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

Long-term neuropeptide modulation of female sexual drive via the TRP channel in Drosophila melanogaster

Connectomics research has made it more feasible to explore how neural circuits can generate multiple outputs. Female sexual drive provides a good model for understanding reversible, long-term functional changes in motivational circuits. After emerging, female flies avoid male courtship, but they become sexually receptive over 2 d. Mating causes females to reject further mating for several days. Here, we report that pC1 neurons, which process male courtship and regulate copulation behavior, exhibit increased CREB (cAMP response element binding protein) activity during sexual maturation and decreased CREB activity after mating. This increased CREB activity requires the neuropeptide Dh44 (Diuretic hormone 44) and its receptors. A subset of the pC1 neurons secretes Dh44, which stimulates CREB activity and increases expression of the TRP channel Pyrexia (Pyx) in more pC1 neurons. This, in turn, increases pC1 excitability and sexual drive. Mating suppresses pyx expression and pC1 excitability. Dh44 is orthologous to the conserved corticotrophin-releasing hormone family, suggesting similar roles in other species.

Experimental Evidence for Sex Differences in Sexual Variety Preferences: Support for the Coolidge Effect in Humans

We examined sex differences in preferences for sexual variety and novelty to determine whether the Coolidge effect plays a role in human sexuality. In two experimental studies that employed different manipulations, we found converging evidence that men showed a greater preference for variety in potential short-term mates than did women. In the first study, men (n = 281) were more likely than women (n = 353) to select a variety of mates when given the opportunity to distribute chances to have sex with different individuals in hypothetical situations. This sex difference was evident regardless of the targets' attractiveness and age. Further, men found it more appealing if their committed romantic/sexual partners frequently changed their physical appearance, while women reported that they modified their physical appearance more frequently than did men, potentially appealing to male desires for novelty. In the second study, when participants were given a hypothetical dating task using photographs of potential short-term mates, men (n = 40) were more likely than women (n = 56) to select a novel person to date. Collectively, these findings lend support to the idea that sex differences in preferences for sexual variety and novelty are a salient sex-specific evolved component of the repertoire of human mating strategies.

Fos expression is increased in oxytocin neurons of female rats with a sexually conditioned mate preference for an individual male rat

Evidence suggests an important role of Pavlovian learning in sexual partner selection. Female rats that experience paced copulation with a male scented with a neutral odor selectively solicit and receive ejaculations from the scented male relative to an unscented male. Exposure to the conditioned odor alone induces Fos protein in regions of the brain associated with sexual excitation. Here we tested whether female rats can be conditioned to show a sexual preference for an unscented male rat of the same strain. Female Long-Evans rats were given 10 copulatory trials with either a one-hole pacing divider or a four-hole pacing divider in a unilevel chamber with the same conspecific male (n = 16). Females were then given an open-field partner preference test with the paired male versus a novel male. After two reconditioning trials females were exposed to the partner or a novel male to induce Fos expression. Females that paced with the one-hole divider received the first ejaculation and more ejaculations overall from the paired compared to novel male. Fos immunoreactivity within oxytocin neurons in the PVN, mPOA, and VMH was increased in females with a preference that were exposed to the paired male. These data indicate that female rats can form selective sexual preferences for an individual conspecific and that their formation depends on the type of pacing during conditioning. These findings further suggest the involvement of oxytocin in the display of conditioned preferences. Thus, early copulatory experience appears to determine the mating strategy used by female rats.

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.