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J Balthazart

Publications and source records attributed to J Balthazart.

At least 91 records · Page 5Linked to original sources
PubMed1998

Distribution of androgen receptor-immunoreactive cells in the quail forebrain and their relationship with aromatase immunoreactivity.

The distribution of androgen receptor-like immunoreactive (AR-ir) cells in the quail brain was analyzed by immunocytochemistry with the use of the affinity-purified antibody PG-21-19A raised against a synthetic peptide representing the first 21 N-terminal amino acids of the rat and human AR. This antibody is known to bind to the receptor in the absence as well as in the presence of endogenous ligands, and it was therefore expected that a more complete and accurate characterization of AR-ir cells would be obtained in comparison with previous studies using an antibody that preferentially recognizes the occupied receptor. Selected sections were double labeled for aromatase (ARO) by a technique that uses alkaline phosphatase as the reporter enzyme and Fast blue as the chromogen. AR-ir material was detected in the nucleus of cells located in a variety of brain areas in the preoptic region and the hypothalamus including the medial preoptic (POM), the supraoptic, the paraventricular (PVN), and the ventromedial (VMN) nuclei, but also in the tuberculum olfactorium, the nucleus accumbens/ventral striatum, the nucleus taeniae, the tuberal hypothalamus, the substantia grisea centralis (GCt), and the locus ceruleus. Cells exhibiting a dense AR-ir label were also detected in the nucleus intercollicularis. Preincubation of the primary antibody with an excess of the synthetic peptide used for immunization completely eliminated this nuclear staining. A significant number of AR-ir cells in the POM, VMN, PVN, and tuberal hypothalamus also contained ARO-ir material in their cytoplasm. These data confirm and extend previous studies localizing AR in the avian brain, and raise questions about the possible regulation by androgens of the metabolizing enzyme aromatase.

Animals↗
PubMed1997

Induction of the Zenk protein after sexual interactions in male Japanese quail.

We mapped cells immunoreactive (ir) for the protein encoded by the immediate early gene zenk in the brains of male Japanese quail after they engaged in either appetitive or consummatory sexual behavior (i.e. copulation). Castrated males treated with testosterone were either allowed to copulate with a female or exhibited a learned social proximity response indicative of appetitive sexual behavior, and were compared with control males in their home cage or in the experimental chamber but not exhibiting the proximity response. Copulation increased the number of ZENK-ir cells in the nucleus striae terminalis and the nucleus intercollicularis, while both copulation and the proximity response induced increases in the medial and anterior ventral hyperstriatum. These results indicate that zenk is induced in the context of sexual behavior.

Analysis of Variance↗
PubMed1997

Identification of catecholaminergic inputs to and outputs from aromatase-containing brain areas of the Japanese quail by tract tracing combined with tyrosine hydroxylase immunocytochemistry.

In the quail brain, aromatase-immunoreactive (ARO-ir) neurons located in the medial preoptic nucleus (POM) and caudal paleostriatum ventrale/nucleus accumbens/nucleus striae terminalis complex (PVT/nAc/nST) receive catecholaminergic inputs identified by the presence of tyrosine hydroxylase-immunoreactive (TH-ir) fibers and punctate structures. The origin of these inputs was analyzed by retrograde tracing with cholera toxin B subunit (CTB) or red latex fluospheres (RLF) combined with TH immunocytochemistry. CTB and RLF injected in the POM or PVT/nAc/nST were found in cells located in anatomically discrete areas in the telencephalon (hippocampus, septum, archistriatum), hypothalamus (many areas in periventricular position), thalamus, mesencephalon, and pons. In these last two regions, many retrogradely labeled cells were located in dopaminergic areas such as the retroruberal field (RRF), substantia nigra (SN), and area ventralis of Tsai (AVT) but also in noradrenergic cell groups such as the locus ceruleus and subceruleus. CTB tracing showed that most of these connections are bidirectional. Many retrogradely labeled cells contained TH-ir material. As a mean, 10-20% and 40-60% of the RLF-containing cells in the dopaminergic areas were TH-ir when RLF had been injected in the POM or PVT/nAc/nST, respectively. TH-ir cells projecting to the POM appeared to be mostly located in the periventricular hypothalamus and in AVT, whereas projections to the PVT/nAc/nST originated mainly in the SN (with significant contributions from the RRF and AVT). These data support the existence of functional relationships between aromatase and catecholamines.

Animals↗
PubMed1997

Differential effects of D1 and D2 dopamine-receptor agonists and antagonists on appetitive and consummatory aspects of male sexual behavior in Japanese quail.

Pharmacological studies in Japanese quail based on behavioral tests with a variety of dopaminergic compounds suggest that the activation of D2 dopamine receptors inhibits, and the activation of D1 dopamine receptors enhances, appetitive and consummatory components of male sexual behavior. This hypothesis was tested by studying the behavioral effects of specific D1 and D2 dopaminergic-receptor agonists and antagonists in castrated male Japanese quail chronically treated with exogenous testosterone (subcutaneous Silastic implants). The effects of 5 compounds were tested: 1 D1 (SKF38393) and 2 D2 (PPHT and quinpirole) agonists, and 1 D1 (SCH23390) and 1 D2 (Spiperone) antagonist. All compounds were tested at a low and a high dose (0.1 and 1 mg/kg, respectively, for all drugs, except spiperone where the doses were 2 and 10 mg/kg). A consistent effect of all drugs on consummatory sexual behavior was observed: it was stimulated by the D1 agonist and the D2 antagonist, but inhibited by the D1 antagonist and the D2 agonists. Far fewer effects of the treatments were detected on the measures of appetitive behavior. Measures of appetitive behavior were decreased by the 2 D2 agonists, but not affected by the other treatments. These data suggest that male copulatory behavior in quail is stimulated by dopamine acting on D1 receptors, but inhibited by activation of the D2 receptor subtype. The partial dissociation observed between the effects of the same treatments on appetitive and consummatory aspects of sexual behavior also suggests that these 2 behavioral systems may be controlled by the action of dopamine on different neuronal systems.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1997

Effects of dopamine agonists on appetitive and consummatory male sexual behavior in Japanese quail.

The effects of pharmacological manipulations of dopaminergic transmission on appetitive and consummatory aspects of male sexual behavior were investigated in castrated male Japanese quail treated with exogenous testosterone. Appetitive male sexual behavior was assessed by measuring a learned social proximity response and consummatory behavior was assessed by measuring copulatory behavior per se. The nonselective dopamine receptor agonist, apomorphine, inhibited in a dose-dependent manner both components of male sexual behavior. Two indirect dopamine agonists were also tested. Nomifensine, a dopamine re-uptake inhibitor, decreased appetitive sexual behavior but increased the frequency of mount attempts, a measure of consummatory sexual behavior. Amfonelic acid, a compound that enhances dopaminergic tone by a complex mechanism, increased aspects of both appetitive and consummatory behaviors. These data suggest that, in quail, as in rodents, increases in dopaminergic tone facilitate both appetitive and consummatory aspects of male sexual behavior. Apomorphine may be inhibitory in quail because it acts primarily on D2-like receptors, unlike in rats, where it stimulates sexual behavior and acts primarily on D1-like receptors at low doses but interacts with D2-like receptors at higher doses. This is supported by the observation that stereotyped pecking, a behavior stimulated selectively in quail by D2 agonists, was increased by apomorphine but not by the two indirect agonists. The observed partial dissociation between the effects of these dopaminergic agonists on appetitive and consummatory sexual behaviors suggests that these two components of male sexual behavior may be controlled by the action of dopamine through different neuronal systems.

Animals↗
PubMed1997

Copulation activates Fos-like immunoreactivity in the male quail forebrain.

It has been demonstrated using Fos immunocytochemistry that copulation activates specific cell populations in the mammalian brain. Prior to this study, no similar work has been carried out in birds. In mammals, Fos has identified brain circuits activated by genital (penile)/somatosensory and by olfactory/vomeronasal stimuli. Such inputs, of course, should play little or no role in birds (no penis, little or no role for olfaction) and a differential responsiveness could therefore be expected. Male Japanese quail (Coturnix japonica) were allowed to interact freely with adult females and the presence of active sexual behavior, including cloacal contact movements, was confirmed in each case. Control subjects were exposed to a domestic chick (same size as an adult quail) and no sexual behavior was observed. Copulation induced the appearance of Fos-like immunoreactive (FLI) cells in the preoptic area, the hyperstriatum ventrale, parts of the archistriatum, and the nucleus intercollicularis. Induction of FLI cells was observed throughout the rostral to caudal extent of the preoptic region of males from the level of the tractus septomesencephalicus to the level of the anterior commissure, and in the rostral part of the hypothalamus to the level of the supraoptic decussation. The FLI cells did not lie directly adjacent to the third ventricle, but were located 500-1000 microns from the ventricle wall at the level of the lateral edge of the medial preoptic nucleus or, in more caudal sections, in a position ventrolateral to the bed nucleus striae terminalis. It is unlikely that the Fos induction in males resulted from copulation-induced endocrine changes because copulation did not affect plasma levels of luteinizing hormone or testosterone. It is concluded that the responses were due to copulation-associated somatosensory inputs and/or to stimuli originating from the female.

Animals↗
PubMed1997

Aromatase inhibition blocks the activation and sexual differentiation of appetitive male sexual behavior in Japanese quail.

Two experiments investigated the role of estrogens in the activation and sexual differentiation of appetitive sexual behavior (ASB) in Japanese quail (Coturnix japonica) as measured by a learned social proximity response. Injection of the aromatase inhibitor R767 13 in castrated, testosterone (T)-treated male quail completely suppressed ASB, confirming that, like consummatory sexual behavior, ASB is mediated by T aromatization. ASB is not observed in female quail, even if they are treated with T as adults. The role of embryonic estrogens in the sexual differentiation of ASB was tested by blocking estrogen synthesis in ovo. Control male and T-treated female quail deprived of estrogens during embryonic life learned the social proximity response used to assess ASB, whereas control female quail did not, despite the presence of high T. Thus, ASB is demasculinized by the action of embryonic estrogens during ontogeny as is consummatory behavior.

Animals↗
PubMed1997

Vasotocinergic innervation of areas containing aromatase-immunoreactive cells in the quail forebrain.

In the male quail forebrain, aromatase-immunoreactive (ARO-ir) elements are clustered within the sexually dimorphic medial preoptic nucleus (POM), nucleus striae terminalis (nST), nucleus accumbens (nAc), and ventromedial and tuberal hypothalamus. These ARO-ir cells are sensitive to testosterone and its metabolites: Their number and size increase after exposure to these steroids. The POM and lateral septum are also characterized by a dense vasotocinergic innervation that is also sensitive to testosterone. We analyzed here the anatomical relationships between ARO-ir elements and VT-ir fibers in the quail prosencephalon. Sequential staining for vasotocin, aromatase, or vasotocin plus aromatase was performed on adjacent 30-microm-thick cryostat sections. High concentrations of thin VT-ir fibers were observed within the POM, nST, lateral septum, periventricular mesencephalic central gray, and ventromedial and tuberal hypothalamus. There was a close correspondence between the extension of the ARO-ir cells and of VT-ir fibers. In double-labeled sections, all clusters of ARO-ir cells with the exception of those located in the nAc were embedded in a dense network of VT-ir fibers. Many of the VT-ir terminals appeared to end in the neuropile surrounding ARO-ir elements rather than directly on their cell bodies. This study supports the idea that the testosterone-dependent aromatase system is directly innervated by a testosterone-dependent peptidergic system. Aromatase-containing cells could therefore be modulated by steroids both directly and indirectly through the vasotocin system. Alternatively, this neuroanatomical arrangement may mediate the control of vasotocin synthesis or release by steroids. Functional studies demonstrate that both aromatase and vasotocin affect reproductive behavior in quail, and the present data provide anatomical support for the integration of these effects.

Animals↗
PubMed1997

Steroid control and sexual differentiation of brain aromatase.

Brain aromatase (ARO) activity in the quail is markedly enhanced by testosterone (T). This effect only becomes detectable after several hours and reaches its maximum within a few days, which suggests enzymatic induction at the genomic level. This idea is reinforced by the fact that T also increases the ARO protein, as observed by immunocytochemistry (ICC) and the ARO mRNA, as measured by reverse transcriptase-polymerase chain reaction (RT-PCR). These changes can be mimicked by the administration of estrogens and therefore presumably require T aromatization. In our first test, injection of the non-steroidal ARO inhibitor, R76713 (racemic vorozole), unexpectedly revealed an increase in ARO immunoreactivity in the preoptic area (POA) of treated birds. This property of R76713 was shared by another non-steroidal inhibitor, fadrozole, but not by two steroidal inhibitors, androstatrienedione (ATD) and 4-hydroxy-androstenedione (OHA). These last two compounds markedly decreased the concentration of brain ARO as estimated by ICC. In parallel, ATD and OHA decreased ARO mRNA concentration measured by RT-PCR but vorozole and fadrozole had no effect on these concentrations in the POA, and only caused them to decrease slightly in the posterior hypothalamus. Together, these data indicate that the removal of estrogens caused by steroidal inhibitors decreases the synthesis of ARO, presumably at the transcriptional level. Additional regulatory mechanisms apparently take place after the injection of non-steroidal inhibitors and probably include increased half-life of the protein. The induction of ARO activity by steroids appears to be greater in males than in females, but this difference has been difficult to localize and confirm by assay methods. We therefore analysed by ICC the tridimensional distribution of ARO-ir neurons in the POA of males and females that were sexually mature or gonadectomized and treated with T-filled or control empty implants. Localized sex differences and effects of T were detected in this way. In particular, males had more ARO-ir cells than females in the lateral POA but a difference in the opposite direction was evident in the medial part of this area. These sex differences are largely activational (i.e. caused by the higher T levels in males) but they may also reflect organizational effects of neonatal steroids. Castration decreased ARO-ir cell numbers in the lateral POA, but increased it in the periventricular region. This anatomically specialized control by T may be mediated by three potential mechanisms that are discussed and comparatively evaluated: a migration of ARO neurons towards the ventricle after castration; a differential colocalization of ARO with estrogen receptors or a differential modulation of ARO neurons by catecholaminergic inputs.

Animals↗
PubMed1996

Distribution of aromatase-immunoreactive cells in the forebrain of zebra finches (Taeniopygia guttata): implications for the neural action of steroids and nuclear definition in the avian hypothalamus.

Cells immunoreactive for the enzyme aromatase were localized in the forebrain of male zebra finches with the use of an immunocytochemistry procedure. Two polyclonal antibodies, one directed against human placental aromatase and the other directed against quail recombinant aromatase, revealed a heterogeneous distribution of the enzyme in the telencephalon, diencephalon, and mesencephalon. Staining was enhanced in some birds by the administration of the nonsteroidal aromatase inhibitor, R76713 racemic Vorozole) prior to the perfusion of the birds as previously described in Japanese quail. Large numbers of cells immunoreactive for aromatase were found in nuclei in the preoptic region and in the tuberal hypothalamus. A nucleus was identified in the preoptic region based on the high density of aromatase immunoreactive cells within its boundaries that appears to be homologous to the preoptic medial nucleus (POM) described previously in Japanese quail. In several birds alternate sections were stained for immunoreactive vasotocin, a marker of the paraventricular nucleus (PVN). This information facilitated the clear separation of the POM in zebra finches from nuclei that are adjacent to the POM in the preoptic area-hypothalamus, such as the PVN and the ventromedial nucleus of the hypothalamus. Positively staining cells were also detected widely throughout the telencephalon. Cells were discerned in the medial parts of the ventral hyperstriatum and neostriatum near the lateral ventricle and in dorsal and medial parts of the hippocampus. They were most abundant in the caudal neostriatum where they clustered in the dorsomedial neostriatum, and as a band of cells coursing along the dorsal edge of the lamina archistriatalis dorsalis. They were also present in high numbers in the ventrolateral aspect of the neostriatum and in the nucleus taeniae. None of the telencephalic vocal control nuclei had appreciable numbers of cells immunoreactive for aromatase within their boundaries, with the possible exception of a group of cells that may correspond to the medial part of the magnocellular nucleus of the neostriatum. The distribution of immunoreactive aromatase cells in the zebra finch brain is in excellent agreement with the distribution of cells expressing the mRNA for aromatase recently described in the finch telencephalon. This widespread telencephalic distribution of cells immunoreactive for aromatase has not been described in non-songbird species such as the Japanese quail, the ring dove, and the domestic fowl.

Animals↗
PubMed1996

The sexually dimorphic medial preoptic nucleus of quail: a key brain area mediating steroid action on male sexual behavior.

About 10 years ago, a sexually differentiated nucleus was identified in the preoptic area (POA) of the Japanese quail in the course of studies analyzing the dimorphic mechanisms involved in the activation of sexual behavior. In this species, males exposed to testosterone copulate while females never show this masculine behavior. The present paper reviews anatomical, neurochemical, and functional data that have been collected since that time about the quail dimorphic nucleus. The medial preoptic nucleus (POM) is significantly larger in adult male than in adult female quail. Its volume is also steroid-sensitive in adulthood: it decreases when circulating levels of testosterone are low (castration, exposure to short-days) and it increases when testosterone levels are high (treatment with testosterone, exposure to long-days). The POM is a necessary and sufficient site of steroid action for the activation of male copulatory behavior. The volumetric difference of the POM results from a difference in the adult hormonal milieu of males and females (activational effect) and is not affected by embryonic treatments that permanently modify sexual behavior (no organizational effects on POM). In contrast, the size of neurons in the dorsolateral part of POM appears to be irreversibly affected by embryonic steroids and this feature is therefore a better correlate of the behavioral sex difference. The POM is characterized by the presence of a wide variety of neurotransmitters, neuropeptides, and receptors. It can, in addition, be specifically distinguished from the surrounding POA by the presence of aromatase-immunoreactive cells, by a high density of alpha 2-adrenergic receptors, and by a dense vasotocinergic innervation. Some of these neurochemical markers of the dimorphic nucleus are themselves modulated by steroids. In particular, the aromatase-immunoreactive cells of the lateral POM appear to be a key target for steroids in the activation of male copulatory behavior. The POM is bidirectionally connected to many brain areas. It receives inputs from a variety of sensory areas and from a number of regulatory areas (e.g., catecholaminergic cell groups). This nucleus also sends outputs to "neurovegetative" centers and to brain regions directly connected to the motor pathways. These connections fully support the role of the POM as an integrative center for the control of male sexual behavior. The available data indicate that there is a high degree of steroid-induced neuronal plasticity in the POM, including changes in neuronal function, in protein synthesis, and in specific inputs. These phenomena can easily be studied in the POM because they are of a large magnitude, they are localized in a specific brain site, and they develop rapidly after exposure to steroids. They are also directly related to a clear functional output, the activation of male sexual behavior. The quail POM therefore constitutes an exceptional model for the analysis of steroid-induced brain plasticity in a functionally relevant context.

Androgens↗
PubMed1996

Do sex differences in the brain explain sex differences in the hormonal induction of reproductive behavior? What 25 years of research on the Japanese quail tells us.

Early workers interested in the mechanisms mediating sex differences in morphology and behavior assumed that differences in behavior that are commonly observed between males and females result from the sex specificity of androgens and estrogens. Androgens were thought to facilitate male-typical traits, and estrogens were thought to facilitate female-typical traits. By the mid-20th century, however, it was apparent that administering androgens to females or estrogens to males was not always effective in sex-reversing behavior and that in some cases a "female" hormone such as an estrogen could produce male-typical behavior and an androgen could induce female-typical behavior. These conceptual difficulties were resolved to a large extent by the seminal paper of C. H. Phoenix, R. W. Goy, A. A. Gerall, and W. C. Young in (1959, Endocrinology 65, 369-382) that illustrated that several aspects of sexual behavior are different between males and females because the sexes have been exposed during their perinatal life to a different endocrine milieu that has irreversibly modified their response to steroids in adulthood. Phoenix et al. (1959) therefore formalized a clear dichotomy between the organizational and activational effects of sex steroid hormones. Since this paper, a substantial amount of research has been carried out in an attempt to identify the aspects of brain morphology or neurochemistry that differentiate under the embryonic/neonatal effects of steroids and are responsible for the different behavioral response of males and females to the activation by steroids in adulthood. During the past 25 years, research in behavioral neuroendocrinology has identified many sex differences in brain morphology or neurochemistry; however many of these sex differences disappear when male and female subjects are placed in similar endocrine conditions (e.g., are gonadectomized and treated with the same amount of steroids) so that these differences appear to be of an activational nature and cannot therefore explain sex differences in behavior that are still present in gonadectomized steroid-treated adults. This research has also revealed many aspects of brain morphology and chemistry that are markedly affected by steroids in adulthood and are thought to mediate the activation of behavior at the central level. It has been explicitly, or in some cases, implicitly assumed that the sexual differentiation of brain and behavior driven by early exposure to steroids concerns primarily those neuroanatomical/neurochemical characteristics that are altered by steroids in adulthood and presumably mediate the activation of behavior. Extensive efforts to identify these sexually differentiated brain characteristics over the past 20 years has only met with limited success, however. As regards reproductive behavior, in all model species that have been studied it is still impossible to identify satisfactorily brain characteristics that differentiate under early steroid action and explain the sex differences in behavioral activating effects of steroids. This problem is illustrated by research conducted on Japanese quail (Coturnix japonica), an avian model system that displays prominent sex differences in the sexual behavioral response to testosterone, and in which the endocrine mechanisms that control sexual differentiation of behavior have been clearly identified so that subjects with a fully sex-reversed behavioral phenotype can be easily produced. In this species, studies of sex differences in the neural substrate mediating the action of steroids in the brain, including the activity of the enzymes that metabolize steroids such as aromatase and the distribution of steroid hormone receptors as well as related neurotransmitter systems, did not result in a satisfactory explanation of sex differences in the behavioral effectiveness of testosterone. Possible explanations for the relative failure to identify the organized brain characteristics responsible for behavio

Animals↗
PubMed1996

Testosterone effects on the neuronal ultrastructure in the medial preoptic nucleus of male Japanese quail.

Dorsolateral neurons of the medial preoptic nucleus (POM) of male Japanese quail are sensitive to the plasma levels of testosterone: their volume and optical density in Nissl-stained sections increase in castrated birds treated with testosterone. The present study was performed on castrated male quail treated or not with Silastic implants filled with testosterone to describe the ultrastructural variations induced by testosterone in these neurons. Gonadally intact male birds were included as controls. The ultrastructure of neurons, taken from the dorsolateral portion of the POM, was dramatically affected by the endocrine manipulations. Quantitative evaluations demonstrated a significant decrease in castrated birds of the rough endoplasmic reticulum (RER), of free polyribosomes, of Golgi complexes, and of dense bodies; these changes paralleled the decrease in cell size. The cell size and the percentage of volume occupied by the intracellular organelles in castrated birds treated with testosterone were comparable to values observed in controls. These ultrastructural changes are similar to those observed in neuronal targets for other gonadal hormones, supporting the idea that testosterone stimulates the development of cytoplasmic structures involved in protein synthesis and secretion. In addition, exposure to testosterone affects the synaptic inputs to POM. These ultrastructural changes are presumably related to the physiological effects (e.g., activation of male sexual behavior) exerted by testosterone on this preoptic region.

Analysis of Variance↗
PubMed1996

Localization of testosterone-sensitive and sexually dimorphic aromatase-immunoreactive cells in the quail preoptic area.

The distribution of aromatase-immunoreactive cells was studied in the medial preoptic nucleus of male and female quail that were sexually mature and gonadally intact, or gonadectomized, or gonadectomized and treated with testosterone. The study first confirmed the existence of a significant difference in the number of aromatase-immunoreactive cells between males and females (males > females) and the marked effect of castration and testosterone treatment which, respectively, decrease and restore the number of these cells. An analysis of the distribution in space of this neurochemically defined cell population was also carried out. This study revealed that castration does not uniformly decrease the density of aromatase-immunoreactive cells, but local increases are observed in an area directly adjacent to the third ventricle. A number of new sex differences in the organization of the medial preoptic nucleus and its population of aromatase cells have, in addition, been identified. The density of aromatase-immunoreactive cells is not higher in males than in females throughout the nucleus, but a higher density of immunoreactive cells is present in the ventromedial part of the nucleus in females as compared to males. In addition, the cross-sectional area of the nucleus as defined by the population of aromatase-immunoreactive cells is larger in males than in females in its rostral part and its shape is more elongated in the dorso-ventral direction in females than in males. Some of these differences (e.g. higher density of ARC-ir cells in the ventromedial part of the female POM, shape of the nucleus) appear to be organizational in nature, because they are still present in birds exposed to the same endocrine conditions during adult life (e.g. gonadectomized and treated with a same dose of testosterone). This conclusion should now be tested by experiments manipulating the endocrine environment of quail embryos. The anatomical heterogeneity of the medial preoptic nucleus revealed by this study also suggests a functional heterogeneity and the specific roles of the medial and lateral parts of the nucleus should also be investigated.

Animals↗
PubMed1996

Effects of testosterone and its metabolites on aromatase-immunoreactive cells in the quail brain: relationship with the activation of male reproductive behavior.

The enzyme aromatase converts testosterone (T) into 17 beta-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- omicron - 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 synthesis of aromatase should also be controlled by estrogens in an indirect, transynaptic manner very reminiscent of the way in which steroids indirectly control the production of LHRH. Fibers that are immunoreactive for tyrosine hydroxylase (synthesis of dopamine), dopamine beta-hydroxylase (synthesis of norepinephrine) or vasotocine have been identified in the close vicinity of ARO-ir cells in the POM and retrograde tracing has identified the origin of the dopaminergic and noradrenergic innervation of these areas. A few preliminary physiological experiments suggest that these catecholaminergic inputs regulate AA and presumably synthesis.

Androgens↗
PubMed1996

Aromatase immunoreactivity in axon terminals of the vertebrate brain. An immunocytochemical study on quail, rat, monkey and human tissues.

Intraneuronal production of estradiol from testosterone has been shown to play a pivotal role in gender-specific brain development of most vertebrates, and to participate in numerous functions of the adult central nervous system. Previous biochemical and morphological approaches demonstrated that estrogen synthetase (aromatase) is present in specific limbic and hypothalamic structures. On the other hand, less attention has been paid to revealing its subcellular distribution. The possibility of aromatase presence in axonal processes has been indicated by recent biochemical and morphological observations suggesting new insights for the role of aromatase in neural functions. The objective of the present study was to provide morphological evidence for the subcellular location of aromatase in neurons of different vertebrate species including Japanese quail, rat, monkey, and human. Immunocytochemistry using a purified polyclonal antiserum against human placental aromatase localized immunoreactivity to hypothalamic and limbic cell groups in all of these species. Light and electron microscopic examination of vibratome sections revealed the presence of aromatase immunoreactivity throughout the neuronal perikarya, including dendrites and axonal processes. In each species there were numerous boutons which contained labeled small clear synaptic vesicles. Many of these axon terminals formed synapses with immuno-negative and immuno-positive dendrites and perikarya. This study furnishes the first immunolocalization of aromatase in the brains of two primate species, humans and monkeys. The provision of further evidence for estrogen synthesis in axons and axon terminals may help resolve apparent differences between the measurement of aromatase activity and the lack of aromatase-immunopositive cell bodies in previous studies. The present findings may be coupled with recent evidence regarding the molecular biology and the diversity of functional properties of P450 aromatase to indicate previously unexpected effects of brain aromatase at the synaptic level.

Adult↗