title: Effects of heroin/cocaine combinations in rats trained to discriminate heroin or cocaine from saline.
abstract: The effects of heroin and cocaine administered alone or in combination were examined in rats trained to discriminate either heroin (0.56 mg/kg i.p.; n = 6) or cocaine (5.6 mg/kg i.p.; n = 6) from saline. Heroin (0.032-1.8 mg/kg) substituted completely for the heroin training stimulus in all six heroin-trained rats, but failed to substitute for cocaine in any of the cocaine-trained rats. Cocaine (0.1-32 mg/kg) substituted completely for the cocaine training stimulus in all six cocaine-trained rats, and substituted for heroin in two of six heroin-trained rats. The opioid antagonist naltrexone (0.01-1.0 mg/kg) antagonized the discriminative stimulus effects of heroin, but naltrexone at doses up to 10 mg/kg had no effect on the discriminative stimulus effects of cocaine. The dopamine receptor antagonist flupenthixol (0.032-0.56 mg/kg) attenuated the discriminative stimulus effects of heroin and completely blocked the discriminative stimulus effects of cocaine. When heroin-cocaine combinations were administered to the heroin-trained rats, cocaine (1-5.6 mg/kg) did not significantly alter the mean heroin dose-effect curve. Similarly, in the cocaine-trained rats, heroin (0.1-0.56 mg/kg) did not significantly alter the mean cocaine dose-effect curve. These results suggest that combinations of heroin and cocaine usually produce discriminative stimulus effects similar to either heroin or cocaine alone.
authors.affiliation: Alcohol and Drug Abuse Research Center, McLean Hospital, Harvard Medical School, Belmont, MA 01278, USA.
authors.forename: X
authors.initials: X
authors.lastname: Lamas
authors.forename: S S
authors.initials: SS
authors.lastname: Negus
authors.forename: M B
authors.initials: MB
authors.lastname: Gatch
authors.forename: N K
authors.initials: NK
authors.lastname: Mello
mesh_terms: D000818:Animals; D003042:Cocaine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004193:Discrimination Learning / Q000187:drug effects; D004192:Discrimination, Psychological / Q000187:drug effects*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004347:Drug Interactions; D005475:Flupenthixol / Q000494:pharmacology; D003932:Heroin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D018492:Dopamine Antagonists; D004338:Drug Combinations; D009292:Narcotic Antagonists; D009294:Narcotics; D003932:Heroin; D005475:Flupenthixol; D003042:Cocaine