Fig. 1.

Scheme of experimental design of the stress treatments: (a) unstressed control animals (CTL), where litters were left undisturbed with their family. The siblings remained together until PND 90, and thereafter they were raised in sex-matched groups of three siblings from PND 91 until the end of the experiment (n = 13♀ and 13♂). (b) Partial isolation group (PI), from PND 1 to PND 35 (day of weaning), the degus pups were removed from their mothers and home cage and were kept individually for 1 h daily. After 1-h of separation pups were returned to their family and home cage and left undisturbed until the next day. After PND 35 the whole litter was left undisturbed with their family. The siblings remained together until PND 90, and thereafter they were raised as sex-matched groups of three siblings (one focal degus and two respective brothers/sisters that were not included in our experimental design) from PND 91 until the end of the experiment (n = 13♀ and 13♂). (c) Chronic isolation group (CI), from PND 1 to PND 35 (day of weaning), the degus pups were removed from their mothers and home cage and were kept individually for 1 h daily. After 1-h of separation pups were returned to their family and home cage and left undisturbed until the next day. From PND 36 until the end of the experiment, female and male degus were individually housed (n = 26♀ and 26♂). (d) Re-socialization group (CI-R), after a period of 24-months, half of CI-reared degus were randomly reassigned and housed in sex-matched pairs with CI-reared brothers or sisters (one focal degus and one sibling not included in our experimental design) during a period of 6-month (n = 13♀ and 13♂).