Inhibition by Ginsenosides Rb 1 and Rg 1 of Cocaine-Induced Hyperactivity, Conditioned Place Preference, and Postsynaptic Dopamine Receptor Supersensitivity in Mice

Abstract

A single or repeated administration of cocaine (15 mg/kg) in mice produced hyperactivity and conditioned place preference (CPP). Ginsenoside Rb 1 (Rb 1) and ginsenoside Rg 1 (Rg 1), prior to and during the cocaine treatment in mice, inhibited cocaine-induced hyperactivity and CPP. The development of enhanced postsynaptic dopamine (DA) receptor sensitivity in mice displaying a cocaine-induced CPP was evidenced by the enhanced response in ambulatory activity to the DA agonist, apomorphine (2 mg/kg). Rb 1 and Rg 1 inhibited the development of postsynaptic DA receptor supersensitivity. However, Rb 1 and Rg 1 did not show any antidopaminergic activity at the postsynaptic DA receptors, because the apomorphine-induced climbing behavior was not inhibited by Rb 1 and Rg 1. Therefore, it is presumed that Rb 1 and Rg 1 modulate DA activity induced by cocaine at the presynaptic DA receptors, and this modulation results in the inhibition of postsynaptic dopaminergic activation. These results suggest that the cocaine-induced CPP may be associated with enhanced DA receptor sensitivity. The inhibition by Rb 1 and Rg 1 of cocaine-induced hyperactivity and CPP may be closely related with the inhibition of dopaminergic activation induced by cocaine at the presynaptic DA receptors.