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Different conditions induce proliferation, migration and integration of new neurons in the adult brain. This process of neurogenesis is a clear example of long lasting plastic changes in the brain of different species. Sexual behavior is a motivated behavior that is crucial for the survival of the species, but an individual can spend all his life without displaying sexual behavior. In the present review, we briefly describe some of the effects of pheromones on neurogenesis. We review in detail studies describing the effects of sexual behavior in both males and females on proliferation, migration and integration of new cells and neurons. It will become evident that most of the studies have been done in rodents, assessing the effects of this behavior on neurogenesis within the dentate gyrus of the hippocampus and in the subventricular zone - rostral migratory stream - olfactory bulb system. more...

Sexually naive female mice do not display high levels of sexual receptivity in their first sexual experience; they require around 4-5 sexual encounters to display the full receptive response, assessed by the lordosis reflex. In this study, we evaluated if repeated sexual stimulation with the same male is associated with changes in synaptic remodeling evaluated by synaptophysin (SYP) in brain structures involved in the control of sexual behavior such as the main and accessory olfactory bulbs (MOB and AOB, respectively), medial preoptic area (MPOA), ventromedial hypothalamus (VMH), and amygdala (AMG). Female mice were ovariectomized and hormonally primed to induce sexual receptivity. They were randomly distributed into three groups: a) sexually naive (SN), with no prior sexual stimulation; b) sexually inexperienced (SI), with one prior mating session; and c) sexually experienced (SE), with six mating sessions. The SI group showed a significant decrease in SYP in the glomerular, mitral and granular layers of the AOB in comparison to SN and SE females. SYP expression increased in the SE group in comparison to SN and SI females in the glomerular and mitral cell layers of the AOB. No significant differences between groups were found in the other brain regions (MOB, MPOA, VMH or AMG). These changes in SYP expression in the AOB suggest that plastic modifications in this brain region can be associated with receptivity increase in sexual experience in female mice. more...

In rodents, sexual stimulation induces a positive affective state that is evaluated by the conditioned place preference (CPP) test. Opioids are released during sexual behavior and modulate the rewarding properties of this behavior. Prairie voles (Microtus ochrogaster) are a socially monogamous species, in which copulation with cohabitation for 6 h induces a pair bond. However, the mating-induced reward state that could contribute to the establishment of the long-term pair bond has not been evaluated in this species. The present study aimed to determine whether one ejaculation or cohabitation with mating for 6 h is rewarding for voles. We also evaluated whether this state is opioid dependent. Our results demonstrate that mating with one ejaculation and social cohabitation with mating for 6 h induce a CPP in males, while exposure to a sexually receptive female without mating did not induce CPP. In the female vole, mating until one ejaculation, social cohabitation with mating, or exposure to a male without physical interaction for 6 h did not induce CPP. To evaluate whether the rewarding state in males is opioid dependent, the antagonist naloxone was injected i.p. The administration of naloxone blocked the rewarding state induced by one ejaculation and by social cohabitation with mating. Our results demonstrate that in the prairie vole, on the basis of the CPP in the testing conditions used here, the stimulation received with one ejaculation and the mating conditions that lead to pair bonding formation may be rewarding for males, and this reward state is opioid dependent. more...

Non-copulating (NC) males are those animals that do not mate in spite of repeated testing with sexually receptive females. They have been observed in several species including rats and mice. The present experiment was designed to perform a detailed behavioral characterization of NC male mice. Thus, we evaluated their sexual incentive motivation for a sexually receptive female or a sexually active male, olfactory preference for volatile and non-volatile odors from females or males, and olfactory discrimination between female and male volatile odors and food related odors (milk versus vinegar). We compared the activity of the accessory olfactory system (AOS) in copulating (C) and NC males in response to estrous bedding using the induction of Fos-immunoreactivity (Fos-IR) as a measure of neuronal activation. We also determined if estradiol or dopamine treatment could induce sexual behavior in NC males. Finally, we compared the testis weight and the number of penile spines in C, NC, and gonadectomized males. In the sexual incentive motivation test C males spend significantly more time in the female incentive zone than in the male incentive zone. On the other hand, NC males spend the same amount of time in both incentive zones. In tests of olfactory preference, NC males spent less time investigating estrous odors than C males. As well, NC males discriminate urine from conspecifics but they spend less time smelling these odors than C males. In addition, no increase in Fos expression is observed in NC males when they are exposed to odors from estrous females. Our data also suggest that the deficits observed in NC males are not due to lower circulating levels of gonadal hormones, because estradiol supplementation does not induce sexual behavior in these animals, and their testis weight and the number of penile spines are normal. The results suggest that NC males are not sexually motivated by the receptive females and their odors. more...

We have previously shown that the first-paced mating encounter increases the number of newborn cells in the granule cell layer (Gra; also known as internal cell layer, ICL) of the accessory olfactory bulb (AOB) in the adult female rat (Corona et al., 2011). In the present study we evaluated if repetition of the stimulus (paced mating) could increase the arrival of more newborn neurons in the olfactory bulb generated during the first session of paced sexual contact. Sexually naive female rats were bilaterally ovariectomized, hormonally supplemented with estradiol (E2) and progesterone (P) and randomly assigned to one of four groups: (1) without sexual contact, (2) one session of paced mating, (3) four sessions of paced mating, and (4) four sessions of non-paced mating. We also included a group of gonadally intact females. On the first day of the experiment, all females were i.p. injected with the marker of DNA synthesis bromodeoxyuridine and were killed 16 days later. Blood was collected at sacrifice to determine the plasma levels of E2 and P. The number of newborn neurons that arrived at the ICL of the AOB and the Gra of the main olfactory bulb (MOB) increased, relative to all other groups, only in the group that repeatedly mated under pacing conditions. No differences were found in E2 and P levels between supplemented groups indicating that our results are not influenced by changes in hormone concentrations. We suggest that repeated paced mating promotes the arrival of more newborn neurons in the AOB and MOB. more...

One way to evaluate sexual arousal is by measuring approach behavior to sexual incentive stimuli. In our case we measure approach behavior to an originally non-preferred compartment which is associated with the physiological state induced by mating. This change of preference indicative of a positive affective (reward) state can be evaluated by conditioned place preference (CPP). We have shown that the CPP induced by paced mating is mediated by opioids. The administration of opioids also induces a reward state. The present study was designed to compare the rewarding properties of paced mating and a morphine injection. One group of females was allowed to pace the sexual interaction before being placed in the non-preferred compartment. In alternate sessions they received a morphine injection before being placed in the preferred compartment. In another group of females, the treatments were reversed. Only the females placed in the originally non-preferred compartment after paced mating changed their original preference, suggesting that paced mating induces a positive affective, reward, state of higher intensity than a morphine injection of 1mg/kg. In a second experiment we determined if females allowed to pace the sexual interaction for 1h would still developed CPP. No change in preference was observed in the females that mated for 1h without pacing the sexual interaction. On the other hand, females that received between 10 and 15 paced intromissions as well as females that paced the sexual interaction for 1h developed a clear CPP. The second experiment demonstrated that pacing is rewarding even in an extended mating session in which the females received around 25 intromissions and several ejaculations. These results further demonstrate the biological relevance associated with the ability of the female to space coital stimulation received during mating. This positive affective state will contribute to increase sexual arousal the next time a rat finds an appropriate mate. more...

An important number of Sprague-Dawley males selected by strict inbreeding process for their high spontaneous yawing frequency (HY) fail to copulate after repeated exposure to receptive females. These HY males that fail to mate are called non-copulators (HYNC). The causes of this behavioral deficit are still unknown. The aim of the present study was to make a detailed behavioral characterization of these animals by evaluating: their partner preference between a sexually receptive female as opposed to a sexually active male; their ability to detect food related odors and their preference for sexually relevant chemosensory cues between bedding from estrous females, bedding from sexually active males and clean bedding. We also evaluated whether these males had alterations in motor function using a rotarod or in their general reward system mediated by opioids by injecting them with 1 mg/kg of morphine to evaluate if they develop conditioned place preference (CPP). At the end of these behavioral tests, we measured their plasmatic levels of testosterone (T). Together, these results will contribute to elucidate the causes of their deficient copulatory performance. Both HYNC and HY copulators (HYC) males showed a clear preference for receptive females as opposed to sexually active males. As well, both groups of animals had a similar ability to detect food related odors. HYC males had a clear preference for estrous female odors as opposed to male or clean bedding, but HYNC males spend the same amount of time sniffing estrous, anestrous, male and clean bedding. In both, HYC and HYNC, morphine induced CPP suggesting that in these males the reward system is functional. No differences were found in motor coordination or in T levels between HY and HYNC males. The behavioral deficit in HYNC male rats cannot be explained by an alteration in: partner preference, food related odor recognition, motor coordination, general reward system, or differences in plasmatic levels of T. However, HYNC males present clear deficits in recognizing sexually relevant odors. These results could, at least in part, explain the deficient execution of copulatory pattern in HYNC males. more...

Sexually sluggish (S) male rats take a long time to ejaculate or sometimes they don't achieve ejaculation when tested on repeated occasions with receptive females. In order to further understand what factors might contribute to the inconsistent display of sexual behavior in these animals and determine if S and non-copulating males have a different neurobiological profile, the present study was design to characterize sex-related behaviors of S male rats. We tested their preference to physically interact between a sexually receptive female and a sexually active male. We also tested whether S males have a preference to investigate soiled bedding from females in estrous, anestrous or clean bedding. We also evaluated if the serum hormonal levels of testosterone (T) and estradiol (E) are different between copulating (C) and S male rats. Finally, we compared the neuronal activity of the vomeronasal projection pathway of C and S male rats exposed to estrous bedding. The results indicate that S male rats increased the percentage of animals displaying mounts and intromissions after repeated testing with receptive females but no increased was observed in the percentage of animals displaying ejaculations (a total of nine tests were performed). Both C and S males had a clear preference to interact with a sexually receptive female. Both groups showed a clear preference for bedding from estrous females as opposed to anestrous or clean bedding. However, the time investigating the estrous bedding was significantly lower for the S in comparison to C rats. No differences in the serum levels of T and E were found. The structures of the vomeronasal projection pathway were equally activated by estrous bedding in C and S male rats. The results indicate that S male rats do not have hormonal alterations or deficient processing of sexually relevant olfactory cues. Although S males showed a reduced preference for estrous bedding, no changes in preference for a receptive female were observed. more...