Preoptic implants of estradiol increase wheel running but not the open field activity of female rats

In order to localize the neural substrate for estrogen induction of increases in activity, bilateral implants of dilute estradiol (in concentrations of 1:10, 1:100, and 1:250) were made into the medial preoptic area (n = 5), the anterior hypothalamus (n = 8), the ventromedial hypothalamus (n = 6), and the posterior hypothalamus (n = 4) of ovariectomized female rats housed in running wheels. The same animals were also tested for open field activity and lordosis. The preoptic area was the most effective site tested for estrogenic stimulation of running wheel activity, with 3/5 animals responding consistently to estradiol application. 3/8 animals with cannulae in the anterior hypothalamus (AHA) responded with increases in activity measured in the running wheel on at least two out of three estradiol treatments. No animals with cannula placements posterior to the AHA exhibited consistent running wheel responses to estradiol. No estrogen-induced increase in open field activity was found, regardless of cannula location or concentration of estradiol; however, there was a tendency for the number of squares entered during the later tests to decrease in the ventromedial hypothalamic nucleus group and in the subgroup of animals not showing estrogen-sensitive wheel running in the anterior hypothalamic area group. Only the ventromedial hypothalamic estradiol treatments stimulated lordosis behavior. These results support earlier reports suggesting that the medial preoptic area (and possibly the adjacent anterior hypothalamic area) is the critical brain site for estrogenic stimulation of running wheel activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of ovarian hormones on synchrony of hamster circadian rhythms

Adult ovariectomized hamsters which were implanted with Silastic capsules containing estradiol benzoate (EB), progesterone (P) or nothing (Blank) were exposed to prolonged constant light (LL) with free access to running wheels. Freerunning locomotor rhythms were recorded on an event recorder. Light energy levels averaged 12.2 uwatts/cm² or 48.3 Lux. Rhythm splitting occurred in $\text{1}\text{7}$ animals given EB, $\text{5}\text{7}$ given P and $\text{5}\text{11}$ Blank implanted animals. Altogether, $\text{1}\text{7}$ EB, $\text{6}\text{7}$ P and $\text{8}\text{11}$ Blank implanted animals showed some form of splitting or other rhythm anomaly such as desynchrony of endogenous oscillations. There was a high incidence ($\text{10}\text{11}$) of animals showing an additional transient rhythmical component running across the split condition. The study supports the concept that a multi-oscillatory system normally generates a cohesive circadian behavioral rhythm. Estradiol appears to facilitate the synchrony of these oscillations.     

Effects of estradiol on food intake and meal patterns for diets that differ in flavor and fat content

Apart from the well known inhibitory effects of estradiol on food intake, meal size, and body weight in female rats that have been documented over the past thirty years, a more recent report presents the opposite finding; that a large dose of estradiol can increase food intake and weight gain in gonadally intact female rats presented with a palatable diet. The purpose of the present experiment was to further examine this hypothesis by evaluating the ability of estradiol to influence feeding behavior in ovariectomized rats presented with diets that differ in flavor and fat content. Female rats were given a cyclic regimen of estradiol benzoate treatment (5.0 or 20.0 µg) or the oil vehicle and were presented with the standard chow diet or a diet with a higher fat content and chocolate flavor. Food intake, meal size, and meal number were monitored three days after the first injection of estradiol or oil. Compared to the chow diet, food intake increased when animals had access to the chocolate/fat diet during the vehicle treatment condition. Both doses of estradiol significantly decreased food intake, meal size, and body weight gain when animals were presented with either the standard chow diet or the chocolate/fat diet. These findings indicate that estradiol does not stimulate the intake of a palatable diet in ovariectomized rats, and suggest that previous results showing that estradiol enhanced eating and weight gain stemmed from a disruption of the hypothalamic-pituitary-gonadal axis when intact females received a large dose of exogenous estradiol.     

Effects of acute ovariectomy on the lordosis response of female rats

The sexual receptivity of intact females with 4- or 5-day estrous cycles was compared to that of other females which had been ovariectomized at particular times during their cycles. The quality and frequency of lordosis responding were more degraded the earlier during the cycle ovariectomy was performed. This effect was more pronounced in 4-day than in 5-day cyclic females. Because exogenous progesterone was administered to all ovariectomized females, these behavioral deficits were attributed to removal of ovarian estradiol. Ovariectomy 6 hr before the critical period for luteinizing hormone release significantly shortened the duration of behavioral estrus, even though it had no effect when lordosis was tested at the time intact estrous females are maximally receptive. These findings are consistent with the hypothesis that the continual availability of estradiol throughout the 18--24 hr interval perior to the onset of behavioral estrus is essential for optimal conditioning of sexual receptivity to occur under physiological conditions. The relevance of triggering and maintenance functions of estradiol to these results is discussed.     

Exercise reduces gonadal atrophy caused by short photoperiod or blinding of hamsters

The effect of voluntary exercise upon several reproductive parameters was assessed in male Syrian hamsters. Forty-two animals were caged in five groups and then blinded: Ten housed five per plastic cage; eight housed individually in plastic cages; six housed individually in plastic cages with 15 cm exercise wheels in the cage; eight housed in Wahmann steel activity cages with 36 cm wheels locked to prevent rotation; ten housed in functional Wahmann running wheel cages. At 16 weeks after blinding, animals with access to functional running wheels had significantly larger testes (3.7 +/- 1.0 g) than those with no wheels or locked wheels (1.86 +/- 0.6 g; mean +/- SD; p less than 0.001). These results suggested that voluntary exercise reduces testicular atrophy caused by blinding. A second experiment was run in which the animals were subjected to a short photoperiod (LD 6:18) for 12 weeks instead of blinding. Similar results were obtained except that access to the small exercise wheels did not affect testicular atrophy: Mean testicular mass of animals in individual cages = 0.79 +/- 0.3 g, small wheels = 0.74 +/- 0.4 g, functional Wahmann wheels, 2.56 +/- 1.0 g, locked Wahmann wheels 0.52 +/- 0.1 g (p less than 0.01).     

Behavioral consequences of hormonal deprivation on the responsiveness of female rats to estradiol

Female rats which had been ovariectomized either 7 days earlier (short-term deprivation, N = 11) or 35 days earlier (long-term deprivation, N = 11) were tested for their response to treatments of estradiol benzoate (6.0 micrograms/kg body weight) and progesterone (1.2 mg/kg). The long-term deprived females showed less sexual behavior than females deprived for only 7 days prior to treatment. In particular, lordosis quotients after treatment with estradiol alone were significantly lower in the long-term deprived females, t(20) = 3.194, p less than 0.01. Following a supplemental progesterone injection, the lordosis scores and the number of proceptive behaviors displayed by long-term deprived females were also significantly lower than these measures in short-term deprived females, t(20) = 3.481, p less than 0.01 and t(20) = 3.737, p less than 0.01, respectively. In contrast, the two groups did not differ in the degree to which estradiol treatment suppressed food intake, F(1,20) = 2.306, N.S. Likewise, the changes in water intake and body weight produced by estradiol treatment did not differ significantly between the two groups, F(1,20) = 0.118, N.S. and F(1,20) = 0.452, N.S., respectively. The results obtained from the sex behavior tests are generally consistent with the notion that hormonal deprivation alters the responsivity or sensitivity of female rats to estradiol. However, these changes do not appear to involve a general decline in receptor sensitivity or number, because the ability of estradiol to suppress ingestive behaviors was not diminished in the long-term deprived females.     

Hormonal control of the perception of the olfactory signals which facilitate lordosis behavior in the male rat

This study was designed to evaluate in the male rat the hormonal requirements for the facilitation of feminine behavior by the odor of male urine. Wistar rats from the WI and WII strains in our colony were orchidectomized (ORCH) as adults. A first group was given a single dose of 75 micrograms estradiol benzoate (EB) and tested for lordosis behavior 48 hr later. Exposure to the odor of male urine by 9 +/- 1 hr before the behavioral session did not increase the number of animals showing lordosis behavior as compared to non exposed controls. A second group of WI rats was given 0.5 micrograms EB every day for 4 to 8 days. A similar number of animals displayed lordosis behavior irrespective of whether they were exposed to the odor of urine before testing. A third group of WI rats was injected with 75 micrograms EB and 1 mg progesterone (P) 39 hr apart. Exposure to the odor of urine during estrogen treatment remained ineffective but significantly increased the number of animals showing lordosis behavior when performed at the time of P injection. A last group of WII rats was given 25 micrograms EB and 100 micrograms or 150 micrograms P 39 hr apart. Although uncapable as such to facilitate lordosis behavior the dose of 100 micrograms P rendered the animals responsive to the odor of urine. It was concluded that (1) the perception by feminized males of olfactory signals from the male was dependent on P; (2) an interaction between hormonal and sensory mechanisms was involved in the facilitation of lordosis behavior in the male rat.     

Lack of estradiol modulation of sleep deprivation-induced c-Fos in the rat brain

Women recover from sleep deprivation more efficiently than men, but the mechanism for this difference is unknown. Effects of estrogen on sleep suggest that it could play a role, but the brain targets on which estrogen may act to have this effect have not been identified. Sleep deprivation increases levels of the immediate-early gene protein c-Fos in selected brain regions, but it is unknown whether estrogen modulates this response. We investigated the influence of different levels of exogenous estradiol on the c-Fos response to sleep deprivation in ovariectomized female rats. Female rats were treated with low or high levels of estradiol (mimicking diestrous and proestrous levels, respectively) delivered via subcutaneous silastic tubes. Control ovariectomized females and sham-operated males were implanted with tubes filled with cholesterol. One week after surgery, half of the rats underwent a 3 h period of sleep deprivation during the light phase in a motorized Wahmann activity wheel that rotated constantly at a slow speed, while half were confined to fixed wheels. Immediately after sleep deprivation, animals were killed and their brains processed to detect c-Fos using immunohistochemistry. Sleep deprivation increased the number of c-Fos positive cells in a number of brain areas, including the caudate putamen, medial preoptic area, perifornical hypothalamus, and anterior paraventricular thalamic nucleus. Other areas, including the suprachiasmatic nucleus, posterior paraventricular hypothalamic nucleus, posterior paraventricular thalamic nucleus, arcuate nucleus, and central amygdala, did not respond to 3 h sleep deprivation with a significant increase in c-Fos levels. Levels of c-Fos induced in the selected brain regions by sleep deprivation were not modulated by estrogen levels, nor by sex.     

Effects of Silastic progesterone implants on activity cycles and steroid levels in ovariectomized and intact female rats

We have previously shown that although Silastic implants of progesterone reduce the amount of running of animals living in activity wheels, progesterone-treated animals continue to show periodic fluctuations or peaks in activity. We hypothesized that although progesterone treatment inhibited estrous cycles, ovaries of animals treated with Silastic implants of progesterone continued to secrete estradiol in amounts adequate to stimulate moderate levels of running. In the present study we tested this hypothesis by removing ovaries from progesterone-treated animals and comparing their running behavior and steroid levels to progesterone-treated animals who received sham ovariectomies. Although progesterone treatment significantly inhibited running activity, removal of ovaries in progesterone-treated animals further suppressed running activity. In addition, both estradiol and progesterone levels were significantly reduced following removal of ovaries in progesterone-treated animals. We conclude that although Silastic progesterone implants inhibit normal ovarian and estrous activity cycles, ovaries produce sufficient estradiol to stimulate running behavior.     

Self-starvation: A problem of overriding the satiety signal?

Rats housed in either activity wheels or standard laboratory cages received access to food either ad lib or for one 60-min, two 30-min, or four 15-min periods per day. Imposition of restricted feeding schedules led to reductions in food intake and body weight which were greater for animals with access to activity wheels. Increases in activity reflected the percent of body weight loss, which varied directly with frequency of food access. Subsequent recovery of intake was facilitated by partitioning total feeding time into briefer but more frequent periods. In the most extreme frequency-of-access condition, animals with access to running wheels failed to recover from the reduction of intake incurred by imposition of the restricted feeding schedule, even though their total feeding time was the same as that of animals that did recover. These data indicate that self-starvation is not induced by activity per se but results from a general failure to recover intake which, in turn, results from a failure to override the satiety signal within a meal.     

Identification of proteins regulated by estradiol in focal cerebral ischemic injury—A proteomics approach

Estradiol protects neuronal cells against permanent and focal ischemic brain damage. We identified the proteins that are expressed following estradiol administration during cerebral ischemia in an animal model. Adult female rats were ovariectomized and treated with oil or estradiol prior to middle cerebral artery occlusion (MCAO) to induce cerebral ischemia, and brains were collected 24 h after MCAO. Protein analysis was performed on the cerebral cortex using two-dimensional gel electrophoresis. Protein spots with difference in intensity between oil- and estradiol-treated groups were identified by mass spectrometry. Among these proteins, levels of protein phosphatase 2A (PP2A) and astrocytic phosphoprotein PEA-15 were significantly decreased in the oil-treated group in comparison to the estradiol-treated group. Moreover, Western blot analysis demonstrated that estradiol treatment prevents injury-induced decrease of PP2A and PEA-15 levels during both MCAO-induced injury and glutamate exposure in HT22 cells. In contrast, levels of the 60 kDa heat shock protein (Hsp 60) were significantly increased in oil-treated animals, while estradiol prevented the injury-induced increase of Hsp 60. The results of this study provide an evidence that estradiol protects neuronal cells against ischemic brain injury through the up- and down-modulation of specific proteins.     

Long-term maintenance of receptivity by subcutaneous implants of estradiol.

Ovariectomized female rats were implanted with Silastic capsules which were either empty (Controls) or contained one of two concentrations of estradiol in oil. The two experimental capsules released levels of estradiol for 7–14 days which resembled either proestrous or diestrus II serum values, then decreased to low levels. In both experimental groups all animals showed sexual receptivity by Day 7 and this response was maintained through Day 32. While no differences in lordosis quotients were found between experimental groups on Days 7 or 11, by Day 14 the group with the less concentrated estradiol capsule showed a significantly lower LQ response, which was maintained until the termination of testing. There was no evidence for day-night differences in receptivity in any estradiol-implanted animals. Body weights declined in a dose-dependent fashion within 3 days after implantation of the estradiol capsules. Weights then began to recover by 11 days after implantation, but remained significantly below those of ovariectomized controls with empty implants for the duration of the experiment.     

The effect of hysterectomy on hormone-induced lordosis behavior in hamsters

Ovariectomized-hysterectomized (OH) and ovariectomized-sham hysterectomized (OSH) hamsters were tested for lordosis behavior following treatments including either 1, 5, or 10 micrograms estradiol benzoate (EB) in combination with 0.1, 0.25, and 0.5 mg progesterone. Few animals responded at the 1 microgram dose of EB and there were no differences in latency to the first display of lordosis or in the total lordosis duration among responding animals in the 5 and 10 micrograms EB groups. However, there was significantly more positive tests in the OSH group injected with 5 micrograms EB than in the OH group and this difference approached statistical significance in the 10 micrograms EB groups. The results are compared to similar studies in rats and possible mechanisms for the effects of hysterectomy are discussed.     

Assessment of estradiol and its metabolites in meat

Most studies related to research on steroids in main edible tissues (muscle, liver or kidney) have focused on measurement of parent or major metabolite residues. In order to evaluate the estradiol content in bovine edible tissues, a multi-step extraction procedure was developed in conjunction with parallel metabolism studies of [14C]-17beta-estradiol in cattle (1-2). Various classes of free estradiol and conjugates were separated: estradiol -17beta and -17alpha, estradiol-17-fatty acid esters, estradiol 17-glycoside, estradiol 3-glucuronide, estradiol-17-glycoside and 3- glucuronide (diconjugates) were separated. No sulphates conjugated forms have been found at the detection level of the method. The quantification was realized by calibration with deuterated 17beta -estradiol -d3 standard and was validated at the ng x kg(-1) (ppt) level. Muscle, liver, kidney and fat samples from control or Revalor S single (licensed implantation) or multi-implanted steers have been assayed. The results show a wide variation between animals, but both the highest value and the mean of total estradiol content in each group proportionally increase from untreated to multi-implanted animals. In accordance with international rules, a calculation of the daily food supply of estradiol by such edible tissues in comparison with the acceptable daily intake was performed.     

Maternal behavior in the mouse: effect of estrogen and progesterone

The administration of 100 μg and 50 μg of estradiol benzoate for 5 consecutive days to adult, nulliparous. Rockland-Swiss mice that previously exhibited maternal behavior resulted in a loss of such behavior. The effect of estradiol was temporary since normal maternal activities were exhibited when the animals were retested two weeks after the termination of hormone treatment. Treatment with 5 μg and 0.5 μg estradiol benzoate did not significantly affect maternal behavior. Progesterone treatment at dosages of 1000 μg and 500 μg was without affect.     

Estradiol prevents the injury-induced decrease of 90 ribosomal S6 kinase (p90RSK) and Bad phosphorylation

Estradiol prevents neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals. This study investigated whether estradiol modulates the anti-apoptotic signal through the activation of Raf-MEK-ERK and its downstream targets, including 90 ribosomal S6 kinase (p90RSK) and Bad. Adult female rats were ovariectomied and treated with estradiol prior to middle cerebral artery occlusion (MCAO). Brains were collected 24h after MCAO and infarct volumes were analyzed. We confirmed that estradiol significantly reduces infarct volume and decreases the positive cells of TUNEL staining in the cerebral cortex. Estradiol prevents the injury-induced decrease of Raf-1, MEK1/2, and ERK1/2 phosphorylation. Also, it inhibits the injury-induced decrease of p90RSK and Bad phosphorylation. Further, in the presence of estradiol, the interaction of phospho-Bad and 14-3-3 increased, compared with that of oil-treated animals. Our findings suggest that estradiol prevents cell death due to brain injury and that Raf-MEK-ERK cascade activation and its downstream targets, p90RSK, Bad phosphorylation by estradiol mediated these protective effects.     

Estradiol and insulin: independent effects on eating and body weight in rats.

The effects of ovariectomy and estradiol replacement were determined in streptozotocin-diabetic female rats maintained on daily injections of protamine zinc insulin. Similar changes in food intake and body weight in these animals and in nondiabetic control animals indicate that the effects of estradiol on these measures are probably not dependent on changes in pancreatic insulin secretion. Acute and chronic insulin challenges in ovariectomized rats maintained on estradiol benzoate, nafoxidine or oil were also examined. The effects of insulin were not attenuated by prior estrogen conditioning, and there was no evidence of insulin resistance. These experiments suggest that the effects of estradiol on body weight and food intake in female rats are not dependent upon altered insulin levels nor attenuation of the effects of insulin. Estradiol may exert its influence on eating and body weight via separate and possibly more direct pathways. The data also are consistent with the suggestion that ovariectomy-induced and hypothalamic obesities are separate phenomena.     

大鼠去卵巢前后血清雌二醇浓度变化及其对输卵管粘膜上皮的影响

目的　研究哺乳动物血清雌二醇与输卵管粘膜上皮细胞高度之间的相关性。　方法　据阴道涂片检查将动物分为 :动情间期 (DE)组 ,动情前期 (PE)组 ,动情期 (E)组 ,动情后期 (ME)组和去卵巢 (OVX)组 ,用放射免疫法检测各组大鼠血清雌二醇浓度 ,同时在光镜下对输卵管壶腹部、峡部的形态结构进行测量分析。　结果　大鼠血清雌二醇浓度依次为 :动情期组 >动情前期组 >动情后期组 >动情间期组 >去卵巢组 ,各组间差异均有显著性 ;输卵管粘膜上皮高度在动情周期中变化为 :动情期组 >动情前期组 >动情间期组 >动情后期组 ;去卵巢后 ,输卵管粘膜上皮萎缩。　结论　上述两项检测结果经回归分析发现 ,从动情间期至动情前期再至动情期两者呈正相关。     

Effects of stereoisomers of estradiol on food intake, body weight and hoarding behavior in female rats

The effects of 17-alpha and 17-beta estradiol on food intake, body weight and hoarding behavior in ovariectomised rats were investigated. For five days, ten animals received subcutaneous injections of both isomers (10 micrograms/kg/day) in a counterbalanced design. Hoarding tests were conducted on the last three days of each 5-day injection period. 17-Alpha estradiol significantly reduced food intake but was without effect on body weight. 17-Beta estradiol reduced food intake significantly more than the alpha form and also significantly reduced body weight. These differential effects suggest that stereoisomers of estradiol may be acting on separate regulatory systems. The treatments did not change hoarding activity compared to pre-treatment levels.     

Interaction of estradiol and photoperiod on activity patterns in the female hamster

The extent of the effects of estradiol on the locomotor rhythm in hamsters is unknown. This study was designed to determine the ability of estradiol alone and in combination with the photoperiod to alter activity patterns. Intact animals displayed higher levels of activity in LD 16:8 than in LD 6:18. Ovariectomy without estradiol treatment caused a sharp decline in activity in LD 16:8; estradiol treatment prevented this. In LD 6:18, activity levels were unaffected by either estradiol or ovariectomy. Estradiol altered the temporal distribution of activity only in LD 6:18, advancing peak activity towards lights-off. Estradiol decreased the variability in day to day onsets of activity in LD 6:18, but did not affect onsets in LD 16:8. The data suggest that the activity rhythm of the hamster is comprised of discrete components; the response of each component to estradiol is differentially altered by photoperiod. Furthermore, estradiol is vital for the expression of high activity levels in the LD 16:8 female.