Technical Abstract: Piperidine and pyridine alkaloids are found in many species of plants including Lobelia spp., Conium spp., Nicotiana spp., and Lupinus spp. Some of these alkaloids cause multiple congenital contracture deformities (MCC) and cleft palates in cattle, pigs, sheep, and goats. The mechanism behind MCC defect formation in livestock is thought to be the inhibition of fetal movement due to stimulation followed by desensitization of fetal muscle-type nAChR. A pharmacodynamic comparison of piperidine and pyridine alkaloids was made in TE-671 cells that express fetal muscle-type nAChR. TE-671 cells were cultured in DMEM supplemented with fetal bovine serum and penicillin/streptomycin. The membrane depolarization responses were measured by changes in fluorescence of a membrane potential-sensitive dye. Alkaloids with a carbon side-chain of at least three carbons or larger attached to the carbon alpha to the piperidine nitrogen were more potent and effective. The presence of a double bond adjacent to the nitrogen of the piperidine or pyridine ring increased potency. The rank order of potency was: anabasine > nicotine > coniine > lobeline > myosmine > ammodendrine. This research supported by ARS-USDA.