Effects of anterior hypothalamic lesions on the sexual behavior of prenatally-stressed male rats

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.

Prenatal stress produces deficits in socio-sexual behavior of cycling, but not hormone-primed, Long-Evans rats

Prenatal stress (PNS) alters behavior of adult offspring in novel environments or in social interactions; variable effects of PNS on female reproductive behavior have been reported. Effects of exposure to restraint and lights for 45 min/day on Gestational Days 14-20 were examined on the motor and socio-sexual behavior of adult female offspring. In a novel arena, proestrous PNS rats displayed greater behavioral inhibition as indicated by significantly fewer beam breaks made in the horizontal crossing task compared to that of proestrous non-PNS rats. In a standard mating test, in which females are exposed to males in a relatively small space for a restricted time or number of sexual contacts, PNS females in proestrus were found to have significant decreases in the intensity of lordosis and in the number of solicitation behaviors that they directed towards the male compared to non-PNS rats. In a seminatural mating test, in which females can control the timing of the sexual contacts from the male, PNS females in proestrus engaged in significantly less pacing of their sexual contacts compared to that of the non-PNS females. When additional PNS and non-PNS rats were ovariectomized (ovx) and tested following hormone priming, behavioral differences were abrogated. PNS decreased motor behavior in a novel arena, lordosis intensity, and solicitation behavior in a standard mating paradigm, as well as adaptive, approach-avoidance behavior in a seminatural mating situation of endogenously cycling proestrous rats but not ovx, hormone-primed rats. Thus, hormone priming may override or mask effects of PNS on some aspects of socio-sexual behavior.

Prenatal dexamethasone or stress but not ACTH or corticosterone alter sexual behavior in male rats

Prenatal maternal stress in rats and mice can demasculinize and feminize the sexual behavior of adult male offspring. Causal mechanisms are unknown, but one attractive hypothesis is that stress activation of maternal adrenal glucocorticoid secretion is the responsible agent. To test this hypothesis, pregnant rats were exposed to a variety of substances which enhance glucocorticoid actions. These included ACTH (20 IU of a gel preparation, SC once daily), corticosterone (CORT; 7 mg/kg SC in oil, three times daily), or dexamethasone (DEX; 0.1 mg/kg, SC once daily). Controls included noninjected dams and a positive stress control group (restraint under bright lights three times daily). All treatments reduced maternal weight gain, DEX most potently. No treatment altered litter size, stillbirths, or sex ratio, but DEX reduced weight at birth, an effect still seen at postnatal day 85. DEX, CORT, and stress reduced male adrenal weight at birth, while DEX and CORT altered sexual differentiation as measured by anogenital distance. Stress impaired adult male sexual performance but not the lordosis quotient following exposure of animals to stud males. DEX affected both measures. No other treatment had any significant effect on sexual behavior. No treatment altered plasma LH levels, either basal or in response to an estrogen challenge in adult gonadectomized males. In adulthood there was no treatment effect on stress reactivity, measured behaviorally or by plasma glucocorticoids. Correlational analysis revealed that weight gain during pregnancy was the single best predictor of subsequent sexual performance. It is concluded that prenatal dexamethasone exposure demasculinizes and feminizes male offspring.(ABSTRACT TRUNCATED AT 250 WORDS)

Paucity of c-fos expression in the medial preoptic area of prenatally stressed male rats following exposure to sexually receptive females

Normal male rats display high levels of sexual activity when paired with sexually receptive females, a behavior regulated, in large part, by the medial preoptic area (MPOA). It has been documented that onset of c-fos proteins in the MPOA accompanies sexual behavior. Because prenatal stress (PS) demasculinizes sexual behavior in male rats, the present study examined whether such effects might be accompanied by a decrease in the neuronal activation in MPOA associated with sexual behavior. Adult prenatally stressed (P-S) and unstressed control males were paired with sexually receptive females, and sexual behavior allowed to commence. After a single mount, the pair was separated by a partition for the remainder of an hour, at the end of which the male was killed and the brain processed for c-fos immunocytochemistry; quantification was performed by means of computerized image analysis. P-S males expressed significantly less c-fos activity in the region of the MPOA, compared to nonstressed control males. Thus, the sexual deficits associated with P-S males may be due to a relative dearth of activity in the MPOA at the neuronal level. Coupled to earlier work showing decreased luteinizing hormone secretion in P-S males under similar conditions, the present data suggest a constellation of factors that contribute to PS-induced deficits in sexual behavior.

Effect of glucocorticoids injected into pregnant female mice and rats on weight of male sexual glands in adult offspring and testosterone level in fetus is genotype-dependent

Injection of corticosterone into CBA/Lac, C57BL/6J and BALB/c mice, or hydrocortisone into aggressive and domesticated rats, on days 16 and 18 of pregnancy decreased the weight of sexual glands in adult male offspring of the C57BL/6J and domesticated mothers but increased these values in male offspring of the CBA/Lac and aggressive mothers. When injected into pregnant aggressive and domesticated rats, corticosterone affected testosterone levels in 21-day-old male fetuses. The changes were also genotype-dependent and followed the course of changes in the weight of the accessory sex glands in adults. It is suggested that glucocorticoids given during the prenatal period can affect plasma testosterone levels of male fetuses and the development of the sexual glands in a genotype-dependent manner.

Sexual behavior of male rats is differentially affected by timing of perinatal ACTH administration

The laboratory rat was used as a model to investigate the effect of pre- and/or postnatal ACTH administration on sexual differentiation of the brain. Pregnant Sprague-Dawley rats were injected with ACTH 1-24 (10 micrograms/kg/2x/day or 500 micrograms/kg/2x/day); postnatally treated neonates were injected with the above dosages once a day. Perinatal treatment with ACTH (10 micrograms/kg/2x/day) altered several sexual behavior measurements, but did not have an overall effect on the number of males that exhibited sexual behavior. At a higher dose (500 micrograms/kg/2x/day) prenatal ACTH administration decreased sexual behavior in male rats, as measured by an increase in the percent of males that did not mount or intromit. In contrast, all males treated postnatally with ACTH (500 micrograms/kg/2x/day) completed 2 ejaculatory series and initiated a third series. No significant differences were observed in adult plasma testosterone or prolactin levels; however, serotonin levels in the preoptic area of adult male rats treated prenatally with ACTH (500 micrograms/kg/2x/day) were significantly higher than in prenatally treated saline males. In addition, an increase in plasma ACTH in adulthood was observed in animals injected postnatally with saline. This study indicates that the decrease in sexual behavior observed in males treated prenatally with ACTH is associated with increased serotonin levels in the preoptic area, which suggests that ACTH may act as a neuromodulator during sexual differentiation of the brain. It also demonstrates that the effect of perinatal manipulations on the development of male sexual behavior may vary depending on the ontogenetic period of the brain.

Maternal stress alters monoamine metabolites in fetal and neonatal rat brain

Heat-restraint stress given rats during the last week of gestation significantly altered dopaminergic dihydroxyphenylacetic acid and homovanillic acid (DOPAC and HVA) and noradrenergic 3-methoxy-4-hydroxy-phenyl-ethylene glycol (MOPEG) forebrain-hypothalamic monoamine (MA) metabolites in female offspring. On gestational day 21, HVA and MOPEG were significantly higher and lower, and on postnatal day 1 all were higher. There were virtually no differences in brain MA concentrations in males. Thus MA metabolic concentrations differ in fetal-neonatal forebrain-hypothalamus as a function of sex differences and maternal stress.

Ethanol sensitivity in rats: effect of prenatal stress

The present study examined whether sensitivity to ethanol could be altered by prenatal stress exposure. Pregnant female rats were handled during the third week of gestation and the offspring were tested for ethanol sensitivity as adults. Compared to control offspring, the following characteristic responses to acute ethanol were significantly attenuated in prenatally stress-exposed rats: the decreases in body temperature, motor coordination and startle amplitude, and the increases in circulating corticosterone and free fatty acids. Ethanol-induced impairment of swim performance, in contrast, was potentiated in these animals. Since no differences were found in blood or breath ethanol levels, the rate of ethanol metabolism was probably not affected by prenatal stress. Rather, the altered responses appear to result from long-term changes in central nervous system sensitivity to ethanol.

Prenatal stress disrupts reproductive behavior and physiology in offspring

Prenatal maternal stress has been related to neonatal activity and irritability in both lower animals and humans in documented research for at least the past 30 years. Contemporary animal research demonstrates that prenatal stress feminizes and demasculinizes the sexual behavior of males and reduces fertility and fecundity in females, producing estrous cycle disorders, spontaneous abortions, or vaginal hemorrhaging and high neonatal mortality. Mechanisms of stress are being sought in the maternal-fetal blood exchange, hormonal alterations in the hypothalamus-pituitary-gonads and adrenals, and in brain catecholamines. Contemporary human research demonstrates that negative maternal attitudes toward pregnancy are related to high incidences of congenital abnormalities and infant deaths. Severe psychosocial stress is related to high incidences of neonatal deaths and neurological impairments in infants, and a high incidence of psychiatric disorders in adulthood. Data derived from both animal and human research may help explain the etiology and mechanisms of prenatal-stress-induced reproductive dysfunctions as well as some forms of human psychopathology.

Repeated failure of prenatal ACTH administration to alter masculine behavior in mice

In four experiments, different preparations and modes of prenatal administration of ACTH all failed to produce any substantial effects upon male sexual behavior in mice. In Experiment 1, CD-1 females implanted during the third trimester of pregnancy with osmotic pumps releasing varied dosages of ACTH1-24 produced male offspring with essentially normal copulatory behavior. In Experiment 2, prenatal injections of high doses of ACTH1-24 had no effect upon male sexual activity. In Experiment 3, osmotic pumps releasing ACTH1-39 during the third trimester of pregnancy had no effect upon sexual behavior of offspring. However, aggressive behavior was significantly reduced, relative to untreated controls, in offspring of all females implanted with pumps, including those releasing only saline. In Experiment 4, third-trimester injections of ACTH1-39 in long-acting gel form had no effect on the sexual behavior or aggression of offspring of C57 strain females. In most of these experiments, ACTH treatment significantly reduced body weight. These results do not confirm previous suggestions that pituitary-adrenal hormones influence the perinatal differentiation of sexually dimorphic behavior.

Naltrexone blocks the effects of prenatal stress on sexual behavior differentiation in male rats

The male offspring of rats stressed three times daily during days 14-21 of pregnancy were more likely to show lordotic behavior when tested in adulthood than were control males. This feminization of sexual behavior was not observed if the mothers were injected with the opioid antagonist naltrexone before being stressed. These data suggest that endogenous opioids released under conditions of stress can alter the normal process of sexual behavior differentiation in the fetal male rat.

Prenatal stress eliminates differential maternal attention to male offspring in Norway rats

Maternal licking behavior was observed in 20 Long-Evans rat dams on two consecutive days. Stimulus pups were male and female foster pups from dams that were either housed with 5 adult males during the last trimester of pregnancy (stressed) or housed alone (unstressed). Unstressed male pups received significantly more maternal licking than their female siblings, but prenatally stressed males and females received similar levels of maternal licking, comparable to that directed to unstressed females. In a second study, urine collected from prenatally stressed male pups elicited significantly less investigation from dams in a choice test than urine from age-matched unstressed males. It is concluded that the chemosignals which stimulate dams normally to provide more maternal attention to male than female neonates are deficient in prenatally stressed males. The results raise the possibility that differential maternal care may mediate some effects of prenatal stress on behavioral development in males.

Prenatal stress and postnatal androgen: effects on reproduction in female rats

Heat-resistant stress applied to pregnant rats during the last trimester disrupts oestrus cycles in female offspring and alters adrenal, ovarian and uterine weights at autopsy. Sexual receptivity is left intact. Prenatal stress may operate by increasing exposure of fetal females to androgens in utero.

Effects of prenatal stress on reproduction in male and female mice

Pregnant mice were exposed to heat-restraint stress from Days 14 through 21 of gestation. Feminine receptivity quotients were significantly higher in prenatally-stressed male offspring than in unhandled males; however there were no differences in testes weights or masculine copulatory behavior. Prenatally stressed females exhibited vaginal opening at a later date, had longer estrus cycles and higher median quality receptivity scores than unhandled controls. Prenatal stress had no profound effects on pregnancy, parturition or survival of young. However there was a significantly smaller proportion of parturient postnatally stressed females compared to unhandled controls.

Reproductive functioning in the prenatally stressed female rat

The reproductive behavior and physiology of female offspring of rats stressed during pregnancy were assessed. Mothers were restrained and placed under bright, hot lights from Day 14 through 21 of gestation. This treatment, which is known to disrupt the sexual behavior of male offspring, did not alter reproductive functioning in the female offspring. The females showed evidence of normal cyclicity, sexual behavior, pregnancy, parturition, pup survival, and maternal behavior when tested beginning at 70 or at 140 days of age.

Maternal stress alters plasma testosterone in fetal males

Titers of testosterone in plasma were determined by radioimmunoassay in male rat fetuses of stressed and control mothers on days 17, 18, 19, 21, and 23 (the day of birth) after conception. In fetuses of stressed mothers, testosterone concentrations were highest on day 17, declined on days 18 and 19, and then remained unchanged. In the control fetuses, testosterone increased from relatively low concentrations on day 17 to the highest amounts on days 18 and 19, and then declined. Thus, the persistence of feminine and impaired masculine sexual behavior in male offspring of stressed mothers could be due to the absence of a surge of circulating testosterone during days 18 and 19 after conception, a period postulated to be critical in the development of the central nervous system in the rat.

Prenatal stress reduces fertility and fecundity in female offspring

Female rats subjected to prenatal stress later experienced fewer conceptions, more spontaneous abortions and vaginal hemorrhaging, longer pregnancies, and fewer viable young than nonstressed rats. The offspring of the prenatally stressed rats were lighter in weight and less likely to survive the neonatal period. Prenatal stress may influence the balance of adrenal and gonadal hormones during a critical stage of fetal hypothalamic differentiation, thereby producing a variety of reproductive dysfunctions in adulthood.

Effects of prenatal stress on the estrous cycle of female offspring as adults

Stress during gestation significantly increased estrous cycle length in female offspring as adults, primarily by lengthening the estrus-metestrus stage. Therefore, prenatal stress may disturb the hormonal milieu of the female fetus during a critical hypothalamic differentiation stage.