BIOGENIC MONOAMINES IN THE FRESH-WATER SNAIL, BIOMPHALARIA-GLABRATA -INFLUENCE OF INFECTION BY THE HUMAN BLOOD FLUKE, SCHISTOSOMA-MANSONI

The biogenic monoamines, serotonin (5-HT), dopamine (DA) and L-dopa we re measured using high performance liquid chromatography with electroc hemical detection (HPLC-ED) in the extracts of the central nervous sys tem (CNS) and plasma of uninfected freshwater snails, Biomphalaria gla brata, and in snails at 7, 14, 21 and 28 days postexposure (PE) to the miracidia of the human blood fluke, Schistosoma mansoni. Relative to age-matched uninfected snails, a general depression of biogenic amine levels was observed in the plasma (cell-free haemolymph) and the CNS o f infected snails, especially during the latter phase of the prepatenc y period. Significant decreases were first observed in the CNS of infe cted snails beginning at Day 14 PE for DA and 5-HT and Day 21 PE for L -dopa. Parasite-exposed snails also exhibited an early and persistent suppression of plasma 5-HT concentrations, starting at 7 days PE and c ontinuing throughout the infection test period. In order to determine the effect of 5-HT on reproduction and, thereby, establish a possible relationship between the observed parasite-induced reduction in 5-HT l evels and parasitic castration, the effect of exogenous 5-HT on indivi dual infected and uninfected B. glabrata was investigated. Repeated tr eatment with 10 mu M 5-HT promoted both ovulation and oviposition in B . glabrata. Snails treated with 5-HT consistently layed more eggs than did sham-treated controls. Infected snails chat were treated with 5-H T exhibited similar egg-laying rates as those of both serotonin treate d and untreated, uninfected snail groups, thus reversing the castratin g effects of larval infection, These findings suggest that 5-HT acts a s a stimulant for egg production in B. glabrata, and that parasitic ca stration may be due, at least in part, to larval-induced suppression o f 5-HT in the snail's CNS and plasma during the course of infection wi th S. mansoni.