Neonatal Isolation Stress Inhibits Pre-Weaning Weight Gain and Mild-Stressor Induced Locomotor Activity in Early Adolescent Male and Female Rats

Abstract

The present study looked at the effects of neonatal isolation, an early life stress experience, in male and female early adolescent rats, an age which is underrepresented in the early stress literature. Four stress-sensitive indices were assessed: weight gain during the pre-weaning period, open field activity, and locomotor activity in response to two mild stressors: exposure to a novel environment, and a single IP saline injection. Rats in the neonatal isolation condition were removed from dam and littermates on postnatal days 2-9 in accord with the procedure used by Kehoe et al . (1995); behavioral testing occurred on PN25-PN30 during the early adolescent period. It was found that neonatally isolated pups weighed less than non-isolate controls on each of three measurement days (PN7, PN14, PN21) throughout the pre-weaning period. Further, neonatal isolation experience consistently reduced horizontal locomotor activity measured in the open field, in a novel environment, and following a single mild acute stressor. On some measures, behavior reflected greater impact of NI in males compared with NI females, suggesting that the effects of NI in early adolescent rats may be sexually dimorphic.