title: Development of tolerance to the effects of morphine: association between analgesia and electrical activity in the periaqueductal gray matter.
mesh_terms: D000698:Analgesia; D000818:Animals; D001933:Brain Stem / Q000187:drug effects / Q000502:physiology*; D004361:Drug Tolerance; D004553:Electric Conductivity; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D051381:Rats
chemical_list: D009020:Morphine