title: Beta-endorphin: dose-dependent suppression of fixed-ratio operant behavior.
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000008:administration & dosage / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000494:pharmacology; D051381:Rats; D012055:Reinforcement Schedule; D013997:Time Factors
chemical_list: D004723:Endorphins; D009020:Morphine