Temporal characteristics of the Coolidge effect in male rat copulatory behavior

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Hormones and the Coolidge effect

The Coolidge effect is the renewal of sexual behavior after the presentation of a novel sexual partner and possibly occurs as the result of habituation and dishabituation processes. This re-motivation to copulate is well studied in males and is commonly related to sexual satiety, which involves several neurobiological changes in steroid receptors and their mRNA expression in the CNS. On the other hand, there are few reports studying sexual novelty in females and have been limited to behavioral aspects. Here we report that the levels of rat proceptive behavior, a sign of sexual motivation, declines after 4 h of continuous mating, particularly in females that were unable to regulate the time of mating. Such reduction was not accompanied by changes in lordosis, suggesting that they were not due to the vanishing of the endocrine optimal milieu necessary for the expression of both components of sexual behavior in the female rat. These and previous data support important differences between sexual behavior in both sexes that would result in natural divergences in the Coolidge effect expression. We here also review some reports in humans showing peculiarities between the pattern of habituation and dishabituation in women and men. This is a growing research field that needs emphasis in female subjects.

An unknown male increases sexual incentive motivation and partner preference: Further evidence for the Coolidge effect in female rats

The Coolidge effect is the resumption of copulatory behavior induced by a novel sexual partner that has been reported in several species. The term is also used in males when they resume mating when exposed to an unknown receptive female after they have reached sexual exhaustion. Only few studies have evaluated the Coolidge effect in females. In the present study we further evaluated this possibility using the sexual incentive motivation (SIM) and the partner preference (PP) tests. Ovariectomized rats were hormonally primed and allowed to mate for 1h controlling the sexual interaction (paced mating) or in a condition where they were unable to pace the sexual encounters. In the SIM and PP tests, females were exposed to the male with whom they had mated before (known male) or with an unknown, sexually experienced one (unknown male). Regardless whether they paced the sexual interaction, all females showed clear preference for the unknown male but females that paced the sexual contacts spent more time in the incentive zone of the unknown male than females that could not pace the sexual interaction. Similar results were observed in the PP test. Both groups of females spent more time in the compartment of the previously unknown male than in that of the known one, but received the same amount of sexual stimulation, i.e., mounts, intromissions and ejaculations from both males. No preference was found when the females were tested in the SIM test between an unknown male and a sexually receptive female. The results further support the existence of a Coolidge effect in female rats that is more apparent if they pace the sexual interaction.

Multiple Orgasms in Men-What We Know So Far

INTRODUCTION

There is much popular discussion on strategies to facilitate multiple orgasms in men (ie, 100,000+ hits in Google), yet the topic has not received an objective comprehensive review in the literature.

AIM

To review the literature on male multiple orgasms.

METHODS

We searched the literature for publications on "male multiple orgasms" and factors influencing male multiple orgasms in Google, PubMed, and PsychINFO. This yielded 15 relevant publications.

MAIN OUTCOME MEASURES

A comprehensive overview on the topic of male multiple orgasms and factors that influence the propensity of men to experience multiple orgasms.

RESULTS

Few men are multiorgasmic: <10% for those in their 20s, and <7% after the age of 30. The literature suggests 2 types of male multiple orgasms: "sporadic" multiorgasms, with interorgasmic intervals of several minutes, and "condensed" multiorgasms, with bursts of 2-4 orgasms within a few seconds to 2 minutes. Multiple orgasms appear physiologically similar to the single orgasm in mono-orgasmic men. However, in a single case study, a multiorgasmic man did not experience with his first orgasm the prolactin surge that usually occurs with orgasm in mono-orgasmic men. Various factors may facilitate multiple orgasms: (1) practicing to have an orgasm without ejaculation; (2) using psychostimulant drugs; (3) having multiple and/or novel sexual partners; or (4) using sex toys to enhance tactile stimulation. However, confirmatory physiological data on any of these factors are few. In some cases, the ability to experience multiple orgasms may increase after medical procedures that reduce ejaculation (eg, prostatectomy or castration), but what factor(s) influence this phenomenon is poorly investigated.

CONCLUSION

Despite popular interest, the topic of male multiple orgasms has received surprisingly little scientific assessment. The role of ejaculation and physiological change during the refractory period in inhibiting multiple orgasms has barely been investigated.

The influence of three genes on whether adolescents use contraception, USA 1994-2002

In a further contribution to recent investigations of the relevance of genetic processes for demographic outcomes, we investigate genetic associations with whether adolescents use contraception. Using data from the National Longitudinal Study of Adolescent Health, we find that variants in the dopamine transporter gene DAT1, the dopamine receptor gene DRD2, and the monoamine oxidase gene MAOA are associated with unprotected sexual intercourse. Consistent with previous analyses of these data, the genotypes DRD2*A1/A2, DRD2*A2/A2, DAT1*9R/10R, and MAOA*2R/ are associated with higher odds of unprotected sexual intercourse than other genotypes at these loci. The DRD2 associations apply to both men and women, whereas the other associations apply to women only. These results are robust to controls for population stratification by continental ancestry, do not vary by contraceptive type, and are consistent with previous research showing that these genetic variants are associated with higher rates of impulsivity.

Intranasal vasopressin affects pair bonding and peripheral gene expression in male Callicebus cupreus

Arginine vasopressin (AVP) is a neuropeptide hormone and neurotransmitter that has peripheral functions in water regulation, and central functions in the stress response and social bonding in male rodents. In this study, we investigated the role of AVP in partner preference behavior in a monogamous primate, the coppery titi monkey (Callicebus cupreus). Seven titi males each received three intranasal treatments: saline, low AVP (40 IU) and high AVP (80 IU) in random order, 1 week apart. They experienced a series of stimulus exposures to their female partner, a female stranger and an empty cage. Males were more likely to contact the stimulus and do so faster when either female stimulus was present. When pretreated with saline, males contacted the stranger more frequently than their partner; when pretreated with the high dosage of AVP, males contacted their partner more frequently than the stranger. We used microarray to measure peripheral changes in gene expression associated with intranasal AVP and found reduced expression of several genes coding for proinflammatory cytokines. The data presented here suggest that intranasally administered AVP has both central influences on social behavior and peripheral influences on inflammation in a nonhuman primate.

Gene by social context interactions for number of sexual partners among white male youths: genetics-informed sociology

This study sets out to investigate whether introducing molecular genetic measures into an analysis of sexual partner variety will yield novel sociological insights. The data source is the white male DNA sample in the National Longitudinal Study of Adolescent Health. The authors' empirical gene-environment interaction analysis produces a robust protective effect of the 9R/9R genotype relative to the Any10R genotype in the dopamine transporter gene (DAT1). This protective effect tends to be lost in schools in which higher proportions of students start having sex early, as well as in individuals with relatively low cognitive ability. The genetics-informed socio logical analysis here suggests that explaining a human trait or behavior may require a theory that accommodates the complex interplay between social contextual and individual influences and genetic predispositions.

Dopamine transporter, gender, and number of sexual partners among young adults

The dopamine transporter gene (DAT1) codes for a dopamine transporter protein, which limits the level and duration of dopamine receptor activation. The DAT1 gene is a strong candidate gene for reward-seeking behavior. This article reports compelling evidence for the association between the 40 bp variable number of tandem repeats in the DAT1 gene and the self-reported number of sexual partners among young adults in the United States using the sibling subsample of more than 2500 individuals who participated in the National Longitudinal Study of Adolescent Health. We performed tests of genotype-gender interaction as well as analyses stratified by gender. Among the males, possessing one or two alleles of the 10 repeat is associated with an 80-100% increase (P<0.0001, 2df) in the number of sexual partners as compared with the homozygotes for the 9 repeat. The association holds in race/ethnicity-stratified analyses, in Allison's procedure that tests population stratification, and in within-family fixed-effects models. Covariate adjustment for a standard set of socioeconomic factors including religiosity, family structure, parental education, marital and cohabitation history, and neighborhood poverty did not attenuate these associations. Discussion is provided why this finding is absent among females.

Effect of small doses of naloxone on sexual exhaustion in White New Zealand male rabbits

The objective of the present study was to determine the effect of small doses of naloxone on sexual exhaustion in White New Zealand male rabbits. Twelve young and 12 adult male rabbits 6-12 months old and 14-20 months of age, respectively, were selected from a commercial farm. Each male rabbit was housed individually in galvanized cages (90 cm x 60 cm x 40 cm). The rabbits were housed in an open shed exposed to natural photoperiod (12 L 12 D, 19 degrees N). Daily temperature fluctuated through the year from 28 to 16 degrees C. Humidity was 45+/-5%. Water and food (rabbit chow PMI) was supplied ad libitum. After sexual behaviour for each studied group was established, the males were given a 6-day rest, and 3 days before next trial, six males of each group (treated) received a subcutaneous implant of 8 mg of naloxone in a crystalline nitrocellulose pellet formulated to be completely absorbed in 15 days. The remaining six males were sham-treated (control). At the end of the resting period as previously described, the sexual behavior of each group was studied and compared using a Mann-Whitney statistical U-test. The effect of naloxone on sexual behavior was analyzed with a Wilcoxon test for correlated samples. With regard to sexual activity between young and adult rabbits, it was observed that there was a significant difference between groups (P=0.00275, Z=2.8823, adjusted Z=2.99.43) showing that younger rabbits mounted/ejaculated from 9 to 10 females compared with 6 to 8 mounted/ejaculated by older rabbits. When naloxone was administered to both groups, there was a significant difference when comparing sexual behavior before and after administration of naloxone (table first and second trial). Young rabbits treated with naloxone mounted/ejaculated 11-12 females while older rabbits mounted nine females before reaching sexual exhaustion. A significant difference was observed when comparing the number of estrous females that were mounted/ejaculated between groups. Environmental photoperiod and temperature changes were not considered. It was concluded that endogenous opioids are important modulators of behavioral and hormonal interactions related to sexual behavior.

Olfactory Conditioned Partner Preference in the Female Rat

Paced copulation induces conditioned place preference in female rats. The authors examined whether associating almond-scented males with paced copulation induces conditioned partner preference. The paired group received 4 paced copulations with almond-scented males and 4 nonpaced copulations with unscented males sequentially at 4-day intervals. The unpaired group received the opposite order of association, whereas the randomly paired group received random associations. A 4th group received a single pairing. On the final test, females were placed into an open field with 2 males, 1 scented and 1 unscented. Females in the paired group solicited the scented male more frequently, and most chose the scented male for their 1st ejaculation. Thus, an odor paired with paced copulation elicits conditioned partner preference in female rats.

Sexual motivation--an inquiry into events determining the occurrence of sexual behavior

For the individual engaged in it, sexual behavior has no finality or purpose other than its own execution. Data are presented showing that the execution of sexual reflexes can promote learning, i.e. it functions as reinforcement. Furthermore, positive affect is generated. Based on these principles, a model of sexual motivation has been elaborated. The conceptual framework is the incentive motivation theory previously proposed by Bindra D, A motivational view of learning, performance, and behavior modification, Psychol Rev 1974: 81:199-213; A Theory of Intelligent Behavior, New York: Wiley, 1976; How adaptive behavior is produced: a perceptual-motivational alternative to response reinforcement, Behav Brain Sci 1978; 1:41-52. Although the model is intended for application to most mammals, the rat is used as example. Essentially, sexual approach behaviors are activated by appropriate incentives (conditioned in the male, unconditioned in the female). Approach is, in the inexperienced male, followed by the execution of copulatory reflexes as a consequence of accidentally obtained tactile stimulation of the perineal region. In the female, copulatory acts are activated by tactile stimulation of the flanks and hinds provided by the mounting male. The role of conditioning for the execution of copulatory reflexes and for the acquisition of incentive value of neutral stimuli is analyzed. It is also shown that the incentive properties of sexual acts are not substantially different from those of other incentives. Sexual exhaustion is suggested to be either a case of negative alliesthesia or of stimulus habituation and the Coolidge effect is, in consequence, an example of dishabituation. Studies in women and men support this proposal. It is emphasized that sexual behavior is best understood as being entirely mechanistic albeit not deterministic.

Dynamic changes in nucleus accumbens dopamine efflux during the Coolidge effect in male rats

The Coolidge effect describes the reinitiation of sexual behavior in a "sexually satiated" animal in response to a novel receptive mate. Given the role of the mesolimbic dopamine (DA) system in the initiation and maintenance of motivated behavior, microdialysis was used to monitor nucleus accumbens (NAC) DA transmission during copulation, sexual satiety, and the reinitiation of sexual behavior. In agreement with earlier reports, the presentation of an estrous female behind a screen and copulation were associated with significant increases in NAC DA efflux. Return of NAC DA concentrations to baseline values coincided with a period of sexual satiety, although concentrations of the DA metabolites, dihydroxyphenylacetic acid and homovanillic acid, remained elevated. The presentation of a novel receptive female behind a screen resulted in a slight increase in NAC DA, which was augmented significantly during renewed copulation with the novel female. The present data suggest that the stimulus properties of a novel receptive female may serve to increase NAC DA transmission in a sexually satiated male rat, and this, in turn, may be related to the reinitiation of sexual behavior.

Involvement of mesolimbic dopamine neurons in sexual behaviors: implications for the neurobiology of motivation

Mesencephalic dopamine-containing neurons that innervate limbic regions, notably nucleus accumbens, are thought to be involved in the control of a variety of species-typical behaviors such as male copulatory behavior, feeding and drinking as well as of behaviors reinforced by many drugs abused by humans. While it is generally agreed that these neurons are an important link in the brain circuitry that mediates these behaviors, their precise function remains a source of conjecture. The present article reviews evidence implicating the mesoaccumbens dopamine projection in sexual behaviors and discusses some of the issues that have contributed to the uncertainty over the exact role of this system in these and other species typical behaviors. This review also describes approaches we have been using in an attempt to address these issues and summarizes recent findings we believe provide important insights into mesoaccumbens dopamine function and the neurobiology of motivation.