Intravenous self-administration of etonitazene, cocaine and phencyclidine in rats during food deprivation and satiation

Lever-pressing responses of rats resulted in i.v. injections of etonitazene, cocaine or phencyclidine under conditions of continuous access (session length was defined as 24 hr). Rats with access to etonitazene (10 μg/kg) or cocaine (0.2 mg/kg) infusions were food-satiated until responding stabilized. Subsequently, they were food-satiated (S) or -deprived (D) according to the following sequence for 12 sessions: S, S, D, S, S, D, S, S, D, S, S, S. The number of responses was nearly twice as high during deprivation sessions as during satiation sessions. Drug intake increased from about 0.045 to 0.075 mg/kg/hr for etonitazene and from about 0.8 to 2.2 mg/kg/hr for cocaine. Of six rats with access to phencyclidine (0.125 mg/kg) only 3 responded while food-satiated. When these 3 were exposed to a satiation-deprivation sequence (S, S, D, S, S), their infusion rates also increased 2-fold during deprivation (0.28-0.6 mg/kg/hr). The remaining 3 rats were given a different sequence (D, S, D, S, D, S, D, S) and they showed substantial responding only while deprived (approximately 0.50 mg/kg/hr). For all groups, increases in deprivation-induced responding began about 8 hr into the session. A saline control group with no drug experience had low response rates that did not increase during repeated cycles of deprivation (S, S, D, S, S, S, S, D, S, S). Another control group had access to cocaine (0.1 mg/kg) for 1 to 3 sessions (until they received more than 100 infusions per 24 hr). They were subsequently given access to saline and their behavior was allowed to stabilize. Under food satiation and deprivation (S, S, D, S, S, D, S, S, D, S, S, S), they did not increase responding as a result of food deprivation. Food deprivation specifically increased i.v. self-administration of etonitazene, cocaine and phencyclidine.