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

Impact of sex hormones on immune function and multiple sclerosis development

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) affecting young people and leading to demyelination and neurodegeneration. The disease is clearly more common in women, in whom incidence has been rising. Gender differences include: earlier disease onset and more frequent relapses in women; and faster progression and worse outcomes in men. Hormone-related physiological conditions in women such as puberty, pregnancy, puerperium, and menopause also exert significant influence both on disease prevalence as well as on outcomes. Hormonal and/or genetic factors are therefore believed to be involved in regulating the course of disease. In this review, we discuss clinical evidence for the impact of sex hormones (estrogens, progesterone, prolactin, and testosterone) on MS and attempt to elucidate the hormonal and immunological mechanisms potentially underlying these changes. We also review current knowledge on the relationship between sex hormones and resident CNS cells and provide new insights in the context of MS. Understanding these molecular mechanisms may contribute to the development of new and safer treatments for both men and women.

Disruptions in aromatase expression in the brain, reproductive behavior, and secondary sexual characteristics in male guppies (Poecilia reticulata) induced by tributyltin

Although bioaccumulation of tributyltin (TBT) in fish has been confirmed, information on possible effects of TBT on reproductive system of fish is still relatively scarce, particularly at environmentally relevant levels. To evaluate the adverse effects and intrinsic toxicological properties of TBT in male fish, we studied aromatase gene expression in the brain, sex steroid contents, primary and secondary sexual characteristics, and reproductive behavior in male guppies (Poecilia reticulata) exposed to tributyltin chloride at the nominal concentrations of 5, 50, and 500 ng/L for 28 days in a semi-static exposure system. Radioimmunoassay demonstrated that treatment with 50 ng/L TBT caused an increase in systemic levels of testosterone of male guppies. Gonopodial index, which showed a positive correlation with testosterone levels, was elevated in the 5 ng/L and 50 ng/L TBT treated groups. Real-time PCR revealed that TBT exposure had inhibiting effects on expression of two isoforms of guppy aromatase in the brain, and these changes at the molecular levels were associated with a disturbance of reproductive behavior of the individuals, as measured by decreases in frequencies of posturing, sigmoid display, and chase activities when males were paired with females. This study provides the first evidence that TBT can cause abnormalities of secondary sexual characteristics in teleosts and that suppression of reproductive behavior in teleosts by TBT is due to its endocrine-disrupting action as an aromatase inhibitor targeting the nervous system.

Gender effect of catechol-O-methyltransferase Val158Met polymorphism on suicidal behavior

Genetic factors and catecholaminergic dysfunction have been suggested as the etiology of suicide. The catechol-O-methyltransferase (COMT) 158Val/Met polymorphism affects COMT activity; that is, the alleles encoding Val and Met are associated with relatively high and relatively low COMT activity, respectively. We aimed to identify the role of the COMT Val158Met polymorphism in suicidal attempt behavior. The COMT 158Val/Met polymorphisms were analyzed in 197 suicide attempters (male/female: 70/127), 170 control subjects (male/female: 85/85). All subjects were ethnic Korean. The Lethality Suicide Attempt Rating Scale (LSARS) and risk-rescue rating (RRR) system were explored. For the male subjects, there was a significant difference in genotype distributions and allele frequencies between control subjects and suicide attempters. That is, Val/Val genotype and Val carriers were more frequent in suicide attempters than in control subjects. For the female subjects, however, no significant difference was shown in genotype distributions and allele frequencies between control subjects and suicide attempters. There were no significant differences in LSARS and RRR according to the genotypes. The distribution of the COMT 158Val/Met polymorphism showed a biologically meaningful difference between control subjects and suicide attempters among the male subjects although selection bias should be considered.

Seasonal changes in courtship behavior, plasma androgen levels and in hypothalamic aromatase immunoreactivity in male free-living European starlings (Sturnus vulgaris)

In songbirds from temperate latitudes, singing during spring has an essential role in mate attraction, while during the non-breeding season it is connected to territorial aggression and/or maintaining dominance hierarchies or flock cohesion. Courtship behavior is regulated by plasma testosterone (T) levels. Other androgens, like dehydroepiandrosterone (DHEA) could be responsible for aggression. The aromatization of androgens in the brain is an essential step in mediating their effects on behavior. Our goal was to determine whether the seasonal changes in male courtship behavior (measured by average song bout length and wing-waving/flicking) are related to seasonal changes in androgen activity (measured by plasma T, DHEA levels) and aromatase (ARO) immunoreactivity in the preoptic area/medial preoptic nucleus (POA/POM) of free-living male starlings. DHEA increased during pair formation, decreased at nesting and remained at low levels. The number of ARO cells - in line with the T levels - increased during the courtship and nesting periods, but outside the breeding season it was low. Song bout length showed a similar pattern, namely the peak was reached during the courtship period, and after that males stopped singing when chicks started to hatch. Short and fast wing-flicking and wing-waving behavior was observed only during the breading season. Summarizing, we have found that song bout length of male starlings changes parallel with plasma T levels and ARO immunoreactivity in the POA/POM. Furthermore, DHEA levels were low during the sexually inactive period which suggests that other mechanisms could be involved in the aggressive non-courtship behavior/vocalization in these birds.

Association study of a functional catechol-O-methyltransferase (COMT) Val108/158Met polymorphism and suicide attempts in patients with alcohol dependence

Alcohol dependence is frequently associated with aggressive and suicidal behaviour. Genetic factors contribute to both behaviours. Candidate genes, related to suicide and aggression, include genes involved in serotonin, norepinephrine and dopamine pathways. The enzyme catechol-O-methyl transferase (COMT) degrades dopamine, epinephrine and norepinephrine. The functional polymorphism (COMT Val108/158Met) affects COMT activity, with the valine (Val) variant associated with higher and the methionine (Met) variant with lower COMT activity. This polymorphism is associated with aggressive and suicidal behaviour, but the literature data on this relationship is contradictory and inconsistent. The hypothesis of this study was that Met allele carriers with alcohol dependence will have a higher frequency of suicide attempts compared to other genotypes. Participants were 312 male and 81 female medication-free patients with alcohol dependence and 487 male and 122 female unrelated, non-suicidal medication-free Caucasian healthy subjects. Our results showed significant (χ2 test with standardized residuals) differences in the frequencies of COMT variants in all alcoholics, alcoholics with different comorbid diagnoses, and in male but not in female alcoholics, with or without suicide attempts. Male alcoholic suicide attempters, compared to male non-attempters, had the higher frequency of Met/Met genotype or Met allele, and significantly (Kruskal-Wallis ANOVA on ranks and Mann-Whitney test) higher aggression and depression scores. These results confirmed the associations between Met allele and aggressive behaviour or violent suicide attempts in various psychiatric diagnoses, and suggested that Met allele of the COMT Val108/158 Met might be used as an independent biomarker of suicidal behaviour across different psychopathologies.

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.

Inhibitory and disinhibitory effects of psychomotor stimulants and depressants on the sexual behavior of male and female rats

Drugs of abuse comprise several pharmacological classes, including psychomotor stimulants, such as amphetamine and cocaine, and CNS depressants, such as morphine and alcohol. Few studies have examined the effects of those drugs systematically on human sexual behavior, although substantial clinical and epidemiological literatures suggest that drugs in both classes either inhibit sexual responding or can be "prosexual" in certain situations, thereby increasing the potential of risky sexual activity and the spread of sexually transmitted diseases. This paper reviews original data in rats showing that both classes of drug inhibit or disinhibit sexual behavior depending on the animal's baseline level of sexual responding, hormonal status, whether the drug is given acutely or chronically, and whether the animal has learned to inhibit sexual responding toward nonreceptive partners or in the presence of conditioned olfactory cues that predict sexual nonreward.

Neuroprotective actions of brain aromatase

The steroidal regulation of vertebrate neuroanatomy and neurophysiology includes a seemingly unending list of brain areas, cellular structures and behaviors modulated by these hormones. Estrogens, in particular have emerged as potent neuromodulators, exerting a range of effects including neuroprotection and perhaps neural repair. In songbirds and mammals, the brain itself appears to be the site of injury-induced estrogen synthesis via the rapid transcription and translation of aromatase (estrogen synthase) in astroglia. This induction seems to occur regardless of the nature and location of primary brain damage. The induced expression of aromatase apparently elevates local estrogen levels enough to interfere with apoptotic pathways, thereby decreasing secondary degeneration and ultimately lessening the extent of damage. There is even evidence suggesting that aromatization may affect injury-induced cytogenesis. Thus, aromatization in the brain appears to confer neuroprotection by an array of mechanisms that involve the deceleration and acceleration of degeneration and repair, respectively. We are only beginning to understand the factors responsible for the injury-induced transcription of aromatase in astroglia. In contrast, much of the manner in which local and circulating estrogens may achieve their neuroprotective effects has been elucidated. However, gaps in our knowledge include issues about the cell-specific regulation of aromatase expression, steroidal influences of aromatization distinct from estrogen formation, and questions about the role of constitutive aromatase in neuroprotection. Here we describe the considerable consensus and some interesting differences in knowledge gained from studies conducted on diverse animal models, experimental paradigms and preparations towards understanding the neuroprotective actions of brain aromatase.

Dopaminergic regulation of mate competition aggression and aromatase-Fos colocalization in vasotocin neurons

Recent experiments demonstrate that aggressive competition for potential mates involves different neural mechanisms than does territorial, resident-intruder aggression. However, despite the obvious importance of mate competition aggression, we know little about its regulation. Immediate early gene experiments show that in contrast to territorial aggression, mate competition in finches is accompanied by the activation of neural populations associated with affiliation and motivation, including vasotocin (VT) neurons in the medial bed nucleus of the stria terminalis (BSTm) and midbrain dopamine (DA) neurons that project to the BSTm. Although VT is known to facilitate mate competition aggression, the role of DA has not previously been examined. We now show that in male zebra finches (Taeniopygia guttata), mate competition aggression is inhibited by the D(2) agonist quinpirole, though not the D(1) agonist SKF-38393 or the D(4) agonist PD168077. The D(3) agonist 7-OH-DPAT also inhibited aggression, but only following high dose treatment that may affect aggression via nonspecific binding to D(2) receptors. Central VT infusion failed to restore D(2) agonist-inhibited aggression in a subsequent experiment, demonstrating that D(2) does not suppress aggression by inhibiting VT release from BSTm neurons. In a final experiment, we detected D(2) agonist-induced increases in immunofluorescent colocalization of the product of the immediate early gene c-fos and the steroid-converting enzyme aromatase (ARO) within VT neurons of the BSTm. Thus, although VT and DA appear to influence mate competition aggression independently, BSTm VT neurons are clearly influenced by the activation of D(2) receptors, which may modify future behaviors.

Experience modulates both aromatase activity and the sensitivity of agonistic behaviour to testosterone in black-headed gulls

In young black-headed gulls (Larus ridibundus), exposure to testosterone increases the sensitivity of agonistic behaviour to a subsequent exposure to this hormone. The aim of this paper is twofold: to analyze whether social experience, gained during testosterone exposure, mediates this increase in hormonal sensitivity (priming), and whether this in turn is mediated by an increase in central aromatase activity. To this end, we performed three experiments. In the first juvenile gulls were exposed to two consecutive treatments with testosterone (T1 and T2), with more than a week interval in between. During T1, half of the birds were housed in social isolation (Iso) and the other half in groups (Soc). All birds were re-housed in a new social situation during the second treatment. The increase in social behaviour during T2 was significantly more rapid in Soc than Iso birds. In experiment 2 we show that 17beta-estradiol treatment facilitates the behaviour measured in experiment 1. In experiment 3 we used a set-up comparable with that of experiment 1, but birds were sacrificed early in the T2 period. Aromatase activity in the preoptic area and the hypothalamus was measured using the tritiated water releasing method. In some parts of the preoptic area and hypothalamus aromatase activity was higher in Soc birds relative to Iso birds. The results indicate that social experience can modulate the increase of social behaviour to testosterone via modulation of aromatase activity and independently of actual hormone levels.

Molecular characterization of the injury-induced aromatase transcript in the adult zebra finch brain

In the zebra finch (Taeniopygia guttata), the aromatase gene is transcribed from one of two promoters resulting in two transcripts constitutively expressed in brain or ovary. These transcripts differ only in Exon 1 which lies in the 5' un-translated region (UTR). An inducible form of aromatase is expressed following brain injury in glia. Towards characterizing this transcript, we (a) examined the up-regulation of amplicons within the aromatase transcript using quantitative PCR (qPCR), (b) performed 5' and 3' rapid amplification of cDNA ends (RACE) on injured brain RNA and (c) sequenced the injury-induced aromatase transcript. qPCR suggested that inducible aromatase may contain a novel 3'UTR. However, neither 3' nor 5' RACE revealed novel UTRs in the injured telencephalon. We then sequenced aromatase from injured entopallium, a region that lacks detectable constitutive aromatase. Inducible aromatase was identical in sequence to the known neural aromatase transcript. These data suggest that injury-induced aromatase differs from ovarian, but is indistinguishable from neuronal aromatase. We suggest that an injury-specific signal in glia may modulate aromatase transcription. Alternatively, injury-induced aromatase transcription may be silenced under constitutive conditions. To the best of our knowledge, this is the first report that documents the sequence of inducible aromatase in any vertebrate.

Interference of endocrine disrupting chemicals with aromatase CYP19 expression or activity, and consequences for reproduction of teleost fish

Many natural and synthetic compounds present in the environment exert a number of adverse effects on the exposed organisms, leading to endocrine disruption, for which they were termed endocrine disrupting chemicals (EDCs). A decrease in reproduction success is one of the most well-documented signs of endocrine disruption in fish. Estrogens are steroid hormones involved in the control of important reproduction-related processes, including sexual differentiation, maturation and a variety of others. Careful spatial and temporal balance of estrogens in the body is crucial for proper functioning. At the final step of estrogen biosynthesis, cytochrome P450 aromatase, encoded by the cyp19 gene, converts androgens into estrogens. Modulation of aromatase CYP19 expression and function can dramatically alter the rate of estrogen production, disturbing the local and systemic levels of estrogens. In the present review, the current progress in CYP19 characterization in teleost fish is summarized and the potential of several classes of EDCs to interfere with CYP19 expression and activity is discussed. Two cyp19 genes are present in most teleosts, cyp19a and cyp19b, primarily expressed in the ovary and brain, respectively. Both aromatase CYP19 isoforms are involved in the sexual differentiation and regulation of the reproductive cycle and male reproductive behavior in diverse teleost species. Alteration of aromatase CYP19 expression and/or activity, be it upregulation or downregulation, may lead to diverse disturbances of the above mentioned processes. Prediction of multiple transcriptional regulatory elements in the promoters of teleost cyp19 genes suggests the possibility for several EDC classes to affect cyp19 expression on the transcriptional level. These sites include cAMP responsive elements, a steroidogenic factor 1/adrenal 4 binding protein site, an estrogen-responsive element (ERE), half-EREs, dioxin-responsive elements, and elements related to diverse other nuclear receptors (peroxisome proliferator activated receptor, retinoid X receptor, retinoic acid receptor). Certain compounds including phytoestrogens, xenoestrogens, fungicides and organotins may modulate aromatase CYP19 activity on the post-transcriptional level. As is shown in this review, diverse EDCs may affect the expression and/or activity of aromatase cyp19 genes through a variety of mechanisms, many of which need further characterization in order to improve the prediction of risks posed by a contaminated environment to teleost fish population.

Sexually dimorphic immunoreactivity of galanin and colocalization with arginine vasotocin in the chicken brain (Gallus gallus domesticus)

The bed nucleus of the stria terminalis medialis (BSTM) of adult chickens (Gallus gallus domesticus) was previously shown to synthesize arginine vasotocin (AVT) in males only and coincides spatially and temporally with steroid activity regulating male reproductive behavior. Galanin has been shown to be a potent modulator of the behavioral and neuroendocrine responses in the mammalian BSTM and in other sexually dimorphic brain regions. In the present study of adult chickens the morphological relationship of AVT and galanin was examined by immunohistochemical analysis of two limbic structures, the BSTM and the lateral septum (SL). The analysis also included the hypothalamic nuclei supraopticus (SON) and paraventricularis (PVN). In males galanin and AVT were both synthesized in the BSTM, while in females neither galanin nor AVT was present. Furthermore, in the males galanin and AVT were colocalized in the majority of neurons within BSTM and in fibers of the SL. In both sexes galanin neurons in the PVN were scattered between the distinct clusters of AVT neurons and there was no colocalization of galanin and AVT in single PVN neurons. Furthermore, AVT immunoreactivity was significantly higher in the SON than in the PVN in both sexes. In the SON, galanin was colocalized with AVT in significantly more neurons in hens than in males (P </= 0.05%). These results demonstrate that the distributions of galanin and AVT are sexually dimorphic not only in the limbic BSTM but also in the hypothalamic SON. It is tempting to speculate that galanin in the SON is involved in regulation of oviposition as an AVT-dependent female-specific function.

Sex-specific effects of androgen and estrogen on proliferation of the embryonic chicken hypothalamic neurons

Effects of androgen and estrogen on proliferation of hypothalamic neurons were evaluated by a chicken hypothalamic neuron-glia coculture model. Hypothalamic cells were dispersed from 17-day-old embryos and challenged with testosterone (T) and 17beta-estradiol (E2) alone or combined with androgen receptor antagonist flutamide, estrogen receptor antagonist tamoxifen, or aromatase inhibitor letrozole for 48 h. The neuron number was counted and the proliferating cells were identified by immunocytochemistry of proliferating cell nuclear antigen (PCNA) and 5-bromo-2-deoxyuridine (BrdU) incorporation. Results showed that both E2 and T stimulated proliferation of hypothalamic neurons. E2 showed more intensive effect on females and this promoting effect was abrogated by tamoxifen. T played more intensive effect on males and the effect was inhibited by flutamide, tamoxifen, or letrozole. The above results indicated that E2 stimulated neuron proliferation through estrogenic actions with more sensitive effect on females and T promoted neuron proliferation through both androgenic and estrogenic actions with more intense effect on males. These observations suggested that steroid hormones influence the proliferation of hypothalamic neurons in a sexually dimorphic manner during the development of chicken embryos.

Display activity and seasonality of faecal sexual steroids in male great bustard (Otis tarda L.)

The non-invasive faecal sampling and RIA was used to measure faecal equivalents of testosterone (T), dehydroepiandrosterone (DHEA), oestradiol-17beta (E2) and progesterone (P4) in juvenile and adult great bustard males. Possible connections of diurnal and seasonal changes of sexual steroid levels and display activity were studied. Correlations were found between sexual steroid equivalent levels of faeces and display activity and agonistic behaviour in the different phases of annual cycle of adult males. In early display period increasing levels of androgens were measured, during main display period very high androgen dominance was observable against E2 and P4. During postnuptial moult strong T decrease and DHEA and P4 increase were detected. Elevation of E2 was measured during wintering. In juveniles level of DHEA was higher than level of T suggesting its importance in immature males. Decrease of T was detected between reproductive period and postnuptial moult and DHEA between reproduction and wintering, accompanying with E2 elevation. The inhibiting effect of inclement weather on gonad functions also was detected in our study. We suppose that the unexpected cold weather with strong wind depressed the levels of androgens both in juveniles and adults and the increase of faecal E2 was also detected.

Molecular genetic findings in suicidal behavior: what is beyond the serotonergic system?

Various studies provide consistent evidence for a genetic component in suicidal behavior. First molecular genetic studies concentrated on genes of the serotonergic system based on the biochemical evidence that serotonergic neurotransmission is implicated in this behavior. Furthermore, genes of the dopaminergic and noradrenergic neurotransmitter systems have also been the subjects of investigations in this context. Some epidemical and clinical studies showed that low serum cholesterol levels are associated with suicidal behavior and genes involved in these pathways have been investigated. Microarray experiments provide the possibility of genome-wide gene expression analysis and help to investigate associated molecular mechanisms. The aim of this article is to review molecular genetic studies in suicidal behavior and to emphasize findings on new genes.

Rapid decreases in preoptic aromatase activity and brain monoamine concentrations after engaging in male sexual behavior

In Japanese quail, as in rats, the expression of male sexual behavior over relatively long time periods (days to weeks) is dependent on the local production of estradiol in the preoptic area via the aromatization of testosterone. On a short-term basis (minutes to hours), central actions of dopamine as well as locally produced estrogens modulate behavioral expression. In rats, a view of and sexual interaction with a female increase dopamine release in the preoptic area. In quail, in vitro brain aromatase activity (AA) is rapidly modulated by calcium-dependent phosphorylations that are likely to occur in vivo as a result of changes in neurotransmitter activity. Furthermore, an acute estradiol injection rapidly stimulates copulation in quail, whereas a single injection of the aromatase inhibitor vorozole rapidly inhibits this behavior. We hypothesized that brain aromatase and dopaminergic activities are regulated in quail in association with the expression of male sexual behavior. Visual access as well as sexual interactions with a female produced a significant decrease in brain AA, which was maximal after 5 min. This expression of sexual behavior also resulted in a significant decrease in dopaminergic as well as serotonergic activity after 1 min, which returned to basal levels after 5 min. These results demonstrate for the first time that AA is rapidly modulated in vivo in parallel with changes in dopamine activity. Sexual interactions with the female decreased aromatase and dopamine activities. These data challenge established views about the causal relationships among dopamine, estrogen action, and male sexual behavior.

Inhibition of steroid receptor coactivator-1 blocks estrogen and androgen action on male sex behavior and associated brain plasticity

Studies of eukaryotic gene expression demonstrate the importance of nuclear steroid receptor coactivators in mediating efficient gene transcription. However, little is known about the physiological role of these coactivators in vivo. In Japanese quail, the steroid receptor coactivator-1 (SRC-1) is broadly expressed in steroid-sensitive brain areas that control the expression of male copulatory behavior, and we investigated the role of this coactivator by antisense technology. Daily intracerebroventricular injections of locked nucleic acid (LNA) antisense (AS) oligonucleotides targeting SRC-1 significantly reduced the expression of androgen- and estrogen-dependent male-typical sexual behaviors compared with control animals that received the vehicle alone or scrambled oligonucleotides. Sexual behavior was restored and even enhanced within 48 h after interruption of LNA injections. Western blot analysis confirmed the decrease of SRC-1 expression in AS animals and suggested an overexpression 48 h after the end of injections. The effects of SRC-1 knock-down on behavior correlated with a reduction in volume of the preoptic medial nucleus (POM) when its borders were defined by Nissl staining or by aromatase immunohistochemistry. The amount of aromatase-immunoreactive material in POM was also reduced in the AS compared with the control group. Previous work on SRC-1 knock-out mice raised questions about the importance of this specific coactivator in the regulation of reproductive behavior and development of sexually dimorphic structures in the CNS. Together, the present findings indicate that SRC-1 modulates steroid-dependent gene transcription and behavior and highlight the rapid time course of steroid-induced brain plasticity in adult quail.

Dopamine modulates male sexual behavior in Japanese quail in part via actions on noradrenergic receptors

In rats, dopamine (DA) facilitates male sexual behavior through its combined action on D1- and D2-like receptors, in the medial preoptic area (MPOA) as well as other brain areas. In Japanese quail, systemic injections of dopaminergic drugs suggested a similar pharmacology but central injections have never been performed. Recent electrophysiological experiments demonstrated that DA effects in the MPOA of quail are mediated mainly through the activation of alpha2-noradrenergic receptors. Previous studies of DA action on behavior used specific dopaminergic agonists/antagonists and therefore unintentionally avoided the potential cross-reaction with alpha2-receptors. The present study was thus designed to investigate directly the effects of DA on male sexual behavior and to test whether the interaction of DA with heterologous receptors affects this behavior. Intracerebroventricular (i.c.v.) injection of DA or NE inhibited copulation in a dose-dependent manner. Systemic injections of yohimbine, an alpha2-noradrenergic antagonist, modulated copulation in a bimodal manner depending on the dose injected. Interestingly, a behaviorally ineffective dose of yohimbine markedly reduced the inhibitory effects of DA when injected 15min before. Together, these results show for the first time that i.c.v. injections of DA itself inhibit male sexual behavior in quail and suggest that the interaction of DA with alpha2-receptors has behavioral significance.

Estrogen receptor beta is expressed in human embryonic brain cells and is regulated by 17beta-estradiol

In order to study estrogen effects on developing human neurons, we have established primary cultures of neurons and glia from 8-13-week human embryo cortex and spinal cord. The neuronal identity of the cultures was verified using the neuronal synaptic vesicle and neuronal endosomal membrane markers synaptotagmin, synapsin and synaptophysin, and the glial contribution to the mixed glial-neuronal cultures was verified using the glial marker glial fibrillary acidic protein (GFAP). We here report expression of estrogen receptor beta (ERbeta) in these cells using RT-PCR and sequencing, RNAse protection assay, immunohistochemistry and immunoblotting. We found that both neuronal and mixed glial-neuronal cultures expressed ERbeta. Treatment with 17beta-estradiol gave an increased expression of ERbeta in both types of cultures. These results suggest that ERbeta is expressed in fetal brain and thus may mediate effects of estrogen in the developing nervous system. Furthermore, the results suggest that expression of ERbeta in fetal brain may be regulated by estrogen.

Association between catechol-O-methyltransferase functional polymorphism and male suicide completers

Suicide has been suggested to involve catecholaminergic dysfunction and to be related to genetics. Catechol-O-methyltransferase (COMT) 158Val/Met polymorphism (GenBank Accession No. Z26491) is a polymorphism of the gene encoding COMT, a major enzyme in catecholamine inactivation. The COMT 158Val/Met polymorphism affects COMT activity, that is, the alleles encoding Val and Met are associated with relatively high and relatively low COMT activity, respectively. In this study, we hypothesized that the COMT 158Val/Met polymorphism is associated with suicide. The study population consisted of 163 suicide completers (112 males and 51 females). We found that the genotype distribution of the COMT 158Val/Met polymorphism was significantly different between male suicide completers and male controls (p=0.036), while the frequency of the Val/Val genotype, a high-activity COMT genotype, was significantly less in male suicide completers than in male controls (OR: 0.52; 95% CL: 0.31-0.89; p=0.016). However, this was not the case in females. Our results suggest that the Val/Val genotype is a protective factor against suicide in males.

Male Japanese quails with female brains do not show male sexual behaviors

During embryonic development, gonadal steroid hormones (androgens and estrogens) are thought to organize the sexual differentiation of the brain in the heterogametic sexes of higher vertebrates (males in mammals, females in birds). Brain differentiation of the homogametic sexes is thought to proceed by default, not requiring sex hormones for sex-specific organization. In gallinaceous birds such as the Japanese quail, female brain organization is thought to develop via estrogen-dependent demasculinization of a default male brain phenotype. We performed male donor-to-female host (MF), female-to-male (FM), male-to-male (MM), and female-to-female (FF) isotopic, isochronic transplantation of the forebrain primordium in Japanese quail embryos before gonadal differentiation had occurred; brain chimeras had a forebrain (including the hypothalamus) originating exclusively from donor cells. MM, FF, and MF chimeras all showed sexual behavior governed by the genetic sex of the host. In contrast, FM chimeras (genetically female forebrain, all other tissues genetically male) showed no mounting and only rudimentary crowing behavior. Although MM, FF, MF, and FM chimeras all showed host-typical production of steroid hormones during embryonic life, only FM chimeras were hypogonadal, had atypical low levels of circulating testosterone in adulthood, and showed reduction (crowing) or absence (mounting) of reproductive behaviors. Morphological features of the medial preoptic nucleus (a sexually dimorphic brain area) also were not male-like in FM males. These data demonstrate a brain-intrinsic, genetically determined component that organizes the sex-typical production of gonadal hormones in adulthood and call for a reevaluation of the mechanisms underlying brain sexual differentiation in other higher-vertebrate species.

Interactions between aromatase (estrogen synthase) and dopamine in the control of male sexual behavior in quail

In male quail, like in other vertebrates including rodents, testosterone acting especially through its estrogenic metabolites is necessary for the activation of male sexual behavior. Also, the administration of dopamine agonists and antagonists profoundly influences male sexual behavior. How the steroid-sensitive neural network and dopamine interact physiologically, remains largely unknown. It is often implicitly assumed that testosterone or its metabolite estradiol, stimulates male sexual behavior via the modification of dopaminergic transmission. We have now identified in quail two possible ways in which dopamine could potentially affect sexual behavior by modulating the aromatization of testosterone into an estrogen. One is a long-acting mechanism that presumably involves the modification of dopaminergic transmission followed by the alteration of the genomic expression of aromatase. The other is a more rapid mechanism that does not appear to be dopamine receptor-mediated and may involve a direct interaction of dopamine with aromatase (possibly via substrate competition). We review here the experimental data supporting the existence of these controls of aromatase activity by dopamine and discuss the possible contribution of these controls to the activation of male sexual behavior.

Phosphorylation processes mediate rapid changes of brain aromatase activity

The enzyme aromatase (also called estrogen synthase) that catalyzes the transformation of testosterone (T) into estradiol plays a key limiting role in the action of T on many aspects of reproduction. The distribution and regulation of aromatase in the quail brain has been studied by radioenzyme assays on microdissected brain areas, immunocytochemistry, RT-PCR and in situ hybridization. High levels of aromatase activity (AA) characterize the sexually dimorphic, steroid-sensitive medial preoptic nucleus (POM), a critical site of T action and aromatization for the activation of male sexual behavior. The boundaries of the POM are clearly outlined by a dense population of aromatase-containing cells as visualized by both immunocytochemistry and in situ hybridization histochemistry. Aromatase synthesis in the POM is controlled by T and its metabolite estradiol, but estradiol receptors alpha (ERalpha) are not normally co-localized with aromatase in this brain area. Estradiol receptor beta (ERbeta) has been recently cloned in quail and localized in POM but we do not yet know whether ERbeta occurs in aromatase cells. It is therefore not known whether estrogens regulate aromatase synthesis directly or by affecting different inputs to aromatase cells as is the case with the gonadotropin releasing hormone neurons. The presence of aromatase in presynaptic boutons suggests that locally formed estrogens may exert part of their effects by non-genomic mechanisms at the membrane level. Rapid effects of estrogens in the brain that presumably take place at the neuronal membrane level have been described in other species. If fast transduction mechanisms for estrogen are available at the membrane level, this will not necessarily result in rapid changes in brain function if the availability of the ligand does not also change rapidly. We demonstrate here that AA in hypothalamic homogenates is rapidly down-regulated by exposure to conditions that enhance protein phosphorylation (addition of Ca2+, Mg2+, ATP). This inhibition is blocked by kinase inhibitors which supports the notion that phosphorylation processes are involved. A rapid (within minutes) and reversible regulation of AA is also observed in hypothalamic explants incubated in vitro and exposed to high Ca2+ levels (K+-induced depolarization, treatment by thapsigargin, by kainate, AMPA or NMDA). The local production and availability of estrogens in the brain can therefore be rapidly changed by Ca2+ based on variation in neurotransmitter activity. Locally-produced estrogens are as a consequence available for non-genomic regulation of neuronal physiology in a manner more akin to the action of a neuropeptide/neurotransmitter than previously thought.

The control of preoptic aromatase activity by afferent inputs in Japanese quail

This review summarizes current knowledge on the mechanisms that control aromatase activity in the quail preoptic area, a brain region that plays a key role in the control of reproduction. Aromatase and aromatase mRNA synthesis in the preoptic area are enhanced by testosterone and its metabolite estradiol, but estradiol receptors of the alpha subtype are not regularly colocalized with aromatase. Estradiol receptors of the beta subtype are present in the preoptic area but it is not yet known whether these receptors are colocalized with aromatase. The regulation by estrogen of aromatase activity may be, in part, trans-synaptically mediated, in a manner that is reminiscent of the ways in which steroids control the activity of gonadotropic hormone releasing hormone neurons. Aromatase-immunoreactive neurons are surrounded by dense networks of vasotocin-immunoreactive and tyrosine hydroxylase-immunoreactive fibers and punctate structures. These inputs are in part steroid-sensitive and could therefore mediate the effects of steroids on aromatase activity. In vivo pharmacological experiments indicate that catecholaminergic depletions significantly affect aromatase activity presumably by modulating aromatase transcription. In addition, in vitro studies on brain homogenates or on preoptic-hypothalamic explants show that aromatase activity can be rapidly modulated by a variety of dopaminergic compounds. These effects do not appear to be mediated by the membrane dopamine receptors and could involve changes in the phosphorylation state of the enzyme. Together, these results provide converging evidence for a direct control of aromatase activity by catecholamines consistent with the anatomical data indicating the presence of a catecholaminergic innervation of aromatase cells. These dopamine-induced changes in aromatase activity are observed after several hours or days and presumably result from changes in aromatase transcription but rapid non-genomic controls have also been identified. The potential significance of these processes for the physiology of reproduction is critically evaluated.

Distribution of DARPP-32 immunoreactive structures in the quail brain: anatomical relationship with dopamine and aromatase

We recently demonstrated that dopamine (DA) as well as different DA receptor agonists and antagonists are able to decrease within a few minutes the aromatase activity (AA) measured in vitro in homogenates or in explants of the quail preoptic area - hypothalamus. In addition, DA also appears to regulate AA, in vivo presumably by modifying enzyme synthesis. The cellular mechanisms and the anatomical substrate that mediate these controls of AA by DA are poorly understood. Tyrosine hydroxylase-immunoreactive (TH-ir) fibers and punctate structures have been previously observed in close vicinity of aromatase-immunoreactive (ARO-ir) cells in the quail medial preoptic nucleus (POM) and bed nucleus striae terminalis (BST) but these fibers could reflect a noradrenergic innervation. We also do not know whether aromatase cells are dopaminoceptive. The main goal of the present study was therefore to bring more information on the anatomical relationships between aromatase expressing neurons and the dopaminergic system in the quail brain. The visualization by immunocytochemistry of DA and of the D1 receptor associated protein DARPP-32 was used to address these questions. DA-ir fibers were observed in the quail forebrain and overlapped extensively with nuclei that contain high densities of ARO-ir cells such as the POM and BST. This confirms that the previously reported TH-ir innervation of ARO-ir cells is, at least in part, of dopaminergic nature. DARPP-32-immunoreactive cells were found in periventricular position throughout the hypothalamus. DARPP-32-ir cells were also observed in telencephalic and mesencephalic areas (hyperstriatum accessorium, paleostriatum, nucleus intercollicularis, optic tectum). DARPP-32-ir fibers were widespread in tel-, di-, and mes-encephalic areas. The highest densities of immunoreactive fibers were detected in the lobus parolfactorius, paleostriatum augmentatum and substantia nigra/area ventralis of Tsai. In double-labeled sections, appositions between DARPP-32 fibers and ARO-ir cells were present in the dorsolateral POM and BST but DARPP-32 immunoreactivity was not detected in the ARO-ir perikarya (no colocalization). These data confirm the presence of a dopaminoceptive structures within the main cell clusters of ARO-ir cells in the quail brain but provide no evidence that these ARO-ir cells are themselves dopaminoceptive. Because DARPP-32 is not present in all types of cells expressing DA receptors, the presence of DA receptors that would not be associated with DARPP-32 in ARO-ir cells still remains to be investigated

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.

Ontogeny of aromatase and tyrosine hydroxylase activity and of aromatase-immunoreactive cells in the preoptic area of male and female Japanese quail

The aromatization of testosterone into oestrogens plays a key role in the control of many behavioural and physiological aspects of reproduction. In the quail preoptic area (POA), aromatase activity and the number of aromatase-immunoreactive (ARO-ir) cells are sexually differentiated (males > females). This sex difference is implicated in the control of the sexually dimorphic behavioural response of quail to testosterone. We analysed the ontogenetic development of this sex difference by measuring aromatase activity and counting ARO-ir cells in the POA of males and females from day 1 post hatch to sexual maturity. We investigated in parallel another enzyme: tyrosine hydroxylase, the rate limiting step in catecholamine synthesis. Between hatching and 4 weeks of age, aromatase activity levels were low and equal in males and females. Aromatase activity then markedly increased in both sexes when subjects initiated their sexual maturation but this increase was more pronounced in males so that a marked difference in aromatase activity was present in 6 and 8 week-old subjects. Tyrosine hydroxylase activity progressively increased with age starting immediately after hatching and there was no abrupt modification in the slope of this increase when birds became sexually mature. No sex difference was detected in the activity of this enzyme. The number of ARO-ir cells in the POA progressively increased with age starting at hatching. No sex difference in ARO-ir cell numbers could be detected before subjects reached full sexual maturity. The analysis of the three-dimensional organization of ARO-ir cells in the POA revealed that, with increasing ages, ARO-ir cells acquire a progressively more lateral position: they are largely periventricular in young birds but they are found at higher density in the lateral part of the medial preoptic nucleus in adults. These data indicate that aromatase activity differentiates sexually when birds reach sexual maturity presumably under the activating effects of the increased testosterone levels in males. The number of ARO-ir cells, however, begins to increase in a non sexually differentiated manner before the rise in plasma testosterone in parallel with the increased tyrosine hydroxylase activity. Whether this temporal coincidence results from a general ontogenetic pattern or from more direct causal links remains to be established.

Photo-induction of hypothalamic gonadotrophin releasing hormone-I mRNA in the domestic chicken: a role for oestrogen?

Photoinduced changes in GnRH neuronal function were investigated in prepubertal and in midpubertal cockerels and somatically mature hens. Photostimulation of short day mid-pubertal cockerels and somatically mature out-of-lay hens for 7 days significantly increased (P<0.05) total hypothalamic gonadotrophin releasing hormone-I (GnRH-I) mRNA. The increase in GnRH-I mRNA was associated with increased (P<0.05) plasma LH in the hens but not mid-pubertal cockerels. Photostimulation of short day prepubertal cockerels for 7 days also stimulated LH release (P<0.05) but in contrast did not increase total hypothalamic GnRH-I mRNA. Plasma LH and hypothalamic GnRH-I mRNA were depressed in (P<0.001) short day prepubertal cockerels chronically treated with oestradiol benzoate (0.5 mg/kg, on alternate days). However, photostimulation of oestrogenized prepubertal cockerels for 7 days stimulated LH release (P<0.001) and increased hypothalamic GnRH-I mRNA (P<0.001). It is concluded that photostimulatory inputs to GnRH neurones have the potential to increase GnRH-I mRNA transcription or stability and to increase GnRH-I release. The extent to which increased levels of GnRH-I mRNA or increased GnRH release from GnRH neurones are observed after photostimulation may depend on the interaction between the drive on GnRH-I neurone function, which increases at the onset of puberty, and the inhibitory action of oestrogen produced locally in the hypothalamus.

Pharmacological characterization, anatomical distribution and sex differences of the non-NMDA excitatory amino acid receptors in the quail brain as identified by CNQX binding

The distribution of non-N-methyl-D-aspartate binding sites was studied in coronal and sagittal sections through the brain of adult Japanese quail by quantitative autoradiography, using tritiated 6-cyano-7-nitroquinoxaline-2,3-dione as a radioligand. Saturation binding experiments were, in addition, carried out in areas showing high levels of binding (cerebellar molecular layer, nucleus anterior medialis and nucleus infundibularis) and demonstrated that the binding of tritiated ligand was specific and saturable. Competition studies with alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid and kainic acid indicated that kainic acid strongly inhibited ligand binding in all brain areas. alpha-Amino-3-hydroxy-methyl-4-isoxazole propionic acid was only a weak inhibitor in the hypothalamic nuclei whereas in the cerebellar molecular layer both high and low affinity inhibitions were detected. The highest binding levels of tritiated ligand were observed in the molecular layer of the cerebellum. Very high levels of binding were detected in various preoptic/hypothalamic sites including the nucleus suprachiasmaticus pars medialis, nucleus anterior medialis hypothalami, nucleus infundibularis, nucleus mammillaris medialis, nucleus posteromediale hypothalami and nucleus hypothalami ventromedialis. High levels of binding were also detected in the bulbus olfactorius, bed nucleus commissuralis anterior, bed nucleus commissuralis pallii, nucleus accumbens, bed nucleus striae terminalis and nucleus interpeduncularis. In the preoptic area/hypothalamus, high levels of binding were clearly present in all areas that contain gonadotropin releasing hormone cells or fibers. In the pons and mesencephalon, moderate levels of binding were associated with catecholaminergic areas such as the area ventralis tegmentalis (area ventralis of Tsai) and the locus coeruleus. Saturation analysis demonstrated the presence of a higher number of binding sites in females than in males in the cerebellar molecular layer, nucleus infundibularis and nucleus anterior medialis. This latter difference was confirmed in the one point assays that also identified higher levels of specific binding in the nucleus suprachiasmaticus pars medialis of males as compared with females. These anatomical data suggest a possible implication of non-N-methyl-D-aspartate receptors in the synthesis and/or release of both gonadotropin releasing hormone and catecholaminergic neurotransmitters that should now be tested by pharmacological experiments.

Neuroanatomical distribution and variations across the reproductive cycle of aromatase activity and aromatase-immunoreactive cells in the pied flycatcher (Ficedula hypoleuca)

The anatomical distribution and seasonal variations in aromatase activity and in the number of aromatase-immunoreactive cells were studied in the brain of free-living male pied flycatchers (Ficedula hypoleuca). A high aromatase activity was detected in the telencephalon and diencephalon but low to negligible levels were present in the optic lobes, cerebellum, and brain stem. In the diencephalon, most aromatase-immunoreactive cells were confined to three nuclei implicated in the control of reproductive behaviors: the medial preoptic nucleus, the nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus. In the telencephalon, the immunopositive cells were clustered in the medial part of the neostriatum and in the hippocampus as previously described in another songbird species, the zebra finch. No immunoreactive cells could be observed in the song control nuclei. A marked drop in aromatase activity was detected in the anterior and posterior diencephalon in the early summer when the behavior of the birds had switched from defending a territory to helping the female in feeding the nestlings. This enzymatic change is presumably controlled by the drop in plasma testosterone levels observed at that stage of the reproductive cycle. No change in enzyme activity, however, was seen at that time in other brain areas. The number of aromatase-immunoreactive cells also decreased at that time in the caudal part of the medial preoptic nucleus but not in the ventromedial nucleus of the hypothalamus (an increase was even observed), suggesting that differential mechanisms control the enzyme concentration and enzyme activity in the hypothalamus. Taken together, these data suggest that changes in diencephalic aromatase activity contribute to the control of seasonal variations in reproductive behavior of male pied flycatchers but the role of the telencephalic aromatase in the control of behavior remains unclear at present.

New insights into the regulation and function of brain estrogen synthase (aromatase)

In the brain, conversion of androgens into estrogens by the enzyme aromatase (estrogen synthase) is a key mechanism by which testosterone regulates many physiological and behavioral processes, including the activation of male sexual behavior, brain sexual differentiation and negative feedback effects of steroid hormones on gonadotropin secretion. Studies on the distribution and regulation of brain aromatase have led to a new perspective on the control and function of this enzyme. A growing body of evidence indicates that the estrogen regulation of aromatase is, at least in part, trans-synaptic. Afferent catecholamine pathways appear to regulate aromatase activity in some brain areas and thereby provide a way for environmental cues to modulate this enzyme. The localization of aromatase in pre-synaptic boutons suggests possible roles for estrogens at the synapse.

Distribution and effects of testosterone on aromatase mRNA in the quail forebrain: a non-radioactive in situ hybridization study

A number of studies have been devoted to the analysis of the anatomical distribution, control by steroids and functional significance of aromatase (the enzyme metabolizing testosterone into 17beta-estradiol) in the quail brain. In particular, the sexually dimorphic nucleus preopticus medialis has been the main focus of investigation because testosterone aromatization in this structure mediates the activation of male sexual behavior and aromatase activity is itself testosterone-dependent in this nucleus. No information on the anatomical distribution of aromatase gene expression is, however, available so far in this avian species. In the present study we applied a non-radioactive in situ hybridization technique to describe the distribution of aromatase mRNA containing neurons in the quail prosencephalon. We also analyzed, at a neuronal level of resolution, the induction by testosterone of this mRNA in the medial preoptic nucleus. Dense clusters of aromatase gene expressing neurons were observed within the medial preoptic nucleus, the nucleus of the stria terminalis, the ventro-medial hypothalamus and the tuberal region. Scattered neurons expressing lower levels of aromatase mRNA were also found in the dorsal thalamic area and central gray. The specificity of the staining was confirmed by demonstrating the absence of signal in sections that had been hybridized with a sense probe. Moreover, the distribution of the aromatase mRNA containing cells completely overlapped with the distribution of the aromatase-immunoreactive cells. Aromatase-mRNA expression was controlled by testosterone (or its metabolites) in the entire medial preoptic nucleus. Castration resulted in a decrease in the number of aromatase mRNA-containing cells and this effect was totally reversed by testosterone treatment. These data further support the idea that testosterone regulates the rate of its own aromatization by modulating the expression of aromatase rather than by acting at a post transcriptional level.

Extrahepatic cytochrome P450: role in in situ toxicity and cell-specific hormone sensitivity

It is clear that members of the Cytochrome P450 supergene family are responsible for the majority of activations of procarcinogens to ultimate carcinogens in the body. These procarcinogens include the food mutagens (heterocyclic amines), pesticides, polycyclic aromatic hydrocarbons and nitrosamines. The Cyp P450 profile in a cell can indicate the capacity of that cell to form reactive metabolites. Furthermore, environmental factors, through their action on P450s, influence the fate of procarcinogens in a cell. This is because different isoforms of P450 are regulated differently by ethanol, diet and environmental inducers, have different substrate specificities and different propensity to be inhibited or activated by dietary components. Cyp P450 (through steroid inactivation), can also influence sensitivity of cells to hormones. Age and hormone related regulation of P450 isoforms such as 1A1, 2B1 and 2A3 in the breast suggest that in situ activation of carcinogens and hormone inactivation can occur in the breast. In the brain and endometrium most of the #P450 isoforms remain to be identified.

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.

A direct dopaminergic control of aromatase activity in the quail preoptic area

In the quail preoptic area (POA) anatomical and pharmacological data suggest that catecholamines may be implicated in the control of testosterone (T) aromatization into estrogens. The biochemical mechanism(s) mediating this control of the enzyme activity is (are) however unexplored. The present studies were carried out to investigate whether the catecholamines, dopamine (DA) and norepinephrine (NE) are able to directly affect aromatase activity (AA) measured during in vitro incubations of POA homogenates. AA was quantified in the POA-hypothalamus of adult male Japanese quail by measuring the tritiated water production from [1beta-3H]-androstenedione. Enzyme activity was linear as a function of the incubation time and of the protein content of homogenates. It exhibited a typical Michaelis-Menten kinetics, with an apparent Km of 2.8 nM and a Vmax of 266.6 fmol h(-1) mg wet weight(-1). AA was then measured at a substrate concentration of 25 nM in the presence of catecholamines and some of their receptor agonists or antagonists, at two concentrations, 10(-3) and 10(-6) M. Norepinephrine and prazosin (alpha1-adrenergic antagonist) had no or very limited effects on AA at both concentrations. In contrast, DA and some D1 and/or D2 receptor agonists (apomorphine[D1/D2], SKF-38393 [D1] and RU-24213 [D2]) depressed AA by 40 to 70% at the 10(-3) M concentration. One D2 receptor antagonist also produced a major inhibition of AA (sulpiride) while other antagonists either had no significant effect or only produced moderate decreases in enzyme activity (SCH-23390 [D1], spiperone [D2], pimozide [D2]) as did two DA indirect agonists, amfonelic acid and nomifensine. The inhibitory effect of the agonists was not antagonized by the less active antagonists, SCH-23390 [D1] or spiperone [D2]. Taken together these results suggest that the inhibitory effects do not involve specific binding of DA or its agonists/antagonists to dopaminergic receptors mediating changes in cAMP concentration. This conclusion is also supported by the observation that addition of dibutyryl cAMP did not change brain AA. It appears more likely that DA and dopaminergic drugs inhibit AA by a direct effect on the enzyme, as suggested by the competitive nature of DA and SKF-38393 inhibition of AA (Ki's of 59 and 84 microM, respectively). The functional significance of this effect should still be demonstrated but this mechanism may represent an important physiological pathway through which neurotransmitters could rapidly affect steroid-dependent processes such as the neural synthesis of estrogens. This would provide a mean by which environmental stimuli could affect reproductive behavior and physiology.

Genotype determining low catechol-O-methyltransferase activity as a risk factor for obsessive-compulsive disorder

In the present study, we address the role of the gene for catechol-O-methyltransferase (COMT), a key modulator of dopaminergic and noradrenergic neurotransmission, in the genetic predisposition to obsessive-compulsive disorder (OCD). We show that a common functional allele of this gene, which results in a 3- to 4-fold reduction in enzyme activity, is significantly associated in a recessive manner with susceptibility to OCD, particularly in males. This association is further supported by psychiatric evaluation of patients who carry microdeletions encompassing the comt gene. The mechanism underlying this sex-selective association remains to be defined and may include a sexual dimorphism in COMT activity, although close linkage with a nearby disease susceptibility locus cannot be excluded at this point.