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Biomedical subjects

I T Landau

Publications and source records attributed to I T Landau.

16 recordsLinked to original sources
PubMed1988

Mating of captive thirteen-lined ground squirrels and the annual timing of estrus.

Thirteen-lined ground squirrels (Spermophilus tridecemlineatus) have a single annual mating season in Michigan, beginning shortly after their spring emergence from hibernation. Captive females were studied during a 3-year period to determine relations among time of removal from the coldroom, vaginal estrus, and mating behavior. Following a 7-month period females spent in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females removed from the coldroom about when free-living animals emerge from hibernation were in vaginal estrus within 24-48 hr and had an initial period of persistent estrus (ca. 3 weeks), followed by briefer (less than 1 week) and more sporadic estrous periods. Females left in the coldroom 3 weeks longer than normal had significantly briefer initial periods of vaginal estrus after being removed from the coldroom. Similarly, virgin Yearlings and virgin 2-Year-Olds had significantly briefer initial periods of estrus than nonvirgin Adults (greater than or equal to 2 years old). In 1985, eight of eight females paired with males mated within the first week after removal from the coldroom and subsequently produced litters. Mated females remained in vaginal diestrus from within a few days of mating until after parturition. In contrast, unmated females remained in prolonged vaginal estrus during this period. Females first paired with males 3 weeks after being taken from the coldroom failed to mate. In 1986, five of six females first paired with males 2 weeks after being removed from the coldroom similarly failed to mate. However, five of six females did mate that were removed from the coldroom 10 days after those in the previously described group and paired with a male 4 days after removal. This first report of reliable mating behavior in captive thirteen-lined ground squirrels should facilitate subsequent analysis of reproductive patterns in this species.

Animals↗
PubMed1986

Vaginal estrus in unmated Belding's ground squirrels.

Belding's ground squirrels are seasonally breeding rodents that have a single annual mating season (ca. 3 weeks long) which begins shortly after their vernal emergence from a 7-month period of hibernation. In this study, changes in vaginal estrus were assessed among unmated captive females. Following a 7-month period in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females were in vaginal estrus within 24-48 hr of removal from the coldroom. Rather than exhibiting repeated cycles, adults (greater than or equal to 2 years old) remained in prolonged estrus (typically 3-4 weeks, but 8-10 weeks in some cases), whereas yearlings exhibited similar but shorter and possibly periodic changes in vaginal condition. The difference between the two age classes persisted in a second year of testing, indicating that the preadult status of yearlings (in the first year of testing) did not primarily account for the difference. In another experiment, removal from the coldroom was delayed for 24 days relative to adults removed at a time coincident with emergence from hibernation of free-living females. The "delayed" adults showed persistent vaginal estrus for a shorter total duration, such that both groups reached anestrus at approximately the same time. This implies that the latency to anestrus is not simply a fixed period from the time of removal from the coldroom.

Age Factors↗
PubMed1983

Hormonal regulation of female proceptivity and its influence on male sexual preference in rats.

Two experiments were conducted that assessed the effect of varying levels of female proceptive/attractive behaviors on male sexual preferences in sexually experienced rats. In Experiment 1, adult ovariectomized Sprague-Dawley rats were brought into behavioral estrus by a combination of estradiol-17 beta-benzoate (EB) (4 micrograms) and progesterone (500 micrograms). In addition, females received an injection of either the anti-estrogen CI-628 (1 mg) or the control vehicle (10% ethanol) only. In tests for sexual responsiveness, CI-628 caused a 3 to 4 fold decline in proceptive behavior along with a small but significant decline in receptivity. When individual males were placed in a testing arena with a pair of receptive females, only one of which received CI-628, males displayed a preference for the control-group females, as measured by overall copulatory rate. However, males did not display a consistent preference towards females of either treatment, as measured by choice of female for ejaculation. Similarly, there were no significant correlations between female proceptive behaviors and either overall copulatory rate or ejaculation. In Experiment 2, females came into behavioral estrus after being given four daily injections of EB followed by either a single injection of progesterone or just the oil vehicle. The absence of progesterone caused a significant decline in receptivity and almost entirely eliminated proceptive behaviors. When males were tested with a pair of females, only one of which received progesterone, males preferred the progesterone-injected female as measured by overall copulatory rate. However, similar to Experiment 1, no consistent preferences were evident when measured by using choice of female for ejaculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Inhibition of lordosis in rats by the antiestrogen CI-628 in the absence of progesterone.

A series of experiments assessed whether the ability of the antiestrogen CI-628 to inhibit estrogen-stimulated lordosis in adult ovariectomized rats depends upon its interference with the synergistic effects of estrogen with progesterone. In Experiment 1, the effect of CI-628 was contrasted in rats brought into estrus by a single subcutaneous injection of estradiol benzoate (EB) combined with an injection of progesterone (P) 42 hr later versus four daily injections of EB (without any P). CI-628 was given at the time of EB injection(s). CI-628 substantially and equally effectively antagonized lordotic responding in both conditions. In the absence of CI-628, rats receiving progesterone had significantly higher lordosis scores than the 4-day EB control animals. In Experiment 2, rats receiving CI-628 on only the first 2 of 4 days of EB injections had significantly decreased lordosis scores unless P was also given on the day of testing. This suggested that the EB from the latter injections was not acting as a progestin "mimic." In Experiment 3, lordotic responding stimulated by EB (without P) was inhibited by CI-628 in rats that were both ovariectomized and adrenalectomized. This suggested that adrenal progestins were not involved in the ability of CI-628 to inhibit lordosis. Taken together, the results suggest that the mechanism of action of CI-628 for the inhibition of lordosis does not depend upon its ability to antagonize an estrogen-induced increase in neural progestin receptors. Implications of this for estrogen-mediated behaviors, for which CI-628 has little or no antagonistic effects, are discussed.

Animals↗
PubMed1976

Effect of subcutaneous vs intraperitoneal administration of an anti-estrogen, CI-628, estradiol-and estradiol benzoate-stimulated lordosis in the ovariectomized rat.

The anti-estrogen CI-628 (3 mg) inhibited estradiol (E, 150 mug, SC in oil)-stimulated lordosis in ovariectomized rats, when the anti-estrogen was given intraperitoneally (IP) at the time of E injection (Hr 0). No lordosis inhibition occurred after similar treatment, if the CI-628 was given subcutaneously. For estradiol benzoate (EB, 2 mug, SC in oil)-stimulated lordosis, CI-628 (Hr 0) had a substantial inhibitory effect whether it was given IP or SC, the greater percentage inhibition occurring after SC CI-628 (Experiment 1). All animals received sequential injections of estrogen and progesterone (500 = s,g, SC in oil) and were then tested to 10 mounts by an intact male. These results suggested that, after E injection, neural tissues mediating lordosis have a shorter period of sensitivity to the behavioral effects of CI-628 than after EB injection. Thus, inhibition of E-stimulated lordosis apparently required the more rapid onset of intracellular estrogen retention inhibition resulting from CI-628 given IP rather than SC. This was not the case for EB-stimulated lordosis, where a longer period of sensitivity to CI-628 seeemed likely. This hypothesis was supported by the data of Experiment 2, in which CI-628 (3 mg, IP) was first given 3 hr after E or EB treatment. In this paradigm, CI-628 no longer inhibited E-stimulated lordosis. In contrast, the anti-estrogen's effect on EB-stimulated lordosis was at least equal to the inhibition occurring after CI-628 (IP) given at Hr 0.

Animals↗
PubMed1975

Light-dark rhythms in aggressive behavior of the male golden hamster.

A nocturnal rhythm in aggressive behavior in the male golden hamster is described. The peak frequency of aggression occurs shortly after the time of dark onset (Experiments 1 and 3). Results suggest that the rhythm is likely to be independent from similar rhythms in non-hostile social behavior and locomotor activity. The aggression rhythm is not dependent on the illumination conditions during the 10 min testing period, but is instead a function of the time of testing relative to the LD 12:12 cycle (Experiment 2). The rhythm persists for over a week in continuous illumination and requires between 2 and 4 weeks to reentrain to a 12 hr phase shift (Experiment 4). These results support the hypothesis that the aggression rhythm is endogenous to the animal. The functional significance of the aggression rhythm and its implications for future research in aggression are also discussed.

Aggression↗
PubMed1975

Effects of adrenalectomy on rhythmic and non-rhythmic aggressive behavior in the male golden hamster.

Male golden hamsters, adrenalectomized and maintained by subcutaneous implants od deoxycorticosterone-acetate (adx-DOCA), show a loss of the nocturnal rhythm in aggression seen in sham operated (sham-op) animals. A similar loss of the nocturnal aggression rhythm is evident in hamsters adrenalectomized and implanted with separate pellets of DOCA and cortisol-acetate (adx-DOCA-cortisol). However, while Adx-DOCA animals do not differ from sham-op animals in the level of aggression summed over all tests (overall aggression), the overall aggression levels of the adx-DOCA-cortisol animals are significantly higher than the levels of either the adx-DOCA or sham-op animals. Nocturnal rhythms in locomotor activity persist in all three groups. It is suggested that circadian rhythms of the pituitary-adrenocoritcal axis are important for the expression of the aggression rhythm. A possible mechanism of action is discussed.

Adrenal Glands↗