Effects of sex steroids on aromatase mRNA expression in the male and female quail brain (original) (raw)
Related papers
Journal of Chemical Neuroanatomy, 1998
A number of studies have been devoted to the analysis of the anatomical distribution, control by steroids and functional significance of aromatase (the enzyme metabolizing testosterone into 17i-estradiol) in the quail brain. In particular, the sexually dimorphic nucleus preopticus medialis has been the main focus of investigation because testosterone aromatization in this structure mediates the activation of male sexual behavior and aromatase activity is itself testosterone-dependent in this nucleus. No information on the anatomical distribution of aromatase gene expression is, however, available so far in this avian species. In the present study we applied a non-radioactive in situ hybridization technique to describe the distribution of aromatase mRNA containing neurons in the quail prosencephalon. We also analyzed, at a neuronal level of resolution, the induction by testosterone of this mRNA in the medial preoptic nucleus. Dense clusters of aromatase gene expressing neurons were observed within the medial preoptic nucleus, the nucleus of the stria terminalis, the ventro-medial hypothalamus and the tuberal region. Scattered neurons expressing lower levels of aromatase mRNA were also found in the dorsal thalamic area and central gray. The specificity of the staining was confirmed by demonstrating the absence of signal in sections that had been hybridized with a sense probe. Moreover, the distribution of the aromatase mRNA containing cells completely overlapped with the distribution of the aromatase-immunoreactive cells. Aromatase-mRNA expression was controlled by testosterone (or its metabolites) in the entire medial preoptic nucleus. Castration resulted in a decrease in the number of aromatase mRNA-containing cells and this effect was totally reversed by testosterone treatment. These data further support the idea that testosterone regulates the rate of its own aromatization by modulating the expression of aromatase rather than by acting at a post transcriptional level.
Neuroanatomical specificity of sex differences in expression of aromatase mRNA in the quail brain
Journal of Chemical Neuroanatomy, 2007
In birds and mammals, aromatase activity in the preoptic-hypothalamic region (HPOA) is usually higher in males than in females. It is, however, not known whether the enzymatic sex difference reflects the differential activation of aromatase transcription or some other control mechanism. Although sex differences in aromatase activity are clearly documented in the HPOA of Japanese quail (Coturnix japonica), only minimal or even no differences at all were observed in the number of aromatase-immunoreactive (ARO-ir) cells in the medial preoptic nucleus (POM) and in the medial part of the bed nucleus striae terminalis (BSTM). We investigated by in situ hybridization the distribution and possible sex differences in aromatase mRNA expression in the brain of sexually active adult quail. The distribution of aromatase mRNA matched very closely the results of previous immunocytochemical studies with the densest signal being observed in the POM, BSTM and in the mediobasal hypothalamus (MBH). Additional weaker signals were detected in the rostral forebrain, arcopallium and mesencephalic regions. No sex difference in the optical density of the hybridization signal could be found in the POM and MBH but the area covered by mRNA was larger in males than in females, indicating a higher overall expression in males. In contrast, in the BSTM, similar areas were covered by the aromatase expression in both sexes but the density of the signal was higher in females than in males. The physiological control of aromatase is thus neuroanatomically specific and with regard to sex differences, these controls are at least partially different if one compares the level of transcription, translation and activity of the enzyme. These results also indirectly suggest that the sex difference in aromatase enzyme activity that is present in the quail HPOA largely results from differentiated controls of enzymatic activity rather than differences in enzyme concentration. #
Sex Differences in the Expression of Sex Steroid Receptor mRNA in the Quail Brain
Journal of Neuroendocrinology, 2009
In Japanese quail, males will readily exhibit the full sequence of male-typical sexual behaviors but females never show this response even after ovariectomy and treatment with male-typical concentrations of exogenous testosterone. Testosterone aromatization plays a key-limiting role in the activation of this behavior but the higher aromatase activity in the brain of males compared to females is not sufficient to explain the behavioral sex difference. The cellular and molecular bases of this prominent sex difference in the functional consequences of testosterone have not been identified so far. We hypothesized that the differential expression of sex steroid receptors in specific brain areas could mediate this behavioral sex difference and therefore quantified by radioactive in situ hybridization histochemistry the expression of the mRNA coding for the androgen receptor (AR) and the estrogen receptors (ER) of the α and β sub-types. All three receptors were expressed in an anatomically discrete manner in various nuclei of the hypothalamus and limbic system and, at usually lower densities, in a few other brain areas. In both sexes, the intensity of the hybridization signal for all steroid receptors was highest in the medial preoptic nucleus (POM), a major site of testosterone action related to the activation of male sexual behavior. Although no sex difference in the optical density of the AR hybridization signal could be found in POM, the area covered by AR mRNA was significantly larger in males than in females, indicating a higher overall degree of AR expression in this region in males. In contrast, females tended to have significantly higher levels of AR expression than males in the lateral septum. ERα was more densely expressed in females than males throughout the medial preoptic and hypothalamic areas (including the POM and the medio-basal hypothalamus [MBH)], an area implicated in the control of female receptivity) and in the mesencephalic nucleus intercollicularis. ERβ was more densely expressed in the medio-basal hypothalamus of females but a difference in the reverse direction (males>females) was observed in the nucleus taeniae of the amygdala. These data suggest that a differential expression of steroid receptors in specific brain areas could mediate at least certain aspects of the sex differences in behavioral responses to testosterone but they do not appear to be sufficient to explain the complete lack of activation by testosterone of maletypical copulatory behavior in females.
The Journal of Steroid Biochemistry and Molecular Biology, 1996
The enzyme aromatase converts testosterone (T) into 17fl-estradiol and plays a pivotal role in the control of reproduction. In particular, the aromatase activity (AA) located in the preoptic area (POA) of male Japanese quail is a limiting step in the activation by T of copulatory behavior. Aromatase-immunoreactive (ARO-ir) cells of the POA are specifically localized within the cytoarchitectonic boundaries of the medial preoptic nucleus (POM), a sexually dimorphic and steroid-sensitive structure that is a necessary and sufficient site of steroid action in the activation of behavior. Stereotaxic implantation of aromatase inhibitors in but not around the POM strongly decreases the behavioral effects of a systemic treatment with T of castrated males. AA is decreased by castration and increased by aromatizable androgens and by estrogens. These changes have been independently documented at three levels of analysis: the enzymatic activity measured by radioenzymatic assays in vitro, the enzyme concentration evaluated semi-quantitatively by immunocytochemistry and the concentration of its messenger RNA quantified by reverse transcription-polymerase chain reaction (RT-PCR). These :studies demonstrate that T acting mostly through its estrogenic metabolites regulates brain aromatase by acting essentially at the transcriptional level. Estrogens produced by central aromatization of T therefore have two independent roles: they activate male copulatory behavior and they :regulate the synthesis of aromatase. Double label immunocytochemical studies demonstrate that estrogen receptors (ER) are found in all brain areas containing ARO-ir cells but the extent to which these markers are colocalized varies from one brain region to the other. More than 70% of ARO-ir cells contain detectable ER in the tuberal hypothalamus but less than 20% of the cells display this colocalization in the POA. This absence of ER in ARO-ir cells is also observed in the POA of the rat brain. This suggests that locally formed estrogens cannot control the behavior and the aromatase synthesis in an autocrine fashion in the cells where they were formed. Multi-neuronal networks need therefore to be considered. The behavioral activation could result from the action of estrogens in ER-positive cells located in the vicinity of the ARO-ir cells where they were produced (paracrine action). Alternatively, actions that do not involve the nuclear ER could be important. Immunocytochemical studies at the electron microscope level and biochemical assays of AA in purified synaptosomes indicate the presence of aromatase in presynaptic boutons. Estrogens formed at this level could directly affect the pre-and post-synaptic membrane or could directly modulate neurotransmission namely through their metabolization into catecholestrogens (CE) which are known to be powerful inhibitors of the catechol-O-methyl transferase (COMT). The inhibition of COMT should increase the catecholaminergic transmission. It is significant to note, in this respect, that high levels of 2-hydroxylase activity, the enzyme that catalyzes the transformation of estrogens in CE, are found in all brain areas that contain aromatase. On the other hand, the
Neuroanatomical distribution of testosterone-metabolizing enzymes in the Japanese quail
Brain Research, 1987
We describe a very sensitive and precise assay which allows one to study the metabolism of testosterone (T) in small brain nuclei dissected out according to the method of Palkovits and Brownstein. With this method, the neuroanatomical distributions of aromatase, and 5a-and 5fl-reductase activities were studied in adult male quail (Coturnix coturnix japonica). The different enzymes show different neuroanatomical distributions. Production of estradiol-17fl (E2) was highest in the sexually dimorphic nucleus preopticus medialis (POM). We showed previously that the preoptic aromatase activity is higher in male than in female quail. As the POM is a central and very large structure within the preoptic area, the present results suggest a relationship between the neuroanatomical and the biochemical sex differences. By contrast, the production of 5a-DHT was highest in the lateral hypothalamic area (LHY), the bed nucleus of the pallial commissure (BPC) and the lateral septum (SL). The 5fl-reductase activity was highest in the lateral septum and in the ventral part of the archistriatum (AV). Moreover, there was a rostral to caudal decrease in 5fl-reductase activity in the hypothalamus.
Hormones and Behavior, 1996
appear to be of an activational nature and cannot there-Early workers interested in the mechanisms mediating fore explain sex differences in behavior that are still sex differences in morphology and behavior assumed present in gonadectomized steroid-treated adults. This that differences in behavior that are commonly observed research has also revealed many aspects of brain morbetween males and females result from the sex specificphology and chemistry that are markedly affected by steity of androgens and estrogens. Androgens were thought roids in adulthood and are thought to mediate the activato facilitate male-typical traits, and estrogens were tion of behavior at the central level. It has been explicitly, thought to facilitate female-typical traits. By the midor in some cases, implicitly assumed that the sexual dif-20th century, however, it was apparent that administerferentiation of brain and behavior driven by early expoing androgens to females or estrogens to males was not sure to steroids concerns primarily those neuroanatomialways effective in sex-reversing behavior and that in cal/neurochemical characteristics that are altered by some cases a ''female'' hormone such as an estrogen steroids in adulthood and presumably mediate the acticould produce male-typical behavior and an androgen vation of behavior. Extensive efforts to identify these could induce female-typical behavior. These conceptual sexually differentiated brain characteristics over the past difficulties were resolved to a large extent by the seminal 20 years has only met with limited success, however. As paper of C. H. Phoenix, R. W. Goy, A. A. Gerall, and W. C. regards reproductive behavior, in all model species that Young in (1959, Endocrinology 65, 369-382) that illushave been studied it is still impossible to identify satistrated that several aspects of sexual behavior are differfactorily brain characteristics that differentiate under ent between males and females because the sexes have early steroid action and explain the sex differences in been exposed during their perinatal life to a different behavioral activating effects of steroids. This problem endocrine milieu that has irreversibly modified their reis illustrated by research conducted on Japanese quail sponse to steroids in adulthood. Phoenix et al. (1959) (Coturnix japonica), an avian model system that displays therefore formalized a clear dichotomy between the orprominent sex differences in the sexual behavioral reganizational and activational effects of sex steroid horsponse to testosterone, and in which the endocrine mones. Since this paper, a substantial amount of remechanisms that control sexual differentiation of behavsearch has been carried out in an attempt to identify ior have been clearly identified so that subjects with a the aspects of brain morphology or neurochemistry that fully sex-reversed behavioral phenotype can be easily differentiate under the embryonic/neonatal effects of produced. In this species, studies of sex differences in steroids and are responsible for the different behavioral the neural substrate mediating the action of steroids in response of males and females to the activation by stethe brain, including the activity of the enzymes that meroids in adulthood. During the past 25 years, research in tabolize steroids such as aromatase and the distribution behavioral neuroendocrinology has identified many sex of steroid hormone receptors as well as related neurodifferences in brain morphology or neurochemistry; transmitter systems, did not result in a satisfactory exhowever many of these sex differences disappear when planation of sex differences in the behavioral effectivemale and female subjects are placed in similar endocrine ness of testosterone. Possible explanations for the relaconditions (e.g., are gonadectomized and treated with tive failure to identify the organized brain characteristics responsible for behavioral sex differences in the respon-the same amount of steroids) so that these differences 627
General and Comparative Endocrinology, 1983
Three experiments were carried out to study whether differences in the intracellular metabolism of testosterone (T) can explain sexually differential responses to T in Japanese quail. In the first experiment, a series of dose-response curves in which length of Silastic testosterone implants was related to effects on several behavioral and physiological variables was established. In Experiment 2, adult males and females were assigned to six experimental groups: intact males and females (I-males and I-females), castrated males and females implanted subcutaneously with 40-mm Silastic implants of T (T-males and T-females), and castrated males and females without hormone treatment (CX-males and CXfemales). No CX-bird (male or female) and no I-female exhibited male sexual behavior. However, I-males and T-males regularly copulated during the behavioral tests. No crowing was ever heard in CX-animals and I-females. T-females crowed less than T-males and their crowing sounded weaker than those of males. The cloaca1 glands of T-females were less deveioped than those of males. Radioimmunoassay of T and So-DHT showed that T-males and T-females have similar plasma levels of androgens. No striking differences were observed in the way testosterone is metabolized by the pituitary gland and central nervous tissues of males and females. By contrast, the production of 5a-dihydrotestosterone (5~ DHT) and 5a-androstane-3a, 17B-dio1&,3a-di01) was higher in the cloaca1 glands of males than in those of females. These sex differences were not detected between T-males and Tfemales. In experiment 3, the cloacal gland of males produced more Se-reduced metabolites than thase of females. The pituitary gland of females also produced more Sp-androstane-3cr,l7Bdiol (.5~,3adiol). In syringeal muscles, the production of SO-dihydrotestosterone (5B-DHT)and $3, 3~diol was higher in females compared to males.
Behavioral Effects of Brain-derived Estrogens in Birds
Annals of the New York Academy of Sciences, 2009
In birds as in other vertebrates, estrogens produced in the brain by aromatization of testosterone have widespread effects on behavior. Research conducted with male Japanese quail demonstrates that effects of brain estrogens on all aspects of sexual behavior, including appetitive and consummatory components as well as learned aspects, can be divided in two main classes based on their time-course. First, estrogens via binding to estrogen receptors regulate the transcription of a variety of genes involved primarily in neurotransmission. These neurochemical effects ultimately result in the activation of male copulatory behavior after a latency of a few days. Correlatively, testosterone and its aromatized metabolites increase the transcription of the aromatase mRNA resulting in an increased concentration and activity of the enzyme that actually precedes behavioral activation. Second, recent studies with quail demonstrate that brain aromatase activity (AA) can also be modulated within minutes by phosphorylation processes regulated by changes in intracellular calcium concentration such as those associated with glutamatergic neurotransmission. The rapid up or down-regulations of brain estrogen concentration presumably resulting from these changes in AA affect, by non-genomic mechanisms with relatively short latencies (frequency increases or decreases respectively within 10-15 min), the expression of male sexual behavior in quail and also in rodents. Brain estrogens thus affect behavior on different timescales by genomic and non-genomic mechanisms similar to those of a hormone or a neurotransmitter.
Hormones and behavior, 2016
Although aromatase is expressed in both male and female brains, its functional significance in females remains poorly understood. In female quail, sexual receptivity is activated by estrogens. However it is not known whether sexual motivation is similarly estrogen-dependent and whether estrogens locally produced in the brain contribute to these behavioral responses. Four main experiments were designed to address these questions. In Experiment 1 chronic treatment of females with the anti-estrogen tamoxifen decreased their receptivity, confirming that this response is under the control of estrogens. In Experiment 2 chronic treatment with tamoxifen significantly decreased sexual motivation as treated females no longer approached a sexual partner. In Experiment 3 (a) ovariectomy (OVX) induced a significant decrease of time spent near the male and a significantly decreased receptivity compared to gonadally intact females, (b) treatment with testosterone (OVX+T) partially restored these r...
The Journal of Comparative Neurology, 2007
In many vertebrate species the medial preoptic area projects to a premotor nucleus, the periaqueductal central gray (PAG). This connection plays an important role in the control of reproductive behavior. In male Japanese quail (Coturnix japonica) specifically, the medial preoptic nucleus (POM), where various types of sensory inputs converge, is a critical site for the activational action of testosterone on male sexual behavior. To activate male copulatory behavior, testosterone must be aromatized to estradiol within the POM and aromatase-immunoreactive cells in the POM are the main source of projections to the PAG. The POM-PAG connection is thus an important functional circuit integrating the sensory with premotor components of sexual behavior. Contrary to what is observed in males, testosterone does not activate male-typical copulatory behavior in females and we investigated here via retrograde tracing methods whether this behavioral sexual difference is associated with a sex difference in connectivity between POM and PAG. Fluorescent microspheres were injected in the PAG of male and female quail and retrogradely labeled fluorescent cells counted in four fields of the POM in sections that had been immunolabeled for aromatase. Males had more aromatase-immunoreactive neurons projecting to the PAG than females and this difference was most prominent in the caudolateral part of the nucleus that has been specifically implicated in the control of male copulatory behavior. These data therefore support the hypothesis that sex differences in POM-PAG connectivity are causally linked to the sex difference in the behavioral response to testosterone. J. Comp. Neurol. 500: 894 -907, 2007.