Hypothalamo-pituitary-adrenocortical axis function and hedonic behavior in adult male and female rats prenatally stressed by maternal food restriction

Neuroendocrine activation during stress is affected by many factors contributing to the variability of the stress response. The present study was aimed at evaluating long-term changes in hypothalamo-pituitary-adrenocortical (HPA) axis function and in hedonic behavior in adult offspring prenatally stressed by maternal food restriction, with attention on possible gender differences. Adult offspring were blood sampled via a tail artery cannula. Prenatally stressed females had significantly higher adrenal weights compared to males. Plasma ACTH levels, which rose in response to acute stress induced by handling, were significantly higher in females compared to those in males. A similar pattern was found in plasma corticosterone. The rise in ACTH levels was more pronounced in prenatally stressed rats though the rise in corticosterone failed to be modified. Corticotropin releasing hormone (CRH) and proopiomelanocortin mRNA levels in the hypothalamic paraventricular nucleus and anterior pituitary, respectively, were found to be unchanged. The present experiments failed to reveal a decrease in hedonic behavior in prenatally stressed rats. In contrast, in male offspring a tendency to a higher sucrose preference was observed. These data together with observed changes in hormone and CRH mRNA levels indicate that the gestational stress used did not result in a depression-like state in adult offspring.     

Roles of gonadotropins and releasing hormones in hypothalamic control of lordotic behavior in ovariectomized, estrogen-primed rats.

Intrahypothalamic effects of gonadotropins (luteinizing hormone and follicle-stimulating hormone), thyrotropin-releasing hormone (TRH), and luteinizing-hormone-releasing hormone (LRH) on lordotic behavior were evaluated in ovariectomized (OVX) rats maintained at different receptivity levels. Under conditions of low receptivity in which LRH has been shown to enchance mating behavior, medial preoptic area (MPOA) infusions of luteinizing hormone (LH) caused significant depressions in the lordotic response, whereas LH infusions into the arcuate ventromedial area (ARC-VM) had no sigificant effect. Follicle-stimulating hormone (FSH) infusions into either area did not alter the behavioral response. In the second experiment, in which OVX rats were primed with higher doses of estrone to maintain high ptrinfusion receptivity, MPOA or ARC-VM infusions of either LH or TRH were shown to depress lordotic behavior significantly, whereas neither LRH nor FSH was observed to inhibit the behavioral response. A third experiment evaluated the effects of LH, FSH, and TRH on LRH-facilitated mating behavior. Infusions of LRH into either the MPOA or the ARC-VM significantly enhanced mating behavior, whereas the addition of either TRH or LH to the LRH infusates abolished this response. The addition of FSH to LRH infusates neither enhanced nor depressed the behavioral response to MPOA or ARC-VM infusions of LRH. The antagonistic effects of LH and TRH on LRH-facilitated mating behavior were correlated with previous observations of antagonistic effects on hypothalamic unit activity and monoamine metabolism. The antagonistic interrelation between LRH and LH may represent a mechanism for the activation and coordination of sexual receptivity with ovulation.     

Pituitary-adrenal activity in acute and chronically stressed male and female mice lacking the 5-HT-3A receptor

The serotonin (5-HT)-3A receptor has been localized in limbic and brainstem structures that regulate hypothalamic--pituitary--adrenal (HPA) activity. We previously showed that 5-HT-3A receptor knock-out (KO) male mice displayed lower ACTH responses to acute restraint or lipopolysaccharide administration compared to age-matched wild-type (WT) males. In the present study, we found that pituitary-adrenal responses to acute stress were not different in female WT and KO mice. Furthermore, we examined the role of the 5-HT-3A receptor in regulation of chronic stress-induced HPA activity in both male and female WT and KO mice. The results show that ACTH, but not corticosterone, responses to novel restraint are lower in chronically cold stressed females compared to non-stressed control females but no effect of 5-HT-3A receptor deletion was observed. In contrast, male mice showed facilitated responses to novel restraint after chronic cold stress and this facilitation produced sex differences in ACTH responses to novel restraint between male and female chronically stressed KO mice. Together, these results indicate that there are sex differences in HPA responses to novel restraint in chronically stressed mice and these differences are partly related to 5-HT-3A receptor function.     

Differential sexual activity of isolated and grouped male mice despite testosterone administration

In Experiment 1, adult male C57 mice were castrated, housed individually or in groups of four, and repeatedly injected with either of two doses of testosterone. Control mice were sham-castrated, individually or group housed, and injected with oil vehicle. In repeated tests of sexual behavior with receptive females, isolated males in all surgery-dose combinations showed significantly more mounts and intromissions than did their group-housed counterparts. Ejaculations were fully restored by testosterone in castrated grouped males but not in castrated isolated males. In Experiment 2, administration of either of two doses of testosterone failed to elevate the sexual behavior of intact group-housed males. These experiments show that housing with other males depresses all major measures of sexual behavior, and suggest that this is probably independent of testicular hormones.     

Acute predator stress impairs the consolidation and retrieval of hippocampus-dependent memory in male and female rats

We have studied the effects of an acute predator stress experience on spatial learning and memory in adult male and female Sprague-Dawley rats. All rats were trained to learn the location of a hidden escape platform in the radial-arm water maze (RAWM), a hippocampus-dependent spatial memory task. In the control (non-stress) condition, female rats were superior to the males in the accuracy and consistency of their spatial memory performance tested over multiple days of training. In the stress condition, rats were exposed to the cat for 30 min immediately before or after learning, or before the 24-h memory test. Predator stress dramatically increased corticosterone levels in males and females, with females exhibiting greater baseline and stress-evoked responses than males. Despite these sex differences in the overall magnitudes of corticosterone levels, there were significant sex-independent correlations involving basal and stress-evoked corticosterone levels, and memory performance. Most importantly, predator stress impaired short-term memory, as well as processes involved in memory consolidation and retrieval, in male and female rats. Overall, we have found that an intense, ethologically relevant stressor produced a largely equivalent impairment of memory in male and female rats, and sex-independent corticosterone-memory correlations. These findings may provide insight into commonalities in how traumatic stress affects the brain and memory in men and women.     

Endocrine Mediators of Masculinization in Female Mammals

ABSTRACT— Most mammal species show traditional patterns of sexual dimorphism (e.g., greater male size and aggression), the proximal mechanism of which involves the male's greater pre- and postnatal exposure to circulating androgens. But in several species, females diverge from the traditional pattern, converging on the male form or even reversing sexual dimorphisms. Such "masculinized" females might show elongation of the clitoris, enhanced body size, and aggressively mediated social dominance over males, and they are interesting case studies for examining the role of androgens in females. This review addresses our understanding of the mediating mechanisms of morphological and behavioral development in both traditional and exceptional mammal species. Although certain lines of evidence implicate testosterone in female masculinization, the role for sex steroids in female development remains unclear. The results call for continued study of both hormonal and nonhormonal mechanisms of sexual differentiation, particularly focused on active processes of feminine development.     

Dexamethasone and stressor-magnitude regulation of stress-induced transcription of HPA axis secretagogues in the rat

Regulation of the production of hypothalamic-pituitary-adrenal (HPA) axis secretagogues, corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), may be differentially sensitive to the negative feedback effects of glucocorticoids. We chose to study this phenomenon by examining the ability of dexamethasone to influence CRH and AVP heteronuclear RNA (hnRNA) levels in an escapable/inescapable (ES/IS) foot-shock stress paradigm. On Day 1, adult male rats were subjected to either ES or IS foot-shock; on Day 2, saline or dexamethasone (100 microg/kg) was administered 2 h prior to the stressor. We found that ES/IS foot-shock stimulated similar robust increases in plasma adrenocorticotrophic hormone (ACTH) and corticosterone concentrations, and medial parvocellular division of the paraventricular nucleus (mpPVN) AVP and CRH hnRNA and c-fos mRNA levels in saline-treated ES/IS rats. Dexamethasone pretreatment suppressed ACTH and corticosterone levels similarly in IS and ES animals. Dexamethasone pretreatment also suppressed mpPVN CRH and AVP hnRNA levels at 30 min. However, by 120 min, the mpPVN AVP hnRNA levels in dexamethasone-treated rats were similar to those measured in the saline group. We also found that rats that received the most shocks on Day 1 had greater HPA axis activation on Day 2. We conclude that the magnitude of the foot-shock stressor, determined by learned and immediate cues, is important in determining the magnitude of the HPA response.     

Male-related chemical cues promote sexual receptivity in the female musk shrew

The role of conspecific chemical cues in the activation of sexual behavior was investigated in the female musk shrew (Suncus murinus). In Experiment 1, virgin female musk shrews were exposed to either clean cages or cages recently vacated by an adult male. Regardless of whether the male used for the sexual behavior test was "familiar" to the female (having spent the 24 h exposure in his vacant cage) or "unfamiliar," females exposed to male-related cues received mounts from males significantly sooner than females exposed to clean cages. In Experiment 2, females housed for 24 h in a cage soiled by an adult male allowed males to mount significantly sooner than females housed in a cage soiled by a castrated male, another female, or a clean cage. These results demonstrate that chemical cues, produced exclusively by adult males, promote sexual receptivity in female musk shrews.     

An assessment of factors contributing to instrumental performance for sexual reward in the rat

Male and female rats were gonadectomized, implanted in adulthood with capsules containing either testosterone propionate (TP) or cholesterol, and were trained to lever press for access to an oestrous female. When lever press performance was tested in extinction, only the male rats implanted with TP displayed significantly higher levels of responding than controls, demonstrating that lever pressing for oestrous females as a reward is sexually dimorphic. Ejaculation patterns from a separate assessment of these rats' copulatory ability were significantly correlated with their instrumental performance. In a second experiment, "masculinized" females exposed to TP postnatally and given TP implants responded in extinction at mean levels equivalent to those exhibited by adult males that were either intact or castrated with androgen replacement. These data suggest that organizational steroid exposure perinatally affects the actual reward value assigned to oestrous females inadulthood, in combination withconsummatory sexual experience.     

Sexually coercive tactics used by university students: a clear role for primary psychopathy

Current research suggests that people with psychopathic traits engage in sexual coercion as an alternative mating strategy. Research overlooks the relation between psychopathic traits and coercive behavior in male and female samples that engage in dating quite frequently. Male and female university students reported on their current relationship styles and their use of minor and severe sexually coercive tactics. Results indicate that primary psychopathy (using the Levenson's SRPS), but not secondary psychopathy, predicts the use of all measures of sexual coercion for both females and males, although males were more likely to exploit an intoxicated partner than females. Additionally, females with high levels of primary psychopathy were more likely to use physical forms of coercion. The findings show that the primary psychopathy features (callousness, charm, and selfishness) predict a shortterm mating strategy that focuses on gaining sex through minor forms of coercion and manipulation.     

Sexual orientation and visuo-spatial ability

On the basis of a literature review it was concluded that sex differences in cognitive ability and the etiology of male homosexuality may have a common biological base, leading to the prediction that in terms of cognitive ability homosexual males (HmM) would resemble heterosexual females (HtF) rather than heterosexual males (HtM). This prediction was investigated using visuo-spatial tasks on which males are known to perform better than females. In Experiment 1 HtM performed better on a water level task than HmM and HtF whose performances did not differ significantly. A different version of the water level task and the Vincent Mechanical Diagrams Test were used in Experiment 2; on both tasks the HtM performed better than the HmM and the HtF whose performance did not differ significantly. The results are interpreted as support for a common biological determinant of cognitive ability and male sexual orientation.     

Sex differences in the duration of visual attention

Normal adult males and females looked at a series of photographs containing either a single adult male or female. Ss viewed each picture for as long as they wished. Assuming that measures of the duration of attention would reflect Ss attraction for the opposite sex, it was hypothesized that Ss would spend relatively more time viewing photographs of the opposite sex. The results failed to support the hypothesis. Although males did not differentially attend to the stimuli, females looked significantly longer at the females than they did at the males. The results were interpreted in terms of the “overt sexual content” of the stimuli and socially conditioned attentiveness and inattentiveness.     

Sex differences in the duration of visual attention

Normal adult males and females looked at a series of photographs containing either a single adult male or female. Ss viewed each picture for as long as they wished. Assuming that measures of the duration of attention would reflect Ss attraction for the opposite sex, it was hypothesized that Ss would spend relatively more time viewing photographs of the opposite sex. The results failed to support the hypothesis. Although males did not differentially attend to the stimuli, females looked significantly longer at the females than they did at the males. The results were interpreted in terms of the “overt sexual content” of the stimuli and socially conditioned attentiveness and inattentiveness.     

Partial mediation of strange-male-induced pregnancy blocks by sexual activity in mice (Mus musculus)

Novel male house mice (Mus musculus) can disrupt early pregnancy in females. Previous research focused on pheromonal rather than behavioral mediation of this phenomenon. In Experiment 1, novel males were housed with females shortly after insemination. Litter production was negatively correlated with the males' sexual activity. Experiment 2 replicated this finding with a larger sample. In Experiment 3, females were exposed to castrated males. Testosterone-treated males completely blocked pregnancy, whereas untreated males did not. In Experiment 4, castrated testosterone-treated males were presented at intervals after insemination. Pregnancy was totally blocked at Days 3 and 4 and mostly blocked at Days 1 and 2 but was less affected at Days 5 and 6. In Experiment 5, females were exposed through a wire-mesh grid to castrated males. Pregnancies occurred in all conditions, even with testosterone-treated males. These data suggest a role for sexual activity in male-induced pregnancy blocks.     

Female Japanese quail (Coturnix japonica) mated with males that harassed them are unlikely to lay fertilized eggs

Results of previous studies of courtship and mating in Japanese quail (Coturnix japonica) suggest that females avoid conspecific males because, while courting and mating, males engage in behaviors that are potentially injurious to females. However, prior experiments provided no direct evidence that females avoided harassing males. Here the authors show that a female quail choosing between a previous sex partner and an unfamiliar male avoids the former if he engaged in relatively many potentially injurious acts while courting and mating, (Experiments 1 and 2) and that males behaving aggressively toward mates are less likely than are gentler males to fertilize the females' eggs (Experiment 3). Male sexual harassment appears to be a tactic both aversive to female quail and relatively ineffective in fertilizing them.     

Gender Differences in Self-Serving Attributions About Sexual Experiences1

Two studies investigated sex differences in attributions about sexual experiences. Subjects were asked to provide causal explanations for satisfying and unsatisfying past experiences. Men were expected to display a greater self-serving bias than women. This hypothesis was supported for unsatisfying but not for satisfying experiences. In both experiments, males were found to blame their partners more for unsatisfying experiences than females. Males used self-serving attributions, assigning more responsibility to the partner than to themselves (Experiment I), whereas women displayed self-derogatory attributions, attributing negative outcomes more to themselves than to their partners (Experiment II). Furthermore, self-derogatory attribution patterns were correlated with unsatisfactory sexual histories in women but not in men. Implications for the treatment of sexual dysfunctions via reattribution training are discussed.     

Medial preoptic area/anterior hypothalamus and sexual motivation

The medial preoptic area/anterior hypothalamus (MPOA/AH) is a brain site derived from proliferative zones from the diencephalon and telencephalon. It is probably this characteristic that makes this brain region participate in different physiological and behavioral functions. The present review addresses the role of the MPOA/AH in the control of male sexual behavior. It is clear that the MPOA/AH is a crucial site in the control of sexual behavior in males of all species studied to date. But although many different publications have followed the contribution of Heimer and Larsson there is no agreement as to what is specifically the role of the MPOA/AH in sexual behavior. At least three hypotheses have been presented. The first one suggests that this brain region is involved in the consummatory aspects (execution) of sexual behavior. The second indicates that the MPOA/AH is involved in the appetitive components (motivation) of masculine sexual behavior. The third hypothesis considers that MPOA/AH neurons are involved in the regulation of consummatory and appetitive aspects of sexual behavior. From the literature reviewed, it will become evident that the evidence supporting a role of the MPOA/AH in the execution of sexual behavior is based on a number of limited studies not easy to interpret. On the other hand, several lines of evidence using a variety of methodologies support the notion that the MPOA/AH is involved in the motivational aspects of male sexual behavior.     

Medial preoptic area and onset of maternal behavior in the rat.

The present series of experiments examined whether the medial preoptic area (MPOA) is involved in the onset of maternal behavior in the rat. Previously, the MPOA had been shown to be important in the maintenance of maternal behavior in the lactating rat. The first experiment investigated whether estradiol benzoate (EB) acts on the MPOA to facilitate the onset of maternal behavior in the 16-day pregnant, hysterectomized, and ovariectomized female rat. Such rats when given EB implants in the MPOA had significantly shorter latencies for the onset of maternal behavior than had females implanted with cholesterol in the MPOA or with EB in the ventromedial hypothalamus, in mammillary bodies, or under the skin. A second experiment showed that estrogen-induced prolactin release was not involved in this facilitation. A third experiment indicated that MPOA lesions disrupt the onset of maternal behavior that is induced by pup stimulation in virgin females. It was concluded that the MPOA is involved not only in the maintenance of maternal behavior but in the hormonally mediated onset of maternal behavior and the onset of maternal behavior induced in virgin females by pup stimulation.     

Peer victimization in adolescence has different effects on the sexual behavior of male and female college students

We studied levels of peer victimization from an evolutionary perspective by investigating self-reported victimization during adolescence in relation to sexual behavior in college students. One-hundred and twelve (47 female) undergraduates completed self-report measures of victimization during middle and high school, onset of sexual activity, and number of sexual partners. Nearly 85% of victimization during adolescence was perpetrated by members of the same sex. Furthermore, results show that this intrasexual victimization (particularly indirect forms) was negatively correlated with reproductive opportunities in males, but positively correlated in females. Males who were frequently victimized had fewer total sexual partners and partners per year on average, while females who were often victims of aggression reported having more sexual partners and an earlier onset of sexual activity. Regression analysis revealed that demeaning, diminishing and embarrassing was the most significant predictor of the rate of sexual activity in both sexes (although this relationship was inverted between them), while teasing was the best predictor of total sexual partners in females. This evidence is consistent with evolutionary interpretations regarding human aggression and competition, as well as with recent findings suggesting that indirect victimization during adolescence is a form of intrasexual competition associated with reproductive opportunities.     

Evaluation of prenatal androgen and ovarian secretions on receptivity in female and male rats

Offspring of rats infected daily from Day 16 through Day 20 of gestation with either 2 mg of testosterone propionate (TP) in .1 ml of sesame oil or oil alone were tested for sexual receptivity following injections of 3.3 microgram of estradiol benzoate (EB) and .5 mg of progesterone (P) beginning at 40, 80, or 120 days of age. At each age, neonatally gonadectomized males and females from TP-injected litters exhibited less receptivity than corresponding oil-injected controls. Prenatally androgenized females were similar to neonatally castrated oil-injected males at all ages. Ovarian implants from birth to 35 days of age significantly increased receptivity in neonatally castrated males and androgenized females. Increasing the age at which testing was initiated systematically reduced receptivity in all groups.