Intragastric self-administration in rhesus monkeys under limited access conditions: methodological studies.

Rhesus monkeys were trained to self-administer psychoactive drugs by the intragastric route of administration under limited access conditions and intermittent schedules of drug delivery. Under a fixed-ratio 10 schedule, pentobarbital, diazepam, and cocaine maintained self-administration in some monkeys. Responding was not maintained by d-amphetamine under these conditions. Under fixed-ratio 10 (timeout 2 min) conditions, cocaine maintained self-administration in all animals (5/5) tested, while pentobarbital maintained responding in 2/3. At doses higher than that which maintained maximal rates, responding was inversely related to dose/injection. Drug intake was relatively constant across dose/injection of cocaine, but was a direct function of dose/injection of pentobarbital and diazepam. The procedure may be useful in assessing behavioral and pharmacological variables controlling oral self-administration of drugs.