Isolation modifies the behavioural response in rats.

Twenty-four male wister rats were reared from weaning either alone (isolation reared) or in groups of five (socially reared) for 6 weeks. Thereafter, the present study examined and compared the behaviour of isolation and socially reared rats in the test of social interaction, in the elevated plus-maze test of anxiety, in the open field behavior of exploration and locomotion activity, and the depressive behaviour in forced swim test. Under high light in unfamiliar conditions isolation reared rats spent significantly more time in aggressive interactions (P < 0.05) and high levels of aggressive behaviour compared to the socially reared rats (P < 0.05). Isolation reared rats had spent less time in the open arms than the socially reared rats in the maze test (P < 0.05). Isolation reared rats were more exploratory than the socially reared rats in the open field test and the defaecation scores were less compared to the socially reared controls (P < 0.05). Isolated rats spent less time immobile on the rats' forced swim test behaviour but the difference was not statistically significant. These findings suggest that isolation reared rats are nervous, aggressive and hyperactive animals in a novel field. It appears that isolation rearing in the early stages of life has modified a variety of behaviour in the adult rats, and the investigation of the pattern of behavioural changes in isolation reared rats may help to explore the environmental influences on the development of human psychopathology.