Isolation, Reactivity and Aggression: Evidence for an Involvement of Brain Catecholamines and Serotonin

Environmental enrichment and crowding: Behavioral and hormonal effects

“…The lack of correlation between home cage and social interaction aggression is in agreement with several recent papers which have questioned the unitary concept of dominance by pointing out that cross-situational dominant/submissive relationships frequently do not hold [ 14,22,34]. Difference in mean levels of social or environmental stimulation in the 2 situations may have been a factor in this lack of correlation [35] as well as familiarity vs. strangeness of the test conditions and conspecifics encountered.…”

The effects of social isolation on two shock-induced aggressive responses in rats

“…Moyer (1976) recently noted that isolation results in increased aggression or aggression that is topographically atypical for the species. Increased aggression in mice following isolation has been reported when testing involved placing two males in a neutral chamber or when a resident-intruder paradigm was adopted (e.g., Cairns, 1973;Denenberg, 1973;Goldsmith, Brain, & Benton, 1976;Valzelli, 1969;Welch & Welch, 1971). Similarly, isolation has been shown to increase the spontaneous home-cage aggression of rats (Wahlstrand, 1977) and to increase serious fighting in resident-intruder tests (Luciano & Lore, 1975).…”

“…Two recent analyses of the effect of social isolation on aggressive behavior (Cairns, 1973;Welch & Welch, 1971) have implicated hyperreactivity or irritability as the factor mediating the increased aggression in isolated subjects. Such analyses suggest that isolation should result in an increase in an irritable aggressive response (Moyer, 1973(Moyer, , 1976.…”

Effects of prior housing on endocrine responses to differential caging in male TO-strain mice

“…A number of studies have reported that subordinates have heavier adrenals than dominant males (Brain, 1972;Brain & Nowell, 1971b;Chapman et aI., 1969;Louch & Higginbotham, 1967;McKinney & Pasley, 1973;Welch & Welch, 1971). The present results, however, failed to produce a significant difference, although a similar trend was evident.…”

“…Varying group size may result in different ratios of dominant to subordinate animals, as the laboratory mouse often exhibits despotic dominance (Brain & Evans, 1975). Brain (1975), Brain and Benton (1977), and Welch and Welch (1971) have drawn attention to behavioral and physiological similarities between individually housed male mice and dominant males in a group. It· has been suggested that "isolated" males may have affinities with territorial animals, in that they are not SUbjected to defeat in a specified area.…”