Sleep ECoG Rhythm in the High Mesencephalic Rat

Abstract

The sleep-waking circadian rhythm in the rat is supposed to be influenced by the SCN. However, how the SCN influences the sleep-waking circadian rhythm is largely unknown. We performed an experiment which eliminates the serotonergic input from the raphe nuclei to the SCN. In this particular preparation, the midbrain was transected at a rostral level so that a part of the mesencephalic reticular formation was still within the forebrain, whereas the raphe and locus coeruleus were totally isolated from the forebrain (Hanada and Kawamura 1981). In this high mesencephalic preparation the appearance of a desynchronized electrocorticographic (ECoG) pattern is earlier than with the transection described by Batsel (1960) and Villablanca (1962). After such a mesencephalic transection, Bremer (1935) first described the appearance of a continuous slow sleep pattern in his acute experiment. Later, Batsel and Villablanca described the reappearance of a ECoG desynchronization pattern 2–3 weeks after transection in chronic cerveau isolé cats and dogs. Unfortunately they did not record the ECoG continuously for 24 h per day. We recorded the ECoG of cerveau isolé rats continuously for periods up to 3 weeks. Rats were fed through a stomach cannula. A desynchronized pattern appeared in the ECoG 2 to 4 days after transection (Fig. 1). Further continuous recording revealed that 4 to 7 days after surgery a circadian sleep-wakefulness rhythm reappeared (Figs. 1, 3). The circadian rhythm of sleep and wakefulness in the cerveau isolé rat can be eliminated by bilateral lesions of the SCN. After lesions, no circadian rhythm was observed in the forebrain ECoG.