Effects of heroin/cocaine combinations in rats trained to discriminate heroin or cocaine from saline

Xavier Lamas, S. Stevens Negus, Michael B. Gatch, Nancy K. Mello

Research output: Contribution to journalArticlepeer-review

29 Scopus citations

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 IP; n = 6) or cocaine (5.6 mg/kg IP; 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.

Original languageEnglish
Pages (from-to)357-364
Number of pages8
JournalPharmacology Biochemistry and Behavior
Volume60
Issue number2
DOIs
StatePublished - Jun 1998

Keywords

  • Cocaine
  • Drug discrimination
  • Heroin
  • Rats

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