Abstract
The effects of eptazocine on spontaneous movements in mice were investigated by using a multi-dimensional behavioral analyzer (Animex II) in comparison with those of pentazocine and morphine. Eptazocine at 20, 40 and 80 mg/kg increased the spontaneous movements in a dose-dependent fashion. On the contrary, the spontaneous movements in mice were significantly decreased by pentazocine in the same dose range. On the other hand, morphine produced biphasic effects: 20 mg/kg morphine inhibited the spontaneous movements, but it potentiated them at doses of 40 and 80 mg/kg. The effects of these three drugs on the spontaneous movements were antagonized by naloxone. The effects of pentazocine and morphine on the spontaneous movements were modified by the successive administration of these drugs, but not by eptazocine administration. The eptazocine-induced hyperactive movements were potentiated by apomorphine and were inhibited by haloperidol, α-methyl-ρ-tyrosine and disulfiram. On the contrary, the inhibitory effects of pentazocine on the spontaneous movements were antagonized by apomorphine. On the other hand, the inhibitory effects of 20 mg/kg morphine on the spontaneous movements were also inhibited by apomorphine and haloperidol. These results suggest that the pharmacological effects of eptazocine on the spontaneous movements in mice are different from those of pentazocine and morphine. The effects of eptazocine may be mediated by opiate receptors and catecholaminergic neurons, but the potency of eptazocine to induce tolerance is less than pentazocine and morphine.
