The effects of cholinergic and serotoninergic drugs on motility in vitro of Haplometra cylindracea (Trematoda: Digenea).

The spontaneous activity of the somatic muscle of the amphibian lung fluke, Haplometra cylindracea has been recorded in vitro, using an isometric force transducer system. Normal movement consisted of a continuous series of regular contractions which were maintained for over 4 h. Acetylcholine (ACh) inhibited motility at a concentration of 1 X 10(-3)M induced a flaccid paralysis. A similar response occurred with the cholinomimetric drugs, carbachol and nicotine, although in these instances the inhibition was less easily reversed by washing with frog Ringer. The inhibitory effect of ACh was blocked by d-tubocurarine but not by atropine. Serotonin (5-HT) caused an increase in the frequency and amplitude of contractions and the effect was blocked by methysergide. No uniform response was observed with 3-hydroxytryptamine (3-HT), but both reserpine and fluoxetine inhibited worm movement. Results suggest that the somatic musculature of the worm is controlled, at least in part, by an inhibitory cholinergic and an excitatory serotoninergic system.