Nucleus basalis magnocellularis and pedunculopontine tegmental nucleus: control of the slow EEG waves in rats

Certain human disorders, which are characterized by learning and memory disturbances, are also accompanied by synchronizations of the cortical electroencephalogram (EEG). Although the EEG synchronization was casually related to the degeneration of the cholinergic basal forebrain, degenerations were found also in the cholinergic pontomesencephalic tegmentum. The present study was carried out to prove whether lesions of rat's pedunculopontine tegmental nucleus (PPTg) may cause EEG synchronizations like lesions of the basal forebrain. The effects of the unilateral ibotenic acid lesions of the nucleus basalis magnocellularis (NBM) and of the PPTg on the frontal and occipital EEG were compared in different behavioural states. The NBM lesion caused unilateral spectral power increases of all frequencies up to 20 Hz in the frontal EEG that were stronger with increased arousal level. Additionally, synchronized spike and wave discharges appeared in the frontal EEG. The NBM may suppress especially the delta EEG waves in the frontal motor cortex during motor active behaviours. The PPTg lesion caused unilateral suppressions of the occipital theta rhythm during exploratoring sniffing. During grooming the power of the frontal delta waves were elevated. Furthermore, the PPTg lesion caused a suppression of slow sleep waves. The results may indicate that a degeneration of both brain regions may change differently the power of the cortical slow EEG waves.