Activational and organizational effects of estradiol on male behavioral neuroendocrine function

Evidence is reviewed that establishes an essential role for estradiol, synthesized locally via aromatization of testosterone in the adult as well as the developing male nervous system of rats, ferrets, and mice, in both the organization and adult activation of neural circuits that control appetitive as well as consummatory components of masculine sexual behavior. Evidence is also reviewed suggesting that perinatal estradiol biosynthesis and action in the female's nervous system may contribute to the development of female-typical sexual behavior.     

Relationship between maternal aggression and maternal care in the rat

Aggression among female rats is almost entirely confined to the period of late pregnancy and lactation. Behaviorally it is similar to the aggression of males including piloerection and lateral attacks, but it differs in its function. Unlike male aggression which serves to establish a social hierarchy and a territory, i. e., is competitive, maternal aggression is protective, i. e., it serves to prevent predation of the mother's offspring. In this respect it is closely related temporally and causally to maternal care; if the offspring are removed maternal aggression wanes almost immediately–its function no longer exists! Studies on aggression by mothers, among rats, from the author's laboratory are reviewed and comparisons made with maternal care. As noted, maternal aggression and maternal care are closely related during the cycle of maternal behavior and they share a similar hormonal basis and possibly the effect of uterine stimulation, but maternal care requires prolactin and the decline of progesterone while maternal aggression appears independent of pituitary hormones and does not require a decline in progesterone. Maternal aggression like maternal care appears to be organized into a hormonal phase, during pregnancy, parturition, and for about a week postpartum and a nonhormonal phase thereafter. Bilateral radiofrequency lesions of the lateral midbrain peripeduncular nucleus (PPN) produce deficits in maternal aggression if made on lactation day 7 (L7), but not earlier, without producing significant deficits in maternal behavior. Experiments showed that the PPN does not mediate hormonally stimulated maternal aggression; it appears to mediate only nonhormonally stimulated maternal aggression. Studies on the role of pregnancy hormones on long-term retention of maternal aggression and the role of olfaction in maternal aggression are also reviewed. © 1994 Wiley-Liss, Inc.     

The physiology of women’s power motive: Implicit power motivation is positively associated with estradiol levels in women

This study examined the relationship between implicit power motivation (n Power) and salivary estradiol in women. Forty participants completed the Picture Story Exercise, a measure of n Power, and salivary estradiol levels from two saliva samples were determined with radioimmunoassay. We found that n Power was positively associated with estradiol levels. The positive correlation between n Power and estradiol was stronger in single women and women not taking oral contraceptives than in the overall sample of women. These findings replicate those of Stanton and Schultheiss (2007), giving further credence to the argument that women’s dominance striving is positively associated with their endogenous estradiol levels and that both social and biological factors influence the nature of that association.     

Agonistic behavior,plasma testosterone,and hypothalamic estradiol binding in male rabbits

The purpose of this study was to establish a relation between agonistic behavior, gonadal hormones, and their receptorial capacity at the central level. Male rabbits were observed in seminatural conditions and three components of their agonistic behavior were recorded: follow, attack, and chase. The three behaviors were mutually correlated and clearly differed among the four members of each group. Within the social group, one rabbit was agonistically more active than the others and his supremacy was associated with an increased level of peripheral testosterone and higher estradiol binding in the hypothalamus. On the whole, the values of the hypothalamic estradiol binding were positively correlated with the behaviors. The results show that, in the male rabbit, agonistic activity is associated with changes in testosterone concentration and in the binding at the central level of its aromatized metabolite estradiol. Aggr. Behav. 23:33–40, 1997. © 1997 Wiley-Liss, Inc.     

Relationships between testosterone metabolism in the brain,other endocrine variables and intermale aggression in mice

Relationships between some endocrine variables (plasma testosterone and estradiol; in vitro gonadal biosynthesis from pregnenolone precursor and adrenocortical biosynthesis from progesterone precursor; in vitro activity of 17β-hydroxysteroid de-hydrogenase (17β-HSDH) and of aromatizing enzymes in the subcellular fractions of the brain) and isolation-induced inter-male aggressiveness were studied. A significant positive correlation was found between fighting behavior, measured by the number of wins in a series of paired encounters, and the activity of brain 17β-HSDH. A significant inverse correlation was found between fighting behavior and the activity of aromatizing enzymes in the nuclear fraction of the brain. No significant correlations were found between fighting and the other endocrine variables investigated. These results may suggest that the conversions testosterone → androstenedione and testosterone → estradiol in the brain play a role in the control of inter-male fighting in the mouse. These results may also account for the effect of repeated wins and defeats on brain steroidogenesis.     

Reactive aggression tracks within‐participant changes in women's salivary testosterone

The relation between testosterone and aggression has been relatively well documented in men, but it is less well understood in women. Here we assessed the relationship between salivary testosterone and reactive aggression (i.e., rejection rate for unfair offers) in the Ultimatum Game. Forty naturally cycling women were tested twice, once in the late follicular phase (around ovulation) and once during the luteal phase. Ovulation was determined using urine test strips measuring luteinizing hormone levels. Salivary samples were assayed for testosterone, estradiol, progesterone, and cortisol at both test sessions. There was no association with the cycle, but multilevel modeling revealed a significant within‐participant association between testosterone and rejection rate for extremely unfair offers (i.e., high reactive aggression), indicating that women showed greater reactive aggression when their testosterone levels were higher. Additionally, we found that women with relatively high individual concentrations of testosterone were more likely to reject extremely unfair offers than women with relatively low concentrations of testosterone. This study is the first to demonstrate that women react more aggressively in response to provocation when their testosterone level is high than when their testosterone is low, suggesting that testosterone plays an important role in the regulation of women's aggressive behavior following social provocation.

     

The effects of estradiol on avoidance learning in ovariectomized adult rats

The present study examined the effects of ovariectomy and subsequent estradiol replacement on learning in young adult rats using a set of instrumental avoidance paradigms differing in the nature and extent of prior experience in the learning context. Thus, one group of animals was placed directly into avoidance learning (AV). A second group was trained on an appetitive task first, and then transferred into the aversive context (AP-AV). The third group was exposed to the training context without any specific appetitive response requirement, and then required to learn an active avoidance response (Context-AV). We found that estradiol (OVX+E) impaired avoidance acquisition in all cases relative ovariectomized controls (OVX). In contrast, while avoidance learning is improved following appetitive training or context exposure in both OVX+E and OVX animals, the OVX+E animals profit to a greater extent from the appetitive or context experience than do the OVX controls. We suggest that this difference may be due to enhanced attentional processes or improved hippocampal processing of contextual factors. Thus, estradiol negatively influences simple associative avoidance learning in ovariectomized rats, but appears to promote positive transfer.     

Adrenal mediation of intermale aggression maintained by aromatized and reduced metabolites of testosterone

Individually housed CD-1 mice were either sham castrated or castrated and treated with testosterone (T), estradiol benzoate (EB), dihydrotestosterone (DHT), a combination of EB and DHT (EB+DHT), or the injection vehicle. Following 16 days of isolation and subcutaneous injections, animals were tested repeatedly for fighting behavior in paired encounters with nonaggressive stimulus males. Results indicated that the T and EB+DHT groups fought to the same extent as the gonadally intact group. Both the EB and DHT groups fought more than the vehicle-treated group but less than the T, EB+DHT and sham castrated groups. A similar study was subsequently performed with adrenalectomized animsls. Adrenalectomy eliminated agonistic responses in animals receiving metabolites of testosterone (EB, DHT, EB+DHT) but had only slight effects in gonadally intact and T-treated, castrated mice. The results suggested that a) EB and DHT, either singly or in combination, maintain aggression through a synergism with adrenal steroids; b) the combined effects of EB and DHT reflect an additive action rather than synergistic interaction, notwithstanding the synergism with adrenal steroids; c) metabolism of testosterone to estrogen and dihydrotestosterone does not sufficiently account for the action of testosterone.