Monoamines and their metabolites in the freshwater snail Biomphalaria glabrata

Metabolism of the major monoamines and their functions were studied in the freshwater snail Biomphalaria glabrata. In both juvenile and adult snails, the plasma (cell-free hemolymph) appears to act as a reservoir for most of these monoamines and their metabolites including among others, L-dopa and dopamine as major constituents. Significant quantities of L-tryptophan, precursor of indoleamines, also was found in the plasma. L-dopa, serotonin, homovanillic acid and dopamine were prominently represented in the central nervous system of the snail, while serotonin and its metabolites, 5-hydroxyindole acetic acid and 5-hydroxytryptophol were found in the ovotestis. Catecholamines such as L-dopa, dopamine and homovanillic acid were identified in the albumen gland. Functional aspects of both dopamine and serotonin were studied using in vitro cultures of albumen glands, the site of perivitelline fluid and galactogen synthesis in B. glabrata. Dopamine was found to stimulate the release of secretory proteins when exogenously added to gland cultures and this process was inhibited by chlorpromazine, a dopamine receptor antagonist. Similarly, exogenous serotonin stimulated in vitro protein secretion by albumen glands. Thus, these results suggest that monoamines may play important roles in regulating reproductive activity of this snail and provides an excellent model for studying neurotransmitter function and metabolism in molluscs.