Fibrinolytic activity in ovaries of rats and golden hamsters after gonadotrophic stimulation and hypophysectomy

The fibrinolytic activity (FA) in immature ovaries of rats was compared with that of golden hamsters on days 3 and 4 after stimulation with pregnant mares' serum gonadotrophin (PMSG). In addition, FA of immature PMSG-stimulated rats was compared with that of adult rats 18 days after hypophysectomy. By means of the fibrin slide method, FA was localized in serial sections and evaluated semiquantitatively. On PMSG day 3, FA occurred in preovulatory follicles and developing corpora lutea. On PMSG day 4, FA was mostly localized in medullary vessels. This was also the case for hypophysectomized rats. While both species showed a comparably high FA on PMSG day 3, hamsters had a lower FA than rats on PMSG day 4. Similar low FA values were obtained in hypophysectomized rats. Non-vascular FA localization may be attributed to granulosa and thecal cells of preovulatory follicles and to luteinizing cells of developing corpora lutea. Vascular FA localization is ascribed to capillary sprouting in these two structures and to medullary vessels.     

Vascularization of ovaries from golden hamsters following implantation into the chick chorioallantoic membrane

In order to study the angiogenic activity, entire ovaries of immature or adult golden hamsters in different functional stages were implanted into the chick chorioallantoic membrane (CAM). Ovaries or other organs (heart, lung, liver, spleen, kidney, adrenal gland, testis) were applied during days 9-14 of incubation. Histological serial sections and ultrastructural studies displayed vascularization from the host to the ovary. Vascularization was marked for unstimulated immature ovaries compared to superstimulated immature ovaries or adult ovaries obtained during the period of proestrus-estrus. When no vascularization developed, grafted ovaries of immature or adult animals induced a mild erosive reaction of the CAM. In contrast, few other implanted organs obtained from immature animals caused a response with vascularization which was absent in grafted organs from adult hamsters. The erosive reaction of the CAM was rare, but the ulcerative response accompanied by infiltrating eosinophils was frequently seen both in immature and adult animals. These results may indicate that angiogenetic activity of the ovary is not the sole cause for vascularization of grafts. Other factors such as tissue death or a low histocompatibility barrier are likely to be involved.     

X-ray induced dominant lethal mutations in mature and immature oocytes of guinea-pigs and golden hamsters.

The induction of dominant lethal mutations by doses of 100-400 rad X-rays in oocytes of the guinea-pig and golden hamster was studied using criteria of embryonic mortality. For both species higher yields were obtained from mature than from immature oocytes, in contrast to results for the mouse. Data on fertility indicated that in the golden hamster, as in the mouse, immature oocytes were more sensitive to killing by X-rays than mature oocytes but that the converse was true in the guinea-pig. The dose-response relationship for mutation to dominant lethals in pre-ovulatory oocytes of guinea-pig and golden hamsters was linear, both when based on pre- and post-implantation loss and when on post-implantation loss only. The rate per unit dose was higher for the golden hamster, and the old golden hamsters were possibly slightly more sensitive than young ones. The mutation rate data for mature oocytes of the mouse, using post-implantation loss alone, also fitted a linear dose-response relationship, except that the rate per unit dose was lower than for the other two species.     

Experimental visceral leishmaniasis in golden hamsters

As a result of a long passage of L. donovani isolate on golden hamsters (21 passages were observed), in transplanting the agent from animals with a distinct clinical picture there was formed a highly virulent strain "G" of L. donovani for this species of animals. The weight arrest and then body mass losses were the most early signs of the disease. Parasites were regularly accumulated in spleen and liver and to a less extent in bone marrow. The main manifestations of visceral leishmaniasis in hamsters are cachexia, lienal syndrome, polyglandular deficiency on the background of hypoplasia of lymphoid tissue and defects of the system of monocytic phagocytes. Such symptom-complex can be a result of neuroendocrine deficiency during visceral leishmaniasis. Pathohistological picture of experimental visceral leishmaniasis is similar to that of man, so L. donovani infection in hamsters can serve as a model for studies of different medical and biological aspects of leishmaniasis.     

Superovulation in immature and mature Chinese hamsters

Mature female Chinese hamsters ovulate an average of 8.8 ± 1.0 (mean ± SD) eggs per female in each estrous cycle. Superovulation can be induced in both immature and mature females by subcutaneous or intraperitoneal injections of pregnant mare serum gonadotropin (PMSG) and either human chorionic gonadotropin (hCG) or pituitary luteinizing hormone (PLH). The best superovulation in immature females was induced by the administration of 15 IU of PMSG followed 72 hr later by injection of 15 IU of hCG (about 25 eggs per female) or 0.2 mg (200 IU) PLH (about 46 eggs per female). Ovulation started about 13–15 hr after administration of hCG (or PLH) and was completed during the next 5–6 hr. Superovulation in mature females could be induced by injecting PMSG any day of the estrous cycle, but the best superovulation (about 39 eggs per female) was induced by injecting 15 IU of PMSG on day 1 (day of ovulation) followed by the injection of 0.4 mg of PLH 72 hr later. When immature females treated with the best superovulatory protocol were mated on the evening of PLH injection, only 5% of the eggs were found fertilized 50 hr after PLH administration. On the other hand, about 60% of the eggs were found fertilized in mature females mated following treatment with the best superovulatory protocol. The majority (83–85%) of superovulated eggs obtained from both immature and mature females were normally fertilized in vitro.     

Isolation and transportation ofTreponema pertenue in golden hamsters

Ten golden hamsters of the CB/Ss LAK strain were flown to Africa, and six of them were inoculated with lesion exudate from yaws patients in an attempt to isolate newer strains ofTreponema pertenue. Three of the six hamsters developed yaws lesions from which treponemes were isolated. Two isolates have been successfully maintained in laboratory animals; these have been designated CDC isolates numbers 1 and 2. Since older stock strains may be altered through repeated animal passage, these fresh isolates will be useful in antigenic and immunological analyses of the pathogenic treponemes. This strain of golden hamster is susceptible to yaws infection, easy to care for, and shipped safely by air; therefore, they are a practical means of transportingT. pertenue.     

Melatonin-pineal relationships in female golden hamsters.

Light deprivation by blinding in female hamsters was followed by a regression of the reproductive organs, an elevation of pituitary LH concentration and a depression of pituitary prolactin levels. Pinealectomy negated almost completely the effects of light deprivation on the neuroendocrine-reproductive axis. Weekly subcutaneous implants of a melatonin:beeswax pellet completely prevented the pineal gland from inhibiting reproductive physiology in blinded hamsters. The findings suggest that melatonin is not pineal antigonadotrophic factor in female golden hamsters. Melatonin implanted hamsters also had higher than normal levels of plasma prolactin.     

Characterization of serum dehydroepiandrosterone secretion in golden hamsters

Dehydroepiandrosterone (DHEA) is an adrenal androgen whose function is poorly understood. Although DHEA and DHEA sulfate (DHEAS) are secreted in relatively high quantities by the human adrenal, the laboratory rat secretes very little, thus hindering experimental studies of the hormone. In this paper, we measured the changes in serum DHEA and DHEAS under various physiological conditions in golden hamsters. Evening serum DHEAS fell from 6.30 +/- 0.78 microg/dl (mean +/- SE) before surgery to 3.03 +/- 0.23 microg/dl 12 days after bilateral adrenalectomy. Hamsters had higher levels of DHEA and DHEAS in the evening than in the morning, but removal of the gonads did not consistently decrease serum DHEA or DHEAS in males or females. Evening levels of DHEA and DHEAS reached a peak around 7 weeks of age and then gradually decreased to about one-third of these levels by one year of age. These results suggest that DHEA and DHEAS are secreted at least in part from the hamster adrenal, that they do not originate from the gonads, and that there is a daily rhythm with peak levels at a time of day just preceding the active phase. In addition, the levels of these hormones decrease with aging.     

Factor of familiarity in sibling recognition in golden hamsters

Male hamsters, reared with their siblings and non-siblings, were tested for their exploratory behavior of conspecific in the 4th and 8th week after their birth. During the tests, a familiar sibling, an unfamiliar sibling, a familiar non-sibling and an unfamiliar non-siblings was presented in a choice box. Subjective distance among these testing animals was measured using the caseV of Thurston's paired-comparison test. The hamsters spent more time with the unfamiliar animals than with the familiar ones. Although biological relation (sibling or non-sibling) had a significant effect in the 4th-week test, only the familiarity determined the investigatory behavior in the 8th-week test. These results suggest sibling recognition based on learning in hamsters.     

Stress and the development of agonistic behavior in golden hamsters

Aggressive behavior can be studied as either offensive or defensive responses to a stimulus. The studies discussed in this review are focused on the peripubertal development of offensive aggression in male golden hamsters and its responsiveness to repeated social stress. Quantitative and qualitative changes in offensive responses were analyzed during this period. Quantitative changes in offensive responses were observed as decreased frequency of attacks. Qualitative changes were observed as changes in attack types, as animals reorient their attacks gradually from the face to the lower belly and rump. These developmental changes were altered by repeated exposure to social stress during early puberty. Daily exposure to aggressive adults during early puberty accelerated the qualitative development of offensive responses and the onset of adult-like offensive responses. In contrast, social stress had little effect on the quantitative changes associated with early puberty. However, social stress was associated with higher attack frequency during adulthood. These effects of stress during early puberty contrast with those observed with animals in late puberty. At that time, repeated exposure to aggressive adults inhibits offensive aggression. These data constitute the basis for a new theory on the development of agonistic behavior that includes the following hypotheses. First, it is hypothesized that mid-puberty is marked by a change in responsiveness to repeated social stress. As such, differences in stress responsiveness from social interactions are interpreted as a basic distinction between play fighting and adult aggression. Second, it is also hypothesized that a common neural circuitry mediates the activation of offensive responses during play fighting and adult aggressive interactions.