Schistosoma mansoni: effects of serotonin and serotonin receptor antagonists on motility and length of primary sporocysts in vitro

The effects of serotonin (5-hydroxytryptamine; 5-HT) on in vitro transforme d primary sporocysts of Schistosoma mansoni were investigated. Serotonin tr eatment significantly increased parasite motility (percentage of motile spo rocysts) and length at concentrations as low as 1 mu M. These effects were mimicked by the 5-HT agonist tryptamine, albeit with 10- to 100-fold less p otency, The effects of 10 mu M 5-HT on sporocyst motility were observed wit hin 15 min posttreatment and on parasite length by 6 h posttreatment, and b oth effects were stable for up to 48 h, Receptor antagonists with varying a ffinities for defined vertebrate neurotransmitter receptor subtypes were ex amined for their effects on parasite behavior in the absence and presence o f 10 mu M 5-HT. In the absence of 5-HT, only methiothepin significantly inh ibited normal parasite growth after 48 h of incubation. In the presence of 10 mu M 5-HT. the serotonin receptor antagonists mianserin, ketanserin (bot h at 100 mu M), and methiothepin (at 10 mu M) significantly inhibited 5-HT- induced lengthening of primary sporocysts, while 3-tropanyl-indole-3-carbox ylate and chlorpromazine had no significant effect. The effects of these sa me drugs on parasite motility were also examined. In the absence of 5-HT, 1 0 mu M chlorpromazine increased parasite motility, while the other antagoni sts had no effect. When sporocysts were treated with 10 mu M 5-HT for 2 h i n the continued presence of antagonist, 100 mu M mianserin, ketanserin, 3-t ropanyl-indole-3-carboxylate, and 10 mu M methiothepin inhibited 5-HT induc ed increases in parasite motility, while 10 mu M chlorpromazine had no effe ct. These results show that primary sporocysts of S. mansoni exhibit behavi oral responses to serotonin much like adult stages of this parasite. Furthe rmore, these responses appear to be mediated via receptors with pharmacolog ical similarities to those previously described in adult worms. (C) 2000 Ac ademic Press.