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

Peter Villavecchia,Mindy J D Miserendino

doi:10.4236/jbbs.2015.57031

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.

Highlights

Adverse experiences very early in life impact the development of neurochemical, neurophysiological and neuroendocrine systems, resulting in altered function of those systems later in life [1]-[3]
Behavior was measured over 5 days during adolescence (PN26 through PN30) and included total horizontal activity in the open field, locomotor activity in a novel circular corridor, and locomotor activity measured a second time in the same circular corridor immediately following administration of a mild stressor (IP saline injection)
Prior to culling litters on PN2, 90 animals from odd number litters assigned to be in the Neonatal isolation (NI) Environment condition, and 80 animals from even number litters assigned to be in the number litters to the Non-Isolation (NO NI) Environment condition, were weighed

Summary

Introduction

Adverse experiences very early in life impact the development of neurochemical, neurophysiological and neuroendocrine systems, resulting in altered function of those systems later in life [1]-[3]. Neonatal isolation (NI), by contrast, involves removal of the pups from the dam and from each other in a controlled environment for some duration of time each day over several days Both models significantly disrupt normal dam-pup interactions throughout much or all of the early postnatal period [4], including the stress hypo-responsive period (SHRP) in the first 2 weeks of life [5]. Stressors experienced during this developmentally sensitive period produce long-term neurobiological changes that last into adulthood [6] [7]

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Discussion

Conclusion