Biomedical subjects
Publications and source records attributed to B Svare.
Prenatal stress (heat and restraint) significantly reduced intermale aggression (percentage of animals fighting and the number of attacks and lunges) in Rockland-Swiss Albino mice. These data, in combination with previous reports showing deficits in male copulatory responses, suggest that a wide array of androgen-dependent social behaviors may be influenced by prenatal stress.
Heat and restraint stress reduced maternal food and water intake as well as body weight gain in pregnant Rockland-Swiss (R-S) Albino mice. Because maternal undernutrition during pregnancy has been reported to disrupt sociosexual behavior in male and female rodent offspring, prenatal stress effects may be modulated, in part, by alterations in essential regulatory behaviors of pregnant animals.
Intrauterine position (IUP), the proximity of a fetus relative to same and opposite sex fetuses, is a reliable predictor of the direction and intensity of social and regulatory behaviors in adult male and female mice. In the present experiment, female Rockland-Swiss (R-S) mice who had resided in utero between two females (OM) and females who had resided between two males (2M) were compared with respect to five indices of maternal behavior: Spontaneous parental responses exhibited toward neonates; nestbuilding during pregnancy; aggression during pregnancy; aggression during lactation; and reproductive/lactation performance. There was no significant difference between 0M and 2M females in their spontaneous parental responses toward neonates or their level of nestbuilding behavior during pregnancy. However, when tested for aggression during pregnancy and lactation, 2M females exhibited aggression on a greater number of test days during pregnancy than did 0M females. Also, during pregnancy and lactation, 2M females displayed more lunges and attacks toward adult male intruders than 0M females. Although 0M females tended to have larger litters than 2M females, the animals did not differ with respect to any other measure of reproductive/lactation performance. Intrauterine position, therefore, modulates some aspects of maternal behavior but apparently not others.
A series of six experiments was performed in order to explore the potential involvement of progesterone (P) in pregnancy-induced aggression (PIA) displayed by Rockland-Swiss mice toward adult male intruders. In Experiment 1, circulating levels of P and aggression were low on gestation Days 6 and 10 while both the behavior and the steroid reached peak levels by gestation Day 14. By gestation Day 18 (the day prior to parturition), serum P was at its lowest level yet aggressive behavior was still intense. Also, individual differences in the display of fighting behavior by pregnant females were not related to circulating P. Experiments 2 and 3 showed that supplemental P treatment to early pregnant female mice did not advance the onset of aggression. Experiment 4 showed that P treatment promoted the onset and elevated the incidence of aggression in virgin mice, but only in those females with intact ovaries. Experiment 5 showed that the aggressive behavior of P-stimulated virgin females was qualitatively and quantitatively different from that exhibited by pregnant mice in that the former exhibited fewer attacks and lunges than the latter. Finally, Experiment 6 showed that the removal of P from aggressive, P-stimulated virgins dramatically attenuated levels of the behavior. This contrasts sharply with the continued fighting behavior observed in late pregnant P-deficient mice. Thus, although P augments aggression in female mice it apparently is not a sufficient stimulus for producing pregnancy-like aggressive behavior.
A series of six experiments was performed to examine the influence of postnatal-gonadal-hormone exposure on home-cage activity in Rockland-Swiss albino mice. Intact females were more active than their male counterparts and gonadectomy in adulthood, while reducing levels of the behavior in both sexes, did not eliminate the gender difference. Males that were castrated on the day of birth were more active than animals castrated 5, 10, or 25 days later. Also, females treated with testosterone propionate on the day of birth were less active than oil-treated controls and females exposed to the steroid 10 days after birth. Thus, perinatal exposure to gonadal hormones suppresses adult levels of home-cage activity in mice.
Infanticide, the killing of young, is one of a number of sexually-dimorphic traits in mice that is dependent upon androgen stimulation during perinatal life and during adulthood. Genotype also influences infanticide in that males of some strains of mice (C57BL/6J) exhibit high levels of this behavior while males of other strains (DBA/2J) seldom kill young. The experiments conducted here show that strain differences in pup killing behavior exhibited by males are not related to postweaning social factors nor are they due to differences in perinatal, pubertal, or adult levels of circulating hormones. These results, in combination with those previously reported, suggest that strain differences in the tendency of mice to kill young may instead depend upon the interaction of genotypic features such as prenatal hormone titers and/or sensitivity to these hormones, as well as on extra organismic factors such as intrauterine position. A model for understanding the manner in which genes and hormones may interact to influence infanticide and other hormone dependent sexually-dimorphic behaviors in mice is presented.
Immediately following defeat inflicted by lactating Rockland-Swiss (R-S) albino mice, adult R-S male mice exhibited significant reductions in circulating prolactin (PRL) and luteinizing hormone (LH), but not corticosterone (CORT). These results suggest that acute neuroendocrine responses to intersex competition may be as dramatic as those previously reported for intermale encounters.
Adult castration significantly reduced the homecage locomotor activity of both inbred C57BL/6J and DBA/2J and outbred Rockland-Swiss (R-S) male mice. Castrated C57BL animals exhibited greater reductions in this behavior than did the other genotypes. Locomotor activity in a novel environment (reactivity) was also reduced by castration but only for inbred males. In both test situations, postcastration reductions in ambulation were prevented by implants of testosterone (T)-containing Silastic capsules. Thus, testicular hormones promote activity and reactivity in the male mouse in a genotype-dependent fashion.
Approximately 25-40% of 25-45 day old C57BL/6J females killed young (1-3 day old Rockland-Swiss (R-S) albino mouse pups) while similarly aged DBA/2J females were parental or ignored neonates. Beyond 45 days of age C57BL and DBA females seldom killed young. When ovariectomized at weaning and tested for infanticide at 65 days of age, DBA females rarely killed neonates while 40% of C57BL females exhibited the behavior. In contrast to DBA females, significantly more C57BL females killed young in response to the adult administration of testosterone propionate (TP) and estradiol benzoate (EB), but not dihydrotestosterone propionate (DHTP). It is tentatively proposed that strain differences in spontaneous and steroid aroused infanticide in female mice may be related to differences in the prenatal hormone environment.
Pregnant Rockland-Swiss (R-S) female mice were injected with oil, 0.5, 1.0 or 2.0 micrograms of testosterone propionate (TP) on days 12, 14 and 16 of gestation and the maternal aggressive behavior of their resulting female offspring was examined in adulthood. Prenatal exposure to 1 or 2 micrograms of TP, but not 0.5 micrograms of the steroid, significantly increased the number of attacks displayed by parturient mice toward adult male intruders. The behavioral effects on aggression were observed in the absence of effects on external morphology, body weight, or lactational performance. The findings support previous research showing that the development of feminine behavior may be sensitive to prenatal androgens. The possibility that the presence of fetal testosterone augments both male and female aggressive behavior is discussed.
Healthy aged adult (24-26 months of age) and young adult (2-4 months of age) c57BL/6J male mice were assessed for intermale aggression, pup-killing behavior (infanticide), and circulating levels of testosterone (T). When compared to young adult male mice, aged adult males were highly variable in the exhibition of both androgen-dependent behaviors. Significant numbers of aged males exhibited deficits in aggression and pup-killing while other animals were as behaviorally active as their young male counterparts. Assessment of serum T showed that aging did not produce a reduction in levels of the steroid and individual variability in androgen-dependent behavior of aged males was not related to plasma levels of the hormone. When aged non-aggressive and non-killer males were exposed to supplemental T by way of subcutaneously implanted silastic capsules, circulating levels of the steroid were elevated but T-dependent behavior was not recovered. These findings, in combination with those previously reported for copulatory behavior, indicate that the deficits observed in the androgen-dependent behavior of aged male mice cannot be attributed to a breakdown in the production of testicular androgens. While neural refractoriness to T may account in part for deficits in androgen-dependent behavior of aged males, the variability that is observed in the reproductive behaviors of aged male rodents ultimately may be related to other sources of variation such as the perinatal environment.
Pregnant DBA/2J females built significantly larger and more completely enclosed nests than did pregnant C57BL/6J mice. This strain difference was restricted to the last half of gestation and was not observed during either the virgin state or lactation. Genotype-based differences in pregnancy-induced nest building were not related to circulating levels of progesterone (P), core temperature, or body weight. Exposure to supplemented P during pregnancy elevated nest building exhibited by pregnant C57BL females but did not induce DBA-like levels of the behavior. Also, virgin DBA females built larger nests in response to P than did C57BL females. These findings suggest that differences in the sensitivity of central neural tissue to steroid hormones may account for genotypically determined variation in patterns of pregnancy-induced nest building.
Rockland-Swiss (R-S) Albino female mice that receive suckling stimulation from young consume significantly more water and food and gain significantly more weight than dams without young. Excision of nipples (thelectomy) prevents postpartum increases in these consummatory behaviors and in body weight gain even in dams with extensive prior suckling exposure. Thus, both the initiation and maintenance of postpartum ingestive behaviors depend primarily upon suckling stimulation from young.
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Approximately 20-30% of adult, 60-70 day old, dBA/2J male mice exhibit infanticide toward standard stimulus 1-3 day old Rockland-Swiss Albino mouse pups, while 50-80% of adult C57BL/6J males display the behavior. Reciprocally-crossed hybrid males exhibit DBA-like levels of low pup-killing behavior and cross-fostered DBA and C57BL males retain their strain-typical phenotype. Also DBA males continue to exhibit low levels of infanticide and C57bL males display high levels of the behavior regardless of the length of pup exposure, or the sex, age, or strain of the stimulus newborn. Thus, strain differences in pup-killing behavior are not related to differences in the prenatal or postnatal maternal environment, or to situational or experiential factors. Inherent biological differences may be responsible for the strain differences in infanticidal behavior.
Pregnant C57BL/6J mice incorporate less material into maternal nests and build fewer fully enclosed nests than do pregnant DBA/2J mice. These strain differences are not ameliorated by additional reproductive experience since multiparous animals also exhibit a similar pattern. Reciprocally-crossed hybrid females exhibit DBA-like levels of pregnancy-induced nestbuilding and cross-fostered C57BL and DBA females retain the phenotype of their strain. Experiential and maternal environmental factors apparently are not responsible for strain differences in pregnancy-induced nestbuilding. Differences in ovarian function and/or central neural tissue sensitivity to ovarian hormones may modulate strain differences in pregnancy-induced nestbuilding.
Plasma levels of prolactin (PRL), growth hormone (GH), luteinizing hormone (LH), and corticosterone (CORT) were measured in parturient Rockland-Swiss (R-S) albino mice following the daily administration for 10 days of 0.5 mg ergocornine (ERGO), 0.5 mg bromocriptine (BROMO), or sesame oil (OIL). The dams were provided with replete foster young on a daily basis so as to prevent the decline in suckling activity that normally occurs in undernourished pups of ergot-treated dams. Circulating PRL levels were significantly reduced by both ergot drugs but plasma levels of the other hormones measured were not altered. Thus, ergot drugs have relatively specific effects on PRL even in parturient animals receiving sustained high levels of suckling stimulation.
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