title: Morphine lowering of self-stimulation thresholds: lack of tolerance with long-term administration.
abstract: Rats were given increasing amounts of morphine over a period of weeks in order to achieve tolerance. Doses of the drug which initially reduced the threshold for self-stimulation behavior continued to do so after long-term administration. These results demonstrate a persistent central effect of morphine which may be related to the opiate "high."
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D012653:Self Stimulation / Q000187:drug effects*; D013997:Time Factors
chemical_list: D009020:Morphine