Mesencephalic Reticular Activating System and Cortical Acetylcholine Output

THERE is a great deal of indirect evidence 1,2 for the participation of cholinergic pathways in the electroencephalographic (EEG) arousal response. Parasympathomimetic agents, including acetylcholine (ACh) and cholinesterase inhibitors, cause EEG desynchronization similar to the EEG changes accompanying behavioural arousal or the stimulation of the mesencephalic reticular formation. Furthermore, atropine blocks EEG desynchronization produced by the above methods. Mitchell 3 has reported that stimulation of specific afferent pathways leading to the somatosensory cortex caused an increased release of ACh from this area. Using similar techniques we investigated the effect of mesencephalic reticular formation stimulation on cortical ACh output.