Effects of early handling on basal and stress-induced sleep parameters in rats

Abstract

Exposure of humans and animals to stressful events early in life leads to significant and often permanent behavioural, neuroendocrine and central alterations. Early handling consists of removing the litter from the nest for 15 min/day, from post-natal days 2 to 14 and results in lowered ACTH and corticosterone stress response and reduced anxiety-like and fear behaviours. Stress-induced sleep alterations usually consists of increased sleep time, known as sleep rebound. In the present study, basal and stress-induced sleep pattern of control non-manipulated (CTL) and early handled (EH) adult male rats was investigated. Sleep was evaluated by 21-h polysomnographic recordings (from 10:00 to 07:00 h of the next day) before and after a 1-h session of restraint stress. The results showed that in the first 3 h following stress, both CTL and EH animals exhibited an impairment of sleep, with a reduction of sleep efficiency, duration of slow wave sleep and of paradoxical sleep. On the contrary, time awake and awakening bouts were augmented in this period. Sleep rebound was observed mainly in the dark period of the light–dark cycle. Stress-induced sleep changes were similar between CTL and EH animals for most sleep parameters. However, EH animals exhibited more bouts of paradoxical sleep on the night following stress exposure and longer bouts of paradoxical sleep in the light period that followed restraint stress. These data indicate that stress-induced alterations of sleep in early handled animals are similar to that observed in control animals, except for some parameters related to paradoxical sleep.