Copulation and intermale aggression in rats

Attack behavior of reliably aggressive male Long-Evans rats against unfamiliar male intruders was observed immediately following copulation to one or more ejaculations. Compulatory series to five ejaculations did not differ from copulation to a single ejaculation or from a noncopulatory control in affecting aggressive behavior. Repetitive biting attacks occurred in all conditions, with comparable wounding. Evidently, the male postejaculatory state of insensitivity to sexual stimuli does not extend to stimuli eliciting intermale aggression. A second experiment determined the attack-eliciting capacity of foreign males placed in the home cage of an actively copulating male. As intromissions increased and the interval to ejaculation decreased, the probability of intermale aggression and interruption of copulation diminished. The results are discussed in reference to sexual and aggressive strategies of the copulating male.     

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.     

Studies on wild house mice VI: Differential effects of the Y chromosome on intermale aggression

The aim of this study is to determine the effects of different parts of the Y chromosome of wild house mice on aggression. To reach this goal, intercrosses were made between two selection lines for attack latency (SAL and LAL) and their congenic strains (SAL. LY and LAL. SY). This procedure resulted in F₁ hybrids that carried the same autosomes, but differed in their X chromosome and the two different parts of their Y chromosomes, the different parts of the Y chromosome being a recombining part called the pseudoautosomal region (PAR) and a non-recombining part (non-PAR). We conclude that both parts of the Y chromosome contribute slightly but significantly to variation in aggression. The major effect is accomplished by the PAR of the aggressive parent; a mirror effect is achieved by the non-PAR of the aggressive parent in interaction with the PAR. © 1994 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.     

Activation of intermale aggression by combined estrogen-androgen treatment

Adult CD-1 male mice were gonadectomized and tested for their response to the aggression-promoting property of androgens, estrogens, or combined androgen-estrogen treatment. The results showed that the combined treatment was the most effective, although androgens alone were sufficient for behavioral restoration. These findings suggest that testosterone may activate aggression through both its androgenic and estrogenic metabolites.     

Olfactory stimuli and intermale aggression in androgen-treated castrated sheep

The ability of olfactory stimuli to elicit aggression in male sheep was assessed in testosterone-treated castrates. Ablation of the olfactory bulbs (Exp. 1) did not reduce the capacity of sheep to participate in aggressive behaviour after testosterone treatment. Topical application of urine from castrates treated with propionated testosterone, 5α-dihydrotestosterone, 17β-oestradiol, or an oil vehicle to the fleeces of untreated castrates (Exp. 2) did not result in different levels of aggressive responsiveness in testosterone-treated castrates.     

Anger and aggression in women: Influence of sports choice and testosterone administration

We report on two studies of anger and aggression in women. One study concerns an experimental study of anger induction in aggressive and non-aggressive sportswomen. It was found that sports choice in itself, contrary to expectation, does not predict anger arousal and aggressive behavior in the laboratory. However, at an individual level the anger proneness of the subject, as measured by a questionnaire we developed, was related to the intensity of aggressive behavior and subjectively reported anger. The second study concerns the activating effects of androgens on aggression and anger proneness. In a group of 22 female-to-male transsexuals, a battery of anger proneness and aggression questionnaires was administered twice: shortly before and 3 months after the start of androgen treatment. Administration of androgens was clearly associated with an increaese in anger proneness, although there were no changes in several aspects of overt aggressive behavior. © 1994 Wiley-Liss, Inc.     

The effect of ethanol treatment on social behavior in male rats

The effect of 0.50 g/kg of EtOH in male rats interacting with a stimulus male juvenile in a newly developed test of social interaction was examined. The adult male rats were treated with EtOH (8.0 to 12.0 g/kg/day) or equicaloric dextrin maltose for 2 weeks (studies 1 and 2) or 8 weeks (study 3) and social interaction was assessed both before and after chronic drug treatment was ended in study 1 and after chronic drug treatment was ended in studies 2 and 3. It was found that prior to chronic drug treatment, in study 1, 0.50 g/kg of EtOH increased both aggressive behavior and time spent interacting with the stimulus juvenile male from the first presentation of the juvenile to the second presentation (20 min apart) while saline injection decreased it. After chronic drug treatment was ended, in study 1 animals treated chronically with EtOH were more aggressive when they were not intoxicated than when they had been treated with 0.50 g/kg of EtOH. In studies 2 and 3, after chronic drug treatment was ended, aggressive behavior and time spent interacting with the juvenile were greater in the animals treated chronically with EtOH, regardless of whether they were injected with saline or 0.50 g/kg of EtOH. The results of these studies showed that chronic EtOH treatment can produce long-lasting changes in social behavior after drug treatment is over and can alter the animal's normal response to EtOH in a social setting.     

An empirically derived scoring system for intermale aggression in mice

Scoring systems used to assess intermale aggression have been characterized by arbitrary scales and wide variability in the behaviors selected for measurement. The use of such different systems severely limits the ability of investigators to make meaningful comparisons among studies and indicates that there is a need for a common, statistically derived evaluative system for intermale aggression. We measured the frequency and duration of five major components of agonistic behavior exhibited by intact males toward olfactory bulbectomized stimulus males and then analyzed the data using a number of univariate and multivariate procedures. The results were used to generate two statistically based scoring systems, one a short-form index and the other a composite index for more detailed studies of aggression. It is hoped that these statistically derived systems will be adopted by other investigators to increase methodological congruence in the field.     

Effects of prenatal ethanol exposure on juvenile play-fighting and postpubertal aggression in rats

The effects of prenatal ethanol exposure on juvenile play-fighting and postpubertal aggressive behavior in rats were longitudinally assessed in the context of more conventionally applied physical and behavioral measures. Pregnant animals were treated with either 2 gm/kg/day ethanol or isocaloric sucrose over gestation Days 6-19. Reproduction and somatic variables included maternal weight over gestation, offspring weight over Days 1-90, and age at eye opening and incisor eruption. Behavioral variables consisted of negative geotaxis, olfactory discrimination, activity, juvenile play-fighting, and postpubertal aggression. Ethanol offspring had lower birth weights, but there was no significant prenatal treatment effect on subsequent offspring weights or on any other reproductive or somatic variable. Both male and female ethanol-exposed offspring exhibited more play-fighting responses when paired with same-sex controls. Postpubertal aggression levels were assessed in males only. Ethanol-exposed offspring were more aggressive than controls and there was a significant positive correlation between play-fighting and postpubertal aggression ranks. No other behavioral measures discriminated between prenatal treatment groups and none were significantly correlated with either play-fighting or postpubertal aggression rank. The results are consistent with the position that juvenile play-fighting and postpubertal aggression are subserved by common substrates. They also are consistent with predictions derived from the hypothesis concerning a response-inhibition deficit as an effect of prenatal ethanol exposure on behavior.     

Association between intermale aggression and genetically-defined tryptophan hydroxylase activity in the mouse brain

The relationship between the genetically defined intensity of intermale aggression and the activity of brain tryptophan hydroxylase (TPH) has been studied in inbred mice. No association between the enzyme activity and the percentage of aggressive mice (reflecting the predisposition to aggressive reaction) was revealed. However, a significant positive interstrain correlation between brain TPH activity and accumulated attacking time (reflecting fight intensity) was identified. No correlation was found between TPH activity and the accumulated attacking time in segregating F2 (BALB × C57BL) mice. In conclusion, TPH is an important, but not the only factor controlling the intensity of intermale aggression in mice. © 1996 Wiley-Liss, Inc.     

Some adrenal correlates of aggression in isolated female mice

Forty-six female mice (CFW) were isolated for a period of 23 weeks. The effect of isolation on fighting behavior was tested weekly by introducing a naive brown female mouse into the subject's home cage. Total leucocyte counts were obtained at 8 and 14 weeks of isolation. The appearance of leucopenia was used as an index of elevated adrenocortical activity. After 23 weeks of isolation all animals were sacrificed by decapitation. Plasma was collected for corticosterone assay, and paired adrenals were used to assay catecholamine levels. On the basis of the frequency and/or the absence of fighting, the mice were segregated into fighters (n = 22) and non-fighters (n = 17). Analysis of the data by Pearson's product moment correlation and Student's t-test showed that elevated sympathetic-adrenal activity was positively correlated with aggression and that elevated adrenocortical activity was negatively correlated with aggression.     

Genetic analysis of “Spontaneous” intermale aggression in mice

“Spontaneous” intermale aggression was investigated in seven inbred strains of mice. A positive interstrain correlation and cross-correlation was found for two indices of fighting intensity, ie, accumulated attacking time and number of attacks. The strain aggressiveness level (percent of mice fighting in each strain) does not correlate with the intensity of aggressive behavior. It has been shown by using a genetical analysis performed on C57BL/6 and BALB/c strains, their reciprocal F₁ hybrids, and back-crosses that these indices of intermale aggression are under different genetic control. Aggressive behavior intensity depends on the additive effects of genes. The control of strain aggressiveness level revealed that a high level of aggressiveness was dominant. No reciprocal effects were found. The level of aggressiveness and the intensity of fighting seem to represent different aspects of aggression and may be controlled by different genetic mechanisms.     

Effects of chronic ethanol consumption on gestation and lactation in rats

Chronic consumption of ethanol during pregnancy and lactation may lead to abnormalities in the fetus or infant. A group of female Wistar rats was submitted to ethanol treatment over a period of a month. A pair-fed control group received sucrose solution isocaloric to ethanol and the control group received water “ad libitum.” Afterward, the females were mated with males over a period of 20 days. At birth, each litter was maximized to eight pups and the remaining ones were decapitated to remove the fetal blood and brains. No significant difference was observed in fetal body and brain weight at birth. During lactation the ethanol and pair-fed groups gained less weight than the control group. After weaning, their weight became similar. Fetal blood glucose levels were decreased in the ethanol-treated group. One hundred percent of the pair-fed and control females delivered live fetuses at term and all survived; only 40% of the females in the ethanol group delivered, and one pup did not survive. Chronic ethanol treatment pointed to a possible reduction in the fertility. It seems likely that the change in body weight of ethanol-fed dams was caused by undernutrition.     

Pregrouping aggression and defense scores influences alcohol consumption for dominant and subordinate rats in visible burrow systems

Five male/two female rat colonies were established in visible burrow systems, with males selected for pregrouping attack scores and also evaluated in open field and cat odor tests. Dominant-subordinate pregrouping attack differences suggested that the males becoming dominant are those showing more persistent and higher level attack. For six colonies showing dominant-subordinate behavioral differences, pregrouping defense tests failed to predict subordinate status. However, pregrouping defense scores were reliably correlated with subordinate pre-postgrouping change scores for voluntary ethanol consumption. Subordinates showed higher ranked ethanol consumption than dominants, but these groups were not different on pregrouping ethanol consumption. Subordinate postgrouping ethanol consumption was positively correlated with pregrouping attack toward an adult intruder, consonant with previous findings that highly aggressive subordinates are the targets of more intense attack by dominants. These results provide further support for a view that subordination stress increases voluntary ethanol consumption in male rats and suggest some additional individual differences factors that may be involved in increased ethanol consumption for male subordinates. © 1992 Wiley-Liss, Inc.     

Hormones and competitive aggression in women

This study used diaries of competitive interactions to explore the relationship between hormones and competitive aggression in women. Thirty women completed approximately 10 diary entries each. In each entry, the women described a recent competitive interaction they had engaged in and noted whether it was expressed aggressively or through other tactics. Each woman received a score for the fraction of her competitive interactions that were expressed using physical aggression, verbal aggression, nothing overt, and so on. Hormones (total testosterone, free testosterone, androstenedione, estradiol, and cortisol) were measured in serum early in the follicular phase. Results indicate that women with low levels of androstenedione and total testosterone were less likely to express their competitive feelings overtly, while women with high levels of androstenedione were more likely than other women to express their competitive feelings through verbal aggression. Estradiol was unrelated to competitive tactics, but women with high estradiol levels reported fewer competitive interactions over athletics than did other women. Aggr. Behav. 29:107–115, 2003. © 2003 Wiley‐Liss, Inc.     

Androgens and aggression in man: A controlled case study

A controlled case study is reported of the behavioural effects of androgen treatment in an institutionalised hypogonadal mentally retarded male patient. This man was previously treated with intramuscular depot injections of testosterone esters; however, treatment had to be stopped as the androgens allegedly precipitated frequent bouts of violent behaviour. Using ratings of behaviour by hostel staff, replacement therapy was restarted using the new orally effective androgen, testosterone undecanoate (TU). Gradually increasing the replacement dose of TU in a double-blind fashion resulted in no stimulatory effect on aggressive behaviour. Possible reasons for the differential behavioural response to the two androgen preparations are presented.