David A. Goldfoot

Sexual behavior in ovariectomized and seasonally anovulatory pony mares (Equus caballus).

Abstract Ten ovariectomized (OVEX) and ten intact, but seasonally anovulatory (ANOV), pony mares were observed for sexual activity with five stallions, using a “harem group” social testing paradigm (two OVEX and two ANOV mares plus one stallion per group) for 15 consecutive daily tests lasting 20 min each. All mares in both conditions showed proceptive behavior in at least one test, all mares but one were mounted, and 14 of 20 mares received ejaculations. No statistical differences were found between the two conditions for any measure of proceptivity, copulatory activity, or days in estrus. The quality of estrus was judged to be equivalent to that displayed by periovulatory mares during their initial and terminal days of estrus, but less intense than that seen near ovulation. Mares in both groups were in estrus during approximately 60–70% of the tests and only 3 of the 20 mares were sexually refractory for more than five consecutive tests. Thus, the typical 2-week phase of sexual refractoriness seen in intact diestrous mares was absent in OVEX and ANOV mares, suggesting that the ovary plays a major role in actively suppressing estrous responses during the luteal phase of the cycle.

Sociosexual behavior and the ovulatory cycle of ponies (Equus caballus) observed in harem groups

Abstract Observations of sociosexual behavior of adult ponies, made on two harem groups (each comprised of one vasectomized male and three females), were correlated with follicular development and ovulation for a total of 15 cycles (minimum of 2 cycles per female). Mean cycle length (interovulatory interval) was found to be 19.7 days, with behavioral estrus lasting 7–8 days (5.5 days preovulatory; 2.3 days postovulatory). Estrous females typically showed increased frequencies of approaching and following the stallion, urinating, presenting, clitoral winking, and tail raising. Approaching and following the stallion appeared earlier and persisted longer than other estrous responses. Deviations from the modal estrous pattern included cycles with subestrus, continual estrus, behavioral estrus in the absence of ovulation, and displays of female mounting. Dominance tests revealed that a mares status was unaffected by the phases of the estrous cycle. The presence of more than one estrous female affected the copulatory performance of both stallions, most notably in reduced latencies to first mount, intromission, and ejaculation, in spite of differences between the stallions in sexual vigor. Each stallion usually selected the dominant mare for copulation when there were multiple estrous females present, but mounts were not displayed exclusively to one female per test. The social testing situation made apparent the importance of use of space in sociosexual communication in this species, particularly in avoidance of the stallion by diestrous mares and standing alone or in proximity to him by estrous mares.

Comparative facilitation and inhibition of lordosis in the guinea pig with progesterone, 5α-pregnane-3,20-dione, or 3α-hydroxy-5α-pregnan-20-one

Abstract The major 5α-reduced metabolites of progesterone tentatively identified in neural tissue of the guinea pig were evaluated in this species for their ability to facilitate and inhibit lordosis responses of spayed females after estradiol benzoate (EB) pretreatment. 5α-Dihydroprogesterone was found to be an effective facilitative agent, but at doses of 0.05-0.3 mg administered at time intervals from 12–60 hr after estradiol, it was not as potent as progesterone. The steroids 3α-hydroxy-5α-pregnan-20-one and 5β-pregnane-3,20-dione, evaluated at only one dose level (0.18 mg) and at one time interval after estradiol (36 hr), were found to have moderate facilitative effects, but they were not as effective as 5α-dihydroprogesterone. The inhibitory influences of the metabolites studied were found to be weak relative to progesterone when given at doses of 0.6 mg 1 hr after EB. However, when 5α-dihydroprogesterone was given at a higher dose (3.6 mg) it was then found to be an effective inhibitor of the lordosis response. The results indicate that this metabolite has behavioral influences similar to those of progesterone for both facilitation and inhibition of estrus. It was suggested that the superior potency of injected progesterone may be due to mechanisms of bioavailability, including relative solubility differences of the two steroids when administered subcutaneously.

Social influences on the display of sexually dimorphic behavior in rhesus monkeys: Isosexual rearing

AbstractGroups containing 5 or 6 infant rhesus monkeys and their mothers were formed when the infants were approximately 3 months old by random assignment from an available pool. There were 33 males and 38 females assigned to groups containing infants of both sexes (heterosexual groups); 15 males and 15 females were assigned to groups containing only infants of the same sex (isosexual groups). The social behavior of subjects in each group was observed and recorded during six 50-day periods from 3 months of age to 31/2years of age. Two sexually dimorphic patterns, mounting and presenting, were recorded for each subject as indices of protosexual (i.e., patterns eventually used in adult mating behavior) development. In addition, rough play, a dimorphic response that is not protosexual, was also recorded. Both males and females in the isosexual condition were characterized by a partial inversion of the manifestation of protosexual behavior. Isosexual males showed statistically less foot-clasp mounting and more presenting than heterosexual males. Conversely, isosexually reared females showed statistically more mounting and less presenting than heterosexual females. The effect of rearing animals in same-sex groups was greater on heterotypical than on homotypical protosexual behavior. Among isosexual males, presenting responses deviated from the heterosexual male standard to a greater extent than did mounting. Among isosexual females, mounting behavior deviated from the heterosexual female standard more than presenting.Results suggested that presenting behavior by males was more easily augmented by isosexual rearing conditions than was mounting by females. At no time during the experiments did isosexual females mount at frequencies or at group proportions that were indistinguishable from those of heterosexually reared males. In contrast, males reared isosexually showed average frequencies of presenting that equaled or exceeded means for females reared heterosexually. While mounting and presenting were both modified by same-sex rearing, rough-and-tumble-play frequencies were not influenced markedly in either sex. However, isosexual males did show statistically higher frequencies of rough play than heterosexual males during the final period of observation (3 to 31/2years of age), and isosexual females showed less rough play than heterosexually reared females during the first year of life. Results support the conclusion that isosexual conditions can have a selective effect on the developmental expression of protosexual responses without altering the probability of display of other sexually dimorphic social behavior. Interpretations are offered within a framework of a biological-social interaction model.

Social Factors Affecting the Development of Mounting Behavior in Male Rhesus Monkeys

In primates as well as in other mammalian species, the development of normal sexual behavior in the male depends upon adequate social experience (Nissen, 1954; Valenstein et al., 1955, Mason, 1960; Gerall, 1963; Harlow et al., 1966; Evans, 1967; Beach, 1968; Gruendel and Arnold, 1969; Davenport and Rogers, 1970; Riesen, 1971). In such nonprimate mammals as rats, guinea pigs, and dogs, the effects of early social deprivation on the later expression of sexual behavior seem to be less profound and less permanent than in primates (Kagan and Beach, 1953; Valenstein and Goy, 1957; Zimbardo, 1958; Beach, 1968). These effects are often transitory and can be eliminated with repeated opportunities for sexual and social experience at advanced ages. In male rhesus monkeys, by contrast, deprivation of early social experience has led to long-lasting and probably permanent inadequacies in sexual behavior (Senko, 1966; Missakian, 1969).

Dexamethasone suppression of sexual behavior in the ovariectomized mare

Abstract The influence of steroids of adrenal cortical origin on estrous behavior in the ovariectomized mare was evaluated by adrenal suppression via dexamethasone (DEX) administration in two experiments. In Experiment I, 12 mares (six DEX, six control) were tested for sexual behavior in harem groups (two DEX and two control mares plus one stallion per group) for 9 consecutive days. In Experiment II, estradiol (E 2 ) was given to a group of DEX-treated mares as an additional control. Twelve mares (four DEX, four DEX + E 2 , and four control) were tested in harem groups (one DEX, one DEX + E 2 , and one control mare plus one stallion per group) for 10 days. All DEX mares showed a clear suppression of sexual response compared to control or DEX + E 2 mares, indicating that the estrous behavior seen in ovariectomized mares may be due to steroids from the adrenal cortex. The control and DEX + E 2 mares were similar in all measures of proceptivity. Despite being more receptive, as indicated by fewer negative responses, the DEX + E 2 mares received fewer intromissions and ejaculations than did the control animals. The ability of estradiol to induce estrous behavior in the dexamethasone-suppressed mare notwithstanding, other adrenal steroids, e.g., androgens, may be involved in estrous behavior in the untreated, ovariectomized mare.

The effect of estradiol and progesterone on the sexual behavior of ovariectomized mares.

Daily treatment (5 days) with estradiol resulted in increased levels (p less than 0.05) of proceptive behavior in ovariectomized as compared to control mares (N = 8 per treatment) within 4 hr of injection and for the 4 subsequent days. Ejaculations occurred more often (p less than 0.05) in estrogen-treated mares on days 2-5, but the number of precopulatory investigations by the stallions was not altered. Progesterone treatment resulted in an absence of sexual behavior except in one mare on Day 1. Control mares exhibited varying levels of sexual interest. The concurrent administration of estradiol and progesterone produced a biphasic effect on proximity-related behaviors. Proximity behaviors were initially (Day 1) greater and subsequently less in the group treated with both hormones than in the group treated with estradiol alone. Injections of free estradiol resulted in a shorter latency to effect for two measures of proceptivity than did injections of estradiol benzoate. A dose response test for progesterone showed no effect with 0, 1, or 10 mg, but 100 mg was inhibitory (p less than 0.05). These results demonstrated that within 4 hr estradiol stimulated, while progesterone inhibited estrous behavior in ovariectomized mares and that concurrent administration of estradiol and progesterone produced a biphasic effect, first enhancing, then suppressing some aspects of the estrous response. The relatively short latency to action of all treatments and the biphasic effect of concurrent estradiol and progesterone may be attributable to low level, endogenous hormones.

Continued copulation in ovariectomized adrenal-suppressed stumptail macaques (Macaca arctoides)

Abstract Female stumptail macaques continue to copulate at moderate to high levels for years after gonadectomy. This study examined the extent to which sexual behavior of ovariectomized stumptail females was maintained by steroids of adrenal origin, and second, considered the possibility that ovarian fragments might have been left in situ following surgery. Daily injections of 0.1 mg of dexamethasone sodium phosphate suppressed serum cortisol, estradiol, and testosterone by at least 85% in three of four ovariectomized females, but dihydrotestosterone was suppressed by only 50 to 70%. The fourth female showed maximal suppression of cortisol but maintained much higher levels of the other steroids, in particular estradiol, and therefore it was strongly suspected that this animal had an ovarian fragment. Within the limits to which sex steroids were depressed with dexamethasone, no correlation was found between steroid levels and sexual performance. Ejaculatory frequencies and measures of attractivity, proceptivity, and receptivity collected during heterosexual pair tests remained unaffected in all four females during 4 weeks of dexamethasone treatment. Thus it was concluded that the maintenance of copulatory activity after ovariectomy in this species was largely due to nonsteroidal mechanisms.

Assessment of the sexual behavior of pregnant mares

Pregnant mares (N = 12) were observed with a stallion from early gestation until parturition for sexual behavior. Observations were conducted for 20 min per day for 5 days each month from September until July. No mares exhibited full estrus and no intromissions or ejaculations occurred at any time during the study. Social interactions such as male approach and female/female mutual grooming occurred with greater mean frequency or duration in some months of spring and fall than in winter months. (P less than 0.05). None of the recorded behaviors differed by month of gestation. In a comparison of the behavior of diestrous and pregnant mares in harem groups, no estrous behavior occurred and no differences in social interactions were found. Although progesterone may be sufficient to cause the absence of sexual behavior in diestrous mares, another estrous-inhibiting substance may be present during pregnancy at times of high estrogen and low progesterone.

Pentobarbital inhibition of progesterone-induced behavioral estrus in ovariectomized guinea pigs.

Administration of pentobarbital inhibits the facilitatory effects of progesterone on the release of gonadotropins. In this experiment facilitatory effects of progesterone on lordosis behavior in guinea pigs were examined with pentobarbital anesthesia. Two major animal groups were subjects: one was short-term ovariectomized (2 weeks) and the other was long-term ovariectomized (several months). All animals received estradiol benzoate (6.6 mug s.c.) followed by progesterone (0.4 mg s.c.) 40 h later. Lordosis behavior was induced by the manual stimulation method of Young et al.29 Sodium pentobarbital (30 mg/kg) was injected 8,4 or 2 h before, simultaneously or 1, 2, 6, or 7 h after progesterone. Animals which received pentobarbital slept for 4.5-5 h with subsequent drowsiness for an additional 0.5-1 h. Pentobarbital injections given 8 h before progesterone had no effect on latency to the first lordosis or on other parameters of estrous behavior. However, pentobarbital delayed the onset of heat in estrogen treated ovariectomized guinea pigs when given 4 h before, 2 h before, or simultaneously with progesterone. The delay was directly related to the length of time the animals remained asleep after the progesterone injection, since estrous behavior was invariably displayed with the latency of controls after the animal awoke. Moreover, in animals which were awake for 1-2 h immediately after the progesterone injection before receiving pentobarbital, the latency of recovery from anesthesia to the first display of lordosis was about 1-1.5 h shorter than in the other pentobarbital groups. In contrast to the latency effects of pentobarbital, the duration of heat was unaffected by the anesthetic for all groups mentioned. In animals which received pentobarbital after they were already in heat, pentobarbital injection terminated heat and abolished it completely, since lordosis behavior was not displayed in the hours after recovery from anesthesia. Gross hypothalamic uptake of progesterone was not influenced by pentobarbital administration. Thus, it is tentatively concluded that an incubation period is necessary for progesterone to mediate the display of estrous behavior in the guinea pig in addition to the time necessary for neural uptake. The way in which pentobarbital interferes with the period of progesterone incubation is not currently known.