Sensitization of anorexia and locomotion induced by chronic administrationof ephedrine in rats

Repeated daily administration of the sympathomimetic agent ephedrine (EPH) leads to an augmentation (sensitization) of locomotor activity in rats. The present experiments examined the impact of repeated administration of the (-)- and (+)-EPH enantiomers on feeding in rats to assess whether the anore xic activity of EPH exhibits tolerance or sensitization during chronic expo sure and whether the time course of these effects follows that observed in studies of locomotion. Adult male rats were injected once daily for 12 days with either vehicle or 5, 10 or 20 mg/kg (-)EPH or with 10 or 20 mg/kg (+) -EPH. Horizontal locomotion and diet consumption were assessed for 60 min i n an activity chamber. Suppression of feeding and the induction of locomoti on were augmented over the first four days of administration of either 10 m g/kg or 20 mg/kg of the (-)-EPH enantiomer. In contrast, repeated administr ation of 20 mg/kg (+)-EPH resulted in augmentation of appetite suppression but not locomotion. These results confirm and extend the phenomenon of loco motor and feeding sensitization for ephedrine, but suggest that these effec ts may differ for the two enantiomers of ephedrine.