Estrogen-treated Rats Research Articles

The Role of the Bed Nucleus of the Stria Terminalis in Stress-Induced Inhibition of Pulsatile Luteinising Hormone Secretion in the Female Rat

The bed nucleus of the stria terminalis (BNST) occupies a central position in the neural circuitry regulating the hypothalamic-pituitary-adrenocortical axis response to stress. The potential role of the BNST in stress-induced suppression of the gondotrophin-releasing hormone (GnRH) pulse generator, the central regulator of the reproductive system, was assessed by examining the effects of micro-infusion of corticotrophin-releasing factor (CRF) or its antagonist into the BNST on pulsatile luteinising hormone (LH) secretion or stress-induced inhibition of LH pulses, respectively. Ovariectomised oestrogen-treated rats were implanted chronically with bilateral cannulae in the dorsolateral BNST and i.v. catheters. CRF (25, 50 or 100 pmol in 200 nl of artificial cerebrospinal fluid) administered bilaterally into the BNST resulted in a dose-dependent decrease in LH pulse frequency, and induced Fos expression in glutamic acid decarboxylase immunostained neurones in the medial preoptic area. These results suggest that the activation of hypothalamic GABAergic neurones in response to intra-BNST administration of CRF may be involved in the suppression of LH pulses. Furthermore, administration of CRF antagonist (280 pmol astressin-B, three times at 20-min intervals) into the BNST effectively blocked the suppression of pulsatile LH secretion in response to restraint (1 h) but not hypoglycaemic (0.25 U insulin/kg, i.v.) stress. These data suggest that CRF innervation of the dorsolateral BNST plays a key, but differential, role in stress-induced suppression of the GnRH pulse generator.

Genetically-Induced Estrogen Receptor Alpha (ESR1) Overexpression Does Not Adversely Affect Fertility or Penile Development in Male Mice.

Previously, we reported that ESR1 overexpression resulting from neonatal exposure to estrogens in rats and wild-type mice was associated with infertility and mal-developed penis characterized by reduced length and weight and abnormal accumulation of fat cells. The objective of this study was to determine if mutant male mice overexpressing ESR1 are naturally infertile or have reduced fertility and/or develop abnormal penis. The fertility parameters, including fertility and fecundity indices, numbers of days from the day of cohabitation to the day of delivery, and numbers of pups per female, were not altered from controls, as a result of ESR1 overexpression. Likewise, penile morphology, including the length, weight, and diameter and os penis development, was not altered from controls. Conversely, weights of the seminal vesicles and bulbospongiosus and levator ani (BS/LA) muscles were significantly (P < 0.05) lower as compared to controls; however, the weight of the testis, the morphology of the testis and epididymis, and the plasma and testicular testosterone concentration were not different from controls. Hence, this study concludes that the genetically-induced ESR1 overexpression in male mice does not adversely affect fertility, penis, testis or epididymis, but significantly reduces weights of the seminal vesicles and BS/LA muscles. (poster)

Effect of ramipril on bone mechanical properties in the presence and deficiency of estrogens in rats

Effect of ramipril on bone mechanical properties in the presence and deficiency of estrogens in rats

Effects of lithium on bone mechanical properties in the presence and deficiency of estrogens in rats

Effects of lithium on bone mechanical properties in the presence and deficiency of estrogens in rats

The effect of estrogen supplementation on cell proliferation and expression of c‐kit positive cells in the rat prostate

Benign prostatic hyperplasia (BPH) is associated with the proliferation of prostate tissue and an increase in smooth muscle tone. However, the way in which the hormonal environment affects cell proliferation and prostatic interstitial cells (PIC) responsible for the maintenance of the smooth muscle tone is not clear. The present study investigated the effect of estrogen supplementation on cell proliferation, androgen/estrogen ratio, and expression and/or distribution of PIC. Male Sprague-Dawley rats were anesthetized with isoflurane/oxygen breathing mixture and subcutaneously implanted with silastic capsules. These capsules were either empty or filled with a 10 or 20 mg of crystalline estrogen. Estrogen exerted a potent effect on ventral prostate weight, which was manifested as a significant decrease between controls and the E(10)- and E(20)-treated rats. Active cell proliferation detected as Ki67-positive nuclei was observed in the stromal and epithelial cells of the ventral prostatic lobes from estrogen-treated rats and controls. Estrogen supplementation caused a significant and dose-dependent increase in prostatic estradiol and 5alpha-dihydrotestosterone (DHT) concentration but the ratios of either DHT/E(2) or E(2)/DHT were not significantly affected. PIC were observed in the region between the fibromuscular stroma and the glandular epithelium in all three experimental groups. E(20)-treated rats showed a higher expression of PIC than controls and E(10)-treated rats. The present study provides novel information regarding the synergistic role of estrogens and androgens in the prostate: estrogen may prevent prostatic hyperplasia via mechanisms other than affecting cell proliferation or DHT/estrogen ratio.

QSAR models for reproductive toxicity and endocrine disruption activity.

Reproductive toxicity is an important regulatory endpoint, which is required in registration procedures of chemicals used for different purposes (for example pesticides). The in vivo tests are expensive, time consuming and require large numbers of animals, which must be sacrificed. Therefore an effort is ongoing to develop alternative In vitro and in silico methods to evaluate reproductive toxicity. In this review we describe some modeling approaches. In the first example we describe the CAESAR model for prediction of reproductive toxicity; the second example shows a classification model for endocrine disruption potential based on counter propagation artificial neural networks; the third example shows a modeling of relative binding affinity to rat estrogen receptor, and the fourth one shows a receptor dependent modeling experiment.

Gonadal hormones modulate the potency of the disruptive effects of donepezil in male rats responding under a nonspatial operant learning and performance task

In contrast to estrogen in female rats, testosterone in male rats may decrease cholinergic activity in the brain, thereby attenuating behaviors mediated by the cholinergic system. To investigate this possibility, the interactive effects of the gonadal hormones and donepezil, an acetylcholinesterase (AChE) inhibitor, on the responding of male rats were examined under a multiple schedule of repeated acquisition and performance of response sequences and on AChE activity in specific brain regions. Donepezil dose-effect curves (0.56-10 mg/kg) were determined in males that were gonadally intact, gonadectomized (GX), GX with testosterone replacement (GX+T) or GX with estradiol replacement (GX+E). In all four groups, donepezil produced dose-dependent rate-decreasing and error-increasing effects in the acquisition and performance components. However, disruptions of response rate and accuracy in both components occurred at lower doses in GX and GX+E males than in intact males. The GX+E males also had the highest percentage of errors under control (saline) conditions in the acquisition components. In terms of AChE activity, GX males had higher levels in the prefrontal cortex, striatum and hippocampus, but lower levels in the midbrain, compared with intact males; hypothalamic and cortical levels were comparable for the GX and intact groups. Together, these results in male rats indicate that the potency of donepezil's disruptive effects on the responding under a complex operant procedure requiring learning and performance of response sequences depends upon the gonadal hormone status, and that the effects of testosterone on cholinergic activity vary among brain regions.

Estradiol valerate elicits antidepressant-like effects in middle-aged female rats under chronic mild stress

The purpose of this study was to analyze the antidepressant-like actions of estradiol valerate (1 or 2 mg/rat, single injection) or citalopram (5 or 10 mg/kg, chronically administered for 21 days) given independently or combined at low doses, to middle-aged ovariectomized female rats, as a model of human menopause. Animals were exposed to chronic mild stress, a model of depression that mimics anhedonia as revealed by diminished sucrose solution intake. Stressed rats decreased their sucrose preference 1 week after chronic stress and treatment with vehicle did not reverse this reduction. A single injection of estradiol valerate (2 mg/rat) produced an antidepressant-like action, evidenced as an increase in sucrose preference specific to stressed rats. Chronic citalopram (10 mg/kg) produced an antidepressant-like effect after 1 week. A single low-dose of estradiol valerate (1 mg/rat) did not potentiate or shorten the latency of action of chronic citalopram (5 mg/kg). These results reveal the antidepressant-like action of estrogens in middle-aged rats exposed to chronic stress. These data may be of importance for clinical depression in menopausal women.

Biochanin A induction of sulfotransferases in rats

Biochanin A (BCA) is a dietary isoflavone present in red clover (Trifoliumn pretense) and many herbal products. BCA has been reported to have chemopreventive actions against various cancers including prostate, breast, colon cancer, and so on. Sulfotransferases are a family of phase II drug-metabolizing enzymes, which are important for xenobiotic detoxification and regulation of biological signaling molecule biological activities. Sulfotransferase gene expressions are regulated by different hormones and xenobiotics. Improper regulation of sulfotransferases leads to improper functions of biological signaling molecules, which in turn can cause cancer or other diseases. BCA inhibits the enzyme activities of the phase I drug-metabolizing enzymes CYP1A1 and CYP1B1 in Chinese hamster ovary cells and induces the phase II drug-metabolizing enzymes UDP-glucuronosyltransferases in human prostate cancer cells. BCA induction of sulfotransferases has not been studied. This investigation evaluates the in vivo regulation of sulfotransferases at protein and mRNA levels in the liver and intestine of Sprague-Dawley rats treated with BCA (0, 2, 10, and 50 mg/kg/day) for 7 days. Our experimental results demonstrate for the first time that chronic BCA treatment can significantly induce the expression of rat sulfotransferase 1A1 (rSULT1A1, AST-IV), sulfotransferase 2A1 (rSULT2A1, STa), and rat estrogen sulfotransferase (rSULT1E1, EST) in rat liver and intestine. Our Western blot results are in good agreement with real-time RT-PCR data, suggesting that BCA induction of sulfotransferases occurs at the transcriptional level.

The mutual effects between orthodontic tooth movement and estrous cycle or estrogen1

The mutual effects between orthodontic tooth movement and estrous cycle or estrogen of female rats were studied. Animals were randomly divided into control group, force-loading for one time group, force-loading for five times group and sham groups. Each group included four subgroups, based on the estrous cycle stage. Serum estradiol, the change of estrous cycle, and tooth movement distance were measured. Significant variations in the estradiol level were found among the groups receiving force during the same stage of the estrous cycle (p < 0.01) and among the subgroups within each group (p < 0.01). The experimental treatments affected the estrous cycle of the groups receiving force in metestrus and diestrus. There were significant variations in the amount of tooth movement among the groups receiving force during different stages of the estrous cycle (p < 0.01). The largest amount of tooth movement was in the estrus group. The results show it was more desirable to wear appliances and apply force during estrus.

259 SODIUM/POTASSIUM/CALCIUM EXCHANGER 3 IS REGULATED BY STEROID HORMONES, ESTROGEN AND PROGESTERONE, IN THE UTERUS OF RAT DURING ESTROUS CYCLE

As a member of the family of potassium-dependent sodium/calcium exchangers, a sodium/calcium/potassium exchanger, NCKX3, plays a critical role in transport of 1 intracellular calcium and potassium ion in exchange for 4 extracellular sodium ions. Transcripts of NCKX3 were most abundant in the brain and smooth muscle, but in the uterus, aorta, and intestine, this gene expressed at lower levels. Its expression and role in the rat uterus during the estrus cycle have not been elucidated yet. In this study, we further examined the uterine expressions of NCKX3 mRNA and protein in stages during the estrous cycle of mature female Sprague-Dawley (SD) rats and in the absence or presence of sex-steroid hormones estrogen (E2) and progesterone (P4) in immature female SD rats. NCKX3 mRNA was verified by RT-PCR. Western blot analysis was applied to detect NCKX3 with an anti-NCKX3 goat polyclonal antibody. During the rat estrous cycle, uterus expressions of NCKX3 mRNA and proteins were highly expressed 2.5-fold at proestrus compared with those at estrus and diestrus. To examine the role(s) of sex steroids on the regulation of NCKX3 in the uterus of the immature female rat, hormones were prepared in ethanol and the rats were treated with E2 [40 (μg/kg of body weight (BW)], P4 (4 mg/kg of BW), or E2 plus P4 for 3 days. The expression of NCKX3 mRNA and protein increased 2-fold with E2, whereas P4 antagonized E2-stimulated NCKX3 expression, as similarly observed in the uterus. In addition, spatial expression of NCKX3 protein was detected by immunohistochemistry. Uterine NCKX3 protein was abundantly localized in the cytoplasm of the luminal and glandular epithelial cells at proestrus. Taken together, these results indicate that uterine NCKX3 is abundantly expressed in the uterus and controlled by steroid hormones E2 and P4, suggesting that uterine expression of NCKX3 might be involved in reproductive function during the cycle in female rat.

Age-related changes in serum and brain levels of androgens in male Brown Norway rats

Age-related depletion of androgens in men results in functional impairments in androgen-responsive tissues, such as the brain, resulting in increased risk for Alzheimer's disease. To investigate the relationship between normal age-related hormone loss and Alzheimer's disease risk, we evaluated the brain and serum levels of androgens and estrogen in aging male rats. We observed that increasing age was associated with a significant reduction in brain levels of the potent androgen dihydrotestosterone and a trend toward decreased testosterone. Brain levels of soluble beta-amyloid were observed to increase with age. Collectively, these findings highlight differences in brain and circulating levels of androgens during aging, and identify an inverse correlation with beta-amyloid levels that may be relevant to Alzheimer's disease risk.

Estrogen attenuates chronic volume overload induced structural and functional remodeling in male rat hearts

We have previously reported gender differences in ventricular remodeling and development of heart failure using the aortocaval fistula model of chronic volume overload in rats. In contrast to males, female rats exhibited no adverse ventricular remodeling and less mortality in response to volume overload. This gender-specific cardioprotection was lost following ovariectomy and was partially restored using estrogen replacement. However, it is not known if estrogen treatment would be as effective in males. The purpose of this study was to evaluate the structural and functional effects of estrogen in male rats subjected to chronic volume overload. Four groups of male rats were studied at 3 days and 8 wk postsurgery as follows: fistula and sham-operated controls, with and without estrogen treatment. Biochemical and histological studies were performed at 3 days postsurgery, with chronic structural and functional effects studied at 8 wk. Measurement of systolic and diastolic pressure-volume relationships was obtained using a blood-perfused isolated heart preparation. Both fistula groups developed significant ventricular hypertrophy after 8 wk of volume overload. Untreated rats with fistula exhibited extensive ventricular dilatation, which was coupled with a loss of systolic function. Estrogen attenuated left ventricular dilatation and maintained function in treated rats. Estrogen treatment was also associated with a reduction in oxidative stress and circulating endothelin-1 levels, as well as prevention of matrix metalloproteinase-2 and -9 activation and breakdown of ventricular collagen in the early stage of remodeling. These data demonstrate that estrogen attenuates ventricular remodeling and disease progression in male rats subjected to chronic volume overload.

Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

BackgroundPatients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.MethodsIn this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.ResultsIn burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).ConclusionFollowing severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Alternative promoter usage and alternative splicing of the rat estrogen receptor α gene generate numerous mRNA variants with distinct 5′-ends

The 5′-untranslated region (UTR) of the estrogen receptor α (ERα) gene plays an important role in determining tissue-specific expression. To elucidate the regulatory mechanisms of rat ERα gene expression, the genomic organization must be investigated. We therefore analyzed the structure of the rat ERα mRNA 5′-UTR using rapid amplification of 5′-cDNA ends (5′-RACE) and RT-PCR. The analysis showed the presence of multiple variants containing unique 5′-UTRs. We mapped the cDNA sequences on the rat genome, and newly identified one leader exon (exon 0U) and ten untranslated internal exons (exons I1–10). Both splicing from four different leader exons (exons 0S, 0N, 0U, and 0/B) onto exon 1 and alternative splicing in combination with eleven internal exons (exons I1–10, and 0T) produce multiple transcripts. RT-PCR analysis revealed that each variant had preferred expression sites, suggesting that promoter usage and splicing are regulated in tissue-specific manners. Moreover, we determined a splicing event to yield Δexon 1 variants (0S-2-3-4-5-6-7-8), which are translated into rat 46 kDa ERα proteins. Our results indicate that the rat ERα gene is more complex than previously thought in terms of genomic organization and that both alternative promoter usage and alternative splicing contribute to the remarkable diversity of ERα mRNAs.

Morphological Changes Induced by the Absence of Ovarian Hormones in Nucleus Accumbens of Ovariectomized Rats

Abstract: Ovariectomy (OVX) has been widely used to explore the effect of ovarian hormones on brain regions. It has been observed that estrogen in OVX rats increases the dopaminergic function in nucleus accumbens (NAcc). To determine whether absence or presence of estradiol changes the dendritic structure of some dopaminergic neurons, we investigated the consequences of a daily injection for 2 weeks of 17-beta estradiol (E2) on the dendritic morphology of NAcc neurons in two groups of rats, immediately or 10 weeks administered after OVX. The structure of dendrites was measured by using the Golgi-Cox procedure followed by a Sholl analysis. We found a reduction in the number of spiny dendrites of the medium spiny neurons of the NAcc in animals in which E2 was administrated without delay after OVX. However, when the same treatment was administered 10 weeks after OVX, not any difference was observed. Independently of the hormone treatment, rats from the group of 10 weeks after OVX showed a reduction in the number of spiny dendrites of the medium spiny neurons when compared with their counterparts at 2 weeks. Data suggest that estrogens or their absence regulate synaptogenesis in the NAcc.

Testosterone is essential for α 2-adrenoceptor-induced antinociception in the trigeminal region of the male rat

Activation of the α 2-adrenoceptor has been shown to produce antinociception. We have previously shown that the antinociceptive effect of clonidine, an α 2-adrenoceptor agonist, is sex-specific and is abolished by exogenous estrogen in ovariectomized rats or high level of endogenous estrogen in proestrous females. Here, we investigated whether testosterone mediates the antinociceptive effect of clonidine in the trigeminal region of the male rat. Clonidine (7 μg/5 μl) was injected intracisternally through a PE-10 cannula implanted dorsal to the trigeminal region in orchidectomized (GDX) male Sprague–Dawley rats. In separate groups, testosterone propionate (250 μg/100 μl; GDX+T) or β-estradiol benzoate (100 μg/100 μl; GDX+E) were injected subcutaneously 24 and 48 h respectively prior to the N-methyl- d-aspartic acid (NMDA)—or heat-evoked nociceptive test. NMDA-induced number of scratches or duration of scratching behavior did not change significantly in control groups with or without hormonal replacement. Clonidine significantly reduced both measures only in the GDX+T group but not in GDX or GDX+E group. Clonidine also significantly increased head withdrawal latency (HWL) in the GDX+T group, but not in GDX or GDX+E group. The antinociceptive effect of clonidine was reversed by yohimbine, an α 2-adrenoceptor antagonist, in GDX+T group. We conclude that testosterone is required for the expression of antinociception produced by selective activation of the α 2-adrenoceptor in the trigeminal region of the male rat. These findings further our understanding of sex-related differences in the modulation of nociception and may provide insight into development and administration of analgesic agents in young vs. aging men.

Pancreatic Lipase: A Neuro-Hormonal Regulated Enzyme. II Hormonal Influences

Purpose: We have shown in rats that vagotomy (V), celiac ganglionectomy (CG), V plus CG, and peri-Vaterian section and reanastomosis of the duodenal wall above and below the Vaterian papilla (PV-SRA) were associated with a sig. fall of lipase output in basal bile-pancreatic secretion (BPS). In contrast, Häkanson vagal reflex (2-hr pyloric ligation), that triggers an enhancement of the intrapancreatic cholinergic tone, reveals a non-significant modification of amylase but a marked sig. increase of lipasemia values. The aim of the present tests was to evaluate, taking into account our findings with the secretin test in menopause women of a sig. fall of lipase secretion in respect to those observed in men of the same age (>45 years), the effects of estradiol administration in male rats in comparison with a control solvent-treated series. Methods: Experiments were performed in male Wistar rats, bw˜300g. The experimental series was subjected to a subcutaneous injection of 50 μg of estradiol benzoate in 0.1 ml of peanut oil solvent. Estrogen was administered every other day for 15 days. In a control group of 13 animals, only the sucutaneous estrogen solvent was given for the same period. A biliary pancreatic fistula was created. BPS was collected for 180 minutes, in 30 min samples. Volume, bicarbonate concentration and output, both protein and lipase concentration and output were determined. Results: The 180 min cumulative data comparing estrogen-treated and control rodents disclosed no differences in the pattern of secretion (rate of flow and bicarbonate). Basal ecbolic secretion was augmented for protein and lipase concentration and output but only the latter revealed a markedly statistical significant increase. The present results, that of a selective rise in protein but primarily of lipase secretion (>200%) in the estrogen-treated rats, support the speculation that estradiol, in a potentiated interaction with the intrapancreatic cholinergic tone, constitute the main pivotal physiologic mechanism. The histologic finding in the estradiol-treated rats of “pancreon” acinar cells relatively clear and vitreous, without the classical granular appearance, suggestively reminds of what is seen after a pilocarpine injection. Conclusion: The present results, coherent with preceding ones, provide solid basis to our speculation that, indeed, estradiol effects on “pancreon” units are exerted in a close interplay with the level degree of an intrapancreatic cholinergic tone. Am J Gastroenterol 2009; 104:S82-S102; doi:10.1038/ajg.2009.492

Molecular Modeling for Screening Environmental Chemicals for Estrogenicity: Use of the Toxicant-Target Approach

There is a paucity of relevant experimental information available for the evaluation of the potential health and environmental effects of many man made chemicals. Knowledge of the potential pathways for activity provides a rational basis for the extrapolations inherent in the preliminary evaluation of risk and the establishment of priorities for obtaining missing data for environmental chemicals. The differential step in many mechanisms of toxicity may be generalized as the interaction between a small molecule (a potential toxicant) and one or more macromolecular targets. An approach based on computation of the interaction between a potential molecular toxicant and a library of macromolecular targets of toxicity has been proposed for preliminary chemical screening. In the current study, the interaction between a series of environmentally relevant chemicals and models of the rat estrogen receptors (ER) was computed and the results compared to an experimental data set of their relative binding affinities. The experimental data set consists of 281 chemicals, selected from the U.S. EPA's Toxic Substances Control Act (TSCA) inventory, that were initially screened using the rat uterine cytosolic ER-competitive binding assay. Secondary analysis, using Lineweaver-Burk plots and slope replots, was applied to confirm that only 15 of these test chemicals were true competitive inhibitors of ER binding with experimental inhibition constants (K(i)) less than 100 microM. Two different rapid computational docking methods have been applied. Each provides a score that is a surrogate for the strength of the interaction between each ligand-receptor pair. Using the score that indicates the strongest interaction for each pair, without consideration of the geometry of binding between the toxicant and the target, all of the active molecules were discovered in the first 16% of the chemicals. When a filter is applied on the basis of the geometry of a simplified pharmacophore for binding to the ER, the results are improved, and all of the active molecules were discovered in the first 8% of the chemicals. In order to obtain no false negatives in the model that includes the pharmacophore filter, only 8 molecules are false positives. These results indicate that molecular docking algorithms that were designed to find the chemicals that act most strongly at a receptor (and therefore are potential pharmaceuticals) can efficiently separate weakly active chemicals from a library of primarily inactive chemicals. The advantage of using a pharmacophore filter suggests that the development of filters of this type for other receptors will prove valuable.

Increase of FSH secretion in immature female rats following lesioning of the medial amygdaloid nucleus.

Immature female rats were bilaterally lesioned or sham-lesioned in the anterior part of the medial amygdaloid nucleus (AMN) at 21 days of age, and the serum FSH and LH concentrations were estimated in groups of rats autopsied at daily intervals from day 21 through day 28. Whereas the LH concentration did not differ between lesioned females and the controls, a highly significant elevation of the circulating FSH level was recorded in the lesioned rats from day 22 till day 24. A further experiment demonstrated that similar lesions did not change the FSH and LH-inhibiting effect of estrogen in rats that were ovariectomized on day 22, daily injected with 0.05 microgram estradiol benzoate per 100 g b.w. on days 22 and 23, and sacrificed 24 hr after the last injection. The results suggest that the AMN exerts a restraining influence on the hypophyseal FSH secretion around 21 days of age, and that this inhibitory activity does not depend upon sensitization to the negative feed-back of estrogen.