Specific contributions of the basal forebrain corticopetal cholinergic system to electroencephalographic activity and sleep/waking behaviour

The present study examined the role of the basal forebrain corticopetal cholinergic projection in the regulation of cortical electroencephalographic activity across sleep/wake states in rats. Selective lesions of this projection were effected by local intraparenchymal infusions of the immunotoxin 192 IgG-saporin. Lesions spared the septo-hippocampal cholinergic system, as well as p75-receptor-bearing noncholinergic neurons in the suprachiasmatic nucleus. Relative to sham-lesioned control animals, rats with lesions of basal forebrain cholinergic neurons displayed a significant reduction in high frequency EEG activity, characterized especially by a reduction in gamma EEG power. Lesions did not significantly alter the overall proportion of sleeping and waking states as defined behaviourally, but the attenuation of high frequency EEG activity was apparent across all stages, including REM-like periods. Results are consistent with the view that the basal forebrain corticopetal cholinergic system exerts a general activational effect on the cortical mantle. Although this system may not be essential for sleep/wake stage-switching, it does impact on the cortical states associated with those stages.