Sleep Changes in a Rat Prenatal Stress Model of Depression

Major depression is one of the most frequently occurring mental health disorders, but is characterized by diverse symptomatology. Sleep disturbances, however, are commonplace in depressive patients. These alterations include increased duration of Rapid Eye Movement Sleep (REMS) and increased sleep fragmentation. Stressful life events during the second trimester of human pregnancy increase the risk of depression in the offspring. Similarly, rodents exposed to prenatal stress (PNS) during gestation express depression- like behavioral changes. Accordingly, we investigated sleep changes in a rat PNS model of depression, to elucidate whether these are similar to those seen in clinical depression. Pregnant Sprague-Dawley rats were submitted to repeated variable stress during gestational days 13-21. The young adult offspring were surgically implanted with electrodes for subsequent electroencephalographic determination of sleep-wakefulness state. As traumatic episodes can trigger episodes of clinical depression, we also investigated effects of an acute stressor during the recording period. PNS animals (n=21) had an 82% increase in amount of REMS (11.6±1.4% vs 6.3±0.9%; p<0.05) during the first hours of the dark phase, compared to controls (n=24). Interestingly, this was due to a larger number of REMS bouts (16±2 vs 10±2; p<0.05), rather than altered bout lengths. After acute stressor-exposure, control animals had 68% more REMS after lights-off, compared to the day before (p<0.05; n=21-24). The PNS-related increase in REMS after lights-off (p<0.05), was also seen after acute stress (43%), but to a lesser extent than on the baseline day. REMS rebound thus seems blunted in PNS animals. PNS alters sleep-wakefulness behavior under baseline conditions and after acute stress. This underscores the value of the PNS model for addressing scientific questions regarding core symptoms of depression.