Organizational effects of estrogens on brain vasotocin and sexual behavior in quail

Reproductive behavior is sexually differentiated in quail: The male-typical copulatory behavior is never observed in females even after treatment with high doses of testosterone (T). This sex difference in behavioral responsiveness to T is organized during the embryonic period by the exposure of female embryo to estrogens. We showed recently that the sexually dimorphic medial preoptic nucleus (POM), a structure that plays a key role in the activation of male copulatory behavior, is innervated by a dense steroid-sensitive network of vasotocin-immunoreactive (VT-ir) fibers in male quail. This innervation is almost completely absent in the female POM and is not induced by a chronic treatment with T, suggesting that this neurochemical difference could be organizational in nature. This idea was tested by injecting fertilized quail eggs of both sexes on day 9 of incubation with either estradiol benzoate (EB) (25 μg, a treatment that suppresses the capacity to show copulatory behavior in adulthood) or the aromatase inhibitor R76713 (10 μg, a treatment that makes adult females behaviorally responsive to T), or with the solvents as a control (C). At 3 weeks posthatch, all subjects were gonadectomized and later implanted with Silastic capsules filled with T. Two weeks later, all birds were perfused and brain sections were processed for VT immunocytochemistry. Despite the similarity of the adult endocrine conditions of the subjects (all were gonadectomized and treated with T Silastic implants providing the same plasma level of steroid to all subjects), major qualitative differences were observed in the density of VT-ir structures in the POM of the different groups. Dense immunoreactive structures (fibers and a few cells) were observed in the POM of C males but not females; EB males had completely lost this immunoreactivity (and lost the capacity to display copulatory behavior); and, conversely, R76713 females displayed a male-typical VT-ir system in the nucleus (and also high levels of copulatory behavior). Similar changes in immunoreactivity were seen in the nucleus of the stria terminalis and in the lateral septum (VT-ir fibers only in this case) but not in the magnocellular vasotocinergic system. These neurochemical changes closely parallel the effects of the embryonic treatments on male copulatory behavior. The vasotocinergic system of the POM can therefore be considered an accurate marker of the sexual differentiation of brain circuits mediating this behavior. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 684–699, 1998     

Stimulatory effects of the noradrenergic neurotoxin DSP4 on sexual behavior in male quail

Four separate experiments were carried out to test in castrated male Japanese quail the effects on testosterone-induced sexual behavior of the neurotoxic drug N-(2-chlorethyl)-N-ethyl-2- bromobenzylamine hydrochloride (DSP4). In each experiment, DSP4 enhanced some aspects of the testosterone-induced sexual behavior. The latency between the start of testosterone treatment and the first occurence of copulatory behavior was decreased, the behavior frequency and duration were increased, and the latency between the introduction of a stimulus female and the first sexual behavior was decreased. The effects could be reversed by concurrent treatment with the alpha-adrenergic agonist, phenylephrine. The stimulatory effects of DSP4 on behavior were not seen in castrated birds which did not receive a concurrent treatment with testosterone and they were associated with a significant decrease of the norepinephrine concentration in the hypothalamus. These results suggest that the noradrenergic system plays an inhibitory role in the control of copulatory behavior of quail similar to what has been described in the ring dove.     

Study of pharmacological activation of the male sexual behavior

The model of sexual exhaustion of male rats was used in the study. The specific aim was to compare the effects of cocaine on the mount latency, number of mounts, intromissions and ejaculations during the entire copulatory cycle with the same indices during the first 30 min of observation (the latter is most frequently used in laboratory settings). Experiments consisted of four 3-day test periods. On days 1 and 2, male rats were allowed to interact with receptive females until the satiation criterion was reached (30 min without mounts). On day 3, male rats were injected with cocaine (5, 10, or 30 mg/kg, i.p.) or its vehicle 15 min prior to testing. Cocaine administration in a dose-dependent way increased the total number of mounts and ejaculations during the entire observation session but not during the initial 30-min period. The mount latency was unaffected by cocaine treatment. The results suggest that the expression of the stimulating effects of cocaine on sexual behavior depends on the duration of the observation period.     

Conditioning and sexual behavior: a review

Sexual behavior is directed by a sophisticated interplay between steroid hormone actions in the brain that give rise to sexual arousability and experience with sexual reward that gives rise to expectations of competent sexual activity, sexual desire, arousal, and performance. Sexual experience allows animals to form instrumental associations between internal or external stimuli and behaviors that lead to different sexual rewards. Furthermore, Pavlovian associations between internal and external stimuli allow animals to predict sexual outcomes. These two types of learning build upon instinctual mechanisms to create distinctive, and seemingly "automated," patterns of sexual response. This article reviews the literature on conditioning and sexual behavior with a particular emphasis on incentive sequences of sexual behavior that move animals from distal to proximal with regard to sexual stimuli during appetitive phases of behavior and ultimately result in copulatory interaction and mating during consummatory phases of behavior. Accordingly, the role of learning in sexual excitement, in behaviors that bring about the opportunity to mate, in courtship and solicitation displays, in sexual arousal and copulatory behaviors, in sexual partner preferences, and the short- and long-term influence of copulatory experience on sexual and reproductive function is examined. Although hormone actions set the stage for sexual activity by generating the ability of animals to become sexually excited and aroused, it is each animal's unique experience with sexual behavior and sexual reward that molds the strength of responses made toward sexual incentives.     

Acute and chronic continuous methamphetamine have different long-term behavioral and neurochemical consequences

We compared two different methamphetamine dosing regimens and found distinct long-term behavioral and neurochemical changes. Adult rats were treated with 1-day methamphetamine injection (3x5 mg/kg s.c., 3 h apart) or 7-day methamphetamine minipump (20 mg/kg/day s.c.). The minipump regimen models the sustained methamphetamine plasma levels in some human bingers whereas the 1-day regimen models a naive user overdose. On withdrawal days 7 and 28, rats were acutely challenged with cocaine to test for behavioral sensitization and subsequently sacrificed for caudate and accumbens dopamine tissue content. Other rats were analyzed on withdrawal days 3, 7 or 28 using voltammetry in caudate slices. On withdrawal days 7 and 28, the methamphetamine injection but not the minipump rats showed behavioral cross-sensitization to cocaine. There was no change in baseline dopamine release, reuptake or sensitivity to quinpirole in any treatment group on either withdrawal day. However, consistent with the behavioral sensitization, cocaine had a greater effect in potentiating dopamine release and in blocking dopamine reuptake in methamphetamine injection versus saline irrespective of withdrawal day. The minipump group showed tolerance to the dopamine releasing effect of cocaine on withdrawal day 28 and had lower dopamine tissue content in the caudate versus the methamphetamine injection group. Dopamine turnover as measured by the DOPAC/dopamine ratio tended to be higher in the minipump-treated rats. These data suggest that the behavioral cross-sensitization seen in the methamphetamine injection rats could be in part due to the increased potency of cocaine in blocking dopamine reuptake and in increasing dopamine release. The decreased potency of cocaine in the caudate slices from the minipump-treated group may be related to decreased dopamine tissue content.     

Effects of beta-carboline-ethyl ester on plasma corticosterone--a parallel with antagonist-precipitated diazepam withdrawal

Diazepam has been shown to produce physical dependence based on observations of behavioral stimulation or, in our laboratory, by increases in plasma corticosterone (CS) during antagonist-precipitated withdrawal. The behavioral excitation appears similar to that observed following the administration of beta-carboline esters--agents reported to interact with benzodiazepine receptors and termed "inverse agonists." The focus of the present study is to correlate the occurrence of changes in CS with behavioral excitation previously observed by others. Further, these studies are designed to show a parallel between the manifestations of benzodiazepine withdrawal and the pharmacologic effects of beta-carboline ethyl ester. Experiments were done in conscious unrestrained male Sprague-Dawley rats, with chronic i.v. catheters, using sound-attenuated one-way vision boxes. These studies compared the hormonal and behavioral changes induced by beta-carboline ethyl ester (beta CCE) with CGS-8216-precipitated withdrawal in rats treated with diazepam for 8 days. Rats treated chronically with diazepam (5 mg/kg/day), showed a significant increase in plasma (CS) following CGS-8216. Behavioral abstinence scores were also significantly elevated. beta CCE (0.5-5.0 mg/kg) showed a significant dose-related increase in plasma CS. Behavioral scores were also increased at doses of 0.5 and 2.0 mg/kg. beta CCE-induced plasma CS increases were antagonized by CGS-8216 at doses of 1.0 and 2.0 mg/kg but not by 0.5 mg/kg. In animals chronically treated with diazepam, beta CCE evoked a more prolonged plasma CS elevation than in vehicle-treated animals suggesting a dual agonist/antagonist effect. These data suggest a parallel between CS elevations and behavioral effects during withdrawal as well as similarities between the action of beta CCE and the manifestations of this withdrawal.     

Evolution of sexual size monomorphism: the influence of passive mate guarding

Some species have potential for intense mate competition yet exhibit little or no sexual size dimorphism, despite predictions from sexual selection theory. Using a conceptual model, we show the conditions for which passive mate guarding with copulatory plugs can be an alternative and more successful strategy to active (direct) guarding, reducing selection pressure on large male size. The model predicts that copulatory plugs in mammals should be favoured in species for which females have short sexual receptivity periods. Using data on 62 primate species and a phylogenetic regression approach, we show that, as predicted, copulatory plugs are negatively associated with degree of sexual dimorphism and females’ sexual receptivity length. Penile spines are also significantly associated with plug use and short receptivity periods suggesting a possible offensive role in sperm competition. Results highlight that life‐history characteristics, such as sexual receptivity lengths, may alter the costs and benefits of alternative male strategies and thus alter the strength of sexual selection.     

Effects of the nonsteroidal inhibitor R76713 on testosterone-induced sexual behavior in the Japanese quail (Coturnix coturnix japonica)

A new triazole derivative, R76713 (6-[4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-methyl-1H- benzotriazole), was recently shown to inhibit aromatase selectively without affecting other steroid-metabolizing enzymes and without interacting with estrogen, progestin, or androgen receptors. This compound was tested for its capacity to intefere with the induction of copulatory behavior by testosterone (T) in castrated Japanese quail (Coturnix coturnix japonica). In a first experiment, R76713 inhibited (range 0.01 to 1 mg/kg) the activation of sexual behavior by T silastic implants and hypothalamic aromatase activity in castrated male quail in a dose-dependent manner. The 5 alpha- and 5 beta- reductases of T were not systematically affected. Stereotaxic implantation of R76713 in the medial preoptic area similarly blocked the behavior activated by systemic treatment with T, demonstrating that central aromatization of androgen is implicated in the activation of behavior. These inhibiting effects of R76713 on behavior were observed when implants were placed in the medial part of the nucleus preopticus medialis, confirming the implication of this brain area in the control of male copulatory behavior. Finally, the behavioral inhibition produced by R76713 could be reversed by simultaneous treatment with a dose of estradiol, which was not behaviorally effective by itself. This suggests that the behavioral deficit induced by the inhibitor was specifically due to the suppression of estrogen production. This also shows that the activation of copulatory behavior probably results from the interaction of androgens and estrogens at the brain level, as the two treatments separately providing these hormonal stimuli (T with the aromatase inhibitor on one hand and a low dose of estradiol on the other hand) had almost no behavioral effects but they synergized to activate copulation when given concurrently. These data confirm the critical role of preoptic aromatase in the activation of reproductive behavior and demonstrate that R76713 is a useful tool for the in vivo study of estrogen-dependent processes.     

Aromatase inhibition blocks the expression of sexually-motivated cloacal gland movements in male quail

In Japanese quail (Coturnix japonica), activation of appetitive and consummatory aspects of male sexual behavior requires aromatization of testosterone (T) into estrogens. Appetitive male sexual behavior (ASB) is usually assessed with the use of a learned social proximity procedure. In the present experiment, we investigated the role of estrogens in the activation of an another index of ASB, the female-induced activation of rhythmic cloacal sphincter movements (RCSMs) that are produced in reaction to the visual presentation of a female. Consummatory sexual behavior (CSB) was also assessed by the frequency and latency of copulatory behaviors. Castrated male quail were treated with Silastic implants filled with T in association with chronic injections of the aromatase inhibitor Vorozole (R83842; 1mg/kg twice a day; CX + T + VOR group). Control birds were implanted with T capsules only (CX + T group). CSB was almost completely blocked by injections of the aromatase inhibitor. The RCSM frequency decreased progressively in the CX + T + VOR group by comparison with the CX + T group and was therefore significantly reduced at the end of the experiment. These results demonstrate that the frequency of RCSM, a second measure of ASB is, like the social proximity response and CSB, blocked by inhibition of estrogen production. It was shown previously that lesions of the preoptic area inhibit both aspects of the appetitive sexual behavior (proximity response and RCSM). It is therefore, likely that both responses are controlled, like copulation, by aromatase-containing neurons of the preoptic area.     

Estradiol Mediates Effects of Testosterone on Vasotocin Immunoreactivity in the Adult Quail Brain

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

Conditioning of sexual proceptivity in female quail: measures of conditioned place preference

The present experiments were conducted to explore the nature of conditioned sexual proceptivity in female quail. Females exposed to males subsequently approached the area where the males were previously housed (Experiment 1). This increased preference for the male's area reflected an increase in female sexual proceptivity and not an increase in non-directed locomotor activity (Experiment 2). These findings provide the first evidence that female quail show conditioned responses that may be considered to be proceptive responses toward male conspecifics. The proceptive responses are expressed as tonic changes in preference for areas where males have been observed in the past rather than as specific phasic conditioned responses.     

Activation of sexual behavior by implantation of testosterone propionate and estradiol benzoate into the preoptic area of the male Japanese quail (Coturnix japonica)

Intracranial implantation of minute pellets of gonadal steroids was performed to determine neuroanatomical loci at which steroids activate sexual behavior in the Japanese quail (Coturnix japonica). In this species, systemic treatment of castrated males with either testosterone propionate (TP) or estradiol benzoate (EB) restores male-typical copulatory behavior (head grabbing, mounting, and cloacal contact movements). In addition, EB activates female-typical receptive behavior (crouching). Adult male castrated quail were implanted intracranially with 300-micrograms pellets containing TP, EB, or cholesterol (CHOL) and behavior was tested with intact males and females. Either TP or EB pellets in the preoptic area (POA) activated male-typical copulatory behavior. Mounting was specifically activated without concomitant activation of other steroid-sensitive sexual and courtship behaviors. TP and EB implants in adjacent nuclei containing receptors for these steroids and CHOL implants in POA had no effect on male-typical copulatory behavior. Eighteen percent of all males tested for female-typical receptivity crouched, but no specific effect of EB was seen at any site. The similarity of the POA sites for activation of mounting by TP and EB is consistent with the hypothesis that cells within the POA aromatize testosterone to estrogens, which directly stimulate the cellular processes leading to behavioral activation.     

Influence of Griffonia simplicifolia on male sexual behavior in rats: Behavioral and neurochemical study

The seeds of Griffonia simplicifolia Baill. are rich in 5-HTP (5-hydroxytryptophan), a direct precursor of the neurotransmitter serotonin. In the present study we investigated the influence of the plant extract on male sexual behavior. The seed extract was orally administered to Sprague-Dawley male rats at three dose levels (25, 50 and 100 mg/kg) both acutely and subchronically (daily for 9 days). Mating test with receptive female rats was performed 60 min after the acute treatment or the last dose when repetitively administered. Mount, intromission and ejaculation latencies and post-ejaculatory interval were recorded. Food intake and body weight were measured over the 9-day period of treatment. Microdialysis technique was used to detect the extracellular levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in rat brain following the acute administration of the extract dosed at 100 mg/kg. The acute treatment significantly increased mount latency (at any dosage), intromission and ejaculation latencies (at 100 mg/kg) and post-ejaculatory interval (at 50 and 100 mg/kg). On the contrary the subchronic treatment failed to exert a significant influence on copulatory behavior. The daily administration of the extract dosed at 50 and 100 mg/kg for 9 days significantly reduced food intake and body weight. Finally in the microdialysis experiments we found a dramatic increase in 5-HT and its metabolite 5-HIAA.     

Decline of sexual behavior in castrated male rats: Effects of female precopulatory behavior

From the population of 89 adult sexually inexperienced Wistar male rats 20 animals that initiated copulatory behavior with females exhibiting low intensity of precopulatory behavior (presenting females) were preselected. Prior to castration all 20 males had the same sexual experience: three ejaculatory series in four weekly sessions with females exhibiting high intensity of precopulatory behavior (darting females). Following castration, the decline of copulatory behavior was much slower for the nine males tested with darting females as compared to the 11 males tested with presenting females. Male precopulatory behaviors (anogenital sniffing, touching flanks, etc) outlasted the loss of copulatory behavior and seem to be less dependent on both external and internal determinants. It is concluded that intensive external sexual stimuli can function to compensate, and therefore mask, the subnormal operation of androgen-dependent mechanisms in initiating the copulatory behavior.     

Differential effect of testosterone and dihydrotestosterone on the sexual behavior of prepuberally castrated male rabbits

The effect of testosterone propionate (Tp) and dihydrotestosterone propionate (DHTp) at doses of 1, 3 and 9 mg daily for 30 days on the copulatory behavior of prepuberally castrated male New Zealand white rabbits was studied. Tp was significantly more effective than DHTp in eliciting copulatory behavior at each dose level tested. Three milligrams Tp was the minimal dose required to elicit mounting consistently. DHTp at the high dose level (9 mg) only elicited sexual activity comparable to that observed with the low dose of Tp (1 mg). The results suggest that T does not need to be reduced to DHT to stimulate sexual behavior in the male rabbit.     

Paternity analyses in wild‐caught and laboratory‐reared Caribbean cricket females reveal the influence of mating environment on post‐copulatory sexual selection

Polyandry is ubiquitous in insects and provides the conditions necessary for male‐ and female‐driven forms of post‐copulatory sexual selection to arise. Populations of Amphiacusta sanctaecrucis exhibit significant divergence in portions of the male genitalia that are inserted directly into the female reproductive tract, suggesting that males may exercise some post‐copulatory control over fertilization success. We examine the potential for male–male and male–female post‐copulatory interactions to influence paternity in wild‐caught females of A. sanctaecrucis and contrast our findings with those obtained from females reared in a high‐density laboratory environment. We find that female A. sanctaecrucis exercise control by mating multiple times (females mount males), but that male–male post‐copulatory interactions may influence paternity success. Moreover, post‐copulatory interactions that affect reproductive success of males are not independent of mating environment: clutches of wild‐caught females exhibit higher sire diversity and lower paternity skew than clutches of laboratory‐reared females. There was no strong evidence for last male precedence in either case. Most attempts at disentangling the contributions of male–male and male–female interactions towards post‐copulatory sexual selection have been undertaken in a laboratory setting and may not capture the full context in which they take place – such as the relationship between premating and post‐mating interactions. Our results reinforce the importance of designing studies that can capture the multifaceted nature of sexual selection for elucidating the role of post‐copulatory sexual selection in driving the evolution of male and female reproductive traits, especially when different components (e.g. precopulatory and post‐copulatory interactions) do not exert independent effects on reproductive outcomes.     

Role of aromatization in anticipatory and consummatory aspects of sexual behavior in male rats

The present study was designed to test the hypothesis that aromatization is involved in the maintenance by testosterone of the appetitive component of male sexual behavior. We measured appetitive sexual behavior by administering behavioral tests in bilevel chambers and quantifying anticipatory level changes during a 5-min period prior to introduction of a stimulus female. In addition, we recorded standard measures of consummatory male sexual behavior after the female was introduced. Following 3 weekly tests, level-changing behavior reached a plateau and remained stable for up to 10 weeks. After 10 bilevel tests, rats were given subcutaneous testosterone capsules to clamp circulating androgen at physiological levels. Rats were tested and divided into two groups that were matched for measures of sexual behavior. One group was then treated with the nonsteroidal aromatase inhibitor, Fadrozole (2.5 mg/kg/day), given subcutaneously in beta-cyclodextrin and the other group was treated with vehicle. Within 1 week of Fadrozole treatment, the number of anticipatory levels changes was significantly reduced, but not the latency to begin searching. Fadrozole treatment also significantly reduced all measures of copulatory behavior over the period of treatment and increased latencies to first mount, intromission, and ejaculation. After 8 weeks, both treatment groups were given an additional Silastic capsule filled with estradiol and tested for 4 additional weeks. Estrogen treatment partially restored level-changing behavior, mounts, and intromissions but had little effect on ejaculations. These results support the view that aromatization is important for maintaining both the appetitive and the consummatory aspects of sexual behavior in male rats.     

Goings‐on inside a worm: functional hypotheses derived from sexual conflict thinking

Different interests between mating partners regarding the fate of their gametes can lead to sexual conflicts in many species. Although these conflicts can sometimes be dealt with pre‐copulatorily (e.g. by choosing with which partners to mate), they often extend beyond copulation. Post‐copulatory sexual conflicts are expected to be particularly strong in simultaneous hermaphrodites because an individual may have to accept sperm in order to obtain an opportunity to donate sperm, reducing the effectiveness of pre‐copulatory conflict resolution. The present study investigates the post‐copulatory interactions between male and female sexual traits of a highly promiscuous simultaneous hermaphrodite, the free‐living flatworm Macrostomum lignano. Using light and electron microscopy, we show the different levels of complexity of the sperm and the genitalia, and derive hypotheses about how the different traits may represent evolutionary responses to such sexual conflicts. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 370–383.     

Polysaccharides from wolfberry prevents corticosterone-induced inhibition of sexual behavior and increases neurogenesis

Lycium barbarum, commonly known as wolfberry, has been used as a traditional Chinese medicine for the treatment of infertility and sexual dysfunction. However, there is still a scarcity of experimental evidence to support the pro-sexual effect of wolfberry. The aim of this study is to determine the effect of Lycium barbarum polysaccharides (LBP) on male sexual behavior of rats. Here we report that oral feeding of LBP for 21 days significantly improved the male copulatory performance including increase of copulatory efficiency, increase of ejaculation frequency and shortening of ejaculation latency. Furthermore, sexual inhibition caused by chronic corticosterone was prevented by LBP. Simultaneously, corticosterone suppressed neurogenesis in subventricular zone and hippocampus in adult rats, which could be reversed by LBP. The neurogenic effect of LBP was also shown in vitro. Significant correlation was found between neurogenesis and sexual performance, suggesting that the newborn neurons are associated with reproductive successfulness. Blocking neurogenesis in male rats abolished the pro-sexual effect of LBP. Taken together, these results demonstrate the pro-sexual effect of LBP on normal and sexually-inhibited rats, and LBP may modulate sexual behavior by regulating neurogenesis.