Reproduction-related behaviors of Swiss-Webster female mice living in a cold environment

Effect of cold stress on ovarian & uterine microcirculation in rats and the role of endothelin system

BACKGROUND

Cold, an environmental factor, induces many reproductive diseases. It is known that endothelin (ET) is a potent vasoconstrictor, and cold stress can increase the expression of ET and its receptors. The cold stress rat model was developed to examine two parameters: (1) the effects of cold stress on ovarian and uterine morphology, function, and microvascular circulation and (2) possible mechanisms of ET and its receptors involved in cold stress-induced menstruation disorders.

METHODS

The rat cold stress model was prepared with an ice water bath. The estrous cycle was observed by methylene blue and hematoxylin and eosin (H&E) staining. Serum estradiol 2 (E₂), testosterone (T), progesterone (P) were detected by radioimmunoassay. Hemorheology indices were measured. The real-time blood flow of auricle and uterine surfaces was measured. Expressions of CD34 and α-SMA in ovarian and uterine tissues were detected by immunohistochemistry. ET-1 contents in serum were tested, and expressions of ET-receptor types A and B (ET-AR and ET-BR) in ovarian tissues were detected via Western blotting.

RESULTS

Cold stress extended the estrous cycle, thereby causing reproductive hormone disorder, imbalance of local endothelin/nitric oxide expression, and microcirculation disturbance. Cold-stress led to up-regulation of ET-AR expression and protein and down-regulation of ET-BR expression in rats.

CONCLUSIONS

This study suggests that the reason for cold stress-induced dysfunction in reproductive organs may be closely related to the imbalance of ET-1 and its receptor expressions, leading to microvascular circulation disorders in local tissues.

Impact of Cold Exposure on the Reproductive Function in Female Rats

Female reproductive system diseases caused by exposure to a cold environment are widely considered as important human health challenges. Although the projection of female reproduction in cold temperature has been studied, a holistic view on the probable effects of cold exposure on the functions of the female reproductive system has not been achieved. Our aim was to evaluate the effects of cold exposure to the functions of the ovary and uterus in female rats. For this purpose, female rats were randomly grouped as follows: (1) the cold group was exposed to -10°C, 4 h per day for 2 weeks, and (2) the normal temperature (23 ± 1°C) group was used as control. Alterations were observed in different parameters, including body weight gain, organ coefficients, estrus cycle, and pathology of the cold-exposed female rats. Similarly, the serum reproductive hormones and mRNA expression were evaluated. Cold exposure induced estrus cycle irregularity and some alterations in the morphology of the ovary. Cold exposure impairs the function of the ovary probably by changing the level of serum LH and increasing LHR expression. Cold exposure induced a significant reduction of uterine epithelium height. Cold exposure causes alterations in the morphology of the uterus probably because of the effect of progesterone, the increase in the PR level, and the decrease in the ER level.

Role of thyroid hormone deiodination in the hypothalamus

Iodothyronine deiodinases (D1, D2, and D3) comprise a family of selenoproteins that are involved in the conversion of thyroxine (T(4)) to active triiodothyronine (T(3)), and also the inactivation of both thyroid hormones. The deiodinase enzymes are of critical importance for the normal development and function of the central nervous system. D1 is absent from the human brain, suggesting that D2 and D3 are the two main enzymes involved in the maintenance of thyroid hormone homeostasis in the central nervous system, D2 as the primary T(3)-producing enzyme, and D3 as the primary inactivating enzyme. While the coordinated action of D2 and D3 maintain constant T(3) levels in the cortex independently from the circulating thyroid hormone levels, the role of deiodinases in the hypothalamus may be more complex, as suggested by the regulation of D2 activity in the hypothalamus by infection, fasting and changes in photoperiod. Tanycytes, the primary source of D2 activity in the hypothalamus, integrate hormonal and probably neuronal signals, and under specific conditions, may influence neuroendocrine functions by altering local T(3) tissue concentrations. This function may be of particular importance in the regulation of the hypothalamic-pituitary-thyroid axis during fasting and infection, and in the regulation of appetite and reproductive function. Transient expression of D3 in the preoptic region during a critical time of development suggests a special role for this deiodinase in sexual differentiation of the brain.

Effects of galanin-like peptide (GALP) on locomotion, reproduction, and body weight in female and male mice

Galanin-like peptide (GALP) has been implicated in the neuroendocrine regulation of both feeding and reproduction. In male rodents and primates, intracerebroventricular (icv) infusions of GALP stimulate luteinizing hormone (LH) release, induce Fos expression in brain areas implicated in feeding and reproduction, and affect food intake and body weight in rodents. In gonad-intact and castrated male rats, icv administration of GALP also stimulates male sexual behavior. While the effects of GALP on male physiology and behavior are well documented, no studies have addressed such a role of GALP in females. We tested the effects of icv GALP infusions on LH release, locomotor activity, motor control, and body weight regulation in adult ovariectomized female mice hormonally primed with estradiol benzoate and progesterone. In addition, sexually-experienced male and female mice were treated with GALP and tested for sexual behavior. In females, GALP reduced open-field locomotor activity, the ability to maintain grip on an accelerating rotarod, and 24-h body weight in a dose-dependent manner. GALP also increased LH secretion in female mice, an effect that was blocked by pre-treatment with Antide, a gonadotropin-releasing hormone (GnRH) type-1 receptor antagonist. GALP infusions slightly decreased the occurrence of lordosis behavior in female mice and significantly increased the latencies with which females displayed receptivity. Unlike previous reports in male rats, GALP inhibited male sexual behavior in mice. Our data indicate that in female mice, GALP stimulates LH release via GnRH, and decreases body weight, motor control, and locomotor activity via GnRH-independent pathways. Furthermore, our sexual behavior and locomotor findings suggest species-specific differences in the mechanism and/or location of GALP action in the brains of rats and mice.

Temporal and spatial quantitation of nesting and mating behaviors among mice housed in a semi-natural environment

Enhanced behavioral complexity may be observed when animals are tested in naturalistic environments and engaging in nonforced social interactions. For each of six experimental runs, different groups of five adult Swiss-Webster mice (four ovariectomized females and a single male) were maintained under 12h dark:12h light in a 122 x 122 x 30.5-cm open box containing six peripheral "nestboxes." On Day 1, females were released into the box first and their nesting behavior was observed. Two days later, each female was injected with estradiol benzoate and the male was introduced into the environment. Females were injected with progesterone (P) 48 h later and the animals were observed for an additional 14 h. Behaviors were recorded with a video camera suspended over the apparatus. Mating occurred only post-P and males always mated preferentially with certain females. The amount of nesting behavior per female on Day 1 correlated significantly with the number of times each female was mated by the male (r = 0.57, P < 0.005). In all but one run, the male ejaculated with the female who performed the most nesting behavior. While 63% of mating was in the open, 56% of nestbox matings resulted in female postmating darting to alternate nestboxes; in 19% of these cases, the female quickly returned to the mating nestbox and was mated there again. Direct approaches by females to the male and behaviors which affect pacing were observed. These behaviors have not been reported previously for mice and may provide additional endpoints for the exploration of hormonal and genetic influences on reproductive behaviors.