TV-Methyl lycaconitine is the most effective low molecular weight antagonist reported for an insect neuronal nicotinic receptor. In the present study, the citrate salt of this neurotoxin from the plant Delphinium brownii was found to inhibit [H]-o^bungarotoxin binding to nerve cord extracts of the cockroach Periplaneta americana with a K, of l^x lO^ 'mol l" 1 . At a concentration of 1-Oxl0~moll...