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PubMed2004

Photoperiod affects neuronal nitric oxide synthase and aggressive behaviour in male Siberian hamsters (Phodopus sungorus).

Many nontropical animals display physiological and behavioural changes in response to seasonal environmental cues including photoperiod (day length). Male Siberian hamsters (Phodopus sungorus) housed in short photoperiod undergo testicular regression accompanied by reduced circulating testosterone and decreased reproductive behaviour. By contrast to the majority of small mammals studied, aggressive behaviour is elevated in short-day Siberian hamsters when blood testosterone concentrations are not detectable. Because gonadal steroid hormones influence neuronal nitric oxide synthase (nNOS), and this enzyme has been implicated in aggressive behaviour, we hypothesized that nNOS expression would be decreased in short-day male Siberian hamsters and negatively correlated with the display of territorial aggression. Adult male Siberian hamsters were individually housed in either long (LD 16:8 h) or short (LD 8:16 h) photoperiods for 10 weeks. Hamsters were assigned to one of two categories by assessing testicular volume and plasma testosterone values: (i) photoperiodic responsive (i.e. regressed testes and low testosterone concentrations) or (ii) photoperiodic nonresponsive (i.e. testes size and circulating testosterone concentrations equivalent to hamsters maintained in long days). At week 10, aggression was assessed using a resident-intruder test. Latency to initial attack, frequency of attacks and duration of total attacks were recorded during a 10-min aggression trial. Brains were collected immediately after behavioural testing and stained for nNOS expression using immunohistochemistry. All short day-housed hamsters were significantly more aggressive than long-day animals, regardless of gonadal size or testosterone concentrations. Short-day animals, both reproductively responsive and nonresponsive morphs, also had significantly less nNOS-immunoreactive cells in the anterior and basolateral amygdaloid areas and paraventricular nuclei compared to long-day hamsters. Together, these results suggest that seasonal aggression in male Siberian hamsters is regulated by photoperiod, through mechanisms that are likely independent from gonadal steroid hormones.

Aggression↗

PubMed2006

Testosterone and aggression: Berthold, birds and beyond.

Berthold's classic study of domesticated roosters in 1849 demonstrated that testicular secretions are necessary for the normal expression of aggressive behaviour. Although this conclusion is undoubtedly correct, field studies of wild songbirds have yielded important modifications and limitations of Berthold's original hypothesis. For example, studies of the North American song sparrow (Melospiza melodia) during the breeding season reveal that not only does testosterone increase aggression, but aggressive interactions also increase plasma testosterone levels. Furthermore, in winter, nonbreeding song sparrows have low plasma testosterone levels but are very aggressive, and castration of nonbreeding song sparrows does not decrease aggression. Interestingly, an aromatase inhibitor (fadrozole) does decrease male aggression in the nonbreeding season, and the effects of fadrozole can be rescued with oestradiol. In winter, dehydroepiandrosterone (DHEA) from the periphery can be metabolised within the brain to supply oestradiol to specific neural circuits. Additionally, oestradiol might be synthesised de novo from cholesterol entirely within the brain. These mechanisms may have evolved to avoid the 'costs' of circulating testosterone in the nonbreeding season. Recent studies in tropical birds, hamsters, and humans suggest that these neuroendocrine mechanisms are important for the control of aggression in many vertebrate species.

Aggression↗

PubMed2006

Effects of early life stress on adult male aggression and hypothalamic vasopressin and serotonin.

Early life stress in humans enhances the risk for psychopathologies, including excessive aggression and violence. In rodents, maternal separation is a potent early life stressor inducing long-lasting changes in emotional and neuroendocrine responsiveness to stress, associated with depression- and anxiety-like symptoms. However, effects of maternal separation on adult male aggression and underlying neurobiological mechanisms remain unknown. Therefore, we investigated the effects of maternal separation on adult intermale aggression in Wistar rats and on hypothalamic arginine vasopressin (AVP) mRNA expression, and AVP and serotonin (5-HT) immunoreactivity, as both AVP and 5-HT have been implicated in stress-coping and aggression. We showed that maternal separation induced depression-like behaviour (increased immobility) and higher adrenocorticotropin hormone responses to an acute stressor (forced swimming). Intermale aggression (lateral threat, offensive upright and keep down) was significantly higher in maternally separated rats compared with control rats. AVP mRNA expression and AVP immunoreactivity were higher in the hypothalamic paraventricular and supraoptic nuclei upon resident-intruder test exposure, whereas 5-HT immunoreactivity was decreased in the anterior hypothalamus of maternally separated rats. Moreover, 5-HT immunoreactivity in the anterior hypothalamus and supraoptic nucleus correlated negatively with aggression. These findings show that exposure to early life stress increases adult male aggression in an animal model of maternal separation. Furthermore, the maternal separation-induced changes in hypothalamic AVP and 5-HT systems may underlie these behavioural alterations.

Adrenocorticotropic Hormone↗

PubMed1978

Physical/verbal aggression: sex differences in style.

Two studies exploring the use of physical/verbal aggression are reported, the first using women and the second using men as subjects. Both studies allowed subjects to choose between and control the intensity of two response modes: verbal aggression (insults) and physical aggression (electric shock). Aggressive style was investigated over two levels of arousal, sex of experimenter, and sex of provocateur-victim. Results indicated that women aggressed discriminatively in the verbal mode as a function of their arousal, while men were capable of aggressing discriminatively in both the verbal and physical modes. Men who had been disagreed with and punished by a female victim-provocateur in the presence of a male experimenter or by a male victim in the presence of a male experimenter demonstrated high levels of physical aggression compared to the other groups.

Aggression↗

PubMed1978

Direct and vicarious censure in the control of interracial aggression.

An experimental explored the relative effectiveness of two strategies for controlling interracial aggression: observing other individuals censured for aggression and potential direct censure of the aggressor himself. Subjects were provided with an opportunity to agress under conditions designed to maximize or reduce each type of censure. A principal components analysis of the data revealed two orthogonal variates: direct aggression and indirect aggression. It was found that both observed censure and potential direct censure were effective in modifying directly aggressive responses. However, these forms of censure interacted in their effect on indirect aggression, such that observed censure was effective in reducing indirect aggression only under conditions of potential direct censure.

Aggression↗

PubMed1988

Social attributional biases of peer-rejected and aggressive children.

Peer-rejected high-aggressive, rejected low-aggressive, and non-rejected third- and fifth-grade boys were shown sets of drawn pictures differently balanced on Kelley's social dimensions of distinctiveness (i.e., depicting a hypothetical peer interacting with other children) and consistency (i.e., depicting the peer interacting with the subject) information. Following each set, a provoking incident involving the subject and peer was described in which the subject experienced a negative outcome and the peer exhibited ambiguous intent. When given no social information, rejected high-aggressive and rejected low-aggressive boys made more hostile attributions and suggested more hostile responses. When provided social information, however, all groups made similar attributions and weighted consistency information more heavily in their evaluations. All groups maintained a consistent response style across information conditions, with rejected high-aggressive boys suggesting the most aggressive responses. Implications for the treatment of childhood aggression are discussed.

Aggression↗

PubMed2006

Attenuating the link between threatened egotism and aggression.

Research has found that narcissists behave aggressively when they receive a blow to their ego. The current studies examined whether narcissistic aggression could be reduced by inducing a unit relation between the target of aggression and the aggressor. Experimental participants were told that they shared either a birthday (Study 1) or a fingerprint type (Study 2) with a partner. Control participants were not given any information indicating similarity to their partner. Before aggression was measured, the partners criticized essays written by the participants. Aggression was measured by allowing participants to give their partner loud blasts of noise through a pair of headphones. In the control groups, narcissists were especially aggressive toward their partner. However, narcissistic aggression was completely attenuated, even under ego threat, when participants believed they shared a key similarity with their partner.

Adolescent↗

PubMed1995

Contributing factors in the manifestation of aggression in preschoolers with hyperactivity.

This study examined family characteristics of preschoolers with hyperactivity. We assessed child-rearing practices, maternal depression, marital conflict, and social support. Sixty-three preschool boys were placed in a hyperactivity-aggressive, hyperactive, aggressive or comparison group based on behavioral ratings. Parents were given questionnaires, mothers were interviewed, and children were administered the Woodcock-Johnson Psycho-Educational Battery and were observed playing. Compared to preschoolers with hyperactivity, preschoolers with hyperactivity plus aggression had families with (a) more restrictive fathers, (b) siblings who retaliated aggressively, and (c) mothers who reported more physical aggression directed to their partners and more verbal aggression received. Follow-forward aggression ratings were predicted by initial child manageability and maternal depression, perceived support, and low income.

Aggression↗

PubMed1995

Aggressivity in adolescent alcohol abusers: relationship with conduct disorder.

Several longitudinal and retrospective studies have documented an association between premorbid aggression and an increased risk for an alcohol-use disorder in adulthood. However, few data are available examining the relationship between trait aggressivity, alcohol use behavior, and the presence of an early-onset alcohol use disorder diagnosis among the adolescent population. To address this deficiency, this study had three goals. First, the relationship between aggressivity and adolescent alcohol consuming behavior was examined. Second, the presence and magnitude of trait aggressivity were determined among adolescents who met psychiatric diagnostic criteria for alcohol abuse/dependence (ALC), while controlling for the presence of a conduct disorder (CD). Third, because CD is overrepresented among adolescent alcohol abuse cases and is a priori defined by the presence of certain aggressive behaviors, the simultaneous contributions of CD and ALC on trait aggressivity were also investigated through structural equation modeling. The results confirm the salience of heightened aggressivity as an essential feature of this early-onset alcohol-abusing population and indicate the importance of addressing this behavioral domain in prevention and treatment efforts.

Adolescent↗

PubMed1986

Social determinants of aggression in a sample of Chinese primary school children.

The aim of the present study was to relate children's aggression levels to social determinants of interest (i.e., child-rearing measures, day-care attendance, peer group influence, and TV-watching) in a sample of Chinese children in the People's Republic of China. A sample of 290 primary school students (155 boys and 135 girls, mean age 10.3) in grade four in Beijing were investigated using the Multi-Faceted Aggression Inventory. The children's parents were asked about child-rearing measures and day-care experience for the child. Teachers rated the children's aggression, school achievement level, and membership in the Young Pioneers. Despite acknowledged limitations, the findings in this study gave evidence that according to a person-environment interaction perspective, the Chinese children's individual differences in aggression were influenced by the restricted environment. As aggressive behaviour is undesired and suppressed in the Chinese culture in and outside the home, the Chinese children seemed to show lower levels and less variation of aggression behaviour than children in permissive environments (e.g., Sweden). However, when analysing sex differences in aggression environmental influences alone might not explain the differences.

Adolescent↗

PubMed1992

Aggressive behaviour in elderly psychiatric inpatients.

We describe the types of aggressive behaviour and determine their prevalence in a sample of hospitalized elderly psychiatric patients. Data were obtained by nurse ratings of aggressive behaviour using the recently developed Rating Scale for Aggressive Behaviour in the Elderly; 90 patients were rated over a 3-d period. Nearly half the sample were at least mildly aggressive; the frequencies of some specific types of aggressive behaviour were high. In contrast, the frequency of injuries and the use of restraints and medication for aggressive behaviour were low. Some correlates of the aggressive behaviour were also analysed.

Aged↗

PubMed2004

Genetic and environmental (inter)actions in male mouse lines selected for aggressive and nonaggressive behavior.

The purpose of this study was to investigate the effects of genetic and environmental factors, as well as their interaction, in the etiology of aggressive behavior in two mouse lines bidirectionally selected for offensive aggression. To this end, we raised the Finnish TA (aggressive) and TNA (nonagressive) selection lines either in isolation or in cohabitation with a female after weaning. At the age of 3 months we determined their aggressive behavior in three paradigms (intruder resident, neutral cage, resident intruder) against a male standard opponent. We also determined the animals' aggressive behavior against a female mouse. The results show genetic and environmental effects, as well as gene-environment interaction. We see prominent genotype effects under all conditions but each test is sensitive to a specific combination of environmental effects. A particularly noteworthy result is that variation in the unusual behavior of aggression towards a female is largely explained by the interaction of genotype with isolation. We also examined whether test experience influenced the outcome of an encounter between an experimental animal and an opponent, and found that this factor should not be underestimated, its effect size and direction depending on the type of paradigm and way of housing. These data suggest that the identification of genes underlying aggressive behavior in mice is by no means straightforward and that the result of this search will depend on the environmental design of the study (type of paradigm, housing conditions). These data also suggest that the use of 'test battery' mice might produce different results than the use of test-naïve animals.

Aggression↗

PubMed1999

On some clinical implications of the ventral striatum and the extended amygdala. Investigations of aggression.

In this paper, we have first reviewed the animal studies which suggest an association between the amygdala and aggressive behavior. This is followed by a review of the literature of aggression in epilepsy, emphasizing the less controversial peri-ictal aggressions, with the more controversial assertion that temporal lobe epilepsy in particular is associated with an increase in interictal aggression. We then go on to describe the results of some investigations using the MRI to examine amygdala pathology in a group of patients presenting with affective aggression in comparison with a control group. The main findings are that the patients with aggression tend to have lower IQs and more psychopathology than the control group. There is no difference in amygdala T2 and volumetric assessments between the groups, but a subgroup of patients are defined with aggression, left-sided amygdala atrophy, and a history of encephalitis.

Aggression↗

PubMed1993

The reduction of aggression in people with learning difficulties: a review of psychological methods.

The literature on the reduction of aggression in people with learning difficulties is reviewed. The methods of reducing aggression identified were predominantly evaluated in staffed settings and with target behaviours more frequent than once a day. This contrasts with the findings of a recent survey that found the majority of aggressive individuals to live in the community and show aggression less than once a day. It is argued that the reasons for this disparity are as follows. That it is easier to do a controlled study in staffed settings with high-frequency aggression. That it is more difficult to do an analysis of the target behaviour if it is low frequency or if the subject is in the community; and that the methods that have been traditionally used to reduce aggression may not be effective with all subjects in all settings. It is suggested that it may be necessary to develop and evaluate a new technology for reducing aggression.

Adolescent↗

PubMed1993

Proximate causes of aggressive fighting in middle school children.

In study 1, 8- and 11-year-old girls and boys (N = 110) were interviewed individually and asked about why children in general, and themselves in particular, fight with fellow pupils in the playground. A substantial proportion of children (51 per cent) reported having had at least one aggressive fight during the previous year. The most common reasons for children resorting to fighting were retaliations to teasing, retaliations to unprovoked assaults, disagreements over aspects of the game that was being played, because another child was disliked, and to settle dominance disputes. In study 2, a direct observational methodology was employed to examine how often children of these ages engage in aggressive fighting, how long fights last, and their proximate causes. Among the younger pupils, a large proportion of fights (43.3 per cent) had no obvious immediate cause to an adult observer, but others were caused when a playful assault received an aggressive retaliation (15.4 per cent), and by disputes over space in the playground (13.5 per cent). Among the 11-year-old pupils, a smaller percentage of fights (14.8 per cent) had no obvious immediate cause. The two most common causes of fighting at this age were aggressive retaliations to teasing (25.9 per cent) and aggressive retaliations to accidental injury/hurt (18.5 per cent). In study 3, in situ interviews were combined with direct playground observations in order to reveal participants' views (or onlookers' views if participants were not available to be interviewed) about the causes of fights. Again, the most common causes of fighting were disputes over some aspect of the game being played (33.3 per cent), aggressive retaliations to teasing (25.0 per cent), disagreements over possession of toys/equipment (14.6 per cent), and aggressive retaliations to accidental injury/hurt (14.6 per cent). Age and sex differences are reported in some measures across all three studies. The results are discussed in terms of their implications for interventions aimed at improving children's experiences of life on the school playground.

Age Factors↗

PubMed1984

Audience effects when viewing aggressive movies.

In order to examine audience effects when viewing filmed violence, male subjects watched an aggressive or a neutral movie either alone, accompanied by a passive confederate (i.e. mere presence of a co-spectator), or an active one (i.e. reacting to the movie). The subsequent behavioural measures of subjects' aggression were collected via a modified aggression apparatus. The usual instigation effect of filmed violence was found. Furthermore, the type of audience also influenced aggression: subjects accompanied by an active confederate during the violent movie displayed their aggressive behaviour most. These findings stress the importance of the social context when filmed violence is viewed. The results are discussed in terms of social facilitation and disinhibition effects. It is suggested that an active audience may promote a reduction of restraints against aggressing by showing the subject that aggression is permissible.

Adult↗

PubMed1988

Aggressive behaviour of children aged 6-11: gender differences and their magnitude.

A total of 72 boys and 72 girls, of six age groups from 6 to 11 years, was observed in the school classroom over eight 5-minute periods, under conditions of low structure, non-directive teaching; aggressive and other categories of behaviour were recorded. There were no overall gender differences in aggression, but boys showed significantly more physical aggression than girls (overall effect size d = 0.36), whereas girls showed significantly more verbal aggression than boys (overall effect size d = 0.66). The physical aggression difference was variable both in direction and magnitude across the age categories and included a large reversal at 9 years. Boy's higher levels of physical aggression were not associated with higher levels of activity or more time spent in social interactions. The gender difference in verbal aggression was consistent in direction and magnitude across age categories, but in the opposite direction to the majority of previous findings. There were no gender differences in other categories of verbal behaviour.

Aggression↗

PubMed1994

Sex differences in aggression: social representation and social roles.

Previous research suggests that men hold an instrumental social representation of aggression in which aggression is viewed as a functional interpersonal act aimed at imposing control over other people while women view aggression in expressive terms as a breakdown of self-control over anger. The present study examines the relative contribution of gendered personality differences (communality-agency) and occupational role in accounting for these differences. Men and women in the armed forces and nursing profession completed the Personal Attributes Questionnaire (PAQ: Spence & Helmreich, 1976) together with a psychometric measure of their tendency to view aggression as expressive rather than instrumental (Expagg: Campbell, Muncer & Coyle, 1992). The results indicate that occupational role and sex are both important correlates of individuals' representations of aggression. Though agency showed a significant negative zero-order correlation with expressive aggression, the impact of gendered personality traits was diminished when occupation and sex were taken into account. The data strongly support social role theory's emphasis upon contemporaneous occupational factors in explaining sex differences in the understanding of aggression but are less supportive of the role of masculine and feminine personality traits.

Aggression↗