Effect of Immobilization Stress on Gonadotropins and Sex Steroids

The effects of the acute immobilization stress on follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol, and testosterone levels in rats were evaluated. The male and female rats were grouped in control and stress groups (7 animals in each group). Vaginal smears were taken daily from female rats and the rats in the proestrus were involved in the experiments. After a 1-h immobilization stress, blood samples from the heart were taken and the serum FSH, LH, estradiol and testosterone levels were measured by radioimmunoassay (RIA). The results were statistically analyzed using the Mann–Whitney U-test. A statistically significant increase of the levels of FSH and estradiol, but not of LH, was found in the female rats after the stress. A statistically significant increase of the FSH concentration was also revealed in the male rats, but there were no significant changes of the LH and testosterone levels. The scientific and applied (medical) aspects of the data obtained are discussed.     

Sex Steroids and the Differentiation of Avian Reproductive Behavior

Experiments in which avian embryos are treated with sex steroidsor steroid antagonists suggest that sexual differentiation ofreproductive behavior (and thus differentiation of the brainmechanisms for such behavior) is controlled by steroids producedby the embryonic gonads. In chickens and Japanese quail, maleshatched from eggs treated with estradiol or testosterone duringincubation are feminized (demasculinized); they fail to exhibitmasculine sexual behavior as adults, and no longer are behaviorallydistinguishable from females. Some evidence suggests that testosteronemay mimic the feminizing action of estradiol by being convertedto an estrogen in the embryonic brain. Genetic female quailexposed to an antiestrogen during embryonic development aremasculinized; they exhibit an increased ability to display themasculine copulatory pattern. Thus the behavior of these speciesis feminized by embryonic exposure to sex steroids, the anhormonal(neutral) sex for behavioral differentiation appears to be themale, and females appear to result from estrogen produced bythe embryonic ovaries. In contrast, sex steroid treatment ofmammals early in development masculinizes behavior, the femaleis the neutral sex, and males result from fetal androgen secretion.These opposite patterns of psychosexual differentiation in birdsand mammals are correlated with a major difference between theavian and mammalian sex-determining mechanism. Implicationsfor other vertebrates are discussed.     

Frequent Fire Reduces the Magnitude of Positive Interactions Between an Invasive Grass and Soil Microbes in Temperate Forests

Ecosystems - Fire activity is increasing in many regions. Although increased fire activity is expected to promote plant invasion, over longer time periods, frequent fire can shift the nutrient...     

Elizabethkingia anophelis: Molecular Manipulation and Interactions with Mosquito Hosts

Flavobacteria (members of the family Flavobacteriaceae) dominate the bacterial community in the Anopheles mosquito midgut. One such commensal, Elizabethkingia anophelis, is closely associated with Anopheles mosquitoes through transstadial persistence (i.e., from one life stage to the next); these and other properties favor its development for paratransgenic applications in control of malaria parasite transmission. However, the physiological requirements of E. anophelis have not been investigated, nor has its capacity to perpetuate despite digestion pressure in the gut been quantified. To this end, we first developed techniques for genetic manipulation of E. anophelis, including selectable markers, reporter systems (green fluorescent protein [GFP] and NanoLuc), and transposons that function in E. anophelis. A flavobacterial expression system based on the promoter PompA was integrated into the E. anophelis chromosome and showed strong promoter activity to drive GFP and NanoLuc reporter production. Introduced, GFP-tagged E. anophelis associated with mosquitoes at successive developmental stages and propagated in Anopheles gambiae and Anopheles stephensi but not in Aedes triseriatus mosquitoes. Feeding NanoLuc-tagged cells to A. gambiae and A. stephensi in the larval stage led to infection rates of 71% and 82%, respectively. In contrast, a very low infection rate (3%) was detected in Aedes triseriatus mosquitoes under the same conditions. Of the initial E. anophelis cells provided to larvae, 23%, 71%, and 85% were digested in A. stephensi, A. gambiae, and Aedes triseriatus, respectively, demonstrating that E. anophelis adapted to various mosquito midgut environments differently. Bacterial cell growth increased up to 3-fold when arginine was supplemented in the defined medium. Furthermore, the number of NanoLuc-tagged cells in A. stephensi significantly increased when arginine was added to a sugar diet, showing it to be an important amino acid for E. anophelis. Animal erythrocytes promoted E. anophelis growth in vivo and in vitro, indicating that this bacterium could obtain nutrients by participating in erythrocyte lysis in the mosquito midgut.     

Molecular Analysis of the Interactions between Cyst Nematodes and Their Hosts

In order to complete its life cycle, a cyst nematode must stimulate the production of a specialized syncytial feeding site within host root tissues. This process is characterized by major changes in local root morphology, including enlargement of affected nuclei and nucleoli, cell wall degradation, and proliferation of subcellular organelles. At the molecular level very little is known about the processes involved in this host response, but recent evidence suggests that cyst nematodes are able to regulate specific host genes. The host-parasite model system provided by Arabidopsis thaliana and Heterodera schachtii will be fundamental to our future understanding of the formation of syncytia. Molecular biology now offers us the opportunity to study this complex host-parasite interaction in great detail. A better understanding of the host genes regulated by cyst nematodes and the mechanisms by which this regulation is achieved will facilitate the engineering of crop cultivars that possess novel forms of resistance to these adept parasites.     

Cations Mediate Interactions between the Nicotinic Acetylcholine Receptor and Anionic Lipids

Interactions between the nicotinic acetylcholine receptor (nAChR) and phosphatidic acid (PA) are bidirectional in that membranes containing PA are effective at stabilizing an agonist-responsive nAChR, whereas incorporation of the nAChR into the same membranes leads to a substantial increase in lipid lateral packing density. A previous study suggested that the ability of PA to adopt a dianionic ionization state is key. We monitored the ionization state of PA in both reconstituted and protein-free membranes. In model membranes composed of PA and 3:2 (mol/mol) phosphatidylcholine (PC)/PA, the monoanionic-to-dianionic transition of PA was detected with a pKa of 8.7 and 6.5, respectively. In the reconstituted 3:2 PC/PA membranes, however, PA was stabilized in a monoanionic state at pH values up to 10. Although dianionic PA does not play a role in nAChR function, we found that both the stabilization of monoanionic PA and the concentration of other cations at the bilayer surface can account for changes in bilayer physical properties that are observed upon incorporation of the nAChR into 3:2 PC/PA membranes. A nAChR-induced concentration of cations at the bilayer surface likely mediates interactions between the nAChR and the anionic lipids in its membrane environment.     

Sex Steroids Inhibit Osmotic Swelling of Retinal Glial Cells

Osmotic swelling of glial cells may contribute to the development of retinal edema. We investigated whether sex steroids inhibit the swelling of glial somata in acutely isolated retinal slices and glial cells of the rat. Superfusion of retinal slices or cells from control animals with a hypoosmolar solution did not induce glial swelling, whereas glial swelling was observed in slices of postischemic and diabetic retinas. Progesterone, testosterone, estriol, and 17ß-estradiol prevented glial swelling with half-maximal effects at approximately 0.3, 0.6, 6, and 20 μM, respectively. The effect of progesterone was apparently mediated by transactivation of metabotropic glutamate receptors, P2Y₁, and adenosine A₁ receptors. The data suggest that sex steroids may inhibit cytotoxic edema in the retina.     

Systemic Non-Reproductive Effects of Sex Steroids in Adult Males and Females

Sex steroids are well known for their reproductive actions, however, their roles are not confined to reproduction only and they have been shown to exert wide ranging effects on systemic physiology. Further, the effects of the so-called male and female sex steroids are not limited to their respective genders but they are present in both sexes where they have a significant impact upon systemic functions, reproductive as well as non-reproductive. This work reviews the existing knowledge base and recent reports on the effects of sex steroids on non-reproductive physiology.     

Cospeciation Between the Primary Endosymbionts of Mealybugs and Their Hosts

Mealybugs have an association with prokaryotic endosymbionts that are located in specialized cells called bacteriocytes. In order to compare the phylogeny of the host with that of the previously published phylogeny of the endosymbionts, 3.1 to 3.2 kilobase DNA fragments containing mitochondrial cytB (part), nd1,16S ribosomal DNA(rDNA), and 12S rDNA (part) were amplified and sequenced. A phylogenetic analysis of the data and a comparison with the trees obtained from endosymbiont genes and host 18S and 28S rDNA indicated that all the trees were similar. This result is consistent with an infection of a mealybug ancestor with a precursor of the endosymbiont followed by the vertical transmission of the endosymbiont to progeny. Comparison of the guanine + cytosine (G + C) contents of the mealybug mitochondrial genes with the same genes from other members of Sternorrhyncha and Arthropoda indicated that the mealybug genes had unusually low G + C contents in their DNAs (10.2 to 11.1 mol%).     

A Cooperative System of Two Species with Bidirectional Interactions

Cooperation between species is often regarded to mean that the increase of each species promotes the growth of the other. The well-known cooperative model is the Lotka–Volterra equations (LVEs). In the LVEs, population densities of species increase infinitely as the cooperation is strong, which is called the divergence problem. Moreover, LVEs never exhibit an Allee effect in the case of obligate cooperation. In order to avoid these problems, several models have been established although most of them are rather complex. In this paper, we consider a cooperative system of two species with bidirectional interactions, in which each species also has negative feedback on the other. Population densities of the species will not increase infinitely because of the limited resource and negative feedback. Then, we focus on an extended lattice model of cooperation, which is deduced from reactions on lattice and has the same form as that of LVEs. In the case of obligate cooperation, the model predicts an Allee effect. Global dynamics of the system exhibit essential features of cooperation and basic mechanisms by which the cooperation can lead to coexistence/extinction of species. Intermediate cooperation is shown to be beneficial in cooperation under certain conditions, while extremely strong cooperation is demonstrated to lead to extinction of one/both species. Numerical simulations confirm and extend our results.     

Lack of Evidence for Cospeciation Between Retroelements and Their Hosts

Some literature is available on cospeciation and on reconstructing the phylogenetic relationships of retroelements, but relatively little consideration has been given to whether there is cospeciation between retroelements and their hosts. Here we address this problem in detail. We conclude that there is no significant evidence for cospeciation between retroelements and their hosts. This conclusion was reached by noting that the branching order of the two phylogenies was no more similar than would be expected by chance. Received: 18 February 1999 / Accepted: 1 October 1999     

Intradomain Interactions in an NMDA Receptor Fragment Mediate N-Glycan Processing and Conformational Sampling

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Interactions Between Rhinanthus minor and Its Hosts: A Review of Water, Mineral Nutrient and Hormone Flows and Exchanges in the Hemiparasitic Association

At the ecological level, the effects of the facultative root hemiparasite Rhinanthus minor on the structure and functioning of its host communities are relative well described; yet until recently, the mechanistic basis for parasitic plant-driven community change and the physiological basis for the host-parasite interaction were poorly understood. Empirical incremental flow models, based on the increase in water, mineral nutrients, carbon assimilates or phytohormones between two defined time points, have been successfully employed to investigate the physiology of resource acquisition by- and distribution within host-parasitic plant associations. In this study we review the application of these empirical flow models to Rhinanthus-host associations showing the extent of and physiological basis of resource abstraction from the host and how this is profoundly influenced by soil nutrient status. We show that Rhinanthus primarily abstracts water and mineral nutrients via the apoplastic pathway through direct lumen-lumen connections with little resource acquisition via symplastic pathways. Nutrient status of the soil is shown to significantly influence the resource acquisition. We also investigate the hormonal regulation of resource acquisition by Rhinanthus showing pivotal roles for the key for the phytohormones abscisic acid (ABA) and cytokinins.     

The Influence of Sex Steroids on Structural Brain Maturation in Adolescence

Puberty reflects a period of hormonal changes, physical maturation and structural brain reorganization. However, little attention has been paid to what extent sex steroids and pituitary hormones are associated with the refinement of brain maturation across adolescent development. Here we used high-resolution structural MRI scans from 215 typically developing individuals between ages 8–25, to examine the association between cortical thickness, surface area and (sub)cortical brain volumes with luteinizing hormone, testosterone and estradiol, and pubertal stage based on self-reports. Our results indicate sex-specific differences in testosterone related influences on gray matter volumes of the anterior cingulate cortex after controlling for age effects. No significant associations between subcortical structures and sex hormones were found. Pubertal stage was not a stronger predictor than chronological age for brain anatomical differences. Our findings indicate that sex steroids are associated with cerebral gray matter morphology in a sex specific manner. These hormonal and morphological differences may explain in part differences in brain development between boys and girls.