Effects of azadirachtin on the regulation of midgut peristalsis by the stomatogastric nervous system in Locusta migratoria

A single injection of azadirachtin into nymphal and adult locusts results i n a decrease of food intake but not in reduced food utilization. Feeding de terrency is correlated with a gradual inhibition of midgut peristalsis. Gut movement is under the control of the stomatogastric nervous system, especi ally the ingluvial ganglion, as demonstrated in an in vitro system. Seroton in is the most potent peristalsis-stimulating drug in vitro. Concurrent wit h the cessation of midgut peristalsis after azadirachtin injection, a deple tion of the serotoninergic cell bodies in the frontal ganglion can be obser ved. Midgut preparations which show strongly inhibited contractions due to previous azadirachtin treatment in vivo are minimally, or not at all, stimu lated in vitro by serotonin, depending on the amount of time that has elaps ed since treatment. When midgut preparations of untreated locusts are chall enged with azadirachtin in I,irm, peristalsis is suppressed in a dose-depen dent manner. Simultaneous application of azadirachtin and serotonin results in a slight stimulation of midgut peristalsis. We propose the hypothesis t hat azadirachtin interferes with the serotoninergic system of the stomatoga stric ganglia and thus inhibits midgut peristalsis. The molecular mechanism of the action of azadirachtin remains to be determined.