Copulatory behavior of roof rats (Rattus rattus).

Investigated the copulatory behavior of a total of 71 male and 48 female roof rats (Rattus rattus) in 3 experiments. In Exp I, females were brought into behavioral estrus with exogenous hormones, and each pair was observed until 30 min elapsed without copulation. Roof rats appeared to be similar to laboratory rats (Rattus norvegicus) with regard to basic motor patterns of copulation, quantitative measures of copulation, behaviors accompanying copulation, and postejaculatory ultrasonic vocalizations. Only (a) patterns of tail rattling in females, (b) climbing and allogrooming in both sexes, and (c) an ability to ejaculate on a single insertion by males were observed in roof rats but not reported for laboratory rats. Exps II and III were designed to assess the role of various components of the copulatory pattern of male roof rats on the induction of pregnancy in normally cycling young females. A single ejaculation preceded by an abnormally high number of intromissions or 3 normal ejaculatory series maximized the incidence of pregnancy, whereas 1 normal ejaculatory series or 1 ejaculation preceded by an abnormally low number of intromissions did not. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitative and inhibitory influences of reproductive behavior on sperm transport in rats.

Six experiments investigated the effects of the rat's copulatory behavior on sperm transport in the female's reproductive tract. Data from 236 female and 87 male rats show that (a) transcervical sperm transport in rats required 6–20 min after ejaculation for completion; (b) transcervical transport of large numbers of sperm required that the vaginal plug remain lodged tightly in the vaginal-cervical junction; (c) maintenance of an immobile posture by the male, and possibly by the female, at ejaculation facilitated the deposition of a tightly lodged vaginal plug and the transport of large numbers of sperm through the cervix; (d) a single intromission occurring within 2 min after ejaculation disrupted sperm transport, but more copulatory stimulation was required to disrupt sperm transport when delivered between 4 and 10 min after ejaculation; and (e) the average postejaculatory interval was long enough to prevent a male from disrupting the transport of most of his own sperm from the preceding ejaculation. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of olfactory stimuli during copulation in male and female rats.

Describes 3 experiments with a total of 74 gonadally-normal male and 29 ovariectomized female Long-Evans rats. Male and female reactions toward odors from novel and original partners were observed prior to the male's attaining his 1st or 2nd ejaculation. The male's reaction depended upon the sexual condition of the female. Only prior to their initial ejaculation did the males prefer their original partner's odors to those of novel females and only if the odors were collected from the females prior to copulation. This finding corresponded with observations of the male's random choice of partner during copulation. Females responded nonpreferentially if they had copulated prior to testing and showed a marked decrease in responsiveness as copulation continued. Prior to copulation females preferred the odors from males which had not copulated to those of males which had. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of prolonged copulatory behavior in facilitating reproductive success in a competitive mating situation in laboratory rats.

Results of 3 experiments (with 50 female F344/MA, 19 male F344, 12 male Long-Evans, 9 male BN/MA, and 9 male MAXX/MA rats) lend support to the hypothesis that the multiple ejaculatory pattern of male rats is of functional significance in that it increases the proportion of offspring sired by a given male when his female partner subsequently mates with a 2nd male, thus establishing conditions for sperm competition. When each male attained just 1 ejaculatory series, there was little effect of mating order (Exp I). Exp II revealed that when the 1st male completed 5 ejaculatory series, he sired a significantly higher porportion of the offspring relative to a 2nd male than when the 1st male attained just 1 ejaculation. The mechanism underlying the advantage of multiple ejaculations appears to lie in the proportion of sperm from each male in the female's tract rather than in either the mere passage of time or the effects of stimulation per se (Exp III). The multiple ejaculation pattern with a single female can be seen not as "wasted activity" but rather as functional in maximizing the reproductive success of individual males. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context-dependent acquisition of copulatory behavior in the male rat: Role of female availability.

The effect of the environment in which sexual experience is acquired was examined on patterns of male rat copulatory behavior. Males trained in a pacing chamber with a 4-hole partition had significantly shorter ejaculation latencies compared with males trained in chambers with a 1-hole partition. Those differences persisted when males were switched into the other pacing condition, suggesting that the pattern of copulation in these males had become "fixed." In the second experiment, males were trained to associate an almond odor with copulation in either the 1-hole or 4-hole condition. Males ejaculated preferentially with females associated with the 4-hole pacing condition. Copulatory behavior in male rats is sensitive to female availability, and females associated with greater availability are preferred. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pacing of copulatory behavior in the male rat: Effects of receptive females and intermittent shocks.

Describes 2 experiments with 7 male hooded Long-Evans rats. In Exp I, Ss were tested with females continuously present and with the presence of the female after each sex act contingent upon a barpress. The sole effect of the barpress requirement was to increase the intervals between copulations before ejaculation. In Exp II, intermittent shocks were superimposed upon the conditions of Exp I. Shocks were followed with short latency by mounts in the ad-lib condition and by barpress and mounts in the operant condition. The pacing of copulatory acts before ejaculation is inferred to result from an interaction of stimuli from the female and feedback from the copulatory acts; after ejaculation, factors primarily endogenous to the male govern the timing of resumption of copulation. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Female presence during postejaculatory interval facilitates penile erection and 22-kHz vocalization in male rats.

During the postejaculatory interval (PEI), male rats exhibit prolonged immobility, 22-kHz vocalization, and penile erections. To test whether females modulate these behaviors, females were removed after the first or second ejaculation or left in the test chamber. Female presence during the PEI delayed exploratory behavior and facilitated vocalization and erection. Female stimulation of vocalization is consistent with the hypothesis that vocalization has a communicative function, not just a thermoregulatory one. The timing of the effect of females on erection suggests that males are sexually arousable well before they resume copulation. Therefore, erection may be better than vocalization as an indicator of the male's sexual refractoriness. The findings also challenge the conventional view that the PEI comprises absolute and relative sexual refractory periods marked, respectively, by the presence and absence of 22-kHz vocalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological correlates of copulatory behavior in the male rat: Evidence for a sexual inhibitory process.

Investigated the dynamics of hippocampal and cortical activity during copulation in 8 male Sprague-Dawley rats. Hippocampal theta rhythm accompanied appetitive behaviors, e.g., watching, sniffing, approaching, and mounting the female. Theta continued after most mounts without intromission, whereas intromission or ejaculation was followed by slowing and desynchronization of hippocampal activity. During rest, high-amplitude irregular slow waves and spindling appeared in the hippocampus and eventually in the cortex. Rest occurred primarily as S approached ejaculation and in the initial part of the postejaculation interval. Rest and its accompanying EEG spindling are interpreted as a developing sexual inhibitory process. A model involving interaction between a postulated arousal process and opponent sexual inhibitory process is presented. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrical stimulation of dorsal and ventral striatum differentially alters the copulatory behavior of male rats.

Sexual behavior is a natural reward that activates striatal dopaminergic (DA) circuits, and dopamine exerts a facilitative influence on copulation. Electrical stimulation of the striatum has been shown to be rewarding, but its effect on male sexual behavior display has not been established. The objective of the present work was to assess the effects of low- and high-frequency electrical stimulation of the dorsal and ventral striatum on male rat sexual behavior expression. To this aim, copulatory activity of sexually experienced male rats was recorded during electrical stimulation of the nucleus accumbens (NAcc) or caudate-putamen (CP), at each stimulation frequency, before and after sexual exhaustion. Results showed that electrical stimulation of the NAcc at both frequencies increased the number of ejaculations that male rats were able to show in a 30-min period. By contrast, stimulation delivered to the CP inhibited sexual behavior by slowing its display. Each effect was more pronounced at low than at high stimulation frequencies. In the same rats, once sexually exhausted, electrical stimulation of these brain areas did not reverse the sexual behavior inhibition that characterizes the sexual exhaustion state. It is concluded that dorsal and ventral striatal DA brain regions exert opposite influences on copulatory behavior expression of sexually experienced male rats. Also, that the facilitative effect of NAcc electrical stimulation on sexual activity, with the stimulation parameters used, cannot surmount the sexual behavior inhibition resulting from copulation to satiation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postejaculatory quiescence in female and male rats: Consequences for sperm transport during group mating.

Studied the pattern of postejaculatory mating in the social context of a multimale–multifemale group of Sprague-Dawley rats (N?=?21), analyzing its timing and sequence from the females' as well as the males' perspective. During mating, females had a quiescent period following each ejaculation, which was comparable with the males' (a postejaculatory interval, PEI). The PEIs of both sexes were characterized by 3 behaviorally distinguishable phases: a stationary, an interactive, and a sexual phase. There was no significant sex difference in the total length of the PEI. Nonetheless, females began active sexual behavior and entered the sexual phase more quickly than males. The time course of each phase of the PEI is compared with the time course of sperm transport in the female, and the similarities and differences between the two sexes' reproductive strategies following an ejaculation are emphasized. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction between penile reflexes and copulation in male rats.

Placed intact, unanesthetized Long-Evans male rats in a supine position, with the penile sheath continuously retracted. Three forms of penile reflex were displayed: erections, cups, and flips. The reciprocal relation between copulation and the penile reflexes occurring in supine tests was explored in 4 experiments. In Exp I, sexual exhaustion depressed all penile reflexes, but the reflexes returned to baseline levels within 8 hrs, long before copulatory potential. In Exp II, reflexes were depressed to exhaustion levels after fewer ejaculations than were required for sexual exhaustion, an indication that reflexes are more readily evoked during copulation than in supine tests. Exp III determined that a rat's penile-reflex potential may be enhanced by placing the rat in a copulation-test cage, by allowing the male a few antecedent intromissions, or by allowing an antecedent ejaculation. The display of penile reflexes within 1 min after ejaculation suggested that the period of reduced sexual arousability following ejaculation is not due to reduced excitability in the spinal mechanisms controlling penile reflexes. In Exp IV, 1 hr of penile-reflex elicitation had no effect on subsequent copulatory behavior. Thus, sexual stimulation may increase or decrease penile-reflex potential, but a reciprocal influence was not detectable. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of male pre-ejaculatory vocalizations on female receptive behavior in the rat (Rattus norvegicus).

Both male and female rats (Rattus norvegicus) emit ultrasounds during copulation. Bursts of ultrasounds from males that occur as ejaculation approaches are lower in frequency, longer in duration, and louder than those that appear earlier in the ejaculatory series. We attempted to determine if these pre-ejaculatory calls affect female sexual behavior. The behavior of females paired with devocalized males was compared with that of females paired with intact males, and in a second experiment tape-recorded vocalizations were played to females paired with devocalized males. Females were less receptive when paired with devocalized males; they were less likely to remain stationary when males attempted to mount. Playback of both types of calls restored female immobility toward control levels, although pre-ejaculatory calls were more effective than mating ones. Pre-ejaculatory calls restored running and trailing levels somewhat toward control level but to a lesser extent than female immobility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Copulation and intermale aggression in rats.

Exp I observed attack behavior of 9 reliably aggressive male Long-Evans rats against unfamiliar male intruders immediately following copulation to one or more ejaculations. Copulatory series to 5 ejaculations did not differ from copulation to a single ejaculation or from a noncopulatory control in affecting aggressive behavior. Repetitive biting attacks occurred in all conditions, with comparable wounding. Evidently, the male postejaculatory state of insensitivity to sexual stimuli does not extend to stimuli eliciting intermale aggression. A 2nd experiment determined the attack-eliciting capacity of foreign males placed in the home cage of an actively copulating S. As intromissions increased and the interval to ejaculation decreased, the probability of intermale aggression and interruption of copulation diminished. Findings suggest that a postejaculatory mechanism for behavioral inhibition exists in the male rat, preventing his interference with fertilization but without affecting his capacity to prevent other males from attempting to displace the fruits of his labors. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopamine release in the medial preoptic area of female rats in response to hormonal manipulation and sexual activity.

Dopamine (DA) is responsive to hormonal manipulations and has been implicated in the regulation of female rat sexual behavior. In the present studies, extracellular DA levels were assessed in the medial preoptic area (MPOA) of ovariectomized female rats in response to exogenous ovarian hormones and during sexual activity. In female rats primed with a low dose of estradiol benzoate (2 μg), but not with a higher dose (20 μg), a 500-μg progesterone injection increased extracellular DA and facilitated copulatory behavior. Extracellular DA levels in the MPOA were further augmented during sexual interactions with a male rat in a nonpacing copulatory chamber by either perineal or vaginal stimulation. However, in a pacing chamber, DA efflux did not increase, although the metabolites rose significantly during copulation. Together, these findings suggest that extracellular DA in the MPOA responds to the hormonal state of the female rat and may contribute to her expression of sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serotonin impairs copulation and attenuates ejaculation-induced glutamate activity in the medial preoptic area.

The medial preoptic area (MPOA) is critical for male sexual behavior. Glutamate is released in the MPOA of male rats during copulation, and increasing glutamate levels by reverse dialysis of glutamate uptake inhibitors facilitates mating. Conversely, increased release of serotonin (5-HT) inhibits sexual behavior. In both rats and men, selective serotonin reuptake inhibitors (SSRIs) impair erection, ejaculation, and libido. Here we reverse-dialyzed 5-HT through concentric microdialysis probes in the MPOA of male rats; concurrently we collected 2-min samples for analysis of glutamate and measured sexual behavior. Sexual activity, and especially ejaculation, increased levels of glutamate in the MPOA. However, reverse dialysis of 5-HT into the MPOA impaired ejaculatory ability and attenuated glutamate release. Implications of these results for impairment of sexual behavior that results from administration of SSRIs are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The function of Barbary macaque copulation calls

In a wide variety of animal species, females produce vocalizations specific to mating contexts. It has been proposed that these copulation calls function to incite males to compete for access to the calling female. Two separate advantages of inciting male-male competition in this way have been put forward. The first suggests that as a result of calling, females are only mated by the highest ranking male in the vicinity (indirect mate choice hypothesis). The second proposes that copulation calling results in a female being mated by many males, thus promoting competition at the level of sperm (sperm competition hypothesis). In this paper, I give results from the first experimental study to test these hypotheses. Playback was used to examine the function of copulation calls of female Barbary macaques (Macaca sylvanus) in Gibraltar. Although rank did not affect lone males' likelihood of approaching copulation calls, when playbacks were given to pairs of males only the higher ranking individual approached. Moreover, females were mated significantly sooner after playback of their copulation call than after playback of a control stimulus. These results suggest that the copulation calls of female Barbary macaques play a key role in affecting patterns of male reproductive behaviour, not only providing an indirect mechanism of female choice, but also promoting sperm competition by reducing the interval between copulations. Potential fitness benefits of inciting male-male competition at these two levels are discussed.     

Ejaculate disruption in two species of voles (Microtus): On the PEI matching law.

Male prairie and montane voles (Microtus ochrogaster and M. montanus) were permitted 5 thrusts, without ejaculation, with a female at variable times after a 1st male ejaculated. In both prairie and montane voles, there were fewer sperm, in relation to control conditions, in the female's tract 1 hr after ejaculation if the female received thrusts immediately or 15 min after the ejaculate. There was no such effect after a 50-min delay. There was no significant decrease in litter production in prairie voles caused by thrusts delivered either immediately or after a 15-min delay. Sperm transport in these species is susceptible to disruption for a longer period than in deer mice or rats. The proposal that the postejaculatory interval (PEI) protects a male from disrupting its own sperm transport (the PEI matching law) appears not to hold for these species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determinants of mating success in the golden hamster (Mesocricetus auratus): I. Male capacity.

Studied the maximum copulatory capacity of 102 male golden hamsters to determine what effect a steady state of copulatory activity would have on the chronic fertility of the male, and to determine the rate of recovery from copulatory recovery. Rested Ss produced a mean of 13 ejaculations and then showed a modified copulatory pattern consisting of long intromissions (10–30 sec of intravaginal thrusting) during which no sperm transfer occurred. When a 2nd (fresh) female was introduced, 58% of the Ss produced at least 1 more ejaculation, and 17% of the Ss produced 1 further ejaculation when placed with a 3rd female. In similar 3-female tests conducted 24 hrs later, all Ss ejaculated (mean 4 ejaculations); this level of ejaculatory output was maintained over a subsequent 10-day period of daily testing. Four ejaculations ensured a nearly 100% pregnancy rate and maximum litter size in the 1st females. Second and 3rd females, however, received fewer ejaculations and subsequently showed reduced fertility. Two or 8 hrs of rest resulted in fewer than 50% of the Ss being capable of 1 further ejaculation. However, most of these single ejaculations were accompanied by long intromissions and resulted in successful pregnancies. Findings show that the male golden hamster has a higher ejaculatory output and more rapid recovery from sexual exhaustion than other small rodents that have been studied. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The presence of genital mycoplasmas in women of reproductive age

Although 5-HT1 and 5-HT2 receptor activity is known to influence copulation, the effects of 5-HT3 receptor-selective drugs on sexual activity have yet to be systematically studied. The following experiments investigated the effects of the 5-HT3-selective antagonists MDL 72222, ondansetron and ICS 205-930 on female sexual behaviour; male rats were studied using ondansetron and granisetron. These compounds influenced neither male nor female copulatory behaviours, suggesting that 5-HT3 receptors contribute little to the modulation of sexual activity. 5-HT3 receptor antagonists block certain opioid-induced behaviours and opioids selectively inhibit sexual behaviours; therefore, the ability of ondansetron and ICS 205-930 to modify morphine-attenuated copulatory activity was also tested. While morphine inhibited copulation, 5-HT3 antagonists failed to reverse the effects.