Inhibitory effects of ginseng total saponin on nicotine-induced hyperactivity, reverse tolerance and dopamine receptor supersensitivity

Abstract

A single administration of a low dose of nicotine produced hyperactivity in mice. A repeated administration of nicotine developed reverse tolerance to the ambulation-accelerating activity of nicotine and also developed postsynaptic dopamine (DA) receptor supersensitivity. The development of reverse tolerance was evidenced by an increased ambulatory response to nicotine, and the development of postsynaptic DA receptor supersensitivity was evidenced by the enhanced response in ambulatory activity to apomorphine, a DA receptor agonist. Administration of ginseng total saponin (GTS) prior to and during the nicotine treatment in mice inhibited not only nicotine-induced hyperactivity and reverse tolerance, but also postsynaptic DA receptor supersensitivity in nicotine-induced reverse tolerant mice. These results suggest that inhibition by GTS of nicotine-induced hyperactivity and reverse tolerance may be closely related with the inhibition of the dopaminergic activation induced by nicotine and that the development of nicotine-induced reverse tolerance may be associated with enhanced DA receptor sensitivity.