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)     

Electrophysiological and ultrasonic correlates of reproductive behavior in the male rat.

Monitored the ultrasonic vocalizations of 13 male Long-Evans rats and determined the correlation of these vocalizations with electrophysiological activity measured by chronically implanted hippocampal and cortical electrodes during mating with a female rat. Hippocampal theta rhythms were significantly correlated with high activity, mounting, intromissions, and preejaculatory excitatory behavior and were also significantly associated with 50-kHz short ultrasonic vocalizations. Postmount or postintromission behaviors (grooming, exploration) were closely correlated with an absence of ultrasonic vocalizations and the onset of irregular low-amplitude hippocampal EEG recordings. Long 22-kHz vocalizations occurred during the postejaculatory refractory period. Shorter 22-kHz vocalizations occurred during mating and were associated with unsuccessful intromissions or mounting attempts. Postejaculatory long 22-kHz vocalizations were significantly associated with irregular high-amplitude hippocampal EEG tracings, while preejaculatory short 22-kHz vocalizations were also accompanied by sleeplike irregular high-amplitude hippocampal EEG tracings with cortical spindling. Findings suggest that ultrasonic vocalizations are indicators of the sexual arousal of mating rats. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of ibotenic acid lesions of the nucleus accumbens on paced mating behavior in the female rat.

The present study investigated the role of the nucleus accumbens (NAcc) in paced mating behavior in female rats. A sexually receptive female rat will approach and withdraw from a sexually active male, thereby controlling the timing of the receipt of sexual stimulation (e.g., mounts, intromissions, ejaculations). In this study, ibotenic acid lesions in the NAcc core increased the likelihood that a female rat would withdraw from a male rat after a mount but did not affect contact return latency or sexual receptivity. lbotenic acid lesions in the NAcc shell did not affect paced mating behavior or sexual receptivity. The results suggest that the NAcc core plays a role in suppressing withdrawal behavior in response to less intense mating stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Roles of estrogen receptor-alpha gene expression in reproduction-related behaviors in female mice

The role of gene expression of the estrogen receptor-alpha form (ER alpha) in the regulation of female reproductive behavior was investigated in estrogen receptor knockout (ERKO) mice, deficient specifically for the ER alpha, but not the ER beta, gene. Estrogen- or estrogen- plus progesterone-treated gonadectomized ERKO mice did not show any lordosis response. Detailed behavioral analysis revealed that ERKO females were also deficient in sexual behavioral interactions preceding the lordosis response. They were extremely rejective toward attempted mounts by stud male mice, which could not show any intromissions. During resident-intruder aggression tests, gonadally intact ERKO females were more aggressive toward female intruder mice than wild-type (WT) mice. Gonadectomy did not influence the levels of aggressive behavior, and their genotype differences when mice were tested both before and after gonadectomy. However, when mice were tested after gonadectomy for the first time, very few ERKO mice showed aggression. In contrast to aggression, male-type sexual behavior shown by resident mice toward female intruder mice during aggression tests was not different between ERKO and WT mice and was completely abolished after gonadectomy of the resident mice. Finally, it was also found that ERKO females showed greatly reduced levels of parental behavior toward newborn pups placed in their home cage. These changes in parental behavior were not influenced by gonadectomy. ERKO females retrieved significantly fewer numbers of pups with longer latencies compared with wild-type (WT) or heterozygous (HZ) littermates when they were tested as gonadally intact or 20-65 days after gonadectomy. In addition, during parental behavior tests, a significantly higher percentage of ERKO mice exhibited infanticide compared with WT and HZ mice, which rarely showed infanticide. Taken together, these findings suggest that ER alpha gene expression plays a key role in female mice, not only for sexual behavior but also for other interrelated behaviors, such as parental and aggressive behaviors. In addition, persistence of genotype differences in parental and aggressive behavior after gonadectomy indicates that ER alpha activation during neural developmental processes may also be involved in the regulation of these behaviors.     

Lead toxicosis in a captive bottlenose dolphin (Tursiops truncatus) consequent to ingestion of air gun pellets

Male rats of the Wistar strain were selected as good copulators (displaying at least 1 ejaculation in each of three consecutive tests for male sexual behavior) and sexually sluggish animals (displaying no ejaculations in each of three consecutive tests). The administration of low doses (1 and 2.5 mg/kg, i.p.) of kainic acid in sexually sluggish rats induced an enhancement of some parameters of copulatory behavior. In particular, significant reductions in latency to the first mount and intromission and increases in frequency of mounts and intromissions were observed. In contrast, the drug failed to exert any effect in good copulators. At the dose of 5 mg/kg (i.p.) kainic acid exerted an inhibitory effect on sexual behavior parameters both in good copulators and in sluggish rats. A persistent increase in latency to the first mount, intromission and ejaculation, and reduction in frequency of mounts, intromissions and ejaculation both in good copulators and in sluggish rats were observed 20 days after kainic acid treatment at the higher dose. No persistent effect of kainic acid 1 and 2.5 mg/kg was observed 20 days after treatment. These results suggest that kainic acid may affect in a dose-dependent manner several copulatory parameters of male sexual behavior repertoire. The bimodal effects could be explained considering a possible interaction of kainic acid with different neurotransmissions or receptor subtypes.     

Mating-induced inhibition of receptivity in the female golden hamster (Mesocricetus auratus): II. Stimuli mediating short-term effects.

In the female golden hamster, mating with an intact male results in reduced receptivity toward a second male. In Experiment 1, females received various types of mating stimuli (e.g., mounts from an aproned male, intromissions from a vasectomized male, a simulated copulatory plug, a male in a hardware cloth cylinder, or several of these stimuli in combination). Although stimuli associated with male intromissions appeared to be most effective in altering the female's responsiveness to a subsequent male, treatments that included intromissive stimuli also resulted in the longest periods of lordosis. In Experiment 2 we found a highly significant inverse relation between the duration of lordosis in the presence of a male enclosed in a hardware cloth cylinder and lordosis duration with a second male that was free to copulate. In Experiment 3 we further showed that it was not the presence of a male in the cylinder that was the essential stimulus for producing this effect but rather the act of lordosis itself. By varying lordosis time and the number of intromissions independently (Experiment 4), we convincingly showed that short-term inhibition of receptivity in the hamster is attributable to lordosis duration per se rather than to male intromissions, as had been previously reported. (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)     

Sexual free behavior in male rats (Rattus norvegicus).

Male rats ( Rattus norvegicus) were given continuous access to estrous female rats for 24 hrs each day for 10 days. During the 1st 12 hrs, the rats achieved an average of 10 ejaculations, followed by a 1- to 2-day period with little sexual activity. During the last 7 days, the rats maintained a reasonably stable equilibrium level of 3 ejaculations per day. These occurred predominantly during the dark phase of the diurnal cycle, they frequently occurred in a cluster, and they usually occurred shortly after the introduction of a novel estrous female. Except for quantitative differences, these results are generally consistent with conventional research but systematically extend the generality of the results to the context of the free behavior situation. The availability of sexual activity had no appreciable effect on food and water intake, but it did decrease the amount of running activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Studies of instrumental behavior with sexual reinforcement in male rats (Rattus norvegicus): II. Effects of preoptic area lesions, castration, and testosterone.

We studied effects of lesions to the medial preoptic area (POA), castration, and testosterone replacement on instrumental and unconditioned sexual behavior in male rats. We achieved instrumental measures of sexual motivation by training males to work for an estrous female, presented in an operant chamber under a second-order schedule of reinforcement. POA lesions abolished mounts, intromissions, and ejaculation but did not disrupt instrumental responses, investigation of the female, or abortive mounting attempts. Castration abolished attempts to copulate and also caused a marked decrease in instrumental responses. Testosterone resulted in the prompt reinstatement of instrumental responses and more gradual recovery of unconditioned sexual behavior. We discuss these results in terms of the motivational and performance effects of these neuroendocrine manipulations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses to copulatory stimulation in neonatally androgenized female rats.

Five experiments evaluated the extent to which copulatory stimulation could ameliorate the anestrus and sterility exhibited by neonatally androgenized female Long-Evans rats (N?=?102). The age at which Ss began to exhibit persistent vaginal estrus and the degree of sexual receptivity exhibited under several testing paradigms were found to be inversely related to the dose of testosterone propionate (TP) injected neonatally. With increasing numbers of mounts received, both the number of androgenized Ss exhibiting sexual receptivity and the quality of the estrous behavior exhibited tended to increase. Ss injected with high doses of TP (500 μg) usually showed little or no receptive behavior even in the most extensive behavioral tests. However, under some testing conditions Ss receiving 50 μg of TP neonatally, while showing little or no receptivity during initial mounts, showed increased receptivity as behavioral tests were extended. Following matings that included 1–5 ejaculations, only control Ss were observed to become pregnant. However, when androgenized females cohabited with males for an extended period, Ss that had neonatally received .5 μg of TP, but not higher doses, did become pregnant. It is concluded that (1) the capacity of systems mediating reproductive physiology and behavior is facilitated by stimuli associated with males; and (2) mating is a characteristic of the female rat, which can be manipulated by injection of hormones during the neonatal period. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motion picture analysis of rat mating behavior.

Studied the interaction and coordination of male and female rats during mounting and lordosis, using 12 primiparous female and 4 male Sprague-Dawley rats. Head, body, and limb movements of the female are described in relation to forelimb and pelvic movements of the male during mounting. Data show that (a) mounts with ejaculation were longer than mounts without ejaculation; (b) during mounts with ejaculation or intromission, the elevation of the female's head was maintained after perineal contact was lost; whereas when there was no deep vaginal penetration, the head began lowering before loss of perineal contact; and (c) lordosis persisted longest after dismount when intromission accompanied mounts. The following objective definition of lordosis is provided: Onset is the beginning of head elevation; termination is the raising of a paw from the floor of the cage after dorsiflexion of the vertebral column. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Copulatory behavior of male rats given intermittent electric shocks: Theoretical implications.

Results of 3 experiments show that mildly painful .5-sec shocks, delivered to the skin of 17 Long-Evans and 6 Sprague-Dawley male rats every 30 sec in the presence of a receptive female, reduced the intervals between intromissions and the latencies to resume mounts and intromissions after ejaculation, but did not affect the number of intromissions preceding ejaculation. The effects of shock on postejaculatory intromission and mount latencies support F. A. Beach and A. M. Holz-Tucker's concept of the postejaculatory period consisting of absolute and relative phases. The pattern of results led to the development of a model of the fluctuation in sexual arousal during copulation and to a modification of existing theories of the accumulation of ejaculatory potential. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anatomical, electrophysiological and pharmacological studies of ascending brainstem hippocampal synchronizing pathways

The present review has provided evidence that very potent ascending brainstem hippocampal synchronizing pathways originate in the rostral pons region (RPO and PPT), and ascend to and synapse with several midline caudal diencephalic nuclei (posterior hypothalamic and supramammillary) which send projections to the medial septal region (MS/vDBB). The medial septal region in turn is a critical nodal point, sending projections to limbic structures such as the hippocampal formation, cingulate cortex, and entorhinal cortex. The pontine and diencephalic nuclei appear to play a critical role in determining the translation of increasing levels of activation into moment to moment changes in the frequency of hippocampal theta field and theta-related cellular discharges, relayed to the MS/vDBB nuclei. The MS/vDBB nuclei appear to play a critical role in translating increasing levels of ascending synchronizing activation into moment to moment changes in the amplitude of hippocampal theta field activity and the accompanying rate and pattern of phasic theta-ON cells. The MS/vDBB carries out this role through a balance of activity in the septohippocampal cholinergic and GABA-ergic projections. Cholinergic projections provide the afferent excitatory drive for hippocampal theta-ON cells and the GABA-ergic projections act to reduce the overall level of inhibition by inhibiting hippocampal GABA-ergic interneurons (theta-OFF cells). Both activities must be present for the generation of hippocampal theta and theta-related cellular activities. The balance between the cholinergic and GABA-ergic projections may determine whether hippocampal synchrony (theta) or asynchrony (LIA, large amplitude irregular activity) occurs. These same ascending pathways influence the electrophysiological and pharmacological properties of the neocortex as well. The functional significance of the ascending brainstem synchronizing pathways is the generalized regulation of activities in these cortical structures as they relate to sensorimotor behavior.     

Determinants of mating success in the golden hamster (Mesocricetus auratus): II. Pregnancy initiation.

Investigated the initiation of pregnancy and the physiological significance of long intromissions (10–30 sec of intravaginal thrusting), in 4 experiments with 425 virgin and 808 multiparous female LVG golden hamsters and 102 stud males. Results show that virgin females required significantly less copulatory stimulation to induce pregnancy and maximize litter size. Ss receiving only long intromissions showed a 100% pseudopregnancy rate, suggesting that long intromissions can initiate the neuroendocrine response necessary to maintain pregnancy. When the male delivered only 1 or a few ejaculations, the inclusion of long intromissions significantly increased the percentage of both virgin and multiparous females that became pregnant. Order of ejaculations did not affect the proportion of multiparous females that delivered litters. However, litter size of females receiving the 1st or 5th ejaculation was significantly larger than that of females receiving the 10th or 15th ejaculation. Multiple-male matings did not augment pregnancy rates or litter sizes compared with matings with a single, rested male. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences among ovariectomized female rhesus macaques in the display of sexual behavior without and with estradiol treatment.

Ovariectomized, estrogen-primed, adult female rhesus macaques were preselected for the display of high (HLP) and low (LLP) levels of sexual performance. Eight sexually vigorous adult males were selected as partners. For 13 consecutive days each month, females received 0, 2.5, 5.0, and 10.0 μg of estradiol benzoate (EB) and were tested on Days 12 and 13 of injection. Blood samples were taken before and on the last day of each of the four injection series, and serum levels of estradiol, progesterone, and testosterone were determined with a radioimmunoassay. The HLP females (n?=?5) displayed higher levels of receptivity and proceptivity and received more mounts, intromissions, and ejaculations when tested without EB treatment than LLP females (n?=?5) did when they were tested with 10.0 μg of EB. Female receptivity, proceptivity, and attractiveness cannot be explained by estrogen action alone. The effectiveness of estrogen is limited by the somatic characteristics of the individual on which it acts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of a muscarinic antagonist on various components of female sexual behavior in the rat.

Effects of the muscarinic antagonist scopolamine on lordosis, solicitation, pacing, approach, attractivity, and activity were evaluated in ovariectomized rats brought into sexual receptivity with estrogen and progesterone. Systemic (1 mg/rat) or intraventricular (10 μg bilaterally) administration of scopolamine significantly reduced the incidence of lordosis and solicitation behaviors and disrupted typical pacing of sexual contacts with a stimulus male. In addition, females avoided contact with a stimulus male, but not a stimulus female, following intraventricular infusion of scopolamine. The levels of general activity and frequencies of sexual contacts were similar in females treated intraventricularly with scopolamine and vehicle solutions. Consequently, scopolamine disrupted various components of sexual behavior, including lordosis, solicitation, pacing, and approach, without altering female attractivity or general activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovery from sexual satiety in deer mice (Peromyscus maniculatus bairdi).

Conducted 2 experiments with 20 deer mice to delineate the time course of recovery from sexual satiety. In Exp I, the total numbers of ejaculations and intromissions attained in satiety tests were significantly decreased on the day following satiation and recovered gradually as measured in tests run after 3 and 7 days of recovery. Whereas some measures characteristic of individual series were altered by incomplete recovery, others were unaffected. In Exp II, most males ejaculated every day when tested for 5 consecutive days; the number of ejaculations per test was lowered after Day 1, but then remained relatively constant. The pattern of measures changing with recovery has implications for the development of control models of sexual behavior. The limited capacity of males to produce ejaculates implies that males should be selected for prudence in allocating ejaculates. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Receptivity of the female rat (Rattus norvegicus) after male devocalization: A ventral perspective.

Male rats (Rattus norvegicus) emit at least two patterns of vocalization during copulation, the mating call and the pre-ejaculatory call. Both calls promote immobility of the female during lordosis, but the pre-ejaculatory calls are more effective. We undertook, through ventral observations of the mating pair, to determine if the female failed to assume or maintain the lordosis posture when mounted by a devocalized male and also to determine if the devocalized male was providing adequate stimulation to induce receptive behavior. Females were more likely to move away from the devocalized males before assuming the full lordosis posture. Furthermore, they were more likely to move away before the males had a chance to engage in intromissive behavior. However, when the females remained immobile along enough for the males to achieve a mount or intromission, there was little difference in the behavior of either animal that resulted from the devocalization of the male. (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)     

Copulatory behavior of deer mice (Peromyscus maniculatus): I. Normative data, subspecific differences, and effects of cross-fostering.

In Exp I, normative data were collected on copulatory behavior in 16 male–female pairs of Peromyscus maniculatus bairdi, each mated for 5 tests. P. m. bairdi display a pattern with no lock, no intravaginal thrusting, multiple intromissions prerequisite to ejaculation, and multiple ejaculations. They had a mean of 3.6 ejaculations, with the 1st ejaculation preceded by a mean of 6.4 intromissions spaced 72 sec apart. In Exp II, data from 17 male–female pairs of P. m. Blandus were compared with data from 2 samples of P. m. bairdi and a sample of P. m. gambeli from an earlier study. Although there were no qualitative differences among subspecies, significant quantitative differences were found for 11 of the 14 measures considered. In Exp III, data from 17 males cross-fostered to Mus musculus parents on the day of birth were compared with those of deer mice reared by their own parents. Cross-fostering produced no major qualitative alterations of copulatory behavior, with significant differences from normally reared males in 4 of 18 comparisons. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)