MAO-A and -B inhibitors selectivity alter Xenopus mucus-induced behaviors of snakes

Abstract

Skin mucus of the frog Xenopus laevis, contacted orally by snakes, induces dyskinetic oral movements and climbing behavior that promote escape. The mucus contains peptides and indoleamines known to produce drug-induced movement disorders in other species. We hypothesized that inhibition of monoamine oxidase-A (MAO-A) by N-methyl- N-propargyl-3-(2,4-dichlorophenoxy)-propylamine [clorgyline (CLG)] and MAO-B by R(-)-N,a- Dimethyl-N-2- propynyl-benzeneethanam ine [ L-deprenyl (LDL) ] would selectively modify mucus-induced behaviors by elevating norepinephrine and serotonin (with CLG), phenylethylamine (with LDL), or dopamine (with both drugs). In Experiment 1 (EXP1), adult snakes received mucus and/or 20 μg/g (IP) of both drugs. In EXP2, juveniles received mucus and/or 5, 10, and 20 μg CLG or LDL. CLG given alone had no effect on tongue flicking, activity, and climbing (EXP1,2). LDL alone decreased tongue flicking in EXP2 and increased climbing (EXP1,2). Given with mucus, both drugs further lowered the tongue flicking rates attenuated by mucus (EXP1,2); only LDL potentiated mucus-induced climbing. Yawning was the only mucus-induced dyskinesia attenuated (20 μg CLG, adults; 20 μg LDL, juveniles). We suggest that dopamine and/or phenylethylamine, the substrates for MAO-B, may promote mucus-induced climbing and tongue flicking but may have some protective role against mucus-induced yawning in water snakes.