Modulation of the copulatory sequence of the male rat by a schedule of reinforcement

Opioid mediation of learned sexual behavior

Identifying the role of opioids in the mediation of learned sexual behaviors has been complicated by the use of differing methodologies in the investigations. In this review addressing multiple species, techniques, and pharmaceutical manipulations, several features of opioid mediation become apparent. Opioids are differentially involved in conditioned and unconditioned sexual behaviors. The timing of the delivery of a sexual reinforcer during conditioning trials, especially those using male subjects, acutely influences the role that opioids have in learning. Opioids may be particularly important in the maintenance of conditioned sexual behaviors during periods of non-reinforcement. This appears to be true both for probe trials and procedures designed explicitly to extinguish a sexual conditioned response. These features of opioid mediation of learning do not appear to be restricted to sexual conditioning paradigms. This suggests that, as for other aspects of sexual learning that despite distinctive features conform to underlying behavioral principles, the mediation of conditioned sexual behavior by opioids relies on processes common across reinforcement systems.

Who, what, where, when (and maybe even why)? How the experience of sexual reward connects sexual desire, preference, and performance

Although sexual behavior is controlled by hormonal and neurochemical actions in the brain, sexual experience induces a degree of plasticity that allows animals to form instrumental and Pavlovian associations that predict sexual outcomes, thereby directing the strength of sexual responding. This review describes how experience with sexual reward strengthens the development of sexual behavior and induces sexually-conditioned place and partner preferences in rats. In both male and female rats, early sexual experience with partners scented with a neutral or even noxious odor induces a preference for scented partners in subsequent choice tests. Those preferences can also be induced by injections of morphine or oxytocin paired with a male rat's first exposure to scented females, indicating that pharmacological activation of opioid or oxytocin receptors can "stand in" for the sexual reward-related neurochemical processes normally activated by sexual stimulation. Conversely, conditioned place or partner preferences can be blocked by the opioid receptor antagonist naloxone. A somatosensory cue (a rodent jacket) paired with sexual reward comes to elicit sexual arousal in male rats, such that paired rats with the jacket off show dramatic copulatory deficits. We propose that endogenous opioid activation forms the basis of sexual reward, which also sensitizes hypothalamic and mesolimbic dopamine systems in the presence of cues that predict sexual reward. Those systems act to focus attention on, and activate goal-directed behavior toward, reward-related stimuli. Thus, a critical period exists during an individual's early sexual experience that creates a "love map" or Gestalt of features, movements, feelings, and interpersonal interactions associated with sexual reward.

Context alters the ability of clitoral stimulation to induce a sexually-conditioned partner preference in the rat

We have shown previously that clitoral stimulation (CLS) of female rats induces significant conditioned place preference (CPP), indicating that it is rewarding. The present study asked whether CLS could induce a conditioned partner preference. In the first experiment, sexually naïve females received 10 alternating trials of CLS and No-CLS in the presence of a male rat behind a wire-mesh screen. For one group, CLS was made in the presence of the male scented with almond extract. On alternating trials, those females received sham CLS in the presence of an unscented male behind the screen. The order was reversed for the other group. After 5 trials in each condition, females were placed into an open field with two sexually vigorous males, one scented and the other unscented. Contrary to expectation, females displayed a preference for the male associated with sham CLS. The second experiment examined whether a partner preference could be conditioned by associating CLS with the almond odor alone. A new group of sexually naive females received the same CLS-odor, No-CLS-No Odor pairings as above, but with the odor presented on cotton gauze in the chamber. During the final open field test, those females selectively solicited the scented male. We conclude that CLS that induces CPP also induces conditioned partner preference. However, we propose that CLS in the presence of an inaccessible male created a sexual inhibitory state for female rats.

Learning enhances female control over reproductive investment in the Japanese quail

The adaptive significance of learning is supported by studies showing its positive effects on mating behaviour, but they rarely go beyond fertilization success. Here we studied how learning contributes to qualitative reproductive investment, by testing the hypothesis that mating in the context that predicts male appearance has positive effects on female reproductive investment compared with unsignalled mating. Using Japanese quail (Coturnix japonica), we found that effects of mating in the context predicting mating opportunity depend on female body condition and receptivity, while the outcome of unexpected mating depends on male behaviour. In particular, among females mated with the familiar male in the context predicting that he will appear, female condition positively affected the number of fertilized eggs and egg mass and more receptive females tended to produce more sons. Additionally, conditioned females laid heavier eggs for daughters than for sons. In contrast, in females that were mated unexpectedly and with a novel male, the number of fertilized eggs was highly dependent on male behaviour and was negatively related to maternal body condition. Egg mass was not related to body condition, and there were no indications of sex allocation. This is, to our knowledge, the first study demonstrating how female body condition and behaviour interact with the context of mating in shaping maternal reproductive investment.

Enhanced neural activation in brain regions mediating sexual responses following exposure to a conditioned stimulus that predicts copulation

Stimuli associated with sexual behavior increase reproductive success if presented prior to copulation. In Japanese quail, inseminations that take place in a context that predicts the arrival of a female are more likely to result in fertilized eggs. We demonstrate here that in male Japanese quail a sexual conditioned stimulus (CS) also enhances activity in two brain regions that mediate sexual behavior, the medial preoptic area and the medial part of the bed nucleus of the stria terminalis. C-fos expression, a marker of neural activation, was higher in these areas in subjects exposed sequentially to a sexual CS and copulation than in subjects exposed to copulation or the CS alone or in subjects exposed to no sexual stimulus, either an identical, untrained CS or an empty arena. These results suggest a link between a proximate result of sexual CS presentation, male brain activation, and a known ultimate outcome, increased fertilizations.

Differential c-fos expression in the brain of male Japanese quail following exposure to stimuli that predict or do not predict the arrival of a female

We investigated the effects of presenting a sexual conditioned stimulus on the expression of c-fos in male Japanese quail. Eight brain sites were selected for analysis based on previous reports of c-fos expression in these areas correlated with sexual behaviour or learning. Males received either paired or explicitly unpaired presentations of an arbitrary stimulus and visual access to a female. Nine conditioning trials were conducted, one per day, for each subject. On the day following the ninth trial, subjects were exposed to the conditional stimulus (CS) for 5 min. Conditioning was confirmed by analysis of rhythmic cloacal sphincter movements (RCSM), an appetitive sexual behaviour, made in response to the CS presentation. Subjects in the paired condition performed significantly more RCSM than subjects in the unpaired group. Brains were collected 90 min following the stimulus exposure and stained by immunohistochemistry for the FOS protein. Significant group differences in the number of FOS-immunoreactive (FOS-ir) cells were found in two brain regions, the nucleus taeniae of the amygdala (TnA) and the hippocampus (Hp). Subjects in the paired condition had fewer FOS-ir cells in both areas than subjects in the unpaired condition. These data provide additional support to the hypothesis that TnA is implicated in the expression of appetitive sexual behaviours in male quail and corroborate numerous previous reports of the involvement of the hippocampus in conditioning. Further, these data suggest that conditioned and unconditioned sexual stimuli activate different brain regions but have similar behavioural consequences.

Androgen mediation of conditioned rhythmic cloacal sphincter movements in Japanese Quail (Coturnix japonica)

Demonstrations of increased reproductive success due to sexual conditioning in Japanese quail (Coturnix japonica) have been reported, although the mechanisms that underlie these effects have remained elusive. One possible mechanism is conditioned rhythmic cloacal sphincter movements (RCSM). Two experiments were conducted with male quail to determine whether associations between a conditioned stimulus (CS) and a hen would result in the ability of the CS to elicit RCSM, and to explore the androgen mediation of conditioned RCSM. The results suggest that a focal CS paired with visual access to a female will elicit RCSM via a representation of the hen activated by the CS. Further, the available evidence indicates that conditioned RCSM is androgen mediated and that this learning may transfer across breeding seasons.

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.

The nature of sexual reinforcement

Sexual reinforcers are not part of a regulatory system involved in the maintenance of critical metabolic processes, they differ for males and females, they differ as a function of species and mating system, and they show ontogenetic and seasonal changes related to endocrine conditions. Exposure to a member of the opposite sex without copulation can be sufficient for sexual reinforcement. However, copulatory access is a stronger reinforcer, and copulatory opportunity can serve to enhance the reinforcing efficacy of stimulus features of a sexual partner. Conversely, under certain conditions, noncopulatory exposure serves to decrease reinforcer efficacy. Many common learning phenomena such as acquisition, extinction, discrimination learning, second-order conditioning, and latent inhibition have been demonstrated in sexual conditioning. These observations extend the generality of findings obtained with more conventional reinforcers, but the mechanisms of these effects and their gender and species specificity remain to be explored.

Opioids and sexual behavior

Opioids have long been known to inhibit sexual behavior. However, it is only within the last decade that the effects of opioids on sexual behavior have been studied extensively and a number of hormonal and neurochemical correlates established. In this review, the experimental literature on opioids and sexual behavior in humans and laboratory animals is examined. Clinical and anecdotal accounts of opioid use are also discussed, in addition to the pharmacology, neuroendocrinology, and biochemistry of opioid administration, to provide a synthesis of critical information. New research directions involving the study of endogenous opioid systems, opioid receptor subtypes, and the opioid modulation of neurotransmitter systems are outlined. Finally, a comprehensive bibliography of the human and animal literature is included.

The pre-ejaculatory behavior of male and female rats affects the number of sperm in the vagina and uterus

The number of pre-ejaculatory intromissions a female rat receives affects the probability of becoming progestational and transporting sperm into the uterus. We now report that the number of intromissions a male rat delivers affects his ejaculatory performance. Males and females were given different copulatory experience by switching females during mating. When either the male or female had few intromissions, few sperm were recovered and the copulatory plugs fit less well. Intromission-dependent sperm recovery was also observed in a review of 94 copulatory tests drawn from archival data. Several possible mechanisms are discussed, including poor placement of the copulatory plug and reduced sperm output. The potential significance for reproductive success in social mating situations is discussed.