This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many polydrug abusers self-administer combinations of cocaine and heroin, commonly known as a speedball. Heroin is thought to enhance the behavioral effects of cocaine through a mu opioid receptor mechanism. To further evaluate the role of mu receptors in opioid-induced enhancement of the behavioral effects of cocaine, this subproject investigated the modulation of cocaine self-administration by etonitazene, a potent putative mu-1 receptor agonist. When combined with cocaine, doses of etonitazene that did not maintain self-administration resulted in a leftward shift in the cocaine dose-response curve. Pretreatment with the putative mu-1 receptor antagonist naloxonazine did not attenuate etonitazene-induced enhancement of cocaine self-administration when administered at 1 h or 24 h prior to the self-administration session.
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