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PubMed1990

Sexual behavior enhances central dopamine transmission in the male rat.

Central dopamine transmission was examined in the nucleus accumbens and striatum of sexually experienced male rats during mating behaviour using in vivo brain microdialysis. Dopamine release increased significantly in the nucleus accumbens when males were placed in a novel mating chamber and when a receptive female was introduced behind a screen partitioning this chamber. Subsequently, during copulation dopamine transmission increased sharply, this being followed by a gradual decrease after the female was removed. In contrast, striatal dopamine transmission increased significantly only during copulation. These data provide a neurochemical basis for the well-known interactions between dopaminergic drugs and male sexual behaviour and demonstrate the feasibility of using brain microdialysis to elucidate the neurochemical correlates of motivated behaviour.

Animals↗
PubMed1992

The stimulation of central kappa opioid receptors decreases male sexual behavior and locomotor activity.

Systemic injections of the kappa (kappa) opioid receptor agonist U-50,488H decreased male sexual behavior, locomotor activity, body temperature and bodily grooming, and induced body flattening. The U-50,488H-induced inhibitions of male sexual behavior were prevented by systemic injections of naloxone and by intra-cranial injections of the kappa opioid antagonist nor-binaltorphimine (NBNI). Injections of NBNI to either the ventral tegmental area (VTA) or the nucleus accumbens septi (NAS) increased female-directed behavior, and prevented the U-50,488H-induced decreases in female-directed behavior. Intra-VTA NBNI prevented U-50,488H-induced decreases in the mean number of ejaculations, intra-NAS NBNI prevented U-50,488H-induced increases in copulation latencies. Intra-medial preoptic area (mPOA) injections of NBNI increased female-directed behavior, and attenuated U-50,488H-induced decreases in female-directed behavior as well as U-50,488H-induced increases in both copulation and ejaculation latencies. Injections of NBNI dorsal to the mPOA were ineffective. Two of 26 days following the central injection of NBNI, systemic injections of U-50,488H remained behaviorally ineffective, leaving both sexual behavior and locomotor activity undiminished. These results suggest that the stimulation of central kappa opioid receptors inhibits sexual behavior in the male rat; perhaps endogenous kappa opioid agonists induce sexual refractory periods.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1993

Dopamine transmission increases in the nucleus accumbens of male rats during their first exposure to sexually receptive female rats.

In vivo microdialysis was used to monitor extracellular concentrations of dopamine (DA), and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the nucleus accumbens of sexually naive male rats during their first exposure to sexually receptive or nonreceptive females. DA, DOPAC, and HVA increased progressively and significantly in males that copulated to ejaculation with receptive females. In contrast, DA, DOPAC, and HVA did not increase significantly in males exposed to non-receptive females, despite several attempts by these males to mount the non-receptive females. These results indicate that DA is released unconditionally in the nucleus accumbens of male rats by exposure to sexually receptive female rats, and that copulation with intromission, but not mounting alone, leads to further increases in DA release.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

The medial and lateral cell groups of the sexually dimorphic area of the gerbil hypothalamus are essential for male sex behavior and act via separate pathways.

Male reptiles, birds and mammals do not copulate if the medial preoptic area (MPOA) is destroyed but the MPOA cell groups necessary for male sexual behavior were not known. Here, two cell groups essential for copulation are identified in the sexually dimorphic area (SDA) of the gerbil (Meriones unguiculatus) MPOA. Bilateral cell-body lesions of either the medial or lateral SDA eliminated mating in sexually experienced male gerbils given testosterone. Nearby MPOA lesions did not. The medial and lateral SDA affect sex behavior via separate pathways since lesioning the medial SDA on one side of the brain and the lateral SDA on the other did not stop sexual behavior.

Animals↗
PubMed1994

Changes in monoamine turnover in forebrain areas associated with masculine sexual behavior: a microdialysis study.

This report compares the changes in the main dopamine (DA) and serotonin (5-HT) metabolites, respectively dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy indoleacetic acid (5-HIAA) in three relatively close brain regions, namely the nucleus accumbens (ACB), the medial preoptic area, and the medial basal hypothalamus (MBH), as well as DA in the ACB, of copulating male rats. All these neurochemicals remained fairly stable when the animals were exposed to non sexual social stimuli (castrated females), and they increased during mating with receptive females. There were regional differences in these copulation-related changes, however, with those in the MBH being shorter-lived. There were also differences in the time-course of the changes in DOPAC and 5-HIAA the latter being slower. It is suggested that they reflect the involvement of the DA and 5-HT innervation of diencephalic structures in, respectively the appetitive and consummatory/satiation mechanisms of sexual behavior. The physiological relevance of these neurochemical changes is supported by the lack of differences between the standard measures for sexual behavior recorded before surgery and during the dialysis session.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

Behavior performed at onset of drug action and apomorphine stereotypy.

This study tests the hypothesis that stereotyped behavior induced by apomorphine reflects strengthening of behavior observed at the onset of drug action. Rats (n = 26) were injected with apomorphine (1.25 mg/kg) while being engaged in copulation. Contrary to the hypothesis, apomorphine did not strengthen ongoing copulation but arrested it. Instead of mating the males became engaged in behavior typically exhibited by rats injected with the drug. It is speculated that stereotyped behavior may be an expression of a drug-induced shift of attention or responsiveness to some particular range of stimuli.

Animals↗
PubMed1988

Patterns of sexual receptivity in the female musk shrew (Suncus murinus).

Female musk shrews (Suncus murinus) were tested daily to examine patterns of sexual receptivity. When only mounting was used as a criterion (to avoid pregnancy), nonpregnant females remained sexually receptive to males every day for 14 consecutive days. When insemination was allowed, most females continued to copulate for the first 5 days of pregnancy. Receptivity declined markedly around Day 10 of gestation, but a few females were receptive even into late pregnancy. Lactating females copulated with males 5 and 10 days after parturition. In general, unlike most mammals studied in the laboratory, the nonpregnant female musk shrew has no behavioral estrous cycle. Musk shrews are ready to mate anytime except in mild to late pregnancy, and even then occasionally mating is found.

Animals↗
PubMed1982

Effects of rank and novel females on behaviour and hormones in male talapoin monkeys.

Two social groups of captive talapoin monkeys (Miopithecus talapoin), each with three intact adult males and three or four ovariectomized, estrogen-treated adult females, were observed. Socio-sexual and aggressive interactions were recorded, and levels of testosterone, cortisol, and prolactin were measured in male serum. Cortisol and prolactin titers did not reflect male rank, nor did changes in one of these hormones parallel changes in the other. In both groups males formed a linear dominance hierarchy, defined in terms of the direction of aggression among animals. Highest male rank was associated with frequent socio-sexual interaction and elevated testosterone levels, even in the absence of ejaculations. Males in one group copulated with females, but no male in the other group copulated. All males of each group were then housed with all females of the other group which resulted in marked changes in males' behaviour; socio-sexual interactions increased in C group males and decreased in B group males. This illustrates the influence that females may have on male behaviour in general, and in particular outlines the potential for female dominance and the consequences this may have especially on reproductive behaviour.

Aggression↗
PubMed1983

The effect of the ovarian cycle on the sexual behaviour of the common marmoset (Callithrix jacchus).

The sexual behaviour of 7 pairs of marmosets was observed during 30 minute tests for 44-68 days and blood samples were collected from females for measurement of plasma progesterone, testosterone and oestrone. Copulations occurred throughout the ovarian cycle of 24-30 days. Females used a "tongue-flicking" display both as an invitational behaviour (proceptive tongue-flicks) and during copulation (receptive tongue-flicks) most frequently during the peri-ovulatory period. Frequencies of proceptivity were correlated positively with high mean levels of testosterone and oestrone during the cycle and with a short follicular phase. Males showed significant increases in tongue-flicks, mounts and ejaculations during the peri-ovulatory phase, together with a shortened post-ejaculatory interval and increased duration of penile erection after ejaculation. A retrospective analysis showed that these changes in the males' behaviour occurred only during tests where females were proceptive and not during other tests in the peri-ovulatory period. Females refused significantly more of the males' mounting attempts during the luteal phase and a corresponding reduction in mount frequency occurred at this time. Grooming, scent-marking, olfactory inspections and some other behaviours did not alter significantly in either sex during the ovarian cycle.

Animals↗
PubMed1986

Stimulus qualities of a preferred female partner and sexual behavior of old rhesus males.

A vaginal lavage from a preferred female sexual partner (donor) with whom old (21-27 yr) rhesus males readily copulated or a distilled water lavage was applied to the perineum of non-preferred females (N = 8) with whom old males rarely copulated. The donor and recipients were ovariectomized and were treated with estradiol benzoate (EB) before being tested. Sexual performance of the males did not differ under the two conditions of testing, but the rate of sexual solicitation by the females was significantly higher when treated with the vaginal lavage. One month later the non-preferred females were again treated with EB and paired with the old males. In these tests the preferred female was present in a cage adjacent to and in view of the test pairs. Sexual behavior was not altered significantly, but whereas these males had never threatened or aggressed their partners in previous tests, there was a significant increase in the rate at which they threatened their partners and aggression occurred for the first time. When paired with the preferred female, males ejaculated in 100% of the tests and the average ejaculation latency was less than 2.5 minutes.

Aging↗
PubMed1987

Silent ovulation in rhesus monkeys (M. mulatta): dissociation of hormonal and behavioral states.

Ovarian hormone levels were monitored in rhesus monkeys during the breeding and non-breeding seasons. Ovulation (as inferred from progesterone levels in blood serum in excess of 1.5 ng/ml) was most frequent in the breeding season but was absent only during the month of August. Summer (non-breeding season) ovulations were more frequently "silent," or without heterosexual behavior, than were winter ovulations. This finding suggested that estradiol stimulation may cause different behavioral responses at different times of the year. To test this hypothesis, ovariectomized females were treated with subcutaneously implanted estradiol capsules at different times within and outside the normal breeding season. In either season, treatment with estradiol resulted in increased female-to-female sexual behavior. Only during the breeding season, however, did the estradiol-treated ovariectomized females interact sexually with males. Although males copulated with both estradiol-treated and gonadally intact, untreated females during the breeding season, their rate of copulation with the intact females was higher. The results suggest that: (1) Some female rhesus monkeys displaying strictly seasonal breeding behavior continue to have luteal activity indicative of ovulation in May, June and July, (2) Summer ovulatory cycles are rarely accompanied by sexual behavior, (3) Estradiol treatment of ovariectomized females induces female-to-female sexual behavior both in the breeding and non-breeding seasons, and (4) Males are less responsive to the presence of estrogen-stimulated females in the non-breeding season than in the breeding season.

Animals↗
PubMed1987

Alpha 2-adrenoceptor antagonists and male sexual behavior: I. Mating behavior.

Three alpha 2-adrenoceptor antagonists yohimbine, idazoxan, and imiloxan were compared by examining the effects of a single injection on male rat copulatory behavior. Dose ranges were: yohimbine: 0.25-8.0 mg/kg; idazoxan: 0.25-8.0 mg/kg; imiloxan: 12.5-50.0 mg/kg. Yohimbine and idazoxan administration produced significant increases in the number of animals copulating to ejaculation and all three drugs increased the rate of copulation as evidenced by reductions in ejaculation latency and intercopulatory interval. Only yohimbine significantly reduced mount latency and postejaculatory interval, but yohimbine and imiloxan significantly reduced intromission latency and idazoxan showed a similar trend. The highest yohimbine dose suppressed sexual activity. A time-course experiment with yohimbine (2.0 mg/kg) and idazoxan (4.0 mg/kg) showed stimulation at 75 min and a trend at 5. To further explore the arousal-stimulating capacity of the two more effective drugs, a mounting test with genital anesthetization was used. Yohimbine but not idazoxan showed marked increases in mounting at 1.0-4.0 mg/kg. Both drugs had a suppressive effect at the highest doses. These data support the involvement of alpha 2-adrenoceptors in the regulation of male sexual behavior, specifically by facilitating sexual arousal, with no effects on ejaculatory threshold, as measured by intromission frequency. Yohimbine is the most globally effective agent and it is likely that factors other than yohimbine's alpha 2-antagonism may play a role in its unique, consistent and broad behavioral effects.

Adrenergic alpha-Antagonists↗
PubMed1979

Quantitative analysis of mating behavior in aging male Drosophila melanogaster.

Dynamic changes in quantitative aspects of mating behavior of the male fruit fly as its life unfolds, from eclosion through maturity (peak performance) and "physiological death" (loss of fertility followed by complete loss of ability to mate), towards actual death, have been identified in this work by observations and measurements on 28 male fruit flies of the Oregon R strain studied individually. At weekly sessions from the first day of their imaginal life until their natural death, each fly was given the opportunity to mate with up to three virgin females during a one-hour period. Length of the latency period of each accomplished mating and duration of copulation were recorded. After mating the females were allowed to lay eggs for 24 hours and the number of offspring was counted 26 days later. The period between 1 and 4 weeks of age is characterized by peak and fairly constant performance: multiple matings, short latencies, long durations of copulation, and high degree of fertility (number of offspring); then a decline sets in, in some measures slower than in others, as the flies age. Large intra- and inter-individual variabilities were, however, found which obscure possible correlations between individual measures of mating ability and length of life. At the individual level, a preliminary analysis showed a good correlation (r = 0.80 and 0.79) between life span and week of last mating (onset of impotence) or week of last fertile mating (onset of sterility). At the population level it was found that a number of measures, i.e. number of remaining maters at each age, number of remaining fertile maters and total number of matings, had an age-course similar to survivorship but anticipated it by 4--6 weeks. Other measures, such as number of multiple matings and number of offspring declined with age faster than survivorship.

Aging↗
PubMed1989

Inhibitory action of various 5-HT1B receptor agonists on rat masculine sexual behaviour.

The systemic administration of the 5-HT1B receptor agonists, RU 24969 (0.25 and 0.5 mg/kg), TFMPP (0.25 and 0.5 mg/kg) and mCPP (0.75 and 1.0 mg/kg) resulted in an inhibition of rat masculine sexual behaviour reflected as a reduction in the proportion of copulating animals. Additionally, the analysis of the sexual behaviour of the animals obtaining ejaculation revealed that RU 24969 and TFMPP administration resulted in an increase in the number of mounts and in a prolongation of the intromission and ejaculation latencies and of the postejaculatory interval. Administration of mCPP increased the number of mounts preceding ejaculation. None of these changes could be attributed to a motor coordination impairment since none of these drugs, at the doses tested, produced changes in a treadmill test. The administration of the 5-HT1A agonist, ipsapirone (2.5, 5 and 10 mg/kg) resulted in a facilitation of the sexual behaviour expressed as a reduction in the number of intromissions preceding ejaculation accompanied by a shortening of the ejaculation latency. Present data show a differential action of 5-HT1A and 5-HT1B receptor subtypes in the control of rat masculine sexual behaviour. The hypothesis that the endogenous serotonin inhibitory action on copulation is mediated via the 5-HT1B receptor subtype is proposed.

Animals↗
PubMed1992

Effect of yohimbine on the reproductive behavior of the male Nile crocodile Crocodylus niloticus.

The effect of yohimbine, an alpha 2-adrenergic blocker, on the reproductive activity of 12-year-old male, captive Nile crocodiles was tested on 18 animals equally divided into 3 ponds. In each pond, there were 6 males and 30 females. In the first group, six of six males received yohimbine capsules of 30 mg, twice a day, for 1 week. In the second group, two males of a group of six were administered a similar dose of yohimbine. Another group of six males in a separate pond were used as a control group. The yohimbine treatment had a significant (p less than 0.05) effect on the frequency of headslap display (the main behavioral pattern of reproductive activity) in all treated animals but did not result in a significant increase in copulation frequency. In the two treated groups, the reproductive period was prolonged by 3 weeks, 8-11 weeks. We found a significant increase in the fertility percentage of eggs laid by females in the male-treated groups (30.5% in control group females, 34.1% in the partly treated, and 39.0% in the pond where all six males were treated), even though no increase in mating frequencies was noted. This might be due to more successful copulations. During the treatment period, the daily activity peak, when the male's headslap performance was the most frequent, was shifted from 5:00-6:00 p.m. in the control to 4:00-5:00 p.m. in the treated group. This effect caused females to enter the water earlier than in the control group.

Alligators and Crocodiles↗
PubMed1995

Sexual function in altered physiological states: comparison of effects of hypertension, diabetes, hyperprolactinemia, and others to "normal" aging in male rats.

In this review, we examine the changes in sexual function that accompany deviations from "normal" physiological states. We propose that the changes one observes in many altered physiological states should not be viewed in isolation. We describe our paradigms for assessing sexual function, and proceed to evaluate how sexual function changes with hormonal deprivation and aging, in rat models for hypertension, in severe hyperprolactinemia, in streptozotocin-induced diabetes, after chronic alcohol intake, after chronic morphine administration, and after exposure to the heavy metal, cadmium. We will provide evidence for the involvement of adrenergic transmitters and two neuropeptides, neuropeptide Y and somatostatin, in the neuroendocrine regulation of sexual behavior. Finally, we compare and contrast the changes observed relative to the changes seen in "normal" aging in rats. The sequence of age-related changes in sexual function is distinct. The first change observed is a decrement in ex copula erectile reflexes. Next are decreases in ejaculatory threshold, followed shortly by increases in initiation and reinitiation of copulation after ejaculation. This is followed by a decrement in the number of males copulating to ejaculation. Finally, there is a failure to initiate the copulatory process. This sequelae is relatively common, being evident after castration, with hyperprolactinemia, and after exposure to cadmium. The data available for sexual function in hypertension is incomplete and modified by the etiology, but a suggestion for this sequelae is seen in SHR. In contrast, sexual dysfunction associated with chronic morphine administration appears to be due to an initial deficit in motivational aspects. Testosterone reverses sexual dysfunction associated with castration, but not with idiopathic sexual inactivity, nor with sexual dysfunction associated with aging, diabetes, or chronic morphine administration. Comparing sexual function in rat models for hypertension, diabetes and chronic ethanol leads to the conclusion that increases in blood pressure, like decreases in testosterone, cannot be the primary causal factor for sexual dysfunction. Age, hormonal history of the subject, and the age at castration influence changes in sexual function. Age-related sexual dysfunction appears to be contributed to by changes in adrenergic-neuropeptidergic, to include sympathetic, systems. Site-specific administration of NPY induces alterations in parameters of copulatory behavior which mimic those seen in aging and the retention of ejaculatory behavior with aging is associated with site-selective attenuation (or reversal) of age-associated changes in NPY content. Yohimbine enhances copulatory activity in castrated and aging rats, and attenuates or reverses the antisexual effects of clonidine, epinephrine and somatostatin.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1987

Selective effects of beta-endorphin infused into the hypothalamus, preoptic area and bed nucleus of the stria terminalis on the sexual and ingestive behaviour of male rats.

beta-Endorphin was infused bilaterally into the medial preoptic area-anterior hypothalamic continuum at doses of 5, 10 and 40 pmol each side. The highest dose selectively abolished mounting, intromitting and ejaculating in sexually experienced male rats paired with an oestrous female. Males infused with 40 pmol beta-endorphin still followed the female, investigated her anogenital region and other parts of her body, but made abortive attempts to mount. A dose of 5 pmol beta-endorphin had no effect, but 10 pmol proved partially effective. The same males, in other tests, were allowed to ingest a highly preferred, sweet, non-calorific solution (acesulfame-K) in the absence of a female. beta-Endorphin infusions (up to 40 pmol) into the same area of the hypothalamus had no effect on this behaviour. Control males allowed simultaneous access both to an oestrous female and to the sweet solution copulated normally but reduced their ingestive behaviour, despite there being sufficient time during tests for both to occur. beta-Endorphin (40 pmol) infused into the preoptic area-anterior hypothalamic continuum under these conditions suppressed sexual interaction, but ingestion of acesulfame-K increased to values observed when the female was absent. beta-Endorphin infused into neighbouring areas of the brain had different behavioural effects. Sexual behaviour was not inhibited, and ingestion of acesulfame-K was unaltered, when beta-endorphin was infused either into the bed nucleus of the stria terminalis or the rostral ventromedial hypothalamus. However, infusions of cholecystokinin-8 into the ventromedial hypothalamus suppressed acesulfame-K ingestion in most animals, showing that the cannulae were placed in an area regulating ingestive behaviour. The inhibition of sexual behaviour after preoptic area-anterior hypothalamic continuum infusions of beta-endorphin was prevented by either pretreating rats with 1 mg/kg naloxone intraperitoneally, or by infusing a putative delta opiate receptor blocker (0.5 pmols ICI 174864) into the preoptic area-anterior hypothalamic continuum 5 min prior to beta-endorphin treatment. ICI 174864 administered alone significantly increased mount rate and reduced the post-ejaculatory refractory period in copulating males. These experiments suggest that there is both neurochemical and neuroanatomical specificity relating beta-endorphin to sexual behaviour in the male rat.

Animals↗
PubMed1989

Expression of the egg-laying hormone genes in peripheral neurons and exocrine cells in the reproductive tract of the mollusc Lymnaea stagnalis.

The neuroendocrine caudodorsal cells play an important role in the control of reproduction in Lymnaea stagnalis. These neurons produce at least nine neuropeptides which are encoded by caudodorsal cell hormone-I and -II genes. The role of some of these peptides in the control of reproduction has been established. The present study demonstrates that the transcription and translation of the caudodorsal cell hormone genes also proceeds abundantly in the reproductive tract of this hermaphroditic animal. In the female part of the reproductive tract neurons were found to express gene I. These neurons are most likely involved in the control of transport of the eggs and egg-masses and in the regulation of secretory activity from the female accessory sex glands. In the male part of the reproductive tract exocrine secretory cells express gene I or gene II. The gene products are secreted into the male duct and transferred to the female copulant during copulation. Furthermore, putative sensory neurons in the skin were found to express gene I. The results indicate that in L. stagnalis the complex process of reproduction is regulated--at least in part--by a set of neuropeptides which are encoded by a small multigene family, viz. the caudodorsal cell gene family.

Animals↗