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

Abstract

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.Numerous investigators have shown that repeated exposure to a laboratory stressor, such as electric shock, produces alterations in behavioral and neurophysiological processes. In mice and rats, experiencing inescapable shock has been shown to interfere with the subsequent acquisition of escape responses (e.g., Anisman, Suissa,

Social defeat and subordination as models of social stress in laboratory rodents: A review

“…Defeated or subordinate animals show a motor inhibition with a decrease in general activity, especially in the locomotor and exploratory activities and in movement celerity [Kudryavtseva et al, 1991a;Meerlo et al, 1996aMeerlo et al, , 1996cPuglisi-Allegra and Cabib, 1988;Raab et al, 1986;Williams and Lierle, 1988;see Hebert et al, this issue], although no significant decrease in activity has also been reported [Albonetti and Farabollini, 1994;Flannelly and Lore, 1975;Scholtens and van de Poll, 1987]. A reduction in food and water intake has been found after repeated defeats but not after a single defeat [Meerlo et al, 1996c].…”

“…Repeated defeat causes hyperthermia [Harper et al, 1996;Meerlo et al, 1996b;Miczek, 1993, 1994], and both an increase and a reduction in the circadian amplitude of this variable have been found [Harper et al, 1996;Meerlo et al, 1996a]. In addition, body weight is usually decreased by social stress [Albonetti and Farabollini, 1994;De Goeij et al, 1992;Kudryavtseva et al, 1991a;Meerlo et al, 1996c;Raab et al, 1986;van de Poll et al, 1982;Williams and Lierle, 1988]. Finally, other changes, such as (a) a reduction in reproduction and fertility [Herbert, 1995], (b) renal pathology [Barnett et al, 1975], and (c) a reduction of longevity [Blanchard and Blanchard, 1990; R.J. Blanchard et al, 1985;Sachser et al, 1994] have also been reported.…”

“…Another model in which a male loses its dominant status with respect to another male is presented by Marrow and Brain in this issue [Willner et al, 1995]. Finally, the intrudercolony model obviously consists of introducing an intruder male in a mixed-sex colony, the intruder being attacked by the dominant male of the colony [Williams and Lierle, 1988].…”

Behavioral and neuroendocrine consequences of social subjugation across adolescence and adulthood

“…Social subjugation in adult male talapoin monkeys reduces social activity and sexual behavior even in the absence of dominant conspecifics [2]. Defeated adult mice and rats display less aggressive and more submissive behavior [3-5]. Individually housed adult hamsters will routinely attack and bite an equal or smaller sized intruder placed into their home cage.…”

Important Hints in Behavioural Teratology of Rodents

“…Some rodent species are very aggressive and before using an unknown rodent species or strain (particularly inbred or genetically transformed), the available literature on territorial behaviour, parental nest defence, and major changes in intermale aggression around puberty should be checked. It has to be remembered that prolonged and repeated defeat by a dominant conspecific produces profound physiological and behavioural alterations [298,299], including immune system failure also under natural conditions [300][301][302].…”