BEHAVIORAL AND CELLULAR EFFECTS OF SEROTONIN ON LOCOMOTION AND MALE MATING POSTURE IN ASCARIS-SUUM (NEMATODA)

The site and mode of action of serotonin on locomotion were investigat ed in the parasitic nematode Ascaris suum. Injection of serotonin into Ascaris immediately caused paralysis in animals that were generating locomotory waveforms. Injected serotonin also increased body length an d decreased the number of propagating body waves. Similar injections i nto the male tail produced a ventral tail curl. Injection of N-acetyl- serotonin had no effect on the generation of locomotory waveforms, but increased the body length and decreased the number of body waves in t he waveform. Other biogenic amines were also tested but were much less potent. Serotonin decreased the amplitude of a submaximal acetylcholi ne-induced muscle contraction and increased the time to attain this co ntraction. The time course of this effect on the response to ACh was m uch slower than the action of injected serotonin on locomotory wavefor ms, suggesting that additional elements are involved in the action of serotonin on locomotory behavior. Serotonin abolished spontaneous slow potentials in VI motor neurons and decreased the frequency of EPSPs i n DE2 motorneurons, probably by a pre-synaptic mechanism. In the male tail, serotonin depolarized the male-specific transverse ventral muscl e cells, but did not affect either dorsal or ventral longitudinal musc le cells.