Copulatory Experience Research Articles

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.

Region-specific effects of copulation on dendritic spine morphology and gene expression related to spinogenesis in the medial preoptic nucleus of male rats

The medial preoptic nucleus (MPN) plays an essential role in the control of male sexual behavior. In rats, the central part of the MPN (MPNc) contains a sexually dimorphic nucleus exhibiting male-biased morphological sex differences. Although it has been suggested that the MPNc of male rats functions to induce sexual arousal, the mechanisms by which male rats are sexually aroused to successfully achieve copulation are poorly understood. We recently showed that increased neuronal activity in the MPNc of male rats during copulation is higher at their first copulation compared with later copulations, indicating that a plastic change in excitatory synaptic transmission occurs with copulatory experience. In this study, we tested the hypothesis that changes to dendritic spines at structural and molecular levels occur following copulatory experience. First, we examined the effects of at least two copulations on the morphology of dendrites and spines in the MPNc and in the lateral and medial parts of the MPN (MPNlm) of male rats. In the MPNc, the total number of dendrites and their branches, and the surface area of dendrites were not significantly affected by copulation. However, the copulatory experience, specifically experience of ejaculation, significantly reduced the density of mushroom spines but not of filopodia, thin or stubby spines in the MPNc. In the MPNlm, the copulatory experience, specifically experience of ejaculation, significantly increased the surface area of dendrites, although there was no significant effect of copulation on spine density. Next, we measured the mRNA levels of genes encoding actin-binding proteins related to spinogenesis after male rats had copulated for their first and second times. Copulatory stimuli, especially stimuli from ejaculation, significantly reduced the mRNA levels of drebrin A and spinophilin in the MPNc but not in the MPNlm. These results indicate that copulatory experiences, especially experience of ejaculation, reduce spine density in the MPNc of male rats, which may result, in part, from downregulation of genes encoding actin-binding proteins.

Maternal stress during pregnancy predicts methylation of the glucocorticoid receptor gene (NR3C1) in borderline personality disorder

The medial preoptic nucleus (MPN) plays an essential role in the control of male sexual behavior. In rats, the central part of the MPN (MPNc) contains a sexually dimorphic nucleus exhibiting male-biased morphological sex differences. Although it has been suggested that the MPNc of male rats functions to induce sexual arousal, the mechanisms by which male rats are sexually aroused to successfully achieve copulation are poorly understood. We recently showed that increased neuronal activity in the MPNc of male rats during copulation is higher at their first copulation compared with later copulations, indicating that a plastic change in excitatory synaptic transmission occurs with copulatory experience. In this study, we tested the hypothesis that changes to dendritic spines at structural and molecular levels occur following copulatory experience. First, we examined the effects of at least two copulations on the morphology of dendrites and spines in the MPNc and in the lateral and medial parts of the MPN (MPNlm) of male rats. In the MPNc, the total number of dendrites and their branches, and the surface area of dendrites were not significantly affected by copulation. However, the copulatory experience, specifically experience of ejaculation, significantly reduced the density of mushroom spines but not of filopodia, thin or stubby spines in the MPNc. In the MPNlm, the copulatory experience, specifically experience of ejaculation, significantly increased the surface area of dendrites, although there was no significant effect of copulation on spine density. Next, we measured the mRNA levels of genes encoding actin-binding proteins related to spinogenesis after male rats had copulated for their first and second times. Copulatory stimuli, especially stimuli from ejaculation, significantly reduced the mRNA levels of drebrin A and spinophilin in the MPNc but not in the MPNlm. These results indicate that copulatory experiences, especially experience of ejaculation, reduce spine density in the MPNc of male rats, which may result, in part, from downregulation of genes encoding actin-binding proteins.

Sexual odor preference and dopamine release in the nucleus accumbens by estrous olfactory cues in sexually naïve and experienced male rats

Sexual behavior is a natural reward that activates mesolimbic dopaminergic system. Microdialysis studies have shown that extracellular level of dopamine (DA) in the nucleus accumbens (NAcc) significantly increases during copulation in male rats. The NAcc DA level is also known to be increased during the presentation of a sexually receptive female before mating. This rise in DA was probably associated with sexual motivation elicited by incentive stimuli from the receptive female. These microdialysis studies, however, did not thoroughly investigated if olfactory stimuli from estrous females could significantly increase the extracellular DA in the NAcc of male rats. The present study was designed to examine systematically the relationship between the expression of preference for the olfactory stimuli from estrous females and the effects of these stimuli on the extracellular DA levels in the NAcc measured by in vivo microdialysis in male Long-Evans (LE) rats. We used two types of olfactory stimuli, either airborne odors (volatile stimuli) or soiled bedding (volatile plus nonvolatile stimuli). The sexually experienced male rats, which experienced six ejaculations, significantly preferred both of these olfactory stimuli from estrous females as opposed to males. Exposure to these female olfactory stimuli gradually increased extracellular DA in the NAcc, which reached significantly higher level above baseline during the period following the removal of the stimuli although not during the 15-min stimulus presentation period. The sexually naïve male rats, on the other hand, showed neither preference for olfactory stimuli from estrous females nor increase in the NAcc DA after exposure to these stimuli. These data suggest that in male LE rats olfactory stimuli from estrous females in and of themselves can be conditional cues that induce both incentive motivation and a significant increase in the NAcc DA probably as a result of being associated with sexual reward through copulatory experience.

The role of oxytocin and vasopressin in conditioned mate guarding behavior in the female rat

We have shown previously that female rats given their first copulatory experiences with the same male rat display mate guarding behavior in the presence of that male provided a female competitor is also present. Females given access to the familiar male show more Fos induction within regions of the brain that contain oxytocin (OT) and vasopressin (AVP) cell bodies, notably the supraoptic (SON) and paraventricular nuclei (PVN) relative to females given sexual experience with different males. The present experiments examined whether the Fos induction we previously observed within the SON and PVN occurred within OT and/or AVP neurons, and whether exogenous administration of OT or AVP prior to female rats first sexual experience could potentiate the acquisition of mate guarding behavior. Female rats that display conditioned mate guarding had significantly more double-labeled Fos/OT neurons in both SON and PVN, and significantly more Fos/AVP neurons in the PVN. Peripheral administration of OT or AVP prior to their first sexual experience with the familiar male facilitated different aspects of mate guarding: OT augmented affiliative behaviors and presenting responses whereas AVP augmented interference behavior. These results indicate that female rats' first experiences with sexual reward when paired with the same male induce changes to bonding networks in the brain. Moreover peripheral administration of OT or AVP during their first sexual experience can augment different aspects of mate guarding behavior.

Somatosensory conditioning of sexual arousal and copulatory behavior in the male rat: A model of fetish development

Previous studies have established that neutral olfactory cues associated with sexual reward or inhibition become conditioned stimuli that direct male or female rats toward or away from potential sex partners bearing the cue. Here we examined the ability of a somatosensory cue to exert stimulus control over sexual arousal and copulation in male rats. In the first experiment, two groups of sexually naïve male rats had their first copulatory experiences with receptive females in bilevel chambers with or without a rodent jacket. On a final copulatory test, half of the rats in each group were tested with the jacket on or off. Rats trained and tested without the jacket copulated normally, as did rats trained and tested with the jacket on, and rats trained without the jacket but tested with the jacket on. However, significantly fewer rats trained with the jacket on but tested with the jacket off copulated to ejaculation, and those that did made significantly fewer anticipatory level changes and had fewer significantly longer mount, intromission, and ejaculatory latencies, and fewer ejaculations. In the second experiment, one group of sexually naïve males was given differential conditioning trials in bilevel chambers to associate the jacket on with sexual reward (copulation to ejaculation with a sexually receptive female) and the jacket off with sexual inhibition (thwarted copulatory attempts with a sexually nonreceptive female). A second group had the opposite order of association. A final test with receptive females was made for all males with the jacket on. Males trained to associate the jacket with excitation displayed normal copulation whereas males trained to associate the jacket with inhibition displayed significantly fewer anticipatory level changes and ejaculations, and had significantly longer ejaculation latencies. Thus, somatosensory cues can signal sexual excitation or inhibition in male rats depending on the conditioning history.

Sexual experience blocks the ability of clitoral stimulation to induce a conditioned place preference in the rat

We have previously established the rewarding value of clitoral stimulation (CLS) through the demonstration that manual, distributed, CLS induces a significant conditioned place preference (CPP) and conditioned partner preference in naïve, hormonally primed and non-hormonally primed rats. The present experiment asks whether previous sexual experience might inhibit the ability of clitoral stimulation to induce a conditioned place preference.Female Long–Evans rats were ovariectomized and treated with 10μg of estradiol benzoate (EB) 48h and 500μg of progesterone (P) 4h prior to receiving either 0, 1, or 5 consecutive copulatory sessions with a sexually vigorous male. Each copulatory session ended when females received at least 1 ejaculation. Females then experienced 10 alternating trials of distributed CLS or no CLS paired with one side of a non-biased CPP box under the same hormone-priming regimen. Females that experienced 5 consecutive copulatory sessions did not develop a significant place preference indicated by both a preference score (the proportion of time spent in the reinforced chamber) and a difference score (time in the non-reinforced chamber minus the time in the reinforced chamber) compared prior to and following the 10 conditioning trials. This suggests that repeated copulatory experience might induce a desensitization of the genitosensory circuit since copulation includes both clitoral, and vaginocervical stimulation from mounts plus intromissions. Alternatively, repeated sexual experience prior to conditioning may generate a UCS pre-exposure effect that cannot be altered when manual clitoral stimulation is paired with a new environment.

Influence of Progesterone on Sexual Performance in Male Rats

It has been documented that copulatory experience can alter or improve sexual performance in male rats. However, the hormonal basis and the number of sexual encounters needed for a rat to acquire sufficient performance remains unclear. The aim of this study was to examine whether levels of testosterone and progesterone are associated with sexual performance in male rats. Adult male Wistar Hannover rats were exposed to a receptive female for 15 minutes every other day for 9 days for acquiring sexual experience. After training protocol, rats were scored as low or high sexual performers. Hormonal levels (testosterone and progesterone) were evaluated in both trained and non-trained control groups. Our results showed that a 9-day training period was not sufficient for some male rats to acquire a good level of sexual performance. While 42.5% of the rats displayed excellent sexual performance during the training sessions, 17.5% showed adequate performance, 7.5% had low sexual activity, and 32.5% of the rats did not display any sexual behaviors whatsoever. Additionally, after 4 days of training, rats with excellent/adequate performance showed a significant decrease in ejaculation latency relative to the first day of training. The rats with low or no sexual activity had lower progesterone levels relative to those displaying the highest sexual performance after 9 days of training. Testosterone, in turn, was also significantly reduced in animals with low/no sexual performance compared with excellent/adequate rats. In conclusion, progesterone may be a limiting factor to promoting sexual performance in male rats.

成虫照射したアリモドキゾウムシ雄とペア飼育した雌の交尾・産卵行動

The effects of irradiation on copulatory and oviposition behavior in the sweetpotato weevil , Cylas formicarius (Fabricius) were evaluated using females irradiated with 50 Gy gamma rays during the pupal stage, females irradiated at 200 Gy during the adult stage, and non-irradiated normal females. All types of females copulated with males irradiated during the adult stage or normal males. The females irradiated during the pupal stage did not complete oviposition or produce offspring after copulation when paired with irradiated or normal males, similar to females that did not copulate. The females irradiated during the adult stage exhibited oviposition behavior during a short period just after copulation but gradually stopped , and none produced offspring. Normal females that copulated with males irradiated during the adult stage laid eggs but produced no offspring, whereas they produced offspring when mated with normal males. These results can be used to estimate the competitive ability of released males irradiated during the adult stages against wild males. Using a normal virgin female trap in the field, her copulatory experience and partner can be detected; i.e. , if the female lays eggs, then this indicates she has copulated, and if she fails to produce offspring, this indicates that she has copulated with a released male irradiated as an a adult.

Effects of mating experience on subsequent reproductive behaviour and sperm release in the spider Nesticodes rufipes

During a mating season, individuals encounter potential mates that have varied copulatory experiences. Such experience may influence the likelihood and nature of subsequent reproductive behaviour and sperm release within a female/male dyad. We examined the influence of an individual's sexual experience on its subsequent mating activities and that of a potential partner in a cobweb spider, Nesticodes rufipes. Our results suggest that an individual's prior sexual experience influenced its own subsequent motivation, but had little effect on that of the potential partner. For females, their prior experience decreased receptivity and increased aggressiveness towards the second male, while having little effect on the subsequent male's motivation (i.e. approach). Specific aspects of a female's initial mating experience (i.e. plug formation) did however influence the nature of subsequent copulation, which in turn influenced sperm release. For males, their prior experience decreased the latency to approach the female and increased the efficiency of pedipalp insertion, but male experience had little effect on the behaviour of the female. Our results suggest that mating experience may benefit both sexes in that (1) females that are not sperm limited may incur high costs from remating (time) and (2) males show experience-related improvement in copulatory efficiency.

Exposure to female rats produces differences in c- fos induction between sexually-naı̈ve and experienced male rats

Sexual incentive-induced Fos-like immunoreactivity (Fos-Li) within six neural regions implicated in male sexual behavior was investigated in both sexually-naı̈ve and experienced male rats. Sexual experience was limited to one copulation culminating in ejaculation 24 h prior to testing. On test-day, subjects were placed within a cylindrical arena for 15 min on the opposite side of a perforated, Plexiglas partition from one of three targets: an uninhabited area, a non-estrous female, or an estrous female. Then 1 h later, each subject was sacrificed and its brain prepared for subsequent immunocytochemical staining. Analyses revealed a main effect of target stimulus on c- fos expression within the nucleus accumbens shell and core of male subjects. In addition, sexually-experienced subjects demonstrated significantly more Fos-Li within the nucleus accumbens shell in response to an estrous female versus a non-estrous female. There was also greater estrous cue-induced Fos-Li in the nucleus accumbens shell of experienced subjects when compared to naı̈ve subjects. These data support previous suggestions implicating the nucleus accumbens in the generation of male sexual motivation. In addition, copulatory experience, even when limited to one ejaculation, seems to mediate long-term changes in the response properties of nucleus accumbens neurons that may reflect the value enhancement of primary female incentives.

Conditioning and Sexual Behavior: A Review

Sexual behavior is directed by a sophisticated interplay between steroid hormone actions in the brain that give rise to sexual arousability and experience with sexual reward that gives rise to expectations of competent sexual activity, sexual desire, arousal, and performance. Sexual experience allows animals to form instrumental associations between internal or external stimuli and behaviors that lead to different sexual rewards. Furthermore, Pavlovian associations between internal and external stimuli allow animals to predict sexual outcomes. These two types of learning build upon instinctual mechanisms to create distinctive, and seemingly “automated,” patterns of sexual response. This article reviews the literature on conditioning and sexual behavior with a particular emphasis on incentive sequences of sexual behavior that move animals from distal to proximal with regard to sexual stimuli during appetitive phases of behavior and ultimately result in copulatory interaction and mating during consummatory phases of behavior. Accordingly, the role of learning in sexual excitement, in behaviors that bring about the opportunity to mate, in courtship and solicitation displays, in sexual arousal and copulatory behaviors, in sexual partner preferences, and the short- and long-term influence of copulatory experience on sexual and reproductive function is examined. Although hormone actions set the stage for sexual activity by generating the ability of animals to become sexually excited and aroused, it is each animal's unique experience with sexual behavior and sexual reward that molds the strength of responses made toward sexual incentives.

Sexual Motivation in the Male Rat: The Role of Primary Incentives and Copulatory Experience

Two experiments explored the motivational impact of primary incentive female cues on the operant behavior of sexually naive and experienced male rats. In the first experiment, a straight-arm runway was used to assess the subjects' motivation to approach a goalbox containing either male or female “targets.” Twelve sexually naive Long-Evans males ran for: (1) an empty goalbox; (2) a male conspecific; (3) an ovariectomized (OVX) female; (4) an OVX female given estradiol; (5) or an OVX female treated with estradiol and progesterone. A perforated Plexiglas partition in the goalbox prevented the subject males from physically interacting with the targets, although olfactory, visual, and auditory cues were accessible. We hypothesized that subjects would manifest shorter run times (reflecting greater motivation) when the goalbox contained a receptive/proceptive female as opposed to a nonreceptive female target. Subjects' run times were ordered depending on the nature of the target (from slowest to fastest): empty goalbox, male conspecific, OVX female, OVX + estradiol female, and OVX + estradiol + progesterone female. As predicted, subjects ran significantly faster for a receptive/proceptive female than for a nonreceptive female, indicating that sexually naive males are inherently motivated by female precopulatory cues. In the second experiment, 30 sexually naive male subjects ran for a goalbox containing either a nonestrous (OVX) or an estrous (OVX + estradiol + progesterone) female. Following six trials, 10 males were allowed one intromission with a receptive female, 10 males experienced one ejaculation, and 10 remained sexually naive. Only those males having experienced an ejaculation subsequently decreased their run times for both nonestrous and estrous females, indicating that sexual reinforcement produced by ejaculation, but not intromission, further enhances the motivational impact of female incentive cues.

Erection Evoked in Male Rats by Airborne Scent from Estrous Females

In the presence of inaccessible estrous females, male rats display penile erections and associated stereotypic behavior indicative of sexual arousal. The effective stimuli for these noncontact erections (NCEs) had not been determined, but bedding soiled by estrous females was known to be ineffective. The present experiments tested for a potential role for volatile olfactory cues in evoking NCE. In Experiment 1, sexually naive male rats were observed for NCEs when tested with inaccessible, estrous females upwind ( n = 20) or downwind ( n = 20) from them under conditions that permitted or prevented visual communication. After half the males in each condition had copulatory experience, they were retested under the same conditions. In each test, only one male of 20 responded with females downwind, whereas about half the 20 males displayed NCEs with females upwind, irrespective of barrier type or, in Test 2, of sexual experience. Olfactory cues from estrous females were apparently necessary to induce NCE, whereas visual and auditory stimuli from estrous females were not sufficient to evoke NCE, nor did they affect the response to olfactory stimulation. In Experiment 2, males were downwind from estrous females ( n = 10) or anestrous females ( n = 10) that were behind opaque barriers and were anesthetized to preclude auditory communication. Results indicated that olfactory cues were also sufficient to provoke NCE in sexually experienced males. Receptive female rats apparently broadcast a volatile pheromone that promotes erection. Pheromones are well known to attract potential mates and to act in concert with other stimuli to promote mating. However, this is the first mammalian evidence for a volatile pheromone acting alone to evoke a sexual fixed-action pattern and, in that sense, acting as an airborne aphrodisiac.

Hemispheric specialization for the control of copulation in the young chick and effects of 5 α-dihydrotestosterone and 17 β-oestradiol

After intramuscular treatment with either oestradiol (1 mg/day for 4 days) or 5 alpha-dihydrotestosterone (0.5 mg/day for 7 days) the copulatory behaviour of young male chicks was tested monocularly using removable eye-patches. From day 11 to 14 copulation scores were significantly elevated in chicks treated with oestradiol or 5 alpha-dihydrotestosterone (5 alpha-DHT) and tested either binocularly or monocularly using the left eye. There was no elevation of copulation when the treated chicks were tested monocularly using the right eye. Thus, in the binocular condition neural circuits receiving input from the left eye, and therefore likely to be on the right side of the brain, are specialized for the activation of copulation. This result confirms previous findings using chicks treated with testosterone. On day 14 the eye-patches were changed to the other eye. For chicks treated with oestradiol, those now tested using the left eye showed significantly higher levels of copulation than those now using the right. In other words, there was very little interocular transfer from left eye to right eye. However, after transferring the eye patches, the chicks treated with 5 alpha-DHT had high copulation scores irrespective of the eye used. This suggests that there may be an interaction between prior copulatory experience and 5 alpha-DHT levels which leads to either interocular transfer of copulation behaviour or equal access of both eyes to the brain regions which control copulation.

Behavioral endocrinology of male rats with periodic sexual contacts with exclusive or varied females.

Sexual contact keys a profound series of acute and chronic changes in males that, presumably, are orchestrated by acute pulsatile release of hormones. An experimental paradigm is reported in which male rats were paired periodically with either the same or different estrous females to receive identical amounts of copulatory experiences. Results confirmed the hypothesis that exposure to an unfamiliar female would induce a different endocrine response which would be reflected in various androgen-sensitive systems. The "successively polygynous" males showed more sexual behavior than "monogamous" males, and their respective females solicited the males differently, as well. Circulating levels of testosterone were higher immediately after sexual contact with an unfamiliar than with a familiar female partner. There were no differences in testosterone titers among the groups when the animals were killed at either 2 or 7 weeks after the final copulatory experiences. Yet, necropsies at 2 weeks postcopulation revealed that primary and secondary sex structures from polygynous males clearly were larger. Differences between the two experimental groups were reduced after 7 weeks of sexual rest, yet, polygnous males continued to show a different structural profile than the other groups. Conclusions were that males may experience greater activation of androgen-sensitive behavior and physiology following qualitatively different sexual contacts.

Reproductive behavior and physiology of nulliparous female rats after sexual experience

There is an extensive literature suggesting that following sexual experience male mammals show chronic elevation of sexual behavior and growth of reproductive organs and glands. An hypothesis was examined in the present research that a similar pattern of changes would be revealed in females after sexual contact without the confounding influences of pregnancy and parturition. Initiatially virgin gonadally intact (Experiment I) and ovariectomized/hormone-injected (Experiment 1) female rats received precisely controlled interactions either with intact males to gain copulatory experience or with castrated males to gain social experience without copulating. Subsequently, females from each condition were observed during behavioral estrus with unfamiliar males, and all females were sacrificed the following day. Behavioral results were similar for the two experiments and failed to support the hypothesis. It was the virgin, rather than the experienced female, which solicited a male more frequently and aggressively rejected his approaches less often. Moreover, the male exhibited more and faster intromissions and ejaculations with inexperienced than with experienced females. Physiological analyses of ovaries, uteri, utero-tubal junctions, vaginae, clitorides and preputials suggested subtle quantitative and qualitative changes after sexual contact, but only in intact females and without any clear pattern of changes. Conclusions were that the striking modifications in behavior are centrally mediated in the female and are unlike those observed in the sexually experienced male. Nevertheless, the consequence for fecundity may be the same for both genders.

The relationship of male-male mounting to the sexual preferences of young rams

The purpose of this study was to determine the relationship between the frequency of male-male mounting of young rams in all-male groups and their subsequent preferences for female vs. male sexual partners. Mount interactions were monitored in the home pen of 29 rams reared in 1984 and 25 rams reared in 1985. At ∼ 8–10 months of age, and prior to copulatory experience, individual rams were simultaneously exposed to two unfamiliar estrous ewes and two unfamiliar rams. The four stimulus animals were restrained and cloth covers were placed over their perinea to prevent copulations. The Binomial Test was used to verify sexual preferences. Of the 44 rams that were sexually active in the sexual performance tests, 30 (68.2%) met the criterion for female preference, 4 (9.1%) preferred males and 10 (22.7%) exhibited no preference (i.e., were bisexual in orientation). There was little relationship between the frequency of male-male mounting by rams in all-male rearing groups and their subsequent sexual preferences. The majority of young rams prefer to mount ewes, even prior to copulatory experience, but in the absence of females will often mount other males.

The role of penile stimulation and ejaculatory experience on the development and maintenance of reproductive behavior in the bull (Bos taurus).

To determine the role of afferent input from the penis and copulatory experience on the ontogeny of reproductive behavior, 49 bulls were randomly assigned to the following groups: control; surgical penile deflection (penis deviation), which prevents intromission; penile neurectomy; or penis deviation plus neurectomy. Sexual performance tests were conducted at 3-month intervals from 9 to 24 months of age. Bulls deviated but not neurectomized mounted more frequently than bulls in the other groups. The low mount frequency for control bulls in tests in which copulation occurred was due to the sexually quiescent postejaculatory refractory period. Preventing control bulls from copulating by affixing cloth patches to females' perinea increased mount frequency to the level of deviated bulls. It is concluded that copulatory experience is not essential to the development and maintenance of normal mounting activity. However, sensory stimulation from the penis facilitates the expression of sexual behaviors.

Caffeine and copulatory experience: Interactive effects on social investigatory behavior

Three experiments test the interaction of prior copulatory experience with acute caffeine exposure on social investigatory behavior of the male Norway rat. At a dosage of 20 mg/kg or greater, caffeine counteracts a decrease in social investigation attributed to copulatory experience. At a 10 mg/kg dosage, caffeine increases social investigatory behavior prior to sexual exposure but has no comparable effect after sexual exposure. The results are interpreted as confirming a long-term effect of copulatory exposure on social investigatory behavior and as describing a dose-related interaction of caffeine exposure with prior copulatory experience. Social investigation is viewed as a preliminary component of sexual behavior and the decrease in social investigation following copulatory experience as a gain in efficiency of social discrimination. Acute caffeine exposure apparently interferes with access or retrieval of reference information in long-term memory.