Maternal aggression in rats: Changes over pregnancy and lactation in a sprague-dawley strain

Maternal aggression in a Sprague-Dawley strain of laboratory rat (Charles River CD) was explored from Day 1 after mating on Day 0 through Day 24 of lactation (L0-L24). Aggression toward unfamiliar male “intruders” during 10-min tests was low among nonpregnant, nonlactating females and during the first 10 days of gestation. Frequency of attack on intruders increased moderately but significantly by Gestation Day 16 (G16; Experiment 1) or G21 (Experiment 2), a prepartum phenomenon not previously reported in laboratory rats. Levels of aggression were highest, however, during the first 9 days of lactation, when attacks averaged more than 6 per 10-min session. Attacks declined sharply in frequency after L14 and by L24 did not exceed levels observed among nonpregnant females. Experiment 3 examined the importance of the test site (home cage with nest and pups, if any, vs unfamiliar cage without nest or pups) to agonistic behavior associated with pregnancy and lactation. Late pregnant females tested in a novel cage were not aggressive; however, females tested shortly after delivering their pups were highly aggressive, averaging over four attacks per 5-min session. In novel cage tests frequency of attack remained high through L4 but declined significantly by L7. These data are consistent with the hypothesis that maternal aggression at its onset is primarily under hormonal control, but becomes increasingly dependent upon external factors, presumably pup stimulation, during the postpartum period.     

The development of territorial-induced intermale agonistic behavior in albino laboratory mice

Male mice of the CF-1 strain (Mus musculus) were allowed to take up lone residence in a small territory consisting of a 60-cm enclosure attached by a tubular runway to a standard mouse cage with food, water, and bedding. A group of ten mice, each of which resided in its own separate enclosure for 24 hours, were more aggressive toward intruders than other groups of ten mice following six-hour residence periods, or no such residence. Aggression toward intruders increased in repeated weekly tests of the six-hour residents, but after four weeks of testing did not reach the maximum stable level displayed by the 24-hour residents over four weeks of testing. In another experiment, the 24-hour residence period of groups of 20 CF-1 male mice was disturbed by briefly removing the mouse from the enclosure, before introducing the intruder, at various intervals prior to testing. Removal of the resident five minutes before testing resulted in a marked decrease in aggression toward intruders. Although lesser decreases in aggression followed intervals of 30, 45, and 60 minutes, a 180 minute interval resulted in no appreciable effects compared to undisturbed controls. It is concluded that exposure to the stimuli provided by the enclosure results in an aggressive readiness in the resident mouse which reaches a high level within a 24-hour period.     

Sensory control of maternal aggression in Rattus norvegicus

Female rats become aggressive toward adult conspecifics during lactation. This change in social affect is dependent on the presence of the offspring, because maternal aggression disappears when the pups are removed. It was found that a similar decline occurs when the litter is placed in a glass flask while remaining in the home cage. In contrast, maternal aggression persists following placement of the pups in a nylon mesh bag. The pups did not vocalize while being in the mesh bags, so it appears that olfactory cues from the offspring constitute a critical element in the maintenance of maternal aggression in the rat. It has been suggested that the odor not only of the pups but also of the intruder may contribute to eliciting aggressive behavior in lactating rodents. In line with this proposal, it was found that mother rats spend about one third of the time preceding the first attack sniffing the body of the intruder. In contrast to findings in mice, housing of the prospective intruder behind a double wire mesh partition in the lactating female's home cage failed to reduce her aggressiveness toward him. Rats, then, may require more intimate contact with an individual than do mice for the aggression-reducing effect of familiarization to be observed.     

Attack priming and satiation in female golden hamsters: Tests of some alternatives to the aggression arousal interpretation

“Priming” a female hamster by allowing it a single attack on an intruder placed into its home cage transiently decreases the latency and increases the probability of attack on a second trial. Although we have previously argued that this priming effect reflects an increase in aggressive arousal, an alternative interpretation is that the fear elicited by placing a foreign object into the subject's home cage is reduced when it happens again on the second trial. Another interpretation is that priming is an effect of intruder novelty, i.e., the subject perceives a difference between the first and second intruders which causes it to attack the second more quickly. Experiment 1 compared the standard two trial paradigm with different intruders to trials in which (1) the first intruder was withdrawn and used again in the second trial, and (2) the intruder remained in the cage following the first attack. All intruders were pretreated with the analgesic-sedative methotrimeprazine to reduce the variability of their behavior. Neither hypothesis tested in Experiment 1 was supported, strengthening the interpretation of attack priming as a manipulation that affects primarily internal motivational mechanisms specific to aggression. Allowing a hamster to carry out a protracted series of attacks produces a “satiation” effect that is the reverse of priming, i.e., the latency of a subsequent attack is increased and its probability reduced. It is possible that the attack satiation observed in our earlier studies was not the result of processes internal to the subject, but could have been due to habituation to a particular intruder or to certain stimuli emitted by it during the protracted interaction. In Experiment 2 subjects were given three sessions of 10 successive trials using either 1 intruder presented repeatedly, 2 intruders presented alternately, or 10 different intruders presented once each. No difference among conditions was found in this study either suggesting that subject's aggressive behavior is insensitive to whatever changes may occur in intruders' behavior or other stimulus characteristics when they have been treated with methotrimeprazine. The lack of differences among test conditions in both experiments is most likely due to the efficacy of the drug in “standardizing” intruder behavior. Experiment 2 also revealed an interesting difference in two measures of attack latency. The time elapsing between intruder presentation and attack, i.e., the standard measure of latency, decreased from the first to the fourth trail; it then increased steadily over the remaining trials. The cumulative time that the subject remained in contact with the intruder prior to attack, a measure more indicative of attention to the intruder, dropped to an asymptotic value by the second trial. This difference suggests that the satiation effect may be accounted for by subjects' increasing avoidance of the intruders over trails, perhaps as a way of regualting their level of aggressive arousal.     

Moral judgments of aggressive and nonaggressive children

Moral judgments were studied in 103 aggressive and 79 nonaggressive 10-year-old Finnish children. Their aggressiveness was evaluated by means of peer ratings. Moral judgments were assessed by presenting them with stories from their daily lives that contained moral conflicts. The results showed that the children did not adopt a constant level of moral reasoning; instead, judgments were situation specific. Furthermore, the moral cognitions of aggressive children did not differ from those of their nonaggressive peers, although sex-related differences tended to be significant: Boys adopted absolute moral standards, whereas girls' judgments were more relative.     

Social dominance and individual aggressiveness

Male rats exhibiting high, moderate, or low levels of offensive aggressive behavior in interactions with intruders in their home cage were grouped in mixed-sex colonies with 1 male of each aggression-level group in each colony. Agonistic interactions measured 1, 2, 3, 7, 14, 21, and 22 days after colony formation indicated that highly aggressive males on pretests continued to be more aggressive, becoming the dominant colony male in five of seven colonies and attacking intruders more often than less aggressive males. In the two remaining colonies the moderately aggressive male became dominant. This relationship, which was consistent over a number of indices, including offensive and defensive behaviors, and wound counts and wound sites, was seen even when a substantial weight differential favored the less aggressive animal. Dominance relationships were rapidly established and within-group fighting declined significantly over the 21-day test period. Pretest offensive levels also influenced the behavior of subordinates, with high or moderately aggressive subordinates showing more defense in interactions with dominants and receiving more wounds than did low-aggression subordinates. Dominant males also showed more defense in interacting with those subordinates which had been more aggressive during pretests. This pattern of results suggests that aggression level of the subordinate as well as the dominant may be an important factor determining the intensity of agonistic interactions in male rats.     

Moral Judgments of Aggressive and Nonaggressive Children

Abstract

Moral judgments were studied in 103 aggressive and 79 nonaggressive 10-year-old Finnish children. Their aggressiveness was evaluated by means of peer ratings. Moral judgments were assessed by presenting them with stories from their daily lives that contained moral conflicts. The results showed that the children did not adopt a constant level of moral reasoning; instead, judgments were situation specific. Furthermore, the moral cognitions of aggressive children did not differ from those of their nonaggressive peers, although sex-related differences tended to be significant: Boys adopted absolute moral standards, whereas girls' judgments were more relative.     

Effects of imprinting and isolation on aggressive responses in chicks

The importance of isolation and imprinting as separate factors influencing early aggressive responses in chicks (Gallus gallus) was studied in two separate experiments. In addition the effect of the presence or absence of the imprinting stimulus in the test situation was examined in Experiment 1. Neither imprinting per se, nor the presence of the imprinting stimulus significantly affected aggressiveness. Rearing conditions (isolation vs social rearing) did, however, influence aggressive responses. Isolated chicks were significantly more aggressive than socially reared buds. The adaptedness of selective aggression in socially (naturally) reared chicks, as well as the indiscriminant aggressiveness caused by social deprivation is discussed.     

Sex differences in aggressive behaviour in various strains of mice

Two nonalbino inbred (C57 BL/6 and C3H/He) and one albino strain (Swiss) of mice were compared for female aggression toward intruders: 1 in period of lactation, 2 in nonlactating state and (3) in nonlactating state but previously rubbed with urine of lactating females; and for male aggression toward familiar or unfamiliar opponents. The results showed that resident females of the C57 and Swiss strain vigorously attack lactating intruders introduced into their cages. This effect was mediated by urinary cues emitted by the latter mice. It was also shown that Swiss residents displayed aggression towards nonlactating females, irrespective of their strain. Groups of C57 residents reacted most aggressively towards Swiss females, less aggressively towards C3H intruders, but did not show any aggression towards their own nonlactating conspecifics. In contrast, none of the C3H resident female groups displayed aggression towards intruding females of any category or strain. The results also showed that the males of the three strains displayed little (Swiss and C3H) or no aggression (C57) towards familiar opponents, whereas they directed increased aggressive responses towards unfamiliar ones. Comparisons among the three strains of mice revealed that Swiss males were the most aggressive in either situation. On the other hand, the finding that C3H males showed aggressive responses suggested that male and female aggression are, in this strain, under separate genetic or hormonal control.     

An aggression machine II. Interindividual differences in the aggressive defence responses aroused by varying stimulus conditions

PitkÄnen, L. An aggression machine. II. Interindividual differences in the aggressive defence responses aroused by varying stimulus conditions. Scand. J. Psychol., 1973, 14, 65–74.-The subjects, six aggressive and nonaggressive groups of ten 9-year old boys, selected by rating method, were tested with an "aggression machine" (PAM) constructed by the writer. The varying stimulus conditions included two situations of impulsive aggression and six variations of specified attackers. The results showed that (1) the larger part of the variance of the intensity of aggression in the PAM was accounted for by the situational variations than by interindividual differences in coping with thwarting situations as measured by a rating method. (2) The overtly aggressive boys showed strong discrimination between the situations, while the overtly nonaggressive boys were quite insensitive to situational variations. (3) The intensity of aggressive defence towards a boy of the same age correlated most highly with rated aggressiveness. (4) The latency, duration, and number of aggressive responses did not vary as easily as the intensity according to situations.     

Attributional style in aggressive adolescent boys

Past research suggests that aggressive children misattribute hostile intentions to peers during ambiguous provocative interactions. This study sought to extend the analysis of attributional differences between aggressive and nonaggressive boys to a sample of court-involved adolescents and their perceptions of interactions involving both peers and adults. Three groups of youngsters (nonoffenders, nonaggressive offenders, and aggressive offenders) participated in a structured interview and provided causal attributions for interpersonal problems commonly faced by teenagers. Results indicated that offenders were more likely than nonoffenders to attribute blame to others in ambiguous problem situations. Among offenders, external, person-centered blame attributions were significantly related to aggressiveness. This relationship was found only in ambiguous situations, and the correlation between such person-centered attributions and aggressiveness was higher in adult-oriented interactions than in peer-oriented ones. Overall, the results suggest that aggressiveness among offenders is associated with an attributional style that is characterized by the tendency to attribute blame for problems in ambiguous interactions to global, dispositional characteristics of others.     

The introduction of a group of alien mice (Mus musculus L.) into hierarchically organized groups of five male mice

Groups of 3 male or female Mus musculus were introduced into hierarchically organized colonies of 5 male mice for a period of 8 days. The colonies were of 2 kinds; high-level aggressive (HLA), which had been set up 3 days prior to the introduction of the aliens, and low-level aggressive (LLA), which had been established for 21 days before strangers were introduced. Both males and anestrous females were attacked, but males were attacked 5 times more frequently than females. In HLA colonies most of the attacks on the aliens were by the dominant; in LLA colonies there was no difference in the behavior of dominant and subordinate mice toward strangers. Both aggression toward aliens and intracolony aggression declined over the 8 day experimental period. In HLA colonies the dominant mouse mounted females 5 times more frequently than did either his subordinates or male mice in the LLA colonies. In HLA colonies aliens huddled with subordinates to form a single colony with 1 dominant and 7 subordinates. In LLA colonies alien males remained as a discrete group spatially separated in the cage. Female aliens were incorporated into the main colony. In all cases dominant male mice made more attacks on aliens as compared with familiar mice.     

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.     

Problem-solving strategies in aggressive and nonaggressive children

Problem-solving strategies in hypothetical social situations were studied in 103 aggressive and 79 nonaggressive children. Subjects solved six aggression-provoking situations from children's ordinary lives. Causal thinking, alternative thinking, and prognosticating consequences were evaluated. Cognitions of aggressive children differed from those of nonaggressive children. The greatest differences were found not in high aggressiveness but in aggressive childrens' inability to detect constructive alternatives to aggressive behavior. A child's aggressiveness was a more important determinant than was sex. These findings combined with the finding that strategies can be learned offer an approach to primary prevention.     

Maternal aggression in mice: Protection of young is a by-product of attacks at the home site

Lactating female mice attacked male intruders in their home cages but showed little attack behavior either in novel cages or in cages with which they had been familiarized. Presence or absence of young did not determine the occurrence of maternal aggression, whereas attacks on the young by the intruder decreased maternal aggression and increased cannibalism of pups by the dams. Apparently, if the function of maternal aggression in mice is protection of the young, such protection occurs because the pups are in a place where attacks are likely to occur and not because the dam “defends” the young.     

Aggressive response sets and subtle-obvious MMPI scale distinctions in male offenders

The effects of aggressive and nonaggressive response sets on the MMPI subtle and obvious clinical subscales were investigated. Fifty-eight male prison inmates answered the MMPI as if they were either highly aggressive or highly nonaggressive. The clinical scales with sufficient items in each category were scored for subtle, neutral, and obvious subscales. Inmates successfully feigned aggressiveness on several of the obvious subscales (p = .0056) and one neutral scale; the subtle subscales were not significantly different across groups, consistent with previous research on this population in terms of the resistance of subtle items to these response sets.     

CHANGES IN THE AGGRESSIVENESS OF MICE RESULTING FROM SELECTIVE BREEDING, LEARNING AND SOCIAL ISOLATION

LAGERSPETZ, K. M. J. & LAGERSPETZ, K. Y. H. Changes in the aggressiveness of mice resulting from selective breeding, learning and social isolation. Scand. J. Psychol. 1971, 12, 241–248.–Selective breeding for aggressiveness and non-aggressiveness in mice has now been going on for 19 generations. The aggressiveness score distributions of the males have not changed since the 7th generation. Socially naive male mice which had been living in isolation, had five encounters with submissive males, and five with receptive females. Learning of aggressive and sexual behaviour occurred in males of both the aggressive and the non-aggessive strain. When living in groups, the males of both strains show no aggressiveness towards a submissive opponent. Social isolation for 1–2 weeks greatly increases the aggressiveness level of the animals of the aggressive strain. The effects of grouping is interpreted as social learning of non-aggressive behaviour, the effect of isolation as return of the inter-individually variable aggressiveness level, determined by genetic variation and early experience. Some neurochemical findings are in agreement with the observed behavioural effects.     

Fantasy as a medium for the reduction of trait versus state aggression

In the first phase of an experiment reducing hostility through fantasy, 203 first and second-year high school students completed a daydreaming scale, Rotter ISB, and a sociometric scale designed to ascertain which of their peers behave aggressively. The students of the upper and lower quarters of the daydreaming scale were classified as high and low fantasy, and as aggressive or nonaggressive subjects. The second phase, two weeks later, consisted of 94 subjects forming three groups: a trait aggressive group, a nonaggressive control group, and a group of nonaggressive subjects experimentally manipulated for aggression. Half of the subjects composed stories to four high-cue aggressive TAT cards; the other half read neutral stories. All the subjects then again completed the Rotter ISB which was scored for aggression. Analysis of covariance of the scores indicated that a reduction in hostility occurred only for the group experimentally aroused to aggression in the TAT condition. The scores of the trait-aggressive subjects, tested in a before-after analysis, showed an increase in their hostility level. Fantasy capacity did not influence the scores.     

Generalization of aggressive behavior in adolescent delinquent boys

The generalization of conditioned aggressive and nonaggressive responses in a group of six adolescent delinquent boys was investigated. Responses were reinforced in card games where a token reinforcement system with money as a back-up rinforcer was used. Conditioning of responses was rapid. Generalization, measured in terms of frequency of physical contact, was tested in a group game for which no reinforcement was given. Generalization occurred during aggressive contingencies. During nonaggressive contingencies, responses did not return completely to the baseline level.     

Gonadal hormones and intrasexual aggressive behavior in female bank voles (Clethrionomys glareolus)

The effects of gonadal hormones on aggressive behavior in the female bank vole was investigated in 10 min home cage tests. Ovariectomized (ovx) or intact females injected with oil, with progesterone (P), with a mixture of progesterone and estrogen (P+E), or with testosterone (T) alone were confronted in a resident-intruder test with unfamiliar, nonoperated females as intruders. Intact females showed aggressive behavior more frequently than ovx females. Ovx females injected with P, with P+E, or with T made significantly more attacks, and these attacks lasted longer than those observed for oil-treated voles. The results indicate that P, the typical female hormone, is responsible for aggressive behavior in female bank voles; however, only T increased the duration of interfemale aggression. Aggr. Behav. 24:63–70, 1998. © 1998 Wiley-Liss, Inc.