Antagonism of morphine analgesia by intracerebroventricular naloxonazine

Donald A. Simone, Richard J. Bodnar, Thomas Portzline, Gavril W. Pasternak

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13 Scopus citations


Intravenous pretreatment with naloxonazine, an irreversible and selective antagonist of mu-1 sites for over 24 hr, reduces analgesia induced by morphine as well as a series of opiates and enkephalins. The present study evaluated whether intracerebroventricular (ICV) administration of naloxonazine produces similar long-term (24 hr) reductions in morphine analgesia on the tail-flick and jump tests. Naloxonazine failed to alter baseline tail-flick latencies or jump thresholds, but antagonized in a dose-dependent manner morphine analgesia for 24 hr. Naloxone had no effect at 24 hr. Morphine actions in the jump test were quite sensitive to doses of naloxonazine as low as 1 μg/rat. Although tail-flick assays also revealed naloxonazine effects, far greater doses (30 μg/rat) were needed. Naloxonazine also shifted full morphine dose-response curves to the right. Again, naloxonazine antagonized morphine in the jump test more effectively than in the tail-flick assay. These data provide support for the involvement of the mu-1 opioid binding site in the central mediation of morphine analgesia and point out the differing sensitivities of two analgesiometric assay systems to naloxonazine.

Original languageEnglish (US)
Pages (from-to)1721-1727
Number of pages7
JournalPharmacology, Biochemistry and Behavior
Issue number6
StatePublished - Jun 1986
Externally publishedYes

Bibliographical note

Funding Information:
We thank Drs. J. Posner and W. Shapiro for their support. This research was supported in part by grants from PSC/CUNY (6-64187 and 6-65193) to R.J.B., and grants from NIDA (DA02615) and the American Cancer Society (PDT169) and a core grant from the NCI (CA08748) to MSKCC. We thank Pennick Laboratories for their gift of morphine sulfate and Endo Laboratories for their gift of naloxone.


  • Jump test
  • Morphine analgesia
  • Naloxonazine
  • Rats
  • Tail-flick test


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