EFFECTS OF (-)-EPHEDRINE ON LOCOMOTION, FEEDING, AND NUCLEUS-ACCUMBENS DOPAMINE IN RATS

The intent of the present study was to determine the effects of system ic injections of the sympathomimetic agent ephedrine (EPH) on extracel lular dopamine (DA) levels within the rat nucleus accumbens (NAC) and to compare these effects with those of EPH on locomotion and on feedin g. In experiment 1, adult male rats were prepared with an indwelling 3 mm microdialysis probe positioned within the NAC. The rats were injec ted (IP) with vehicle, 5, 10, or 20 mg/kg (-)-EPH with dialysates coll ected every 20 min for 100 min after drug injection. Systemic injectio ns of 5, 10 or 20 mg/kg (-)-EPH significantly enhanced extracellular l evels of NAC DA over baseline by 79%, 130%, and 400%. Systemic injecti on of 20 mg/kg EPH significantly reduced NAC levels of DOPAC and HVA b y 37% and 31%. The effects of EPH on brain dopamine activity were ster eospecific given that an additional group of rats injected with 20 mg/ kg (+)-EPH exhibited smaller changes in NAC DA (<25%), DOPAC (<10%), a nd HVA levels (<20%) than did rats injected with 20 mg/kg (-)-EPH. In experiment 2, adult male rats were injected (IP) with 0, 5, 10, or 20 mg/kg (-)-EPH prior to placement in automated activity chambers. Total distance traveled was significantly increased by 10 and 20 mg/kg (-)- EPH, but not by 5 mg/kg (-)-EPH. In experiment 3, adult male rats were injected (IF) with 0, 2.5, 5, or 10 mg/kg (-)-EPH or with 0, 2.5, 5, or 10 mg/kg (+)-EPH prior to a 30-min feeding test. Although each EPH enantiomer decreased feeding, (-)-EPH was more potent in feeding suppr ession than was (+)-EPH. The present results suggest that EPH may alte r locomotion and feeding via an indirect action on brain dopamine acti vity.