Effects of an ACTH 4--9 related peptide upon intracranial self stimulation and general activity in the rat.

Adult male Sprague-Dawley rats were stereotactically implanted with electrodes within the anterior medial forebrain bundle. The rats were trained to respond for intracranial self-stimulation (ICS) and treated with control solution or varying doses of an ACTH 4--9 related synthetic peptide (Org 2766; H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH). The drug affected ICS as measured in overnight response records, with the highest dose reliably increasing the amount of responding. In a second experiment rats were similarly treated and general activity was assessed. No remarkable changes in activity were present at any tested dose. The findings corroborate previous reports suggesting ACTH-related peptides may be active in a variety of motivated tasks, but less active with respect to general activity.