Biomedical subjects

R D Lisk

Publications and source records attributed to R D Lisk.

At least 37 records · Page 2Linked to original sources

PubMed1987

Offspring sex ratio in hamsters is correlated with vaginal pH at certain times of mating.

Golden hamsters (Mesocricetus auratus) are sexually receptive for 19-21 h around the time of ovulation. Vaginal pH was measured immediately before mating in four groups of animals each mated at a different time during the female's receptive period. Litter size and sex ratio (percentage male offspring) were recorded at parturition. Mean litter size decreased while offspring sex ratio increased in matings occurring later in estrus. Significant negative correlations were found between vaginal pH and sex ratio of subsequent litters when matings occurred during midestrus. Fluctuations in vaginal pH may differentially affect longevity, motility, or fertilizing capacity of X and Y sperm and/or may reflect other physiological changes in the female which occur over the receptive period. Such a prefertilization mechanism for sex ratio regulation could be highly adaptive since little or no parental reproductive potential is lost.

Acid-Base Equilibrium↗

PubMed1987

Localization of hypothalamic sites for the estrogen-priming of sexual receptivity in female hamsters.

Ovariectomized female hamsters received small unilateral implants of estradiol at a variety of anterior-posterior levels of the medial preoptic area and hypothalamus. The results of an initial experiment using 27-ga. implants showed that females with estradiol implants in the ventromedial hypothalamus (VMN) or nearby anterior hypothalamus consistently showed higher levels of sexual receptivity than did females with implants farther rostral, in the preoptic area, or farther caudal, in the posterior hypothalamus. A second experiment used smaller, 28-ga. implants to compare directly the two areas at which implants were effective in the first experiment. The results confirm the findings of other recent studies of hamsters and rats by identifying the VMN as the most effective hypothalamic site for the estrogen priming of sexual receptivity.

Animals↗

PubMed1987

Food-restricting first generation juvenile female hamsters (Mesocricetus auratus) affects sex ratio and growth of third generation offspring.

Female hamsters (Generation 1) were fed ad libitum or were food-restricted to 65-75% of the amount consumed by controls during their first 50 days of life. Subjects were mated at 91 days of age. Their offspring (Generation 2) were fed ad libitum throughout the experiment, and female offspring were also mated at 91 days of age. Generation 3 litters were monitored every fifth day from birth until Day 25 post partum for litter size, sex ratio, and pup weights. Although there were no significant differences in Generation 3 litter sizes at birth, litters descended from food-restricted Generation 1 females (Group R) were significantly smaller on Days 5-25 than litters descended from control Generation 1 females (Group A). Sex ratios remained significantly greater in Group A than in Group R litters from birth to Day 25 but did not vary over time, suggesting similar post-partum mortality rates for both male and female pups. Weights of Generation 3 male and female pups did not vary significantly within treatments at any time. Group A males weighed significantly more than Group R males from birth through Day 25, but weights of Group A and Group R females were always similar. Food restriction early in life may have long-term consequences on sex ratios of subsequent generations in hamsters.

Animals↗

PubMed1987

Cyclic Djungarian hamsters, Phodopus campbelli, lack the progesterone surge normally associated with ovulation and behavioral receptivity.

Serum levels of 17 beta-estradiol and progesterone were assayed at 4- to 5-h intervals across the estrous cycle in female Djungarian hamsters, Phodopus campbelli. The pattern of secretion for estradiol is similar to that described for the rat and the Syrian hamster, rising slowly from a baseline of 54 +/- 2 pg/ml during the morning of estrus to a peak of 187 +/- 16 pg/ml in the early afternoon of proestrus, then falling rapidly back to baseline levels. The pattern of progesterone secretion is significantly different from that of any estrous cycle previously described for a 4-day cyclic mammal. There is no evidence for a significant peak in serum progesterone levels associated with ovulation and receptivity. The highest levels of serum progesterone occur during the early afternoon of diestrous day 2 (8046 +/- 1063 pg/ml). The lowest levels of serum progesterone occur in the early morning of proestrus (720 +/- 125 pg/ml). During the period of sexual receptivity only 2504 +/- 654 pg/ml progesterone are found in the serum. Ovariectomized females show behavioral receptivity after 48 h of treatment with 50 micrograms estradiol benzoate/kg BW in sesame oil. Progesterone is not necessary for receptivity and will not facilitate receptivity when administered in conjunction with a subthreshold dose of estrogen. The presence of tubular ova confirms the time of ovulation to be a period of approximately 7 h between 2200 h on proestrus and 0500 h on estrus. Histological examination of ovarian sections from each of the 4 days of the estrous cycle shows follicular development to differ from that in the Syrian hamster in that the total number of follicles in the ovary is variable and low, and the ovulated follicles (new corpora lutea) are blood filled. Djungarian hamster primary follicles averaged 83 +/- 2 microns in diameter, and preovulatory follicles averaged 455 +/- 17 microns in diameter. The total number of intact follicles per ovary rose from 21 +/- 5 on the evening of estrus to 73 +/- 29 on the evening of diestrous day 2, then fell to 32 +/- 26 by the evening of proestrus. Preovulatory follicles increased in number from 1.0 +/- 0.6/ovary early on estrus to a maximum of 4 +/- 1 on the evening of diestrous day 2. However, at ovulation a combined total of only 5.1 +/- 0.8 ova are shed.

Animals↗

PubMed1987

Influence of pre- and post-copulatory pair contact on pregnancy success in Djungarian hamsters, Phodopus campbelli.

Females housed with their mates for 3 or 4 days before mating took place (i.e. early in the oestrous cycle at the time of introduction to the mate) were significantly more likely to litter than were females housed with their mates for only 1 or 2 days before mating. The duration of post-copulatory pair contact had a complex effect on pregnancy success. While only 41% of females littered when they had 24 h of post-copulatory pair contact, females exposed to either longer or shorter durations of post-copulatory pair contact littered at significantly higher rates. Exposure to a strange male 24-48 h after mating did not produce a strange-male induced pregnancy block. The critical parameter responsible for the decrease in the number of females littering was the absence of the mate, irrespective of the presence or absence of a strange male. If this pattern of pregnancy block is adaptive for females, it seems probable that females in the wild require substantial levels of paternal investment by their mates.

Animals↗

PubMed1987

Male-female interactions across the female estrous cycle: a comparison of two species of dwarf hamster (Phodopus campbelli and Phodopus sungorus).

Recent studies in our laboratory have suggested that monogamy may be the preferred mating system in the Djungarian hamster (Phodopus campbelli), whereas the available evidence for the closely related Siberian hamster (P. sungorus) does not show the same pattern. Here we examine the behavior of male-female dyads of both species interacting during 1-hr tests in large, familiar habitats containing defensible nest boxes, food, and water. Levels of aggression within pairs were low, compared with those seen during brief intrasexual encounters, whereas affiliative behaviors, such as sniffs, were high. P. campbelli scent marked more than twice as frequently as P. sungorus. Females of both species scent marked at a constant rate irrespective of their location in the habitat, whereas males scent marked at a higher rate in the female's home area. Two major features of the copulatory pattern differed between the two species: (a) The duration of the ejaculatory lock was five times longer in P. sungorus than in P. campbelli. (b) Both species had approximately the same number of mounts in each ejaculatory series, but the intromission/mount ratio was significantly higher in P. sungorus.

Agonistic Behavior↗

PubMed1986

Androgen and estradiol levels in plasma and amniotic fluid of late gestational male and female hamsters: uterine position effects.

Using radioimmunoassay we have measured the plasma and amniotic fluid levels of androgen and estradiol in male and female hamster fetuses nearing parturition. On Days 14 and 15 of gestation (day of birth = Day 16), plasma levels of androgen are higher in males than females while estradiol levels are equal. Amniotic fluid levels of these hormones, while lower than plasma, reflect the difference in androgen and the similarity in estradiol between sexes. Uterine position analysis on Day 14 suggests that female siblings located caudally suppress amniotic fluid androgen and elevate estradiol levels of male siblings. Comparison of Day 18 gestation male and female rat amniotic fluid androgen to Day 14 hamsters reveals that male rats are bathed in high levels of androgen. Female rats have lower levels which are not different from those of male hamsters. Female hamsters are exposed to little androgen. Relevance to behavioral sexual differentiation and the display of adult behavior is discussed.

Amniotic Fluid↗

PubMed1986

Facilitation of lordosis by estradiol in the mesencephalic central gray.

Ovariectomized female hamsters received unilateral implants of estradiol aimed at the mesencephalic central gray (MCG). Postoperative levels of lordosis and ultrasonic vocalization were used to evaluate implant effects on sexual receptivity and proceptivity. Females with large MCG implants showed higher levels of receptivity than females with similar implants at control sites. In addition, females with small MCG implants showed little receptivity while the implant served as the sole source of estrogen, but diverged from controls by showing elevated receptivity during supplemental treatment with low systemic doses of estradiol. These results suggest that estradiol implants in the MCG facilitate receptivity if, and only if, accompanied by exposure of other brain areas to low estrogen levels. In turn, this suggests that the MCG, though not a self-sufficient site for the hormonal priming of lordosis, does modulate sexual motivation by mediating facilitatory effects of estrogen on receptivity and mating.

Animals↗

PubMed1986

Mating-induced inhibition of receptivity in the female golden hamster. I. Short-term and long-term effects.

Female golden hamsters (Mesocricetus auratus) which have actively terminated mating with one male will respond in succession to two or more novel males. However, mating with the first male results in a reduction in receptivity shown toward a second male, with the size of the decrease being proportional to the amount of copulatory stimuli provided by the first male. Furthermore, the decreased receptivity shown toward the second male results in his achieving fewer ejaculations. These effects are more pronounced when the second mating occurs 5 min or 8 h after the first mating than when it occurs 1 or 4 h later, suggesting both short-term and long-term inhibitory effects. Copulation with a single male also effects a 40% shortening of behavioral receptivity. In a promiscuous species such as the hamster, prolonged copulation by the male may enhance the short-term inhibition of female receptivity, thereby reducing the risk of subsequent sperm displacement. The long-term effect occurs too late to affect sperm competition and may, instead, function to reduce the risk of predation as a result of unnecessary further mating.

Animals↗

PubMed1986

Food restricting young hamsters (Mesocricetus auratus) affects sex ratio and growth of subsequent offspring.

Trivers and Willard (1973) predicted that stressed adult female mammals may enhance their fitness by skewing offspring sex ratios and maternal investment to favor daughters. The present study investigated whether stressing young hamsters might also influence sex ratio and growth of subsequent offspring. Control females received food ad libitum (A) on Days 1-50 postpartum (AA). Experimental females were food-restricted (R) either on Days 1-25 (RA), Days 26-50 (AR), or Days 1-50 (RR) postpartum. Subjects were mated when 91-95 days old. Litter sizes and survivorship (= % litters within a treatment that contained at least one pup), sex ratio (= % males), and pup weights in the next generation were recorded every fifth day from parturition until Day 25 postpartum. Control litters contained significantly more offspring at birth than did RR litters. Sex ratio was significantly higher at birth for AA litters than for the other treatments. Postpartum sex ratio within each group remained similar to that recorded at birth. RR litters contained significantly fewer pups compared to the other three treatments from Days 5-25. RR female pups weighed significantly more at birth than their counterparts in the other treatments. Weights of males at birth were similar in all treatments. By Day 25, both male and female RR pups weighed significantly less than control, AR, and RA pups. Food restriction early in life may have long-term consequences on sex ratio and pup growth in golden hamsters.

Animals↗

PubMed1986

Intracranial sites regulating the biphasic action of progesterone in estrogen-primed golden hamsters.

Diencephalic and mesencephalic neural sites regulating the biphasic effect of progesterone (P) were investigated using the hormone implantation technique in ovariectomized female golden hamsters primed with estrogen. Double barreled cannulae were implanted unilaterally and bilaterally in the medial preoptic area, anterior hypothalamus, ventromedial hypothalamus (VMH), central gray, or interpeduncular nucleus. Testing was conducted using a sequential paradigm; facilitation tests commenced after 44 h of estrogen priming. P-filled cannulae placed in the VMH region facilitated lordosis behavior in 42% and 60% of unilaterally and bilaterally implanted females, respectively. In the anterior hypothalamus, only P implants adjacent to the VMH area effectively promoted receptivity. Lordosis behavior was also observed in 20-36% of females with P implants in the medial preoptic area. P implants in central gray and interpeduncular nucleus regions had no significant facilitating effect on sexual behavior. Tests for inhibition occurred 24 h after facilitation testing and consisted of a pretest, followed by systemic P administration and a behavioral test 4-5 h later. During the pretest for inhibition, females that were receptive in the facilitation test attacked males more rapidly than previously nonreceptive animals and showed decrements in lordosis scores after systemic P delivery. This biphasic effect of P completely inhibited receptivity among several animals in the VMH group. Additional experiments, however, investigating the biphasic effect of P implants in the VMH suggested that the occurrence of copulation in the facilitation test may have been involved in mediating the subsequent increase in aggressive behavior and the suppression of sexual responsiveness in the inhibition test. Nevertheless, a final experiment showed that when P was implanted sequentially in the VMH, facilitation and, more importantly, a later reduction in lordosis behavioral scores occurred even when copulation was eliminated in the facilitation test. P implants in mesencephalic regions exerted no significant inhibitory effect on receptivity. These findings demonstrate that the biphasic action of P in the female hamster is regulated by nerve cells located in the diencephalon, especially in the VMH region.

Animals↗

PubMed1986

Stimulus requirements for pregnancy initiation in the golden hamster (Mesocricetus auratus) change with time of mating during the receptive period.

When maintained under a 14L:10D photoperiod, the duration of behavioural receptivity in female golden hamsters was about 18-21 h depending on age and/or parity. The effectiveness of mating stimuli in initiating pregnancy was shown to be a function of when in the receptive period (early, middle, late) that mating occurred. During the 9-h period before ovulation, 5 ejaculatory series were sufficient to produce a nearly 100% pregnancy rate and maximum litter size. During the ovulation period, however, high pregnancy rates were achieved only when mating continued to satiety (12-15 ejaculatory series plus 10-24 long intromissions). Late in the receptive period even mating to satiety failed to result in a pregnancy. In general, pregnancy rates were significantly higher for young virgin than for older multiparous females when mating occurred during or after the ovulation period. The reduced fecundity of females mating during or after ovulation was due to insufficient vaginocervical stimulation to induce functional luteal activity and not to lack of spermatozoa. Females mating late in the receptive period did not show a cessation of oestrous cycles which characteristically follows the induction of a luteal phase. Greater amounts of vaginocervical stimulation during this time increased the number of females which delivered litters but had no significant effect on litter size. These results suggest that levels of male copulatory behaviour considered 'excessive' when mating occurs early in the receptive period are essential for pregnancy initiation when mating occurs later.

Animals↗

PubMed1985

Dual estradiol action in diencephalon and the regulation of sociosexual behavior in female golden hamsters.

Previously, we found that single implants of estradiol (E2) placed in the ventromedial hypothalamus (VMH) but not the anterior hypothalamus (AH) facilitated precopulatory, i.e. vaginal scent marking, and copulatory, i.e. lordosis, behavior following progesterone administration. However, the duration of lordosis was markedly attenuated in comparison to the duration shown by intact cycling females. This study was designed to examine whether dual implantation of E2 in the diencephalon would facilitate patterns of precopulatory and copulatory behaviors similar to those shown by intact cycling females. One E2 implant was placed in either the medial preoptic area (MPO) or AH and a second E2 implant was placed in the VMH. Control females were tested following E2 application at only the MPO or AH region in conjunction with a cholesterol implant in the VMH. An additional control group was tested with females implanted with cholesterol at both MPO-AH regions and the VMH. During a 2-day postimplantation test period, vaginal marking scores were elevated for both single and dual E2 implanted females and agonistic response patterns toward males declined significantly. In addition, a significant inverse relationship was found between the number of vaginal marks and bites exhibited by females with single E2 implants in the MPO, whereas these two response patterns were positively correlated in females with E2 stimulation occurring only in the AH region. No significant relationship was found between vaginal marking and biting attack for females receiving dual E2 stimulation. Systemic progesterone administration on the third postimplantation day facilitated sexual receptivity in the majority of females with dual E2 implants (greater than 90%). These receptive females displayed lordotic responsiveness that closely matches the full display of sexual receptivity shown by intact cycling females. In contrast, only one female with a single E2 implant in the AH region showed sexual responsiveness. The results demonstrate that: precopulatory vaginal marking and biting attack are mediated by E2 action in the MPO and AH but in a different manner; additional action of E2 in the VMH diminishes the distinctive precopulatory behavioral effects of E2 in the MPO and AH suggesting an influential role of the VMH in regulating sociosexual activities; and E2 action in either the MPO or AH region in conjunction with E2 action in the VMH may be necessary in order to facilitate the species-typical display of lordotic responsiveness.

Aggression↗

PubMed1985

Estrogen action in anterior and ventromedial hypothalamus and the modulation of heterosexual behavior in female golden hamsters.

Changes in heterosexual patterns of agonistic, marking, and sexual behavior were examined in female hamsters over a three day period following implantation of either estrogen or cholesterol in the hypothalamus. Animals were habituated to large arenas that permit the display of a wide range of behavior. Estrogen implants located in the ventromedial (VMH) but not the anterior (AH) portion of the hypothalamus were effective in facilitating the occurrence of vaginal marking, over a two day estrogen priming period. During this two day period, the exhibition of agonistic behavioral patterns declined significantly. Systemic administration of progesterone elicited sexual receptivity in 75% of the females in the VMH group, in contrast to only 25% in the AH group. Females with hypothalamic implants of cholesterol remained unreceptive following progesterone injections. The results provide important information on the estrogen sites of action at the hypothalamus in mediating heterosexual interactions.

Agonistic Behavior↗

PubMed1985

Scent marking and mate choice in the golden hamster.

Test groups consisting of three males and one female were adapted to home areas within a 244 X 122 cm enclosure for a 4-day period. Subsequently, agonistic interactions and patterns of scent marking were recorded daily for 30 min over the duration of the female's 4-day estrous cycle. Alpha males flank marked significantly more than the two subordinates. The former accounted for over 95% of flank gland marking by males on the two days prior to the female's period of sexual receptivity. The female showed increased frequencies of both flank gland and vaginal marking over the three nonreceptive days of the cycle with the highest frequency of marking occurring 24 hr prior to sexual receptivity. During the two days prior to receptivity, the female both vaginal marked and flank marked significantly more in and about the home area of the alpha male. We conclude that the female hamster shows mate choice prior to the onset of sexual receptivity and that both vaginal marks and flank marks are employed to facilitate mating with the alpha male.

Animals↗

PubMed1985

Determinants of mating success in the golden hamster (Mesocricetus auratus): I. Male capacity.

Rested adult golden hamsters produced a mean of 13 ejaculations and then showed a modified copulatory pattern consisting of long intromissions (10-30 s of intravaginal thrusting) during which no sperm transfer occurs. When a second (fresh) female was introduced, 58% of the males produced at least one more ejaculation, and 17% of the males produced one further ejaculation when placed with a third female. In similar three-female tests conducted 24 hr later, all males ejaculated (M = 4 ejaculations); this level of ejaculatory output was maintained over a subsequent 10-day period of daily testing. Four ejaculations ensured a nearly 100% pregnancy rate and maximum litter size in the first females. Second and third females, however, received fewer ejaculations and subsequently showed reduced fertility and produced smaller litters. Most males showed high levels of long intromissions on all days and with all females. The physiological significance of these long intromissions may be to trigger the progestational response. Examination of the rate of recovery from sexual exhaustion indicated that 2 or 8 hr of rest resulted in fewer than 50% of the males being capable of one further ejaculation. However, most of these single ejaculations were accompanied by long intromissions and resulted in successful pregnancies. Four to eight days were required for full recovery of ejaculatory capacity. This study showed that the male golden hamster has a higher ejaculatory output and more rapid recovery from sexual exhaustion than other small rodents that have been studied. Thus, the limits of male capacity appear to vary widely among species.

Animals↗

PubMed1985

Diencephalic sites of progesterone action for inhibiting aggression and facilitating sexual receptivity in estrogen-primed golden hamsters.

Diencephalic sites of action of progesterone (P) responsible for inhibiting aggression and facilitating sexual receptivity were examined in ovariectomized golden hamsters primed with Silastic capsules of estradiol. P was applied centrally by inserting a hormone-filled, 27-gauge cannula into a 22-gauge guide cannula that was implanted unilaterally in the medial preoptic area (MPO), the anterior hypothalamus (AH), or the ventromedial hypothalamus (VMH). Control implants consisted of cholesterol-filled cannulae placed within the same regions of the brain. Tests for sexual and aggressive behavior occurred 1, 2, 4, and 6 h after hormone implantation by introducing a sexually experienced male into the home cage of the female. Nine of 20 females with P in the VMH exhibited lordosis in comparison to 1 of 12 females in the MPO group and 5 of 16 animals in the AH group. The induction of sexual responsiveness after P implantation in the VMH was further demonstrated in 6 of 11 ovariectomized-adrenalectomized females, indicating that the observed receptivity was not contingent upon activation of the hypothalamic-pituitary-adrenal axis. In addition to the receptive promoting action of P in the VMH, P implantation in the MPO and VMH but not in AH regions was highly effective in inhibiting female biting attacks upon males. In summary, these findings indicate that P can both facilitate sexual receptivity and inhibit aggressive behavior and that P induces these changes in behavior at different locations in the diencephalon.

Aggression↗

PubMed1984

Effects of progesterone on lordotic responses to specific mating stimuli in hamsters.

Mating-induced inhibition of sexual receptivity was examined in ovariectomized, estrogen (E) treated and estrogen plus progesterone (E + P) treated hamsters given 10 min of exposure to male mounting stimulation alone or to mounts, intromissions, and ejaculations at eight hourly intervals. In E + P treated females, no differential effects of exposure to full mating stimulation vs. mounting stimulation alone were observed. In contrast, females given E treatment alone showed a marked differential response. Fully mated, E-treated females showed more lordosis than E-treated females exposed to mounts alone during the initial test. However, total lordosis duration declined precipitiously in the fully mated group by 2 hr and remained significantly below that in other groups during subsequent tests. Levels of receptivity in E-treated females mounted-only remained relatively constant until 8 hr. These results suggest that P reduces the inhibitory effects of vaginocervical cues received during mating without affecting the response to mounting stimulation alone. In addition, vaginocervical stimulation may initially facilitate lordosis in E-treated females.

Animals↗