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published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

Female golden Syrian hamsters are seasonally breeding animals, capable of maintaining continuous estrous cycles when the daylength is 12.5 hrs. or longer. In shorter photoperiod (SP) the ovaries of anovulatory animals are characterized by few small growing follicles, an absence of corpora lutea and extensive hypertrophied interstitium. Steroid-histochemical studies revealed that enzymes related to steroidogenesis show intense activity in the interstitial tissue of SP-exposed animals. The major objectives of these studies were to examine SP-induced hormonal and ovarian changes which occur prior to onset of the acyclic condition in inbred LSH/SsLak hamsters. Other experiments explored hormonal changes in the absence of ovarian hormones and the interaction of SP and steroids. Initial results revealed that the LSH/SsLak hamster ceased estrous cyclicity between 14 and 31 days of SP exposure, a response far more uniform than generally seen in outbred hamsters. Experiments carried out in SP-exposed cyclic animals indicated that the secondary FSH surge and follicular recruitment were not affected by SP treatment, follicular recruitment were not affected by SP treatment, and that no major changes in gonadotropin levels and ovarian steroids were present on individual days of the estrous cycle. Once the animals were anestrous, daily gonadotropin surges were present and pituitary gonadotropin contents increases. Serum PRL levels showed a slight, yet significant, decrease in SP cycling animals followed by a further reduction in pituitary and serum levels after animals ceased cycling. Medial basal hypothalamic LHRH contents did change in SP, yet there was a significant increase in the preoptic area, and LHRH became significantly elevated in both areas after the animals became anestrous. Ovarian histology revealed fewer corpora lutea and a slight shift from healthy to atretic antral follicles. Experiments carried out in ovariectomized SP-treated animals showed that serum gonadotropin levels were significantly reduced, and that estrogen treatment was either equally or less effective in reducing levels in SP animals. In contrast, PRL levels did not change and responded in a dose dependent way to estrogen treatment. Although the studies yielded no definite proof, the result suggest that SP impairs the maintenance of follicular growth leading eventually to the acyclic state.

Thesis (Ph.D.)--Boston University / The golden hamster, Mesocricetus auratus, is unique in that it frequently accepts not only homografts but even heterografts of normal and malignant tissues. One of the many theories a tterpting an explanation of this phenomenon, namely that lymphatic tissues that drain the sites of imphntation do not respond in a t;rpicol fashion, motivated this study. Thus, the weight changes ,and the c;'tolof'ical variations of the superficial cervical nodes in response to homologous and heterologous normal and malignant tissue transplants in the cheek pouch of the hamster were studied. The major objectives were: (1) to determine if there be any "defect" in the hamster's lymphatic tissue response to the various transplants; (2) to investigate the effects of the grafts on the large lymphoid cells of the cortex and on the plasma cells of the medulla; and ( 3) to investigate the feasibility of employing the histological picture of a regional node draining the site of a tumor heterotransplant as a base line for anti-tumor studies during the cortisone conditioning. [TRUNCATED]

Thesis (M.A.)--Boston University / In view of the success of the Danish investigators Christensen and Kjems in inducing regressions of malignant tumors with streptococcus bacteriophage lysates, it was decided to test lysates of hemolytic Staphylococcus aureus upon malignancies in hamsters and mice. [TRUNCATED]

Thèse de doctorat : Sciences du Vivant. Aspects cellulaires et moléculaires de la Biologie. Neurosciences : Strasbourg 1 : 2008. / Thèse soutenue sur un ensemble de travaux. Titre provenant de l'écran-titre. Bibliogr. 23 p.

Thesis (M. Phil.)--University of Hong Kong, 1982.

Thesis (M.D.)--University of Hong Kong, 1988.

In male golden hamsters, puberty is marked by dramatic changes in agonistic behavior. Attack frequency gradually decreases as agonistic behavior evolves from play fighting to adult aggression. Attack types change as targets of attack mature from play fighting to adult attacks. In adult hamsters, serotonin plays an inhibitory role in aggression. Thus, the decline in attack frequency during puberty could be associated with an up-regulation of the activity of the serotonergic system. In adults, acute Fluoxetine treatment inhibited aggressive behavior at all doses. In juveniles, only the highest dose reduced attack frequency. Interestingly, juveniles treated with the lowest dose showed an increase in aggressive behavior. Attack type was also affected as treatment with Fluoxetine accelerated the maturation of attack targets. This same effect had been observed in previous studies in response to chronic social stress and dexamethasone treatment. Consequently, the role of cortisol on the development of the serotonergic system was also investigated. Furthermore, the density of serotonin innervation in the anterior hypothalamus and medial amygdala was found to be higher in adults than juveniles and consistent with the inhibition of attacks by the high dose of Fluoxetine. However, the differential effects of Fluoxetine at the lower doses were investigated through analysis of different serotonin receptor subtypes. In adult hamsters, aggression can be facilitated by activation of 5-HT₃ receptors and inhibited by 5-HT[subscript 1A] receptors. During puberty, the density of immunoreactive 5-HT1A receptors increased in the anterior hypothalamus and medial amydala while 5-HT₃ receptor immunoreactivity did not change. Thus, it is possible that in these areas the ratio of 5-HT₃ to 5-HT[subscript 1A] receptors decreases during puberty. This change is consistent with the decline in the frequency of offensive responses during puberty. The functionality of 5-HT[subscript 1A] and 5-HT₃ receptors on offensive aggression in juveniles was tested via peripheral injections of a 5-HT[subscript 1A] receptor agonist and a 5-HT₃ receptors antagonist. At the high dose, both drug treatments inhibited attack frequency and attack repetition. Together, these data examine the role of the serotonergic system on the development of agonistic behavior. / text

published_or_final_version / Anatomy / Master / Master of Philosophy