Hormonal regulation of aggression toward juveniles in female house mice

No correlation between serum testosterone levels and state-level anger intensity in transgender people: Results from the European Network for the Investigation of Gender Incongruence

INTRODUCTION

Anger is a state of emotions ranging from irritation to intense rage. Aggression implies externalizing anger through destructive/punitive behaviour. The World Professional Association for Transgender Health (WPATH) Standards of Care, Edition 7 (SOC7) guidelines warn about aggression in transgender men (TM) on testosterone treatment. We aimed to assess whether anger intensity increases in TM and decreases in transgender women (TW) after initiation of gender affirming hormone therapy and to identify predictors for anger intensity in transgender people.

METHODS

This prospective cohort study was part of the European Network for the Investigation of Gender Incongruence (ENIGI). Anger intensity was prospectively assessed in 898 participants (440 TM, 468 TW) by STAXI-2 (State-Trait Anger Expression Inventory-2) State Anger (S-Anger) during a three-year follow-up period, starting at the initiation of hormone treatment. Data were analysed cross-sectionally and prospectively.

RESULTS

There was no change in STAXI-2 S-Anger scores. At three, twelve and thirty-six months of gender affirming hormone therapy, STAXI-2 S-Anger scores were not correlated to serum testosterone levels, although there was a correlation with various psychological measures after three and twelve months. TM experiencing menstrual spotting after three months had higher STAXI-2 S-Anger scores compared to those without (median 26.5 [18.0-29.8] versus 15.0 [15.0-17.0], P = 0.020). Changes in STAXI-2 S-Anger scores were not correlated to changes in serum testosterone levels after three, twelve and thirty-six months in TM or TW.

CONCLUSIONS

State-level anger intensity is associated with psychological and/or psychiatric vulnerability, but not exogenous testosterone therapy or serum testosterone levels in transgender people.

Effects of an estrogen receptor alpha agonist on agonistic behaviour in intact and gonadectomized male and female mice

Gonadal hormones mediate both affiliative and agonistic social interactions. Research in estrogen receptor alpha (ERα) or beta (ERβ) knockout (KO) mice suggests that ERα increases and ERβ decreases male aggression, while the opposite is found for female ERαKO and ERβKO mice. Using a detailed behavioural analysis of the resident-intruder test, we have shown that the ERβ selective agonist WAY-200070 increased agonistic behaviours, such as aggressive grooming and pushing down a gonadectomized (gonadex) intruder, in gonadally intact but not gonadex male and female resident mice, while leaving attacks unaffected. The role of acute activation of ERα in agonistic behaviour in adult non-KO CD1 mice is presently unknown. The current study assesses the effects of the ERα selective agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT) on the social and agonistic responses of gonadally intact and gonadex male and female CD1 mice to a gonadex, same-sex intruder. PPT had few effects in gonadally intact mice, but seems to increase sex-typical aggression (i.e., attacks in males, other dominance-related behaviours in females) in gonadex mice. In untreated mice, we confirmed our previous findings that gonadally intact males attacked the intruder more than females, but females spent more time engaged in agonistic behaviour than males. As in our previous results, we observed that gonadex mice generally show behaviour patterns more like those of the gonadally intact opposite sex, while leaving overall levels of agonistic behaviour unaffected. Taken together, our current and previous results show that exogenous activation of ERα had no effects in gonadally intact mice, but increased sex-typical agonistic behaviour in gonadex mice, while ERβ had no effects in gonadex mice, but increased non-attack agonistic behaviour in gonadally intact animals. This suggests that, as in social recognition, ERα may be necessary for the activation of agonistic responses, while ERβ may play a modulatory role.

Agonistic behavior in males and females: effects of an estrogen receptor beta agonist in gonadectomized and gonadally intact mice

Affiliative and agonistic social interactions are mediated by gonadal hormones. Research with estrogen receptor alpha (ERalpha) or beta (ERbeta) knockout (KO) mice show that long-term inactivation of ERalpha decreases, while inactivation of ERbeta increases, male aggression. Opposite effects were found in female alphaERKO and betaERKO mice. The role of acute activation of ERalpha or ERbeta in the agonistic responses of adult non-KO mice is unknown. We report here the effects of the ERbeta selective agonist WAY-200070 on agonistic and social behavior in gonadally intact and gonadectomized (gonadex) male and female CD-1 mice towards a gonadex, same-sex intruder. All 15min resident-intruder tests were videotaped for comprehensive behavioral analysis. Separate analyses assessed: (1) effects of WAY-200070 on each sex and gonadal condition; (2) differences between sexes, and between gonadally intact and gonadex mice, in untreated animals. Results show that in gonadally intact male and female mice, WAY-200070 increased agonistic behaviors such as pushing down the intruder and aggressive grooming, while leaving attacks unaffected. In untreated mice, males attacked more than females, and gonadex animals showed less agonistic behavior than same-sex, gonadally intact mice. Overall, our detailed behavioral analysis suggested that in gonadally intact male and female mice, ERbeta mediates patterns of agonistic behavior that are not directly involved in attacks. This suggests that specific aspects of aggressive behavior are acutely mediated by ERbeta in adult mice. Our results also showed that, in resident-intruder tests, female mice spend as much time in intrasexual agonistic interactions as males, but use agonistic behaviors that involve extremely low levels of direct attacks. This non-attack aggression in females is increased by acute activation of ERbeta. Thus, acute activation of ERbeta similarly mediates agonistic behavior in adult male and female CD-1 mice.

Testosterone and human aggression: an evaluation of the challenge hypothesis

Research on testosterone-behavior relationships in humans is assessed in relation to a version of the challenge hypothesis, originally proposed to account for testosterone-aggression associations in monogamous birds. Predictions were that that testosterone would rise at puberty to moderate levels, which supported reproductive physiology and behavior. Sexual arousal and challenges involving young males would raise testosterone levels further. In turn, this would facilitate direct competitive behavior, including aggression. When males are required to care for offspring, testosterone levels will decrease. Testosterone levels will also be associated with different behavioral profiles among men, associated with life history strategies involving emphasis on either mating or parental effort. Most of these predictions were supported by the review of current research, although most studies were not designed to specifically test the challenge hypothesis.

Aggression and arginine vasopressin immunoreactivity regulation by androgen receptor and estrogen receptor alpha

In the following study, we asked which steroid receptors regulate aggression and arginine vasopressin (AVP) immunoreactivity (-ir) in several limbic regions. Using spontaneous mutant and knockout mice, we generated a novel cross of mice whose offspring lacked estrogen receptor alpha (ER alpha), androgen receptor (AR) or both ER alpha and AR. The wild-type (WT) males and females were compared with ER alpha knockout (ER alphaKO) male, mutated AR (Tfm) male and ER alphaKO/Tfm (double knockout; DKO) male littermates. Animals were gonadectomized and treated with 17beta-estradiol (E2) prior to resident-intruder aggression tests. WT and Tfm males showed aggression whereas WT females, ER alphaKO and DKO males did not. In the lateral septum, WT and Tfm male brains had significantly denser AVP-ir as compared with WT females and DKO males. ER alphaKO male brains were intermediate in the amount of AVP-ir present. In the medial amygdala, brains from all genotypes had equivalent AVP-ir, except DKO males, which had significantly less AVP-ir. Overall, the expression of aggressive behavior coincided with AVP-ir in WT, Tfm and DKO males. However, in ER alphaKO males and WT females, the amount of AVP-ir was not associated with resident-intruder aggression. In sum we have shown that E2 acts via ER alpha to regulate aggression in male mice. In contrast both ER alpha and AR contribute to AVP-ir in limbic brain regions.

The progesterone challenge: steroid hormone changes following a simulated territorial intrusion in female Peromyscus californicus

There is a growing body of evidence that the rapid but transient increase in male androgens, particularly testosterone (T), following a single social encounter such as a territorial intrusion occurs in a wide array of vertebrate taxa. Yet, this phenomenon, often called the Challenge Hypothesis, has rarely been investigated in females. Moreover, when studying male challenge effects, researchers have rarely investigated other hormones that can be important to the expression of aggression, such as progesterone (P4) and estradiol (E2). We conducted 10-min aggression trials using the resident-intruder paradigm in cycling female California mice, Peromyscus californicus, a species in which both sexes show territorial behavior. By comparing the hormone levels of test females to control females, we found a decrease in P(4) and the P4/T ratio, but no change in T, E2, corticosterone, E2/P4, or E2/T. Interestingly, these hormone changes were observed even when the resident was not aggressive toward the intruder, suggesting that the stimulus cueing the hormone changes was the mere presence of the intruder and not the amount of aggression displayed by the resident. Generally, T has a positive relationship with aggression, whereas P4 inhibits male and nonmaternal female aggression. Thus, decreasing the P4/T ratio following an encounter may serve to increase future aggression in females. These results suggest that females may use different hormonal mechanisms than do males to mediate aggression in a challenge situation.

Analysis of steroid hormone levels in female mice at high population density

Populations of predominantly female house mice (Mus musculus) were created by placing virgin female mice in cages (0.045 m2 to 0.48 m2) with a single stud male, and removing all ensuing male offspring at weaning. At maximum population size, the females in these all-female/one-male populations exhibited male-like aggressive behavior. Termination of the populations and subsequent measurement of steroid hormone levels indicated that the aggressive females had high circulating level of testosterone and corticosterone, and elevated baseline levels of progesterone. The high levels of corticosterone could be lowered by dexamethasone, but not the high levels of testosterone.

Aggressive behaviour of female prairie deer mice in laboratory populations

Prairie deer mice (Peromyscus maniculatus bairdii), living in asymptotic laboratory populations established two years earlier, were observed for agonistic responses to conspecific intruders. In the first experiment, intruders of six age-sex classes were placed into 10 of the populations for 10 min. The sex of the intruder did not influence the behaviour of the residents, but juveniles elicited more regression than did adults. A second experiment revealed that female residents were responsible for almost all of the attacks upon juveniles. Experiment 3, in which the responses of pairs of deer mice to juvenile intruders were recorded, demonstrated that the aggressiveness of a female was enhanced by the presence of a male. In the final experiment, females were observed to be highly aggressive during the first few days after giving birth. The aggressive behaviour of the female deer mouse may have greater significance for population dynamics than that of the male.