Neonatal novelty exposure ameliorates anoxia-induced hyperactivity in the open field

Abstract

We investigated in an animal model of neonatal anoxia whether effects of oxygen deprivation on emotional reactivity can be reversed by neonatal novelty exposure, a behavioral method, involving daily 3 min away from the home cage for the first 3 weeks of life. Male neonates were exposed to either 100% N 2 gas (Anoxia) or room air (Control) for 25 min on postnatal day 1. Within each of the two treatment conditions, one-half of the neonates were further individually exposed to relatively novel non-home cages for 3 min daily during postnatal days 2-21 (Novel: NAnoxia = 20; NControl = 16), while the other half remained in the home cage (Home: NAnoxia = 19; NControl = 19). Emotional reactivity to an open field was evaluated on postnatal day 25 during four 20-s trials. Among home rats, temporal patterns of open-field activity across multiple trials and initial-trial activity significantly differed between the Anoxia and Control rats. In contrast, these differences were eliminated among the Novel rats. These results show that neonatal novelty exposure, an early-stimulation method that has recently been shown to enhance spatial and social memory, adaptive control of stress response, and hippocampal synaptic plasticity, can also eliminate neonatal anoxia-induced changes in emotional reactivity. These findings suggest that brief and repeated, but mild, changes in the postnatal environment may serve to counteract some of the aversive effects induced by neonatal trauma associated with oxygen deprivation. © 2005 Elsevier B.V. All rights reserved.