Pharmacological and physiological aspects of sexual exhaustion in male rats

The present article reviews the current findings on the interesting phenomenon of sexual satiety. Knut Larsson in 1956 reported on the development of sexual exhaustion in the male rat after repeated copulation. We have studied the process and found the following results. (1) One day after 4 hours of ad libitum copulation, two-thirds of the population showed complete inhibition of sexual behavior, while the other third displayed a single ejaculatory series from which they did not recover. (2) Several pharmacological treatments, including 8-OH-DPAT, yohimbine, naloxone and naltrexone, reverse this sexual satiety, indicating that the noradrenergic, serotonergic and opiate systems are involved in this process. Indeed, direct neurochemical determinations showed changes in various neurotransmitters during sexual exhaustion. (3) Given enough stimulation, by changing the stimulus female, sexual satiety was prevented, suggesting that there are motivational components of the sexual inhibition that characterizes sexual exhaustion. (4) The GABA antagonist bicuculline, or the electrical stimulation of the medial preoptic area, did not reverse sexual exhaustion. These data suggest, on the one hand, that sexual exhaustion and the postejaculatory interval (which is shortened by bicuculline administration) are not mediated by similar mechanisms and, on the other, that the medial preoptic area does not regulate sexual satiety. (5) The androgen receptor density in brain areas closely related to the expression of masculine sexual behavior, such as the medial preoptic nucleus, was drastically reduced in sexually exhausted animals. Such reduction was specific to certain brain areas and was not related to changes in the levels of androgens. These results suggest that changes in brain androgen receptors account for the inhibition of sexual behavior present during sexual exhaustion. (6) The recovery process of sexual satiety after 4 hours of ad libitum copulation reveals that, after 4 days, only 63% of the males are able to show sexual behavior while after 7 days all animals display copulatory activity.     

Differential sexual activity of isolated and grouped male mice despite testosterone administration

In Experiment 1, adult male C57 mice were castrated, housed individually or in groups of four, and repeatedly injected with either of two doses of testosterone. Control mice were sham-castrated, individually or group housed, and injected with oil vehicle. In repeated tests of sexual behavior with receptive females, isolated males in all surgery-dose combinations showed significantly more mounts and intromissions than did their group-housed counterparts. Ejaculations were fully restored by testosterone in castrated grouped males but not in castrated isolated males. In Experiment 2, administration of either of two doses of testosterone failed to elevate the sexual behavior of intact group-housed males. These experiments show that housing with other males depresses all major measures of sexual behavior, and suggest that this is probably independent of testicular hormones.     

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.     

The relationship between aggressive and sexual behavior in male mice: Effects of testosterone and parachlorophenylalanine

The purpose of this study was to clarify the connection between aggressive and sexual behavior with the aid of testosterone propionate (TP) and parachlorophenylalanine (PCPA). Previous studies have indicated that aggressive and sexual behavior are positively correlated, and it has been suggested that both behaviors are related to the level of general arousal. Testosterone has documented effects on both aggressive and sexual behavior. It has been hypothesized that these effects are due to an increased level of general arousal. If this is the case, aggressive and sexual behavior could be restored by administration of drugs excitating the central nervous system, e.g., PCPA. The present study examined the effects of TP and PCPA on aggressive and sexual behavior in gonadectomized male mice. Control animals were injected with sesame seed oil or saline. The level of aggressiveness was assessed by means of dyadic tests with gonad-intact male opponents. For the sexuality tests, a receptive female was placed in the home cage of the experimental male. The results showed that male mice injected with PCPA were more aggressive than the males of the other groups, while the TP-exposed males expressed the most sexual activity. Compared to the control group, the PCPA and TP groups were more active in both the aggression and the sexuality tests. These findings lend support to the hypothesis that the earlier documented correlations between aggressive and sexual behavior could be due to both behaviors being dependent on a certain level of general activation. Aggr. Behav. 24:367–377, 1998. © 1998 Wiley-Liss, Inc.     

Some aspects of Rashevsky's theory of delayed reflexes

A closed solution of the integral equation obtained by N. Rashevsky, with the assumption that the inhibitory influence between centers is a constant, i.e., independent of the distance apart, is obtained. Furthermore, a more general kernel, representing a variable inhibitory influence, which in our case is a monotonic (increasing or decreasing) function of the distance between centers, is introduced. The resulting integral equation is solved and some properties of the solution discussed.     

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.     

Isolation-induced facilitation of male sexual behavior in mice

Sexual performance of male mice housed individually or in groups of 3 or 12 was compared. Experiment 1 examined naive males presented at weekly intervals with ovariectomized, estrogen-primed, progesterone-treated females. Performance in isolates was consistently superior and reached an asymptote that was twice that of grouped animals. Reversal of housing conditions reversed performance. Experiment 2 varied intervals of isolation among subjects, finding facilitation at several intervals. Experiment 3 compared animals under different population densities. Density did not alter the effects of isolation and grouping. In all experiments, additional tests with target males indicated that aggressive and sexual performance were moderately correlated and responded similarly to parametric manipulations. These results parallel and extend studies of isolation-induced aggression.     

Histories of sexual abuse in adolescent male runaways

In this study, data on sexual victimization in the histories of 89 Canadian male runaways as well as information on physical victimization, family structure, family financial stability, delinquent and criminal activities, and reasons for running away from home were evaluated. The population of male runaways evidenced dramatically higher rates of sexual and physical abuse than did randomly sampled populations. Sexually abused and nonsexually abused male runaways shared characteristics noted in the literature as common to runaways: problem families, high rates of delinquency, depression, tension, low self-image, and history of physical abuse. Sexually abused male runaways differed from nonsexually abused runaways in their reactions to their runaway event, with sexually abused male runaways responding in highly avoidant patterns coupled with extreme withdrawal from all types of interpersonal relationships. These differences are explained as consistent with known sequelae of sexual abuse, and the implications for treatment by runaway shelters and for further research are suggested.     

Hormonal control of sexual attraction in pseudohermaphroditic female dogs

Groups of female dogs exposed to different degrees of androgenic stimulation during development and a control group of ovariectomized females were tested for their attraction to tethered male and female stimulus animals. Attraction to the male was measured before and after administration of estradiol, and attraction to an estrous female was tested before and after administration of testosterone propionate (TP). Time spent visiting the tethered male was approximately equal for all groups prior to hormone treatment, but after receiving estradiol, control females exhibited a pronounced increase in visiting time; the second longest visits were paid by females that had received moderate amounts of androgen before birth; more heavily androgenized females exhibited no increase in attraction to the male despite estradiol injections. Visits to the estrous female before administration of TP were longer for some groups than for others, but there was no relation between the degree of perinatal androgenization and mean visiting time. After injections to TP the most pronounced increase in visiting was shown by females that had received the largest amounts of androgen during development, and the second largest increase occurred in the prenatally androgenized group. Control females showed the smallest increase in visiting time.     

Neurochemical aspects of the sexual response cycle

What drives the human sexual response cycle? The human sexual response cycle is a highly complex phenomenon that encompasses many transmitters and transmitter systems centrally and peripherally. The endocrine system is also intricately involved in the brain and in the periphery organs. Integration of these systems is a function of the nervous system that ultimately produces a vast array of cognitive, emotional, physiological, and behavioral responses. Therefore, it is not surprising that a disturbance in even a single system will lead to dysfunction in one or more phases of the sexual response cycle. This article highlights the complex roles the aminergic system plays along with key hormones that are equally involved. The article also points out how rudimentary and fragmented our knowledge is in this field and how few controlled studies are available. The potential for development of specific agents that target selective sexual dysfunctions is exemplified in sildenafil, the first such agent ever to be brought to market.     

Cultural aspects of male sex aggression

Sex aggression is the forceful pursuit of a sexual goal that offends the victim. Most college women report encountering sex aggression, and about one quarter of college males admit forcefully persisting in their pursuit of a sexual goal after they realize that it is disagreeable and offensive to the female. Three explanations for the existence of this substantial number of sex aggressors are discussed and tested. The data are not consistent with the explanation that the young men are responding to feelings of powerlessness. The data are consistent with the explanation that sex aggression is a socially learned aggressive behavior. The data are also consistent with the explanation that sex aggression is a response to structural strain (Merton's anomie) that is mediated by cultural legitimations.     

Adult male survivors of childhood sexual abuse

This paper outlines the conclusions drawn from a qualitative research study which involved in-depth interviews with 2.5 adult males who had been sexually abused during childhood. The full findings have been described in Adult Male Survivors of Childhood Sexual Abuse published by Pitman (1995). The book includes many of the men's first person accounts of their experiences of abuse.     

Alterations of male sexual behavior by learned aversions to hamster vaginal secretion

Male hamsters poisoned after their first adult exposure to the vaginal secretion of female hamsters became hesitant to approach and ingest the secretion. The same aversion-training procedure also altered the responses of males to estrous females, changing the latency, frequency, and duration of a variety of behaviors that are commonly taken as indexes of sexual attraction or arousal and of copulatory performance. The effects suggest that the aversions to vaginal secretion alter the perceived meaning of the secretion for male hamsters, and analysis of the correlations between various measures of sexual arousal and performance support the hypothesis that separate mechanisms underlie the effects of the secretion on appetitive and consummatory sexual behavior.