ORAL SELF-ADMINISTRATION OF ETONITAZENE IN RHESUS-MONKEYS - USE OF A FADING PROCEDURE TO ESTABLISH ETONITAZENE AS A REINFORCER

The establishment of orally delivered etonitazene (a potent opioid) as a reinforcer, was studied in eight rhesus monkeys. Initially, when gi ven concurrent access to 2.5 mu g/ml etonitazene and the water vehicle , five of the monkeys rejected the drug, whereas the other three monke ys consumed more drug solution than water. The five monkeys that rejec ted the drug solution underwent an acquisition phase to establish the drug as a reinforcer. A fading procedure was used to transfer control of responding from a 2% (wt/vol) ethanol solution to a 2.5 mu g/ml eto nitazene solution. Initially, responding was maintained by contingent deliveries of 2% ethanol. Next, across blocks of six or more sessions, increasing amounts of etonitazene were added in steps to the 2% ethan ol solution. Subsequently, the 2% ethanol solution was decreased in st eps to zero, leaving only the 2.5 mu g/ml etonitazene present. When th e fading procedure was completed, dose of etonitazene was varied by in creasing the volume delivered, first under fixed ratio (FR 4) and then under an FR 8 reinforcement schedule. The same dose manipulations wer e made with the three monkeys who did not undergo the fading procedure because they preferred etonitazene over water when first tested. Eton itazene was established as a reinforcer for six of the eight monkeys b ecause drug deliveries exceeded vehicle deliveries across a range of d rug doses.