Heroin and morphine: aversive and analgesic effects in rats.

Although a number of studies demonstrate morphine-induced taste aversions, no such reports exist for heroin. In a conventional taste aversion paradigm, rats were injected with one of six heroin doses (0.5-12.0 mg/kg) after consuming a novel saccharin solution (Experiment 1). When the saccharin was reintroduced a second time no significant reduction in consumption occurred at any of the doses tested. It was therefore concluded that heroin does not readily induce a taste aversion. In Experiment 2, morphine was tested in an identical taste aversion paradigm and, as expected, a significant taste aversion did result at two of the doses tested. Experiment 3 demonstrated that heroin produced analgesia equal to or greater than morphine when comparing dosages of heroin which failed to induce a CTA with CTA-inducing morphine dosages. Thus, whereas heroin is more potent than morphine as an analgesic, heroin is less potent than morphine as a CTA-inducing agent.