Pairing pentobarbital with one toxin causes it to attenuate taste aversions produced by a different toxin: implications for conditioned antisickness theory.

Normally, if pentobarbital and then a toxin are injected after a rat drinks saccharin solution, a taste aversion produced by the pentobarbital summates with that produced by the toxin. An opposite effect is obtained after a preconditioning series in which pentobarbital is injected prior to a toxic dose of lithium or amphetamine in the absence of saccharin drinking: The pentobarbital attenuates the saccharin aversion normally produced by the toxin. Lett (1983) theorized that a conditioned antisickness response (CAR) to pentobarbital is responsible for this conditioned attenuation of saccharin aversion. It is reported here that this attenuation of taste aversion occurs even if the toxin paired with pentobarbital is different from the toxin used during saccharin aversion conditioning. Preconditioning pentobarbital with a high dose of amphetamine allows it to attenuate saccharin aversions produced by lithium and by gamma radiation (as well as by amphetamine itself). Preconditioning pentobarbital with a high dose of lithium allows it to attenuate aversions produced by amphetamine, gamma radiation, cisplatin, mechlorethamine, dactinomycin, and doxorubicin (as well as by lithium itself). This means that the CAR cannot be due to conditioned amelioration of specific effects of specific toxins (which would not be effective if the toxin were changed) and suggests a central alleviation of nausea, perhaps like the alleviation of pain by endogenous opiates. However, aversions produced by intraperitoneal copper sulfate were not attenuated by lithium-conditioned pentobarbital.