Crowding and isolation: Determinants of agonistic and food-seeking behavior in Norway rats.

Abstract

Two groups of 12 Long-Evans rats were alternately isolated and crowded. Order of housing and familiarity of the subjects with the test apparatus were also varied systematically. Subjects were deprived of food, trained to bar press, and allowed to compete in pairs for sugar water in a Skinner box. Isolated pairs produced more agonistic and contact behaviors and fewer bar presses than did crowded pairs. Weight was found to increase more rapidly during free feeding when animals were isolated. Familiarity of only 1 isolate with the testing environment led to the display of less aggression than was observed in other isolate conditions.Animal experimental findings seem equivocal regarding the hypothesis that crowding leads to aggression. This uncertainty exists because investigators have employed 2 different manipulations of the independent variable. Studies have been designed to examine the effects of (a) differences in population size and (b) differences between grouped and isolated housing conditions.Two conclusions may be drawn from such studies: (a) Larger groups of animals exhibit more aggression than do smaller groups (Gregor, Smith, Simons, & Parker, 1972); and (b) isolated animals exhibit more aggression than do grouped animals

Cooperative social coordination and aggression: Sex and strain differences in the effects of housing on gonadectomized rats with hormone replacement

“…Animals housed individually, in "social isolation," show increased levels of aggression when compared with animals housed socially. This effect has been documented in the Norway rat Ruttus nowegicus [Conner and Gregor, 1973;Flannelly and Lore, 1975;Powell and Buchanan, 1978;Brain et al, 19801, in other rodents [Valzelli, 1969;Cairns, 1972;Brain and Benton, 19831, and in a variety of other species [for a review, see Johnson, 19721. Other deficits can include hyperreactivity, exaggerated approach tendencies, and learning deficits.…”

Cooperative social coordination and aggression: Sex and strain differences in the effects of housing on gonadectomized rats with hormone replacement

“…Animals housed individually, in "social isolation, " show increased levels of aggression when compared with animals housed socially. This effect has been documented in the Norway rat Ruttus nontegicus [Conner and Gregor, 1973;Flannelly and Lore, 1975;Powell and Buchanan, 1978;Brain et al, 19801, in other rodents [Valzelli, 1969;Cairns, 1972;Brain and Benton, 19831, and in a variety of other species [for a review, see Johnson, 19721. Other deficits can include hyper-reactivity, exaggerated approach tendencies, and learning deficits.…”