Heterosexual interactions of pairs of laboratory-housed stumptail macaques (Macaca arctoides) under continuous observation with closed-circuit video recording

Female-male interaction of heterosexual pairs of stumptail macaques, housed together continuously, was studied 24 hr per day using closed-circuit video recording. Two pairs were studied for approximately 2 months each. Although no generalizations can be made from such a small sample, no aspect of behavioral interaction varied significantly with the stage of the menstrual cycle of the female partner. Copulation occurred regularly but only during the daylight hours. Both pairs showed several peak ejaculation days (5-21 ejaculations/day), which were distributed throughout the entire menstrual cycle. In general, the highest number of ejaculations was observed to occur when the animals were put together either for the first time or following a separation of a few days. In one pair the female became pregnant, and from the fifth week of pregnancy onward there was a gradual increase in male aggression, coinciding with a decrease in male sexual and grooming behavior. In a second study eight different pairs were observed during the first day together and male copulatory behavior was studied. Two patterns of copulatory behavior could be discerned: pairs displaying a high number of ejaculations (19-38) and pairs displaying a low number of ejaculations (4-8). With regard to the interejaculatory interval (IEI), the male stumptail appeared to be unique. In contrast to what has been reported for other mammals, i.e., a steady increase in IEI with subsequent ejaculations, the stumptail showed increasing IEIs only during the first three to four, as well as between the last, ejaculations; in between, the IEI remained relatively constant. The maximum number of consecutive ejaculations observed was 38, displayed during a 10-hr time period (mean (± SEM)IEI, 12.9 ± 3.5 min)

Sexual maturation in the female rat

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Model of antral follicle dynamics during the 5-day cycle in rats based on measurement of antral follicle inflow

Antral follicles were counted in ovaries from young adult Wistar rats, collected on the 5 days of the ovarian cycle. Follicles were classified as healthy, early atretic or late atretic and divided into five volume classes. From these data, a model was developed in which the inflow of healthy follicles into the various size classes was quantified. This model describes the follicle dynamics during a normal 5-day cycle. It was concluded that the stage of early atresia takes between 20 and 24 h. The inflow of follicles into the antral stage (volume ≥ 100 x 105 μm3) was continuous but not constant. The highest inflow was found during pro-oestrus and oestrus, at about the time of the first and second FSH surge. The total inflow during each cycle was about 120 follicles of which only 10% ovulated. These ovulating follicles were recruited during the previous pro-oestrus and oestrus. Follicle selection took place in volume classes I and ≥ (volume 100-350 x 105 μm3) during oestrus and dioestrus 1. At dioestrus 2, the follicles that will ovulate have been selected and can be recognized on the basis of their bigger size

Short- and long-term effects of an LHRH antagonist given during the prepubertal period on follicle dynamics in the rat

The effects of the suppression of the high gonadotrophin concentrations normally present by the end of the second week of life on ovarian follicle dynamics were studied in immature rats. Gonadotrophins were suppressed by treatment with an LHRH antagonist (LHRH-A; Org. 30276) on days 6, 9, 12 and 15, and the total population of ovarian follicles was studied at 15 and 28 days, on the day of first oestrus and on the day of oestrus at or following 90 and 300 days of age. Primordial follicles were counted and growing follicles were counted and measured. In rats treated with LHRH-A, follicle recruitment into the growing pool was clearly diminished; the number of growing follicles was significantly (P < 0.01) lower up to the day of first oestrus and the pool of primordial follicles was significantly (P < 0.05) larger at 15 and 28 days. Ovarian weights were significantly lower in rats treated with LHRH-A until at least 90 days of age. However, on the day of oestrus at or after 90 and 300 days of age, there were no differences in either the pool of primordial follicles or the pool of growing follicles between rats treated with LHRH-A and control rats. There was also no difference between groups in the number of fresh corpora lutea at these ages. It was concluded that the early peak in gonadotrophin concentrations in immature rats causes substantial recruitment of follicles into the growing pool. Thus, the number of follicles entering the growing pool is not solely dependent upon the size of the pool of primordial follicles but is clearly influenced by the level of circulating gonadotrophins. In contrast, the large gonadotrophic stimulation that normally takes place during the second and third week of life is neither a prerequisite for functional sexual maturation nor for later cyclic function. Shortly before the time of first ovulation a tight control of follicle dynamics is established which is largely independent of previous gonadotrophin concentrations and follicle dynamics

Prepubertal reduction of the ovarian follicle population by combined LH-releasing hormone antagonist treatment and unilateral ovariectomy influences follicle characteristics but not the ovulation rate at first oestrus

The effect on first ovulation of the massive reduction of the total pool of ovarian follicles during the infantile and late juvenile period was studied in rats. Treatment with an LH-releasing hormone antagonist (LHRH-A) during infancy (5 mg/kg body weight on days 6, 9, 12 and 15 of life) was combined with unilateral ovariectomy performed on either day 15 (early ULO) or 2-5 days before the expected day of first ovulation (late ULO). Rats were killed on the day of first or second oestrus, when blood was collected and the (remaining) ovaries were prepared for differential counting of follicles and corpora lutea. In addition, blood was sampled 8 h after ULO and the ovaries studied histologically in the group of rats which were unilaterally ovariectomized 2-5 days before first ovulation. The time of first ovulation was not influenced by treatment with LHRH-A, early or late ULO, or a combination of LHRH-A treatment and ULO. Ovulation rate after LHRH-A treatment was decreased, but was still within the normal range in intact rats and in early ULO rats compared with saline-treated controls. Serum FSH concentrations 8 h after ULO performed 2-5 days before first ovulation were similar in saline- and LHRH-A-treated rats (845 ± 59 and 801 ± 99 (S.E.M.) μg/l respectively) and had increased compared with intact controls (216 ± 15 μg/l). Treatment with LHRH-A resulted in a reduction of more than 50% in healthy and atretic follicles, and late ULO reduced the number of healthy follicles even further. In saline-treated rats late ULO decreased the rate of atresia, but in LHRH-A-treated rats atresia was not reduced further by (late or early) ULO. It is concluded that even after massive reduction of the pool of ovarian follicles by early LHRH-A treatment combined with late or early ULO, the timing of the first ovulation was normal and ovulation rates, although somewhat lower in some LHRH-A-treated rats, were within the normal range

Effects of a luteinizing hormone-releasing hormone antagonist in late-juvenile female rats: Blockade of follicle growth and delay of first ovulation following suppression of gonadotropin concentrations

Subcutaneous injections of an antagonist against luteinizing hormone-releasing hormone (LHRH-A, Org. 30276) were administered to late-juvenile female rats. The effects on timing of vaginal opening and first ovulation on serum gonadotropin concentrations and on follicle growth were studied. The dose of 100 μg LHRH-A/100 g body wt, given on Days 28, 31, and 34, did not influence timing of first ovulation. After administration of 500 μg LHRH-A/100 g body wt, ovulation was retarded by 4.7 days if injections were given on Days 28 and 31; by 6.7 days if given on Days 28, 31, and 34; and by 11.5 days if given on Days 28, 31, 34, and 37. Serum LH and FSH concentrations 3 days after the first, second, and third injections of 500 μg LHRH-A were significantly (p < 0.01) lower than in saline-treated controls. Ovarian follicle counts showed decreased numbers of (antral) Class 2, 3, and 4 follicles 3 days after injection of 500 μg LHRH-A/100 g body wt on Day 28; a significantly higher number of Class 1 follicles and a further decrease in Class 2, 3, and 4 follicles 3 days after the second LHRH-A injection; and total absence of Class 3, 4, and 5 follicles 3 days after the third LHRH-A injection. Six days after the third LHRH-A injection, Class 3 and 4 follicles reappeared in the ovaries. A single, low-dose injection of LHRH-A administered at 0900 h on the day of first proestrus blocked first ovulation in 3 of 11 rats given 2.5 μg and in all (8/8 and 12/12) rats given 5 and 10 μg; ovulation was not blocked with 1 μg LHRH-A (0/6 rats) or saline (0/8 rats). It was concluded that administration of LHRH-A to late-juvenile female rats may delay sexual maturation by a decrease in gonadotropin levels, causing arrest of follicle growth at an early antral stage. The dose of LHRH-A needed for acute inhibition of the first ovulatory gonadotropin surge is only a fraction of that causing chronically lowered gonadotropin levels and subsequent blockade of follicle growth

Inhibin increases in the ovaries of female rats approaching first ovulation: Relationships with follicle growth and serum FSH concentrations

In order to relate various prepubertal events in a group of 95 late prepubertal female rats, the following data were obtained during the last 10 days before the day of first ovulation: (1) amounts of ovarian inhibin-like activity (ILA) in some animals (n = 47); (2) size and numbers of healthy (antral) follicles with a volume ≥ 100 x 105 μm3 (or diameter ≥ 260 μm) present per ovary in their litter-mates (n = 48); (3) serum FSH concentrations in both groups. Rats were unilaterally ovariectomized to obtain an ovary for either estimation of ILA content or for histological procedures and counting of follicles. At the time of unilateral ovariectomy they were bled to obtain serum for estimation of FSH concentrations. Rats were kept until the day after the day of first ovulation to determine the time-interval between the day of unilateral ovariectomy and first ovulation. They were studied between 10 and 1 days (days -10 to -1, maturational age) before first ovulation. In addition, adult cyclic rats were bilaterally ovariectomized on different days of the oestrous cycle for estimation of ovarian ILA content. The amount of ovarian ILA was estimated in steroid-free ovarian cytosols using an in-vitro bioassay system with dispersed anterior pituitary cells and subsequent measurement of FSH and LH in the spent medium. The amount of ovarian ILA was about 83 units/ovary from days -10 to -5, and subsequently increased (P < 0.005) to reach a maximum on day -1, the day of pro-oestrus (213 units/ovary). Inhibin-like activity in adult rat ovaries at pro-oestrus amounted to 374 units/ovary. A significant relationship was found between ovarian ILA content and total volume of follicles of classes III-V (≥ 350 x 105 μm3) (r = 0.9683, P < 0.005) except for the period between days -7 and -5 when this volume increased earlier than did the ILA content. The total volume of all follicles ≥ 100 x 105 μm3 was steady from days -10 to -7. On day -6 this volume increased, mainly as a result of an increase of total volume of class II follicles. Thereafter, the total volume of follicles in classes III-V started to increase and was maximal on day -1, while the total volume of follicles in classes I plus II decreased and reached a minimum on day -1. The serum FSH concentration declined between days -10 and -1 from 400 to 100 μg/l (P < 0.001); the presence of follicles of classes III-V was always associated with FSH concentrations ≤200 μg/l (P < 0.005). The presence of class I and II follicles was not related to FSH concentrations. This suggested that mainly follicles of classes III-V contribute to ovarian ILA. The present data show that in immature rats ovarian ILA content increases towards the day of first pro-estrus, as it does later during pro-oestrus in adult cyclic rats. Inhibin-like activity seems to be produced mainly by follicles of classes III-V which are present in the ovaries during the last 5 days preceding first ovulation. In this time same period FSH concentrations are kept within narrow limits (<200 μg/l) as is the case during the adult cycle. Thus, ILA probably plays a role in the fine regulation of FSH secretion

Changes in serum concentration and ovarian content of5α-androstane-3α,17β-diol in the female rat approaching firstovulation

Concentrations of 5α-androstane-3α, 17β-diol (3α-diol) in serum were estimated in rats bled once during a 10-day period preceding first ovulation; ovarian contents of 3α-diol were estimated over the same period. Serum values of 3α-diol, measured at 1100 h, showed a significant decrease towards first ovulation; there was good correlation between mean serum and ovarian concentrations. In 33-day-old rats no significant difference was found in serum concentrations measured at either 1100 or 1500 h. However at first proestrus, significantly elevated serum and ovarian concentrations of 3α-diol were found between 1400 and 2100 h as compared to those at 1100 h. A similar pattern was seen on the afternoon of second proestrus. On the days following first ovulation, serum and ovarian concentrations of 3α-diol were comparable to those during the days preceding this ovulation. The prepubertal decrease in 3α-diol production is discussed in relation to concomitant changes in secretion of estradiol and luteinizing hormone. It is concluded that, in view of the preovulatory resynthesis of considerable amounts of 3α-diol, it is inappropriate to view loss of biosynthetic capacity for 3α-diol as a key event in the onset of puberty