G.A. van Oortmerssen

Artificial selection for short and long attack latencies in wildMus musculus domesticus

Artificial selection for short and long attack latency levels in wild maleMus musculus over 11 generations was successful for short latencies. The realized heritability of 0.30 is comparable to those found in other selection studies on aggression. In part selection may have been for faster ontogenetic development of short attack latencies. Four attempts to select for longer attack latencies failed because the lines died out immediately or within two generations for unknown reasons. But neither the physical condition of the animals nor their behavior appeared to have been the cause. Female aggressiveness as measured in female-female encounters was not affected by the selection exerted on the males. This suggests that no genetic correlation exists between aggressiveness of males and females, confirming results of P. D. Ebert and J. S. Hyde [(1976).Behav. Genet.6:291–304] obtained in a selection experiment on aggression using females.

Neuroendocrine states and behavioral and physiological stress responses.

Publisher Summary This chapter presents a novel, behavioral physiological stress concept that originates from the classical view that stress is a response. This new concept is extended to environment, behavior, and physiology, and it incorporates the novel neuroendocrine views including the neuropeptide concept. Stress is viewed as a general biological and usually functional response to environmental and bodily demands. A stress depends on interactions among environment, individual characteristics and the properties of stressors, stress, and the physiological systems, and also among the nervous system, peripheral organ systems, and the neuroendocrine system. To adapt to the altering social and physical environmental demands, man and other animals require a chain of behavioral, neuroendocrine, and autonomic physiological and metabolic responses to maintain bodily and mental homeostasis. The neuroendocrine state of the brain is given a central position in determining the state of health or disease of mind and body.

Individual Differences in Behavioural Reaction to a Changing Environment in Mice and Rats

Aggressive and non-aggressive male mice differ in their reaction to a changing social environment. In order to investigate if this differentiation holds also for non-social situations male mice are trained in a standard maze task, whereafter a change (extramaze and intramaze, respectively) is introduced. The results indicate that aggressive males fulfil their task fairly routine-like and do not react to a change which is in contrast to the non-aggressive individuals. In a second experiment a more continuously changing situation is created by testing the animals every 3 trials in a different maze configuration. In this situation in which a routine cannot be developed c.q. used, the aggressive males performed worse than the non-aggressive animals. It is suggested that the behaviour of aggressive males is mainly controlled by intrinsic factors whereas the behaviour of non-aggressive males is more dependent on external factors. Similar results are obtained when repeating the experiments with rats. This indicates that the relation between aggression and behavioural reaction to a changing environment has more general validity. The possibly underlying mechanism is discussed as well as the consequences for the functioning of the animals in a social setting.

Routine Formation and Flexibility in Social and Non-Social Behaviour of Aggressive and Non-Aggressive Male Mice

To investigate the relationship between aggression and routine-like behaviour the response of male mice of bidirectionally selected lines for attack latency to a change in the social and non-social environment has been measured. In a non-social situation the extent of routine-like behaviour was measured in a Y-maze in which only one of the two arms gave access to the food compartments. The number of errors made in response to reversal of the arm that was blocked was taken as indicator for the degree of routine formation. Males of the short attack latency (SAL) line made significantly more errors, and hence were more routine-like in their performance, than mice of the long attack latency (LAL) line. Males of the LAL line that nevertheless had short attack latencies (i. e. aggressive LAL mice) turned out to be flexible in their behaviour; their response was similar to that of the non-aggressive LAL males. In a social situation SAL and aggressive LAL mice were used to investigate routine formation in attacking behaviour. The males were given different amounts of experience with male opponents after which their own female was introduced as opponent. The more extended the experience with male intruders was, the more SAL males subsequently attacked their female. In contrast, LAL mice appropriately changed their behaviour towards the female opponent. Thus, the attacking behaviour of SAL mice gets routine-like, whereas that of LAL males remains flexible. It is concluded that selection for attack latency generally coincides with selection for routine-like behaviour, suggesting that these two factors are influenced by many of the same genes. Regarding the fact that aggressive males of the LAL line show flexible behaviour, it may be proposed that with the phenotypic selection for attack latency there has in fact been selected for a mechanism that determines the organization (routine-like vs flexible) of behaviour.

Behavioral stress response of genetically selected aggressive and nonaggressive wild house mice in the shock-probe/defensive burying test

Genetically selected aggressive and nonaggressive male wild house mice were tested in the shock-probe/defensive burying test: Five distinct behaviors (burying, immobility, rearing, grooming, and exploration) were recorded in two environmental situations: fresh and home cage sawdust. Nonaggressive animals, characterized by a Long Attack Latency (LAL), showed more immobility in both test situations than animals having Short Attack Latencies (SAL), whereas SAL males displayed more defensive burying than LAL ones when tested with fresh sawdust. Testing with home cage sawdust, however, resulted in the same duration of defensive burying in SAL and LAL. These results support earlier findings about the existence of two heritable, fundamentally different strategies to cope with aversive situations. Aggressive (SAL) animal react actively to environmental challenges, whereas nonaggressive animals react actively or passively, depending on the characteristics of the stressful environment. These mouse lines, selected for attack latency, i.e., aggression, may, therefore, be important tools to unravel the genetic architecture underlying the physiological and neuronal mechanisms of behavioral strategies towards stressful events.

Behavioural strategies of aggressive and non-aggressive male mice in active shock avoidance

The hypothesis, partly based on findings in social interactions, that aggressive mice generally adopt an active behavioural strategy (cf. fight-flight) in threatening situations, while non-aggressive ones generally assume a passive strategy (cf. conservation-withdrawal) was tested using a two-way active shock avoidance paradigm. Overall, aggressive mice were found to be better active shock avoiders than non-aggressive animals; a finding that is consistent with our hypothesis. However, within the non-aggressive mice a clear dichotomy in high and low avoidance individuals was found. The high intertrial activity in the superior avoidance groups and the low activity in the poor avoidance group was interpreted as another indication of an active versus passive strategy respectively. Accordingly, it was concluded that not all non-aggressive mice assume a passive strategy, but that some mice adopt an active strategy, like all aggressive males.

Aggression and Adaptation to the Light-Dark Cycle: Role of Intrinsic and Extrinsic Control

In wild house mice, the hypothesis that in the organization of behavior the relative contribution of intrinsic factors is more important in aggressive males, while that of extrinsic factors is more important in nonaggressive individuals was confirmed using the circadian rhythmicity of activity. The faster rate of reentrainment and the suppression of activity during a subjective night and during adaptation to the new LD cycle in the nonaggressive males indicate that their circadian rhythmicity of activity is to a large extent determined by the Zeitgeber, an extrinsic factor. The slower reentrainment rate, the lack of response to a subjective night and the normal activity level seen during reentrainment in the aggressive mice suggest strong control by the pacemaker, an intrinsic factor. Tau differences between the aggressive and nonaggressive mice provide some evidence that the pacemaker of nonaggressive males is fairly labile and is easily influenced by external factors, whereas the pacemaker of aggressive animals is rather stable.

Studies in wild house mice II. Testosterone and aggression

The relationship between testosterone level and attack latency was studied in genetically different wild house mice by means of castration and subsequent testosterone therapy. This was done to provide adequate physiological knowledge for further research on the genetic basis of individual differences in these mice. The findings show that individual variation in attack latency is related not only to variation in baseline plasma testosterone level (via a dose-response relation), but also to variation in responsiveness to testosterone that is induced before puberty. In addition it is shown that in fast-attacking mice the maintenance of the attack latency level reached by maturation is independent of testosterone, whereas this is not the case in mice that are reluctant to attack.

Behavioural strategies of aggressive and non-aggressive male mice in response to inescapable shock

The effect of exposure to inescapable long-duration shocks of moderate intensity on intershock activity and on subsequent escape or avoidance performance was studied in aggressive and non-aggressive male mice. The activity of the non-aggressive mice was severely suppressed during the inescapable shock session, while that of the aggressive males was hardly influenced. The decremental effect of prior shock exposure on subsequent response latency and activity in an active two-way escape or avoidance task was greater in the non-aggressive than in the aggressive mice. There was no evidence that learned inactivity or learned helplessness (an associative deficit) could explain the results. Instead, individual differences in behavioural strategy in response to threatening situations appeared to account for the effects of inescapable shock. Aggressive male mice predominantly adopted an active behavioural strategy in challenging situations, which resulted in persistent attempts to exercise control over the external situation and hence in a sustained tendency to initiate responses. Non-aggressive mice primarily assumed a passive strategy; their tendency to exercise control was low, which readily resulted in a reduced tendency to initiate responses.

Individual Differences in Blood Pressure Reactivity and Behavior of Male Rats

One of the major concerns in research on the aetiology of coronary heart disease (CHD) and hypertension has been the question why some individuals suffer from these diseases while others are healthy, although exposed to seemingly identical external conditions. Since the early studies by Friedman and Roseman (1959), it has become increasingly clear that apart from environmental circumstances, personality factors are also important. In order to study the complex interplay between environmental variables and personality factors in the pathophysiology of the cardiovascular system, animal research is indispensable.