Prenatal malnutrition and sleep states in adult rats: Effects of restraint stress

Independently, prenatal malnutrition and psychological/physical stress have been shown to affect sleep architecture in adult rats. As malnutrition and stress commonly co-exist in malnourished human populations, the objective of the present study was to ascertain the combined effects of these two insults by examining sleep-wake parameters following a brief restraint stress in prenatally protein malnourished rats. The male offspring of rats provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy were implanted with recording electrodes beginning at postnatal day 90. Polygraph recordings were obtained to quantify sleep states during the first 4 h of the dark phase of the cycle on 2 consecutive days. The first followed a 24-h habituation session to the recording chamber (baseline). The second occurred at the same time of day but followed 20 min of restraint stress in a Plexiglas tube. During baseline, prenatally malnourished rats spent more time in rapid eye movement sleep (REMS) in the first 2 h after “lights off” (block 1), and greater amounts of wakefulness (W) with a corresponding reduction in slow wave sleep (SWS) in the second two hours (block 2), as compared with controls. Following stress, the sleep architecture of both groups of rats remained unaltered in block 1 relative to their baseline day. In block 2, both groups exhibited significant reductions in SWS and REMS with significantly greater reductions being expressed in the prenatally malnourished group (most dramatically, REMS was completely eliminated). These findings suggest that sleep disturbances may be more severe in those malnourished human populations subjected to acutely stressful experiences.