The effects of naftidrofuryl oxalate on cycloheximide- and 5-hydroxytryptophan (5-HTP)-induced amnesia were investigated using a passive avoidance task in mice. Naftidrofuryl oxalate significantly improved the cycloheximide-induced amnesia. This effect of naftidrofuryl oxalate was antagonized by 5-HTP, a serotonin (5-HT) precursor, and by p-chloroamphetamine (PCA), a 5-HT releaser. Single administration of 5-HTP in combination with pargyline, a monoamine oxidase inhibitor, induced amnesia (5-HTP-induced amnesia). This amnesia was attenuated by ritanserin, a 5-HT2-selective antagonist, but not by pindolol a 5-HT1-selective antagonist. Naftidrofuryl oxalate also attenuated the 5-HTP-induced amnesia. A binding study reveaied that naftidrofuryl oxalate inhibited the binding of [3H]ketanserin to 5-HT2 receptors in mouse brain synaptic membrane in a dose-dependent fashion (IC50 = 1.42 × 10-7 M), but did not inhibit that of [3H]serotonin to 5-HT1 receptors. These resu suggest that naftidrofuryl oxalate may attenuate cycloheximide- and 5-HTP-induced amnesia by blocking 5-HT2 receptor subtypes.
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