Group-housed female mice, when introduced to a male, will undergo a synchronized estrous cycle with a characteristic pattern of mating where the majority of animals mate on the third day. This phenomenon is termed the Whitten effect. Exposure of pregnant mice to diethylstilbestrol (DES), a potent nonsteroidal estrogen, is capable of inducing premature parturition. The purpose of this study was to evaluate abortion induced by a single injection of DES on day 15 of gestation and compare the sensitivity depending on the day of mating. Initial observations confirmed that those animals that mated on day 3 were significantly more susceptible to DES-induced abortion than animals that mated on any other day. The possibility that this increase in sensitivity to abortion may be the result of differences in number or size of embryos at the time of DES exposure was examined. No significant difference was observed in the number of embryos at day 4 of gestation, at day 15 of gestation, or at birth. There was no difference in the weight of embryos at day 15 of gestation or at birth. A significant increase in the ratio of embryos between uterine horns was observed in the animals that mated on day 3 (ratio = 2.13) compared to animals mating on other days (ratio = 1.23 to 1.48). The cause of increased sensitivity to DES in animals that mated on day 3 is unclear. Our results may indicate that the induction of ovulation associated with the Whitten effect causes unequal embryo distribution leading to functional differences in sensitivity of the pregnancy to exogenous stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental autoimmune enchephalomyelltis (EAE) is a disease which can be induced in Lewis rats by exposure of the animal to a source of myelin in the presence of adjuvant. Similar symptoms and histopathology are observed In people with multiple sclerosis (MS) leading to the widespread use ofEAEas an animal model forMS (1). Induction ofEAEin the male Lewis rat results In a monophasic disease characterized by a single severe occurrence of symptoms followed by spontaneous recovery. Female Lewis rats when exposed to identical stimuli will develop a recurrent form of the disease (rEAE) characterized by a temporally consistent, spontaneous secondary occurrence of clinical symptoms(2), which more closely mimics humanMS.The goal of this preliminary study was to characterize the disease process in female Lewis rats (rEAE) using both light and transmission electron microscopy (TEM). Samples of lumbrosacral spinal cord were chosen for Initial examination. This tissue was sampled at four stages of the disease process, namely: in the primary occurrence phase (Peak 1, Day 12), the first recovery phase (Day 18), the secondary occurrence (Peak 2, Day 24) and the second recovery phase (Day 31) (seeFigure 1). Lumbrosacral spinal cord tissue from non-sensitized female Lewis rats, were used as control tissue.

The appearance of increased levels of histamine in the central nervous system (CNS) concomitant with the development of clinically significant acute experimental autoimmune encephalomyelitis (EAE) in male Lewis rats suggests that CNS-associated mast cells may mediate acute EAE in Lewis rats. We now report that, compared to controls, rats with acute EAE exhibit fewer detectable mast cells in their dura mater and velum interpositum. In addition, intracisternal, but not intraperitoneal administration of Compound 48/80 just prior to the appearance of clinical signs of acute or recurrent EAE in male and female rats, respectively, significantly attenuates the clinical severity of both forms of EAE. These results further support the hypothesis that CNS-associated, but not peripheral mast cells are mediators or modulators of acute and recurrent EAE in Lewis rats.

This study examines the changes in uterine histamine content in mast-cell normal and deficient mice during deciduoma formation. Surgical trauma (e.g., sutures) and intraluminal injection of oil produce deciduoma formation in ovariectomized mast-cell normal (+/+) and mast-cell deficient (W/WV) pseudopregnant mice that had previously received a single control ovary transplanted under the kidney capsule. Mast-cell normal (+/+) mice exhibit significant elevation of total uterine histamine content during both trauma and oil induced deciduoma formation. Mast-cell deficient (W/WV) mice under conditions of similar deciduoma formation did not show any change in total uterine histamine content. These results indicate that the change in histamine observed in mast-cell normal mice during deciduoma formation is most likely of mast cell origin. The lack of any measurable change in uterine histamine in mast-cell deficient mice indicates that an increase of non-mast cell histamine is not a prerequisite for deciduoma formation.

The effect of chronic daily afternoon injections of melatonin upon basal and melatonin-modulated release of FSH and LH was investigated in supervised hamster anterior pituitary glands. The basal release rate of both FSH and LH began to decline following the beginning of melatonin injections, and reached a nadir after six weeks. Basal release rate of FSH and LH then began to spontaneously increase and reached a plateau at 13 weeks of injections. The inhibition by melatonin upon FSH and LH release in vitro gradually declined during the period of melatonin injections. After six weeks of melatonin injections the release rate of FSH was no longer suppressed by melatonin superfusion, while the release rate of LH became refractory to melatonin suppression in vitro after nine weeks of melatonin injections. These results demonstrate a change in the release rates of both basal and melatonin-inhibited gonadotropin release during melatonin-induced testicular regression and recrudescence in hamsters.