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

Conservation and dimorphism in androgen receptor distribution in Alston's singing mouse (Scotinomys teguina)

Because of their roles in courtship and intrasexual competition, sexual displays are often sexually dimorphic, but we know little about the mechanisms that produce such dimorphism. Among mammals, one example is the vocalization of Alston's singing mouse (Scotinomys teguina), which consists of a series of rapidly repeated, frequency-modulated notes. The rate and duration of songs is sexually dimorphic and androgen responsive. To understand the neuronal mechanisms underlying this sexual dimorphism, we map the sites of androgen sensitivity throughout the brain, focusing analysis along a pathway that spans from limbic structures to vocal motor regions. We find widespread expression of AR immunoreactivity (AR-ir) throughout limbic structures important for social behavior and vocalization, including the lateral septum, extended amygdala, preoptic area and hypothalamus. We also find extensive AR staining along previously documented vocal motor pathways, including the periaqueductal gray, parabrachial nucleus, and nucleus ambiguus, the last of which innervates intrinsic laryngeal muscles. Lastly, AR-ir is also evident in sensory areas such as the medial geniculate, inferior, and superior colliculi. A quantitative analysis revealed that males exhibited more AR-ir than females, a pattern that was most pronounced in the hypothalamus. Despite the elaboration of vocalization in singing mice, comparison with prior literature suggests that the broad pattern of AR-ir may be conserved across a wide range of rodents. Together these data identify brain nuclei well positioned to shape the sexually dimorphic vocalization of S. teguina and suggest that such androgen modulation of vocalization is evolutionary conserved among rodents.

Molecular architecture of the zebra finch arcopallium

The arcopallium, a key avian forebrain region, receives inputs from numerous brain areas and is a major source of descending sensory and motor projections. While there is evidence of arcopallial subdivisions, the internal organization or the arcopallium is not well understood. The arcopallium is also considered the avian homologue of mammalian deep cortical layers and/or amygdalar subdivisions, but one-to-one correspondences are controversial. Here we present a molecular characterization of the arcopallium in the zebra finch, a passerine songbird species and a major model organism for vocal learning studies. Based on in situ hybridization for arcopallial-expressed transcripts (AQP1, C1QL3, CBLN2, CNTN4, CYP19A1, ESR1/2, FEZF2, MGP, NECAB2, PCP4, PVALB, SCN3B, SCUBE1, ZBTB20, and others) in comparison with cytoarchitectonic features, we have defined 20 distinct regions that can be grouped into six major domains (anterior, posterior, dorsal, ventral, medial, and intermediate arcopallium, respectively; AA, AP, AD, AV, AM, and AI). The data also help to establish the arcopallium as primarily pallial, support a unique topography of the arcopallium in passerines, highlight similarities between the vocal robust nucleus of the arcopallium (RA) and AI, and provide insights into the similarities and differences of cortical and amygdalar regions between birds and mammals. We also propose the use of AMV (instead of nucleus taenia/TnA), AMD, AD, and AI as initial steps toward a universal arcopallial nomenclature. Besides clarifying the internal organization of the arcopallium, the data provide a coherent basis for further functional and comparative studies of this complex avian brain region.

Expression of androgen receptor in the brain of a sub-oscine bird with an elaborate courtship display

Sex steroids control vertebrate behavior by modulating neural circuits specialized for sex steroid sensitivity. In birds, receptors for androgens (AR) and estrogens (ERα) show conserved expression in neural circuits controlling copulatory and vocal behaviors. Male golden-collared manakins have become a model for evaluating hormonal control of complex physical courtship displays. These birds perform visually and acoustically elaborate displays involving considerable neuromuscular coordination. Androgens activate manakin courtship and AR are expressed widely in spinal circuits and peripheral muscles utilized in courtship. Using in situ hybridization, we report here the distributions of AR and ERα mRNA in the brains of golden-collared manakins. Overall patterns of AR and ERα mRNA expression resemble what has been observed in non-vocal learning species. Notably, however, we detected a large area of AR expression in the arcopallium, a forebrain region that contains a crucial premotor song nucleus in vocal learning species. These results support the idea that AR signaling both centrally and peripherally is responsible for the activation of male manakin courtship, and the arcopallium is likely a premotor site for AR-mediated displays.

Status-appropriate singing behavior, testosterone and androgen receptor immunolabeling in male European starlings (Sturnus vulgaris)

Vocalizations convey information about an individual's motivational, internal, and social status. As circumstances change, individuals respond by adjusting vocal behavior accordingly. In European starlings, a male that acquires a nest site socially dominates other males and dramatically increases courtship song. Although circulating testosterone is associated with social status and vocal production it is possible that steroid receptors fine-tune status-appropriate changes in behavior. Here we explored a possible role for androgen receptors. Male starlings that acquired nest sites produced high rates of courtship song. For a subset of males this occurred even in the absence of elevated circulating testosterone. Immunolabeling for androgen receptors (ARir) was highest in the medial preoptic nucleus (POM) in males with both a nest site and elevated testosterone. For HVC, ARir was higher in dominant males with high testosterone (males that sang longer songs) than dominant males with low testosterone (males that sang shorter songs). ARir in the dorsal medial portion of the nucleus intercollicularis (DM) was elevated in males with high testosterone irrespective of dominance status. Song bout length related positively to ARir in POM, HVC and DM, and testosterone concentrations related positively to ARir in POM and DM. Results suggest that the role of testosterone in vocal behavior differs across brain regions and support the hypothesis that testosterone in POM underlies motivation, testosterone in HVC relates to song quality, and testosterone in DM stimulates vocalizations. Our data also suggest that singing may influence AR independent of testosterone and that alternative androgen-independent pathways regulate status-appropriate singing behavior.

Vasotocin mRNA expression is sensitive to testosterone and oestradiol in the bed nucleus of the stria terminalis in female Japanese quail

Vasotocin-producing parvocellular neurones in the medial part of the bed nucleus of the stria terminalis (BSTM) of many species of birds and mammals show sexual dimorphism and great plasticity in response to hormonal and environmental stimuli. In the BSTM of Japanese quail, vasotocin-immunoreactive neurones are visible and sensitive to testosterone exclusively in males. In males, gonadectomy decreases and testosterone restores vasotocin-immunoreactive cells and fibres by acting on vasotocin mRNA transcription. The insensitivity of female vasotocin-immunoreactive neurones to the activating effects of testosterone is the result of organisational effects of early exposure to oestradiol. Female quail also show vasotocin mRNA-expressing neurones in the BSTM, although it is not known whether the insensitivity of the vasotocinergic neurones to testosterone originates at the level of vasotocin gene transcription in this sex. Therefore, initially, the present study analysed the effects of acute treatment with testosterone on vasotocin mRNA expression in the BSTM of gonadectomised male and female quail using in situ hybridisation. Gonadectomy decreased (and a single injection of testosterone increased) the number of vasotocin mRNA-expressing neurones and intensity of the vasotocin mRNA hybridisation signal similarly in both sexes. Notably, testosterone increased vasotocin mRNA expression in ovariectomised females over that shown by intact quail. However, this treatment had no effect on vasotocin immunoreactivity. A second experiment analysed the effects of testosterone metabolites, oestradiol and 5α-dihydrotestosterone, on vasotocin mRNA expression in female quail. Oestradiol (but not 5α-dihydrotestosterone) fully mimicked the effects of testosterone on the number of vasotocin mRNA-expressing neurones and the intensity of the vasotocin mRNA hybridisation signal. Taken together, these results show, for the first time, that gonadal steroids strongly activate vasotocin mRNA expression in the BSTM of female quail.

Testosterone alters genomic responses to song and monoaminergic innervation of auditory areas in a seasonally breeding songbird

Behavioral responses to social stimuli often vary according to endocrine state. Our previous work has suggested that such changes in behavior may be due in part to hormone-dependent sensory processing. In the auditory forebrain of female white-throated sparrows, expression of the immediate early gene ZENK (egr-1) is higher in response to conspecific song than to a control sound only when plasma estradiol reaches breeding-typical levels. Estradiol also increases the number of detectable noradrenergic neurons in the locus coeruleus and the density of noradrenergic and serotonergic fibers innervating auditory areas. We hypothesize, therefore, that reproductive hormones alter auditory responses by acting on monoaminergic systems. This possibility has not been examined in males. Here, we treated non-breeding male white-throated sparrows with testosterone to mimic breeding-typical levels and then exposed them to conspecific male song or frequency-matched tones. We observed selective ZENK responses in the caudomedial nidopallium only in the testosterone-treated males. Responses in another auditory area, the caudomedial mesopallium, were selective regardless of hormone treatment. Testosterone treatment reduced serotonergic fiber density in the auditory forebrain, thalamus, and midbrain, and although it increased the number of noradrenergic neurons detected in the locus coeruleus, it reduced noradrenergic fiber density in the auditory midbrain. Thus, whereas we previously reported that estradiol enhances monoaminergic innervation of the auditory pathway in females, we show here that testosterone decreases it in males. Mechanisms underlying testosterone-dependent selectivity of the ZENK response may differ from estradiol-dependent ones

Testosterone modulation of angiogenesis and neurogenesis in the adult songbird brain

Throughout life, new neurons arise from the ventricular zone of the adult songbird brain and are recruited to the song control nucleus higher vocal center (HVC), from which they extend projections to its target, nucleus robustus of the arcopallium (RA). This process of ongoing parenchymal neuronal addition and circuit integration is both triggered and modulated by seasonal surges in systemic testosterone. Brain aromatase converts circulating testosterone to estradiol, so that HVC is concurrently exposed to both androgenic and estrogenic stimulation. These two signals cooperate to trigger HVC endothelial cell division and angiogenesis, by inducing the regionally-restricted expression of vascular endothelial growth factor (VEGF), its matrix-releasing protease MMP9, and its endothelial receptor VEGFR2. The expanded HVC microvascular network then secretes the neurotrophic factor BDNF, which in turn supports the recruitment of newly generated neurons. This process is striking for its spatial restriction and hence functional specificity. While androgen receptors are broadly expressed by the nuclei of the vocal control system, estrogen receptor (ERα) expression is largely restricted to HVC and its adjacent mediocaudal neopallium. The geographic overlap of these receptor phenotypes in HVC provides the basis for a regionally-defined set of paracrine interactions between the vascular bed and neuronal progenitor pool that both characterize and distinguish this nucleus. These interactions culminate in the focal attraction of new neurons to the adult HVC, the integration of those neurons into the extant vocal control circuits, and ultimately the acquisition and elaboration of song.

Evolution of a vertebrate social decision-making network

Animals evaluate and respond to their social environment with adaptive decisions. Revealing the neural mechanisms of such decisions is a major goal in biology. We analyzed expression profiles for 10 neurochemical genes across 12 brain regions important for decision-making in 88 species representing five vertebrate lineages. We found that behaviorally relevant brain regions are remarkably conserved over 450 million years of evolution. We also find evidence that different brain regions have experienced different selection pressures, because spatial distribution of neuroendocrine ligands are more flexible than their receptors across vertebrates. Our analysis suggests that the diversity of social behavior in vertebrates can be explained, in part, by variations on a theme of conserved neural and gene expression networks.

The vertebrate mesolimbic reward system and social behavior network: a comparative synthesis

All animals evaluate the salience of external stimuli and integrate them with internal physiological information into adaptive behavior. Natural and sexual selection impinge on these processes, yet our understanding of behavioral decision-making mechanisms and their evolution is still very limited. Insights from mammals indicate that two neural circuits are of crucial importance in this context: the social behavior network and the mesolimbic reward system. Here we review evidence from neurochemical, tract-tracing, developmental, and functional lesion/stimulation studies that delineates homology relationships for most of the nodes of these two circuits across the five major vertebrate lineages: mammals, birds, reptiles, amphibians, and teleost fish. We provide for the first time a comprehensive comparative analysis of the two neural circuits and conclude that they were already present in early vertebrates. We also propose that these circuits form a larger social decision-making (SDM) network that regulates adaptive behavior. Our synthesis thus provides an important foundation for understanding the evolution of the neural mechanisms underlying reward processing and behavioral regulation.

Steroid receptor coactivator 2 modulates steroid-dependent male sexual behavior and neuroplasticity in Japanese quail (Coturnix japonica)

Steroid receptor coactivators are necessary for efficient transcriptional regulation by ligand-bound nuclear receptors, including estrogen and androgen receptors. Steroid receptor coactivator-2 (SRC-2) modulates estrogen- and progesterone-dependent sexual behavior in female rats but its implication in the control of male sexual behavior has not been studied to our knowledge. We cloned and sequenced the complete quail SRC-2 transcript and showed by semi-quantitative PCR that SRC-2 expression is nearly ubiquitous, with high levels of expression in the kidney, cerebellum and diencephalon. Real-time quantitative PCR did not reveal any differences between intact males and females the medial preoptic nucleus (POM), optic lobes and cerebellum. We next investigated the physiological and behavioral role of this coactivator using in vivo antisense oligonucleotide techniques. Daily injections in the third ventricle at the level of the POM of locked nucleic acid antisense targeting SRC-2 significantly reduced the expression of testosterone-dependent male-typical copulatory behavior but no inhibition of one aspect of the appetitive sexual behavior was observed. The volume of POM, defined by aromatase-immunoreactive cells, was markedly decreased in animals treated with antisense as compared with controls. These results demonstrate that SRC-2 plays a prominent role in the control of steroid-dependent male sexual behavior and its associated neuroplasticity in Japanese quail.

Specific activation of estrogen receptor alpha and beta enhances male sexual behavior and neuroplasticity in male Japanese quail

Two subtypes of estrogen receptors (ER), ERα and ERβ, have been identified in humans and numerous vertebrates, including the Japanese quail. We investigated in this species the specific role(s) of each receptor in the activation of male sexual behavior and the underlying estrogen-dependent neural plasticity. Castrated male Japanese quail received empty (CX) or testosterone-filled (T) implants or were daily injected with the ER general agonist diethylstilbestrol (DES), the ERα-specific agonist PPT, the ERβ-specific agonist DPN or the vehicle, propylene glycol. Three days after receiving the first treatment, subjects were alternatively tested for appetitive (rhythmic cloacal sphincter movements, RCSM) and consummatory aspects (copulatory behavior) of male sexual behavior. 24 hours after the last behavioral testing, brains were collected and analyzed for aromatase expression and vasotocinergic innervation in the medial preoptic nucleus. The expression of RCSM was activated by T and to a lesser extent by DES and PPT but not by the ERβagonist DPN. In parallel, T fully restored the complete sequence of copulation, DES was partially active and the specific activation of ERα or ERβ only resulted in a very low frequency of mount attempts in few subjects. T increased the volume of the medial preoptic nucleus as measured by the dense cluster of aromatase-immunoreactive cells and the density of the vasotocinergic innervation within this nucleus. DES had only a weak action on vasotocinergic fibers and the two specific ER agonists did not affect these neural responses. Simultaneous activation of both receptors or treatments with higher doses may be required to fully activate sexual behavior and the associated neurochemical events.

Aromatase mRNA in the brain of adult green anole lizards: effects of sex and season

Neural testosterone metabolism, particularly the synthesis of oestradiol (E(2)) via the aromatase enzyme, is important for sexual behaviours in many vertebrates. In green anole lizards, E(2) metabolised from testosterone facilitates female receptivity and increases sexual motivation in males. Testosterone treatment increases aromatase activity in the whole brain homogenates of gonadectomised male, but not female, anoles, which is an effect limited to the breeding season (BS). To investigate the potential for local effects of this enzyme in reproductive behaviour, we used in situ hybridisation for aromatase mRNA to examine expression during the BS and nonbreeding season (NBS) in areas of the brain that control male sexual behaviours [preoptic area (POA) and amygdala (AMY)], as well as one regulating female reproductive behaviours ventromedial hypothalamus (VMH). Males had a greater total number of aromatase-expressing cells in the POA than females, and the density of aromatase-expressing cells (number per unit volume) was greater in the VMH and AMY of females. This density was also higher during the BS than NBS in the POA. Expression of aromatase in the AMY appeared to be lateralised because trends were detected for the left side to have more total cells and more cells per unit volume than the right. These results suggest that, similar to other vertebrates, regional aromatisation of testosterone may be important for the control of sex-specific reproductive behaviours.

Distribution of sex steroid hormone receptors in the brain of an African cichlid fish, Astatotilapia burtoni

Sex steroid hormones released from the gonads play an important role in mediating social behavior across all vertebrates. Many effects of these gonadal hormones are mediated by nuclear steroid hormone receptors, which are crucial for integration in the brain of external (e.g., social) signals with internal physiological cues to produce an appropriate behavioral output. The African cichlid fish Astatotilapia burtoni presents an attractive model system for the study of how internal cues and external social signals are integrated in the brain as males display robust plasticity in the form of two distinct, yet reversible, behavioral and physiological phenotypes depending on the social environment. In order to better understand where sex steroid hormones act to regulate social behavior in this species, we have determined the distribution of the androgen receptor, estrogen receptor alpha, estrogen receptor beta, and progesterone receptor mRNA and protein throughout the telencephalon and diencephalon and some mesencephalic structures of A. burtoni. All steroid hormone receptors were found in key brain regions known to modulate social behavior in other vertebrates including the proposed teleost homologs of the mammalian amygdalar complex, hippocampus, striatum, preoptic area, anterior hypothalamus, ventromedial hypothalamus, and ventral tegmental area. Overall, there is high concordance of mRNA and protein labeling. Our results significantly extend our understanding of sex steroid pathways in the cichlid brain and support the important role of nuclear sex steroid hormone receptors in modulating social behaviors in teleosts and across vertebrates.

Testosterone selectively affects aromatase and 5alpha-reductase activities in the green anole lizard brain

Testosterone (T) and its metabolites are important in the regulation of reproductive behavior in males of a variety of vertebrate species. Aromatase converts T to estradiol and 5alpha-reductase converts T to 5alpha-dihydrotestosterone (DHT). Male green anole reproduction depends on androgens, yet 5alpha-reductase in the brain is not sexually dimorphic and does not vary with season. In contrast, aromatase activity in the male brain is increased during the breeding compared to non-breeding season, and males have higher levels than females during the breeding season. Aromatase is important for female, but not male, sexual behaviors. The present experiment was conducted to determine whether 5alpha-reductase and aromatase are regulated by T. Enzyme activity was quantified in whole brain homogenates in both the breeding and non-breeding seasons in males and females that had been treated with either a T or blank implant. In males only, T increased 5alpha-reductase activity regardless of season and up-regulated aromatase during the breeding season specifically. Thus, regulation of both enzymes occurs in males, whereas females do not show parallel sensitivity to T. When considered with previous results, the data suggest that aromatase might influence a male function associated with the breeding season other than sexual behavior. 5alpha-Reductase can be mediated by T availability, but this regulation may not serve a sex- or season-specific purpose.

Sex differences in the expression of sex steroid receptor mRNA in the quail brain

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 aromatisation 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 behavioural 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 hypothesised that the differential expression of sex steroid receptors in specific brain areas could mediate this behavioural sex difference. Therefore, using radioactive in situ hybridisation histochemistry, we quantified the expression of the mRNA coding for the androgen receptor (AR) and the oestrogen receptors (ER) of the alpha and beta subtypes. 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 hybridisation signal for all steroid receptors was highest in the medial preoptic nucleus (POM), a major site of testosterone action that is related to the activation of male sexual behaviour. Although no sex difference in the optical density of the AR hybridisation 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. By contrast, females tended to have significantly higher levels of AR expression than males in the lateral septum. ERalpha was more densely expressed in females than males throughout the medial preoptic and hypothalamic areas (including the POM and the medio-basal hypothalamus), an area implicated in the control of female receptivity) and in the mesencephalic nucleus intercollicularis. ERbeta 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 behavioural responses to testosterone, although they do not appear to be sufficient to explain the complete lack of activation by testosterone of male-typical copulatory behaviour in females.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Vertebrate sex steroid receptors: evolution, ligands, and neurodistribution

This review focuses on our current understanding of vertebrate sex steroid receptors, with an emphasis on their evolutionary relationships. These relationships are discussed based on nucleotide and amino acid sequence data, which provide clues to the process by which structure-function relations have originated, evolved, and been maintained over time. The importance of the distribution of sex steroid receptors in the vertebrate brain is discussed using the example of androgen receptor sites and their relatively conserved localizations in the vertebrate brain.

Organizational effects of DDE on brain vasotocin system in male Japanese quail

p,p'-DDE, or ethylene, 1,1-dichloro-2,2-bis(p-chlorophenyl), is the main metabolite of the pesticide DDT, or 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane. It is an androgen receptor antagonist and testosterone hydroxylase modulator that is also more persistent than its parent compound. In a previous study we demonstrated that embryonic exposure to different doses of p,p'-DDE accelerated onset of puberty in females and reduced male reproductive behavior. In the present study we investigated the long-term effects of the exposure to p,p'-DDE on the differentiation of male Japanese quail (Coturnix japonica) limbic circuits related to male copulatory behavior: the parvocellular vasotocin (VT) system. We observed a decrease in the density of VT-immunoreactive fibers within the medial preoptic nucleus, bed nucleus of the stria terminalis, and lateral septum in p,p'-DDE-treated birds, while no differences could be detected in the magnocellular neurons of the supraoptic nucleus. In particular the lowest dose of p,p'-DDE causes the highest decrease of VT immunoreactivity. This study provides further evidence for VT system sensitivity towards endocrine disrupting chemicals and demonstrates that the VT system may be an appropriate and sensitive biomarker for early p,p'-DDE exposure in birds.

Embryonic and posthatching treatments with sex steroids demasculinize the motivational aspects of crowing behavior in male Japanese quail

Demasculinizing action of embryonic estrogen on crowing behavior in male Japanese quails was examined. Eggs were treated with either 20 microg of estradiol benzoate (EB) or vehicle on the 10th day of incubation. Chicks hatched from both groups of eggs were injected daily with either testosterone propionate (TP; 10 microg/g b.w.), 5alpha-dihydrotestosterone (DHT, a non-aromatizable androgen; 10 microg/g b.w.), or vehicle from 11 to 50 days after hatching, and during this period their calling behaviors were observed. Irrespective of embryonic treatments, all birds received posthatching treatment with either TP or DHT, but not with vehicle, emitted crows in place of distress calls in a stress (non-sexual) context of being isolated in a recording chamber. The posthatching TP, but not posthatching DHT, induced crowing in a sexual context (crowing in their home-cages) from much earlier age than posthatching vehicle in the birds received control embryonic treatment with vehicle. The same TP treatment, however, completely eliminated the crowing in a sexual context in the birds received EB during their embryonic life. In the birds treated with either posthatching DHT or posthatching vehicle, the crowing in a sexual context was only slightly decreased by embryonic EB treatment. These data suggest that posthatching estrogen, derived from testosterone aromatization, enhances the demasculinizing action of embryonic estrogen, and thus strongly reduces the sexual motivation for crowing behavior. This demasculinizing action, however, would not influence vocal control system which generates acoustic pattern of crowing in the presence of androgens allowing the birds to crow in a non-sexual context.

Low sex steroids, high steroid receptors: Increasing the sensitivity of the nonreproductive brain

Male aggressive behavior is generally regulated by testosterone (T). In most temperate breeding males, aggressive behavior is only expressed during the reproductive period. At this time circulating T concentrations, brain steroid receptors, and steroid metabolic enzymes are elevated in many species relative to the nonreproductive period. Many tropical birds, however, display aggressive behavior both during the breeding and the nonbreeding season, but plasma levels of T can remain low throughout the year and show little seasonal fluctuation. Studies on the year-round territorial spotted antbird (Hylophylax n. naevioides) suggest that T nevertheless regulates aggressive behavior in both the breeding and nonbreeding season. We hypothesize that to regulate aggressive behaviors during the nonbreeding season, when T is at its minimum, male spotted antbirds increase brain sensitivity to steroids. This can be achieved by locally up-regulating androgen receptors (ARs), estrogen receptors (ERs), or the enzyme aromatase (AROM) that converts T into estradiol. We therefore compared mRNA expression of AR, ERalpha, and AROM in free- living male spotted antbirds across reproductive and nonreproductive seasons in two brain regions known to regulate both reproductive and aggressive behaviors. mRNA expression of ERalpha in the preoptic area and AR in the nucleus taeniae were elevated in male spotted antbirds during the nonbreeding season when circulating T concentrations were low. This unusual seasonal receptor regulation may represent a means for the year-round regulation of vertebrate aggressive behavior via steroids by increasing the brain's sensitivity to sex steroids during the nonbreeding season.

Neuroanatomical specificity of sex differences in expression of aromatase mRNA in the quail brain

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.

Region-specific expression and sex-steroidal regulation on aromatase and its mRNA in the male rat brain: immunohistochemical and in situ hybridization analyses

The brain has an estrogen-biosynthetic potential resulting from the presence of neuronal aromatase, which controls the intraneural sex-steroidal milieu and is involved in brain sexual differentiation, psychobehavioral regulation, and neuroprotection. In the rat brain, three distinct aromatase-P450-immunoreactive (AromP450-I) neural groups have been categorized in terms of their peak expression time (fetal, fetoneonatal, and young-to-adult groups), suggesting the presence of region-specific regulation on brain AromP450. In the present study, we compared the expressions between AromP450 protein and mRNA by using immunohistochemistry and in situ hybridization with an ovary-derived cRNA probe in serial sections of fetal, fetoneonatal, and adult male rat brains and then performed steroidal manipulations to evaluate the sex-steroidal effects on AromP450 in adult orchiectomized and adrenalectomized (OCX + ADX) male rats. As a result, prominent mRNA signals were detected in the fetal (i.e., the anterior medial preoptic nucleus) and fetoneonatal (i.e., the medial preopticoamygdaloid neuronal arc) groups, although no detectable signal was found in the "young-to-adult" group (i.e., the central amygdaloid nucleus). In addition, the "fetoneonatal" AromP450-I neurons were prominently reduced in number and intensity after OCX + ADX and then were reinstated by the administration of dihydrotestosterone, testosterone, or 17beta-estradiol. In contrast, none of the sex steroids had any significant effects on the young-to-adult group. Several possible explanations were explored for why the young-to-adult group may differ in aromatase expression and regulation, including the possibility that distinct splicing variants or isozymes for aromatase exist in the rat brain.

FnTm2, a novel brain-specific transcript, is dynamically expressed in the song learning circuit of the zebra finch

Zebra finch males learn their song by imitation, a process influenced by social variables. The neural pathways for acquisition and production of learned song are known, but the cellular and molecular underpinnings are not. Here we describe a novel gene named "FnTm2" ("Phantom 2") that is predicted to encode a small protein (220 aa) with a single fibronectin type III domain and a single transmembrane domain. This gene shows great variability in its expression in song system neurons of the anterior forebrain pathway (AFP), a circuit that influences song discrimination and is necessary for normal song acquisition. AFP nuclei that express FnTm2 include the nucleus HVC (its Area X-projecting neurons), Area X, and LMAN (core and shell). FnTm2 expression does not correlate with singing behavior like the immediate early gene ZENK. It is expressed variably during sleeping hours and is not dependent on an intact song circuit. FnTm2's expression is sensitive to hearing, because in deafened birds its expression is substantially reduced in the core of LMAN. Furthermore, a comparison of FnTm2 expression between mice and zebra finches revealed a conserved pattern of expression in the "limbic system." We suggest that FnTm2 may be sensitive to affective and/or attentional states and thus may provide insights on how social variables influence the production and discrimination of learned vocalizations.

Utilization of a zebra finch BAC library to determine the structure of an avian androgen receptor genomic region

The zebra finch (Taeniopygia guttata) is an important model organism for studying behavior, neuroscience, avian biology, and evolution. To support the study of its genome, we constructed a BAC library (TG__Ba) using DNA from livers of females. The BAC library consists of 147,456 clones with 98% containing inserts of an average size of 134 kb and represents 15.5 haploid genome equivalents. By sequencing a whole BAC, a full-length androgen receptor open reading frame was identified, the first in an avian species. Comparison of BAC end sequences and the whole BAC sequence with the chicken genome draft sequence showed a high degree of conserved synteny between the zebra finch and the chicken genome.

Effects of androgens and estrogens on crowings and distress callings in male Japanese quail, Coturnix japonica

In male Japanese quail, crowing behavior is considered to be strictly androgen-dependent. It was previously shown that in chicks, treatment with either testosterone or 5alpha-dihydrotestosterone (5alpha-DHT; a non-aromatizable androgen) induced crowing with motivation for distress calling in acutely isolated conditions. Many studies, however, have shown that the potencies of testosterone and 5alpha-DHT in activating crowing in castrated males are different. To clarify the effects of androgenic and estrogenic actions on the production of crows and distress calls, we injected quail daily from 11 to 42 days after hatching (Day 11 to 42) with testosterone propionate (TP), 5alpha-DHT, estradiol benzoate (EB) or vehicle and examined their calling behaviors both in a recording chamber (acutely isolated conditions) and in their home-cages (well-acclimated conditions). Both TP- and 5alpha-DHT-treated birds began to crow by Day 13 when isolated in the recording chamber. The TP-treated birds, however, crowed less frequently than 5alpha-DHT-treated ones. This, combined with the observations that distress calling was strongly inhibited in EB-treated birds, suggests that estrogen converted from testosterone may inhibit the motivation for distress calling. On the other hand, after chronic treatment of TP, but not of 5alpha-DHT, birds began to crow intensely in their home-cages earlier than vehicle treated controls, suggesting that estrogen is needed to initiate crowing behavior in sexually active males. Taken together, it is suggested that estrogenic actions affect the motivation underlying vocal behaviors, while the androgenic action is indispensable in generating crowing.

Effects of estradiol on spatial learning, hippocampal cytochrome P450 19, and estrogen alpha and beta mRNA levels in ovariectomized female mice

The brain is an important target organ for peripherally synthesized estrogen but it also has its own steroid biosynthesis producing estrogen from testosterone catalyzed by the aromatase enzyme. This study examined the effects of estrogen treatment in two spatial memory tasks, one-arm-baited radial arm maze and a position discrimination task in the T-maze in ovariectomized female mice. Hippocampal cytochrome P450 19 (encoding aromatase), and estrogen receptor alpha and beta gene expressions were also measured using real time quantitative polymerase chain reaction analysis. Estrogen (17beta-estradiol) was administered either tonically via s.c. minipellets or phasically via daily i.p. injections. In ovariectomized mice, the tonic estrogen decreased the number of reference memory errors in radial arm maze. Tonic estrogen treatment also up-regulated the expression of cytochrome P450 19 and estrogen receptors. In contrast, estrogen injections decreased the expression of cytochrome P450 19 and estrogen receptor alpha genes. The number of reference memory errors correlated negatively with estrogen receptor alpha expression. These findings indicate that peripheral estrogen levels affect neuronal estrogen synthesis by regulating the cytochrome P450 19 gene expression and also influence estrogen receptor alpha expression. The results also suggest that tonic rather than cyclic estrogen treatment might be more beneficial for cognitive functions.

Subpallial amygdala and nucleus taeniae in birds resemble extended amygdala and medial amygdala in mammals in their expression of markers of regional identity

Two regions were recently recognized as subpallial amygdaloid nuclei in birds, the nucleus taeniae of the amygdala (TnA) and the newly identified subpallial amygdala (SpA). Here we further confirm these nuclei to be subpallial and amygdaloid and show similarity to specific mammalian subpallial amygdaloid nuclei. By its topological, connectional and neurochemical traits, avian TnA has been suggested to be comparable to mammalian medial amygdala (MeA) and SpA to be comparable to the sublenticular part of mammalian extended amygdala (ExA). We examined molecular traits of these areas using immunohistochemistry for limbic system-associated membrane protein (LAMP) and in situ hybridization for glutamic acid decarboxylase-65 (GAD65) and chicken ovalbumin upstream promoter-transcription factor II (COUP-TF II). Mammalian GAD65 is a subpallial marker and was enriched in ExA and MeA. Chick GAD65 was enriched in SpA and TnA, indicating that they are subpallial. LAMP, which is enriched in limbic regions such as mammalian ExA and MeA, was enriched in avian SpA and TnA. COUP-TF II was enriched in mammalian amygdala including MeA and ExA to a lesser extent. In birds, COUP-TF II was enriched in TnA and moderate in SpA. Overlap of these markers confirms avian TnA resembles mammalian MeA and SpA resembles ExA.

Sexual behavior activates the expression of the immediate early genes c-fos and Zenk (egr-1) in catecholaminergic neurons of male Japanese quail

We analyzed the expression of the immediate early genes c-fos and Zenk (egr-1) in the brain of male quail that were gonadally intact (I) or castrated and treated (CX+T) or not (CX) with testosterone and had been exposed for 60 min either to a sexually mature female (F), or to an empty arena (EA) or were left in their home cage (HC). Alternate sections in the brains collected 90 min after the start of behavioral interactions were stained by immunocytochemistry for the proteins FOS or ZENK alone or in association with tyrosine hydroxylase (TH), a marker of catecholaminergic neurons. C-fos and Zenk expression was statistically increased in six brain areas of sexually active birds (I+F, CX+T+F) compared with controls (CX+F, CX+T+EA, CX+T+HC), i.e. the preoptic area, bed nucleus striae terminalis, arcopallium, nucleus intercollicularis, periaqueductal gray and the ventral tegmental area. Interestingly, c-fos and Zenk expression was high in the nucleus intercollicularis, a midbrain vocal control nucleus, of I+F and CX+T+F birds that displayed copulatory behavior but emitted few crows but not in the nucleus intercollicularis of CX+T+EA birds that crowed frequently. Increases in c-fos expression were observed in TH-immunoreactive cells in the periaqueductal gray and ventral tegmental area, but not in the substantia nigra, of I+F and CX+T+F birds indicating the activation of dopaminergic neurons during sexual behavior. Together, these data confirm the implication of the steroid-sensitive preoptic area and bed nucleus striae terminalis in the control of copulation and support the notion that dopamine is involved in its control.

Electrophysiological and neurochemical characterization of neurons of the medial preoptic area in Japanese quail (Coturnix japonica)

Intracellular recordings of medial preoptic neurons demonstrated that most neurons show a spontaneous firing, a linear I-V relationship and low-threshold-like events suppressed by the application of Ni2+. Some neurons had a depolarizing sag of the membrane potential in response to hyperpolarizing current pulses. The majority of the cells exhibited a robust spontaneous synaptic activity suppressed by SR95531 (100 microM), a GABAA receptor antagonist, and/or by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), an (RS)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) glutamate receptor antagonist. Most neurons were affected by the application of AMPA (10 microM), kainate (30 microM), N-methyl-D-aspartic acid (NMDA, 10 microM), isoguvacine (a GABAA receptor agonist, 100 microM), dopamine (100 microM), and norepinephrine (100 microM). Biocytin injections coupled to aromatase immunocytochemistry identified 19 recorded neurons including 3 displaying a dense aromatase immunoreactivity. All of them responded to kainate, dopamine, and norepinephrine, while only one responded to isoguvacine and NMDA. Taken together, these results demonstrate a relative electrical and neurochemical homogeneity of the medial preoptic neurons, including a few aromatase-immunoreactive neurons that could be identified by immunocytochemistry after biocytin labeling of the recorded neurons.

Chemoarchitectonic subdivisions of the songbird septum and a comparative overview of septum chemical anatomy in jawed vertebrates

Available data demonstrate that the avian septal region shares a number of social behavior functions and neurochemical features in common with mammals. However, the structural and functional subdivisions of the avian septum remain largely unexplored. In order to delineate chemoarchitectural zones of the avian septum, we prepared a large dataset of double-, triple-, and quadruple-labeled material in a variety of songbird species (finches and waxbills of the family Estrildidae and a limited number of emberizid sparrows) using antibodies against 10 neuropeptides and enzymes. Ten septal zones were identified that were placed into lateral, medial, caudocentral, and septohippocampal divisions, with the lateral and medial divisions each containing multiple zones. The distributions of numerous immunoreactive substances in the lateral septum closely match those of mammals (i.e., distributions of met-enkephalin, vasotocin, galanin, calcitonin gene-related peptide, tyrosine hydroxylase, vasoactive intestinal polypeptide, substance P, corticotropin-releasing factor, and neuropeptide Y), enabling detailed comparisons with numerous chemoarchitectonic zones of the mammalian lateral septum. Our septohippocampal and caudocentral divisions are topographically comparable to the mammalian septohippocampal and septofimbrial nuclei, respectively, although additional data will be required to establish homology. The present data also demonstrate the presence of a medial septal nucleus that is histochemically comparable to the medial septum of mammals. The avian medial septum is clearly defined by peptidergic markers and choline acetyltransferase immunoreactivity. These findings should provide a useful framework for functional and comparative studies, as they suggest that many features of the septum are highly conserved across vertebrate taxa.

Revised nomenclature for avian telencephalon and some related brainstem nuclei

The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon). Recognizing that this promotes misunderstanding of the functional organization of avian brains and their evolutionary relationship to mammalian brains, avian brain specialists began discussions to rectify this problem, culminating in the Avian Brain Nomenclature Forum held at Duke University in July 2002, which approved a new terminology for avian telencephalon and some allied brainstem cell groups. Details of this new terminology are presented here, as is a rationale for each name change and evidence for any homologies implied by the new names. Revisions for the brainstem focused on vocal control, catecholaminergic, cholinergic, and basal ganglia-related nuclei. For example, the Forum recognized that the hypoglossal nucleus had been incorrectly identified as the nucleus intermedius in the Karten and Hodos (1967) pigeon brain atlas, and what was identified as the hypoglossal nucleus in that atlas should instead be called the supraspinal nucleus. The locus ceruleus of this and other avian atlases was noted to consist of a caudal noradrenergic part homologous to the mammalian locus coeruleus and a rostral region corresponding to the mammalian A8 dopaminergic cell group. The midbrain dopaminergic cell group in birds known as the nucleus tegmenti pedunculopontinus pars compacta was recognized as homologous to the mammalian substantia nigra pars compacta and was renamed accordingly; a group of gamma-aminobutyric acid (GABA)ergic neurons at the lateral edge of this region was identified as homologous to the mammalian substantia nigra pars reticulata and was also renamed accordingly. A field of cholinergic neurons in the rostral avian hindbrain was named the nucleus pedunculopontinus tegmenti, whereas the anterior nucleus of the ansa lenticularis in the avian diencephalon was renamed the subthalamic nucleus, both for their evident mammalian homologues. For the basal (i.e., subpallial) telencephalon, the actual parts of the basal ganglia were given names reflecting their now evident homologues. For example, the lobus parolfactorius and paleostriatum augmentatum were acknowledged to make up the dorsal subdivision of the striatal part of the basal ganglia and were renamed as the medial and lateral striatum. The paleostriatum primitivum was recognized as homologous to the mammalian globus pallidus and renamed as such. Additionally, the rostroventral part of what was called the lobus parolfactorius was acknowledged as comparable to the mammalian nucleus accumbens, which, together with the olfactory tubercle, was noted to be part of the ventral striatum in birds. A ventral pallidum, a basal cholinergic cell group, and medial and lateral bed nuclei of the stria terminalis were also recognized. The dorsal (i.e., pallial) telencephalic regions that had been erroneously named to reflect presumed homology to striatal parts of mammalian basal ganglia were renamed as part of the pallium, using prefixes that retain most established abbreviations, to maintain continuity with the outdated nomenclature. We concluded, however, that one-to-one (i.e., discrete) homologies with mammals are still uncertain for most of the telencephalic pallium in birds and thus the new pallial terminology is largely devoid of assumptions of one-to-one homologies with mammals. The sectors of the hyperstriatum composing the Wulst (i.e., the hyperstriatum accessorium intermedium, and dorsale), the hyperstriatum ventrale, the neostriatum, and the archistriatum have been renamed (respectively) the hyperpallium (hypertrophied pallium), the mesopallium (middle pallium), the nidopallium (nest pallium), and the arcopallium (arched pallium). The posterior part of the archistriatum has been renamed the posterior pallial amygdala, the nucleus taeniae recognized as part of the avian amygdala, and a region inferior to the posterior paleostriatum primitivum included as a subpallial part of the avian amygdala. The names of some of the laminae and fiber tracts were also changed to reflect current understanding of the location of pallial and subpallial sectors of the avian telencephalon. Notably, the lamina medularis dorsalis has been renamed the pallial-subpallial lamina. We urge all to use this new terminology, because we believe it will promote better communication among neuroscientists. Further information is available at http://avianbrain.org

Differential effects of testosterone on protein synthesis activity in male and female quail brain

In Japanese quail, testosterone (T) increases the Nissl staining density in the medial preoptic nucleus (POM) in relation to the differential activation by T of copulatory behavior. The effect of T on protein synthesis was quantified here in 97 discrete brain regions by the in vivo autoradiographic (14)C-leucine (Leu) incorporation method in adult gonadectomized male and female quail that had been treated for 4 weeks with T or left without hormone. T activated male sexual behaviors in males but not females. Overall Leu incorporation was increased by T in five brain regions, many of which contain sex steroid receptors such as the POM, archistriatum and lateral hypothalamus. T decreased Leu incorporation in the medial septum. Leu incorporation was higher in males than females in two nuclei but higher in females in three nuclei including the hypothalamic ventromedial nucleus. Significant interactions between effects of T and sex were seen in 13 nuclei: in most nuclei (n=12), T increased Leu incorporation in males but decreased it in females. The POM boundaries were defined by a denser Leu incorporation than the surrounding area and incorporation was increased by T more in males (25%) than in females (6%). These results confirm that protein synthesis in brain areas relevant to the control of sexual behavior can be affected by the sex of the subjects or their endocrine condition and that T can have differential effects in the two sexes. These anabolic changes should reflect the sexually differentiated neurochemical mechanisms mediating behavioral activation.

Multiple mechanisms control brain aromatase activity at the genomic and non-genomic level

Evidence has recently accumulated indicating that aromatase activity in the preoptic area is modulated in parallel by both slow (hours to days) genomic and rapid (minutes to hours) non-genomic mechanisms. We review here these two types of control mechanisms and their potential contribution to various aspects of brain physiology in quail. High levels of aromatase mRNA, protein and activity (AA) are present in the preoptic area of this species where the transcription of aromatase is controlled mainly by steroids. Estrogens acting in synergy with androgens play a key role in this control and both androgen and estrogen receptors (ER; alpha and beta subtypes) are present in the preoptic area even if they are not necessarily co-localized in the same cells as aromatase. Steroids have more pronounced effects on aromatase transcription in males than in females and this sex difference could be caused, in part, by a sexually differentiated expression of the steroid receptor coactivator 1 in this area. The changes in aromatase concentration presumably control seasonal variations as well as sex differences in brain estrogen production. Aromatase activity in hypothalamic homogenates is also rapidly (within minutes) down-regulated by exposure to conditions that enhance protein phosphorylation such as the presence of high concentrations of calcium, magnesium and ATP. Similarly, pharmacological manipulations such as treatment with thapsigargin or stimulation of various neurotransmitter receptors (alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid (AMPA), kainate, and N-methyl-D-aspartate (NMDA)) leading to enhanced intracellular calcium concentrations depress within minutes the aromatase activity measured in quail preoptic explants. The effects of receptor stimulation are presumably direct: electrophysiological data confirm the presence of these receptors in the membrane of aromatase-expressing cells. Inhibitors of protein kinases interfere with these processes and Western blotting experiments on brain aromatase purified by immunoprecipitation confirm that the phosphorylations regulating aromatase activity directly affect the enzyme rather than another regulatory protein. Accordingly, several phosphorylation consensus sites are present on the deduced amino acid sequence of the recently cloned quail aromatase. Fast changes in the local availability of estrogens in the brain can thus be caused by aromatase phosphorylation so that estrogen could rapidly regulate neuronal physiology and behavior. The rapid as well as slower processes of local estrogen production in the brain thus match well with the genomic and non-genomic actions of steroids in the brain. These two processes potentially provide sufficient temporal variation in the bio-availability of estrogens to support the entire range of established effects for this steroid.

Sex steroid communication in the ring dove brain during courtship

This review examines possible role of progesterone receptor (PR) and androgen receptor (AR) "cross-talk" in the expression of courtship behaviour in the ring dove (Streptopelia risoria). In doves, although androgen has been mostly associated with aggressive courtship behaviour and progesterone with the initiation of incubation, progesterone administration to courting birds terminates the aggressive component of courtship whilst having no effect on nesting behaviour. Recent results in doves have identified a high density of androgen receptor and progesterone receptor immunoreactivity (AR-ir and PR-ir) in the hypothalamus of both sexes in regions known to be directly involved in courtship and incubation behaviour. Nuclear AR-ir in courting birds is widespread throughout the brain. Nuclear PR-ir is only localized in discrete regions of the preoptic hypothalamus of both sexes. In the anterior and posterior hypothalamus of courting birds an increase number of AR-ir and PR-ir neurons colocalizes (70-90%) in the nucleus preopticus anterior (POA), nucleus preopticus medialis (POM), nucleus preopticus paraventricularis magnocellularis (PPM), nucleus hypothalami lateralis posterioris (PLH), and tuberal hypothalamus (Tu). A lower percentage of colocalization is seen in birds at other stages of the breeding cycle. The high percentage of AR-ir and PR-ir colocalization in the preoptic hypothalamus of courting doves supports previous reports involving progesterone acting in these brain regions to terminate the androgen-dependent aggressive courtship behaviour in male doves. The increase in PR-ir staining intensity in AR-ir neurons in courting birds suggests that this progesterone-dependent termination of aggressive courtship display in males occurs at the receptor level and may be orchestrated by central oestrogen.

Expression of androgen receptor mRNA in the late embryonic and early posthatch zebra finch brain

Zebra finch males sing and females do not, and the underlying neural circuitry in males is more developed than that in females. Sex steroid hormones influence the development of sex differences in this circuitry, including differences in androgen receptor (AR) expression, although the role of androgens has been controversial. We isolated a cDNA encoding a portion of the zebra finch AR and used in situ hybridization to examine the spatiotemporal pattern of AR mRNA expression in the brain during late embryonic development and at hatching. We detected AR mRNA in all the major subdivisions of the brain as early as embryonic day 10. No qualitative sex differences in AR mRNA expression patterns were observed. Cells lining the ventral arm of the lateral telencephalic ventricles expressed AR mRNA on embryonic day 11 and posthatching day 1, as did cells lining the third ventricle at all three developmental stages examined, suggesting that androgens may play a role in early stages of cellular proliferation, migration, or differentiation. AR mRNA was also detected in the hippocampus, neostriatum, septum, ventromedial archistriatum, hypothalamic regions, dorsal mesencephalon, and in and around the brainstem nucleus tracheosyringealis. Our results suggested that androgens act early in neural development and therefore may contribute to the process of sexual differentiation.

Anatomical relationships between aromatase-immunoreactive neurons and nitric oxide synthase as evidenced by NOS immunohistochemistry or NADPH diaphorase histochemistry in the quail forebrain

In Japanese quail (Coturnix japonica), previous studies indicated that the distribution of reduced nicotinamide dinucleotide phosphate (NADPH) diaphorase overlaps with steroid-sensitive areas that contain dense populations of aromatase-immunoreactive (ARO-ir) cells. We investigated here the anatomical relationships between aromatase (ARO) and nitric oxide synthase (NOS)-containing cells that were visualized both by NOS-immunohistochemistry and NADPH-histochemistry. The distribution of ARO-ir and of NADPH-positive cells in the forebrain observed here matched exactly the distribution previously reported. The distribution of NOS-immunoreactive material in the vicinity of ARO-ir cell groups appeared similar to the distribution of NADPH-positive structures previously identified by histochemistry. The number of NOS-immunoreactive cells was similar to the number of NADPH-positive cells and they were found in the same brain regions. In contrast, few NOS-immunoreactive fibers were observed whereas numerous NADPH-positive fibers and punctuate structures were present in many areas. Major groups of NOS-immunoreactive/NADPH-positive neurons were adjacent to the main ARO-ir cell groups, such as the medial preoptic nucleus, the bed nucleus of the stria terminalis and the nucleus ventromedialis hypothalamic. However, examination of adjacent sections indicated that there is very little overlap between the NOS-immunoreactive and ARO-ir cell populations. This notion got further support by double-labeled sections where no double-labeled cells could be identified. In sections stained simultaneously by histochemistry for NADPH and immunohistochemistry for ARO, many NADPH-positive fibers and punctate structures were closely associated with ARO-ir perikarya. Taken together, the present data indicate that NOS is not or very rarely colocalized with ARO but that NOS inputs are closely associated with ARO-ir cells. Based on previous work in a variety of model systems, it can be hypothesized that these inputs modulate the expression or activity of ARO in the quail brain.

Evidence for species differences in the pattern of androgen receptor distribution in relation to species differences in an androgen-dependent behavior

Chickens (Gallus gallus domesticus) and Japanese quail (Coturnix japonica), two closely related gallinaceous bird species, exhibit a form of vocalization-crowing-which differs between the species in two components: its temporal acoustic pattern and its accompanying postural motor pattern. Previous work utilizing the quail-chick chimera technique demonstrated that the species-specific characteristics of the two crow components are determined by distinct brain structures: the midbrain confers the acoustic pattern, and the caudal hindbrain confers the postural pattern. Crowing is induced by androgens, acting directly on androgen receptors. As a strategy for identifying candidate neurons in the midbrain and caudal hindbrain that could be involved in crow production, we performed immunocytochemistry for androgen receptors in these brain regions in both species. We also investigated midbrain-to-hindbrain vocal-motor projections. In the midbrain, both species showed prominent androgen receptor immunoreactivity in the nucleus intercollicularis, as had been reported in previous studies. In the caudal hindbrain, we discovered characteristic species differences in the pattern of androgen receptor distribution. Chickens, but not quail, showed strong immunoreactivity in the tracheosyringeal division of the hypoglossal nucleus, whereas quail, but not chickens, possessed strong immunoreactivity in a region of the ventrolateral medulla. Some of these differences in hindbrain androgen receptor distribution may be related to the species differences in the postural component of crowing behavior. The results of the present study imply that the spatial distribution of receptor proteins can vary even between closely related species. Such variation in receptor distribution could underlie the evolution of species differences in behavior.

Neuroendocrinology of song behavior and avian brain plasticity: multiple sites of action of sex steroid hormones

Seasonal changes in the brain of songbirds are one of the most dramatic examples of naturally occurring neuroplasticity that have been described in any vertebrate species. In males of temperate-zone songbird species, the volumes of several telencephalic nuclei that control song behavior are significantly larger in the spring than in the fall. These increases in volume are correlated with high rates of singing and high concentrations of testosterone in the plasma. Several song nuclei express either androgen receptors or estrogen receptors, therefore it is possible that testosterone acting via estrogenic or androgenic metabolites regulates song behavior by seasonally modulating the morphology of these song control nuclei. However, the causal links among these variables have not been established. Dissociations among high concentrations of testosterone, enlarged song nuclei, and high rates of singing behavior have been observed. Singing behavior itself can promote cellular changes associated with increases in the volume of the song control nuclei. Also, testosterone may stimulate song behavior by acting in brain regions outside of the song control system such as in the preoptic area or in catecholamine cell groups in the brainstem. Thus testosterone effects on neuroplasticity in the song system may be indirect in that behavioral activity stimulated by testosterone acting in sites that promote male sexual behavior could in turn promote morphological changes in the song system.

Effects of lesions of the medial preoptic nucleus on the testosterone-induced metabolic changes in specific brain areas in male quail

The effects of bilateral lesions of the medial preoptic nucleus in association with testosterone on the metabolic activity in discrete brain regions was studied quantitatively by the in vivo autoradiographic 2-deoxyglucose method. Adult male quail were castrated and then left without hormone replacement therapy or treated with testosterone or treated with testosterone and submitted to a bilateral lesion of the medial preoptic nucleus, a brain region that plays a key role in the activation of male copulatory behavior by testosterone. Treatment for about 10 days with testosterone activated the expression of the full range of male sexual behaviors and these behaviors were completely suppressed by the medial preoptic nucleus lesions. Mapping of 2-deoxyglucose uptake revealed both increases and decreases of metabolic activity in discrete brain regions associated with the systemic treatment with testosterone as well as with the lesion of the medial preoptic nucleus. Testosterone affected the oxidative metabolism in brain areas that are known to contain sex steroid receptors (such as the nucleus taeniae and the paraventricular and ventromedial nuclei of the hypothalamus) but also in nuclei that are believed to be devoid of such receptors. Effects of testosterone in these nuclei may be indirect or reflect changes in terminals of axons originating in steroid-sensitive areas. Bilateral medial preoptic nucleus lesions affected 2-deoxyglucose uptake in a variety of brain regions. Some of these regions are known to be mono-synaptically connected to the medial preoptic nucleus. Metabolic depression in these areas may reflect retrograde changes in the neurons projecting to the damaged field.The metabolic changes identified in the present study confirm the prominent role of the preoptic area in the control of sexual behavior, show that changes in the physiology of the visual system represent one of the ways through which testosterone influences the occurrence of this behavior and demonstrate that the medial preoptic nucleus has marked effects on the metabolic activity in a variety of limbic and telencephalic structures. This study also indicates that the medial preoptic nucleus affects the activity of the area ventralis of Tsai, a dopaminergic area known to send projections to a variety of hypothalamic, thalamic and mesencephalic nuclei that are implicated in the control of male sexual behavior. These data therefore support the notion that the control of the dopaminergic activity in the area ventralis of Tsai by the medial preoptic nucleus represents one of the ways through which the medial preoptic area regulates male reproductive behavior.

Estradiol mediates effects of testosterone on vasotocin immunoreactivity in the adult quail brain

In adult male quail, the activation of sexual behavior by testosterone (T) is mediated at the cellular level by the interaction of T metabolites with intracellular steroid receptors. In particular, the aromatization of T into an estrogen plays a key limiting role. Nonaromatizable androgens such 5alpha-dihydrotestosterone (DHT) synergize with estradiol (E2) to activate the behavior. Given that the density of vasotocin (VT) immunoreactive structures is increased by T in adult male quail and that VT injections affect male behavior, we wondered whether the expression of VT is also affected by T metabolites such as E2 and DHT. We analyzed here, in castrated male quail, the effects of a treatment with T, E2, DHT, or E2 + DHT on sexual behavior and brain VT immunoreactivity. The restoration by T of the VT immunoreactivity in the medial preoptic nucleus, bed nucleus striae terminalis, and lateral septum of castrated male quail could be fully mimicked by a treatment with E2. The androgen DHT had absolutely no effect on the VT immunoreactivity in these conditions and, at the doses used here, DHT did not synergize with E2 to enhance the density of VT immunoreactive structures. These effects of T metabolites in the brain were not fully correlated with their effects on the activation of male copulatory behavior, suggesting that the increase in VT expression in the brain does not represent a necessary step for the activation of behavior. Although VT expression in the medial preoptic nucleus and bed nucleus striae terminalis is often tightly correlated with the expression of male copulatory behavior, VT presumably does not represent simply one step in the biochemical cascade of events that is induced by T in the brain and leads to the expression of male sexual behavior.