title: In vivo evidence of partial agonist activity exerted by purported 5-hydroxytryptamine antagonists.
abstract: Using a food-reinforced two-lever operant method, rats (n = 9) were trained to discriminate 0.16 mg/kg LSD from saline. Tests for stimulus generalization in rats so trained indicated that the purported 5-HT antagonists cyproheptadine (1.25 and 10 mg/kg), methysergide (0.16 to 10 mg/kg) and mianserin (2.5 to 40 mg/kg) produced partial generalization with LSD. The hallucinogens mescaline (5 to 40 mg/kg) and quipazine (1.25 to 5 mg/kg) were also generalized with LSD. The data suggest that cyproheptadine, methysergide and mianserin may produce partial agonist effects in addition to their antagonist action at central 5-HT receptor sites.
mesh_terms: D000818:Animals; D003533:Cyproheptadine / Q000494:pharmacology; D005795:Generalization, Stimulus / Q000187:drug effects; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008635:Mescaline / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D008803:Mianserin / Q000494:pharmacology; D011287:Prejudice / Q000187:drug effects*; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D012701:Serotonin / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology*
chemical_list: D012702:Serotonin Antagonists; D008803:Mianserin; D003533:Cyproheptadine; D012701:Serotonin; D011814:Quipazine; D008238:Lysergic Acid Diethylamide; D008635:Mescaline; D008784:Methysergide