Effects of reactivity to dorsal stimulation and social role on aggressive behavior in laboratory rats

Rats were selected on the basis of reactivity to dorsal tactile stimulation and then tested in a resident-intruder paradigm. While reactivity of residents did not influence the occurrence of agonistic behaviors or wounding of residents and intruders, reactivity of intruders did affect offensive and defensive patterns of interactions and the wounds sustained by residents and intruders. Subsequent to resident-intruder testing, rats were tested for shock-induced aggression. The pattern of the results and the results of additional experiments demonstrated that resident-intruder experience could affect subsequent shock-induced aggressive behavior.     

Functions of the vibrissae in the defensive and aggressive behavior of the rat

Removal of mystacial vibrissae for strange rats placed in an established rat colony produced reliable decrements in defensive boxing for these animals, and corresponding increases in freezing. In a subsequent experiment, removal of the vibrissae of the attacking colony males did not change the attack behavior of the vibrissectomized animals. These results indicate that the vibrissae are involved in defensive boxing behavior, but play no essential role in the elicitation or maintenance of conspecific attack in the rat.     

Neural correlates of intertemporal choice in aggressive behavior

People often have to make decisions between immediate rewards and more long-term goals. Such intertemporal judgments are often investigated in the context of monetary choice or drug use, yet not in regard to aggressive behavior. We combined a novel intertemporal aggression paradigm with functional neuroimaging to examine the role of temporal delay in aggressive behavior and the neural correlates thereof. Sixty-one participants (aged 18–22 years; 37 females) exhibited substantial variability in the extent to which they selected immediate acts of lesser aggression versus delayed acts of greater aggression against a same-sex opponent. Choosing delayed-yet-more-severe aggression was increased by provocation and associated with greater self-control. Preferences for delayed aggression were associated with greater activity in the ventromedial prefrontal cortex (VMPFC) during such choices, and reduced functional connectivity between the VMPFC and brain regions implicated in motor impulsivity. Preferences for immediate aggression were associated with reduced functional connectivity between the VMPFC and the frontoparietal control network. Dispositionally aggressive participants exhibited reduced VMPFC activity, which partially explained and suppressed their preferences for delayed aggression. Blunted VMPFC activity may thus be a neural mechanism that promotes reactive aggression towards provocateurs among dispositionally aggressive individuals. These findings demonstrate the utility of an intertemporal framework for investigating aggression and provide further evidence for the similar underlying neurobiology between aggression and other rewarding behaviors.     

Effects of fluprazine (DU 27716) upon aggressive and sexual behavior of testosterone-treated female rats

Female rats, chronically treated with Testosterone Propionate (TP), were injected with Fluprazine (DU 27716) or saline and tested for social aggression, masculine and feminine sexual behavior. Fluprazine-treated females were less aggressive than saline-treated females, as indicated by a shift from offensive to less offensive parameters of aggression. At the same time, mounting in Fluprazine-treated females was almost totally abolished, both in aggression tests and in tests for sexual behavior. Feminine sexual responses increased during aggressive encounters but were slightly inhibited when females were confronted with sexually active males. Females treated with Fluprazine and tested for mounting with a receptive female showed a substantial increase of offensive aggression directed at the receptive stimulus female. It is concluded that Fluprazine does not selectively inhibit offensive aggression in TP-treated female rats.     

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.     

Instrumental conditioning of aggressive behavior in rats

A method has been developed for bringing an aggressive response under stimulus control. It was found that the number of conditioned aggyessive responses was maximal when low-weight target rats were used. The latencies of the conditioned responses toward target animals of 124 gm were significantly lower than those toward animals of 221 and 284 gm. The application of an extinction procedure on the conditioned aggressive response substantially increased the total number of emitted aggressive responses.     

The goal to be accepted by friends as underlying function of overt aggressive behaviour in immigrant adolescents

This study investigated (1) to what extent the goal to be accepted by friends is an underlying function of overt aggressive behavior in adolescents, and (2) whether this function is more predictive than reactive aggression for overt aggressive behavior in first and second generation immigrants compared with natives. The sample comprised 339 native Austrians (51.6% girls), 126 first generation immigrants (48.4% girls), and 175 second generation immigrants (54.3% girls) aged 14 to 19 (M = 15.61). Data were collected via self-assessments. Multiple group latent means and covariance structures (MACS) models revealed that the goal to be accepted by friends was a stronger predictor than reactive aggression for overt aggressive behavior in first generation immigrants compared with second generation immigrants and natives. Furthermore, gender moderated these associations. The goal to be accepted by friends was a very strong predictor of overt aggressive behavior in first generation immigrant boys, but not in first generation immigrant girls. Results are discussed regarding the process of acculturation in first generation immigrant youth.     

Jolly fat rats? The effects of diet-induced obesity on territorial fighting

In experiment 1, pairs of young male rats became obese on a palatable and complex diet high in fat, sucrose, and protein. The obese pairs exhibited greater within-group weight variability and, when tested as adults, were significantly more aggressive toward an unfamiliar conspecific than chow-fed controls. The increased aggressivity of obese males was not due to the relatively larger resident-intruder weight disparities in these pairs, since weight-matched pairs of unfamiliar animals were as aggressive toward each other as pairs not matched in body weight (experiment 2). The complex and calorically dense diet may have accelerated the development of the experimental animals, producing subjects whose aggressivity was comparable to that of much older animals.     

Directional interaction of midbrain and hypothalamus in the control of carbachol-induced aggression

Microinjection of carbachol into the ventromedial part of the anterior hypothalamus or the ventrolateral part of the mesencephalic central gray elicits affective aggression in the cat. Pretreatment with atropine in the same site blocks carbachol-induced aggression. Prior administration of atropine into the midbrain blocks aggression induced by carbachol injections into the hypothalamus, but atropine injected into the hypothalamus does not prevent affective aggression elicited by carbachol administered into the midbrain. The results demonstrate a directional interaction between midbrain and hypothalamus, and provide suggestive evidence for a hierarchal organization of these limbic structures in the control of cholinergically-mediated affective aggression.     

The lived experiences of single mothers in Swaziland of their son's aggressive behaviour

The study explored and described the lived experiences of single mothers and described guidelines for psychiatric nurses to facilitate the mental health of single mothers subjected to aggression by their adolescent sons. Participants were a purposive sample of 8 (single mothers, aged between 40 and 50 years, 7 mothers were employed and 3 were professionally trained, 4 mothers were domestic workers and 1 earned living by selling vegetables). The mothers attended the outpatient department at the National Psychiatric Hospital in Swaziland because of being exposed to aggression by their adolescent sons and had adolescent sons living with them 6 months prior to as well as during the study. Data were collected using individual in-depth phenomenological interviews, direct observation and field notes. Analyses used thematic coding. Results reflected that single mothers experienced their adolescent sons as disrespectful and violent, they had negative experiences about their adolescent sons which resulted in anxiety related symptoms, they had negative experiences of self and experienced poor relationships with their neighbours. Guidelines concerning intra- and interpersonal challenges were formulated for the psychiatric nurse to facilitate the mental health of these mothers.     

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.     

Fighting,nonagonistic social behavior,and exploration in isolation‐reared rats

Sixty hooded Long‐Evans rats were assigned to one of three conditions: isolation‐rearing (from 14–30 days of age), brief isolation (from 28–30 days of age), and normal (no isolation). From day 14 to day 21, the isolation‐reared animals were maintained in an incubator set at 35°C to prevent hypothermia and were separated from each other by Plexiglas. They learned to nourish themselves by lapping milk that continuously flowed down one side of the enclosure. Thereafter, they were housed in standard hanging wire cages. Unlike previous studies of isolation at this age, there were no significant weight differences between the isolation‐reared group and the two control groups. At 30 days of age, the three groups were compared on fighting (serious and play), nonagonistic social behaviors (following and crawling under), and exploratory behavior (open‐field ambulation). The isolation‐reared group was significantly different from the normal group on all measures (isolates were higher on all measures except exploration). The isolation‐reared animals showed significantly more serious fighting (aggression) than the brief isolation animals, whereas these two groups did not differ on other behaviors. This methodology allows for the study of isolation‐rearing without the nutritional confounds found in previous research and shows an effect on aggression that is not accounted for by recent isolation. Aggr. Behav. 25:211–223, 1999. © 1999 Wiley‐Liss, Inc.     

The influence of the victim on shock induced aggression in rats.

In two studies, free-roaming male rats (aggressors) were shocked in the presence of male target rats restrained in either an upright or a supine posure. In addition, in Experiment II, two levels of aggressor shock intensity (0.8 mA or 2.0 mA) were used while targets received one of three levels of shock (0.5 mA, 1.5 mA, or 2.5 mA). In both studies, upright targets were attacked less than supine targets. Frequency of aggression was directly related to level of aggressor shock intensity in Experiment II. Also, attack by 0.8-mA aggressors against supine targets was inversely related to level of target shock intensity. The low level of attack against upright targets was interpreted in terms of a threat diaplay. Similarily, it was concluded that the target shock-intensity effect in Experiment II was due to specific threat behaviors displayed by those supine rats that received the highest-intensity shocks.     

The topography of aggressive behavior of an attacking rat is determined by the behavior of the victim

Untreated rats were observed to either bite or box with Pentobarbital-treated opponents in a shockelicited aggression situation. Specific behaviors such as ataxia movements and submissive postures immediately preceded biting attacks, but rarely boxing whereas behaviors such as moving around the chamber and upright threat postures immediately preceded boxing attacks, but rarely biting. These data suggest that the topography of aggressive behavior of an attacking rat is determined by the behavior of the victim.     

Effects of cohabitation with another female on aggressive behaviour in pregnant mice

Pregnant, nonpregnant (but mated) and virgin females were individually housed or lived with a pregnant or nonpregnant cagemate. They were subjected to a series of successive daily encounters with a male intruder, the cagemate being excluded. The most aggressive subjects were pregnant females living with a pregnant cagemate. Isolated pregnant females were as aggressive as pregnant females with a nonpregnant cagemate. Nonpregnant and virgin females were the least aggressive. Nevertheless nonpregnant subjects living with a pregnant cagemate generated higher aggressive scores than nonpregnant females living alone. The way in which a pregnant cagemate influences the aggressive behaviour of another pregnant or nonpregnant female is discussed.     

Effects of medial preoptic hypothalamus anterior lesions on three kinds of behavior in the rat: Intermale aggressive,male-sexual,and mouse-killing behavior

Large lesions in the medial preoptic area-anterior hypothalamus (MPOA-AH) of adult male S3 rats reduce both intermale aggressive behavior and male sexual behavior considerably, but mouse-killing behavior is not impaired. Daily treatment with high doses of testosterone propionate for 21 days does not restore these behavioral effects. Smaller lesions in the same area affect male sexual and intermale aggressive behavior differently; in the frontal part of the MPOA-AH they affect aggressive behavior, while in a more caudal part they affect sexual behavior. Indications were found that lesions in specific parts of the stria terminalis and the medial forebrain bundle inhibit aggressive and sexual behavior.     

The association between high status positions and aggressive behavior in early adolescence

The present study examined the association between high status social positions in early adolescence and both overt and relational aggression. A sample of 234 sixth graders (132 girls, 102 boys) completed peer nominations assessing aggression, social centrality, and coolness. Data analyses were based on all sixth graders who received peer nominations, for a total sample size of 417 students (224 girls, 193 boys). Hierarchical linear modeling was used to examine both within-peer group differences and between-peer group differences. Results indicated relational aggression was related to higher overall social centrality and being nominated as cool even when controlling for overt aggression. Overt aggression appeared to be related to higher overall social centrality and being nominated as cool, but this relationship was much weaker when relational aggression was controlled. Although girls used relational aggression more often and boys used overt aggression more often, the use of relational aggression by either gender was related to membership in high status peer groups and high status within the peer group. Implications of the findings and suggestions for future research are discussed.