Thyrotropin-releasing hormone (TRH) potentiates pentobarbital-based flavor aversion learning

Thyrotropin-releasing hormone (TRH), a hypothalamic polypeptide, will antagonize some of pentobarbital's major effects (sleep time and hypothermia) in rodents when administered in low doses (1-10 mg/kg). At higher doses (30 and 100 mg/kg), TRH has been shown to increase the lethality of high doses of pentobarbital in mice. The present experiments demonstrated that 10 mg/kg of TRH will potentiate the conditioned flavor aversion normally induced in rats by 20 mg/kg of pentobarbital, suggesting that the TRH-pentobarbital combination may have sublethal toxic effects even at low doses of both substances. Furthermore, this result suggests that the mechanism whereby pentobarbital produces a flavor aversion is independent of the drug's hypothermic and sleep-inducing effects.