THE IMPORTANCE OF TIME FOR THE INTROMISSION FREQUENCY IN THE MALE RAT MATING BEHAVIOUR

L arsson , K. The importance of time for the intromission frequency in the male rat mating behaviour. Scand. J. Psychol . 1961, 2 , 149–152.—A prolongation of the intervals separating the intromissions in the male rat mating pattern produces a decrease in the number of intromissions to ejaculate. By comparing the length of the interval effective in inducing a reduction of the response frequency in two groups of subjects, one composed of extremely 'slow' animals and another of extremely 'fast' ones, it was found that the appearance of the reduction effect was dependent on the length of the interco-pulatory interval characteristic of the individual. A reduction appeared in all animals when the interval of enforced rest was longer than the normal inter-copulatory interval.     

Effect of the interintromission interval on lordotic response and attack latency in golden hamsters (Mesocricetus auratus)

After 12-15 ejaculatory series, each consisting of several short intromissions (2- to 3-s vaginal penetration) and an ejaculation, male golden hamsters adopt an altered copulatory pattern consisting of long intromissions (5- to 25-s penetration with intravaginal thrusting). Receptivity declines and the tendency for the female to attack the male increases at about the time of this shift in copulatory pattern. Because the mean interintromission interval (III) between short intromissions is about 8 s compared to 100 s between long intromissions, it is possible that females detect this difference and adjust their mating accordingly. When the III between short intromissions from a rested male was experimentally increased to 100 s by use of a halter and lead device, the duration of lordosis was significantly less than that displayed by females paired with control males (8-s III) and virtually the same as that displayed by females paired with males that produced only long intromissions. This suggests that the female uses the temporal patterning of intravaginal stimulation as one criterion for terminating mating with a particular male.     

Detailed analysis of the male copulatory motor pattern in mammals: hormonal bases

Data obtained, using a polygraphic technique, on the characteristics of the motor and genital copulatory responses of male rabbits, rats, mice, hamsters, and guinea pigs are reviewed. This methodology provided detailed information, not accessible to other analyses, on the frequency and dynamic organization of copulatory pelvic thrusting trains of the species studied. This comparative analysis showed that: (1) The male rat may display two types of ejaculatory responses, differing in the dynamic organization of the pelvic thrusting train, and in the duration of the intravaginal thrusting period preceding ejaculation. (2) In the guinea pigs and small rodents, but not in rabbits, pelvic thrusting at ejaculatory responses persists during intromission, and a period of fast intravaginal thrusting is associated with ejaculation. (3) The motor copulatory pattern of the rabbit, but not of the rat, hamster, or guinea pig, is affected by castration and hormone treatment, suggesting that, in rabbits, androgen acts both on motivation and on the spinal neural systems related to copulation.     

Hippocampal and cortical activity during sexual behavior in the female rat.

Hippocampal and cortical activity were studied during sexual behavior in the female rat. Hippocampal theta appeared during her soliciting behavior. High-frequency theta accompanying the male's pursuit slowed when the male mounted the female and then increased in frequency during the brief continuation of lordosis following mounts without vaginal penetration. During prolonged lordosis after intromissions and ejaculations, slow theta continued. No changes in cortical frequencies were observed during mounts, intromissions, or ejaculations. During immobility (standing, sitting, and lying down) hippocampal activity became slow and irregular. High-amplitude hippocampal and, eventually, cortical spindles developed during immobility as sexual exhaustion was approached. Immobility and its accompanying electroencephalographic spindling are interpreted as indicative of a sexual satiety or inhibitory process.     

Sexual reinforcement in the female rat.

Sexual reinforcement in the female rat was studied in a preparation that allowed continuous operant responding for access to a male rat leading to intromission. Experiment 1 used a high operant level nose-poke response to test the possible reinforcing effects of some components of access to a male. A simple tone stimulus used as a conditioned reinforcer and two odor stimuli, target male bedding and emulsified preputial gland, were tested. None of these contingent events altered responding above or below operant level. Access to the male, which was always accompanied by intromission, immediately increased response rate when it was made contingent upon the nose-poke response. Performance on fixed-ratio schedules was erratic, and response rate was low in comparison to typical food-reinforced responding. An interresponse-time analysis indicated, however, that some effect of the ratio contingency may have been present. In Experiment 2, several modifications of the procedure were tested with the objective of creating a more tractable preparation for behavior analysis. Response type and the hormone delivery method were changed, and 2 target males were used instead of 1. The latter tripled the average number of reinforcers earned in a single session. Differences between sexual and other reinforcers are discussed in terms of procedural, quantitative, and motivational aspects of the sexual reinforcement procedure.     

Self-stimulation and mating behavior in the male rat

Abstract.— A presumed relationship between selfstimulation of the brain and sexual behavior was studied in two experiments. In the first experiment the male rat was allowed self-stimulation during a period of 5 minutes and thereafter transferred to a mating cage with a female. No effects of the self-stimulation were recorded in the mating behavior. In the second experiment the male was allowed one intromission and thereafter presented with a lever for self-stimulation, still having access to the female. The sexual responses were completely inhibited, and selfstimulation at normal rate resumed. It was concluded that there is no necessary link between self-stimulation of the brain and sexual behavior.     

Life-span changes in the copulatory behavior of male rats (Rattus norvegicus)

The copulatory behavior of 5-, 10-, 15-, and 20-month-old sexually naive male rats (Long-Evans) was studied during 2-hr tests with receptive females. There was no apparent change in sexual arousal as measured by latency to initiate copulation across age, with subjects from all groups exhibiting comparable latencies to first mount and first mount with intromission. The numbers of ejaculations achieved were also similar across ages. Significant age differences were found for frequency of mounts, with 20-month-olds having the highest mean frequency. The persistent mounting by older males appeared to account for significant group differences in interintromission interval and ejaculation latency. It is suggested that motor deficits may impair the ability of older males to achieve intromission, increasing the number of mount bouts as well as the number of mounts per bout, thus extending the length of each copulatory series.     

Differential rates of exhaustion and recovery of several parameters of male rat sexual behavior.

Sexual exhaustion of the male rat was studied with respect to several copulatory measures. The ejaculatory latency, intercopulatory interval, and intromission frequency demonstrate a U-shaped curve, exhibiting high values for the initial ejaculatory series, falling to a minimum at an intermediate ejaculatory series, and again increasing at exhaustion. The absolute refractory period of the postejaculatory interval (measured at vocalization termination) increases linerly, whereas the relative refractory period (the remaining portion of the postejaculatory interval) is a postively accelerating function. Partial recovery tests demonstrated that the preejaculatory measures and absolute refractory period have substantially returned to baseline values by Day 6, while the relative refractory period is still extended. The significance of these data to the theoretical modeling of sexual behavior is discussed.     

Sexual activity and satiety over an extended observation period in prairie voles (Microtus ochrogaster)

This study was designed to delineate the course of sexual satiation in prairie voles (Microtus ochrogaster). Fourteen male-female pairs were allowed to copulate freely for 24 hr under continuous observation. Copulations occurred predominantly during the first few hours and decreased in frequency thereafter. The mean number of ejaculations per pair was 5.6 (range, 2-9). Two thirds of the ejaculations occurred during the first 3 hr, and over 90% took place within the first 7 hr after the first intromission. No ejaculations were observed during the last 8 hr. These results suggest that male capacity to deliver ejaculations to a female is limited and that direct observations reveal a more limited capacity than observations made with time-lapse videotape.     

Conditions necessary to the establishment of mating dominance by the male hamster

We tested whether establishment of a dominance hierarchy among four males will ensure the dominant male preferential mating access to a single female. Establishment of the dominance hierarchy in the absence of a female did not result in any competitive mating advantage for the dominant male in terms of mating priority or total number of intromissions. However, establishment of the dominance hierarchy in the presence of a female, with interactions between the males and female occurring throughout the 4-day estrous cycle prior to the female becoming receptive resulted in the dominant male having a clear mating priority. Under these conditions the dominant male achieved more intromissions than the three subordinate males combined. Thus, male dominance status can affect mating success; however, it appears that interaction with the female as well as with other males prior to the onset of receptivity by the female is essential for assurance of a clear mating priority.     

Interaction between penile reflexes and copulation in male rats

Intact, unanesthetized male rats were place 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 four experiments. In Experiment 1, sexual exhaustion depressed all penile reflexes, but the reflexes returned to baseline levels within 8 hr, long before copulatory potential. In Experiment 2, 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. Experiment 3 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 suggests that the period of reduced sexual arousability following ejaculation is not due to reduced excitability in the spinal mechanisms controlling penile reflexes. In Experiment 4, 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.     

Ultrasonic vocalizations during sex behavior of male house mice (Mus musculus): a description

After placing a female house mouse into the home cage of a male, the occurrences of four behaviors were recorded on separate channels of an event recorder: (1) male sniffing female, (2) male mounting female, (3) male intromitting female, and (4) 70-kHz vocalizations. The amount of vocalizing was greatest shortly after pairing and was associated with the male sniffing the female. After the male began mounting, vocalizations also were associated with mounting. Vocalizations were recorded during intromissions and occasionally occurred coincident with pelvic thrusts. Very few vocalizations were detected when the male was not sniffing or mounting the female. Vocalizations ceased following ejaculation but typically resumed several minutes before the resumption of another mounting sequence. Thus 70-kHz vocalizations appear to be closely linked to male sexual arousal.     

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

Rested adult golden hamsters produced a mean of 13 ejaculations and then showed a modified copulatory pattern consisting of long intromissions (10-30 s of intravaginal thrusting) during which no sperm transfer occurs. When a second (fresh) female was introduced, 58% of the males produced at least one more ejaculation, and 17% of the males produced one further ejaculation when placed with a third female. In similar three-female tests conducted 24 hr later, all males ejaculated (M = 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 first females. Second and third females, however, received fewer ejaculations and subsequently showed reduced fertility and produced smaller litters. Most males showed high levels of long intromissions on all days and with all females. The physiological significance of these long intromissions may be to trigger the progestational response. Examination of the rate of recovery from sexual exhaustion indicated that 2 or 8 hr of rest resulted in fewer than 50% of the males being capable of one further ejaculation. However, most of these single ejaculations were accompanied by long intromissions and resulted in successful pregnancies. Four to eight days were required for full recovery of ejaculatory capacity. This study showed 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. Thus, the limits of male capacity appear to vary widely among species.     

Sexual exhaustion and recovery in the male rat

Twelve male rats were left with receptive females and allowed to copulate and ejaculate until they reached a criterion of “sexual exhaustion” They were then retested after 1, 3, 6 and 15 days of sexual inactivity. Following these observations males were tested once each day or once every other day and allowed to achieve a single ejaculation.

In the course of a period of unlimited access to the receptive female males usually need approximately 10 intromissions to produce the initial ejaculation, but successive ejaculations are produced by fewer and fewer intromissions. The time to recover from the effects of an ejaculation increases progressively as exhaustion is approached.

Very few animals copulate when tested 24 hours after sexual exhaustion. Considerably more recovery is evident in tests conducted after a 3-day rest, but it is not complete and rats are not capable of achieving as many ejaculations as they tend to achieve after longer periods of inactivity. As measured by ejaculation-frequency, the curve of sexual recovery is negatively accelerated and probably reaches asymptote after 7 to 10 days of rest.

Various other measures in addition to ejaculation-frequency support this conclusion. Males allowed to ejaculate once each day or every other day are somewhat less responsive than fully rested animals, but do not show any progressive loss in sexual excitability or capacity.

A working hypothesis is proposed to explain most of the findings. It postulates the existence of an Arousal Mechanism which is distinct from a Copulatory Mechanism. The ways in which these hypothetical mechanisms are affected by sexual performance and sexual rest arc discussed.     

Facilitation of the effect testosterone on male sexual behavior in rats deprived of REM sleep

The possibility of rapid eye movement sleep deprivation (REMd) altering the effect of testosterone on masculine sexual behavior was investigated. Adult castrated male Wistar rats with no sexual experience were randomly assigned to the following three groups: REMd (using the water tank technique) for 7 days, large platform control for 7 days, and undisturbed sleep control. All subjects were treated with 1 mg testosterone propionate daily for 14 days. Masculine sexual behavior was assessed 3 consecutive days prior to steroid administration and was evaluated daily during the treatment. Frequencies and latencies of mounts, intromissions, and ejaculations, as well as the postejaculatory refractory period were recorded. One hundred percent of the REMd subjects presented mounts, intromissions, and ejaculations sooner than the control group. In almost all parameters, a clear facilitation of sexual activity was observed in the REMd group.     

Selective approach to a male and subsequent receptivity to mounting comprise mate‐choice behavior of female mice1

Abstract: To ensure the effectiveness of the mate‐choice behavior of female house mice (Mus domesticus), we observed them in two different situations that involved restriction of the area of movement of the male mice. In Experiment 1, we observed 12 trios consisting of two male mice and an estrous female placed in a chamber in which none of the animals was restricted during the 6‐h test. It was found that the female was more receptive to the male that had ejaculated with it first. Additionally, when the female initiated the mating event by approaching the male, the lordosis quotient was higher than that when the male initiated the mating event. In Experiment 2, a female was able to visit two males that were prevented from getting out of small boxes. As a result of the 3‐h observation of 10 cases, it was found that the females were more receptive to the dominant male. The intromission ratio of the dominant male was also higher than that of the subordinate male. The behavioral roles of female mice in mating interactions and their adaptive validity are discussed.     

Copulation and intermale aggression in rats

Attack behavior of reliably aggressive male Long-Evans rats against unfamiliar male intruders was observed immediately following copulation to one or more ejaculations. Compulatory series to five 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 second experiment determined the attack-eliciting capacity of foreign males placed in the home cage of an actively copulating male. As intromissions increased and the interval to ejaculation decreased, the probability of intermale aggression and interruption of copulation diminished. The results are discussed in reference to sexual and aggressive strategies of the copulating male.     

African four-striped grass mice (Rhabdomys pumilio), a diurnal-crepuscular muroid rodent,in the behavioral laboratory

African four-striped grass mice,Rhabdomys pumilio, are potentially valuable animals for laboratory studies of behavior. In nature, they live in the grasslands of much of Africa. In the laboratory, striped mice adapt well to a number of behavioral testing situations. Ten male grass mice tested in running wheels displayed a mean of approximately 10,000 revolutions per day, with a diurnal-crepuscular pattern characterized by sharp peaks near the time of light onset and offset and a generally greater level of wheel running in light than in darkness. The retinal anatomy of this species is characterized by a cone-like organization of the outer segment layer and unusual thickness of the inner plexiform layer, suggesting an unusual high amount of retinal data processing for a muroid rodent. The copulatory pattern ofR. pumilio is characterized by no lock, no intravaginal thrusting, multiple intromissions preceding ejaculation, and multiple ejaculations. The number of intromissions preceding the first ejaculation is unusually high, and postejaculatory intervals are unusually long. Grass mice display intermediate levels of open-field activity, but little climbing or digging.     

An unusual pattern of copulatory behavior in a South American cricetid rodent: Akodon molinae

We describe the copulatory behavior and the morphology of the male genital tract of a member of a tribe (Akodontini) for which no information on copulatory behavior has been available. Copulation in Akodon molinae is characterized by multiple intromissions with no intravaginal thrusting, a single ejaculation, and a brief lock with the deposit of a plug. This pattern is unusual because of the combination of locking with both multiple intromissions and plugs. The latter combination, and similar standard measures of copulatory behavior, have been reported for Acomys cahirinus, a murid that frequently shows more than 1 ejaculation. Also, the standard measures of copulation in A. molinae resemble those of Calomys callosus, another South American cricetid, which shows intravaginal thrusting and infrequent locks. The functional significance and the anatomical correlates of locking and plug deposition in this species are discussed.     

Effects of frequency and duration of exercise sessions on physical activity levels and adherence

The purpose of this study was to assess the relations among physical activity, adherence, and frequency and duration of exercise sessions for 33 male and female sedentary university students. Analysis indicated that frequency and duration of the exercise program did not significantly affect adherence. However, frequency and duration of the exercise sessions did significantly affect leisure activity once the structured exercise program terminated.