Copulatory Behavior In Male Rats Research Articles

Tactile stimulation prevents disruptions in male rat copulatory behavior induced by artificial rearing.

Early life social interactions in gregarious mammals provide an important source of stimulation required for the development of species-typical behaviors. In the present study, complete deprivation of maternal and littermate contact through artificial rearing was used to examine the role of early social stimulation on copulatory behavior and the ejaculate in adult rats. We found that artificially reared naïve male rats were sexually motivated; nevertheless, they did not acquire the level of sexual experience that typically occurs during copulatory training. Disrupted expression of sexual experience of artificially reared rats was demonstrated by an inconsistent pattern of ejaculatory behavior across training tests. Artificial tactile stimulation applied during isolation prevented this disruption and rats achieved ejaculation in most copulatory tests. Despite the irregularity of ejaculatory behavior in isolated rats, their sperm count and seminal plug were similar to control maternally reared (sexually experienced) and artificially-reared rats that received tactile stimulation. These results suggest that tactile sensory information provided by the mother and/or littermates to the offspring is crucial for the development of copulatory behavior. The absence of social and/or tactile stimulation during early life compromises the ability of male rats to gain sexual experience in adulthood.

Sexual Incentive Motivation and Copulatory Behavior in Male Rats Treated With the Adrenergic α2-Adrenoceptor Agonists Tasipimidine and Fadolmidine: Implications for Treatment of Premature Ejaculation

Premature ejaculation is the most common sexual dysfunction in young men, and it often leads to reduced relationship satisfaction and quality of life. To determine the role of central and peripheral α2-adrenoceptors in the control of ejaculation and sexual incentive motivation in rats. Sexual incentive motivation was studied in a large arena in which a male subject could choose between approaching and remaining close to a sexually receptive female or another male. Sexual behavior was studied in standard observation cages in which a male was allowed to freely interact with a receptive female for 30 minutes. Two highly selective agonists at the α2-adrenoceptors, tasipimidine and fadolmidine, were administered before the tests. Low peripheral doses of fadolmidine have been reported to have effects mainly outside of the central nervous system, whereas at large doses also the central effects are evident. The time spent close to the receptive female in relation to the time spent with the male and measures of ambulatory activity were obtained from the test for sexual incentive motivation, while the habitual parameters of sexual behavior were recorded with the copulation test. Tasipimidine prolonged ejaculation latency and the interintromission interval at the dose of 200 µg/kg when data from fast-ejaculating rats were used. No other sexual parameter was modified. A dose of 100 µg/kg was ineffective. There was no consistent effect on sexual incentive motivation, although modest sedation was observed. Fadolmidine, a drug that does not easily penetrate the blood-brain barrier, had no effect on sexual incentive motivation at any of the doses used (3, 30, and 100 µg/kg). The largest dose had clear sedative effects. The lower doses had no systematic effect on sexual behavior, not even when only fast or very fast ejaculating males were analyzed. The findings are relevant to the search for treatments for premature ejaculation that are specific enough to selectively delay ejaculation. The procedures used here are standard in the field and yield the most reliable data. Whether the effects observed in male rats are directly transferrable to men can only be determined through clinical studies. The observation that drugs acting at central but not peripheral α2-adrenoceptors prolong ejaculation latency without affecting any other parameter of sexual behavior or sexual incentive motivation suggests that this kind of drug may be suitable for treating premature ejaculation.

FEATURES OF ASSESSING THE SEXUAL BEHAVIOR OF MALE RATS IN THE STUDY OF THE EFFECTS OF COMPOUNDS THAT HAVE A STIMULATING EFFECT ON SEXUAL FUNCTION

The paper presents a comparative analysis of information content of methods for assessing the copulatory behavior of male rats with the introduction of compounds that have a stimulating effect on the sexual activity of animals. The social significance of the problem of sexual dysfunctions determines the relevance of the development of various experimental models of sexual behavior that allow assessing the effectiveness and safety of new drug. The probability of detecting the activating effect of pharmacological agents on sexual activity directly depends on the correct choice of the experimental model. The drugs of the central mechanism of action galantamine hydrobromide (1mg/kg) and loxidan (1,7mg/kg), were used as pharmacological agents; drugs of peripheral action were yohimbine hydrochloride (2,6mg/kg) and vardenafil hydrochloride (1,7mg/kg). It has been shown that the determination of the stimulating effects of compounds of the central mechanism of action is possible using methods with different testing duration (from 15 to 180min). Thus, the introduction of galantamine enhances the sexual activity of males in terms of the copulation rate, the number of perfect ejaculations and the duration of the post-ejaculatory refractory period, loxidan in terms of the total number of intromissions and relative rest time in tests of limited duration. In the test showing the completed sexual cycle of males, the stimulating effects of galantamine are shown in terms of the number of completed copulatory series and the number of completed ejaculations. To assess the activating effects of compounds of the peripheral mechanism of action, the expediency of using experimental models with a test duration of 30 minutes or more was shown. The most informative test is the test of paired interaction between a male and a female until the male reaches the state of sexual exhaustion. A method with high information content is presented, which provides a high probability of detecting the activating effect of compounds on the sexual function of male rats.
 Determination of the stimulating effects of compounds of the central mechanism of action is possible using methods with different test duration

Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation?

BackgroundLorcaserin is an anti-obesity drug whose weight loss effect results from 5-hydroxytryptamin (5-HT)2C receptors activation. The 5-HT2C receptor was shown to participate in the physiological control of ejaculation, but no data addressing a putative effect of lorcaserin on ejaculation exist. AimTo investigate the effects of lorcaserin in different in vitro and in vivo experimental models of ejaculation in rats. MethodsContractile responses to lorcaserin in rat seminal emission organs in vitro (prostatic and epididymal vas deferens, cauda epididymis, and seminal vesicles), analysis of male rat copulatory behavior, and electromyographic recording of bulbospongiosus muscle in anesthetized animals were studied. Main Outcome MeasuresThe main outcome measures included in vitro contraction of seminal emission organs and evaluation of the male rat copulatory behavior. The male rat sexual behavior in terms of copulation latency, ejaculation latency, mount and intromission frequency, and ejaculation frequency of sexually experienced adult male rats with a receptive female were also recorded. ResultsLorcaserin (1.0 nM to 1.0 mM) had no significant effects on the in vitro contractility of seminal emission organs smooth muscle (cauda epididymis, vas deferens, and seminal vesicles). On the other hand, lorcaserin administration (0.3–1.0 mg/kg, intravenous) induced ejaculation in anesthetized rats, which was prevented by the 5-HT2C-selective antagonist SB 242084 (0.1 and 0.3 mg/kg, intravenous). Single-dose treatment of non-anesthetized male rats with lorcaserin (1.0, 4.0, or 10 mg/kg, per os) induced non-copulating ejaculations in sexually naïve rats. Lorcaserin also had pro-ejaculation effects by decreasing the ejaculation threshold of copulating rats by half. The pro-ejaculatory effects of lorcaserin were reversible as the ejaculation threshold of treated rats recovered after a 1-week washout period. Clinical ImplicationsDue to its reported clinical safety, repurposing lorcaserin for the treatment of delayed ejaculation may be suggested. Strengths & LimitationsThe pro-ejaculatory effect of lorcaserin administration and the role of 5-HT2C were demonstrated in different experimental models of ejaculation in rats. The lack of studies in putative experimental models of delayed ejaculation is a limitation of this study. ConclusionOur results demonstrate that the clinically approved 5-HT2C agonist lorcaserin is a strong facilitator of ejaculation in rats.de Almeida Kiguti LR, Pacheco TL, Antunes E, et al. Lorcaserin Administration has Pro-Ejaculatory Effects in Rats via 5-HT2C Receptors Activation: A Putative Pharmacologic Strategy to Delayed Ejaculation? J Sex Med 2020;17:1060–1071.

Influence of Cyperus esculentus tubers (tiger nut) on male rat copulatory behavior.

BackgroundCyperus esculentus tubers (tiger nut) are one of the ancient food sources known to humanity. It is traditionally used in the Middle East to stimulate sexual arousal in men. However, there has been no scientific evidence about its assumed aphrodisiac properties. This study aimed to investigate the influence of tiger nut on the copulatory behavior of sexually active male rats.MethodsTwo sets of sexually active male rats -highly active and moderately active- were identified depending on baseline sexual activity. Rats in each set were randomly divided into a control and treated groups. Highly active rats were treated with doses of 1 and 2 g/kg/d of raw tiger nut powder, while moderately active rats were treated with a dose of 2 g/kg/d. After 30 days’ treatment, copulatory behavior and serum hormonal levels were measured and compared between the groups within each experimental set. Phytochemical analyses including liquid chromatography/mass spectrometry and atomic absorption were performed to elucidate the main constituents of tiger nut that may be responsible for altering serum hormones.ResultsTiger nut stimulated sexual motivation in both highly and moderately active rats, indicated by reduced mount and intromission latencies in these rats compared to controls. Furthermore, tiger nut improved sexual performance, indicated by increased intromission frequency and ratio, in treated moderately active rats compared to controls. Serum testosterone levels increased significantly after tiger nut administration. Lastly, phytochemical analyses revealed the presence of quercetin, vitamin C, vitamin E, and mineral zinc in tiger nut.ConclusionsTiger nut has positive effects on the copulatory behavior of adult male rats.

Role of dopamine D4 receptors in copulatory behavior: Studies with selective D4 agonists and antagonists in male rats

Dopamine influences the anticipatory and consummatory phases of sexual behavior, by acting on receptors of the D2 family (D2, D3 and D4) and in particular of the D2 subtype, although evidence for a role of D4 receptors in erectile function and copulatory behavior is also available. In order to clarify such a role of D4 receptors, the effect of selective D4 receptor agonists and antagonists on copulatory behavior of sexually potent male rats in classic copulation tests with a receptive female, was compared with that of apomorphine and haloperidol, a classic dopamine receptor agonist and antagonist, respectively. PD-168,077 (0.05–0.2mg/kg) and ABT-724 (0.01–0.04mg/kg), two selective D4 receptor agonists, given subcutaneously, improved dose-dependently copulatory behavior as shown by the decrease of mount frequency and post ejaculatory interval induced by PD-168,077, and of mount frequency, ejaculation latency, post ejaculatory and inter intromission intervals induced by ABT-724, and by the increase of ejaculation frequency and copulatory efficacy induced by both drugs. Conversely, L-745,870 (1–5mg/kg), a selective D4 receptor antagonist, given intraperitoneally, impaired dose-dependently copulatory behavior, as shown by the increase in intromission and ejaculation latencies, mount frequency, post ejaculatory interval and the decrease in ejaculation frequency and copulatory efficacy induced by this drug. L-745,870 (5mg/kg) administered before PD-168,077 (0.2mg/kg) or ABT-724 (0.04mg/kg), also abolished completely the facilitatory effects of both PD-168,077 and ABT-724 on sexual behavior. These results confirm the involvement of D4 receptors in specific aspects of male rat copulatory behavior that overlap only partially with those influenced by apomorphine and haloperidol.

Effects of bupropion on the ejaculatory response of male rats.

Chronic antidepressant treatment is associated with sexual side effects, particularly affecting the ejaculatory response. Bupropion (BP), an antidepressant inhibiting dopamine/noradrenaline reuptake, seems to have a low impact upon male sexual function. Ejaculation is regulated both at the brain and spinal cord by the spinal generator for ejaculation (SGE). We investigated the effects of chronic BP treatment on ejaculatory behavior and on SGE functioning. Sexually experienced male rats were intraperitoneally (i.p.) injected with BP (7.5 or 15 mg kg(-1)) during 14 days and tested for sexual behavior on days 1, 7 and 14 of treatment; these same males were used to evaluate the functioning of the SGE by recording the genital motor pattern for ejaculation (GMPE). Acute and chronic BP administration did not importantly modify copulatory behavior of male rats. Chronic treatment with the low dose of BP produced deficits in the functioning of the SGE that were restored by activation of the SGE through afferent stimulation. Conversely, chronic treatment with the high-dose of BP disrupted the functioning of the SGE, as the deficits were not compensated by activating the SGE through sensory stimulation. It is concluded that chronic BP at high doses alters the functioning of the SGE.

Fresh onion juice enhanced copulatory behavior in male rats with and without paroxetine-induced sexual dysfunction

Onion (Allium cepa) is one of the most commonly cultivated species of the family Liliaceae, and has long been used in dietary and therapeutic applications. Treatment with fresh onion juice has been reported to promote testosterone production in male rats. Testosterone is the male sex hormone responsible for enhancing sexual libido and potency. This study aimed to investigate the effects of onion juice on copulatory behavior of sexually potent male rats and in male rats with paroxetine-induced sexual dysfunction. Sexually experienced male rats were divided into seven groups: a control group, three onion juice-treated groups, a paroxetine-treated group, and two groups treated with paroxetine plus different doses of onion juice. At the end of the treatments, sexual behavior parameters and testosterone levels were measured and compared among the groups. Administration of onion juice significantly reduced mount frequency and latency and increased the copulatory efficacy of potent male rats. In addition, administration of onion juice attenuated the prolonged ejaculatory latency period induced by paroxetine and increased the percentage of ejaculating rats. Serum testosterone levels increased significantly by onion juice administration. However, a significant reduction in testosterone because of paroxetine therapy was observed. This reduction was restored to normal levels by administration of onion juice. This study conclusively demonstrates that fresh onion juice improves copulatory behavior in sexually potent male rats and in those with paroxetine-induced sexual dysfunction by increasing serum testosterone levels.

Effect of dexmedetomidine on ejaculatory behavior and sexual motivation in intact male rats

Premature ejaculation is the most common sexual disorder in young men. Consequently, there is an intense search for efficient and safe pharmacological treatments. Insofar, almost no effective treatment with acute effects is available. In this study, we evaluated the effects of the noradrenergic α2 receptor agonist dexmedetomidine on sexual incentive motivation and copulatory behavior in male rats. Sexual incentive motivation was tested in a large rectangular arena connected to two small incentive stimulus cages containing either a male or sexually receptive female rat. There was no sexual interaction possible between the experimental subjects and the incentives during this test. Approach to the incentives constituted the measure of sexual incentive motivation. After the sexual incentive motivation test, the subjects were tested for copulatory behavior in a regular copulation test for 30min. Doses of 0.1 and 1μg/kg of dexmedetomidine (i.p.) had no effect on any of the indices of locomotor activity or on parameters of sexual incentive motivation. With regard to copulatory behavior, it was found that the dose of 1μg/kg prolonged the latency to the first ejaculation, while the latency to second ejaculation showed a tendency to increase. The absence of an effect on indices of sexual incentive motivation or general activity showed that the actions of dexmedetomidine in this study were limited to ejaculatory mechanisms. Insofar as the ejaculation latency in the male rat is predictive of prolonged ejaculation latency in men, it can be proposed that dexmedetomidine is of potential utility for the treatment of premature ejaculation.

Fluoxetine Chronic Treatment Inhibits Male Rat Sexual Behavior by Affecting Both Copulatory Behavior and the Genital Motor Pattern of Ejaculation

Selective serotonin reuptake inhibitors (SSRIs) are antidepressants that cause sexual dysfunction. The SSRI fluoxetine (FLX) appears to particularly affect the ejaculatory response. Ejaculation is regulated both at brain and spinal levels. To study the acute and chronic effects of FLX on male rat copulatory behavior, trying to distinguish between brain and spinal cord FLX-induced changes on the ejaculatory response. Sexually experienced male rats were intraperitoneally injected with 5 or 10 mg/kg FLX and tested for sexual behavior during 60 minutes on days 1, 7, and 14 of treatment. After a 2-day drug holiday, the males chronically treated with the high FLX dose were spinalized to record spontaneous and mechanically evoked genital motor patterns of ejaculation (GMPEs). In addition, independent groups were used to evaluate the acute effects of 1, 3, or 10 µg/rat FLX (intravenously) on the GMPE. Number of ejaculatory series and their parameters; electromyographic recordings of the GMPE in the bulbospongiosus muscles and their parameters. Acute FLX injection slightly affected sexual behavior display and dose-dependently inhibited the expression of the GMPE. Chronic FLX treatment did not inhibit copulation but produced deficits in the parameters related to ejaculation after the high dose. In these animals, the response capacity of the spinal generator of ejaculation (SGE) as well as the number of discharges in the GMPE was decreased as a result of chronic FLX treatment. Chronic FLX treatment produces inhibitory effects on male rat copulation, particularly on ejaculation, some of which are exerted directly at the SGE.

Effect of novel synthetic evodiamine analogue on sexual behavior in male rats

Currently phosphodiestrase5 (PDE5) inhibitors are the first-line treatment for erectile dysfunction. Drugs such as sildenafil and tadalafil are available as PDE5 inhibitors which are potent and reversible but lack selectivity with side effects such as headache, facial flushing, dyspepsia, and visual disturbances. We herein report for the first time novel condensed thienopyrimidines as evodiamine analogue and their effect on sexual behavior in male rats hitherto unreported. Novel synthetic evodiamine significantly showed improvement in male rat copulatory behavior. The test compound MKAC9 could be of promising importance in the treatment of sexual disorders like desire disorder or erectile dysfunction.FigureEvodiamine analogue on sexual behavior in male rats.

Both olfactory epithelial and vomeronasal inputs are essential for activation of the medial amygdala and preoptic neurons of male rats

Chemosensory inputs signaling volatile and nonvolatile molecules play a pivotal role in sexual and social behavior in rodents. We have demonstrated that olfactory preference in male rats, that is, attraction to receptive female odors, is regulated by the medial amygdala (MeA), the cortical amygdala (CoA), and the preoptic area (POA). In this paper, we investigated the involvement of two chemosensory organs, the olfactory epithelium (OE) and the vomeronasal organ (VNO), in olfactory preference and copulatory behavior in male rats. We found that olfactory preferences were impaired by zinc sulfate lesion of the OE but not surgical removal of the VNO. Copulatory behaviors, especially intromission frequency and ejaculation, were also suppressed by zinc sulfate treatment. Neuronal activation in the accessory olfactory bulb (AOB), the MeA, the CoA, and the POA was analyzed after stimulation by airborne odors or soiled bedding of estrous females using cFos immunohistochemistry. Although the OE and VNO belong to different neural systems, the main and accessory olfactory systems, respectively, both OE lesion and VNO removal almost equally suppressed the number of cFos-immunoreactive cells in those areas that regulate olfactory preference. These results suggest that signals received by the OE and VNO interact and converge in the early stage of olfactory processing, in the AOB and its targets, although they have distinct roles in the regulation of social behaviors.

Effects of Sexual Experience on Sexual Motivation in Copulatory Behavior in Male Rats

The effects of sexual experience on the behavior of one-year-old male Wistar rats in conditions excluding direct interaction and in conditions of direct contact with potential sexual and social partners were studied. Interest in a social partner on the other side of a partition was most strongly demonstrated by sexually experienced males, while sexually naive males showed the greatest interest in conditions of direct contact. All males showed maximum activity levels in the presence of a receptive female. Sexual experience in males had no effect on the motivational component of male sexual behavior, i.e. sexual excitation: the levels of sexual motivation in the presence of a receptive female were identical in sexually naive and experienced male rats. However, sexual experience produced fundamental changes in the nature of the consumatory stage of male sexual behavior on interaction with a receptive female, significantly increasing its expression. There were increases in measures of copulatory behavior such as the numbers of mountings and intromissions while the latent periods of their appearance decreased. There was also an increase in the proportion of males demonstrating elements of copulatory behavior in relation to partners of predominantly social significance.

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

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

DMI-induced sexual effects in male rats: Analysis of DMI's acute and chronic actions on copulatory behavior and on the genital motor pattern of ejaculation

Desipramine (DMI) is a tricyclic antidepressant that alters male sexual function. This work was designed to study the effects of acute and chronic DMI treatments on male rat copulatory behavior, discriminating between spinal and behavioral DMI actions on the ejaculatory response. To this aim, sexually experienced male Wistar rats received DMI (7.5 or 15 mg/kg, i.p.) for 14 days and were tested for sexual behavior on Days 1, 7 and 14 of treatment. Besides, the genital motor pattern of ejaculation (GMPE) was recorded in anaesthetized, spinal male rats after acute (1–10 µg, i.v.) or 14-day chronic DMI (15 mg/kg, i.p.) treatment. Results showed that acute and chronic DMI treatments reduced the ejaculatory threshold by decreasing intromission number and ejaculation latency of male rats, in successive copulatory series. The intensity of the effects depended on the dose and treatment duration. DMI acute treatment activated GMPE expression only at the lower doses and these responses exhibited modified parameters. Chronic DMI reduced the number of discharges and increased the frequency of discharge of spontaneous GMPE responses, affected mechanically evoked ones and increased the number of GMPEs expressed after repeated genital stimulation as compared to control rats. DMI treatments affected copulatory behavior both at brain and spinal levels and its effects on ejaculation, assumed to be similar in behavioral and spinal models, differed.

Muscarinic receptor antagonism at the spinal cord level causes inhibitory effects on male rat sexual behavior

The role of cholinergic neurotransmission in male rat sexual behavior at the brain level has been studied by several researchers. However, little is known about its role at the spinal cord level. In this study, the effects of the intrathecal (IT) administration of the muscarinic receptor antagonist subtypes (MRAs) methoctramine (Meth), tropicamide (Trop) and 4-DAMP on male rat sexual behavior were evaluated during three ejaculatory series. Meth and Trop are preferring antagonists for the M2/M4 receptor subtypes, and 4-DAMP is a preferring antagonist for the M3 receptor subtype. All the MRAs tested noticeably inhibited male rat copulatory behavior, reflected by a reduction in the number of animals engaging in sexual behavior and a gradual decrease in the number of animals able to ejaculate. Significant increases in intromission latency (IL), ejaculation latency (EL) and post-ejaculatory interval (PEI) were observed. The ranking of inhibitory potency in all recorded parameters was Meth ≥ 4-DAMP > Trop. In theory, the effects of Meth and Trop could be a result of interaction with M2/M4 receptors. However, given that the M2 receptor constitutes the greatest population of muscarinic receptors at all spinal cord sites and given the high affinity for Meth on M2 receptors, the high potency in the inhibitory effects of Meth is indicative of the special role of M2 spinal receptors in the implementation of this behavior. The weaker effects of Trop could be linked to the smaller population of M4 receptors in the spinal cord, but some interaction with M2 receptors is probable. Since some differences in the pattern of inhibitory response between Meth and 4-DAMP were observed in this and a previous study, a possible role for M3 receptors must be considered. The data obtained in this study confirm the facilitating effect of acetylcholine (ACh) at the spinal cord level on male rat sexual behavior through muscarinic mechanisms, with an important influence on ejaculatory processes. These data support the hypothesis of the modulating role of ACh on male rat sexual behavior at the spinal cord level.

Age-Related Changes in Heart Rate during Copulatory Behavior of Male Rats

As members of Western societies age, sexual function of older (elderly) individuals becomes an important issue, particularly for men. Specifically, copulatory behavior increases circulatory load, which may be related to reports of cardiac sudden death following ejaculation. To further examine this relationship, we compared heart rate (HR) before and after ejaculation in 48-week-old (aged) and 10-week-old (young) male rats. As compared with resting HR, HR after ejaculation was increased by 54.2 +/- 3.5 and 41.7 +/- 2.7%, respectively, among aged and young male rats. These values were significantly higher than baseline levels (P<0.01). The increases in HR at each time point during copulation were significantly higher in aged male rats than in young male rats (P<0.05 or P<0.01). We also studied decreases in HR following ejaculation and found that aged male rats had a significantly higher HR at 1 and 2 min after ejaculation than young rats (P<0.01). These results suggest that the circulatory load on the aged rat heart is greater than that on a young rat heart during copulatory behavior, especially at ejaculation. In addition, the decrease in HR in aged rats after ejaculation was more gradual than in young male rats. These results suggest that there is a higher risk of sudden cardiac death during sexual behavior in older males.

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

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

Ginkgo biloba extract enhances male copulatory behavior and reduces serum prolactin levels in rats

The aim of this study was to investigate the effects of Ginkgo biloba extract (EGb 761) on male copulatory behavior in rats. EGb 761 (1 mg/ml) induced significant production of testosterone (T) in rat Leydig cells in vitro. Its effects on sexual behavior were then tested in Long–Evans male rats after 7, 14, 21, or 28 days of oral gavage of vehicle (distilled water) or EGb 761 at doses of 10, 50, or 100 mg/kg. Administration of 50 mg/kg of EGb 761 for 28 days and of 100 mg/kg for 14 or 21 days significantly increased intromission frequency compared to controls on the same day. An increase in ejaculation frequency was seen after treatment with 50 mg/kg of EGb 761 for 14, 21, or 28 days when compared to either the control group on the same day or the same group on day 0. A reduction in ejaculation latency was only seen after administration of 50 mg/kg of EGb 761 for 14 days compared to the vehicle-treated group. After treatment for 28 days, no significant difference was seen in mount latency, intromission latency, serum T levels, reproductive organ weight, sperm number, or levels of the metabolite of dopamine, 3,4-dihydroxyphenylacetic acid in the brain with any dose of EGb 761, but significantly reduced serum prolactin levels and increased dopamine levels in the medial preoptic area and arcuate nucleus were seen at the dose of 50 mg/kg. These findings show that EGb 761 (especially at the dose of 50 mg/kg) enhances the copulatory behavior of male rats and suggest that the dopaminergic system, which regulates prolactin secretion, may be involved in the facilitatory effect of EGb 761.

Distribution of gastrin releasing peptide in the rat lumbar spinal cord is sexually dimorphic and regulated by androgen

Mating was studied in sexually experienced, gonadally intact male rats assigned to two surgical groups matched on the basis of mean mounting frequency during behavioral screening trials conducted prior to the study. Estradiol (E2) was delivered bilaterally into the medial preoptic area (MPO) of experimental males by means of hormone-coated implants, and fadrozole was given sc (0.25 mg/kg/day) via osmotic minipumps to block E2 formation from testicular testosterone throughout the brain. Control males received blank bilateral implants in the MPO and sc fadrozole. After the completion of behavioral testing, immunocytochemical comparisons of the brains from experimental and control rats were made using the H222 antiestrogen receptor (ER) antibody, whose labeling is inhibited by the presence of E2. The histology demonstrated that E2 was confined exclusively to the MPO of experimental males but was absent throughout the brains of controls. In controls, mounting decreased significantly by the 7th day after surgery compared with presurgical levels and did not recover. In contrast, on all postsurgical days, the mounting frequency of the experimental group was significantly higher than that of controls. Although experimental males also showed an initial, significant postsurgical decline in mounting frequency, it recovered completely by the 28th postoperative day. Ejaculations declined significantly after surgery in both groups but, unlike in controls whose performance remained low, ejaculations in experimental males partially recovered and were significantly higher than in controls during the postoperative period. Results showed that ER-containing neurons in the MPO influence male rat copulatory behavior.