TRYPTAMINERGIC AND DOPAMINERGIC RESPONSES OF SCHISTOSOMA MANSONI

¹ Department of Pathobiology, School of Hygiene and Public Health and Department of Pharmacology and Experimental Therapeutics, School of Medicine, The Johns Hopkins University, Baltimore, Maryland

Pharmacological evidence is reported indicating that 5-hydroxytryptamine is an excitatory neurotransmitter in Schistosoma manasoni. The stimulation of the motor activity of adult schistosomes brought about by cholinergic blockade is abolished 1) by bromlysergic acid diethylamide and other 5-hydroxytryptamine antagonists and 2) by prior 5-hydroxytryptamine depletion brought about by exposure of the parasites to chlorimipramine and reserpine. Whereas catecholamines have no effect on the motor activity of schistosomes, low concentrations of dopamine, norepinephrine and epinephrine (but not isoproterenol) produce a lengthening response of the worm which is ascribed to a relaxation of the longitudinal musculature. The same response was induced by apomorphine, considered to be a specific dopamine receptor agonist, but not by clonidine, a specific norepinephrine receptor agonist. Apomorphine and dopamine were more potent in this respect than norepinephrine and epinephrine. These effects are blocked more effectively by dopamine-blocking agents than by alpha and beta adrenergic blockers. Male worms from single-sex infections differed in their lengthening response from males paired with females.