Androgen-induced aggression in neonatally androgenized female mice: inhibition by progesterone

Influence of sex hormones on the aggressive behavior during peck order establishment and stabilization in meat and egg type chickens

In the poultry industry, broiler and layer strains are genetically selected for different purposes (e.g., high meat-yield and high egg-production). Genetic selection for productivity can have unintended consequences on the behavioral repertoire of the birds, including aggression. Alongside the increasing societal concern regarding the welfare of animal in agriculture, the number of countries that are advocating the prohibition of using battery cages for laying hens has resulted in the transition and adoption of cage-free or free-range systems. Thus, both broiler and layer chickens are housed in large flocks rather than housed individually in cages. Housing birds in groups increases the opportunity for birds to engage in social behaviors, including aggression, that are used to establish social status. Aggressive interactions are associated with the risk of injury and the potential for a subordinate animal to have unmet needs (e.g., access to feed). The aim of this study was to characterize the relationships among aggressive behavior, neurobiology, and hormones during peck order establishment and social hierarchy stabilization of 2 divergently selected strains (meat- and egg-type chicken). Meat-type strains performed more male on male (P < 0.001), male on female (P < 0.0001), and female on female (P < 0.0001) non-reciprocal aggression behavior (NRA) than egg-type strains. Greater serum testosterone and estradiol concentrations in the weeks after the peck order establishment were observed in meat-type birds compared those in egg-type birds for both males and females (all P < 0.05). Greater (P < 0.05) cellular densities of androgen receptors, but not estrogen receptors, were observed in the hypothalamus of meat-type birds compared to egg-type birds. These findings suggest that greater sex hormone concentrations in the meat-type birds may be a consequence of genetic selection for rapid growth resulting in more sex hormones-induced aggressive behavior.

Functional differences in the hypothalamic-pituitary-gonadal axis are associated with alternative reproductive tactics based on an inversion polymorphism

The evolution of social behavior depends on genetic changes, yet, how genomic variation manifests itself in behavioral diversity is still largely unresolved. Chromosomal inversions can play a pivotal role in producing distinct behavioral phenotypes, in particular, when inversion genes are functionally associated with hormone synthesis and signaling. Male ruffs exhibit alternative reproductive tactics (ARTs) with an autosomal inversion determining two alternative morphs with clear behavioral and hormonal differences from the ancestral morph. We investigated hormonal and transcriptomic differences in the pituitary and gonads. Using a GnRH challenge, we found that the ability to synthesize testosterone in inversion carriers is severely constrained, whereas the synthesis of androstenedione, a testosterone precursor, is not. Inversion morphs were able to produce a transient increase in androstenedione following the GnRH injection, supporting the view that pituitary sensitivity to GnRH is comparable to that of the ancestral morph. We then performed gene expression analyses in a second set of untreated birds and found no evidence of alterations to pituitary sensitivity, gonadotropin production or gonad sensitivity to luteinizing hormone or follicle-stimulating hormone across morphs. Inversion morphs also showed reduced progesterone receptor expression in the pituitary. Strikingly, in the gonads, inversion morphs over-expressed STAR, a gene that is located outside of the inversion and responsible for providing the cholesterol substrate required for the synthesis of sex hormones. In conclusion, our results suggest that the gonads determine morph-specific differences in hormonal regulation.

Early Androgens Are Related to Childhood Sex-Typed Toy Preferences

Girls with congenital adrenal hyperplasia (CAH) who were exposed to high levels of androgen in the prenatal and early postnatal periods showed increased play with boys” toys and reduced play with girls' toys compared with their unexposed female relatives at ages 3 to 8. Boys with CAH did not differ from their male relatives in play with boys' or girls' toys. These results suggest that early hormone exposure in females has a masculinizing effect on sex-typed toy preferences.

Aromatase promoter I.f is regulated by progesterone receptor in mouse hypothalamic neuronal cell lines

Aromatase catalyzes the conversion of C(19) steroids to estrogens. Aromatase and progesterone, both of which function at different steps of steroidogenesis, are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The aromatase gene (Cyp19a1) is selectively expressed in distinct neurons of the mouse hypothalamus through a distal brain-specific promoter, I.f, located ∼40 kb upstream of the coding region. However, the regulation of aromatase expression in the brain is not well understood. In this study, we investigated a short feedback effect of progesterone analogues on aromatase mRNA expression and enzyme activity in estrogen receptor α (Esr1)-positive or -negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. In a hypothalamic neuronal cell line that highly expresses aromatase, progesterone receptor (Pgr), and Esr1, a progesterone agonist, R5020, inhibited aromatase mRNA level and enzyme activity. The inhibitory effect of R5020 was reversed by its antagonist, RU486. Deletion mutants of promoter I.f suggested that inhibition of aromatase expression by progesterone is conferred by the nt -1000/-500 region, and R5020 enhanced binding of Pgr to the nt -800/-600 region of promoter I.f. Small interfering RNA knockdown of Pgr eliminated progesterone-dependent inhibition of aromatase mRNA and enzyme activity. Taken together, progesterone enhances recruitment of Pgr to specific regions of the promoter I.f of Cyp19a1 and regulates aromatase expression in hypothalamic neurons.

The many faces of progesterone: a role in adult and developing male brain

In addition to its well documented action in female-typical behaviors, progesterone exerts an influence on the brain and behavior of males. This review will discuss the role of progesterone and its receptor in male-typical reproductive behaviors in adulthood and the role of progesterone and its receptor in neural development, in both sexual differentiation of the brain as well as in the development of "non-reproductive" functions. The seemingly inconsistent and contradictory results on progesterone in males that exist in the literature illustrate the complexity of progesterone's actions and illuminate the need for further research in this area. As progestin-containing contraceptives in men are currently being tested and progesterone administration to pregnant women and premature newborns increases, a better understanding of the role of this hormone in behavior and brain development becomes essential.

Sex steroid communication in the ring dove brain during courtship

This review examines possible role of progesterone receptor (PR) and androgen receptor (AR) "cross-talk" in the expression of courtship behaviour in the ring dove (Streptopelia risoria). In doves, although androgen has been mostly associated with aggressive courtship behaviour and progesterone with the initiation of incubation, progesterone administration to courting birds terminates the aggressive component of courtship whilst having no effect on nesting behaviour. Recent results in doves have identified a high density of androgen receptor and progesterone receptor immunoreactivity (AR-ir and PR-ir) in the hypothalamus of both sexes in regions known to be directly involved in courtship and incubation behaviour. Nuclear AR-ir in courting birds is widespread throughout the brain. Nuclear PR-ir is only localized in discrete regions of the preoptic hypothalamus of both sexes. In the anterior and posterior hypothalamus of courting birds an increase number of AR-ir and PR-ir neurons colocalizes (70-90%) in the nucleus preopticus anterior (POA), nucleus preopticus medialis (POM), nucleus preopticus paraventricularis magnocellularis (PPM), nucleus hypothalami lateralis posterioris (PLH), and tuberal hypothalamus (Tu). A lower percentage of colocalization is seen in birds at other stages of the breeding cycle. The high percentage of AR-ir and PR-ir colocalization in the preoptic hypothalamus of courting doves supports previous reports involving progesterone acting in these brain regions to terminate the androgen-dependent aggressive courtship behaviour in male doves. The increase in PR-ir staining intensity in AR-ir neurons in courting birds suggests that this progesterone-dependent termination of aggressive courtship display in males occurs at the receptor level and may be orchestrated by central oestrogen.

Early androgen effects on aggression in children and adults with congenital adrenal hyperplasia

Males are more likely than females to show aggressive behavior across species, ages, and situations, and these differences may be partly influenced by early hormones. We studied aggression in three samples of subjects with congenital adrenal hyperplasia (CAH), who were exposed to high levels of androgen in the prenatal and early postnatal periods. Controls were siblings and first cousins similar in age. In Sample 1, adolescents and adults completed the Multidimensional Personality Questionnaire (MPQ), which includes an Aggression scale. In Sample 2, adolescents and adults completed the MPQ and a paper-and-pencil version of Reinisch's Aggression Inventory. In Sample 3, parents rated the aggression of children aged 3-12, using a modification of Reinisch's Inventory. In all three samples, control males had higher aggression scores than control females. Further, as predicted, females with CAH had higher aggression than control females, but the difference was significant only in adolescents and adults. These results suggest that early androgens contribute to variability in human aggression.

Comparative effects of progesterone and alphaxalone on aggressive, reproductive and locomotor behaviors

Progesterone can reduce aggressive behaviors in rodents under various experimental conditions, but it could be argued that this effect is due to the well known anesthetic/sedative properties of some steroids. We have tested this hypothesis by comparing the effects of progesterone and the anesthetic progestin, alphaxalone, on the aggressive, reproductive and locomotor behaviors of hamsters. Locomotion is used as a sensitive index of sedative/soporific effects. Progesterone reduced aggressive behavior without depressing the general locomotor activity of the animals, and it also facilitated feminine sexual behaviors in both sexes. Alphaxalone induced mild sedation in hamsters but this did not decrease their aggressive display. Alphaxalone did not facilitate feminine sexual behavior in either sex. We proposed that the inhibitory effect of progesterone on hamster aggressiveness is unlikely to follow from the hormone's sedative properties.

Progesterone inhibition of aggressive behaviors in hamsters

Effects of progesterone on aggressive behaviors were tested in male-male or female-female pairs of hamsters, after both members of the pair had received the same experimental treatment. In castrated males, progesterone increased the latency to attack, and decreased the frequency of attack and on-back fighting postures. Similarly, in ovariectomized females, progesterone decreased the frequencies of upright and attack fighting responses, as well as the frequency of rolling fights. Estradiol treatment did not produce these effects on aggressive behaviors, and was not required to prime the nervous system for the progesterone effects. These results suggest that progesterone may act by means other than estrogen-inducible progestin receptors to inhibit aggressive behaviors.

Sex-specific interactions between aggressive and sexual behavior in the rat: effects of testosterone and progesterone

The influence of progesterone on sexual and aggressive behaviors during aggressive encounters was investigated in pairs of TP-treated male and female rats. Gonadectomized females, chronically injected with testosterone propionate (TP), showed low but consistent levels of feminine sexual behavior which alternated with aggression. Progesterone when given in addition to TP facilitated receptive and proceptive behaviors, but reduced levels of aggression. In TP-treated males, levels of aggression were the same as observed in TP-treated females. However, TP-treated males seldomly showed sexual behavior during aggressive encounters and additional treatment with progesterone did not affect their behavior. After the aggression tests, animals were tested in a social preference test in which an ovariectomized female cage mate and the opponent from the aggressive encounter served as incentives. Positive correlations between levels of aggression and social preference for an opponent were found in both sexes, although correlations only reached statistical significance when progesterone was given in addition to TP. These correlations were found in both sexes, despite the fact that group analysis revealed pronounced sex differences in social preference: males preferred to spend their time near ovariectomized female cage mates, whereas females divided their time equally among female cage mates and opponents.

The effect of cyproterone acetate on motor activity, aggression, "emotionality", body weight and testes in wild mice

The literature reports on antiandrogenic and antigonadotropic effects of cyproterone acetate (CA) and on its inhibitory influence on the structure and function of the testis and reduction of the sexual drive in man and animals. No one has as yet been able to confirm a reduction of aggression which could be expected under CA. Isolated male wild mice received daily doses of 0.5 mg (17 mg/kg) CA subcutaneously over 32 days and were studied daily for aggressive behavior, motor activity and emotionality during the last 11 days. Aggression was reduced significantly by CA in the form of an increased latent time and continued to decrease during the test period with a reduction of fighting time and the correlated coarse motor activity. A latent period of approximately 4 weeks was determined for the aggression-inhibiting effect of CA. The detection rate was not changed under CA. It is doubted whether it is an adequate parameter of "emotionality". The overall motor activity was not reduced, so that an aggression-specific effect is assumed rather than a general reduction of drive. The body and testicular weight was reduced, the testicular tissue atrophies. Central points of attack of CA probably play a major role in the reduction of aggression.