Hysterectomy facilitates proceptive behavior in rats

The effects of hysterectomy on proceptive behavior were investigated using several doses of estradiol benzoate (EB) and progesterone (P) in female rats. One week after surgery, ovariectomized (OV) and ovariectomized-hysterectomized (OH) rats were given three daily injections of 1.0 or 2.0 micrograms EB followed by 0.5 mg P or oil on the fourth day and were tested for solicitation 4 hr later. The same animals received 1.0 or 2.0 micrograms EB plus 0.1 mg P, or 4.0 micrograms EB plus oil on the same schedule a week following the first test and were tested again. Ovariectomized-hysterectomized animals receiving 0.5 mg P, regardless of the EB dose, showed significantly higher solicitation scores than OV animals, but the scores of the EB-primed OV and OH rats receiving 0.1 mg P or oil vehicle did not differ.     

The effects of estrogen and progesterone on female rat proceptive behavior

The relative importance of estrogen (EB) and progesterone (P) in stimulating proceptivity in ovariectomized female rats was studied. Proceptive behavior was measured quantitatively, providing a clear measure of response to experimental manipulation. When rats were tested biweekly after daily treatment with 0.4 μg/100 g body wt EB for 4 days, they showed maximal lordosis but low levels of proceptive behavior by the second test. Additional EB (3.0 μg/100 g body wt daily) failed to stimulate additional proceptivity. A graded increase in proceptive behavior resulted from administration of increasing doses of P (50, 100, 500 μg and 1.0 mg) to animals receiving EB priming as described above. The level of “soliciting” was significantly higher than EB-only-treated rats when 500 μg or 1.0 mg P was given. Ovariectomized, adrenalectomized rats, primed with 2.5 μg/100 g body wt EB daily for 7 days and tested on Day 8, were significantly less proceptive than ovariectomized, sham-adrenalectomized rats with the same hormone treatment. Four hours after injection of 1.0 mg P, there was no difference in proceptive or receptive behavior between sham- and adrenalectomized rats. It was concluded that if an EB dose is sufficient to induce maximal receptivity, additional estrogen does not stimulate proceptivity; unlike previous studies, the present data are not consistent with a global effect of ovarian steroids on both components of female behavior. Progesterone is more effective than estrogen in stimulating proceptive behavior, although proceptivity is not absolutely dependent on progesterone for expression. Proceptivity in EB-only-treated rats appears to be facilitated by adrenal P.     

Non-intromissive mating stimuli are sufficient to enhance sexual behaviors in ovariectomized female rats

When ovariectomized/adrenalectomized female rats, injected with subthreshold doses of estradiol are given copulatory stimulation by a male rat at half hour intervals, the level of lordosis gradually increases over the course of a few hours. We tested the hypothesis that paracopulatory behaviors (behaviors that occur repetitively prior to and between mounts), also generally considered to be heavily dependent on progesterone, are enhanced by this stimulation as well. We have reported previously that the enhancement of copulatory behavior is dependent to a large extent on intromissive stimulation by the male. In the present study, mating stimulation induced high levels of paracopulatory behaviors, as well as lordosis. Surprisingly, though, and in contrast to previous findings, this increase was seen not only in rats receiving intromissive stimulation, but in those receiving non-intromissive stimulation as well. Furthermore, intromissive stimulation induced high levels of rejection behavior. In a subsequent experiment, experimenter-induced, mechanical stimulation increased only rejection behaviors, not copulatory behavior. The results collectively demonstrate that, under the conditions used in these experiments, non-intromissive stimulation is sufficient for inducing both copulatory and paracopulatory behaviors in estradiol-primed rats. However, under the conditions used in these studies, intromissive stimulation increases rejection behaviors.     

Effects of naloxone and naltrexone on receptive and proceptive behaviors in female rats.

The sexual receptive and proceptive behaviors induced by opiate antagonists, naloxone and naltrexone in estrogen-primed ovariectomized rats were observed under the presence of sexually active males. The females were treated intraperitoneally with naloxone or naltrexone at doses ranging from 0.5 to 4.0 mg/kg and the sexual behavior of females was tested before and after the injection of drug. The results obtained suggest that the opiate antagonists play a role in the regulation of lordosis behavior, but not proceptive behavior in female rats.     

Neonatal hormonal influences on the development of proceptive and receptive feminine sexual behavior in rats

The objective of this study was to examine the influence of androgen and of the inhibiting of aromatization of androgen to estrogen during the early neonatal period on the development of receptive (lordosis and acceptance of stimulus male mounting attempts) and proceptive (affiliation with and solicitation of stimulus males) feminine sexual behavior. Within 8 hr of birth, male rats were castrated or received subcutaneous implants of the aromatase inhibitor androst-1,4,6-triene-3, 17-dione (ATD) while females received injections of testosterone propionate (TP). At 90 days of age all treated animals and controls were tested for receptive and proceptive feminine sexual behavior. It was found that androgen present neonatally blocked proceptive as well as receptive behavior patterns in adult rats. The proceptive and receptive feminine sexual behavior patterns displayed by adult males deprived of the effects of androgen neonatally either by castration or by treatment with ATD were comparable to those of normal females.     

Receptive behavior in developing female rats

In a series of experiments the development of sexual behavior was studied in female rats. Lordosis behavior in response to manual stimulation was induced in 100% of 19-day old females by treatment with 10 μgm estradiol benzoate (EB) and 0.5 mgm progesterone (P) and earwiggling was displayed at earlier ages. During normal development, vaginal opening preceded the display of the first receptivity in most cases, the first two behavioral sex cycles tended to be prolonged and irregular, but the subsequent cycles were of regular 4 or 5 days duration. Although treatment of immature (18-, 23- or 28-day old) females with EB (10 μgm) and P (0.5 mgm) or with EB (0.025, 0.25 or 2.5 μgm until vaginal opening occurred) resulted in precocious vaginal opening and display of sexual receptivity, the treatment did not advance the development of behavioral cyclicity. Progesterone [0.25 mgm/100 gm body weight (bw)] facilitated the display of sexual receptivity in EB-primed (0.5 or 2.5 μgm/100 gm bw) ovariectomized immature and adult female rats. Evidence was presented that behavioral sensitivity to estrogen increases with age.     

Effects of progesterone implants in the habenula and midbrain on proceptive and receptive behavior in the female rat

Two brain areas behaviorally responsive to progesterone (P) were examined to determine their possible involvement in the control of rat preceptive behavior, i.e., solicitation behavior directed at the male. Progesterone implants were placed in the habenular nuclei and the interpeduncular nucleus-ventral tegmental area of the midbrain reticular formation (MRF). Different testing procedures and levels of priming with estradiol benzoate (EB) were used in order to distinguish the effects of P in either region on proceptive and receptive behavior during exposure to 10 mounts by stimulus males. To test for receptivity, sexually experienced 60-day-old ovariectomized (ovx) rats bearing stereotaxically placed guide cannulas extending to the habenula or MRF were given 10 μg EB subcutaneously. Forty-eight hours later, lordosis quotient (LQ) was determined. Immediately following this test, each animal was implanted with cholesterol (C) or P and was retested 2 hr later. Treatments for the proceptivity test were similar except that the animals received 2.5 μg EB/100 g body wt sc for 7 days before testing on the eighth day; LQ as well as hopping, darting, and ear wiggling were scored. In the receptivity test, P implantation in both the medial portions of the habenula and the MRF significantly increased lordosis above the levels found both in their preimplantation tests and following control implantation of C. Little proceptivity was observed. In the proceptivity test, P implants in both regions also significantly increased proceptive behavior above both types of control tests. All animals were highly receptive, and there was no difference in LQ among the groups. There was no increase of plasma P levels in similarly implanted animals during a 24-hr monitoring period, indicating that systemic leakage of the hormone was not responsible for the observed behavior. The data indicate that both the habenula and MRF are P-sensitive regions. Progesterone's action on the two areas facilitates expression of both proceptive and receptive components of female sexual behavior, indicating that the neural regulation of the two kinds of behavior is integrated at these levels.     

Dose-response and time-response relationships between progesterone and the display of patterns of receptive and proceptive behavior in the female rat

The relationship between administration of progesterone and the display of patterns of receptive (response to the male) and preceptive (female initiated) sexual behavior was examined in ovariectomized, estrogen-primed female rats in a “restrained male” test situation. It was found that the degree of receptivity and proceptivity displayed was directly proportional to progesterone dose and time from progesterone injection (up to 4.5 hr). Higher progesterone doses and longer period of time from progesterone injection (up to 4.5 hr) were both associated with shorter latencies to return to the male following intromission and ejaculation. Receptivity could be induced with estrogen alone but progesterone was required for the display of proceptivity and higher doses of progesterone were needed to effect increases in proceptivity relative to receptivity. Proceptive behavior also occurred in a narrower time range than did receptive behavior. Receptivity alone is characterized as the lowest degree, and receptivity plus proceptivity as the highest degree, of expression of the total behavior pattern of the estrous female rat. Receptivity and proceptivity together constitute a continuum of estrous responsiveness. Increasing the progesterone dose from 0 to 200 μg, and increasing the latency from progesterone injection from 0 to 4.5 hr, were associated with increasing degree of expression of the total behavioral continuum.     

Proceptive behavior of female rhesus monkeys during tests with tethered males

Proceptive behavior of female rhesus monkeys during follicular and luteal phases of the ovarian cycle was examined in laboratory tests with a tethered male partner. Cyclical changes in proceptive behavior were observed. In tests during the follicular phase of their cycles, females on the average approached and solicited the male at a higher rate, spent more time sitting within proximity of him, and less time at a maximum distance away from him than during tests in the luteal phase of their cycles. Additionally, in the follicular phase of their cycles, females exhibited an increase in proceptivity following the male's ejaculation. This latter finding was discussed in light of other observations demonstrating that male rhesus monkeys are capable of multiple ejaculations. When females were paired with a tethered, ovariectomized female as a partner, rather than an adult male, none of the cyclical changes in proceptive and sexual behavior were observed.     

Fitness effects of female mate choice: preferred males are detrimental for Drosophila melanogaster females

The evolution of female mate choice, broadly defined to include any female behaviour or morphology which biases matings towards certain male phenotypes, is traditionally thought to result from direct or indirect benefits which females acquire when mating with preferred males. In contrast, new models have shown that female mate choice can be generated by sexual conflict, where preferred males may cause a fitness depression in females. Several studies have shown that female Drosophila melanogaster bias matings towards large males. Here, we use male size as a proxy for male attractiveness and test how female fitness is affected by reproducing with large or small males, under two different male densities. Females housed with large males had reduced lifespan and aged at an accelerated rate compared with females housed with small males, and increased male density depressed female fitness further. These fitness differences were due to effects on several different fitness components. Female fitness covaried negatively with male courtship rate, which suggests a cost of courtship. Mating rate increased with male size, whereas female fitness peaked at an intermediate mating rate. Our results suggest that female mate choice in D. melanogaster is, at least in part, a by-product of sexual conflict over the mating rate.     

Accumbens lesion in female rats increases mount rejection without modifying lordosis

Ovariectomized Wistar rats received bilateral electrolytic (n = 24) or sham (n = 11) lesion of the nucleus accumbens. Following priming with estradiol benzoate (25 micrograms/rat) and progesterone (0.5 mg/rat) they were tested for sexual behavior with a stud male. Tests were carried out once prior to operation and twice postoperatively. Both lordosis and rejection behaviors as responses to male mount attempts were evaluated for each session. Proceptive patterns (hopping, darting and presenting) were also recorded. Females with accumbens lesion did not differ from control animals either with regard to lordosis or to soliciting behaviors. On the contrary, the lesioned group showed a statistically significant increase in rejection behavior in both postoperative sessions (p less than 0.05 and p less than 0.002). In conclusion, nucleus accumbens lesion dissociated the normal correlation between lordosis and rejection responses to male mount attempts without affecting soliciting behaviors. This finding is thought to be related to the hyperreactivity produced by nucleus accumbens lesion.     

Endogenous cholecystokinin's satiating action increases during estrus in female rats.

Food intake and meal size are reduced in female Long-Evans rats during estrus. To investigate the contribution of the satiating action of endogenous cholecystokinin (CCK) to this, rats were injected with 1 mg/kg of the potent, selective CCK(A) receptor antagonist, devazepide, during diestrus, when meal size is maximal, and during estrus, when it is minimal. Devazepide increased spontaneous food intake and meal size during estrus, but not during diestrus. Meal frequency was not affected by devazepide treatment. These results indicate that the potency of the CCK satiety-signaling system increases during estrus.     

Estradiol increases salt intake in female normotensive and hypertensive rats.

The objective of this study was to examine whether or not estradiol (E2) alters sodium intake in hypertensive and normotensive female rats. It was hypothesized that higher doses of E2 would increase sodium consumption and that this response would be greater in spontaneously hypertensive rats (SHR) compared with Wistar Kyoto (WKY) rats. The study involved female SHR and WKY (n = 12/group). All animals were ovariectomized. Six of twelve rats from each strain received three progressively larger doses of beta-estradiol propionate (each dose lasting 2 wk), whereas the other six rats from each strain received sham implants. Blood E2 levels were measured by radioimmunoassay after each 2-wk period, allowing a 10-day washout period before the next E2 dose. Rats had access to 0.0, 0.5, 1.0, and 1.5% NaCl solutions to drink throughout the experiment. There was a significant positive correlation between sodium intake and plasma E2 (r = 0.8, P < 0.001). Both strains avoided the 1.5% NaCl, and the increased sodium intake was achieved by an increase in consumption of the 0.5% NaCl. SHR females consumed more sodium than WKY females, which is similar to what has been observed in males of these strains. In conclusion, E2 was positively correlated with sodium intake in both strains of rat, with the hypertensive rats consuming more sodium than the normotensive rats.     

Evolution of female preference for younger males

Previous theoretical work has suggested that females should prefer to mate with older males, as older males should have higher fitness than the average fitness of the cohort into which they were born. However, studies in humans and model organisms have shown that as males age, they accumulate deleterious mutations in their germ-line at an ever-increasing rate, thereby reducing the quality of genes passed on to the next generation. Thus, older males may produce relatively poor-quality offspring. To better understand how male age influences female mate preference and offspring quality, we used a genetic algorithm model to study the effect of age-related increases in male genetic load on female mate preference. When we incorporate age-related increases in mutation load in males into our model, we find that females evolve a preference for younger males. Females in this model could determine a male's age, but not his inherited genotype nor his mutation load. Nevertheless, females evolved age-preferences that led them to mate with males that had low mutation loads, but showed no preference for males with respect to their somatic quality. These results suggest that germ-line quality, rather than somatic quality, should be the focus of female preference in good genes models.     

Smelling chemosensory signals of males in anxious versus nonanxious condition increases state anxiety of female subjects

The hypothesis of this experiment was that humans in an anxious state compared with a nonanxious state are able to increase anxiety levels in other humans via their body odors. Specifically, we hypothesized that male chemosensory anxiety signals compared with neutral chemosignals increase state anxiety of female subjects. Thirteen male subjects participated in 2 different sweat donation sessions: chemosignals were collected during participation in a high rope course (anxiety condition) and in an ergometer workout (neutral condition). State and trait anxiety were evaluated in 20 female odor recipients using Spielberger's state-trait anxiety inventory in a double-blind design. Comparison of state anxiety of odor donors between control and anxiety condition differed significantly indicating that our model of anxiety induction successfully led to the expected change in emotion. Comparison of state anxiety of odor recipients showed a trend toward higher state anxiety in the anxiety condition compared with the neutral condition after 5 min of odor exposure. After 20 min of odor exposure, state anxiety of female subjects was significantly higher during the perception of sweat collected during the anxiety condition in comparison with the perception of sweat collected during the neutral condition. This experiment gives evidence that male anxiety chemosignals compared with neutral chemosignals are capable of inducing an increased state anxiety in female subjects.     

Delayed development of aggressive behavior in castrate isolated male mice

Male mice were castrated at 21–22 days of age. Intact and castrated mice were isolated to induce aggressive behavior. The incidence of fighting between paired nonisolated and isolated mice was measured at 3, 6, 12, and 23 weeks to determine the effect of time of isolation on aggressive behavior. After 3 weeks isolation, 90% of the intact isolated mice fought, but none of the castrate isolated mice fought. Aggressive behavior equivalent to that of intact isolated mice developed in the castrate mice after 23 weeks of isolation. These results suggest that the presence of gonadal androgen is important in expediting the onset of aggressive behavior in isolated mice, but its absence does not preclude its eventual development.