Effect of sleep deprivation on multi-unit discharge activity of basal forebrain

The basal forebrain (BF) is an important wakefulness/arousal-promoting structure involved in homeostatic responses to sleep deprivation (SD). However, the effects of SD and subsequent sleep recovery on the BF discharge have not been investigated. Multi-unit BF activity was recorded on freely moving rats during 8 h of baseline (BL) and, on the following day, during 4 h of SD by gentle handling followed by 4 h of recovery. The effect of SD on the waking discharge was evaluated during the last 10 min of each hour when attentive waking was induced. The wakefulness level was defined based on the ratio between theta and delta electroencephalogram (EEG) powers, and epochs with ratios >or=1 but <2 (T/D-1) and >or=2 but <4 (T/D-2) were analysed separately. During T/D-1 wakefulness, the BF multi-unit discharge rate increased significantly during the second and third hours of SD and decreased during the third hour of recovery when compared with corresponding hours of BL. Non-rapid eye movement sleep discharge rate during recovery decreased significantly in the second and third versus the first and last hours. The results suggest that maintenance of the level of vigilance necessary for adequate performance during SD requires increased activation of BF neurones when compared with the BL, whereas the same level of vigilance after several hours of recovery can be maintained with lesser activation of BF neurones.