Effects of ephedrine enantiomers on conditioned taste aversion and kaolin intake in rats

The ephedrine (EPH) enantiomers, (-)-EPH and (+)-EPH, have different biolog ical activity in the rat, with the (-)-EPH enantiomer exerting a greater im pact on suppression of feeding, induction of locomotion, and activation of brown adipose tissue thermogenesis. Recent studies document that (-)-EPH tr eatment produces an alteration of extracellular dopamine in the brain, an e ffect that is consistent with the locomotor-stimulating and reinforcing eff ects of this drug. Whether the EPH enantiomers exert aversive actions in th e rat is unknown. Experiment 1 examined the impact of systemically administ ered (+)-EPH (0, 5, 10, or 20 mg/kg) or (-)-EPH (0, 5, 10, or 20 mg/kg) on conditioned taste aversion (CTA) in adult male rats relative to the effect of 32 mg/kg lithium chloride (LiCl). No dose of either enantiomer produced CTA, whereas strong CTA was evident for LiCl. In Experiment 2, consumption of kaolin (a nonnutritive clay) over a 24-h period was used to assess drug toxicity. Rats treated with either 0, 5, 10, 20, or 40 mg/kg (+)-EPH or 0, 5, 10, 20, or 40 mg/kg (-)-EPH did not exhibit alteration of kaolin intake. In contrast, systematic increases in kaolin intake were observed in rats a fter systemic administration of LiCl (0, 16, 32, 64, and 96 mg/kg). These f indings suggest that the enantiomers of EPH do not exert aversive effects a t behaviorally relevant doses. (C) 1999 Elsevier Science Inc.