Effects of apomorphine on sexual behavior in male quail

D2 receptor antagonism enhances cocaine-induced behavioral sensitization in female, but not male Japanese quail ( Coturnix japonica )

Sex differences in cocaine-induced behaviors are well established. In rodents, females show enhanced locomotion to cocaine over multiple trials compared with males, a behavioral response known as sensitization. Estradiol enhances cocaine-induced sensitization in female rats by agonizing dopaminergic activity within the brain. In female quail, cocaine does not increase locomotion regardless of increased estradiol. A higher D2:D1 dopamine receptor ratio in quail compared with rodents may explain this sex and species difference. The goal of the present work was to investigate the role of D2 receptors in cocaine-induced locomotion and sensitization in Japanese quail and to determine whether a greater D2 receptor availability contributed to the lack of cocaine-induced sensitization in female quail found in previous studies. Male and female quail were administered 0, 0.03, 0.05, or 0.07 mg/kg of eticlopride (Eti) followed by 10 mg/kg of cocaine or saline then immediately placed in open-field chambers. Distance traveled was recorded for 30 min daily for 7 days. In female quail, cocaine-induced sensitization was observed with 0.03 or 0.05 mg/kg Eti, but not in cocaine-only females. In male quail, cocaine-induced sensitization was observed similar to previous research. However, Eti did not enhance cocaine-induced locomotion or produce sensitization in male quail. The D2 receptor likely mediates cocaine's motor stimulating effects in quail. In females, this effect is more pronounced. Since high D2 availability is protective against stimulant abuse, Japanese quail may be a useful model for investigating the role of the D2 receptor in cocaine addiction, but further research is needed.

Dopamine, Erectile Function and Male Sexual Behavior from the Past to the Present: A Review

Early and recent studies show that dopamine through its neuronal systems and receptor subtypes plays different roles in the control of male sexual behavior. These studies show that (i) the mesolimbic/mesocortical dopaminergic system plays a key role in the preparatory phase of sexual behavior, e.g., in sexual arousal, motivation and reward, whereas the nigrostriatal system controls the sensory-motor coordination necessary for copulation, (ii) the incertohypothalamic system is involved in the consummatory aspects of sexual behavior (penile erection and copulation), but evidence for its role in sexual motivation is also available, (iii) the pro-sexual effects of dopamine occur in concert with neural systems interconnecting the hypothalamus and preoptic area with the spinal cord, ventral tegmental area and other limbic brain areas and (iv) D₂ and D₄ receptors play a major role in the pro-sexual effects of dopamine. Despite some controversy, increases or decreases, respectively, of brain dopamine activity induced by drugs or that occur physiologically, usually improves or worsens, respectively, sexual activity. These findings suggest that an altered central dopaminergic tone plays a role in mental pathologies characterized by aberrant sexual behavior, and that pro-erectile D₄ receptor agonists may be considered a new strategy for the treatment of erectile dysfunction in men.

Oxytocin, Erectile Function and Sexual Behavior: Last Discoveries and Possible Advances

A continuously increasing amount of research shows that oxytocin is involved in numerous central functions. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered.

Differential control of appetitive and consummatory sexual behavior by neuroestrogens in male quail

Contribution to Special Issue on Fast effects of steroids. Estrogens exert pleiotropic effects on multiple physiological and behavioral traits including sexual behavior. These effects are classically mediated via binding to nuclear receptors and subsequent regulation of target gene transcription. Estrogens also affect neuronal activity and cell-signaling pathways via faster, membrane-initiated events. Although the distinction between appetitive and consummatory aspects of sexual behavior has been criticized, this distinction remains valuable in that it facilitates the causal analysis of certain behavioral systems. Effects of neuroestrogens produced by neuronal aromatization of testosterone on copulatory performance (consummatory aspect) and on sexual motivation (appetitive aspect) are described in male quail. The central administration of estradiol rapidly increases expression of sexual motivation, as assessed by two measures of sexual motivation produced in response to the visual presentation of a female but not sexual performance in male Japanese quail. This effect is mimicked by membrane-impermeable analogs of estradiol, indicating that it is initiated at the cell membrane. Conversely, blocking the action of estrogens or their synthesis by a single intracerebroventricular injection of estrogen receptor antagonists or aromatase inhibitors, respectively, decreases sexual motivation within minutes without affecting performance. The same steroid has thus evolved complementary mechanisms to regulate different behavioral components (motivation vs. performance) in distinct temporal domains (long- vs. short-term) so that diverse reproductive activities can be properly coordinated. Changes in preoptic aromatase activity and estradiol as well as glutamate concentrations are observed during or immediately after copulation. The interaction between these neuroendocrine/neurochemical changes and their functional significance is discussed.

Neuropeptides and central control of sexual behaviour from the past to the present: a review

Of the numerous neuropeptides identified in the central nervous system, only a few are involved in the control of sexual behaviour. Among these, the most studied are oxytocin, adrenocorticotropin, α-melanocyte stimulating hormone and opioid peptides. While opioid peptides inhibit sexual performance, the others facilitate sexual behaviour in most of the species studied so far (rats, mice, monkeys and humans). However, evidence for a sexual role of gonadotropin-releasing hormone, corticotropin releasing factor, neuropeptide Y, galanin and galanin-like peptide, cholecystokinin, substance P, vasoactive intestinal peptide, vasopressin, angiotensin II, hypocretins/orexins and VGF-derived peptides are also available. Corticotropin releasing factor, neuropeptide Y, cholecystokinin, vasopressin and angiotensin II inhibit, while substance P, vasoactive intestinal peptide, hypocretins/orexins and some VGF-derived peptide facilitate sexual behaviour. Neuropeptides influence sexual behaviour by acting mainly in the hypothalamic nuclei (i.e., lateral hypothalamus, paraventricular nucleus, ventromedial nucleus, arcuate nucleus), in the medial preoptic area and in the spinal cord. However, it is often unclear whether neuropeptides influence the anticipatory phase (sexual arousal and/or motivation) or the consummatory phase (performance) of sexual behaviour, except in a few cases (e.g., opioid peptides and oxytocin). Unfortunately, scarce information has been added in the last 15 years on the neural mechanisms by which neuropeptides influence sexual behaviour, most studied neuropeptides apart. This may be due to a decreased interest of researchers on neuropeptides and sexual behaviour or on sexual behaviour in general. Such a decrease may be related to the discovery of orally effective, locally acting type V phosphodiesterase inhibitors for the therapy of erectile dysfunction.

Sexual arousal, is it for mammals only?

Sexual arousal has many dimensions and has consequently been defined in various ways. In humans, sexual arousal can be assessed based in part on verbal communication. In male non-human mammalian species, it has been argued that arousal can only be definitively inferred if the subject exhibits a penile erection in a sexual context. In non-mammalian species that lack an intromittent organ, as is the case for most avian species, the question of how to assess sexual arousal has not been thoroughly addressed. Based on studies performed in male Japanese quail, we argue that several behavioral or physiological characteristics provide suitable measures of sexual arousal in birds and probably also in other tetrapods. These indices include, the performance of appetitive sexual behavior in anticipation of copulation (although anticipation and arousal are not synonymous), the activation of specific brain area as identified by the detection of the expression of immediate early genes (fos, egr-1) or by 2-deoxyglucose quantitative autoradiography, and above all, by the release of dopamine in the medial preoptic area as measured by in vivo dialysis. Based on these criteria, it is possible to assess in birds sexual arousal in its broadest sense but meeting the more restrictive definition of arousal proposed for male mammals (erection in an explicit sexual context) is and will probably remain impossible in birds until refinement of in vivo imaging techniques such fMRI allow us to match in different species, with and without an intromittent organ, the brain areas that are activated in the presence of specific stimuli.

Differential effects of central injections of D1 and D2 receptor agonists and antagonists on male sexual behavior in Japanese quail

A key brain site in the control of male sexual behavior is the medial pre-optic area (mPOA) where dopamine stimulates both D1 and D2 receptor subtypes. Research completed to date in Japanese quail has only utilized systemic injections and therefore much is unknown about the specific role played by dopamine in the brain and mPOA in particular. The present study investigated the role of D1 and D2 receptors on male sexual behavior by examining how intracerebroventricular injections and microinjections into the mPOA of D1 and D2 agonists and antagonists influenced appetitive and consummatory aspects of sexual behavior in male quail. Experiments 1 and 2 investigated the effects of intracerebroventricular injections at three doses of D1 or D2 agonists and antagonists. The results indicated that D1 receptors facilitated consummatory male sexual behavior, whereas D2 receptors inhibited both appetitive and consummatory behaviors. Experiment 3 examined the effects of the same compounds specifically injected in the mPOA and showed that, in this region, both receptors stimulated male sexual behaviors. Together, these data indicated that the stimulatory action of dopamine in the mPOA may require a combined activation of D1 and D2 receptors. Finally, the regulation of male sexual behavior by centrally infused dopaminergic compounds in a species lacking an intromittent organ suggested that dopamine action on male sexual behavior does not simply reflect the modulation of genital reflexes due to general arousal, but relates to the central control of sexual motivation. Together, these data support the claim that dopamine specifically regulates male sexual behavior.

Species differences in the relative densities of D1- and D2-like dopamine receptor subtypes in the Japanese quail and rats: an in vitro quantitative receptor autoradiography study

Evidence has accumulated that the regulation of male sexual behavior by dopamine might not be the same in Japanese quail (and perhaps all birds) as it is in mammals. For example, the non-selective dopamine receptor agonist, apomorphine (APO), facilitates male sexual behavior in rats but inhibits it in quail. Although the general organization of the dopamine system is similar in birds and mammals, it is possible that the relative distribution and/or density of binding sites are different. We therefore compared the relative densities of D1-like and D2-like receptor subtypes in Japanese quail and rats, with the use of in vitro quantitative receptor autoradiography. Brain sections from 8 male rats and 8 male quail were labeled with [(3)H]SCH-23390 and [(3)H]Spiperone. In general we found a systematic species difference in the relative density of D1- vs. D2-like receptors such that the D2/D1 ratio is higher in quail than in rats in areas, known to be important target sites for dopamine action such as striatal regions or the preoptic area, which is also associated with activation of sexual behavior. This difference might explain the variation in the behavioral effectiveness of APO in rats as compared to quail; with a higher relative density of D2-like receptors in quail, a similar dose of APO would be more likely to activate inhibitory processes in quail than in rats.

Interplay among catecholamine systems: dopamine binds to alpha2-adrenergic receptors in birds and mammals

Dopaminergic and adrenergic receptors are G-protein-coupled receptors considered to be different based on their pharmacology and signaling pathways. Some receptor subtypes that are members of one family are actually closer in phylogenetic terms to some subtypes belonging to the other family, suggesting that the pharmacological specificity among these receptors from different families is not perfect. Indeed, evidence is accumulating that one amine can cross-talk with receptors belonging to the other system. However, most of these observations were collected in vitro using artificial cell models transfected with cloned receptors, so that the occurrence of this phenomenon in vivo as well as its distribution in the central nervous system is not known. In this study the pharmacological basis of possible in vivo interactions between dopamine and alpha(2)-adrenergic receptors was investigated in quail, zebra finches, and rats. Binding competitions showed that dopamine displaces the binding of the selective alpha(2)-adrenergic ligand, [(3)H]RX821002, in the brain of the three species with an affinity approximately 10-28-fold lower than that of norepinephrine. Dopamine also displaces with an affinity 3-fold lower than norepinephrine the binding of [(3)H]RX821002 to human alpha(h2A)-adrenergic receptors expressed in Sf9 cells. The anatomical distribution of this interaction was assessed in brain slices of quail and rat based on autoradiographic methods. Both norepinephrine and dopamine significantly displace [(3)H]RX821002 binding in all brain nuclei considered. Together, these data provide evidence for an interaction between the dopaminergic and noradrenergic systems in the vertebrate brain, albeit with species variations.

Fos responses of dopamine neurons to sociosexual stimuli in male zebra finches

Dopamine (DA) is produced in numerous brain areas and influences a wide variety of social behaviors, but very few data are available to establish the socially-relevant response properties of most DA populations, which comprise eight cell groups numbered A8-A15. Anatomically, these DA populations are evolutionarily conserved, and all have been identified in both birds and mammals. We now report the Fos responses of tyrosine hydroxylase-immunoreactive (TH-ir; putatively dopaminergic) neurons in the A8-A15 cell groups of male zebra finches following exposure to a control condition or one of six different social stimuli: a heterospecific male, conspecific male, fighting in a mate competition paradigm (which includes both male and female stimuli), a courtship interaction without physical contact, a courtship interaction with physical contact but no mounting, and a courtship interaction with mounting. We found that the DA cell groups exhibit distinctive profiles of responsiveness to social stimuli. Fos induction in A8, A9, A10 and midbrain A11 neurons increased significantly in response to a variety of conspecific stimuli, but not heterospecific stimuli. In contrast, Fos induction in the preoptic A14 neurons was observed specifically in response to sexual interactions, and Fos induction in hypothalamic A11 neurons appears to primarily reflect the performance of courtship singing. Infundibular A12 neurons, which may be involved in stress-related processes, showed the highest level of TH+Fos colocalization in control subjects. This colocalization decreased in response to all conspecific stimuli except fighting, and did not decrease following exposure to a heterospecific male.

Estradiol rapidly activates male sexual behavior and affects brain monoamine levels in the quail brain

Steroids are generally viewed as transcription factors binding to intracellular receptors and activating gene transcription. Rapid cellular effects mediated via non-genomic mechanisms have however been identified and one report showed that injections of estradiol rapidly stimulate chemoinvestigation and mounting behavior in castrated male rats. It is not known whether such effects take place in other species and what are the cellular underlying mechanisms. We show here that a single injection of estradiol (500 microg/kg) rapidly and transiently activates copulatory behavior in castrated male quail pre-treated with a dose of testosterone behaviorally ineffective by itself. The maximal behavioral effect was observed after 15 min. In a second experiment, the brain of all subjects was immediately collected after behavioral tests performed 15 min after injection. The preoptic area--hypothalamus (HPOA), hindbrain, telencephalon and cerebellum were isolated and monoamines measured by HPLC-ED. Estradiol increased levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and 5-HIAA/serotonin ratios in the telencephalon and hindbrain independently of whether animals had mated or not. Estradiol also affected these measures in HPOA and cerebellum but this effect was correlated with the level of sexual activity so that significant effects of the treatment only appeared when sexual activity was used as a covariate. Interactions between estradiol effects and sexual activity were also observed for dopamine in the HPOA and for serotonin in the hindbrain and cerebellum. Together, these data demonstrate that a single estradiol injection rapidly activates male sexual behavior in quail and that this behavioral effect is correlated with changes in monoaminergic activity.

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.

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.

Tyrosine hydroxylase expression is affected by sexual vigor and social environment in male Cnemidophorus inornatus

Although the distribution of catecholamine-synthesizing cells has been described for a variety of taxa, less is known about the functional significance of particular populations in nonmammalian species, especially reptiles. To understand the role of these populations in the display of social behaviors in lizards, we studied the interactive effects of sexual vigor (sexually vigorous vs. sluggish) and social condition (housing in isolation vs. with females) on the number and somal areas of cells expressing tyrosine hydroxylase (TH), a rate-limiting enzyme in catecholamine synthesis, in male whiptail lizards, Cnemidophorus inornatus. We found that, regardless of social condition, sexually vigorous males had more TH-immunoreactive (TH-ir) cells in the dorsal hypothalamus (DH) relative to sluggish males. Sexually vigorous males also had more TH-ir cells in the substantia nigra pars compacta (SNpc), but this difference was significant only among males housed with females. Sexually vigorous males that had been housed with females had smaller TH-ir cells in the preoptic area (POA) than vigorous males housed in isolation. On the other hand, no significant differences were found in the anterior hypothalamus. These results highlight the regional heterogeneity in the plasticity of TH expression and suggest that, just as in other species, the DH, SNpc, and POA might be involved in the expression of social behaviors and in behavioral plasticity following social experiences in lizards.

Species differences in the regulation of tyrosine hydroxylase inCnemidophorus whiptail lizards

Evolution of behavioral phenotype involves changes in the underlying neural substrates. Cnemidophorus whiptail lizards enable the study of behavioral and neural evolution because ancestral species involved in producing unisexual, hybrid species still exist. Catecholaminergic systems modulate the expression of social behaviors in a number of vertebrates, including whiptails, and therefore we investigated how changes in catecholamine production correlated with evolutionary changes in behavioral phenotype by measuring the size and number of catecholamine producing (tyrosine hydroxylase-immunoreactive, or TH-ir) cells across the reproductive cycle in females from two related whiptail species. Cnemidophorusuniparens is a triploid, parthenogenetic species that arose from hybridization events involving the diploid, sexual species C. inornatus. Prior to ovulation, females from both species display femalelike receptive behaviors. However, after ovulation, only parthenogenetic individuals display malelike mounting behavior. In all nuclei measured, we found larger TH-ir cells in the parthenogen, a difference consistent with species differences in ploidy. In contrast, species differences in the number of TH-ir cells were nucleus specific. In the preoptic area and anterior hypothalamus, parthenogens had fewer TH-ir cells than females of the sexual species. Reproductive state only affected TH-ir cell number in the substantia nigra pars compacta (SNpc), and C. uniparens individuals had more TH-ir cells after ovulation than when previtellogenic. Thus, species differences over the reproductive cycle in the SNpc are correlated with species differences in behavior, and it appears that the process of speciation may have produced a novel neural and behavioral phenotype in the parthenogen.

Tracing the Evolution of Brain and Behavior Using Two Related Species of Whiptail Lizards: Cnemidophorus uniparens and Cnemidophorus inornatus

Cnemidophorus whiptail lizards offer a unique opportunity to study behavioral and neural evolution because unlike most genera, ancestral and descendant species are still extant, and comparisons between species provide a window into correlated changes in biological organization through speciation. This review focuses on the all-female or parthenogenetic species Cnemidophorus uniparens (descendant species), which evolved through several hybridization events involving the sexually reproducing species Cnemidophorus inornatus (ancestral species). Data compiled over more than 2 decades include behavioral, endocrine, and neural differences between these two related species of whiptail lizards. For example, unlike females of the ancestral species, individuals of the descendant species display male-like mounting behavior (pseudocopulatory behavior) after ovulation. Pseudocopulatory behavior in the parthenogen is triggered by the progesterone surge after ovulation, and the behavioral capacity to respond to progesterone appears to be an ancestral trait that was inherited from C. inornatus males through the hybridization events. Interestingly, the regulation of sex steroid hormone receptor mRNA in brain areas critical for the expression of sociosexual behaviors differs between females of the two species and suggests that evolutionary changes in the regulation of gene expression could be a proximate mechanism that underlies the evolution of a novel social behavior in the parthenogen. Finally, because the sexual species is diploid, whereas the parthenogen is triploid, differences between the species could directly assess the effect of ploidy. The behavioral and neuroendocrinological data are pertinent for considering this possibility.

Sex differences and hormone influences on tyrosine hydroxylase immunoreactive cells in the leopard frog

We examined sex differences in tyrosine hydroxylase immunoreactive (TH-ir) cell populations in the preoptic area (POA), suprachiasmatic nucleus (SCN), posterior tuberculum (TP), and caudal hypothalamus (Hy) in the leopard frog (Rana pipiens), in addition to the effects of natural variation in sex steroid hormones on these same populations in both sexes. All four of these populations have been shown to be dopaminergic. Gonadal sex, androgens, and estrogen all influenced TH-ir cell numbers, but in a complicated pattern of interactions. After factoring out the effects of sex steroids by multiple regression, TH-ir cell numbers in all four areas differed between the sexes, with males having a greater number of TH-ir cells. The influence of androgens and estrogen differed by region and sex of the animals. Androgens were the main influence on TH-ir cell numbers in the POA and SCN. Plasma androgen concentrations were positively correlated with TH-ir cell numbers in both areas in males. In females, androgen concentration was negatively correlated with TH-ir cell numbers in the POA; there was no significant relationship in the SCN in females. In the more caudal populations, estrogen (E2) levels were positively correlated with TH-ir cell numbers in the TP of both males and females. In the caudal hypothalamus, E2 levels were positively correlated with TH-ir cell numbers in females, but there was no significant correlation in males. The results indicate that gonadal sex imposes a baseline sex difference in the four TH-ir (dopamine) populations, resulting in a higher number of such cells in males. Individual and sex-linked differences in gonadal steroid hormones lead to variation around this baseline condition, with androgens having a greater influence on rostral populations and estrogen on caudal populations. Last, an individual's gonadal sex determines the effect that androgens and estrogen have on each population.

The neuroendocrinology of reproductive behavior in Japanese quail

Sex steroid hormones such as testosterone have widespread effects on brain physiology and function but one of their best characterized effects arguably involves the activation of male sexual behavior. During the past 20 years we have investigated the testosterone control of male sexual behavior in an avian species, the Japanese quail (Coturnix japonica). We briefly review here the main features and advantages of this species relating to the investigation of fundamental questions in the field of behavioral neuroendocrinology, a field that studies inter-relationship among hormones, brain and behavior. Special attention is given to the intracellular metabolism of testosterone, in particular its aromatization into an estrogen, which plays a critical limiting role in the mediation of the behavioral effects of testosterone. Brain aromatase activity is controlled by steroids which increase the transcription of the enzyme, but afferent inputs that affect the intraneuronal concentrations of calcium also appear to have a pronounced effect on the enzyme activity through rapid changes in its phosphorylation status. The physiological significance of these slow genomic and rapid, presumably non-genomic, changes in brain aromatase activity are also briefly discussed.

Dopamine activates noradrenergic receptors in the preoptic area

Dopamine (DA) facilitates male sexual behavior and modulates aromatase activity in the quail preoptic area (POA). Aromatase neurons in the POA receive dopaminergic inputs, but the anatomical substrate that mediates the behavioral and endocrine effects of DA is poorly understood. Intracellular recordings showed that 100 microm DA hyperpolarizes most neurons in the medial preoptic nucleus (80%) by a direct effect, but depolarizes a few others (10%). DA-induced hyperpolarizations were not blocked by D1 or D2 antagonists (SCH-23390 and sulpiride). Extracellular recordings confirmed that DA inhibits the firing of most cells (52%) but excites a few others (24%). These effects also were not affected by DA antagonists (SCH-23390 and sulpiride) but were blocked by alpha2-(yohimbine) and alpha1-(prazosin) noradrenergic receptor antagonists, respectively. Two dopamine-beta-hydroxylase (DBH) inhibitors (cysteine and fusaric acid) did not block the DA-induced effects, indicating that DA is not converted into norepinephrine (NE) to produce its effects. The pK(B) of yohimbine for the receptor involved in the DA- and NE-induced inhibitions was similar, indicating that the two monoamines interact with the same receptor. Together, these results demonstrate that the effects of DA in the POA are mediated mostly by the activation of alpha2 (inhibition) and alpha1 (excitation) adrenoreceptors. This may explain why DA affects the expression of male sexual behavior through its action in the POA, which contains high densities of alpha2-noradrenergic but limited amounts of DA receptors. This study thus clearly demonstrates the existence of a cross talk within CNS catecholaminergic systems between a neurotransmitter and heterologous receptors.

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.

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.

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

The dopaminergic innervation of the avian telencephalon

The present review provides an overview of the distribution of dopaminergic fibers and dopaminoceptive elements within the avian telencephalon, the possible interactions of dopamine (DA) with other biochemically identified systems as revealed by immunocytochemistry, and the involvement of DA in behavioral processes in birds. Primary sensory structures are largely devoid of dopaminergic fibers, DA receptors and the D1-related phosphoprotein DARPP-32, while all these dopaminergic markers gradually increase in density from the secondary sensory to the multimodal association and the limbic and motor output areas. Structures of the avian basal ganglia are most densely innervated but, in contrast to mammals, show a higher D2 than D1 receptor density. In most of the remaining telencephalon D1 receptors clearly outnumber D2 receptors. Dopaminergic fibers in the avian telencephalon often show a peculiar arrangement where fibers coil around the somata and proximal dendrites of neurons like baskets, probably providing them with a massive dopaminergic input. Basket-like innervation of DARPP-32-positive neurons seems to be most prominent in the multimodal association areas. Taken together, these anatomical findings indicate a specific role of DA in higher order learning and sensory-motor processes, while primary sensory processes are less affected. This conclusion is supported by behavioral findings which show that in birds, as in mammals, DA is specifically involved in sensory-motor integration, attention and arousal, learning and working memory. Thus, despite considerable differences in the anatomical organization of the avian and mammalian forebrain, the organization of the dopaminergic system and its behavioral functions are very similar in birds and mammals.

Appetitive and consummatory male sexual behavior in Japanese quail are differentially regulated by subregions of the preoptic medial nucleus

Central testosterone aromatization is required for the activation of both appetitive (ASB) and consummatory (CSB) male sexual behavior in Japanese quail. There are two major clusters of aromatase immunoreactive (ARO-ir) cells in the rostral forebrain; these outline the nucleus preopticus medialis (POM) and the nucleus striae terminalis (BST). We investigated the role of these nuclei in the regulation of ASB and CSB. Appetitive male sexual behavior was measured with the use of a learned social proximity procedure that quantified the time spent by a male in front of a window with a view of a female who was subsequently released into the cage, providing an opportunity for CSB. Males first acquired the response and then received bilateral electrolytic lesions aimed at the POM or BST, followed by retesting for ASB and CSB. Brain sections were stained for ARO-ir, and lesions to the two ARO-ir cell groups were quantitatively characterized. Lesions damaging the POM completely abolished CSB and also significantly decreased ASB. Lesions of the rostral BST had no effect on ASB, but moderately decreased CSB. Detailed anatomical analysis revealed that lesions of a subdivision of the POM just rostral to the anterior commissure specifically impair CSB, whereas lesions that are more rostral to this subdivision induce a severe deficit in ASB. These data indicate that different subregions of the POM regulate ASB and CSB in a somewhat independent manner, whereas the BST is only important in the regulation of CSB.

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.

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.

Autoradiographic localization of D1-like dopamine receptors in the forebrain of male and female Japanese quail and their relationship with immunoreactive tyrosine hydroxylase

The distribution of D1-like dopamine receptors was studied in the brain of male and female Japanese quail (Coturnix japonica) by means of quantitative autoradiography with 3H-labelled D1 selective antagonist, SCH 23390, serving as a ligand. A specific, saturable, high affinity binding of this ligand was demonstrated. High densities of binding sites were detected in the lobus parolfactorius, olfactory tubercle, and paleostriatum augmentatum. Medium densities were observed in the entire neostriatum and in the external layers of the optic tectum. Similar levels of binding outlined the paleostriatum primitivum, the nucleus pretecalis and the nucleus intercollicularis. Low but significant levels of receptors were also present in the medial preoptic area at the level of the sexually dimorphic medial preoptic nucleus and throughout the infundibulum, as well as in the ectostriatum, medial and lateral septum, and nucleus accumbens. At the level of the medial septum, just dorsal to the anterior commissure, two circular areas of high receptor density corresponding to the nucleus of the septal commissure were also observed. No sex difference in receptor density could be detected in any of the areas. All areas containing high densities of D1 receptors also contained high densities of tyrosine hydroxylase (TH) fibers. However, certain areas characterized by a high density of TH-immunoreactive fibers did not contain appreciable densities of D1-like dopamine receptors. The distribution of this receptor and its relationship to TH-immunoreactivity is consistent with observations made in other vertebrates, suggesting that the dopaminergic system is evolutionarily highly conserved among amniote vertebrates.

Dopamine and sexual behavior

Among central neurotransmitters involved in the control of sexual behavior, dopamine is certainly one of the most extensively studied. Our attempt to review old and recent neuropharmacological, biochemical, electrophysiological, and psychobiological studies performed so far only in rats, monkeys, and humans, provides evidence that dopamine through its different neuronal systems and receptor subtypes plays different roles in the control of several aspects of sexual behavior. In fact, while the nigrostriatal system is necessary for the control of the sensory-motor coordination required for copulation, the mesolimbic-mesocortical system plays a key role in the preparatory phase of the behavior, mainly in sexual arousal, motivation and possibly reward. Conversely, the incertohypothalamic system plays a major role in the consummation of the behavior, mainly in seminal emission and erectile performance, but evidence for its involvement in sexual motivation also exists. The dopaminergic receptors playing the major role in the control of male sexual behavior belong to the D2 receptor subtype. However a D1/D2 receptor interaction is well established and an opposite role for D1 and D2 receptors in the preoptic area suggested. Despite some differences, most studies show that treatments that increase or decrease, respectively, brain dopaminergic activity improve or worsen, respectively, several parameters of copulatory activity, supporting a facilitatory role of dopamine in male sexual behavior. In contrast, no conclusion can be deduced from the available studies on the role of central dopaminergic systems in the control of proceptivity and receptivity, the two main components of female sexual behavior.