Involvement of NMDA receptors in the analgesic properties of psychotridine.

We have previously reported that the alkaloid extract of Psychotria colorata (Willd. ex R. & S.) Muell. Arg., had marked dose-dependent, opioid-like activity. Phytochemical analyses of P. colorata flowers and leaves identified several pyrrolidinoindoline alkaloids, including psychotridine. To further investigate the activity and mechanism of action of Psychotria alkaloids, we studied the effects of psychotridine on thermal and chemical models of analgesia. In the tail-flick model, psychotridine presents a dose-dependent analgesic effect; the effect is not reversed by prior treatment with naloxone. Psychotridine dose-dependently decreased capsaicin-induced pain. Performance in the rotarod test showed that psychotridine does not induce motor deficits at doses effective in analgesia models. Psychotridine inhibited [3H]MK-801 (dizocilpine) binding to cortex membranes in a dose-dependent manner. Binding is completely abolished at 300 nM. The data rule out opioid activity, and the inhibition of capsaicin-induced pain and of radioligand binding strongly suggest the participation of NMDA receptors in psychotridine-induced analgesia.