Mating In Male Rats Research Articles

Comparison of urinary proteome in the first two days after mating in male rats

ObjectiveTo explore whether differences between male rats on the next day of mating and on the day of mating can be reflected by the urine proteome. MethodsUrine samples were collected from male Sprague-Dawley rats on the day of mating and the next day of mating. Urine samples were analysed by the label-free quantitative proteomics technique of high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). Differential proteins of the urine proteome were analysed for protein function and biological pathways. Results54 differential proteins were identified by comparing the urine proteome of rats on the next day of mating with that on the day of mating, and nearly two-thirds of the differential proteins were related to spermatogenesis. ConclusionsThe urine proteome has the potential to reflect spermatogenesis without interfering with it.

Two aromatase inhibitors inhibit the ability of a third to promote mating in male rats

Aromatase, the enzyme that aromatizes androstenedione (A) to estrone and testosterone (T) to estradiol (E), affects androgen control of male sex behavior in many vertebrates. In male monkeys, rats and quail, E mimics the ability of T to promote mating, and aromatase inhibitors block mating induced by T but not E. Aromatase inhibitors include androgens with different A-rings than T and A, e.g., 1,4,6-androstatriene-3,17-dione (ATD), azoles, e.g., fadrozole, and androgens α-halogenated at carbon 6, e.g., 6α-bromoA, 6α-fluoroA and 6α-fluoroT. 6α-FluoroT is the only 6α-halogenated androgen studied in regard to mating. It promotes mating in male rats and quail and was studied, before it was known to inhibit aromatase, because it cannot be aromatized yet has the same A-ring as T. 6α-FluoroT might promote mating by binding estrogen receptors (ER) directly, i.e., unassisted, or by metabolism to an androgen that binds ER. Since neither process would require aromatase, this study tested both hypotheses by determining how mating induced in castrated male rats by 6α-fluoroT is affected by ATD and fadrozole. Both aromatase inhibitors inhibited the effects of 6α-fluoroT on mating. Thus, 6α-fluoroT does not promote mating by direct ER binding or metabolism to another androgen. Since aromatase underlies a process in which 6α-fluoroT, unlike most nonaromatizable androgens, mimics T effects on male sex behavior, the process must involve a feature that 6α-fluoroT shares with T but not other nonaromatizable androgens. A-ring structure is a candidate. A hypothesis is also offered for how aromatase may participate without aromatizing the androgen.

Sexual responses of the male rat medial preoptic area and medial amygdala to estrogen II: Site specific effects of selective estrogenic drugs

In the medial preoptic area (MPO) and medial amygdala (MEA), estradiol (E2) aromatized from testosterone (T) may act via either estrogen receptor (ER) α or ERβ to mediate mating in male rats. We tested the hypothesis that, in the MPO, ERα exclusively mediates sexual responses to E2 by monitoring mating in four groups of castrated male rats administered dihydrotestosterone (DHT) subcutaneously and MPO implants delivering either: cholesterol, E2, propyl pyrazole triol (PPT, ERα-agonist) or diarylpropionitrile (DPN, ER β-agonist); a fifth group of intact males served as DPN toxicity control, receiving DPN MPO implants. In a follow-up study, either 1-methyl-4-phenyl pyridinium (MPP, ERα-antagonist) or blank MPO cannulae were implanted in castrated male rats receiving T subcutaneously, whereas intact MPP toxicity controls received MPP MEA implants. PPT or E2 MPO implants maintained mating, but cholesterol or DPN MPO implants did not. Moreover, MPP MPO implants interfered with T reinstatement of mating suggesting that, in the MPO, ERα is necessary and sufficient for mating in androgen-maintained male rats and ERβ is not sufficient. Because it is unknown which ER subtype(s) mediate sexual responses of the MEA to E2, we examined mating following MEA implants of cholesterol, E2, PPT or DPN in four groups of castrated male rats administered DHT subcutaneously. E2 MEA implants maintained mounting but mating was significantly decreased in groups receiving PPT, DPN or cholesterol MEA implants suggesting that, unlike the MPO where ERα alone is essential, sexual responses of the MEA to E2 require simultaneous interactions among multiple ER subtypes.

An NMDA antagonist in the MPOA impairs copulation and stimulus sensitization in male rats.

Systemic injections of an NMDA antagonist have been shown to impair mating in male rats. One site where glutamate and its NMDA receptors may contribute to mating is the medial preoptic area (MPOA), which is vital for male sexual behavior. Glutamate is released in the MPOA during copulation, and especially at the time of ejaculation. We report here that the NMDA antagonist MK-801, microinjected into the MPOA, impaired copulatory behavior in sexually naïve as well as experienced males. In rats tested both as naïve and after sexual experience, drug treatment produced more profound impairment in naïve males. In addition, MK-801, microinjected into the MPOA before each of 7 noncopulatory exposures to receptive female rats, resulted in copulatory impairments on a drug-free test on Day 8, relative to aCSF-treated rats; their behavior was similar to that of males that had not been preexposed to females. Therefore, NMDA receptors in the MPOA contribute to the control of copulation and stimulus sensitization. Glutamate, acting via NMDA receptors, regulates many neural functions, including neuronal plasticity. This is the first demonstration that a similar mechanism in the MPOA sensitizes male rats to the stimuli from a receptive female, and thereby enhances their behavior.

Attenuation of the neuronal stress responsiveness and corticotrophin releasing hormone synthesis after sexual activity in male rats

Beneficial effects of sexual activity and mating on the responsiveness to environmental stress can be observed in humans and other mammalian species alike, but the underlying neurobiological mechanisms are largely unknown. Sexual activity and mating with a receptive female has recently been shown to reduce the subsequent emotional stress response via activation of the brain oxytocin system. Therefore, we investigated the neuronal and hormonal responses to an acute stressor (forced swimming) after mating in male rats. Attenuation of the stress-induced increase of c- fos and CRH mRNA expression within the hypothalamic paraventricular nucleus 4 h after mating revealed that sexual activity reduced neuronal reactivity in this region. However, this effect was independent of oxytocin as oxytocin receptor blockade, by central administration of an oxytocin receptor antagonist, after mating did not prevent the reduced expression of c- fos mRNA in response to stressor exposure. Mating itself stimulated corticotrophin (ACTH) and corticosterone secretion, which was absent in males after contact with an unreceptive female (non-mated group). However, ACTH and corticosterone responses to forced swimming applied either 45 min or 4 h after female contact were similar between mated and non-mated males. These findings provide evidence for a stress-protective effect of sexual activity and mating in male rats and for dissociation between neuronal and neuroendocrine stress responses.

Implants of Estradiol Conjugated to Bovine Serum Albumin in the Male Rat Medial Preoptic Area Promote Copulatory Behavior

The expression of mating behavior in male rats is dependent on estrogen-responsive neurons in the medial preoptic area (MPO). Previous reports showed that mating is attenuated if the aromatization of testosterone to estradiol (E₂) is blocked in the MPO and that mating is maintained by MPO E₂ implants. However, the mechanisms by which E₂ exerts its action are not fully understood. It had been thought that E₂ acted exclusively by binding to nuclear estrogen receptors to exert it effects; however, recent reports suggest that E₂ also binds to membrane-associated receptors activating downstream intracellular cascade responses. In this study, we aimed to determine if an action of E₂ at the cell surface is sufficient to support mating behavior. Therefore, either vehicle, E₂, or E₂ conjugated to bovine serum albumin (BSA-E₂: a complex of E₂ and a large protein that will not cross the plasma membrane, thereby restricting the action of E₂ to cell surface signaling) was chronically administered bilaterally to the MPO of castrated, dihydrotestosterone-treated male rats. Mating behavior was supported by MPO BSA-E₂ implants, suggesting that E₂ operates in the MPO via a cell surface mechanism to facilitate male rat mating behavior.

Gonadal steroid receptors colocalize with central nervous system neurons projecting to the rat prostate gland

Mating-induced Fos-immunoreactive (-ir) cells are colocalized with androgen receptors (AR), estrogen receptors (ER), or both in limbic and hypothalamic areas known to mediate male rat mating behavior. A steroid-responsive neural network might govern copulatory behavior in male laboratory rats that is analogous to the network described in female rats that governs the lordosis response. This hypothesized network in males may synchronize and coordinate sexual behavioral responses with physiological responses of the genitals and the internal organs of reproduction. Therefore, the pseudorabies virus (PRV; Bartha strain), a transneuronal, viral retrograde tract tracer, was microinjected into the prostate gland to label this network. After 7 days, brains from infected animals were processed for immunohistochemical labeling of AR, ER, and PRV. The majority of PRV-ir cells exhibited either AR or ER immunoreactivity in the medial preoptic area, median preoptic nucleus, bed nucleus of stria terminalis, hypothalamic paraventricular nucleus, and zona incerta, areas known to play roles in male rat mating behavior. Other structures such as the central tegmental field/subparafascicular nucleus of the thalamus, central nucleus of the amygdala, and medial amygdala, also important in the display of male copulatory behavior, were less reliably labeled. Collectively, a steroid receptor-containing neuronal circuit, largely contained in the diencephalon, was revealed that likely is involved in the autonomic control of the prostate gland and the consummatory aspects of male rat mating behavior.

Projection from the ventral bed nucleus of the stria terminalis to the retrorubral field in rats and the effects of cells in these areas on mating in male rats versus gerbils

This research identified the rat counterpart of the lateral cell group of the sexually dimorphic area (SDA) found in medial preoptic area (MPOA) gerbil of gerbils. The lateral SDA (lSDA) is critical for mating in male gerbils and contains most of the SDA cells projecting to the retrorubral field (RRF), a projection that is also important for mating. Therefore, to locate the counterpart of the lateral SDA, we traced the inputs to the rat RRF, which were dense in the ventral part of the bed nucleus of the stria terminalis (BST). To determine if the ventral BST or its projection to the RRF affects mating in male rats, we disrupted them bilaterally by placing cell-body lesions bilaterally in the ventral BST or unilaterally there and in the contralateral RRF. We also studied the effects of RRF lesions in both rats and gerbils. Bilateral ventral BST lesions, which left the medial preoptic nucleus intact, produced persistent and severe mating deficits. Disconnecting the ventral BST from the RRF also had long-lasting, but less severe, consequences. RRF lesions produced only temporary mating deficits in rats, but virtually eliminated mating in gerbils. The recovery of mating in rats after RRF, but not ventral BST, lesions, and the intermediate effects of disconnecting these areas from each other suggest that the ventral BST may contain mating-related projection neurons other than those projecting to the RRF or that its RRF-projecting cells send collaterals to another site. In either case, the pedunculopontine tegmental nucleus or raphe nuclei may be involved.

The endogenous androgen-regulated sialorphin modulates male rat sexual behavior

In sexually mature male rats, sialorphin is synthesized under androgenic control and its surge endocrine secretion is evoked in response to environmental acute stress. These findings led us to suggest that this signaling mediator might play a role in physiological and behavioral integration, especially reproduction. The present study investigates the effects induced by sialorphin on the male sexual behavior pattern. Intact male rats were treated in acute mode, with sialorphin at the 0.3, 1, and 3 μg/kg doses, before being paired with receptive female for 45 min. The data obtained show that sialorphin increased, in a dose-related manner, the occurrence of intromissions across the successive ejaculatory sequences. The rats treated with the highest 3 μg/kg dose significantly ejaculated less often compared to controls; however, 80% of them achieved up to three ejaculations. Further analyses of mount bouts for rats achieving three ejaculations reveal that there were significant stimulatory effects of sialorphin, at all doses, on the frequency of intromissions before ejaculation and on the propensity of males to engage in investigatory behavior directed to the female during the post-ejaculatory interval. Thus, sialorphin has the ability to modulate, at doses related to physiological circulating levels, the male rat mating pattern, that is, exerting a dual facilitative or inhibitory dose-dependent effect on the sexual performance, while stimulating the apparent sexual arousal or motivation. These findings led us to speculate that the endogenous androgen-regulated sialorphin helps modulate the adaptative balance between excitatory and inhibitory mechanisms serving appropriate male rat sexual response, depending on the context.

Expression and regulation of the immediate-early gene product Arc in the accessory olfactory bulb after mating in male rat

Recent studies of the accessory olfactory bulb have shown that the expression of immediate-early genes, e.g., c-fos, c-jun and egr-1, can be used as a marker of neuronal activity in response to pheromonal cues. In this study, we analyzed the expression pattern, in response to mating, of the novel immediate-early gene product Arc (an activity-regulated cytoskeleton-associated protein). Arc is hypothesized to play a role in activity-dependent neuronal plasticity in the hippocampus. In a control group of male rats, only a small number of Arc-immunoreactive cells were observed in the accessory olfactory bulb. In a mating group, however, a marked increase in the number of Arc-immunoreactive cells was observed only in the granule cell layer of the accessory olfactory bulb. The increase in the number of Arc-immunoreactive cells after mating was similar to that observed for other immediate-early genes. However, for the mating group, the increase in Arc-positive cells was limited to the granule cell layer. Granule cells have been shown to exhibit a strong synaptic plasticity in response to pheromonal stimulation. From these findings we suggest that Arc plays an important role in neuronal plasticity in the accessory olfactory bulb.

Naloxone blocks place preference conditioning after paced mating in female rats.

Sexual behavior in male rats induces a positive affect as evaluated by conditioned place preference (CPP). In addition, when females control or "pace" the rate of sexual interaction, a clear CPP is also observed. The reward state induced by mating in male rats is blocked by the injection of the opioid antagonist naloxone. In the present experiment, a dose of 4 mg/kg of naloxone completely blocked the CPP induced in females by paced mating. It appears that a common opioid system is involved in the positive affect induced by sexual behavior in both male and female rats.

Increased expression of c-fos in the medial preoptic area after mating in male rats: Role of afferent inputs from the medial amygdala and midbrain central tegmental field

Immunocytochemical methods were used to localize the protein product of the immediate-early gene, c-fos, in male rats after exposure to, or direct physical interaction with, oestrous females. Increasing amounts of physical contact with a female, with resultant olfactory-vomeronasal and/or genitalsomatosensory inputs, caused corresponding increments in c-fos expression in the medial preoptic area, the caudal part of the bed nucleus of the stria terminalis, the medial amygdala, and the midbrain central tegmental field. Males bearing unilateral electrothermal lesions of the olfactory peduncle showed a significant reduction in c-fos expression in the ipsilateral medial amygdala, but not in other structures, provided their coital interaction with oestrous females was restricted to mount-thrust and occasional intromissive patterns due to repeated application of lidocaine anaesthetic to the penis. No such lateralization of c-fos expression occurred in other males with unilateral olfactory lesions which were allowed to intromit and ejaculate with a female. These results suggest that olfactory inputs, possibly of vomeronasal origin, contribute to the activation of c-fos in the medial amygdala. However, lesion-induced deficits in this type of afferent input to the nervous system appear to be readily compensated for by the genital somatosensory input derived from repeated intromissions. Unilateral excitotoxic lesions of the medial preoptic area, made by infusing quinolinic acid, failed to reduce c-fos expression in the ipsilateral or contralateral medial amygdala or central tegmental field following ejaculation. By contrast, combined, unilateral excitotoxic lesions of the medial amygdala and the central tegmental field significantly reduced c-fos expression in the ipsilateral bed nucleus of the stria terminalis and medial preoptic area after mating; no such assymetry in c-fos expression occurred when lesions were restricted to either the medial amygdala or central tegmental field. This suggests that afferent inputs from the central tegmental field (probably of genital-somatosensory origin) and from the medial amygdala (probably of olfactory-vomeronasal origin) interact to promote cellular activity, and the resultant induction of c-fos, in the ipsilateral bed nucleus of the stria terminalis and medial preoptic area. The monitoring of neuronal c-fos expression provides an effective means of studying the role of sensory factors in governing the activity of integrated neural structures which control the expression of a complex social behaviour.

Structural requirements of some sulphonamides that possess an antifertility activity in male rats

Sulphonamides with different chemical structures were synthesized and these 13 compounds together with 7 commercially available sulpha drugs were tested for antifertility activity by natural mating in male rats. All compounds were given daily by gastric intubation at doses of 125, 150, 250 or 450 mg/kg for 6 weeks. Sulphapyridine caused a dose-related and reversible reduction in fertility at doses between 125 and 450 mg/kg. At the high dose, fertility was reduced to 25.9% of control at 5 weeks after treatment, and complete recovery occurred by 3 weeks after drug withdrawal. This activity was abolished when the pyridine ring was substituted by other heterocyclic rings, except sulphachloropyridazine which had only weak activity. Replacement of the pyridine ring by a hydrogen atom or short aliphatic chains preserved or even enhanced the potency. Thus, sulphanilamide, N1-methylsulphanilamide or N1-diethylsulphanilamide produced a marked but reversible reduction in fertility. Removal or substitution of the N4-amino group on the benzene ring of sulphapyridine with a methyl group destroyed the activity. However, the bromo or nitro analogue (at the para- but not the meta-position of the benzene ring) still possessed some activity. N4-Acetyl derivatives of sulphapyridine, sulphanilamide, and N1-diethylsulphanilamide were as potent as their parent compounds. These results suggest that the presence of pyridine or other heterocyclic rings is not necessary for the antifertility activity of sulphonamide compounds. However, the N4-amino group is indispensable. In addition, acetylation of this amino group does not change the potency. The prototype of the antifertility sulphonamides therefore seems to be sulphanilamide.

Midbrain lesions, dopamine and male sexual behavior

Destruction of the medial preoptic area (MPOA) eliminates mating in male rats and this region is believed to play a major role in the control of male sexual behavior. Efferents from the MPOA pass through and/or terminate in 4 midbrain regions: the dorsolateral tegmentum (DLT), the central gray, and the A9 and A10 areas. The present study reports the effects of bilateral destruction of each of these midbrain regions on brain catecholamines and sexual behavior in male rats. DLT lesions eliminated mating, reproducing the effect of bilateral preoptic lesions. The sexual activity of males with central gray lesions was accelerated in the sense that the mounting rate for these males was significantly faster than for controls and lesioned males ejaculated more frequently and with shorter latencies than did controls. A9 lesions impaired mating - lesioned males mounted at a slower rate and ejaculated less frequently than controls. Males with A10 lesions took longer to re-initiate mating after an ejaculation than controls, but copulation per se (as reflected in mount rate, ejaculation frequency and latency to ejaculate) was not affected by A10 damage. Brain catecholamine levels were not affected by either DLT or central gray lesions. A9 lesions produced a significant depletion in neostriatal dopamine which was highly correlated with mount latency, mount rate, ejaculation latency and ejaculation frequency. A10 lesions produced a significant depletion of dopamine in the nucleus accumbens and cingulate cortex, but these effects were not significantly correlated with any measure of sexual behavior.

Hormonal stimulation of precocious mating in male rats without antecedent effects on sexual clasping or ambulation

Daily administration of 1000 μg testosterone propionate or 5 μg estradiol benzoate per 100 g body weight to intact male rats after postnatal Day 10 accelerated initial intromission without previously stimulating either increased amounts of ambulation or more frequent sexual clasping in tests with sexually receptive and nonreceptive females. It is concluded that the occurrence of precocious mating in these animals did not depend upon a previous increase in the number of opportunities to execute the adult coital response.

Precocious mating in male rats evoked by peripheral shock: M. J. Baum and D. A. Goldfoot — Rotterdam Medical Faculty, Rotterdam (The Netherlands)

Precocious mating in male rats evoked by peripheral shock: M. J. Baum and D. A. Goldfoot — Rotterdam Medical Faculty, Rotterdam (The Netherlands)

Precocious mating in male rats following treatment with androgen or estrogen.

Precocious mating in male rats following treatment with androgen or estrogen.

Seminal discharge and mating behavior in the male rat☆

Abstract In the male rat mating behavior, the ejaculation is preceded by a number of intromissions and followed by a period of sexual inactivity. It was asked whether the refractory period following ejaculation was due to the seminal discharge or to the series of copulations preceding and including ejaculation. Experiments were performed where seminal discharge was induced by electroejaculation. No effects of electroejaculation were found in the normal mating performances thus indicating that the period of sexual inactivity following ejaculation is not due to the expulsion of seminal fluid.

INTROMISSION FREQUENCY AND INTROMISSION DURATION IN THE MALE RAT MATING BEHAVIOR

Carlsson, S. G. & Larsson, K. Intromission frequency and intromission duration in the male rat mating behavior. Scand, J. Psychol., 1962, 3, 189–191.—The male rat attains ejaculation after repeatedly mounting and penetrating the receptive female. By artificially prolonging the intervals of rest separating the intromissions the male is made to ejaculate after fewer intromissions than occurs when he copulates ad libitum. It was found that the reduction in intromission frequency was accompanied by an increase in intromission duration.

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

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