Behavioral correlates of learned aggression in male mice

The aims of this paper are to study the aggressive behavior in male mice with consecutive experience of victories in 2, 10, and 20 days (T2, T10, and T20 winners) of daily agonistic confrontations under the sensory contact model and to determine the most probable behavioral domains that should be used as animal models for learned aggression in humans. It has been shown that the structure of winners' behavior changes from test to test: the attacking behavior prevailed (81% of the total time) in the behavior of T2 winners. Attacks and diggings (herein: digging up and scattering the litter on the partner' territory) prevailed in the behavior of T10 winners (each approximately 40%). T20 winners demonstrated aggressive grooming half of the testing time and digging behavior 25% of the time. Correlational analysis revealed that the number of significant correlations between the behavioral domains (attacking, digging, aggressive grooming, self‐grooming, threats, rotations) and between different behavioral parameters (latency, number, total and average time) of one behavioral domain are growing from the second test to twentieth test, and the relationships between the behavioral domains change qualitatively. The following may be regarded as elements of learned aggression in male mice: (1) appearance of aggressive grooming instead of the intensive attacking behavior and (2) involvement of the digging behavior in the hostile behavior together with the threats and attacking behavior. Negative correlations between parameters of the behavioral domains may testify to the replacement of one behavioral pattern by another and reflect learned behavior. Positive correlations between certain behavioral domains may reflect the formation of a common motivational background for the winners' behavior. Aggr. Behav. 26:386–400, 2000. © 2000 Wiley‐Liss, Inc.     

A sensory contact model for the study of aggressive and submissive behavior in male mice

The technique for simultaneous development of aggressive and submissive behaviors as a result of successive experiences of defeats or victories in daily intermale confrontations in male mice permanently living under sensory contact conditions is offered for behavioral, pharmacological, and neurophysiological studies of mechanisms of agonistic social relations. Distant sensory contact is achieved by placing a pair of males into a common cage separated by a transparent partition with holes permitting visual contact and the individuals perceiving each other's odors but preventing any physical at contact all times except for 10-min daily tests. These conditions essentially elicit aggression in winner males and quickly result in submission by losers of the same strain of mice. The meaning of consecutive stages of the technique, the problem of controls, and applications of this model are discussed.     

Behavioral consequences of agonistic experiences in the male S3 (Tryon Maze Dull) rat

Aggression occurring during an initial confrontation between two rats may result in significant behavioral changes in one or both animals. The present experiment was designed to study behavioral changes occurring in the course of an agonistic interaction and the consequences of winning or losing. In order to ensure winning, male CPB-S3 Tryon Maze Dull) rats were confronted with males of a more aggressive strain (Long Evans); and to ensure losing they were confronted with those of a less aggressive strain Wistar). Winners were tested against losers, this test being repeated after an interval of 17 days. Winners and losers were also tested with naive S3 opponents. Possible effects of winning and losing in nonagonistic behavioral tests were then examined. These measured open field activity, passive avoidance learning, and masculine sexual behavior. The results replicate and extend earlier findings using a different strain, indicating that significant and relatively permanent behavioral changes are induced in male winners and losers. Behavioral change is most prominent in the losers. Despite the behavioral differences between winners and losers in tests for agonistic behavior, no consistent differences were noted in any of the other behavioral tests.     

Violent phenotype in SAL mice is inflexible and fixed in adulthood

Violence was shown to be qualitatively different from functional hyper‐aggression in mice selected for high aggression namely Short Attack Latency (SAL), Turku Aggressive (TA) and North Carolina (NC900) strains. This study aimed at investigating whether this adulthood violent phenotype as seen previously in the SAL mice is fixed and hence behaviorally inflexible right from day 1 of the experiment or consequential, i.e., subject to gradual change from functional aggression to violence. The functionally hyper‐aggressive strains namely TA and NC900 strains served as controls for the study. Methodologically, behavioral (in)flexibility was studied using the overall sequential structure of agonistic behavior. In particular, intra‐individual variations in the overall agonistic behavior as well as offensive, pre‐ and post‐offensive behavior transitions, directly related to the resident–intruder interactions were investigated. The SAL mice showed the least intra‐individual variation in their overall sequential agonistic structure as well as a fixed offense‐oriented agonistic behavior of highest magnitude when compared with the other strains. Additionally, the pre‐ and post‐ offensive transitions were most salient in the functionally hyper‐aggressive TA and NC900 strains, whereas virtually absent in the SAL mice. Thus, the violent behavior of the adult SAL mice is behaviorally inflexible or fixed, whereas the functionally hyper‐aggressive behavior of the adult TA and NC900 mice is behaviorally flexible and constantly adaptive to the opponent behavior, over 3 days of repeated resident–intruder interaction. Aggr. Behav. 35:430–436, 2009. © 2009 Wiley‐Liss, Inc.     

Habituation of aggressive behavior in mice: A parametric study

The decline of aggression as a result of repeated episodes of fighting may represent a habituation phenomenon. The frequency of biting and sideways threat by male mice toward conspecific intruders declined over ten 5-min confrontations. Aggression returned to about 50% of original levels when a new intruder was introduced. Variations in length or frequency of confrontation indicated that the rate of decline of attack bites and sideways threats depended on these confrontation parameters. The condition that provided the fewest opportunities to fight provided the least decline in the frequency of attack and threat. The frequency of attack bites and sideways threats elicited by the presentation of a new intruder after repeated confrontations was greater than the frequency of attack bite and sideways threat in the last confrontation with the original intruder, when the resident and intruder were relatively inexperienced. Spontaneous recovery of attack and threat occurred but rate of recovery did not depend on confrontation parameters. The results indicate that the decrement of aggression in mice in repeated confrontations may be the result of habituation but fatigue is an important cofactor.     

Relationship between shock-induced aggression and other laboratory tests of agonistic behavior in rats

The utility of the shock-induced aggression paradigm has been questioned in recent years. Studies were reviewed that demonstrated similar effects of independent variables on shock-induced, resident-intruder, and home-cage aggressive behavior. Correlations between naturally occurring aggression and shock-induced aggression, studies showing the influence of naturally occurring agonistic experience on shock-induced aggression, and the effects of shock-induced aggressive experience on resident-intruder behavior were also reviewed. It was argued that continued research into shock-induced aggression and its relationship to other laboratory paradigms would be useful, and that abandonment of the paradigm at this time would be premature.     

Effects of losing and testosterone upon subsequent behavior in male and female S3 (Tryon Maze Dull) rats

Attempts were made to determine whether modification of agonistic behavior by experience differs in the sexes and if so, whether testosterone is involved in this response. Gonadectomized male and female CPB-S3 (Tryon Maze Dull) rats were treated with testosterone propionate (TP, 250 μg) or vehicle and subjected to tests in which they became either winners or losers. S3 males and females were tested against Long Evans rats to become losers or against Wistar rats to become winners. Subsequently, S3 winners were tested against losers. In addition, winners and losers were tested against naive S3 opponents of the same sex. After varied agonistic experiences, all animals were tested for social preference in a situation in which they could choose between their respective opponents without the possibility of social interaction. Thereafter, they were also exposed to a two-choice passive avoidance learning procedure to see if the behavioral effects of aggressive interactions generalized to nonsocial learning. Males and females reacted differently to winning or losing, the presence of testosterone being a critical factor in the manifestation of this sex difference. Relatively permanent effects on aggressive and other behaviors were only established in TP-treated males. Losing experiences in the social-preference test generally led to a slight preference for naive, less aggressive animals. Testosterone-treated male losers, the group expected to be most vulnerable to generalized inhibition and impairment of learning, did not differ from other categories in the two-choice passive avoidance procedure, although marked differences were observed between the sexes and between testosterone and oil-treated animals.     

Aggressive behavior in inbred strains of mice during pregnancy

Female aggressive behavior toward adult male ICR/JCl mice was compared for virgin and pregnant mice of five inbred strains (BALB/c, C3H/He, C57BL/6, DBA/2J, and AKR/J). Pregnant females from four strains except BALB exhibited intense aggressive behavior, whereas only virgin AKR females were aggressive. Aggressive behavior began in early pregnancy, was highest in midpregnancy, and declined slightly thereafter until the day of parturition. The level of aggressive behavior showed significant strain differences. The topography of aggressive behavior was also different among the four strains. DBA females showed marked contrast with the other three strains in the temporal changes of aggression in the first phase of encounter. Furthermore, strain specific behavioral pattern of aggression was demonstrated based on six behavioral acts ( Darting , Chasing, Attack, Biting, Wrestling, and Boxing). Virgin and pregnant AKR females showed the identical behavioral pattern of aggression.     

Intra-female aggression in the mouse (Mus musculus domesticus) is linked to the estrous cycle regularity but not to ovulation

Intraspecific communication between mice takes place mainly via urinary chemosignals or "pheromones". Pheromones can influence aggressive and reproductive behavior as well as the neuroendocrine condition of the recipient female mice via their olfactory system. In this study, reproductively cyclic mice in the estrus phase were used to test intraspecific agonistic aggressive behavior. Data were obtained also on the count of the eggs shed in the oviducts. The results showed that (i) individually housed female mice are more aggressive toward an intruder female mouse than grouped mice, (ii) mice in which the vomeronasal organ was removed show aggressive behavior intermediate between individually housed and grouped mice, and (iii) a within group analysis did not show a positive correlation between aggression and presence of shed eggs in the oviducts.     

日常环境中的暴力暴露对攻击行为的长期影响:一个有调节的中介模型

以850名大学生为被试,探讨日常环境中的暴力暴露与攻击行为的关系,并在此基础上提出一个有调节的中介模型,考察攻击性信念的中介作用和人际信任的调节作用。结果发现:(1)日常环境中的暴力暴露对攻击行为有显著的正向预测作用;(2)攻击性信念在日常环境中的暴力暴露与攻击行为的关系中起部分中介作用;(3)攻击性信念的中介作用会受到人际信任的调节。对于低人际信任个体,攻击性信念起部分中介作用;对于高人际信任个体,攻击性信念的中介效应不显著,日常环境中的暴力暴露对攻击行为只有直接作用。     

Effects of ritanserin on offense and defense in male mice

Effects of ritanserin on agonistic behavior of isolated mice exhibiting aggressive or nonaggressive behavioral strategies were studied in pair-wise encounters with group-housed opponents. An ethological approach to behavioral scoring is adopted, which allows for examination of the profiles of individual subjects. Although the data generally support the view that ritanser in has little effect on offense or defense in male mice, the stimulation of pre-aggressive behavior (threats, alerts, tail rattles) was detected in some nonaggressive mice. © 1995 Wiley-Liss, Inc.     

Maternal aggression in mice and rats towards male and female conspecifics

Although postpartum aggression is primarily studied in laboratory mice and rats, it is unclear how the two species compare in terms of the factors associated with peak levels of aggressive behavior. Using the same experimental protocol, we assessed the relative effect of intruder sex and time since parturition on the frequency of maternal aggression in Long-Evans rats and CFW mice. Females were studied for 2 consecutive cycles of pregnancy and lactation. During the first lactation, aggression was tested 2 times per week for 3 weeks in order to select animals that attacked at least once. During the second lactation, both pup care and aggressive behavior were assessed in detail. Testing occurred twice in each lactation week, with postpartum days 1–7, 8–14, and 15–21 considered weeks 1, 2, and 3, respectively. Maternal behavior towards 3 pups was observed for 5 minutes, followed by a confrontation with an intruder. Lactating females encountered female intruders once per week, and male intruders in the alternate weekly test. The same behaviors were measured in the 2 species, except for the tail rattle exhibited by mice and the aggressive posture shown by rats. Lactating rats and mice show similar decreases in pup care behavior as lactation progresses in time; yet the factors associated with peak levels of aggression differ between species. In Long-Evans rats, female intruders receive more attacks, threats, and aggressive postures than males. Frequency of attack bite and sideways threat declines in each passing week of lactation. Lactating mice are more aggressive toward male intruders throughout the lactation period. Mice still attack and threaten during the third week of lactation, but less often in comparison to the first week. Therefore, peak levels of aggression vary in mice and rats both as a function of intruder sex and lactation week.     

Impulsive and premeditated subtypes of aggression in conduct disorder: differences in time estimation

Research aimed at identifying and studying subtypes of aggression have historically dichotomized aggressive subtypes, although specific nomenclature has varied; one approach has been to classify aggressive behavior as predominantly impulsive or predominantly premeditated. There are a number of behavioral and cognitive differences between those exhibiting these different forms of aggression. This study was designed to extend understanding of the impulsive/premeditated aggression dichotomy by comparing time estimation among adolescents exhibiting predominantly impulsive or predominantly premeditated forms of physical aggression who have a psychiatric diagnosis of conduct disorder (CD). Time estimation has previously been shown to be disrupted in impulsive and some aggressive individuals. Time estimation was compared between healthy Controls (n = 37) and two groups of adolescents with CD, those with histories of either predominantly impulsive (CD-Impulsive, n = 26) or predominantly premeditated (CD-Premeditated, n = 38) aggressive behaviors. Participants completed five computerized trials during which they estimated when 1 min had passed. Among aggressive adolescents with CD, the misperception of time was specific to those with histories of impulsive aggression, although time estimates improved with repeated testing and performance feedback. This study confirms the importance of considering the role and type of physical aggression when studying heterogeneous diagnostic groups like CD and supports the relevance of time estimation to certain subgroups of adolescents with CD.     

Cooperative social coordination and aggression: Sex and strain differences in the effects of housing on gonadectomized rats with hormone replacement

Laboratory rats were used to investigate sex and strain differences in the effects of aggression on a cooperative behavior in which pairs learned to coordinate shuttling in a rectangular chamber. The level of aggression was manipulated by comparing males and females of the aggressive S3 strain and a less aggressive Sprague-Dawley-derived strain and housing same-sex partners either together or individually (8 groups, n = 7 pairs per group). Hormone levels were stabilized by gonadectomy and daily injections of the appropriate sex hormone. The only serious coordination deficits were in individually housed males, associated with violent fighting and an extreme dominance/subordinance relationship that was not observed in females. All other groups readily learned and performed the coordination with evidence that low and moderate levels of aggression could facilitate coordination by evoking species-typical behaviors that increased proximity, synchrony, and differentiation within pairs. The discussion focused on models of affiliative behavior in the study of aggression and the compatibility between moderate levels of aggression and cooperation.     

GENETIC AND SOCIAL CAUSES OF AGGRESSIVE BEHAVIOUR IN MICE

L agerspetz , K irsti . Genetic and social causes of aggressive behaviour in mice. Scand. J. Psychol ., 1961, 2 , 167—-173.—Significant differences in the aggressiveness of mice selected for aggressiveness and non-aggressiveness have been found to occur in the 2nd and 3rd generation of selective breeding. In S _a, motor activity scores were significantly higher in mice of the aggressive than of the non-aggressive strain. Defecation and ambulation scores obtained both in a standardized open-field test and in connection with the aggression measurements showed that the S₃ descendants of the aggressive mice were emotionally less reactive than the members of the 3rd non-aggressive generation. Defeats tend to decrease, victories to increase the level of aggressiveness in mice, but the aggression scores tend to return to the original level after the termination of the experiments.     

Social structure features in three inbred strains of mice, C57Bl/6J, Balb/cj, and NIH: a comparative study

Some features of social living were investigated in three inbred strains of mice: C57Bl/6j, Balb/cj, and NIH. Five social behaviors--Aggression, Submission, Allogrooming, Social Rest and Rest Alone, as well as Wheel Running Activity--were recorded 2 h daily for a week, in 26 groups of seven male mice living in an enriched environment. Dominants and subordinates among strains shared some behavioral characteristics, but strain contributions upon social structure were also detected. Similarities among strains included the appearance of a single dominant mouse per group rated as the most aggressive, besides from being the animal presented with most Submissions. Allogrooming was more frequent among subordinates than among dominants and subordinates. Differences among strains were that agonistic behavior among subordinates was higher in the Balb/cj and NIH groups than in the C57Bl/6j mice. NIH mice were recorded in Rest Alone more often than mice from the other strains. C57Bl/6j dominants showed higher rates of Wheel Running Activity than subordinates.     

Restraint increases both aggression and defence in female rats tested against same-sex unfamiliar conspecifics

Female rate living in groups were subjeccted to single and repeated immobllization stress (Restraint, RT). Twenty-four hours after RT, or the last RT session in the case of repeated RT, social behavior was recored in encounters with unfamilar females, matched for age and body weight. Single RT caused an increase in agonistic behavior in both its aggression and defence aspects. This was a specific effect, as other behaviors, including introductory, affiliative (Allo-Grooming), and courting items, were unifluenced by Rate The effect persisted and was even strengthened in the case of aggression, when RT was repeated once a day for 7 consecutive days. These findings, together with previous data showing a reduction in emotionality and an increase in the exploration of the physical environment following RT, suggest that in females mild stress may induce behavioral arousal, with the selective activation of specific social and non-social behavioral parameters. This contrasts with previous findings in male rats, which responded to RT with the depression of several behavioral parameters, including some of the items (aggresion, exploration) activated in females. As already found in males, in females some parameters were affected by repetition of treatment, either RT or control handing. This suggests that manipulation per se does affect social behavior. However, behavioral modifications ascribable to repeated manipulation in no way superimposed, and were clearly distinguish able from, those due to RT. © 1993 Wiley-Liss, Inc.     

Maternal aggression during the mouthbrooding cycle in the Cichlid fish,Oreochromis mossambicus

Maternal aggression was studied in Oreochromis mossambicus during the mouthbrooding cycle. Brooding females were observed in heterosexual captive groups, and their agonistic interactions and behavioural activities were registered. Brooding females were classified into three classes according to the developmental stage of the brood they were incubating: phase 1, brooding eggs; phase 2, brooding fry with yolk-sac; phase 3, brooding fry with exogeneous feeding. The behaviour of the brooding females was compared with the behaviour of control non-incubating females. During the brooding cycle females become increasingly more aggressive toward other individuals, with their aggressiveness reaching a peak in phase 3. During the brooding cycle the females also suppress their feeding activities. The outcome of the agonistic interactions (victories–defeats) of the brooding females was positively correlated with the brooding phase but not with clutch size. The main function of maternal aggression in O. mossambicus seems to be the defence of the vulnerable brood against predators, including conspecifics, at a developmental stage when the fry start to forage outside the mother's mouth. Aggr. Behav. 24:187–196, 1998. © 1998 Wiley-Liss, Inc.     

Effects of neonatal treatment with 1-(2,5-dimethoxy-4-lodophenyl)-2 aminopropane HCI (DOI) and ritanserin on agonistic behavior in adult male and female rats

The role played by the neonatal 5-hydroxytryptamine (5HT) system in the organization and sexual differentiation of adult agonistic behavior was investigated in rats. Focus was on the 5HT2 receptor subtype, which has been demonstrated to be involved in agonism control in the adult. 5HT2 activity was experimentally manipulated by administration of a specific agonist [1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI)] or antagonist (ritanserin) during the second week of life, when serotonin is known to concur to anatomical and behavioral sexual differentiation. Interactions between early 5HT2 activity, genetic sex, and neonatal circulating testosterone (T) were studied by administering the ligands to males, females, and androgenized females. At adulthood, the animals were tested for both aspects of agonism, i. e., aggression and defense, in a 20-min confrontation with an unfamiliar conspecific of the same sex, age, body weight, and social experience. Neonatal administration of the 5HT2 antagonist ritanserin increased aggression independently of sex; it also increased defense, but this effect was confined to males. The agonist DOI had no effect on aggression, but enhanced defense in males and androgenized females, with an effect which depended therefore more on neonatal T than genetic sex. Females appeared in general less sensitive to neonatal 5HT2 manipulation than both androgenized females and males; this suggests that neonatal T is crucial for experimental modifications of neonatal 5HT2 activity to have any consistent effect on adult agonistic behavior. On the other hand, effects observed in males and androgenized females were dependent on the behavior considered and the drug administered. This was especially evident for defense, enhanced by ritanserin in males only, and in both males and androgenized females by DOI. Neonatal 5HT2 activity seems therefore to play a role in the modulation of adult agonistic behaviors, which depends on the behavior considered and is under multiple control of genetic sex and hormonal neonatal substrate. © 1994 Wiley-Liss, Inc.     

Behavioral profile of amisulpride in agonistic encounters between male mice

Amisulpride is a substituted benzamide derivative that acts as a selective dopamine D2/D3 receptor antagonist. Although the anti‐aggressive properties of neuroleptic drugs are well known, the effects of amisulpride on agonistic interactions have not been explored, and there are no studies comparing acute and subchronic effects of this compound on aggression in rodents. In this study, we examined the action of amisulpride (5–25 mg/kg, i.p), administered acutely or subchronically for 10 days, on agonistic behavior elicited by isolation in male mice. Individually housed mice were exposed to anosmic "standard opponents" 30 min after drug administration, and the encounters were videotaped and evaluated using an ethologically based analysis. After acute treatment, amisulpride (5–20 mg/kg) exhibited an ethopharmacological profile characterized by a marked decrease of offensive behaviors (threat and attack) without an impairment of motor activity. By contrast, the anti‐aggressive action of the highest dose used (25 mg/kg) was accompanied by a weak increase of immobility. Body care was also significantly enhanced after treatment with the drug (20 and 25 mg/kg), emphasizing the involvement of dopaminergic receptors in this behavior. After subchronic treatment, no tolerance to amisulpride anti‐aggressive activity was observed. Overall, this behavioral profile is similar to that observed by other atypical neuroleptics. Aggr. Behav. 25:225–232, 1999. © 1999 Wiley‐Liss, Inc.