Biomedical subjects

R D Lisk

Publications and source records attributed to R D Lisk.

At least 19 recordsLinked to original sources

PubMed1998

Reproductive aging in the Djungarian hamster, Phodopus campbelli.

Changes in fertility (delivery success), fecundity (litter size and weaning success), sensitivity to pregnancy-blocking stimuli (mate removal after 24 h), and hypothalamic-pituitary-ovarian function were assessed during reproductive aging in the Djungarian hamster, Phodopus campbelli. All indices of aging occurred earlier in the Djungarian hamster than they do in other laboratory models, including the mouse. Fertility and fecundity were halved by 8 mo of age, and the response to pregnancy-blocking stimuli disappeared by 4-6 mo. Pup birth weight increased with maternal age and decreasing litter size. Older females also tended to lose entire litters rather than to reduce litter size and successfully wean remaining pups. Impaired ovarian function was a major contributor to reproductive aging. Numbers of large antral follicles developing in aged females and in aged females receiving eCG treatment were similar to those in young females. However, a few preovulatory follicles routinely failed to ovulate from each ovary. Healthy preovulatory follicles in old females secreted the large quantities of estradiol-17 beta typical of estrous cycles, but eCG-induced preovulatory follicles did not. As young females of this species have smaller folicular reserves than other rodent species, and follicle numbers in older females are further reduced (with a high incidence of completely degenerate ovaries), follicular exhaustion was coincident with reproductive failure. Neuroendocrine aging of the hypothalamus was also implicated in the loss of a pregnancy-blocking response and the failure of maternal care with increasing maternal age. Similarities to reproductive aging in long-cycle species (including primates) suggest that the Djungarian hamster is a useful laboratory model that deserves further investigation.

Aging↗

PubMed1991

Role of progesterone in mediating stress-related litter deficits in the golden hamster (Mesocricetus auratus).

Primiparous females were mated to proven breeders and half received a subcutaneous implantation of a progesterone-filled silastic capsule on Day 3 which was removed on Day 14. The other half of the group received no treatment. Blood samples were taken from all individuals on Days 3, 7, 11 and 14. The females were paired for brief periods on Days 4, 5 and 6 with a conspecific matched for treatment group, age, weight and stage of pregnancy. Controls were exposed to a novel area instead of a conspecific. Within each of the pairs, one female was consistently dominant to the other. At parturition, all pups were counted, sexed and weighed. Among the untreated group, there were no significant differences between litter sizes or sex ratios (defined as percentage male) produced by control and dominant females. Subordinate females produced significantly smaller litters than control or dominant dams and significantly lower sex ratios than dominant dams. Subordinates produced fewer males than control or dominant dams, but there were no differences in the number of females produced. Among animals given progesterone implants, there were no significant reductions in litter size or sex ratio produced by subordinate dams compared with control or dominant dams. This study showed that female golden hamsters exposed to social subordination early in pregnancy produced smaller and more female-biased litters, and that these effects were accompanied by a significant reduction in circulating progesterone concentrations. When subordinate females were given supplementary doses of progesterone before exposure to stress, they did not show significant litter deficits.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Dexamethasone can prevent stress-related litter deficits in the golden hamster.

This study was designed to examine the effects of social subordination during early pregnancy in the golden hamster (Mesocricetus auratus). Primiparous females were mated to proven breeders and stressed during early pregnancy. Females were housed singly throughout gestation except for Days 4, 5, and 6 when they were paired for 10-min intervals three times each day with another female matched for age, weight, and day of pregnancy. Within each of the pairs, one female was consistently dominant to the other. Controls were exposed to a novel area instead of a conspecific. At parturition, all pups were counted, sexed, and weighed. There were no significant differences between control and dominant females' litter sizes and sex ratios. Subordinate females produced significantly smaller litters than control or dominant dams and significantly lower sex ratios than control dams. Subordinates produced fewer males than control or dominant dams, but there were no differences in the number of females produced. The entire experiment was repeated exactly except that females received a small dosage of dexamethasone in their drinking water on Days 3-7 of pregnancy. In this second group, there were no significant reductions in mean litter size, sex ratio, or pup weights among litters born to subordinate dams. These results suggest that subordinate dams produce smaller litters via selective resorption of males in utero and that the typical adrenal response to stress mediates this response.

Administration, Oral↗

PubMed1989

Differential effects of paternal presence on pup survival in two species of dwarf hamster (Phodopus sungorus and Phodopus campbelli).

The effect of the presence or absence of the male, and of decreased ambient temperature (21 degrees C vs. 4 degrees C) on litter survival, pup survival and pup growth was measured from birth through day 18 after birth in Siberian (P. sungorus) and Djungarian (P. campbelli) hamsters. Siberian hamsters were not significantly affected by the experimental manipulations. In contrast, whereas 100% of litters and 95% of pups were successfully raised to weaning at 21 degrees C by paired Djungarian hamsters, survival fell to 47% when the mate was absent and even further, to 32%, when the ambient temperature was lowered. No significant differences in litter size or pup weight at birth were detected between species at the warmer temperature. However, P. sungorus pups gained weight significantly faster through day 12 after birth (while dependence upon the mother for food was absolute) than P. campbelli pups under all experimental conditions. Although the species are closely related, these data show that male Djungarian hamsters are essential to offspring survival under conditions where Siberian hamsters do not require conspecific help. Species differences in metabolism and thermoregulation may account for the differential pup survival.

Animals↗

PubMed1989

Patterns of 2-deoxyglucose uptake reflect the neural processing of lordosis-inducing somatosensory stimuli in hamsters.

Semi-quantitative [14C]2-deoxyglucose (2DG) autoradiography was used to map the neural responses of female hamsters to lordosis-inducing flank stimuli. Specifically, manual stimulation of one flank was used to maintain estrous females in lordosis for 20 min after an IV injection of 200 muCi/kg of 2DG. Hemispheric differences in 2DG uptake then were sought in brain nuclei implicated in the programming of lordosis, or in the mediation of somatosensory or hormonal influences on this response. The responses to lateralized flank stimulation included reliable contralateral elevations in 2DG uptake in the ventral posterior lateral nucleus of the thalamus (VPL), the dorsal mesencephalic central gray (dCG), and the tectum. Elevated activity on the part of the VPL may not be crucial for lordosis. However, the effects of flank stimulation on 2DG uptake by the dCG and tectum confirm and extend much previous evidence implicating the dorsal midbrain in the mediation of tactile and hormonal effects on sexual responses. For example, these results suggest that somatosensory influences on hamster lordosis are mediated by both the dCG and tectum. In addition, they suggest that these influences are strongly lateralized until at least this stage of sensory processing, leaving for some subsequent element of neural circuitry the task of translating these lateralized inputs into the bilaterally symmetric outputs ultimately required to program the normal, bilaterally symmetric, lordosis response.

Animals↗

PubMed1989

Olfactory discrimination of estrous condition by the male golden hamster (Mesocricetus auratus).

After repeated exposure to receptive and nonreceptive females, male golden hamsters were tested for olfactory preferences in a four-choice olfactometer. Males discriminated between the odor of anesthetized females in different stages of their estrous cycle when the airstreams carrying the stimulus odors were diluted. Previous failures to demonstrate such an ability were probably due to ceiling effects resulting from laboratory testing. Males preferred the odor of females on the day before receptivity (a day coincident with maximal scent marking by the female) and least preferred the odor of females on diestrus-1 (the day on which females attacked and chased males during pretesting encounters). Detection and quick response to an impending estrus would be especially important for males of a solitary and promiscuous species in which there is a first male mating advantage.

Animals↗

PubMed1989

Effects of social stress during early pregnancy on litter size and sex ratio in the golden hamster (Mesocricetus auratus).

Primiparous female hamsters were mated to proven breeders and stressed during early pregnancy. Females were housed singly throughout gestation except for Days 4, 5 and 6 when they were paired for 10-min intervals 3 times each day with another female matched for age, weight and day of pregnancy. Within each of the pairs, one female was consistently dominant to the other. Controls were exposed to a novel area instead of a conspecific. At parturition, all pups were counted, sexed and weighed. There were no significant differences between litter sizes or sex ratios (defined as % male) of control and dominant females. Litter sizes produced by control or dominant dams were significantly larger than those of subordinate dams, and litter sex ratios of dominants were significantly higher than those of subordinates. Subordinate dams produced fewer males than did dominant dams, but there was no difference in the number of females produced. Also, subordinate dams produced smaller pups than control dams. Examination of uterine implantation sites and fetal resorptions indicated that fetal loss occurred between Days 5 and 10 of pregnancy. These results suggest that subordinate dams produce smaller litters via selective resorption or spontaneous abortion of males in utero and that those males they do produce are smaller than those produced by dominant or control dams. We suggest that males are more susceptible in utero to effects of maternal stress in this species, and may require more maternal investment to survive to term.

Animals↗

PubMed1988

Estrogen regulation of agonistic and proceptive responses in the golden hamster.

The role of estrogen in modulation of agonistic (attack-chase) and proceptive (vaginal-marking) responses of the female hamster toward a male was examined in relation to time course of induction and duration of response. In addition, the sex-specific nature of the vaginal-marking response was examined. Cycling females showed a significantly higher frequency of attack-chase when endogenous estrogen levels were minimal in comparison to that at peak estrogen levels during the estrous cycle. Removal of estrogen (ovariectomy) resulted in a significant increase in attack-chase scores compared to high endogenous estrogen. Addition of exogenous estrogen (Silastic capsule) resulted in a significant decrease in attack-chase scores compared to ovariectomized animals. The inverse effect was found for vaginal marking with the lowest frequency of vaginal marking at low endogenous estrogen levels or following ovariectomy. During high endogenous estrogen levels or following treatment with exogenous estrogen vaginal-marking scores were maximal. Maximal induction of vaginal-marking responses and reduction of attack-chase were found between 6 and 48 hr of estrogen treatment. Both behaviors then returned to the prehormonal treatment level. Failure to detect effects beyond 48 hr was not due to repeated testing, as animals lacking hormone, or animals first tested at 96 hr of estrogen exposure, showed no effect of the treatment. Males gonadectomized as adults never showed vaginal marking, whereas males gonadectomized neonatally showed a low level of vaginal marking which was increased significantly following estrogen treatment. Thus both attack-chase and vaginal marking in the presence of a male are modulated by estrogen. Further, since vaginal marking is estrogen sensitive in the neonatally gonadectomized male, expression of vaginal marking is determined by the hormonal environment during the neonatal period. However, peripheral feedback may be important for frequency of occurrence.

Aggression↗

PubMed1988

Social dominance and reproductive success in pregnant and lactating golden hamsters (Mesocricetus auratus) under seminatural conditions.

Pairs of female hamsters were acclimated to seminatural enclosures and permitted to interact for brief periods on days 12-14 of gestation or on days 2-4 of lactation. In one experimental paradigm, food was provided in excess of the daily requirements while in a second, food rations were restricted. Control females were similarly housed and fed but were not exposed to another animal. Paired females readily established dominant-subordinate relationships. Dominant females successfully removed food from the subordinate females and, as a result, accumulated larger food hoards. Subordinate females gave birth to fewer pups than either dominant or subordinate animals when social interactions occurred late in pregnancy and maintained smaller litters when interactions occurred during lactation. Reductions in the fecundity of subordinate females were more pronounced when the food ration was restricted. Under ad lib feeding conditions dominant females also maintained fewer young than control animals, but when food was restricted they were more successful than the control group. Subordinate females successfully defended their burrows against intrusions by dominant animals; maternal cannibalism accounted for most reductions in litter size. These results suggest that a defensible burrow and the acquisition of a food hoard are essential for successful reproduction in this species.

Aggression↗

PubMed1988

Progesterone levels and socially-induced implantation failure and fetal resorption in golden hamsters (Mesocricetus auratus).

Levels of circulating progesterone (P) were significantly reduced in socially subordinate female golden hamsters following brief exposures to another female. Reduced P levels were accompanied by an increased incidence of implantation failure when social interactions occurred on days 2-4 after mating and by increased fetal mortality when interactions occurred later during pregnancy (days 5-7 or 10-12). P levels, the incidence of implantation failure and rate of fetal resorption were highly correlated with the number of attacks and chases sustained by subordinate females. Smaller reductions in plasma P levels and marginally significant decreases in fecundity were also noted among dominant animals and among females paired with unfamiliar males later in pregnancy. The fact that these effects occurred even with relatively brief exposure periods suggests that they could occur in the wild.

Animals↗

PubMed1988

Dual progesterone action in diencephalon facilitates the induction of sexual receptivity in estrogen-primed golden hamsters.

In order to identify and characterize the progesterone (P) sensitive neural system that regulates feminine sexual behavior, 28-gauge P-filled cannulae were implanted in the medial preoptic area (MPO), ventromedial hypothalamus (VMH), and central gray (CG) of ovariectomized estrogen-primed golden hamsters. Dual implants of P were placed either ipsilaterally or contralaterally in brain sites consisting of MPO-VMH, MPO-CG, or VMH-CG combinations. Tests for sexual receptivity commenced 44 hr after estrogen priming and consisted of a preimplantation test followed 4.5 to 5.5 hr later by a postimplantation test. In the preimplantation test, stimulus males were attacked when placed into the female's home cage which indicated that the subsequent display of sexual receptivity occurring in the postimplantation test was due to the action of P. Dual implants of P placed either ipsilaterally or contralaterally in MPO-VMH regions were significantly more effective in facilitating lordosis behavior than dual P implants placed in MPO-CG or VMH-CG regions. However, the duration of lordotic responsiveness produced by dual P implants in MPO and VMH regions appears to be shorter than the duration of lordosis typically observed in intact females on proestrus. Results suggest that MPO and VMH regions are sensitive to the lordosis facilitating actions of small dual implants of P.

Animals↗

PubMed1988

Effect of the interintromission interval on lordotic response and attack latency in golden hamsters (Mesocricetus auratus).

After 12-15 ejaculatory series, each consisting of several short intromissions (2- to 3-s vaginal penetration) and an ejaculation, male golden hamsters adopt an altered copulatory pattern consisting of long intromissions (5- to 25-s penetration with intravaginal thrusting). Receptivity declines and the tendency for the female to attack the male increases at about the time of this shift in copulatory pattern. Because the mean interintromission interval (III) between short intromissions is about 8 s compared to 100 s between long intromissions, it is possible that females detect this difference and adjust their mating accordingly. When the III between short intromissions from a rested male was experimentally increased to 100 s by use of a halter and lead device, the duration of lordosis was significantly less than that displayed by females paired with control males (8-s III) and virtually the same as that displayed by females paired with males that produced only long intromissions. This suggests that the female uses the temporal patterning of intravaginal stimulation as one criterion for terminating mating with a particular male.

Aggression↗

PubMed1988

Effects of age and parity on litter size and offspring sex ratio in golden hamsters (Mesocricetus auratus).

Golden hamsters that were mated repeatedly from 55 days of age produced 6-12 litters. Litter size at birth rose between the 1st and 2nd litters, peaked on the 3rd, and declined steadily after the 5th litter. Offspring sex ratio (% male) at birth followed a similar pattern: increasing between the 1st and 2nd litters, remaining high through the 3rd, and becoming increasingly female-biased thereafter. Weaning success decreased sharply after the 6th litter and most dams failed to raise any young to weaning after the 9th litter. These sequential effects on litter size, offspring sex ratio and weaning success were also observed in females mated once at different ages, but they occurred considerably later in life, i.e. increasing parity hastened the effects of advanced age. These age- and parity-related changes in litter composition are consistent with the Trivers-Willard hypothesis that physiologically-stressed females would skew offspring sex ratios to favour daughters. However, since the observed changes in sex ratio were probably due to differential prenatal mortality, their adaptive significance is unclear.

Aging↗

PubMed1988

Stimulus requirements for pregnancy initiation in the golden hamster (Mesocricetus auratus) change with age and parity.

Hamsters were mated repeatedly at 60, 180, 300 and 420 days of age or once during their lifetime at one of these ages. Copulatory stimulation was varied both for number of ejaculations (2 versus 14) and amount of vaginocervical stimulation (5 versus 50-60 intromissions). Two ejaculations provided sufficient spermatozoa to maximize litter size for all age and parity classes tested. Differences in fecundity depended on the amount of vaginocervical stimulation received. Higher levels of vaginocervical stimulation increased littering success at 300 and 420 days for nulliparous females and at 180, 300 and 420 days for multiparous females. Females which did not deliver litters did not show a cessation of oestrous cycles which characteristically follows the induction of a luteal phase. The decreased fecundity observed with increasing age or parity therefore resulted from a change in sensitivity to the stimulus conditions necessary to activate the neuroendocrine arc for establishment of pregnancy.

Aging↗

PubMed1987

Diencephalic organization of estradiol sensitive sites regulating sociosexual behavior in female golden hamsters: contralateral versus ipsilateral activation.

Dual ipsilateral, contralateral and bilateral 28-gauge estradiol (E2) filled cannulae were implanted in the medial preoptic area (MPO) and ventromedial hypothalamus (VMH) of ovariectomized female golden hamsters housed in large arenas with male partners. Twenty-four hours after implantation, vaginal scent-marking patterns were significantly and equally elevated in all groups. Forty-four hours after implantation, progesterone was administered and females were tested for sexual receptivity 4-5 h later. Bilateral E2 implants in the VMH as well as dual ipsilateral and contralateral MPO-VMH implants were significantly more likely to facilitate sexual responsiveness than bilateral MPO implants. More importantly, ipsilateral MPO-VMH implants produced significantly longer lordosis duration scores than bilateral VMH and contralateral MPO-VMH implants. After mating, females with bilateral MPO implants attacked their mates more frequently than females with bilateral VMH and dual MPO-VMH implants. Taken together, results suggest that: (1) although MPO and VMH regions are equally sensitive to the vaginal marking promoting effects of E2, these same regions require synergistic ipsilateral activation for the effective priming of sexual responsiveness; (2) the heightened duration of lordosis behavior after ipsilateral MPO-VMH E2 implantation may reflect an anterior diencephalic estrogenic removal of an inhibitory process occurring primarily in the ipsilateral VMH region; and (3) the difference in postcopulatory attacks may reflect variable actions of progesterone on E2-induced progestin receptors in the MPO and VMH.

Animals↗

PubMed1987

Hormonal control of sex differences in ultrasound production by hamsters.

Male and female hamsters differ in the stimulus control of the ultrasounds they produce during courtship and mating. In particular, untreated males show greater increases in ultrasound rate after exposure to stimulus females than after contact with other males. Conversely, estrous females are more responsive to stimulus males than females. This sex difference reflects both organizational and activational effects of gonadal hormones. Thus, responses to early castration or treatment with testosterone propionate (TP), estradiol benzoate (EB), or dihydrotestosterone propionate suggest that the development of male-like patterns of ultrasound production is facilitated by perinatal exposure to aromatizable androgen. However, even neonatally feminized subjects will show male-like calling if tested during adult treatment with TP. In contrast, the same subjects respond like naturally estrous females during adult treatment with EB plus progesterone (P). The contrasting responses of neonatally feminized subjects to later TP and EB + P treatments suggest that female hamsters retain a greater capacity for heterotypical patterns of ultrasound production than do males. This obviously differs from the common observation of greater "bipotentiality" for mating behavior in males. In turn, this suggests that the mechanisms controlling sexual bipotentiality are specific to their target behaviors, yielding distinct patterns of hormonal control for at least ultrasound production and lordosis.

Animals↗

PubMed1987

Mating-induced inhibition of receptivity in the female golden hamster (Mesocricetus auratus): III. Stimuli mediating long-term effects.

In the golden hamster, mating with an intact male results in both a reduction in receptivity shown toward a second male (short-term effect) as well as an absolute abbreviation of the receptive period (long-term effect). The present study examined the components of the mating situation responsible for the long-term effect. In experiment 1 we showed that the paradigm used to determine receptivity (i.e., brief hourly exposures to an intact male) did not affect the duration of receptivity whereas an ad lib mating early during the receptive period resulted in a 40% reduction in the length of behavioral estrus. In experiment 2 females received various types of mating stimuli, e.g., mounts from an apronned male, intromissions from a vasectomized male, a simulated copulatory plug, manually-induced lordosis, or several of these stimuli in combination. Only intromissions from an intact or vasectomized male significantly reduced the duration of behavioral estrus. Although as few as 10 intromissions from a vasectomized male were effective in significantly shortening the receptive period, higher levels of vaginocervical stimulation from a single male (experiment 3) or from additional males (experiment 4) effected significantly greater reductions in the length of behavioral estrus. Our results further demonstrated that only those females that subsequently became pseudopregnant showed significant abbreviations of behavioral estrus. The association of these two phenomena is of obvious adaptive value since it provides a mechanism to terminate a behavior once its function has been achieved.

Animals↗

PubMed1987

Effects of sex and reproductive state on acoustic responsiveness in hamsters.

Semi-quantitative [14C]2-deoxyglucose (2DG) autoradiography was used to describe the responses of hamsters to 35 kHz mimics of the "ultrasounds" used for communication during mating. The first study examined the processing of ultrasounds and ambient noise by estrous females, some of which were deafened or hemideafened with plastic ear plugs. These data failed to reveal responses specific to the ultrasounds. However, lateralized responses to the ambient noise were apparent, especially in the hemideafened subjects. For the ventral cochlear nucleus (VCN), 2DG uptake was elevated contralateral to the plug and ipsilateral to the effective stimulus. In contrast, uptake by more rostral structures (dorsal n. of the lateral lemniscus = DNLL; ventral n. of the lateral lemniscus = VNLL; central n. of the inferior colliculus = CIC; medial geniculate n.) was elevated contralateral to the stimulus. A second experiment examined the responses of intact or castrated male and female hamsters to unilaterally presented ultrasounds and ambient noise. As before, relative levels of 2DG uptake differed across hemispheres for structures including the VCN, trapezoid body, VNLL, DNLL, and CIC. More surprisingly, intact females showed more 2DG uptake than males in the DNLL, auditory nerve, and lateral lemniscus. Females also tended to show elevated anterior hypothalamic uptake, but just in the hemisphere contralateral to the stimulus. These results suggest that male and female hamsters differ in acoustic responsiveness, and that this difference is mediated by hormonal effects at several brainstem components of the central auditory system.

Animals↗