Shock-induced aggression and pain sensitivity in the rat: Catecholamine involvement in the corticomedial amygdala

The possible role of amygdaloid catecholamines in the control of shock-induced aggression and pain sensitivity in the rat was investigated. Bilateral microinjections of chlorpromazine into the corticomedial amygdala resulted in decreased fighting and decreased sensitivity to the shock stimulus. Further analysis of this effect, using specific adrenergic antagonists, revealed that neither a- nor Padrenergic systems appeared to be responsible for the behavioral effect of chlorpromazine. Injections of haloperidol into the same region, however, yielded a reduction similar to that produced by chlorpromazine, while dopamine injections resulted in significant elevations in both fighting and pain sensitivity. No effect on any of these behavioral measures was obtained following injection of any of the agents into the basolateral amygdala. These results suggest that the observed effect of catecholamine injections in the corticomedial amygdala is related to changes in pain sensitivity mediated by dopamine.     

The medial amygdala: Serotonergic inhibition of shock-lnduced aggression and pain sensitivity in rats

Two aspects of the amygdaloid complex (corticomedial and basolateral) were examined with reference to serotonergic inhibition of shock-induced aggression. Fighting was significantly depressed by serotonergic stimulation (5-HT, 10 μg bilateral) in the corticomedial amygdala while serotonergic blockade (methysergide, 5 μg bilateral) in this region increased levels of fighting. No consistent effects were obtained with serotonergic manipulation of the basolateral amygdala. Further investigation revealed that the state of serotonergic activity in medial amygdaloid sites was associated with concomitant alterations in the animals' sensitivity to footshock. Results are discussed in relation to a) a general inhibitory role of serotonin in behavioural mechanisms and b) a dopaminergic-serotonergic balance for behavioural arousal involving medial amygdaloid nuclei.     

Amygdaloid function in the central cholinergic mediation of shock-induced aggression in the rat

A series of experiments was designed to examine the role of central cholinergic mechanisms in shock-induced aggression. Cholinergic blockade in the basolateral amygdala, ventral hippocampus, or dorsal hippocampus resulted in greatly reduced levels of fighting in response to footshock. However, while pain sensitivity remained unaltered in the amygdala group, both of the hippocampal groups exhibited decreased shock sensitivity. Further investigation of the amygdala revealed (1) increased fighting in response to increased cholinergic levels, (2) neuroanatomical specificity to the basolateral division of this complex, (3) that an intact basolateral amygdala is essential to the normal manifestation of shock-induced aggression, and (4) that social attraction remains unaltered by cholinergic blockade of the basolateral amygdala. Motor coordination and motor activity were not significantly affected in any treatment condition.     

Escalation of irritable aggression: Control by consequences and antecedents

Two experiments demonstrated that rats could be trained in a negative reinforcement paradigm to display a shock-induced aggressive response on the first shock presented. Later, rats that had been submitted to the negative reinforcement training procedure displayed more shock-induced aggression than did control groups during a test session that was situationally different from the one used during training. A third experiment demonstrated that noxious antecedent events, if presented with sufficient rapidity, can combine to increase the probability of aggressive behavior. The three experiments together suggest that aversive antecedents and reinforcement contingencies could be involved in the escalation of irritable aggression.     

Relationship between mousekilling and conspecific aggression in the male rat

In order to investigate the relationships between mousekilling and conspecific aggression, behavioral variables of killer and nonkiller rats were compared in a “resident-intruder” paradigm, in resident as well as in intruder animals. The occurrence of offensive items (offensive sideways, attack) was significantly higher in killer rats when they were residents; their corresponding opponents displayed more defensive behaviors. No significant difference in aggressive behaviors was noted when the comparison was done in the intruders. These results and those of previous studies suggest that there is a correlation between mousekilling and intraspecific offensive behaviors. Some similarities in the situations where both behaviors are elicited–eg, introduction of an unfamiliar intruder into a familiar environment–may contribute to the existence of such a correlation and the possibility of common mechanisms underlying both behaviors is discussed.     

Interspecific aggression and reactivity in rats: Effects of selective raphe lesions and additional olfactory bulb ablation

Large depletion of brain 5 HT has been shown to induce mouse-killing behavior in the rat. Selective lesions of the raphe nuclei have been investigated in order to determine whether the various components of the 5 HT system exert some specific control over this aggressive behavior. Electrolytic lesions of the dorsal or the median raphe nucleus do not induce mouse killing, whereas combined lesions of these nuclei elicit this behavior in about 40% of naive rats. Consequently, it appears that serotonergic neurons originating in the dorsal and median raphe nuclei work synergistically in mediating inhibitory control over mouse-killing behavior. Loco-motor activity is increased in novel environments by each of the selective lesions and to a larger extent by combined raphe lesions; 24 hours activity in resting conditions is unchanged during the light period, and increased during the dark period of the daily cycle by the various lesions. As it has been shown previously that hyper-activity in response to novelty following raphe lesions is not directly related to the 5 HT decrease in the brain, it appears that interspecific aggression and motor responsiveness must not be dependent on the same neural substrate within the raphe nuclei. The raphe lesions do not facilitate the elicitation of mouse killing by further olfactory bulb ablations, in contrast to earlier results where bulbectomy facilitated the induction of this behavior by raphe lesions.     

Fear and aggression in the rat

The effect of fear on two types of aggression in rats was investigated by adding a cat stimulus to a colony in which the dominant male was attacking an intruder (offensive aggression), or, to a tube test situation in which defensive biting was measured before and during tail shock. The cat completely abolished offense in the colony; when the cat was presented and removed before a strange rat was placed in the colony, attack on the intruder was also reduced. In contrast, defensive biting was unchanged or even slightly potentiated by the presence of the cat, demonstrating a separation of the effects of fear on offensive and defensive aggression.     

Childhood inhibitory control and adolescent impulsivity and novelty seeking as differential predictors of relational and overt aggression

Impulsivity is commonly conflated with novelty seeking, but these traits are conceptually independent and hold different predictive implications. Using a multi-informant, longitudinal design, we examined childhood inhibitory control, as well as adolescent impulsivity and novelty seeking, as predictors of aggression in a sample of 976 twins. Lower childhood inhibitory control and higher adolescent impulsivity predicted both overt and relational aggression in regression analyses that accounted for sex, puberty status, age, and socioeconomic status. As predicted, novelty seeking did not predict aggression, a finding that supports its independence from impulsivity.     

Effects of midbrain central gray lesions on spontaneous and electrically induced aggression in the rat

Large electrolytic lesions were placed in the midbrain central gray of male rats. Their effects on hypothalamically induced aggression, switch-off behaviour, and locomotion were investigated. A number of these animals were also tested for territorial intermale aggression in order to compare electrically induced and spontaneous aggression. Large lesions resulted in an increase of the current threshold to induce aggression by hypo-thalamic stimulation. Smaller, but still quite large, lesions decreased the threshold current for hypothalamic aggression. After the operation a decrease in the threshold for switch-off was present, both in the experimental and the control group. Current thresholds for locomotion were decreased after the lesions only in the experimental group. Spontaneous aggression was temporarily decreased after the lesion. No indication was found that other behavioural elements of the animal were distorted by the lesion. The parallel between the effects on spontaneous and electrically induced aggression makes it attractive to ascribe a role to the neural circuit of hypothalamus and central gray in territorial aggression. However, even with large lesions the animals were still capable of fighting, hence the central gray is not indispensable. An attempt was made to explain the differential effects that differently sized central gray lesions have on hypothalamic aggression.     

Indirect aggression in the media: A content analysis of british television programs

The purpose of this study is to determine how much indirect aggression occurs in television programs popular among British adolescents. Previous research has mainly focused on violence in the media rather than examining this more manipulative and subtle type of aggression. A content analysis of 228 hours of television programming revealed that indirect aggression was portrayed in 92.04% of all episodes analyzed. It was portrayed more frequently than physical and verbal aggression. Females were more likely to be shown as indirect aggressors than were males, while males were more likely to be portrayed as physical aggressors. Attractive aggressors were more likely to use indirect than other types of aggression. Indirect aggression was often found to be justified, realistic, and rewarded. We conclude that programs that are not considered violent may still contain a large amount of other types of aggression. Aggr. Behav. 30:254–271, 2004. © 2004 Wiley‐Liss, Inc.     

The development of social aggression and physical aggression: A narrative analysis of interpersonal conflicts

Using conflict narratives reported by children and adolescents, this study investigated the development and social functions of social aggression in comparison to physical aggression. A total of 510 participants in two cohorts of a longitudinal study were involved (116 girls and 104 boys from Grade 4 and155 girls and 135 boys from Grade 7). Patterns of social aggression and physical aggression were identified based on interview reports in the first year of the study. Results showed that a triadic structure of social relationship was often reported in conflicts where social aggression was employed, whereas a dyadic structure was reported in conflicts involving physical aggression. Girls tended to use social aggression against girls, whereas boys tended to use physical aggression against boys. Children and adolescents who were central in peer social networks were more likely to employ social aggression than those who were peripheral in the networks. Social aggression was not reliably linked to concurrent or future problematic adjustment. Physical aggression, however, was not related to network centrality but was linked to concurrent and future maladjustment (e.g., low academic competence and school dropout). Aggr. Behav. 28:341–355, 2002. © 2002 Wiley‐Liss, Inc.     

攻击动机对特质愤怒与反应性攻击关系的中介作用：一项纵向研究

特质愤怒是影响反应性攻击的重要人格因素, 反应性攻击的提出是基于攻击动机, 但是特质愤怒影响反应性攻击的动机机制尚不清楚。本研究假设特质愤怒可以通过增强反应性攻击的特异性动机(即敌意性动机)以及反应性攻击与主动性攻击的共同性动机(即道德准许动机)来纵向预测反应性攻击。为了检验该假设, 对5个省市共1007名大学生的特质愤怒、敌意归因偏向(代表敌意性动机)和道德推脱(代表道德准许动机)、反应性攻击与主动性攻击进行了3次追踪调查。结果显示：(1)在控制性别后, 第一个时间点的特质愤怒可以通过第二个时间点的敌意归因偏向和道德推脱预测第三个时间点的反应性攻击; (2)敌意归因偏向只能纵向预测反应性攻击, 而不能跨时间预测主动性攻击; (3)道德推脱可以纵向预测反应性攻击和主动性攻击。这一结果支持了特质愤怒影响反应性攻击的动机模型, 发展了人格与攻击关系的理论与研究, 对于揭示反应性攻击形成的动机机制具有积极作用。     

On the dual nature of maternal aggression in rats

Presentation of a natural predator, a cat, was used to differentiate elements of maternal attack by female rats on a male intruder. Following exposure (without direct physical contact) of post-partum females to a cat or to a toy stuffed cat (control group), the females were replaced in their home cages and presented with a male intruder rat. Cat exposure reliably decreased lateral attack to the intruder, as well as locomotion, but had no effect on either jump attack or an upright defensive posture (boxing). Since predator exposure produces a somewhat durable increase in defense, along with inhibition of nondefensive behavior, these results suggest that maternal aggression represents a mixture of offensive, usually related to competition, and defensive (protective) behaviors. The results indicate that maternal aggression, as a parental care behavior, appears to be at least partially resistant to fear. © 1996 Wiley-Liss, Inc.     

The control of alcohol-related aggression: Redirecting the inebriate's attention to socially appropriate conduct

Forty male undergraduates ingested either a high dose of alcohol or a placebo, and were either provided with a nonaggressive norm or not, prior to being provoked by an opponent during a competitive reaction time task. Aggression was assessed by the intensity of shocks administered by the subject to the bogus opponent. Results suggest that the provision of an explicit nonaggressive norm enabled highly intoxicated subjects to moderate their aggressive responding even in a highly competitive situation. These findings are discussed in terms of current cognitive disruption models of alcohol-related aggression which assume intoxicated persons are unable to process information concerning appropriate standards of conduct.     

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 learn 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 by housing same-sex partners either together or individually (eight 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.     

Behavioral tactics control the energy costs of aggression: The example of Macropodus opercularis

Previous experiments on Betta splendens have shown that energy expenditures related to aggression are under social control. The present paper examines the biochemical energetics of social cohabitation in groups of Macropodus opercularis. The species is closely related to Betta splendens, however, dominants use somewhat different behavioral tactics against intruders. In contrast to Bettas, submissive Macropoduses are not harassed by dominants, but are confined to the bottom of the tank. This results in a reduced rate of oxygen consumption in defeated animals (Anabantid fish mainly use atmospheric oxygen). The only metabolic change, compared to isolated controls, is a reduction in hepatic glycogen content. Submissive animals have shifted carbohydrate metabolism towards anaerobic glycolysis. Substantial reductions in muscle proteins, lipids, and glycogen occurred in submissive Betta splendens. Thus, the sharp difference in behavioral strategy results in a sharp difference in the energetic consequences of aggression. A theory is presented regarding the possible role of energetic constraints in the control of behavior. © 1996 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.     

Maternal aggression as a model for acute social stress in the rat: A behavioral-electrocardiographic study

Maternal aggression of lactating rats was used to induce acute social stress in a resident-intruder paradigm. Behavioral and electrocardiographic responses of male intruders were simultaneously recorded. Cardiac electrical activity was measured by means of a telemetry system which ensured preservation of intruder's behavioral repertoire. Behavioral response to maternal attack was evaluated in terms of percent time spent in passive/submissive (p/s) and active/non-submissive (a/ns) patterns. This allowed us to classify the intruders as submissive, non-submissive, and intermediates. During the test, a significant decrease of average R-R interval (R-R) compared to baseline conditions and the occurrence of arrythmias of different nature were found. Ventricular arrhythmias, including premature ventricular beats and ventricular tachycardias, were present in all the intruders while R-R fluctuations and II degree atrioventricular (A-V) blocks only appeared in submissive and intermediate rats. Most ventricular arrhythmias occurred within the upper range of heart rate and were preceded by periods of low R-R variability. These electrocardiographic events were temporally associated with a/ns behavioral patterns and were related to an increased prevalence of sympathetic activity. On the other hand, R-R fluctuations and II degree A-V blocks preceded by high R-R variability were synchronized with p/s behavior and were ascribed to a predominant inhibitory effect of vagal activation which becomes more pronounced as the level of sympathetic activity increases. © 1995 Wiley-Liss, Inc.     

Frustration and successful vs. Unsuccessful aggression: A test of Berkowitz' completion hypothesis

Author experiment using a modified version of the Buss' aggression paradigm tested Berkowitz' completion hypothesis, which states unsuccessful aggressive attempts at the frustrator serve as further frustration and intensify aggression. Testing was done by varying the number of successful aggressive attempts for different experimental groups. The experiment indicated first a positive relationship between subjective levels of frustration and aggression, which supports a general frustration-aggression hypothesis, and second that unsuccessful aggressive attempts lead to increased aggression in terms of shock intensity. This was interpreted as supportive of Berkowitz' completion hypothesis, although alternative interpretations in terms of cognitive and behavioral strategies cannot be excluded.