title: Morphine: conditioned increases in self-administration in rhesus monkeys.
abstract: Operant responding in three monkeys was maintained by intravenous presentations of morphine. Nalorphine produced reliable increases in morphine-reinforced responding. With successive daily nalorphine injections there was a decreased latency of self-administration responding for morphine, and substituted saline injections produced conditioned increases in morphine-reinforced responding.
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects*; D000882:Haplorhini; D007275:Injections, Intravenous; D009020:Morphine / Q000494:pharmacology*; D009269:Nalorphine / Q000494:pharmacology; D012651:Self Medication
chemical_list: D009020:Morphine; D009269:Nalorphine