory heterosexual experiences with intact, sexually experienced males, prior to tests with intact, copulating or castrated, noncopulating males for five tests. Sexually naive females displayed a greater number of mounts relative to the sexually experienced females when tested with castrated, noncopulating males. In contrast, very few FMMs were observed in females of any group tested with intact, copulating males. These data suggest that FMM occurs naturally in rats as a "super-solicitational" behavior that is modified by hormone treatment and prior heterosexual experience.     

Tactile contact is required for early estrogen treatment to alter the sexual partner preference of female zebra finches

Sex steroid actions during early development appear to play a role in the development of sex differences in sexual partner preference (SPP, preference for males vs. females) in several species of mammals and in the socially monogamous pair bonding zebra finch (Taeniopygia guttata). Female finches treated with estrogen as nestlings exhibit varying degrees of masculinized SPP as adults, but only if they have been housed in all-female groups during the juvenile and young adult period, suggesting that the estrogen effect may involve social experience and possibly sexual imprinting. Because tactile contact is important for consolidation of imprinted preferences in this species, it was predicted that early estrogen treatment would alter preferences of females only if they were allowed to have tactile contact with other females. Subjects were injected with estradiol benzoate or with oil (normal controls) daily for the first 2 weeks post-hatching. At age 45 days, they were housed in a mixed sex aviary (normal controls), in an all-female aviary allowing tactile contact (group EB-TC), or in an all-female aviary with no tactile contact (group EB-NTC). At 100+ days, birds were given two-choice SPP tests followed by aviary tests of SPP. EB-TC females did not show the sex-typical preference for male stimuli, and differed significantly from the controls on several measures. EB-NTC females preferred males and never differed significantly from controls. These results show that tactile contact after age 45 days is essential for an EB effect on SPP, supporting the hypothesis that hormones and sexual imprinting together contribute to SPP.     

Chemistry of clitoral gland secretions of the laboratory rat: Assessment of behavioural response to identified compounds

The present investigations were carried out to find out the chemical nature of clitoral gland extracts and their involvement in reproductive and social behaviour. Homogenates of clitoral glands of mature estrous female rats were extracted with n-hexane and dichloromethane (1:1 ratio v/v) and analysed by gas chromatography linked mass spectrometry (GC-MS). Three peaks were found to be in higher concentration, which were identified as 6,11-dihydro-dibenz-b,e-oxepin-11-one (I); 2,6,10-dodecatrien-1-ol-3,7,11-trimethyl(Z) (II); and 1,2-benzene-dicarboxylic acid butyl(2-ethylpropyl) ester (III). Odour preference tests demonstrated that the first compound attracted conspecifics of the opposite sex. By contrast, the second and third compounds were found to attract both sexes. The results conclude that the clitoral gland of laboratory rat contains three major chemical compounds which have a unique function in maintaining social and reproductive status.     

Prolonged morphine administration alters protein expression in the rat myocardium

Background  

Morphine is used in clinical practice as a highly effective painkiller as well as the drug of choice for treatment of certain heart diseases. However, there is lack of information about its effect on protein expression in the heart. Therefore, here we aimed to identify the presumed alterations in rat myocardial protein levels after prolonged morphine treatment.     

Behavioral effects of progesterone on pair bonding and partner preference in the female zebra finch (Taeniopygia guttata)

Progesterone is a sex steroid known to be involved in reproduction, but its role in pair relationships is not well understood. This study explored the effects of exogenous progesterone (P4) on courtship and pairing behaviors in female zebra finches (Taeniopygia guttata) in two separate experiments: the first focused on courtship and initial pair formation and the second examined the effects on pair maintenance. In these experiments, we tested the hypothesis that P4 increases pairing behaviors and consequently influences their partner preference. In Experiment 1, animals engaged in significantly more pairing behaviors when they were treated with P4 than when they received the vehicle. However, this effect was not partner-specific, since the association index (a marker for female partner preference) did not differ between treatment conditions. In Experiment 2, females were given two weeks to form a pair and then injected with P4 or vehicle. Pairs were observed that day and the subsequent day to determine if P4 caused a decrease in mate-directed behavior and an increase in extra pair behavior. P4 did not affect the quality of the pair relationship and did not increase extra pair behavior. These results suggest that P4 influences the overall quantity of initial pairing behaviors and may slightly increase the likelihood of partner preference formation over short time courses. However, P4 does not alter a previously established bond, suggesting there are likely separate mechanisms for initial pairing behaviors and pair maintenance.     

Effects of neonatal testosterone treatment on pacing behaviors and development of a conditioned place preference

Two experiments assessed the effects of neonatal testosterone treatment on paced mating behavior and conditioned place preference in female rats. In both experiments, females received s.c. injections of 5.0 microg testosterone propionate or oil vehicle at three days postpartum. As adults, females were ovariectomized and given s.c. injections of 10 microg estradiol benzoate and 500 microg progesterone, 48 and 4 h before mating, respectively. In Experiment 1, TP- and Oil-treated females exhibited similar high levels of lordosis responsiveness, but TP-treated females showed increased intervals between mounts and between intromissions in paced and non-paced mating conditions compared to control females. The effect was particularly pronounced during paced mating, when contact return latencies were increased approximately 2-fold by TP treatment. TP-treated females showed exaggerated pacing behavior, showing significantly greater return latencies after intromissions than Oil-treated females. In Experiment 2, TP- and Oil-treated groups were tested in a conditioned place preference paradigm to determine if the behavioral changes observed in Experiment 1 were in part a result of changes in the perceived reward produced by paced mating. TP treated and control females developed equivalent preferences for places associated with paced but not non-paced mating, indicating that neonatal TP treatment at this dosage does not disrupt or enhance the conditioned place preference induced by paced mating. The results of the two experiments demonstrate that neonatal TP treatment alters the display of pacing behavior but not the reward state induced by paced mating, and suggest that TP affects neural substrates involved in performance of paced mating without effects on those controlling lordosis or place preference conditioning.     

Anomeric preference of glucose utilization in rat erythrocytes

The -anomer of glucose relative to the -anomer was more rapidly metabolized into lactate by rat erythrocytes at 37° C (/ ratio = ca. 1.3): the amounts of - and -D-glucose metabolized into lactate during 3 min were 0.21 and 0.27 mol/gHb, respectively. Also, the transport of -D-glucose into erythrocytes was more rapid than that of -D-glucose: the amounts of - and -D-glucose transported into erythrocytes during 3 min were approximately 3.5 and 5.0 mol/gHb, respectively. Glucose phosphorylation by rat erythrocyte hexokinase (i.e., a possible rate-limiting step in glycolysis) occurred at higher velocities with the -anomer than with the a-anomer (/ ratio = 1.28). The Km value of hexokinase for either anomer of glucose was 53 M. The glucose concentrations in erythrocytes incubated with - and -D-glucose reached about 1 mM in 1 min, indicating that hexokinase is almost completely saturated with glucose within less than 1 min. The results suggest that glucose phosphorylation and glucose transport are major and minor determinants, respectively, for the anomeric preference of glucose utilization in rat erythrocytes.     

The relative importance of orange spot coloration and total length of males in female guppy mate preference

Female mate choice by multiple male traits is an important current topic in animal behavior. However, the relative importance among the multiple cues in female choice is not explored in most cases. Female guppies Poecilia reticulata use both the color saturation of orange spots and the total length of males as mate choice criteria. In the present study, we used digitally modified video playbacks to examine the relative importance of these two male traits to female mate preferences. We initially examined the effective difference in the color saturation of orange spots as well as that in total length between two stimulus male images. Females only showed a strong preference for a bright male image (compared to the dull image) when the difference in color saturation was large (91% versus 25%). Conversely, females only exhibited a preference for larger size when they were presented a choice between two relatively small male images (total length 26.0 mm versus 23.0 mm). When two male images in which both the two traits were modified were presented to females, they prioritized male images possessing higher color saturation of orange spots, indicating the color saturation of male orange spots to be a more important factor than the total length in their mate choice. The color saturation of orange spots may convey more reliable information about the males to the females than their total lengths. These findings imply that females may rank multiple male criteria depending on relative benefits or costs derived from their mate choice based on each criterion.     

Sexual behavior of female rats in a multiple-partner preference test

In this study, sexually experienced female rats were tested in a multiple-partner preference test (MPPT) in which they were allowed to pace their sexual contacts with four sexually active males. Four cylinders, with a small hole through which only the female could move freely from one cylinder to another, were assembled forming in the center an empty compartment. An intact female was placed in the central compartment and a sexually active male in each cylinder. Female sexual behavior was analyzed throughout the estrus cycle in four consecutive days. Each daily test lasted 15 min. The percentage of exits after intromission or ejaculation was significantly higher than the percentage of exits after each mount. The female spent significantly longer time with one of the males. We designated this male as the preferred male (PM). Although in each of the 4 days studied, females spent significantly longer time with the PM, however, the male selected was not the same throughout the estrus cycle. The number of entries into the compartment of the PM was significantly higher and increased around proestrus. Compared to previous studies, pacing behavior was notably lower in the conditions of the MPPT. No significant differences were observed during the estrous cycle concerning the other parameters recorded. The present results suggest that the MPPT could be a good model to study partner preference in the female rat.     

Female mate preference based on male orange spot patterns in the feral guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis> in Japan

It is known that females prefer males with larger and/or brighter orange spots in many populations of the guppy Poecilia reticulata. However, female preference for male orange spots varies among populations and changes within several years when they are introduced into new habitats with different environment. Guppies were introduced into Okinawa, Japan, more than 20 years ago and were subjected to natural and sexual selection for a long period. The female preference for orange spot patterns of males was examined by the dichotomous choice experiment for a feral guppy population of the Hiji River, Okinawa. We chose full-sibling males as a pair of stimulus males that were simultaneously presented to a test female, because sibling males should resemble each other. To create different orange spot patterns between stimulus males, one male of the stimulus male pair was fed carotenoid-supplement food such as algae and another male was fed low-carotenoid food. High-carotenoid-treatment males showed not only brighter coloration of orange spots but also larger spots than other males as a result of this dietary-manipulation. In the dichotomous choice experiment, females preferred the high-carotenoid-treatment males. In addition, logistic regression analysis clarified that brighter coloration of male orange spots was the most important factor for female mate preference. This finding suggests indirect benefits of female preference for male orange spot patterns if the male foraging ability for algae were heritable.