Changes in dopamine sensitivity in isolated neurons of the preoptic region during the estrous cycle

The dopamine sensitivity of individual neurons of the midbrain preoptic region as a center of the cyclic regulation of hypophyseal gonadotropic function was investigated under conditions of dopamine microiontophoretic delivery during various stages of the estrous cycle in rats. It was shown that most neurons do not respond to dopamine during the diestrus-1 stage. The first half of the day of the diestrus-2 stage was characterized by a high representation of neurons with an activation response. Cells with an inhibitory response to dopamine were observed to increase among the spontaneously active neurons of the preoptic region starting from the second half of the day of this stage of the estrous cycle. The greatest quantity of neurons with an inhibitory response was observed during proestrus.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 68, No. 3, pp. 331–336, March, 1982.     

Effects of ovariectomy and estrogen replacement on rat oral mucosa

OBJECTIVE: Although a close relationship between the oral discomfort and the menopause is suggested, it is not clear if the alteration of sex steroids would cause any histological or even pathological change in the oral mucosa. The aim of this study was to investigate the possible effect of sex steroid deficiency on the rat oral mucosa as well as the effect of its replacement. METHODS: The oral mucosa of ovariectomized rats was compared to that of sham-operated rats both histologically and immunohistochemically. The same evaluation was also performed after hormone replacement therapy for the ovariectomized rats. RESULTS: The ovariectomized animals presented reduced thickness of the mucosal epithelium with an irregular corneal (keratinised) surface. Partial disappearance of lingual papilla with irregular lete-peg was also noted. The corneal (keratinised) layer in the sublingual region was significantly thinner in ovariectomized animals. The results from immunohistochemistry showed the possibility that the turnover period was prolonged in ovariectomized rats. Estrogen replacement could compensate for the reduction in mucosal thickness in the animal model. CONCLUSIONS: The overall results suggest that sex steroids have a specific role in the maintenance of normal oral mucosa, and its deficiency possibly leads to the onset of oral discomfort in postmenopausal women.     

Some effects of ovariectomy and estrogen replacement on body composition in the rat

Sprague-Dawley rats were ovariectomized (OvX) at 3 ages, day 2 (D2), week 4 (W4) and week 7 (W7); a group of OvX W7 rats were treated daily with estrogen (OB; 2 μg for 2 or 5 weeks from 10 weeks of age). Rats were slaughtered at 4 ages, weeks 7, 9, 12 and 15, for the chemical analysis of carcass and skin. Chemical compositions were analysed as % wet weight and as component weights by two-way analysis of variance. Component weights were also analysed by allometry, regressing against nose-anal length. Ovariectomy increased overall body weight without causing obesity. The weight gain of the OvX rat was mainly a true growth response but OvX affected body proportions so that at a given body length the OvX rat had a larger skin and carcass than controls. Ovariectomy at the earliest age (D2) produced the smallest response in body weight and body length but produced the greatest fat redistribution towards the skin and away from the carcass; there was no net change in whole body fat levels following OvX. Long-term daily OB treatment increased fat reserves but slowed the growth of other body components, including the axial skeleton. Whereas OvX redistributed components between skin and carcass, OB treatment reversed this process.     

The influence of gender and the estrous cycle on learned helplessness in the rat

Although the etiology of clinical depression is unknown, women are more likely to suffer from major depressive disorder than men. In addition, in some women, there is a clear association between depression and specific phases of the menstrual cycle. Surprisingly little research has examined gender differences and the influences of the estrous cycle in this and other animal behavioral models of clinical depression. Learned helplessness is a valid animal model of stress-induced behavioral depression in which prior exposure to inescapable stress produces deficits in escape testing. Learned helplessness was studied in rats using an inescapable tail shock stress followed by a shuttle box test to determine escape latencies. Animals with mean escape latencies of >or=20 s after shuttle-box testing are defined as learned helpless. Males and normal cycling female rats in the estrus and diestrus II phases were studied. Female rats in the diestrus II phase had significantly higher escape latencies and exhibited a more helpless behavior than female rats in the estrus phase. Male rat escape latencies were intermediate between the two female phases. These results suggest a role for gonadal hormones in the development of stress-induced behavioral depression or 'learned helplessness.'     

Influence of the estrous cycle, ovariectomy and estradiol replacement upon the acquisition of conditioned avoidance responses in rats

The changes in the acquisition of conditioned avoidance responses (CARs) and the performance of some spontaneous behaviors were examined across the estrous cycle of female rats. CARs were facilitated during diestrus, impaired at proestrus and practically abolished at estrus and metestrus. Motor activity and head shaking were minimally affected with the stages of the cycle. Motor activity was increased at metestrus and head shaking decreased at estrus. At 14 days following ovariectomy, there was a significant enhancement of CARs which was antagonized by the daily administration of estradiol benzoate (10 micrograms/kg) for three days. Ovariectomy also increased grooming behavior and estradiol replacement returned grooming to its basal level. The results suggest an inhibitory control of estradiol on CARs and grooming. The involvement of other hormones which also varied across the estrous cycle and its interaction with brain catecholamine systems, particularly dopamine, are discussed.     

The influence of the estrous cycle on the activity of striatal neurons recorded from freely moving rats

Recordings from striatal neurons in conscious rats at various stages of the estrous cycle revealed differences in the activity of the neurons. Average firing rate was higher in diestrus than in animals in estrus or proestrus. The increase did not seem to depend on the motor activity of the animals nor was it present in ovariectomized rats. Since application of estrogen to ovariectomized rats did not change the firing rate of the neurons, we conclude that differences during the cycle in conscious rats are not mediated by an action of estrogen unlike those seen in anesthetized rats. Differing electrode sampling bias in the two situations, or an action of anesthetic in revealing the estrogen effect may explain the differences.     

Variation of fat intake with estrous cycle, ovariectomy and estradiol replacement in hamsters (Mesocricetus auratus) eating a fractionated diet

Intakes of fats, proteins, and carbohydrates were measured daily for a 3 month period in female hamsters maintained on a fractionated diet consisting of the dietary constituents, dextrose, fat and soybean meal. In the first study, hamsters showed variations in body weight and fat intake across the estrous cycle and following ovariectomy, with elevations during diestrous and after ovariectomy when endogenous estrogens are reduced. In the second study, the effects of exogenous estradiol or cholesterol on intake patterns of ovariectomized hamsters were determined. Hamsters lost weight and decreased fat intake when implanted with a silastic containing estradiol and gained weight and increased fat intake when exposed to cholesterol treatment. In neither of the two studies were the intakes of protein or carbohydrates significantly affected by the animals' hormonal status. These results suggest that in the hamster, estrogenic effects on food intake are specific to some dietary constituents and not to others.     

The effects of microelectrophoretically applied estrogen,cortisol and acetylcholine on medial preoptic-septal unit activity throughout the estrous cycle of the female rat

Summary The technique of microelectrophoresis was utilized to study the effects of 17-estradiol hemisuccinate (17E₂S), cortisol hemisuccinate (CS), and acetylcholine (Ach) on medial preoptic-septal (mPOA-S) neurons throughout the estrous cycle in urethane anesthetized rats. A total of 23 cells were identified antidromically as having their projections to the arcuate-median eminence region of the hypothalamus, and 18 of these were tested with 17E₂S. Only four cells showed an inhibition to the gonadal steroid, while the remaining neurons did not respond. Twelve antidromically identified (AI) neurons were tested with CS, none of which responded, and 2 out of 16 AI neurons showed an excitation to Ach. Extracellular potentials were recorded from 273 non-antidromically identified neurons, 138 of which were successfully tested with 17E₂S. Sixty-two of these responded to the steroid. The predominant response on late diestrus I was excitation, and the majority of estrogen-sensitive cells showed an inhibitory response on late diestrus 2, proestrus and estrus. A Chi-square analysis showed that the response varied significantly throughout the estrous cycle.Cortisol hemisuccinate was tested on 154 non-antidromically identified mPOA-S neurons. The response to the corticosteroid also varied significantly throughout the cycle, but further analysis determined that the response was different from that of 17E₂S. Acetylcholine was also applied to 180 mPOA-S neurons, but no significant change in the response was found from one day of the cycle to the next.It is apparent from these studies that (1) 17E₂S can bring about direct and rapid changes in the firing frequency of neurons, (2) the non-antidromically identified neuron is a site for these effects, and (3) the response differs significantly throughout the estrous cycle.Supported by NIH Grant NS10434-END, awarded to R. L. MossPresently an NIH Postdoctoral Fellow at Max-Planck Institute for Biophysical Chemistry, Göttingen, West GermanyRecipient of an USPHS Career Development Award No. HD00146     

Assessment of micronucleus frequency in the peripheral blood of female rats in persistent estrus treated with selective estrogen receptor modulators

The aim of this study was to evaluate micronucleus (MN) frequency in polychromatic erythrocytes (PCE) of female rats in persistent estrus (a model developed to mimic polycystic ovary syndrome) treated with selective estrogen receptor modulators (SERMs, tamoxifen, and raloxifene). Forty female Wistar-Hannover rats were divided into four groups of 10 animals each: Group I (normally cycling rats) and Group II (persistent estrus) both received only vehicle, while Group III (persistent estrus) was treated with tamoxifen (250 μg/animal/day) and Group IV (persistent estrus) was treated with raloxifene (750 μg/animal/day). Tamoxifen and raloxifene were given by oral gavage beginning on postnatal day 90 and continuing for 30 consecutive days. Peripheral blood samples were collected from tails 1 day following the last exposure. Blood smears were made on glass slides and stained with 10% Giemsa solution. ANOVA and a Tukey post-hoc test were used for data analysis. Mean percentages of MN were 1.82 ± 0.13, 5.20 ± 0.24, 3.32 ± 0.13, and 3.04 ± 0.12 in Groups I, II, III, and IV, respectively. The results indicate that tamoxifen and raloxifene similarly reduced the formation of MNPCE of female rats in persistent estrus (P < 0.0001 for Groups III and IV vs. Group II), using the dosages and time periods applied in the present study. The data suggest possibly antimutagenic effects of SERMs under high levels of estrogens. The findings also suggest that this is an interesting animal model for studying the genotoxicity of estrogens.     

Immunocytochemical characterization of afferents to estrogen receptor-containing neurons in the medial preoptic area of the rat.

Double-label immunocytochemistry has been employed to elucidate the chemical nature of the afferent neuronal projections to the estrogen receptor-containing neurons located in the medial preoptic area of the rat brain. To ensure a clear separation of the immunolabelled afferent profiles from the estrogen receptors, the former were visualized first and the diaminobenzidine reaction product was silver-gold intensified. Using a monoclonal antibody raised against purified human estrogen receptors, we observed an intense nuclear immunoreactivity in Vibratome, semithin and ultrathin sections. Neuropeptide-Y, serotonin-, phenylethanolamine N-methyltransferase- and adrenocorticotrophin-immunoreactive axons and varicosities were observed in close apposition to the estrogen receptor-positive cells. At the ultrastructural level, neuropeptide-Y-immunoreactive boutons were seen in synaptic contact with cells showing estrogen receptor immunoreactivity in their nucleus. These results indicate that neurons located in the medial preoptic area, one of the principal sites for the control of female reproductive function, may be influenced by both estrogen and neurotransmitters/neuropeptides via, respectively, nuclear receptors and synaptic contacts.     

去卵巢和雌激素替代治疗对心肌细胞基因表达谱的影响

目的：本实验通过高通量的cDNA微阵列技术，研究去卵巢和雌激素替代治疗对心肌细胞基因表达谱的影响，寻找雌激素的靶基因。方法:用 1 400 个基因构建的cDNA微阵列检测假手术组（Ⅰ）、去卵巢组（Ⅱ，去势组）和雌激素替代治疗组（Ⅲ，替代组）3组SD雌鼠心肌组织的基因表达差异,随机选2个基因用半定量RT-PCR验证检测结果。结果:假手术组和去势组共检出心肌差异表达的基因177个，其中去卵巢导致上调的基因91个，下调的基因86个；去势组和替代组共检出心肌差异表达的基因164个，其中雌激素替代治疗后导致上调的基因113个，下调的基因54个。Ⅰ/Ⅱ和Ⅲ/Ⅱ比较，相同的差异表达基因54个，雌激素明显影响心肌膜通道和载体（18个）、细胞受体（9个）、信号转导相关基因（7个）和细胞代谢（6个）的mRNA水平。而大部分基因（45个）是在去势组表达下调，在雌激素替代组表达上调。RT-PCR实验证实了cDNA微阵列结果 。结论：长期雌激素替代治疗明显影响心肌细胞膜通道和载体、信号转导、细胞受体和细胞代谢等相关基因的表达。长期雌激素替代治疗可通过增加Na+,K+-ATPase和Na+/H+交换蛋白的基因表达，稳定心肌细胞内Na+和K+的浓度。雌激素还可抑制多巴胺受体基因的表达，预防心肌肥大、充血性心衰等心脏疾病的发生。     

Long-term effects of ovariectomy and estrogen replacement treatment on endothelial function in mature rats

OBJECTIVES: Estrogen replacement therapy (ERT) improves blood flow through various mechanisms including an augmented release of nitric oxide (NO). We report on the long-term effects of estrogen loss on vascular function and endothelial regulation. METHODS: Male, female, ovariectomized and ovariectomized+ERT treated rats were used. Female rats were ovariectomized at 12 weeks of age and received ERT via subcutaneously implanted 90-day release pellets. Vasodilation to acetylcholine (ACh) was studied in tail artery segments; arterial blood was collected for measurements of 17-beta-estradiol and stable metabolites of NO (nitrate/nitrite). Some arterial segments were harvested for TUNEL staining to determine endothelial apoptosis. RESULTS: Ovariectomy caused a rapid loss of estradiol that was negated by ERT. Likewise, there was also a loss in plasma NO. Loss of ACh-mediated dilations were age-dependent and were significant in males and untreated ovariectomized rats, with the change being maximal after 12 weeks of ovariectomy. After 12 weeks post-ovariectomy, there were no time dependent changes in ACh sensitivity in either group. Dilations to ACh were maintained in females and age-matched ERT ovariectomized rats over time. TUNEL staining of the endothelium (at 6 months of age) revealed apoptotic changes with the rank order male>ovariectomized>female, or ERT treated ovariectomized female rats. CONCLUSIONS: In a rat model of surgical menopause, loss of endothelial function is maximal 12 weeks after ovariectomy. Apoptosis of endothelial cells is greatest in arteries from male rats. Our data suggests that early ERT treatment may be an important consideration for reducing endothelium-dependent vascular dysfunction.     

雌激素改善卵巢切除合并慢性铝中毒对大鼠心脏Cx43表达和金属元素变化的影响

目的 探讨雌激素治疗卵巢切除合并慢性铝中毒大鼠,对心脏间隙连接蛋白43(Cx43)表达和金属离子含量的影响. 方法 40只6月龄雌性SD大鼠,随机分为卵巢假切除组(Sham组),卵巢切除组(OVX组)、卵巢切除合并慢性铝中毒组(OVX+Al组)和卵巢切除合并慢性铝中毒及尼尔雌醇灌胃组(OVX+Al+E2组).于术后3个月,利用离子体发射光谱仪测定心脏金属元素含量,采用免疫组织化学和图像分析法观测心肌细胞Cx43表达.结果 1. Cx43表达:Sham组心房肌Cx43遍布于心肌细胞侧面连接和端闰盘处.心室肌分布于心肌闰盘处.OVX组心房肌的Cx43颗粒部分由细胞侧-侧连接处移至闰盘处或杂乱排列,心室肌Cx43由闰盘处移至细胞侧-侧连接处或杂乱地无序排列,少部分出现在细胞质中,OVX+Al组Cx43排列类似于OVX组,且更加紊乱.OVX+Al+E2组心房肌Cx43回复正常分布,但心室肌未发现回复.2.图像分析结果,各组大鼠心肌细胞Cx43的面积构成比比较无显著差异.3.金属元素含量:在Sham组,金属元素在心脏含量的排列顺序如下:Mg＞Ca＞Fe＞Zn＞Al＞Si＞Cu＞Mn＞Se和Cd.各组间比较具有显著差异的是:与Sham组比较,OVX组Zn降低;OVX+Al+E2组Al、Cd、Si、Se均升高;OVX+Al组与OVX组比较,Si升高、Zn降低.OVX+Al+E2组与OVX+Al组比较, Cd、Mn、Se升高. 结论雌激素改善卵巢切除及加铝后引起的心脏金属元素含量改变和心肌细胞间隙连接蛋白Cx43重构.     

Changes in numbers of acidophilic and basophilic connective tissue granulated cells in the intestine of the rat during the estrous cycle

Changes in physiological reproductive states of female Long-Evans hooded rats were directly correlated with changes in the concentration of acidophilic and basophilic connective tissue granulated cells in the lamina propria of the duodenum. Acidophilic granulated cell numbers were significantly higher at estrus and metestrus than at other stages of the estrous cycle or in the immature state. Acidophilic granulated cell numbers during pregnancy were not significantly different from cell numbers quantified during metestrus, diestrus, or proestrus, but were significantly lower than cell numbers during estrus. Late lactation (21-25 days) was associated with significant decreases in the numbers of acidophilic granulated cells from numbers observed during the estrous cycle and during pregnancy. Basophilic granulated cell numbers did not differ significantly during the estrous cycle, although the highest numbers were observed during proestrus. Basophilic granulated cell numbers were significantly higher during pregnancy than during the estrous cycle. Basophilic granulated cell counts in late lactation were comparable to numbers quantified in estrus, metestrus, and diestrus, but were significantly lower than during proestrus and pregnancy.     

The connections of the medial preoptic region and maternal behavior in the rat

Female rats which are hysterectomized and ovariectomized on Day 16 of pregnancy and injected with estrogen show a short latency to onset of maternal behavior when presented with test pups 48 hrs later. In the present experiment, female rats were treated similarly except that on Day 16 of pregnancy they received knife cuts which severed either the lateral, anterior, dorsal, or posterior connections of the medial preoptic area (MPOA), or sham knife cuts. Severing the lateral connections of the MPOA severely disrupted materal behavior, while severing the dorsal or posterior connections of the MPOA produced either minor deficits or no deficits. Severing the anterior connections of the MPOA did produce large deficits in maternal behavior, but this was associated with hypoactivity and loss of body weight. Therefore, the maternal behavior deficits observed in the anterior cut group may have been a secondary effect of the knife cut. The results emphasize the importance of the lateral connections of the MPOA for maternal behavior.     

The reaction of neurons of the amygdaloid complex in the dynamics of the estrous cycle

Neuroscience and Behavioral Physiology -     

Responses of arcuate neurons to some putative neurotransmitters in perfused rat hypothalamic slices: effects of in vivo and in vitro estrogen treatments

The responses of neurons in the arcuate nucleus (ARC) to gamma-aminobutyric acid (GABA), glycine, serotonin (5-HT), norepinephrine (NE), and dopamine (DA) were examined in hypothalamic slices from ovariectomized rats either treated or untreated with estrogen. In estrogen-untreated preparations, spontaneous unit activity of the majority of neurons identified antidromically by the median eminence (ME) stimulation was depressed by GABA and glycine. When effective, 5-HT was predominantly excitatory and DA was predominantly inhibitory, while NE evoked both excitatory and inhibitory responses. The IS-SD block in evoked spikes was also occasionally observed following GABA and glycine perfusion. The responsiveness of unidentified neurons, which were not activated by the ME stimulation, to agents other than 5-HT did not differ from that of antidromically identified neurons. Responses of unidentified neurons to 5-HT were predominantly inhibitory. Subcutaneous injection of 20 micrograms of 17 beta-estradiol-benzoate 2 days prior to the experiments did not significantly affect the responsiveness of both identified and unidentified neurons to GABA, 5-HT, DA, and NE. Contrarily, preincubation of slices in 17 beta-estradiol-containing medium (10 nM) for 1 h significantly increased the responsiveness of unidentified, but not identified, neurons to the inhibitory action of NE. These results suggest that GABA, glycine, 5-HT, NE, and DA play some functional roles in controlling the excitability of tuberoinfundibular (TI) neurons in the ARC. It is also suggested that the negative feedback effect of estrogen is mediated, at least in part, by increased responsiveness of ARC neurons other than TI neurons to the inhibitory action of NE.     

Effect of low estrogen on neurons in the preoptic area of hypothalamus of ovariectomized rats

The purpose of this study was to investigate the difference in neuronal activity in the preoptic area of the hypothalamus (POAH) under low estrogen condition induced by ovariectomy. One hundred and twenty sham-operated (SHAM) and ovariectomized (OVX) rats were placed in different temperatures for 2 h. Twelve rats from each group were stimulated by 4 °C, 10 °C, 25 °C, 33 °C and 38 °C, respectively. c-Fos expression in the POAH was detected by immunohistochemistry. Following exposure to warm and cold stimuli, there were markedly lower c-Fos-positive cell densities in the OVX group compared with the SHAM group in the median preoptic nucleus (MnPO) at 4 °C, 10 °C, 33 °C and 38 °C, in the medial preoptic area (MPA) at 25 °C and 38 °C, in the ventromedial preoptic nucleus (VMPO) at 4 °C, 10 °C and 38 °C and in the ventrolateral preoptic nucleus (VLPO) at 4 °C and 38 °C. Both temperature and surgery had an impact on c-Fos expression by two-way ANOVA method except in the lateral preoptic area (LPO). c-Fos expression differed within different nuclei of the two groups in the same and different temperature stimuli. This indicated that the temperature-sensitive nuclei in the POAH exhibited lower and different activities during temperature stimuli following ovariectomy, which possibly resulted in abnormal thermoregulation and menopausal symptoms.