Effects of age at differential housing and the duration of individual housing/grouping on lntermale fighting behavior and adrenocortical activity in TO strain mice

A study of the effects of the duration of individual and group housing on intermale fighting and adrenocortical activity was conducted in TO strain mice. It was found that fighting and threat increased with progressive isolation up to an asymptote at 56–58 days. ‘Basal’ adrenocortical function differed little under the 2 housing conditions, but after ‘stress,’ mice isolated for short periods, which had not fought when tested for aggression, had lower titers than group-housed counterparts. However, mice that had been isolated for longer periods, and had fought in aggression tests, had higher corticosterone titers than comparable group-housed animals. The effects of a short duration (28–30 days) of differential housing, commencing at different ages, were also studied. The shorter duration adrenocortical changes were largely confirmed. In general, the earlier the age at which the differential housing was imposed, the greater the behavioral differences between animals under each housing condition. It is suggested that this is largely a consequence of a loss of behavioral plasticity in older mice. The data provides little support for the concept of the “isolation stress syndrome,” or for the view that the characteristic fighting exhibited by individually housed mice is a consequence of “social deprivation”.     

Genetic analysis of “Spontaneous” intermale aggression in mice

“Spontaneous” intermale aggression was investigated in seven inbred strains of mice. A positive interstrain correlation and cross-correlation was found for two indices of fighting intensity, ie, accumulated attacking time and number of attacks. The strain aggressiveness level (percent of mice fighting in each strain) does not correlate with the intensity of aggressive behavior. It has been shown by using a genetical analysis performed on C57BL/6 and BALB/c strains, their reciprocal F₁ hybrids, and back-crosses that these indices of intermale aggression are under different genetic control. Aggressive behavior intensity depends on the additive effects of genes. The control of strain aggressiveness level revealed that a high level of aggressiveness was dominant. No reciprocal effects were found. The level of aggressiveness and the intensity of fighting seem to represent different aspects of aggression and may be controlled by different genetic mechanisms.     

Association between intermale aggression and genetically-defined tryptophan hydroxylase activity in the mouse brain

The relationship between the genetically defined intensity of intermale aggression and the activity of brain tryptophan hydroxylase (TPH) has been studied in inbred mice. No association between the enzyme activity and the percentage of aggressive mice (reflecting the predisposition to aggressive reaction) was revealed. However, a significant positive interstrain correlation between brain TPH activity and accumulated attacking time (reflecting fight intensity) was identified. No correlation was found between TPH activity and the accumulated attacking time in segregating F2 (BALB × C57BL) mice. In conclusion, TPH is an important, but not the only factor controlling the intensity of intermale aggression in mice. © 1996 Wiley-Liss, Inc.     

Postaggression footshock inhibits aggressive behavior in dominant but not in isolated mice

Aggressive behavior of dominant and isolated mice was assessed in intermale encounters with nonaggressive intruder mice. After an attack period of 90 s, the aggressor was exposed to a footshock punishment and retested the next day. The shock treatment, independent of the intensity and duration, failed to inhibit spontaneous aggression in isolated DBA/2 mice, while it significantly suppressed spontaneous aggression in dominant C57BL/6 mice. The different effects of post-trial shock punishment were not due to a different shock sensitivity and did not depend on the type of opponent used. Strain differences have been ruled out by the use of dominant and isolated ICR mice. Again, shock punishment was ineffective in isolates, while it reduced aggression in dominant animals. The findings were discussed with reference to the impaired learning performance reported for isolated animals, and suggest a difference between the aggression of isolated and that of dominant mice.     

Effects of prenatal cocaine and genotype on intermale agonistic behavior in Mus musculus

We exposed the pups of three F₁ genotypes of mice to a daily regime of cocaine by injecting their mothers (all C57BL/10J strain) on days 7–18 of gestation with 20 mg/kg subcutaneously. Pups of the cocaine and control groups did not differ on measures of maternal and pup health or size. Male pups were weaned and isolated at 21 days of age and their behaviors measured in an intermale aggression situation at about 80 days of age. Treated and untreated males of each F₁ genotype were paired in dyads with either a C3H/HeJ (hawk-like) or AKR/J (retaliator-like) standard tester male. Standard tester males were not exposed to cocaine. Cocaine treatment alone reduced the overall level of aggression in dyads, and in interaction with genotype or the standard tester it altered the behavior of dyads in all phases of social interaction: the initiation, content, and outcome. Standard testers used as behavioral probes, differentiated cocaine and control males with respect to their stimulus and behavioral qualities. Aggr. Behav. 23:183–196, 1997.© 1997 Wiley-Liss, Inc.     

Effects of D- and L-amphetamine on the predatory behavior of Southern grasshopper mice,onychomys torridus

Adult male and female southern grasshopper mice (Onychomys torridus) were tested for predatory aggression toward cricket prey 1 hr after single injections of d-amphetamine (1 or 10 mg/kg) or 1-amphetamine (1 or 10 mg/kg). At the lower dose, d-amphetamine decreased feeding behaviors, while I-amphetamine altered attack-related behaviors. At the higher dose, both stereoisomers appeared to be equipotent in significantly decreasing 5 measures of predatory aggression. These results suggest that brain dopamine and norepinephrine play important roles in the regulation of predatory aggression of Onychomys torridus.     

An experimental approach to the study of learned aggression

The sensory contact technique increases aggressiveness in male mice and allows aggressive types of behavior to be formed as a result of the repeated experience of victories in daily agonistic confrontations. Some behavioral domains confirm the development of learned aggression in males similar to those in humans. The features are repeated experience of aggression reinforced by victories; elements of learned behavior after periods of confrontation; intent, measured by increase of the aggressive motivation prior to agonistic confrontation; and decreased emotionality, estimated by parameters of open‐field behavior. Relevant situation provokes increases in aggression (boundary aggression). This review summarizes data on the influence of positive fighting experience in daily intermale confrontations on the behavior, neurochemistry, and physiology of aggressive mice (winners). This sort of experience changes many characteristics in individual and social behaviors, these having been estimated in different tests and in varied situations. Some physiological parameters are also changed in the winners. Neurochemical data confirm the activation of brain dopaminergic systems and functional inhibition of serotonergic system in winners under the influence of the repeated experience of aggression. The expression of the neurochemical and behavioral changes observed in winners has been found to depend on the mouse strain and on the duration of their agonistic confrontations. Aggr. Behav. 26:241–256, 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.     

Partial kindling and emotional bias in the cat: lasting aftereffects of partial kindling of the ventral hippocampus. I. Behavioral changes

Repeated electrical evocation of afterdischarges in the perforant-path ventral hippocampal system of the cat produces lasting changes in species characteristic behavioral responses to environmental threat. After 7 to 12 afterdischarges, cats showed greatly enhanced defensive (withdrawal) responses to rats, and mildly enhanced defensive responses toward mice. Measures of predatory attack which negatively correlate with withdrawal from rats were also changed in a direction consistent with the increase in withdrawal tendency. There was little effect of afterdischarges on the same parameters of attack on mice. Thus the stimulation seemed to attenuate predatory aggression by increasing defensive sensitivity to the threat posed by prey self-defense, and not by reducing predatory motivation per se. The change in defensiveness was not restricted to the predatory test situation, however. Tests of defensive response to conspecific threat vocalizations revealed an increased defensive responding to this stimulus as well. On the other hand, there was no change in social responsiveness shown toward a highly familiar human. Given the sudden onset (1 hr to 24 hr after the last afterdischarge), the long-lasting nature of the change (30-60 days) which persisted in the absence of seizures, and the generality of expression of the behavioral change, it was concluded that the afterdischarges produced an interictally maintained alteration in a defensive personality characteristic of the cats.     

An empirically derived scoring system for intermale aggression in mice

Scoring systems used to assess intermale aggression have been characterized by arbitrary scales and wide variability in the behaviors selected for measurement. The use of such different systems severely limits the ability of investigators to make meaningful comparisons among studies and indicates that there is a need for a common, statistically derived evaluative system for intermale aggression. We measured the frequency and duration of five major components of agonistic behavior exhibited by intact males toward olfactory bulbectomized stimulus males and then analyzed the data using a number of univariate and multivariate procedures. The results were used to generate two statistically based scoring systems, one a short-form index and the other a composite index for more detailed studies of aggression. It is hoped that these statistically derived systems will be adopted by other investigators to increase methodological congruence in the field.     

Strain‐specific aggressive behavior of male mice submitted to different husbandry procedures

Severe aggression within groups of male laboratory mice can cause serious welfare problems. Previous experiments have shown that the transfer of specific olfactory cues during cage cleaning and the provision of nesting material decrease aggression and stress in group‐housed male mice. In this study, the combined effect of these husbandry procedures was tested for their long‐term effect on aggression in two strains of male mice (BALB/c and CD‐1). We used postcleaning aggressive behavior, wound counts, and testosterone levels as indicators of aggressiveness. Physiological responses to social challenge were investigated through urinary corticosterone and adrenal tyrosine‐hydroxylase measurements. Furthermore, the aggression‐modulating effects of two enrichment items (ShepherdShack/DesRes and PVC tube) were explored. Marked differences were found between the two strains. CD‐1 mice were more aggressive, had higher testosterone levels but lower corticosterone levels, and had fewer wounds than BALB/c mice. However, in neither of the two strains was long‐term enrichment with nesting material and its transfer after cage cleaning effective in lasting reduction of intermale aggression. This may be explained by the fact that aggression levels were generally low. It seems that housing mice in small, socially stable groups or keeping social disturbances to a minimum considerably modulates aggression in group‐housed male mice. Mice of both strains housed in cages enriched with nesting material had lower urinary corticosterone levels than standard‐housed mice. We therefore conclude that the long‐term provision of nesting material, including the transfer of nesting material during cage cleaning, may enhance the welfare of laboratory mice. Aggr. Behav. 29:69–80, 2003. © 2002 Wiley‐Liss, Inc.     

Differential effect of handling on adult aggression in male mice bidirectionally selected for attack latency

Individual variation in intermale aggression is to a significant degree based upon genetic variation, but environmental factors can also exert their influence on the level of aggression. Moreover, genotype–environment interactions are a well‐known phenomenon. In the present experiment, I tested whether cage size or handling during development had an influence on adult attack latency scores. To be able to study a genotype–environment interaction, mice from two bidirectionally on attack latency selected lines were used. The size of the cage in which the mice grew up had no long‐term effect on aggression, neither in the high‐ nor in the low‐aggressive line. Handling, however, significantly increased the adult aggression of males from the low‐aggressive line. Despite the differential effect of handling on genetically high‐ and low‐aggressive mice, handling was not able to undo the marked differences in attack latencies between mice from both lines. Aggr. Behav. 25:365–368, 1999. © 1999 Wiley‐Liss, Inc.     

Effects of alpha and beta adrenergic antagonists on aggressive behavior in male mice

The effects of a variety of alpha and beta adrenergic antagonists were examined on the social encounters of isolated male mice with anosmic male partners. A range of alpha antagonists, including phentolamine, prazosin, and yohimbine, all suppressed social aggression. A range of beta antagonists, including propranolol, atenolol, metaprolol, and ICI 118, 551, also reduced this type of attack. Ethological assessment of the lowest effective dose of these adrenergic antagonists revealed a marked inhibitor action on offensive, social, and nonsocial behavior, while defensive responses and immobility were enhanced. It is concluded that the noradrenergic system has a significant non-specific role in mediating intermale aggression via both alpha and beta adrenergic receptor subtypes. © 1993 Wiley-Liss, Inc.     

The ventromedial hypothalamus and aggressive behaviour in rats

Male rats were given bilateral lesions in either the anterior or posterior ventromedial hypothalamus (VMH). The intermale aggressive behaviour of these animals within their own territory was observed before and after the surgical procedure and compared with the behaviour of sham-operated animals. The effects of anterior VMH lesions include an increased tendency to respond with frontal threatening upon approach of a conspecific male. This behaviour closely resembles the aggressive responses described in “shock-induced aggression” tests. Posterior VMH lesions facilitate territorial aggressive behaviour characterized by approaching the opponent followed by lateral threatening and fighting. It is suggested that 2 distinct neural substrates exist, which serve to inhibit defensive (anterior-VMH) and offensive (posterior-VMH) intermale aggression, respectively.     

Mousekilling,intermale fighting,and conditioned emotional response in rats

Several possible relationships between two forms of aggression in rats were studied. First, mouse killing and spontaneous intermale fighting were found to be correlated. Rats which attacked other rats were those most likely to kill mice. To determine whether aggressive and nonaggressive rats were also differentially responsive to other situations involving emotional arousal, but not aggression, mouse-killers and nonkillers were compared in a conditioned emotional response (CER) situation. Mouse-killers showed greater suppression to the conditioned stimulus (CS) and to the situational cues of the apparatus. Therefore, a common arousal mechanism may underlie a number of diverse agonistic responses. Nevertheless, extensive mouse-killing experience did not increase the tendency of rats to fight with either adult males or juvenile males.     

Behavioral changes over several successful agonistic encounters between male mice: Effects of type of “standard opponent”

This study assessed whether two types of non-aggressive “standard opponents” (“intact” and “anosmic” group-housed males) produced similar behavioral changes in isolated OF1 male mice given several experiences of victory. Experimental groups confronted either intact or anosmic opponents every two days until they had completed four encounters. The behavioral changes were recorded using a detailed ethologically inspired analysis. These changes were clearly different depending on the opponent type. When intact opponents were used, experimental subjects increased the time spent in digging, non-social exploration, explore from a distance, and attack over encounters, but showed decreased time spent in threat and a decreased latency to the first attack. In encounters with anosmic opponents, only declines in the latencies to threat and attack were noted. Moreover, the experimental groups differed in their behaviors over encounters. Those confronting intact opponents spent less time in social investigation, more time in explore from a distance and threat, and showed a shorter latencies to threat and attack than counterparts confronting anosmics. These results suggest that, although both types of “standard opponents” are similar in their non-aggressiveness, they elicit rather different behavioral responses in their adversaries. These findings provide additional support for the view that the type of opponent used in studies on intermale aggression is of paramount importance. Indeed, the use of different types of “standardized non-aggressive opponents” appears to be an important source of variability between studies. © 1994 Wiley-Liss, Inc.     

Hyperreactivity, muricide, and intraspecific aggression in the rat produced by infusion of local anesthetic into the lateral septum or surrounding areas

Intracranial infusions of a local anesthetic (lidocaine, 2%) were made bilaterally (4 microliter over 20 min) through permanently implanted cannulas ending in the lateral septum or adjacent areas. Increases in irritability and reactivity to the experimenter, muricide, and intermale aggression were produced by injections into the lateral septum and the region ventral to it. The increases in reactivity and interanimal aggresion occurred in varying degrees and were independent of one another, but intermale aggression occurred only in animals showing muricide. The most effective site for eliciting the entire spectrum of aggressive behaviors was the region ventral to the anterior septum. The region ventral to the posterior septum (medial preoptic area, anterior hypothalamic area, straia terminalis) was unique in that it tended to produce a high incidence of muricide, with only modest increases in reactivity. The lateral septum was moderately effective in producing the entire range of aggressive behaviors. No changes in behavior were noted with infusions into the medial septum or th medial forebrain bundle/lateral preoptic area ventrolateral to the septum. It is suggested that the hyperreactivity and irritability may be relat to hyperdefensiveness and that muricide and intermale aggression are points on a continuum of interanimal aggressiveness.     

Various relationships between predatory dominance and aggressive behavior in Pairs of cats

The experiments were performed on adult male cats selected initially as good mousekillers. Cats were tested in pairs and each pair was introduced separately to the experimental compartment. The attitude toward the partner before and during the predatory competition test as well as superiority in catching and killing the mice, considered as an index of dominance, were registered. In the course of experiment five types of relations between the predatory dominance and aggressive behavior were observed. The concept of dominance as an outcome of several factors was discussed. It was concluded that predatory dominance is not based exclusively on aggressive mechanisms, as it may be formed and sustained without overt aggression.     

Effect of MAO A deficiency on different kinds of aggression and social investigation in mice

Monoamine oxidase A (MAO A) degrades serotonin, dopamine and noradrenaline, factors critically involved in the regulation of aggression. Different kinds of aggression were investigated in Tg8, a transgenic mouse strain lacking a functional MAO A gene. MAO A-deficient mice differ from wild-type C3H/HeJ (C3H) in terms of showing higher territorial, predatory and isolation-induced aggression. Tg8 demonstrated shorter latencies to cricket killing and to the first attack after 6 weeks isolation than C3H mice. In the resident-intruder paradigm, MAO A-lacking mice were more aggressive than C3H when tested as intruders. In contrast to C3H, attack in Tg8 mice did not depend on different aggressiveness of intruders of BALB/c, A/Sn and C3H strains. Tg8 mice displayed no increase in aggression but demonstrated reduced social investigation towards anesthetized, as well as towards juvenile BALB/c males. Thus, MAO A deficiency in Tg8 mice is accompanied by increased expression of different kinds of aggression, as well as by disruption of normal pattern of social interaction.     

Genotype modulates prenatal stress effects on aggression in male and female mice

Prenatal stress (heat and restraint) significantly increased postpartum aggression (proportion of animals fighting and/or the intensity of the behavior) in C57BL/6J female mice and reduced the behavior in DBA/2J females. For intermale aggression, prenatal stress increased the behavior (intensity of aggression) in C57BL/6J males but did not affect aggressive behavior in DBA/2J animals. Infanticidal behavior (the killing of young) exhibited by male mice was not influenced by prenatal stress in either strain. Relative anogenital distance measurements in neonates at birth did not serve as a reliable predictor of strain variation in prenatal stress effects. Prenatal stress did not influence this measure of prenatal androgen exposure in DBA/2J or C57BL/6J females. For males, prenatal stress elevated relative anogenital distance in C57BL/6J mice and decreased this measure in DBA/2J animals. Prenatal stress effects on aggressive behavior in male and female mice therefore depend upon genotype. Strain-dependent differences may be modulated by differences in endocrine reactivity to prenatal stress/and or differential central neural tissue sensitivity to hormones.