The study on the factors determining the effects of isolation rearing on social behavior in male laboratory mice

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Isolation and cohabitation with a female in male residents.ICR male mice were reared in isolation or with a female from seven weeks old. Two weeks later ain truder test was performed. The effects of isolation differed from those of cohabitation with a female.Social experiences and adult social behavior.ICR males were reared from four week old in the following conditions :(1)singly housed, or separated with the partition made of (2)transparent plastic board, (3)small- or (4)large-meshed wire net, or (5)paired. Five week later a social encounter test was performed. Compared with condition (5),aggression increased more in conditions (1)and (2)than in conditions (3)and (4),whereas timid responses increased in conditions (1)-(4). The results suggested that different experiences were involved in aggression and timid responses.Isolation and monoaminergic systems.ICR males were (1)singly housed from four weeks old, (2)paired with a female from seven weeks old, or (3)reared in a group from three weeks old. An encounter test was performed at nine weeks old. Four to seven days later the brains were removed and the contents of monoamines and their metabolites were measured. Isolation reduced monoamines and enhanced the mesolimbic dopaminergic activity. Adrenalin and serotonin reduced largely in the animals dominantly showing aggression or timid responses.Isolation and neural activities during social interaction.ICR males were reared in isolation or in a group from four weeks old. Six to seven weeks later they encountered with another male confined in a small wire-mesh cage, and then the brains were perfused and fixed, c-Fos expression was examined as a measure of neural activity. The result suggested that sensitization especially in the main olfactory pathway and excitability in the amygdala and its projecting regions might be enhanced by isolation.