Sexual dimorphism in the synaptogenic effect of estradiol in prepuberal female rats

A study has been made of the effects of estradiol benzoate (EB) on synaptogenic induction in the hypothalamic arcuate nucleus (ARC), medial preoptic area (MPOA), and medial septal area (MSA) of prepuberal male and female rats. Subcutaneous administration of EB to 25-day-old female rats induces accelerated synaptogenesis in the ARC concomitant with a precocious surge of plasma luteinizing hormone (LH) at 1600 h on day 27 of age. The synaptic area densities (No. synapses/unit area of tissue section) of the MPOA and MSA are not increased at 27 days of age in rats treated with EB on day 25 of age. The synaptic area densities of the ARC, MPOA, and MSA are significantly higher on day 31 compared to day 27. However, only the ARC exhibits a further increase of synaptic numbers in EB-treated female rats. Similar estrogen treatment to prepuberal male rats induces neither an LH surge in plasma nor increased synaptogenesis in the ARC, MPOA, or MSA. Male 27-day-old rats of both estrogen-treated and control groups exhibit a synaptic area density in the ARC similar to 27-day-old control female rats. These data indicate that the sexually dimorphic positive response to estrogen with LH secretion has an equally sexually dimorphic neuromorphological response in rats. In addition, the synaptogenic effect of EB in the prepuberal female rat ARC remains manifest for at least 6 days after estrogen treatment.     

Responsiveness to estradiol in central nervous system of aging female rats

The age related decline in reproductive capacity in the female rat is examined in terms of physiological and behavioral changes in responsiveness to estradiol evidenced during the second year of life. After 9–12 months of age, regular estrous cycles are replaced by constant estrous, prolonged pseudopregnancy, or anestrous states, with concurrent alterations in endocrine function. Some of the mechanisms implicated in the mediation of these changes are reviewed. Estrogenic influences on estrous behavior and the control of feeding and body weight in aged rats, as well as the effects of parity on aged endocrinological functioning are discussed.     

Effects of PVN lesions on the responsiveness of female rats to estradiol.

Previous research has shown that the paraventricular nucleus of the hypothalamus (PVN) is an important site of action for the effects of estradiol on feeding behavior. The recent finding that estrogenic stimulation of the PVN lowers food intake without inducing lordosis suggests that the effects of estradiol on feeding and sexual behaviors are organized separately within the brain. Whether the effects of estradiol on food intake can be attenuated by PVN lesions is therefore a question of practical and theoretical interest. In this experiment we examined the behavioral responsiveness of females with PVN lesions to peripheral treatment with estradiol. 32 adult, female rats received either bilateral or sham lesions of the PVN. All subjects were ovariectomized 2 weeks after the lesion. 2 Weeks following ovariectomy, half of the animals were injected with 2 micrograms of estradiol benzoate (EB) for 3 days, and half were injected with the oil vehicle. 10 days later, the treatment conditions for each subject (oil or EB) were reversed. Histological analysis indicated that 9 females had bilateral lesions of the PVN and 4 had bilateral lesions of the dorsomedial nucleus of the hypothalamus (DMN); 11 animals received sham lesions. Compared with oil treatment, EB injections significantly lowered water intake and body weight gain in all groups. However, food intake was suppressed in the DMN and sham but not in PVN-lesioned females. In addition, statistical analyses indicated that EB treatment induced similar levels of female sexual behavior in all groups. Thus, PVN lesions did not interfere with the ability of estradiol to stimulate lordosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

雌二醇对大鼠脑缺血再灌注损伤的保护作用

目的探讨雌二醇对大鼠局灶性脑缺血再灌注损伤的改善作用及其脑保护机制。方法线栓法建立大鼠局灶性脑缺血再灌注损伤模型,通过HE染色在光镜下观察神经细胞损伤变化,TTC染色测脑梗死体积,免疫组化法检测bcl-2阳性表达。结果与脑缺血再灌注组相比,雌二醇用药组大鼠脑标本光镜下细胞损伤变性程度轻,脑梗死体积显著缩小(P<0.01),bcl-2阳性细胞数明显上升(P<0.01)。结论雌二醇对大鼠局灶性脑缺血再灌注损伤有保护作用,雌二醇可通过促进bcl-2的上调发挥脑保护作用。     

雌二醇对大鼠脑缺血再灌注损伤的保护作用

目的探讨雌二醇对大鼠局灶性脑缺血再灌注损伤的改善作用及其脑保护机制。方法线栓法建立大鼠局灶性脑缺血再灌注损伤模型，通过HE染色在光镜下观察神经细胞损伤变化，TTC染色测脑梗死体积．免疫组化法检测bel-2阳性表达。结果与脑缺血再灌注组相比，雌二醇用药组大鼠脑标本光镜下细胞损伤变性程度轻．脑梗死体积显著缩小（P〈0．01），bel-2阳性细胞数明显上升（P〈0．01）。结论雌二醇对大鼠局灶性脑缺血再灌注损伤有保护作用，雌二醇可通过促进bcl-2的上调发挥脑保护作用。     

Postictal events in amygdala-kindled female rats with and without estradiol replacement

This study investigated the effect of estradiol on ictal and postictal events in ovariectomized female rats kindled by daily amygdala stimulation during the presence or absence of estradiol replacement. Although ictal components of kindled seizures were not altered by estradiol, several postictal events such as myoclonic jerks were significantly increased by estradiol. Twelve days after kindling, estradiol-replaced rats with electrodes in the basal, lateral, or cortical amygdala nuclei developed brief postictal "bursts" of behavioral and EEG activity which developed into a secondary seizure in some rats. Rats without estradiol never displayed these postictal events. Pretreatment of rats with pentylenetetrazol, 20 mg/kg, 15 days after kindling, resulted in a further increase in the incidence of bursts and secondary seizures in the presence of estradiol; these events were most prominent in rats kindled in the absence of estradiol. Pentylenetetrazol also caused a significant increase in myoclonic jerks in estradiol-replaced rats, and postictal spikes in all rats. A series of five consecutive generalized seizures at 48-h intervals caused an increase in bursts in rats with estradiol replacement, but not in rats without estradiol. The results indicate that estradiol exerts excitatory effects during the postictal period following amygdala-kindled seizures and suggest that multiple regions mediate the postictal effects of estradiol, perhaps depending on the intraamygdala site of kindling stimulations.     

Chromatin binding of estradiol in the hypothalamus and cortex of male and female rats

Gonadal steroids are thought to act by activation of the genome following cytoplasmic binding, translocation of the hormone--receptor complex to the nucleus and chromatin binding at specific acceptor sites. This study examined the kinetics of chromatin binding of estradiol by hypothalamic and cortical cells of adult gonadectomized male and female rats. In both sexes binding was found to be limited to hypothalamic cells. The kinetics of binding differed between the sexes, estradiol being retained less well in males. In females hypothalamic chromatin binding was shown to be of limited capacity and to be competitively inhibited by unlabeled estradiol. Unlabeled testosterone inhibited estradiol binding when administered subcutaneously 3 h before the estradiol, but not by testosterone when administered either intravenously or concurrently with the estradiol. It was suggested that the observed sex difference in hypothalamic chromatin binding might underlie the relative insensitivity of the male to the lordosis-inducing properties of estradiol.     

Synergistic effect of estradiol and fluoxetine in young adult and middle-aged female rats in two models of experimental depression

Catechol-O-methyltransferase, an enzyme involved in regulating brain catecholamine levels, has been implicated in anxiety, pain and/or stress responsivity. Elements of this putative association remain unclarified, notably whether: (a) COMT variation modulates responses to acute and/or chronic stress equally; (b) acute pharmacological inhibition of COMT produces comparable effects on anxiety to that observed after deletion of the COMT gene; (c) COMT genotype modulates action of anxiolytic drugs.We aimed to further investigate the relationship between reduced COMT function, anxiety and stress responsivity in mice.To compare the effect of acute vs. chronic restraint stress in female COMT KO vs. WT mice, serum corticosterone and cytokine concentrations were measured [Experiment 1]. Sensitivity to the benzodiazepines midazolam and chlordiazepoxide in the light-dark test was assessed in female COMT KO vs. WT mice [Experiment 2]. Effects of acute administration of the COMT inhibitor tolcapone, and of these same benzodiazepines thereon, in the light-dark test were assessed in female C57BL/6 mice [Experiment 3].COMT KO mice demonstrated an increased corticosterone response to acute but not chronic stress, and a modified cytokine profile after chronic, but not acute stress. COMT KO mice showed increased anxiety, but benzodiazepine sensitivity was affected by COMT genotype. Whilst tolcapone had no effect on light/dark performance in C57BL6/J mice it decreased benzodiazepine sensitivity.These data elaborate earlier findings of increased anxiety in female COMT KO mice and also clarify a role for COMT in modulating stress-related hormonal and immune parameters in a manner that depends on chronicity of the stressor.     

Isolation of specific proteins affected by estradiol in the arcuate-median eminence of prepuberal female rats

Prepuberal female rats (25 days of age) were injected with estradiol benzoate (EB 10 μg/rat, s.c. in oil) or oil vehicle. Forty-eight hours after treatment, all animals were decapitated, their brains removed and sectioned. The arcuate nucleus of the hypothalamus and median eminence were microdissected and processed for isoelectric focusing followed by slab electrophoresis. The resulting two-dimensional electrophoretic gels were analyzed to quantitate the specific proteins resolved using a scanning microdensitometric method. Out of 235 proteins measured, 8 proteins were found to be significantly increased and 4 were decreased by EB treatment. The proteins which increased in concentration ranged in molecular weight from 15 to 43 kDa and isoelectric points (pI) of 4.9 to 7.0. The 4 proteins decreased by the EB treatment were 44, 67, 74 and 80 kDa in molecular weight and their pI's ranged from 6.5 to 7.1. It is suggested that these proteins might be involved in some of the neuroendocrine effects that are induced by estradiol in this region of the brain.     

Acute and chronic stress differently affect visceral sensitivity to rectal distension in female rats

Stressful life events are frequently associated with outward signs of irritable bowel syndrome (IBS). Increasing evidence suggests that acute and chronic stress stimuli implicate different physiological mechanisms and neuroendocrine responses. Therefore, we investigated the influence of acute and chronic stress on visceral nociception in female rats and the involvement of colonic mast cells in this effect. The effect of acute and chronic partial restraint stress (PRS) on visceral sensitivity to rectal distension (RD) was assessed by abdominal muscle electromyography. Colonic mast cell activation was determined by measuring histamine release after in vitro stimulation with substance P (SP) in colonic samples from rats experiencing RD vs. controls. Acute PRS significantly enhanced abdominal response to RD compared with sham PRS for all volumes of distension. In contrast, chronic PRS induced a hyperalgesic response for the highest volumes of distension (0.8 and 1.2 mL), but did not affect the number of abdominal contractions for the lowest volume (0.4 mL) compared with controls. Both acute and chronic PRS increased in vitro SP-induced histamine release without affecting mast cell numbers. RD induced similar in vitro histamine release from colonic samples from both acute and chronic PRS rats; this release, however, was significantly higher than that measured in sham-PRS rats. Acute and chronic PRS differently influence visceral sensitivity in response to RD in female rats. This difference, however, cannot be attributed to a different effect of either stress paradigm on mast cell histamine release.     

Synaptic remodelling in arcuate nucleus after injection of estradiol valerate in adult female rats

Adult female rats were injected with a single dose (20 mg/kg) of estradiol valerate (EV). The number of synapses was evaluated in thin sections of arcuate nucleus fixed 3, 8, 16 and 32 weeks after EV treatment and compared with the values obtained in the arcuate nucleus of uninjected proestrus control rats. By 8 weeks after EV treatment a significant (P less than 0.001) decrease was found in the number of axo-somatic and axo-dendritic synapses on dendritic shafts, but not in the number of axo-dendritic synapses on dendritic spines. However, by 32 weeks postinjection, the number of axo-somatic and axo-dendritic synapses had returned to control values. This transient decrease in the number of synapses was preceded by a massive appearance of neuronal degenerative images by 3 weeks after EV injection. These results are interpreted as reflecting a process of circuitry remodelling in the arcuate nucleus after a neuronal lesion induced by estrogen.     

Cyclic estradiol treatment enhances the effects of interleukin-1beta on food intake in female rats

Proinflammatory cytokines elicit behavioral and physiological responses that include decreased food intake, fever, and a general disinterest in usual activities. Ovarian hormones modulate immune system activity and responsiveness to cytokines in female mammals, suggesting that sex differences in immune function may be influenced by gonadal steroids. In this experiment, female adult rats were ovariectomized and given two daily subcutaneous injections of 5.0 or 20.0 microg of estradiol benzoate or the oil vehicle 3 weeks after surgery. Following 2 days of hormone treatment, animals received ip injections of interleukin-1beta (IL-1beta) or saline 1 h before light offset. Food and water intake was measured 2 h after light offset. The results indicate that a cyclic pattern of estradiol treatment enhances the anorectic effect of IL-1beta and suggest that responses to immune system activation are influenced by estradiol.     

17beta-estradiol modulates baroreflex sensitivity and autonomic tone of female rats

The following experiments examine the role of estrogen as a central modulator of autonomic tone and baroreflex sensitivity in the female rat. Female Sprague-Dawley rats were ovariectomized and then supplemented daily for 7 days with a fixed dose of estrogen (5 microg/kg; sc) to produce a stable level of estrogen similar to that present at proestrous (17 pg/ml). The rats were then anaesthetized with sodium thiobutabarbital (100 mg/kg) and instrumented to record blood pressure, heart rate and both vagal and renal efferent nerve activities. The sensitivity of the cardiac baroreflex was tested using intravenous injection of multiple doses of either phenylephrine hydrochloride or sodium nitroprusside. Estrogen-supplemented female rats exhibited a significantly enhanced BRS as compared to male rats from a previous study (0.78 vs. 0.5). Furthermore, bolus injection of estrogen (1x10(-2) mg/kg; iv) in estrogen-supplemented female rats produced a significant increase in vagal nerve activity and a significant decrease in renal nerve activity which together resulted in a further enhancement of the BRS (0.78 vs. 2.4). Injection of the selective estrogen receptor antagonist, ICI 182,780, into nucleus ambiguus and the intrathecal space of the spinal cord blocked the respective changes in parasympathetic and sympathetic nerve activities indicating that intravenously administered estrogen modulates baseline autonomic tone via the activation of central estrogen receptors.     

大脑性分化前外源雄激素对雌鼠性定向影响的研究

目的探讨雌鼠大脑性分化前性激素与性定向的关系并建立雌鼠同性恋模型。方法40只新生SpragueDawley雌鼠随机分4组,每组10只。第1,2,3组雌鼠在出生第1天分别腹腔注射丙酸睾酮(TP)25g·L-1·rat-1(低剂量TP组),50g·L-1·rat-1(中剂量TP组),100g·L-1·rat-1(高剂量TP组),第4组雌鼠注射无菌油(50μl/rat)作为雌鼠对照组。另外对10只新生雄鼠注射无菌油(50μl/rat)作为雄鼠对照组。成年后观察TP组雌鼠的性偏爱、雌性行为及雄性行为的变化。结果(1)中剂量TP组和高剂量TP组雌鼠的接近雌刺激鼠的时间长于雌鼠对照组(P<005,P<005),且高剂量TP组在雄刺激鼠和雌刺激鼠方面,更偏向于接近雌刺激鼠(Z=2521,P<005);(2)中剂量和高剂量TP组雌鼠的雌性行为明显减少于雌鼠对照组(P<005,P<005);(3)高剂量TP组的雄性行为明显增加,且与雄鼠对照组相的差异无统计学意义(P>005);(4)低剂量TP组雌鼠的性偏爱、雌性行为及雄性行为与雌鼠对照组的差异均无统计学意义(均P>005)。结论雌鼠大脑性分化前给予外源雄激素能影响其性偏爱及性行为。     

致痫后雌性大鼠血清及海马雌二醇和孕烯醇酮水平的动态变化

目的 观察致病后雌性大鼠血清及海马雌二醇(E2)和孕烯醇酮(PREG)水平的动态变化,研究海马E2水平与癫痫发作严重程度的关系. 方法 选择动情期雌性大鼠制备海人藻酸(KA)经杏仁核点燃的癫痫模型,观察大鼠癫痫发作的行为学表现.应用放射免疫法和酶联免疫吸附分析分别检测癫痫发作后0、1、2、3、4、5、6、12和24 h的大鼠以及经杏仁核注射生理盐水后相应时间的大鼠血清及海马组织E2和PREG水平.对检测结果进行统计学分析. 结果 杏仁核注入KA后5～10min大鼠均出现痫样发作,3 h达峰值,随后呈下降趋势.致痫后的大鼠血清E2水平无明显变化,但海马E2水平在癫痫发作后1 h开始上升,4 h达峰值,随后呈下降趋势,12 h恢复至对照水平,1～12 h相邻时间点E2水平差异均有统计学意义(P,0.05).此外,随着大鼠的癫痫发作程度的加重,海马E2水平逐渐升高,进行相关性检验后发现.海乌E2水平与癫痫发作严重程度呈正相关(R~2=0.646,P<0.05).致痫前及致痫后24 h内不同时间点各组大鼠海马的PREG水平没有明显变化. 结论 癫痫发作后大鼠海马E2水平的动态变化与癫痫发作程度相关.癫痫发作可以诱导大鼠海马局部E2的合成.     

Prepubertal ontogeny of responsiveness to estradiol in female rat central nervous system

The physiological response to systemic estrogens changes dramatically during the period from birth to puberty. With the onset of puberty, the rat reaches a critical developmental plateau with regard to endocrinological responsiveness to estradiol. Since the appearance of the pubertal response pattern appears to be less a consequence of some intrinsic “trigger” than the natural continuation of a developmental sequence that begins prenatally, its ontogeny should be examined in a broad context that will take account of the impact of each of the dynamic components influencing the interactions between estradiol and the central nervous system on the functional development of the organism as a whole. The prepubertal ontogeny of endocrinological responsiveness to estradiol in the central nervous system of the female rat is examined in the context of several of the important factors that are known to influence the functional development of the hypothalamo-pituitary-gonadal circuit: the rapidly changing hormonal environment of the morphologically and physiologically immature juvenile rat, the shifting predominance of alphafetoprotein and “adult” estradiol-binding protein, sexual differentiation of the neural substrate, and the development of mature pituitary-gonadal feedback machanisms. The availability of ever more sensitive techniques for the measurement of the actions of estradiol in the central nervous system of the immature organism has necessitated a re-evaluation of existing data. This, in turn, suggests that new approaches should be applied to the examination of problems related to the development of reproductive maturity of the central nervous system.     

Effects of estradiol and progesterone on radial maze performance in middle-aged female rats fed a low-calcium diet

There is increasing evidence that ovarian steroids and calcium ions are involved in learning and memory. To examine the effect of ovarian steroids on learning and memory under a low-calcium condition, middle-aged female rats were fed either a low-calcium (0.02% Ca) or a normal-calcium (1.25% Ca) diet. All rats were ovariectomized (OVX), and these animals were divided into eight groups: 1) an OVX group with a normal-calcium diet (OVX-normal-Ca group), 2) an OVX group with 17β-estradiol treatment and a normal-calcium diet (E2 group), 3) an OVX with progesterone treatment and a normal-calcium diet (P4 group), 4) an OVX with 17β-estradiol and progesterone treatments and a normal-calcium diet (E2+P4 group), 5) an OVX group with a low-calcium diet (OVX-low-Ca group), 6) an OVX group with 17β-estradiol treatment and a low-calcium diet (LE2 group), 7) an OVX group with progesterone treatment and a low-calcium diet (LP4 group), and 8) an OVX group with 17β-estradiol and progesterone treatments and a low-calcium diet (LE2+LP4 group). Seventy-seven days after the OVX operation, the learning and memory abilities of the rats were examined by using an eight-arm radial maze task. E2 and E2+P4 groups learned in fewer trials, and performed better in the radial maze and the working memory task than the other groups under the normal-calcium condition. Rats in the LE2 group learned in fewer trials, and performed better in the maze and working memory task than the other low-calcium groups, but in combination with progesterone under the low-calcium condition (LE2+LP4 group), the facilitative effect of estradiol in all the tasks was inhibited. Treatment with progesterone alone did not inhibit the learning and memory task performance. These results suggest the possibility that treatment with estradiol under low-calcium conditions cannot improve impaired learning and memory when progesterone is applied simultaneously, and that the intake of adequate calcium may be necessary and effective for patients with learning and memory hypofunction receiving hormone replacement therapy.     

Aging, estradiol and time of day differentially affect serotonin transporter binding in the central nervous system of female rats

Estrogen-related changes in serotonergic neuronal transmission, including changes in the number of serotonin transporter (SERT) binding sites, have been cited as a possible cause for changes in mood, memory and sleep that occur during the menopausal transition. However, both aging and estradiol regulate SERT binding sites in the brain. The goal of this experiment was to determine how aging and estrogen interact to regulate SERT levels in the forebrain of young and reproductively senescent female Sprague–Dawley rats using [³H]paroxetine. The density of specific [³H]paroxetine binding in various brain regions was compared in young (2–4 months) and reproductively senescent (10–12 months) female rats at three times of day. In most brain regions examined, estrogen and aging independently increased the number of [³H]paroxetine binding sites. The only region that displayed a reduction in [³H]paroxetine binding with age was the suprachiasmatic nucleus (SCN). Time of day influenced [³H]paroxetine binding in the SCN and the paraventricular thalamus (PVT), two regions known to be involved in the regulation of circadian rhythms. Aging and/or estrogen also altered the pattern of binding in these regions. Thus, based on the results of this study, we conclude that aging and estrogen both act to regulate SERT binding sites in the forebrain of female rats, and that this regulation is region specific.     

Neuroprotective effects of estradiol in newborn female rat hippocampus

Perinatal brain injury, consequent to hypoxic/ischemic events, is associated with the release of excess excitatory neurotransmitters, including glutamate. We have previously shown that administration of a glutamate receptor agonist, kainic acid (KA), to postnatal day 0 (PN0) and PN1 rats results in damage selective to the dentate gyrus of females. Pretreatment with the gonadal steroid estradiol prevents KA-induced damage to the female dentate gyrus. To begin to elucidate the cellular mechanism of the neuroprotective effects of estradiol in neonatal females, we have employed the estrogen receptor antagonists Tamoxifen and ICI 182,780 in vivo and in vitro, respectively. Peripheral administration of Tamoxifen, which crosses the blood-brain barrier, prevented estradiol-mediated neuroprotection against KA-induced damage in the dentate gyrus. The highly selective estrogen receptor antagonist ICI 182,780, which does not penetrate into the brain from the periphery, also prevented estradiol's protective effects on KA-induced cell death in cultured hippocampal neurons but only late in the time course of injury. The data suggest that the neuroprotection afforded by estradiol against KA-induced injury in the female is estrogen receptor mediated but may include an additional mechanism that is not antagonized at the receptor.