Effect of Time of Separation from Mother on Behavior in Open Field and on State of the Sympathoadrenal System in Rats Reared under Conditions of Social Isolation

The level of catecholamine excretion with urine and behavior in the open field test were studied in male Wistar rat pups separated from female at the age of 17, 21, 30, and 36 days and reared subsequently for 40 days under conditions either of social isolation or in the group with their kin. It was shown that in rats weaned at the age of 17 and 21 days, the subsequent rearing in isolation led to an increase of the urinary excretion of adrenaline and a decrease, of noradrenaline. After isolation at the 30th day, there was revealed an increase of the excretion level both of adrenaline and of noradrenaline. The social isolation also leads to an increase of horizontal motor activity in rats weaned at the age of 17 days and to a decrease of this activity in rats weaned at the 30-day age. After isolation at the age of 21 days, an earlier extinguishing of the activity it was observed at repeated testing. Isolation at the age of 36 days, on the contrary, led to a decrease of the extinguishing process. Thus, it is shown that the social isolation produces changes in rat behavior and has a stress effect on the animals; the effect of isolation depends on duration of the rearing of rats in the nest with the female.