Behavioral and hormonal responses of male zebra finches to antiandrogens

After it was shown that the sexual behavioral patterns of male zebra finches are dependent on testosterone, the effects of treatment with two antiandrogens were investigated. The antiandrogens cyproterone (Cy) and cyproterone acetate (CyA) were used in this study. The results show that injections of CyA depress the sexual activity of the birds as measured by the amount of courtship song. The undirected song, too, is negatively influenced by a higher dosage of CyA. With the same dosage of Cy neither of these effects is observed. Radioimmunoassay for plasma testosterone showed that birds treated with CyA had lower, and birds treated with Cy had higher, testosterone levels in comparison with control animals. CyA is described as an antiandrogen with gestagenic side effects while Cy acts as a pure antiandrogen without side effects. Presumably the gestagenic side effects of CyA stop the production of testosterone by negative feedback mechanisms. This negative feedback combined with the antiandrogenic activity seems to account for the effects of CyA on behavior. Cy has no gestagenic side effect but is antiandrogenic with respect to blocking of androgen receptors. The organism tries to compensate for this deficit by increasing the testosterone production. The antiandrogenic activity of Cy probably is neutralized by this stimulated testosterone production.     

The male genital tract and the nipples of male and female offspring of rats given the non-steroidal antiandrogens DIMP and Sch 13521, during pregnancy.

Male and female offspring of rats given antiandrogens, the steroidal BOMT or the non steroids DIMP or Sch 13521, daily during the last third of pregnancy were studied. Detailed examinations were made of the genital tract of male, and of the nipples of male and female offspring. A) Male offspring. 1) Genital tract of newborn and 31-91 day old males : Modifications of the development of accessory sexual tissues were found in all treatment groups. As indicated by the severity of deviations from normal (morphology and weight of sex accessories), the antiandrogenic effect of the preparations, in the doses given to the mother rats, increased from BOMT (50 or 75 mg/day) via Sch 13521 (30 mg/day) and DIMP (50 or 60 mg/day) to Sch 13521 (60 mg/day). 2) Nipples of 10-60 day old males : Whole mount preparations were made unilaterally of the row of 6 mammary glands with nipples. The number of intact and abnormal nipples, respectively, was recorded. The relation between intact and abnormal nipples served as indicator of the efficiency of the antiandrogenic substances studied. The result showed that the antiandrogenic effect increased from BOMT to Sch 13521, 60 mg, in the same order as that arrived at from studies of the genital tract. The combined results obtained from the male offspring indicated that the tissues of the genital region, the growth and differentiation of which was most readily impaired by antiandrogens, were the same as those known from other work to be stimulated most easily in female rat fetuses by testosterone. B) Female offspring. Nipples of 31-60 day old females were judged from whole mount preparations and recorded as in the males. The nipples of adult virginal females were examined macroscopically. The same procedure was applied to lactating females, but the results were controlled in consecutive lactational periods and at autopsy. The 3 groups of females showed uniformly that 1) offspring of rats given BOMT during pregnancy had many (about 50 per cent) malformed nipples and 2) the treatment of mother rats with DIMP or Sch 13521 did not influence the development of nipples in female offspring. The result was assumed to be due to an androgenic effect of the steroidal antiandrogen, BOMT, on the nipple anlage.     

Residue 17 of sauvagine cross-links to the first transmembrane domain of corticotropin-releasing factor receptor 1 (CRFR1)

Corticotropin-releasing factor receptor 1 (CRFR1) mediates the physiological actions of corticotropin-releasing factor in the anterior pituitary gland and the central nervous system. Using chemical cross-linking we have previously reported that residue 16 of sauvagine (SVG) is in a close proximity to the second extracellular loop of CRFR1. Here we introduced p-benzoylphenylalanine (Bpa) at position 17 of a sauvagine analog, [Tyr0, Gln1, Bpa17]SVG, to covalently label CRFR1 and characterize the cross-linking site. Using a combination of receptor mutagenesis, peptide mapping, and N-terminal sequencing, we identified His117 within the first transmembrane domain (TM1) of CRFR1 as the cross-linking site for Bpa17 of 125I-[Tyr0, Gln1, Bpa17]SVG. These data indicate that, within the SVG-CRFR1 complex, residue 17 of the ligand lies within a 9 angstroms distance from residue 117 of the TM1 of CRFR1. The molecular proximity between residue 17 of the ligand and TM1 of CRFR1 described here and between residue 16 of the ligand and the CRFR1 second extracellular loop described previously provides useful molecular constraints for modeling ligand-receptor interaction in mammalian cells expressing CRFR1.     

Regulation of testicular function in men: implications for male hormonal contraceptive development

In the adult male, the testes produce both sperm and testosterone. The function of the testicles is directed by the central nervous system and pituitary gland. Precise regulation of testicular function is conferred by an elegant feedback loop in which the secretion of pituitary gonadotropins is stimulated by gonadotropin hormone-releasing hormone (GnRH) from the hypothalamus and modulated by testicular hormones. Testosterone and its metabolites estradiol and dihydrotestosterone (DHT) as well as inhibin B inhibit the secretion of the gonadotropins both directly at the pituitary and centrally at the level of the hypothalamus. In the testes, LH stimulates testosterone synthesis and FSH promotes spermatogenesis, but the exact details of gonadotropin action are incompletely understood. A primary goal of research into understanding the hormonal regulation of testicular function is the development of reversible, safe and effective male hormonal contraceptives. The administration of exogenous testosterone suppresses pituitary gonadotropins and hence spermatogenesis in most, but not all, men. The addition of a second agent such as a progestin or a GnRH antagonist yields more complete gonadotropin suppression; such combination regimens effectively suppress spermatogenesis in almost all men and may soon bring the promise of hormonal male contraception to fruition.     

Binding properties of testosterone receptors in the hypothalamic-preoptic area of the adult male mouse brain.

This study reports the specificity, kinetics and thermodynamics of the binding of tritiated testosterone to specific receptors in the cytosol of the hypothalamic-preoptic area of the adult male mouse brain. Values for the kinetic is parametrs KA, KD, ka, kd and the apparent free energy (delta GOoc) are reported. The specificity of these receptors was investigated by LH-20 chromatography and sucrose-gradient centrifugation. Differences inreceptor specificity between the mouse and that reported for the rat are described. The effects of the antiandrogens, cyproterone acetate and BOMT, and the anti-estrogens MER-25 and clomiphene citrate on the binding of tritiated testosterone to specific 8S receptors are also reported. The effect of these steroid receptor antagonists on testosterone binding is discussed in relation to the current theory on the mechanism by which androgens influence brain function.     

Slow oscillations in blood pressure via a nonlinear feedback model

Blood pressure is well established to contain a potential oscillation between 0.1 and 0.4 Hz, which is proposed to reflect resonant feedback in the baroreflex loop. A linear feedback model, comprising delay and lag terms for the vasculature, and a linear proportional derivative controller have been proposed to account for the 0.4-Hz oscillation in blood pressure in rats. However, although this model can produce oscillations at the required frequency, some strict relationships between the controller and vasculature parameters must be true for the oscillations to be stable. We developed a nonlinear model, containing an amplitude-limiting nonlinearity that allows for similar oscillations under a very mild set of assumptions. Models constructed from arterial pressure and sympathetic nerve activity recordings obtained from conscious rabbits under resting conditions suggest that the nonlinearity in the feedback loop is not contained within the vasculature, but rather is confined to the central nervous system. The advantage of the model is that it provides for sustained stable oscillations under a wide variety of situations even where gain at various points along the feedback loop may be altered, a situation that is not possible with a linear feedback model. Our model shows how variations in some of the nonlinearity characteristics can account for growth or decay in the oscillations and situations where the oscillations can disappear altogether. Such variations are shown to accord well with observed experimental data. Additionally, using a nonlinear feedback model, it is straightforward to show that the variation in frequency of the oscillations in blood pressure in rats (0.4 Hz), rabbits (0.3 Hz), and humans (0.1 Hz) is primarily due to scaling effects of conduction times between species.     

Effects of gonadal steroids and adrenergic agonists on avian growth and feed efficiency

The effects of gonadal steroids and adrenergic agonists in growing poultry are reviewed. Estrogens, used commercially to caponize, improve muscle palatability and weight gain but are hyperlipidemic and adversely affect feed efficiency. Their ability to caponize results from the fact that negative feedback regulation of gonadotropin secretion is mediated by estrogen synthesized within the male's central nervous system. Androgens are strongly anabolic in avian species but are deleterious to growing bone. Thus, androgens depress growth and efficiency when given before epiphyseal closure but stimulate gain and improve efficiency when given afterwards. The beta-adrenergic agonist clenbuterol improves the growth and efficiency of broiler chickens. The effects of beta-agonists on muscle, adipogenic tissue, and the endocrine system are presented as possible mechanisms for these actions.     

Pituitary Androgen Receptor Signalling Regulates Prolactin but Not Gonadotrophins in the Male Mouse

Production of the androgen testosterone is controlled by a negative feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. Stimulation of testicular Leydig cells by pituitary luteinising hormone (LH) is under the control of hypothalamic gonadotrophin releasing hormone (GnRH), while suppression of LH secretion by the pituitary is controlled by circulating testosterone. Exactly how androgens exert their feedback control of gonadotrophin secretion (and whether this is at the level of the pituitary), as well as the role of AR in other pituitary cell types remains unclear. To investigate these questions, we exploited a transgenic mouse line (Foxg1^Cre/+; AR^fl/y) which lacks androgen receptor in the pituitary gland. Both circulating testosterone and gonadotrophins are unchanged in adulthood, demonstrating that AR signalling is dispensable in the male mouse pituitary for testosterone-dependent regulation of LH secretion. In contrast, Foxg1^Cre/+; AR^fl/y males have a significant increase in circulating prolactin, suggesting that, rather than controlling gonadotrophins, AR-signalling in the pituitary acts to suppress aberrant prolactin production in males.     

Negative feedback regulation of the secretion and actions of gonadotropin-releasing hormone in males

This minireview considers the state of knowledge regarding the interactions of testicular hormones to regulate the secretion and actions of GnRH in males, with special focus on research conducted in rams and male rhesus monkeys. In these two species, LH secretion is under the negative feedback regulation of testicular steroids that act predominantly within the central nervous system to suppress GnRH secretion. The extent to which these actions of testicular steroids result from the direct actions of testosterone or its primary metabolites, estradiol or dihydrotestosterone, is unclear. Because GnRH neurons do not contain steroid receptors, the testicular steroids must influence GnRH neurons via afferent neurons, which are largely undefined. The feedback regulation of FSH is controlled by inhibin acting directly at the pituitary gland. In male rhesus monkeys, the feedback regulation of FSH secretion is accounted for totally by the physiologically relevant form of inhibin, which appears to be inhibin B. In rams, the feedback regulation of FSH secretion involves the actions of inhibin and testosterone and interactions between these hormones, but the physiologically relevant form of inhibin has not been determined. The mechanisms of action for inhibin are not known.     

Three-dimensional structure of a mouse-adapted type 2/type 1 poliovirus chimera.

The crystal structure of V510, a chimeric type 2/type 1 poliovirus, has been determined at 2.6 A resolution. Unlike the parental Mahoney strain of type 1 poliovirus, V510 is able to replicate in the mouse central nervous system, due entirely to the replacement of six amino acids in the exposed BC loop of capsid protein VP1. Significant structural differences between the two strains cluster in a major antigenic site of the virus, located at the apex of the radial projection which surrounds the viral five-fold axis. Residues implicated in the mouse-virulence of poliovirus by genetic studies are located in this area, and include the residues which are responsible for stabilizing the conformation of the BC loop in V510. Despite evidence that this area is not involved in receptor binding in cultured primate cells, the genetic and structural observations suggest that this area plays a critical role in receptor interactions in the mouse central nervous system. These results provide a structural framework for further investigation of the molecular determinants of host and tissue tropism in viruses.     

Clinical profile of a new non-steroidal antiandrogen

Recently a new non-steroidal antiandrogen (Casodex®) has been shown in animal experiments to possess a potent peripheral antiandrogen effect. In patients with advanced prostatic cancer however, this drug is not peripherally selectively active and blocked central brain androgenreceptors results in a rise of luteinizing hormone (LH) and testosterone (T).

We treated 18 advanced prostatic cancer patients with 50 mg Casodex® daily for a mean period of 42 weeks. There were no complete objective responses but partial responses were seen in a few patients. In 16 patients there was a greater than 50% reduction of pretreatment PSA levels. Endocrine evaluations showed a significant rise in LH, T and oestradiol (E), reaching peak values within the two first months with subsequent lowering of these levels afterwards but without returning to normal. The general tolerance of the drug was good, gynecomastia being the most frequent side-effect. Libido and potency, when present before start of therapy, were maintained in some patients. We conclude that this compound seems as effective as other antiandrogens, but with improved compliance, and shows less side effects in the management of advanced prostatic cancer.     

Migfilin promotes migration and invasion in glioma by driving EGFR and MMP-2 signalings: A positive feedback loop regulation

Glioma is the most common type of primary brain tumors in the central nervous system(CNS). Migfilin occurs in human glioma and enhances cellular motility via the epidermal growth factor receptor(EGFR)pathway. However, the underlying molecular mechanism is not fully understood. In this study, we found that Migfilin promoted matrix metalloproteinase-2(MMP-2) activity, and restrained the expression of tissue inhibitor of metalloproteinase 2(TIMP2), which is an MMP-2 inhibitor. Functional and structural studies showed that the LIM1 domain of Migfilin was required for Migfilin-mediated TIMP2 expression inhibition and MMP-2 activity, and was also necessary in promoting cell motility. Furthermore, Migfilininduced EGFR phosphorylation was greatly reduced by MMP-2 inhibitor(GM6001) or si RNA, while Migfilin-induced MMP-2 activation was also blocked by the EGFR inhibitor(AG1478) or si RNA. MMP-2 and EGFR inhibitors and their si RNAs can block Migfilin-induced migration and invasion, respectively.These results demonstrated that EGFR and MMP-2 signalings may form a positive feedback loop to enhance Migfilin-induced migration and invasion. Finally, we detected that the expression of Migfilin,EGFR phosphorylation(Tyr1173) and MMP-2 activity had a positive correlation in the clinical glioma sample. Taken together, these results suggest that Migfilin is a critical regulator in cellular motility by driving the EGFR-MMP-2 feedback loop, and may be considered as a potential therapeutic target in glioma.     

Steroid metabolism and effects in central and peripheral glial cells.

Hormonal steroids participate in the control of a large number of functions of the central nervous system (CNS); recent data show that they may also intervene at the level of the peripheral nervous system (PNS). Both the CNS and the PNS metabolize endogenous as well as exogenous steroids; one of the major enzymatic system is represented by the 5alpha-reductase-3alpha-hydroxysteroid complex. This is a versatile system, since every steroid possessing the delta 4-3keto configuration (e.g., testosterone, progesterone, deoxycorticosterone) may be a substrate. High levels of 5alpha-reductase are found in the white matter of the CNS and in purified myelin. The observation that, in addition to neurons, glia may be a target for steroid action is an important recent finding. The effects of progesterone, testosterone, corticoids, and their respective 5alpha and 3alpha-5alpha derivatives on the expression of glial genes are presented and discussed. It has also been found that progesterone and/or its 5alpha-reduced metabolites increase the mRNA for the two major proteins of peripheral myelin, the glycoprotein Po and the peripheral myelin protein 22, in the sciatic nerve of normal and aged animals and in Schwann cells. The hypothesis has been put forward that glycoprotein Po might be under the control of progestagens acting mainly via the progesterone receptor, and that peripheral myelin protein 22 might be controlled via an interaction of steroids with the gamma-aminobutyric acid (GABA)ergic system. It is known that tetrahydroprogesterone, the 3alpha-5alpha-reduced metabolite of progesterone, interacts with the GABA(A) receptor. Our recent data show that several subunits of this receptor are present in sciatic nerve as well as in Schwann cells that reside in this nerve. These data open multiple possibilities for new therapeutic approaches to demyelinating diseases.     

Adiposity signals and food reward: expanding the CNS roles of insulin and leptin

The hormones insulin and leptin have been proposed to act in the central nervous system (CNS) as adiposity signals as part of a theoretical negative feedback loop that senses the caloric stores of an animal and orchestrates adjustments in energy balance and food intake. Much research has provided support for both the existence of such a feedback loop and the specific roles that insulin and leptin may play. Most studies have focused on hypothalamic sites, which historically are implicated in the regulation of energy balance, and on the brain stem, which is a target for neural and humoral signals relating to ingestive acts. More recent lines of research, including studies from our lab, suggest that in addition to these CNS sites, brain reward circuitry may be a target for insulin and leptin action. These studies are reviewed together here with the goals of providing a historical overview of the findings that have substantiated the originally hypothesized negative feedback model and of opening up new lines of investigation that will build on these findings and allow further refinement of the model of adiposity signal/CNS feedback loop. The understanding of how motivational circuitry and its endocrine or neuroendocrine modulation contributes to normal energy balance regulation should expand possibilities for future therapeutic approaches to obesity and may lead to important insights into mental illnesses such as substance abuse or eating disorders.     

Charged residues in the beta2 subunit involved in GABAA receptor activation

Fast synaptic inhibition in the mammalian central nervous system is mediated primarily via activation of the gamma-aminobutyric acid type A receptor (GABAA-R). Upon agonist binding, the receptor undergoes a structural transition from the closed to the open state. This transition, known as gating, is thought to be associated with a sequence of conformational changes originating at the agonist-binding site, ultimately resulting in opening of the channel. Using site-directed mutagenesis and several different GABAA-R agonists, we identified a number of highly conserved charged residues in the GABAA-R beta2 subunit that appear to be involved in receptor activation. We then used charge reversal double mutants and disulfide trapping to investigate the interactions between these flexible loops within the beta2 subunit. The results suggest that interactions between an acidic residue in loop 7 (Asp146) and a basic residue in pre-transmembrane domain-1 (Lys215) are involved in coupling agonist binding to channel gating.     

家兔的开环及闭环视动震颤（OKN）研究

研究了家兔闭环及开环状态的ＯＫＮ反应。闭环时,ＯＫＮ眼动速度与刺激速度成正比,增益接近１。当固定受刺激眼形成开环状态时,ＯＫＮ眼动速度远大于刺激速度,增益可达１０２左右,说明ＯＫＮ系统是由运动跟踪的负反馈机制控制的;刺激范围缩小则眼动反应减弱,表明ＯＫＮ系统对运动信息具有空间总和作用;以视野中不同高度的局部刺激时,发现视网膜中央视带比周边部对ＯＫＮ刺激的敏感性高;单光点刺激视带中央可诱发出清楚的ＯＫＮ反应,这为临床上应用ＯＫＮ客观测定视网膜功能和运动感知提供了可能性。     

Adrenoceptors and the pharmacology of affective illness: a unifying theory

Based on recent clinical and preclinical research, it is theorized that antimanic and antidepressant effects of clinically available drugs can be produced through their actions on alpha-1 adrenoreceptor-mediated neurotransmission in the central nervous system. The theory suggests that final effects on alpha-1 mediated neurotransmission may be produced not only by drugs which have direct effects on the alpha-1 receptor or its second messenger, but also by drugs having effects on neurotransmitter systems such as acetylcholine, GABA, and serotonin, among others, which modulate the activity of central norepinephrine neurons or, via feedback mechanisms, by drugs having effects on adrenergic receptors other than the alpha-1 receptor itself.