Effect of Ginseng Total Saponin on Extracellular Dopamine Release Elicited by Local Infusion of Nicotine into the Striatum of Freely Moving Rats

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Abstract
We investigated the effect of ginseng total saponin (GTS) on nicotine-induced dopamine (DA) release in the striatum of freely moving rats using an in vivo microdialysis technique. In order to further characterize the mechanism by which GTS affects DA release, the effect of GTS on K+-induced DA release was also examined. Local infusion of nicotine (1, 5, and 10 mM) into the striatum produced a dose-dependent increase in extracellular DA in dialysate samples (maximal response = 154.0 ± 10.8 %, 308.1 ± 55.7 %, and 499.9 ± 77.9 % over basal levels, respectively). GTS (100 mg/kg i.p.) had no effect on basal levels of extracellular DA. However, GTS inhibited maximal DA release induced by intra-striatal infusion of nicotine (1, 5, and 10 mM) by 35.3 %, 36.6 %, and 58.5 %, respectively. Intra-striatal infusion of high K+ solution (100 mM) produced an increase in extracellular DA in the striatum (maximal response = 796.6 ± 98.8 % over basal levels). However, GTS had no effect on the K+-induced increase in extracellular DA. The present study demonstrated that GTS inhibited striatal DA release stimulated by local infusion of nicotine. This may reflect the blocking effect of GTS on the striatum-related behavior induced by nicotine as well as other psychostimulants. The results also suggest that GTS may act on presynaptic nicotinic acetylcholine receptors or receptor-operated Na+ channels in dopaminergic nerve terminals, but not on voltage-sensitive ion channels.

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