Midfrequency cortico-thalamic oscillations and the sleep cycle: Genetic, time of day and age effects

WAG/Rij rats have various types of mid frequency cortico-thatamic oscillations, such as anterior and posterior sleep spindles and two types of spike-wave discharges (SWD). The generalized SWD (type 1) preferentially occur at transitions from wake to sleep, type 11 can be found at the occipital cortex during quite wakefulness. In the present experiment sleep spindles, SWD and steep cycle characteristics of 6-month-old WAG/Rij rats were studied and compared with those of younger WAG/Rij rats with much less SWD and age-matched control (ACI) rats. EEG recordings were made during the beginning (morning) and end (afternoon) of the light period in these four groups of rats. Quantitative characteristics of SWD, steep spindles and the steep cycle were determined. There were strain-retated and age-dependent effects in the various cortico-thalamic oscillations, older WAG/Rij had more SWDs than younger WAG/Rij rats (both types I and II) and there were more type I SWDs at the end of the tight period compared to the beginning. Large strain, age and time of day effects on the steep cycle were found. The duration of non-REM steep and the steep cycle was shorter in WAC/Rij rats but only at the end of the tight period and only in older WAG/Rij rats. It can be concluded that the various phasic events and the length of the steep cycle are under genetic control, and that the steep cycle length is also controlled by time of day, age and genetic factors. Non-REM steep and the steep cycle are disrupted by absence seizures but only in fragile periods when drowsiness and tight slow wave steep dominate. (c) 2006 Elsevier B.V. All rights reserved.