Amygdala activation by corticosterone alters visceral and somatic pain in cycling female rats

Irritable bowel syndrome (IBS) is often seen in women, and symptom severity is known to vary over the menstrual cycle. In addition, activation of the hypothalamic-pituitary-adrenal (HPA) axis enhances symptomology and patients with IBS have increased activation of the amygdala, a brain region known to facilitate HPA output. However, little is known about the effects of amygdala activation during different stages of the menstrual cycle. We therefore investigated the effects of amygdala activation on somatic and visceral pain perception over the rat estrous cycle. Female Wistar rats were implanted with either corticosterone (Cort) or cholesterol as a control onto the dorsal margin of the central amygdala. Visceral sensitivity was quantified by recording the visceromotor response (VMR) to colorectal distension (CRD) and somatic sensitivity was assessed via the Von Frey test. In cholesterol controls, both visceral and somatic sensitivity varied over the estrous cycle. Rats in proestrus/estrus responded to CRD with an increased VMR compared with rats in metestrus/diestrus. Somatic sensitivity followed a similar pattern with enhanced sensitivity during proestrus/estrus compared with metestrus/diestrus. Elevated amygdala Cort induced visceral hypersensitivity during metestrus/diestrus but had no effect during proestrus/estrus. In contrast, elevated amygdala Cort increased somatic sensitivity during both metestrus/diestrus and proestrus/estrous. These results suggests that amygdala activation by Cort eliminates spontaneously occurring differences in visceral and somatic pain perception, which could explain the lowered pain thresholds and higher incidence of somatic pain observed in women with IBS.     

Inhibin secretion during the rat estrous cycle: relationships to FSH secretion and FSH beta subunit mRNA concentrations

Serum inhibin and FSH and FSH beta subunit mRNA levels were measured at 3h intervals throughout the 4 day estrous cycle in female rats and hourly between 1000 and 2400 h of proestrus. On proestrus, serum inhibin concentrations fell during the late morning-early afternoon, then increased transiently during the late afternoon gonadotropin surges. Inhibin levels decreased during the late evening of proestrus, coincident with the FSH surge-related rise in FSH beta mRNA levels. Serum inhibin remained relatively stable during estrus and early metestrus, but rose during the late evening of metestrus and remained elevated until early diestrus. FSH beta mRNA levels were elevated on late estrus and early metestrus and declined during the evening of metestrus as serum inhibin levels increased. These data show that concentrations of serum inhibin change during the estrous cycle and that a general inverse relationship exists between serum inhibin and FSH levels and FSH beta mRNA concentrations in the pituitary. This suggests that inhibin may inhibit FSH beta gene expression and FSH secretion during the 4 day cycle in female rats.     

Variations in concentration of oxytocin and vasopressin in the paraventricular nucleus of the hypothalamus during the estrous cycle in rats

Oxytocin (OT) and arginine-8-vasopressin (AVP) were measured by radioimmunoassay in micropunched hypothalamic neurosecretory nuclei of estrous cycling female Sprague-Dawley rats. In the paraventricular nucleus (PVN): the concentration (pg/microgram protein) of OT was significantly higher in rats in diestrus than during proestrus, estrus, or metestrus, while the concentration during metestrus was significantly greater than in proestrus and estrus; the concentration of AVP was significantly lower in animals in estrus than during the other three stages; because the paraventricular OT levels dropped before proestrus, the AVP/OT ratio was significantly greater in animals in proestrus than in diestrus, metestrus, and estrus. In the supraoptic nucleus (SON) a similar trend was noted: the concentration of OT was highest during diestrus, and AVP was lowest during estrus, though neither was significantly different from other stages. Because the OT and AVP cycles in the SON were asynchronous, the ratio of AVP to OT was significantly higher in proestrus than in metestrus or diestrus and significantly greater in estrus than during diestrus. In contrast to these two areas, peptide concentrations did not vary significantly across the estrous cycle in other sites of nonapeptide synthesis, i.e. the anterior commissural nucleus (ACN) and the suprachiasmatic nuclei (SCN).     

Maintenance of lung myeloperoxidase activity in proestrus females after trauma-hemorrhage: upregulation of heme oxygenase-1

Previous studies showed that females in the proestrus stage of the reproductive cycle maintain organ functions after trauma-hemorrhage. However, it remains unknown whether the female reproductive cycle is an important variable in the regulation of lung injury after trauma-hemorrhage and, if so, whether the effect is mediated via upregulation of heme oxygenase (HO)-1. To examine this, female Sprague-Dawley rats during diestrus, proestrus, estrus, and metestrus phases of the reproductive cycle or 14 days after ovariectomy underwent soft tissue trauma and then hemorrhage (mean blood pressure 40 mmHg for 90 min followed by fluid resuscitation). At 2 h after trauma-hemorrhage or sham operation, lung myeloperoxidase (MPO) activity and intercellular adhesion molecule (ICAM)-1, cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-3, and HO-1 protein levels were measured. Plasma 17beta-estradiol concentration was also determined. The results indicated that trauma-hemorrhage increased lung MPO activity and ICAM-1, CINC-1, and CINC-3 levels in ovariectomized females. These parameters were found to be similar to sham-operated animals in proestrus female rats subjected to trauma-hemorrhage. Lung HO-1 protein level in proestrus females was increased significantly compared with female rats subjected to trauma-hemorrhage during diestrus, estrus, and metestrus phases of the reproductive cycle and ovariectomized rats. Furthermore, plasma 17beta-estradiol level was highest in proestrus females. Administration of the HO inhibitor chromium mesoporphyrin prevented the attenuation of shock-induced lung damage in proestrus females. Thus these findings suggest that the female reproductive cycle is an important variable in the regulation of lung injury following trauma-hemorrhage and that the protective effect in proestrus females is likely mediated via upregulation of HO-1.     

Effect of estrous cycle phase on pain threshold in female white rats]

Pain thresholds and body resistance in female Wistar rats were determined during estrous cycle stages. The flinch and shuffle thresholds were increased on the 3rd day of measurement in diestrus and estrus but not in proestrus and metestrus as compared with the thresholds during the 1st day of recording. The thresholds decreased as of the 7th day to the 14th day. Daily threshold measurements raised the body resistance on the 7th day of recording. In contrast to the pain thresholds, the body resistance change had not a stage-dependent character.     

Quantitative differences in immune responses during the various stages of the estrous cycle in female BALB/c mice.

The immune responsiveness of spleens from female BALB/c mice to PHA, Con A, and LPS was greater at proestrus and metestrus as compared with estrus and diestrus. The peaks of responsiveness corresponded to reported elevated levels of estrogen and pregnenolone during these phases of the cycle. Similar results were obtained with the IgM or direct plaque-forming cell responses, which were also increased at proestrus and metestrus. It appears that female hormones may directly or indirectly stimulate immune responsiveness in adult mice.     

Changes of olfactory sensitivity during the estrus cycle in female laboratory mice

In female Albino laboratory mice neural olfactory thresholdswere established by means of evoked potential measurements withpermanently implanted electrodes. The method allowed registrationof the bulbar activity up to 17 consecutive days; each day thesexual status of the animals was determined by the vaginal smears. There is a close correlation between olfactory sensitivity andestrus cycle: All individuals had their maximum olfactory acuityin proestrus; in metestrus the threshold values were up to 1million times higher. During diestrus and estrus the thresholdvalues were inbetween these extremas. This pattern was foundin the three test substances geraniol, butyric acid and butyricmethyl ester. In comparison to the olfactory thresholds in male mice, in theaverage the females had a slightly higher sensitivity in proestrus,whereas in metestrus all of them show a marked increase in theirthreshold values.     

Atrial supersensitivity to noradrenaline in stressed female rats

Stress can change the responses to catecholamines in many tissues. The aim of this study was to investigate the influence of the estrous cycle on the sensitivity of right atria to noradrenaline in female rats subjected to acute swimming stress. Female Wistar rats in proestrus, estrus, metestrus or diestrus were submitted to a 50 min-swimming session. Immediately after the exercise, the rats were killed and their right atria were mounted for isometric recording of the spontaneous beating rate. Concentration-effect curves to noradrenaline were obtained before and after the inhibition of neuronal uptake with phenoxybenzamine (10 microM) and of extraneuronal uptake with estradiol (5 microM). Acute swimming stress did not change the right atrial sensitivity to noradrenaline in rats in estrus, metestrus and diestrus. However, swimming stress produced supersensitivity to noradrenaline in proestrus (pD(2) control: 7.14 +/- 0.03 vs. pD(2) swimming: 7.55 +/- 0.04; p<0.05). This supersensitivity was still observed after uptake inhibition. When catecholamine uptake was inhibited, the concentration-effect curve to noradrenaline was shifted to the left 2.5-fold in the proestrus control group and 1.7-fold in the proestrus stress group (p<0.05). In conclusion, the estrous cycle influenced the acute stress-induced atrial supersensitivity to noradrenaline.     

Relationship of Vaginal Cytology to Alterations of the Vaginal Microflora of Rats During the Estrous Cycle

The influence of cyclic changes occurring in the vaginal tract during the estrous cycle upon the indigenous microflora of the vagina has been investigated by semiquantitative techniques in virgin female rats. By plate counts performed on material lavaged daily from the vaginal tract of several rats, it is apparent that bacterial counts are elevated in the proestrus and estrus phases of the cycle to values several orders of magnitude greater than those observed during metestrus or diestrus phases. Increases in vaginal bacterial counts were associated with the presence of cornified epithelial cells in the vagina; these cells were predominantly nonviable. Decreases in the vaginal bacterial content were related to the influx of leukocytes into the vagina after estrus. When leukocytes were present in the vaginal tract, they were 90 to 100% viable. From these observations it has been concluded that the female vaginal tract and the bacteria which colonize it represent a dynamic ecosystem which is responsive to cyclic events occurring in the estrous cycle. The changing cellular content of the vaginal tract may have relevance to the observed cyclic changes in the bacterial content of the vagina.     

Inhibition of estrus and corpora lutea function with Norgestomet

Forty-five nonpregnant, nonlactating, Angus and Brangus cows were utilized to determine how long a Norgestomet ear implant would inhibit estrus when administered at various stages of an estrous cycle. All cows completed a nontreated estrous cycle to ensure normal cyclicity. At the second observed estrus (estrus = Day 1), cows were randomly allotted to be treated at metestrus (Day 3 or Day 4, n = 15); at diestrus (Day 9 or Day 10, n = 14); or at proestrus (Day 15 or Day 16, n = 16). All cows received a 2-ml intramuscular injection of 3 mg of Norgestomet accompanied by a 6-mg Norgestomet ear implant, which remained in situ for 21 days, or until individual cows were observed in estrus. Estrus was inhibited for a mean (+/- SEM) of 18.7 +/- 0.7, 19.9 +/- 0.8, and 17.0 +/- 0.8 days, respectively, when cows were treated at metestrus, diestrus, and proestrus (metestrus and diestrus vs proestrus; P < 0.05). Estrus was inhibited for an entire 21-day implantation period in 27, 50, and 38% of cows treated at metestrus, diestrus, and proestrus, respectively (P > 0.10). Norgestomet inhibited estrus in all cows for 11, 17, and 11 days after implantation when treatment was initiated at metestrus, diestrus, and proestrus, respectively (P > 0.10). These data indicate that a 6-mg Norgestomet ear implant effectively inhibits estrus in all cows for a maximum of 11 days, with some cows exhibiting estrus by Day 12 with the Norgestomet implant in situ.     

大鼠动情周期中生殖轴系微循环血量的变化

本文采用放射性生物微球技术,对雌性大鼠动情周期中丘脑下部-垂体-卵巢轴系的微循环血量进行了测量。结果指出,周期各期丘脑下部和垂体的血流量无显著差异(p>0.05)。卵巢血流量在动情后期最大,动情期最小,两期血流量的差异显著(p<0.02)。子宮血流量以动情后期最大,间情期仍维持在较高水平,动情期最小。动情后期和间情期与动情期比较均有显著差异(分别为p<0.01和P<0.05)。输卵管血流量动情期最大,动情前期最小,两期血流量的差异也有显著性(p<0.05)。由此表明,卵巢、子宫和输卵管血流量有明显的周期性波动。血流量的多寡与其生理机能状态和性激素的变化有关。     

Hormone-sensitive lipase expression and IHC localization in the rat ovary, oviduct, and uterus

Hormone-sensitive lipase (HSL) is a key regulator of cholesterol esters metabolism. The aim of this study was to determine HSL localization in rat female reproductive organs during the ovarian cycle by IHC methods. HSL was located in the ovarian epithelium. The granulosa cells and oocytes of primordial follicles were immunonegative. In mature follicles, HSL was found in oocytes and theca and granulosa cells. However, HSL expression in theca cells and oocytes decreased during follicular atresia. Luteal cells showed HSL staining in cytoplasm during proestrus and estrus, in the nucleus during metestrus, and in cytoplasm and the nucleus during diestrus. In the tubaric ampulla, HSL was located in the epithelial cells nuclei and in the cilia during proestrus and estrus but mainly in the nucleus during metestrus and diestrus. In the isthmus, cells showed HSL immunolabeling in the nucleus and cilia during proestrus, but only in the cilia during estrus, metestrus, and diestrus. In the uterus, HSL was found in the epithelial cells nuclei. HSL-immunoreactive bands at 84, 67, 54, and 43 kDa were found in rat female reproductive organs. HSL labeling in the nucleus of epithelial and germ cells suggests an as yet unknown function for this protein, probably related to oogenesis and cell proliferation.     

Differentiation of estradiol receptors in rat uterine cytosol by sensitivity to tamoxifen.

Analysis of rat uterine cytosol by means of immobilized antibody discloses the presence of two distinct high affinity, low capacity estradiol binding components. One of these is readily saturable by the antiestrogen tamoxifen (TS = tamoxifen sensitive), the other is tamoxifen insensitive (TI). Only TS-estradiol binding shows positive cooperativity at low ligand concentration. TS but not TI is lost when frozen tissue is thawed at 4°C then refrozen and stored for an additional 12 hours. Experiments with ovariectomized rats show that TI is formed only in the presence of estradiol. In the estrus cycle TS increases in the order: metestrus, diestrus, proestrus and estrus. The quantity of TI is the same in metestrus and diestrus and also the same but fractionally higher in proestrus and estrus.     

Photoaffinity labeling of pituitary gonadotropin releasing hormone receptors during the rat estrous cycle

A bioactive photoaffinity derivative of gonadotropin releasing hormone was used to identify pituitary gonadotropin releasing hormone receptors at various stages of the rat estrous cycle. Sodium dodecyl sulfate polyacrylamide gel electrophoresis resulted in the identification of a single specific component with an apparent molecular weight of 60,000 daltons throughout the estrous cycle. The amount of radioactivity incorporated into the 60K dalton band in diestrus and proestrus female rats increased 2.5-fold to that of metestrus and estrus female rats. These findings provide additional evidence for the identification of pituitary gonadotropin releasing hormone receptors.     

Long-term ovariectomy changes formalin-induced licking in female rats: the role of estrogens

Gonadal hormones have been shown to exert modulatory effects on nociception and analgesia. To investigate the role of gonadal hormones in the response by female rats to both phasic and persistent nociceptive stimulation, we evaluated the effects of long-term ovariectomy (OVX, 6 months) on the thermal pain threshold and on formalin-induced responses. The thermal pain threshold was evaluated with the plantar test apparatus, while persistent pain was induced by a subcutaneous injection of dilute formalin (50 microliter, 10%) in the dorsal hind paw. The formalin test was carried out in an open field apparatus where the animal's spontaneous behavior and formalin-induced responses (licking duration, flinching frequency and flexing duration of the injected paw) were recorded for 60 min. Estradiol and corticosterone plasma levels were determined in blood collected from the anesthetized animals at the end of the test. In OVX females, the duration of formalin-induced licking was longer than in Intact females during both the first and the second phase; flinching and flexing did not differ from Intact. The thermal pain threshold was only slightly affected by OVX. Estradiol and corticosterone were lower in OVX females than Intact ones. These data indicate that long-term depletion of gonadal hormones in female rats modulates the pain-induced behavioral responses related to supraspinal neural circuits (licking of the injected paw) rather than more spinally mediated responses such as formalin-induced flinching and withdrawal latency in the plantar test.     

Estrous cycle fluctuations in aggressiveness of house mice

The purpose of this study was to determine whether interfemale, isolationinduced aggression in house mice varies over the phases of the estrous cycle. The results indicated that there were significant variations, with aggression being higher at proestrus and metestrus and lower at estrus and diestrus. Activity level showed fluctuations across the cycle similar to the pattern established by previous research. The results were interpreted in terms of possible adaptiveness.     

酪氨酸对大鼠子宫胞浆雌,孕激素受体的影响

采用放射受体分析法,测定了动情周期不同阶段及去卵巢大鼠子宫胞浆雌二醇和孕酮受体含量,并观察了子宫腔内注射酪、丝、苏三种氨基酸对子宫胞浆雌。醇、孕酮受体含量的影响。结果表明：（１）Ｌ－酪氨酸对动情前期、动情期、间情期大鼠子宫胞浆雌二醇和孕酮受体都具有明显的降低作用。（２）Ｌ－酪氨酸也降低去卵巢大鼠子宫胞浆雌二醇和孕酮含量,即这一作用不是通过影响卵巢激素分泌实现的。（３）Ｌ－苏氨酸仅可降低动情期和间情期大鼠子宫胞浆孕酮受体含量,而对相应周期雌二醇受体没有明显作用。（４）Ｌ－丝氨酸和Ｌ－苏氨酸对去卵巢大鼠子宫胞浆雌二醇和孕酮受体均无影响。     

Orienting behavior of female white rats in estrus cycle and its dependence on handling

Characteristics of orienting behavior of intact and handled female white rats were studied in the "open field" test. Experimental group of animals were formed according to stages of estrous cycle: (1) diestrus, (2) proestrus, (3) estrus, and (4) metestrus. The stage of the cycle was determined by vaginal smears. Over the period of 10 days rats were handled daily for 5 minutes. No behavioral changes over the course of estrous cycle were found in intact rats. Handling revealed some behavioral features related to the levels of steroid hormones in reproductive cycle. Most prominent changes in orienting behavior were observed at transition from estrous to metestrous. At the stage of estrous motor activity was maximal and grooming was minimal. The maximal contrast in the structure of orienting behavior was observed between estrous and diestrous stages.     

Prolactin receptors in the rat mammary gland. Change during the estrous cycle

Ovine prolactin (o-PRL) binding to mammary gland membranes was studied during the estrous cycle in the rat. Groups of rats were decapitated throughout the 4-day estrous cycle at 10 h00 on the days of diestrus I, diestrus II and estrus and at 10 h00, 12 h00, 16 h00 during the day of proestrus. Daily vaginal smears were taken to determine the stage of the estrous cycle which was also controlled by PRL and LH serum levels. Prolactin receptors were quantified in the 100 000 g pellet. For one Scatchard analysis, mammary gland membranes from 5 animals were pooled. Results given are the mean of 4 or 5 pools. Results obtained showed that the apparent affinity constant (KA) remained unchanged during the days of diestrus II and at all the times studied of proestrus and showed a slight but significant decrease on the days of estrus and diestrus I (or metestrus). The binding capacity did not vary from the day of diestrus II to the proestrus 16h00 (11.3 +/- 2.8 fmoles/mg protein) but sharply increased on the day of estrus (190.4 +/- 35.9 fmoles/mg protein). Binding capacity remained elevated on the day of diestrus I. This increase of PRL receptors on the day of estrous would appear to be an important step in preparing mammary gland for pregnancy and lactation.