Dishabituating effects of an ACTH 4-9 analog in a vigilance task.

Ten male adults were tested in a vigilance task after oral administration of either 40 mg ACTH 4-9 analog, ORG 2766, or placebo in a single three hour session. EEG spectra, averaged auditory evoked responses, heart rate and blood pressure, and behavioral performance were measured during a vigilance task. ACTH 4-9 analog treatment led to a decreased inhibition of the central nervous system across the experiment: to less mean power density and faster center frequencies within the alpha band, and to less attenuated amplitudes of the components of the auditory vertex potential (P50, N100, P200). Treatment effects increased towards the end of the session and might indicate a dishabituating effect, probably due to suppression of inhibitory influences of limbic structures on mesencephalic reticular activity.