Effects of stress controllability,immunization, and therapy on the subsequent defeat of colony intruders

Three experiments investigated the influence that various stress-controllability manipulations had on the defensive behaviors of rats when they were subsequently tested as intruders in previously established, aggressive colonies of conspecifics. In Experiment 1, naive subjects that had received a session of 80 shocks in a tube showed an enhanced series of defensive responses and received more bites than did a group of restrained nonshocked rats as colony intruders 24 h later. These two measures were also found to be positively correlated within each group. In Experiment 2, a group that was given 80 yoked inescapable shocks, in contrast to a group that had wheel-turn escape training and a restrained nonshocked control group, displayed more defeat and was bitten more frequently when tested as intruders on the following day. In Experiment 3, 60 trials of wheel-turn escape training were given 4 h prior to (i.e., immunization) or after (i.e., therapy) a session of 60 inescapable tube shocks. During resident-intruder testing 24 h later, both of these groups showed less defeat and received fewer bites than did an inescapably preshocked group but did not differ from a restrained nonshocked control group. These findings clearly indicate that stress controllability alters species-typical defensive responses, and their implications concerning other learned helplessness effects and interpretations are discussed.     

Prolonged exposure to conspecific and predator odors reduces fear reactions to these odors during subsequent prod-shock tests

In Experiment 1, four groups of male rats were given a session as an intruder in either aggressive (i.e., alpha) or nonaggressive colonies of conspecifics and later received either a 2-h exposure to the odors of the alpha colonies or an exposure-control session with the odors of a nonalpha colony. Two additional groups of rats that had been attacked and defeated by alpha residents were later given a 12-h exposure session with alpha-colony odors or nonaipha-control odors. Twenty-four h after the colony-intruder session, all subjects were given a single 6.5-mA shock from a prod with alpha-colony odors present in the bedding of the test chamber. Attacked rats that had been given exposure-control sessions showed significantly less prod burying and greater freezing than nondefeated subjects. This implies that the alpha-colony odors elicited conditioned fear. In contrast, the attacked subjects that had been given a pretest exposure session with alpha-colony odors showed significantly more prod burying and significantly less freezing. This suggests that the alpha-odor exposure resulted in the extinction of fear to these odors. Furthermore, the 12-h exposure to alpha-colony odors was found to be more effective in reducing fear-mediated responses than was the 2-h exposure. In Experiment 2, three groups of rats were exposed to a cat while they were in a protective cage; later they were given a 12-h exposure session with cat odors, a 12-h exposure-control session with no cat odors, or no exposure treatment. Compared with the two control groups, the subjects that were exposed to cat odors showed less freezing during subsequent prod-shock tests in the presence of cat odors, but they did not show prod burying. The reported changes in fear-mediated reactions to the odors of conspecifics and a predator are discussed in terms of both associative and nonassociative processes.     

Effects of repeated defeat by a dominant conspecific on subsequent pain sensitivity,open-field activity,and escape learning

Male rats were tested as intruders for 25 consecutive days in colonies that had either aggressive (i.e., alpha) or nonaggressive conspecific residents. Alpha-defeated intruders, in contrast to nondefeated rats, showed more defensive behavior, less gain in body weight, and received more bites during the course of these sessions. Tail-flick tests, using a heat source, revealed that both groups of intruders showed comparable sensitivity/reactivity to pain, and there was no evidence of analgesia as a function of resident encounters. Immediately after the last intruder session, all subjects were tested for exploratory activity in an open-field apparatus with the odors (i.e., soiled bedding) from the alpha colonies present. Defeated intruders showed significantly less locomotion, in terms of the number of grid crossings, than nondefeated rats. Twenty-four hours later, randomly selected subgroups of defeated and nondefeated subjects were briefly exposed, without being defeated, to aggressive colonies, and all rats were then retested for activity with alpha odors present. Previously defeated intruders were again less active, and the colony-exposure treatment suppressed the activity of defeated, but not nondefeated, subjects. Finally, 24 h after another resident-intruder session, both groups of intruders showed comparable FR 1 escape performance in a shuttlebox with alpha odors present, but the defeated rats failed to learn a subsequent FR 2 escape task. The findings of this experiment are discussed in terms of the concept of “learned helplessness,” the effects of ethological stressors, and the authors’ stress-coping-fear-defense (SCFD) theory.     

The development of intruder attack in colonies of laboratory rats

Most attacks by rat colony members on strange intruders are made by a single dominant male. Such dominance, and the attack behaviors themselves, develop in a relatively fixed sequence over sessions with strange intruders. The entire sequence of attack on intruders occurs earlier in the intruder sessions for older rat colonies than in those for newly established colonies: conversely, more attack is seen in colonies with prior intruder experience than for intruder-naive colonies of equivalent age. Thus both experience within the colony and specific experience with strange intruders influence the rate of development of attack on intruders by dominant colony rats.     

Influence of conspecific stress odors and shock controllability on conditioned defensive burying

In Experiment 1, rats received a session of 80 inescapable tail shocks or no shocks while restrained in a tube. During tests of conditioned defensive burying 24 h later, the bedding of the chamber contained odors from either stressed or nonstressed conspecific donor rats. Following a single prod shock, subjects that had had prior shocks or that were tested with the stress odors spent significantly less time burying the prod, made smaller piles of bedding, and displayed more freezing behavior. The combination of prior shock and stress odors during later testing enhanced these effects. In Experiment 2, a yoked group of rats that was given inescapable shocks, in contrast to a group that had wheel-turn escape training and one that was restrained but not shocked, later showed significantly less burying and more freezing when tested for defensive burying with stress odors present. In both experiments the duration of burying and the heights of piles were positively correlated, and both of these measures were negatively correlated with freezing. The demonstrated capacity of unconditioned stress odors to mediate different degrees of fear, depending upon the controllability of prior shock, is related to other studies of learned helplessness, and the predominance of freezing over burying is discussed in terms of various types of defensive strategies, stimulus-control processes, and the author’s stress-coping-fear-defense (SCFD) theory.     

Influence of conspecific and predatory Stressors and their associated odors on defensive burying and freezing responses

In Experiment 1, male rats were exposed to either aggressive (i.e., alpha) or nonaggressive conspecific colonies and tested 24 h later, with or without alpha odors, for freezing behavior and burying of a wall prod that had been the source of a brief electric shock. The results indicated that prior defeat experience and the presence of alpha odors alone during testing had no significant effects, but the combination of prior defeat and alpha-odor testing significantly decreased burying and increased freezing behavior. In Experiment 2, we examined the effects of noncontact exposure to a cat, as a predatory Stressor, during subsequent prod-shock tests involving the presence or absence of cat odors. Exposure to a cat failed to disrupt later prod burying and did not produce freezing. However, the presence of cat odors during testing significantly reduced the amount of defensive burying,without resulting in an increment in freezing. In Experiment 3, rats were given 1, 5, or 30 inescapable preshocks in the presence of either cat odors or a hedonically neutral citronella odor and were tested 24 h later for prod burying and freezing with or without these odors. Both the cat and the citronella odors resulted in a significant reduction in burying and an increase in freezing for rats given 5 and 30 preshocks and tested in the presence of these respective conditioned odors. For the groups that were given 5 preshocks, preshock and later testing in the presence of cat odors resulted in significantly less prod burying and more freezing than for rats that were preshocked and tested in the presence of citronella. The findings of these three ethoexperimental studies are discussed in terms of the learned-helplessness theory, the stress-coping-fear-defense (SCFD) theory, and the concept of selective CS-US associability.     

Resident rats’ aggression toward intruders

A study was performed in which attacks by four different types of “resident” rat (males housed with fertile females, males housed with sterile females, paired males, and isolated males) on six different types of intruder (isolated males, grouped males, castrated males, isolated females, grouped females, and ovariectomized females) were investigated. The objective was to study features of resident and intruder rats that would allow the designing of an aggression test that used a minimum of animals and produced a rapid behavioral response. In some combinations of residents and intruders, attack was generated within a 10-min test period. Isolated resident males attacked as much as males housed with females; however, paired rats showed only low incidences of attack. The fertility of the female partner did not influence the male’s aggressiveness. Most male attacks were directed towards like-sexed intruders. Only isolated males differentiated between the different treatment types of male intruder, attacking group-housed and castrated rats less intensely than isolates. Of the females, only those that were fertile produced significant amounts of attack behavior and almost exclusively attacked female intruders. Group-housed intruder females received more attacks than isolates. The results suggest optimal conditions for generating two models of attack behavior in the laboratory rat.     

Breeding,paternal behavior,and their interruption inBetta splendens

Seven experiments examined the reproductive activities of Siamese fighting fish (Betta splendens). Spawning occurred after heterosexual pairs were together for about 24 h, and males cared for eggs, nest, and fry thereafter. The visual cues provided by an intruder male, but not a female, stimulated aggression in the male breeder, and these agonistic behaviors competed with breeding to cause a decrement in reproductive efficiency. Males were found to protect eggs and fry by preventing the growth of a fungus lethal to their offspring.     

Influence of postpartum shock controllability on subsequent maternal behavior in rats

Responses of mother rats were observed 24 h before and 24 and 72 h after exposure to one of three 8-day postpartum treatments: shock escape training, yoked inescapable shock, or restrained with no shock. In contrast to those in the other two groups, the dams given inescapable shock showed slower speed to approach the nest, shorter durations of being on the nest, and lower frequency and shorter total duration of oral contact with their pups. These dams also retrieved their pups less frequently, but this measure, as well as the frequency of leaving the nest, did not result in significant differences between groups. Since the traditional interpretations of the learned-helplessness effect were not entirely able to account for these findings, the observed uncontrollable-stress-produced changes in maternal behavior were examined from an ethological perspective.     

Defensive attack behavior in male and female rats

Male rats in a restraining tube bit and wounded the snout of an anesthetized male conspecific as a direct function of the intensity of tailshock, with bites declining systematically in the time interval after shock. Female rats’ bites on a male rat were also dependent on shock, but did not produce wounds. When an anesthetized cat was presented to rats in the same situation, females bit and wounded the cat before shock was given, while the males again bit only in response to shock. These data were interpreted as indicating that male bites on both a conspecific and a predator fit the same defensive biting pattern. In contrast, females’ bites on a male rat are actively inhibited, while females’ bites on a predator are neither inhibited nor shock dependent: this latter finding may reflect the adaptive value (protection of the young) of attacking a predator before it hurts the female rat.     

Defensive burying in the rat: A behavioral field analysis

Time spent in various behaviors by the rat was recorded in a defensive burying paradigm. Experiment 1 revealed that rats spent more time burying the shock prod than a control prod and that doubling the size of the test chamber did not have a significant effect on the time spent in any behavior. In Experiment 2, the location of bedding material in a two-compartment test chamber was found to affect the occurrence of burying (both the shock and control prods) and burrowing behavior. Burying did not occur when bedding was not available in the shock compartment but was located in the escape compartment. Burrowing was more likely to occur when bedding was in both compartments than when it was in only one compartment. Immobility and escape latencies were shorter than burying latencies in all subjects. Burying was viewed as belonging to a second stage of defensive behavior.     

Behavioral field analysis in two strains of rats in a conditioned defensive burying paradigm

Two strains of rats (albino Wistar and hooded PVG/c) were exposed to a conditioned defensive burying paradigm that consisted of placing rats in a test chamber with bedding material on the floor, shocking them with a shock prod, and recording the time each rat spent in burying responses toward the prod. Various behaviors other than burying (freezing, grooming/paw licking) were observed by a time-sampling procedure during the control, conditioning, and extinction sessions, each of which was 15 min in duration. Wistar rats generally showed behavioral inhibition, as evidenced by less burying, lower exploratory and ambulatory behavior, and higher freezing behavior. PVG/c rats spent significantly more time engaged in burying and accumulated more bedding material in the conditioning session than did the Wistar rats. No significant differences between the two strains of rats were observed during the extinction session in terms of these measurements. The results indicate that Wistar rats have a greater tendency to freeze when coping with the noxious stimulus in a conditioned defensive burying paradigm, whereas the dominant coping style for PVG/c rats is defensive burying.     

Territorial behavior of laboratory rats under conditions of peripheral anosmia

Two experiments investigated the influence of peripheral anosmia with zinc sulfate solution on aggressive and nonaggressive behaviors of rats in the colony intrusion paradigm. Experiment I was a replication of a previous observation that anosmic intruders arenot attacked by resident males. No significant differences were found in aggressive response to normal or anosmic intruders. Experiment II tested colony residents under normal and anosmic conditions for aggressive and nonaggressive response to intruders. The results were in agreement with previous reports that anosmia abolishes differential responding between males and females as well as all aggressive acts normally directed against unfamiliar males.     

Gender Differences in Children's Normative Beliefs about Aggression: How Do I Hurt Thee? Let Me Count the Ways

This research was designed to assess whether children view relationally manipulative behaviors (i.e., those behaviors labeled relational aggression in past research) as "aggressive." 2 studies were conducted to evaluate whether children view relationally manipulative behaviors as associated with 2 defining features of aggression, anger (Study 1) and intent to harm (Study 2). Results of Study 1 ( n = 459, 9–12-year-olds) indicated that relational aggression was the most frequently cited angry behavior for girls' interactions whereas physical aggression was the most frequently cited angry behavior for boys' interactions. Results of Study 2 ( n = 60, 9–11-year-olds) demonstrated that relational aggression and verbal insults were the most frequently cited harmful behaviors for girls whereas physical aggression and verbal insults were the most frequently cited harmful behaviors for boys. These studies provide the first evidence that children view relationally manipulative acts (relational aggression) as angry, harmful behaviors (i.e., as "aggressive").     

Partial control and learned helplessness in rats: Control over shock intensity prevents interference with subsequent escape

The effect upon subsequent escape acquisition of control over shock intensity in the absence of control over other shock characteristics was examined. Pretreatment involved random shocks of 1.6 and .75 mA at a density of about 10/min. The experimental group could avoid the higher shock intensity if they leverpressed at least once every 15 sec. Yoked and no-shock rats completed the triadic design. Experimental and yoked animals received all scheduled shocks. Triads were later tested for FR 2 shuttlebox escape at either the .75 mA (low) or 1.6 mA (high) intensity. During testing, avoidance rats performed as well as no-shock rats at the low intensity and escaped even more rapidly at the high intensity. Yoked rats showed interference at both intensities, with interference very marked, including many failures to escape, at the low intensity. These findings indicate that control over shock intensity, by itself, is sufficient to prevent learned helplessness and suggest that control over any salient characteristic of shock may be sufficient for immunization.     

The early childhood aggression curve: development of physical aggression in 10- to 50-month-old children

This study examines the prevalence, stability, and development of physical aggression, as reported by mothers and fathers, in a sample of children initially recruited at 12, 24, and 36 months (N=2,253) and in a subsample followed up 1 year later (n=271) in a cross-sequential design. Physical aggression occurred in 12-month-olds, but significantly more often in 24- and 36-month-olds. The rates of physically aggressive behaviors increased in the 2nd year of life, and declined from the 3rd birthday onward. Stabilities were moderate for 12-month-olds and high for 24- and 36-month-olds. At the ages of 24 and 36 months, boys were more aggressive than girls. The results confirm and extend R.E. Tremblay's (2004) hypothesis about the early development of physical aggression.     

Childhood Maltreatment and the Development of Relational and Physical Aggression: The Importance of a Gender‐Informed Approach

This investigation examined the associations between maltreatment and aggression using a gender‐informed approach. Peer ratings, peer nominations, and counselor reports of aggression were collected on 211 maltreated and 199 nonmaltreated inner‐city youth (M age = 9.9 years) during a summer day camp. Maltreatment was associated with aggressive conduct; however, these effects were qualified by gender, maltreatment subtype, and the form of aggression under investigation. Findings revealed that maltreatment was associated with physical aggression for boys and relational aggression for girls. Physical abuse was associated with physically aggressive behaviors, but sexual abuse predicted relational aggression for girls only. Findings suggest that investigating the interaction between familial risk and gender is important in understanding aggressive behaviors of boys and girls.     

Functional differences between two shock-induced aggressive behaviors of mice

Five groups of male mice were given either isolation or grouped housing conditions or fight training as manipulations of social backgrounds prior to 5 days of shock-induced aggression under conditions resembling the rat paradigm for shock aggression. Three groups were given similar fight training but different levels of shock intensity during the shock trials. Shocks moderate in intensity as compared to very low intensity shocks produced more biting attacks and upright postures and maintained aggressiveness. Raising the shock intensity further produced fewer biting attacks, more upright postures, and a decline in aggressiveness. Biting attacks proved to be a more discriminating measure of differences created by different social backgrounds than the upright postures.     

Carbohydrate-induced stimulation of saccharin intake: Yoked controls

Dilute, intragastric infusions of carbohydrate stimulate saccharin intake. To determine whether this effect is due to an associative process, a yoked control was employed. One group of rats was trained in the conventional fashion: they received carbohydrate (maltodextrin) infusions whenever they drank saccharin. Whenever these rats were infused with carbohydrate, yoked rats were infused with the same amount of carbohydrate. In an experiment in which saccharin was available continuously, carbohydrate infusions stimulated saccharin intake in conventionally trained rats but not in yoked rats. In a subsequent experiment, in which rats were offered saccharin for only 2.5 h/day, carbohydrate infusions stimulated intake in conventionally trained and in yoked rats. However, when these rats were switched to continuous saccharin availability, saccharin intake declined in yoked rats but remained elevated in conventionally trained rats. Thus, carbohydrate infusions stimulate saccharin intake via an associative process.     

Postshock learning and conditioned defensive burying

Natural sources of aversive stimuli are frequently well-defined material objects that are present both before and after the aversive event. In the present experiment, rats acquired information about such a source after the aversive event and used this information to guide their subsequent defensive reactions to it. The rats were shocked by one of two possible sources, either a black or a striped prod, mounted on opposite end walls of the test chamber. Immediately following the shock, the houselights were momentarily extinguished and the patterns on the two prods were automatically switched for subjects in the experimental condition or left unchanged for subjects in the control condition. The rats were left in the chamber for another 5 min with the patterns in their new positions before being removed for 2 min while the two prods were mounted on the side walls. During the ensuing test of conditioned defensive burying, the rats in the control condition directed the majority of their burying behavior at the prod exhibiting the pattern displayed by the shock source prior to and during the shock administration. In contrast, the rats in the experimental group buried the prod exhibiting the pattern displayed by the shock source during the postshock period more than they did the prod displaying the pattern present on the shock source prior to and during the shock administration.