A group of plants of interest when searching for glycine receptor antagonists are the Apocynaceae, the indole alkaloids of which appear to have glycinergic activities. Pathama et al. made the interesting observation that corymine, an indole alkaloid extracted from the leaves of a medicinal plant of Malaysia and Thailand, Hunteria zeylanica (Retz.) Gardn. & Thw. (Hunteria corymbosa Roxb, Hunteria roxburghiana sensu Ridl.), potentiates the convulsions induced by either strychnine or picrotoxin at doses of 2, 8, and 15 mg/kg in mice and inhibits glycine-induced chloride current in Xenopus oocytes non-competitively by interacting with a site different from that of 4,4'-diisoth-iocyanostilbene-2,2'-disulfonic acid, a Cl" channel blocker (69). All this evidence taken together lends considerable support to the view that monoterpenoid alkaloid-producing families of flowering plants such as Apocynaceae, Loganiaceae, and Rubi-aceae represent an exciting reservoir of potential glycinergic agents.
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