The pond snail (Lymnaea stagnalis) has been shown to be particularly suitable for neurobiological studies. Until recently, nothing was known about the fate and effects of dihalogenated biphenyls (DHBs) in the snail. Also, the occurrence of enzymes, which might be involved in metabolism of DHBs was unknown at the onset of the research described in this paper. Therefore, the presence of cytochrome P-450 and glutathione S-trans-ferases and related substrate metabolism have been examined. The toxicokinetics of a number of 2,2`- and 4,4`-substituted dihalogenated biphenyls and their effects on different parameters (especially reproduction) of the snail have also been studied, in order to get a picture of the metabolic capacity and of the effects of DHBs in the pond snail Lymnaea stagnalis. Summarising the following conclusions were drawn. The snail Lymnaea stagnalis possesses both cytochrome P-450 and glutathione S-transferase enzyme systems, which can bind and transform several model substrates. One or more isoenzymes of cytochrome P-450, involved in the observed mixed-function oxidase activities, possibly resemble rat isoenzymes P-450 2B1/2B2. Elimination of dichlorinated biphenyla (DCBs) appeared to take place in a structure-dependent way, since the 2,2`-DCB isomer was eliminated from the snail more rapidly than the 4,4`-DCB isomer. 2,2`-DCB is transformed most likely towards toxic reactive intermediate(s) during cytochrome P-450-mediated metabolism. Metabolism may play an important role in the elimination and also in the toxic effects of DHBs. Upon oral treatment with DHBs, the reproduction of the snail was also affected in a structure-dependent way: 2,2`-DHBs affected reproduction more explicitly than 4,4`-DHBs. The origin of the effects on reproduction was traced to the level of the neuro-secretory caudo-dorsal cells (CDCs). 2,2`-DCB affected the endocrine function of the CDCs, possibly in combination with interference at the neuronal pathways involved in CDC activation. It was concluded that the pond snail Lymnaea stagnalis can be used as an animal model in toxicological research. Especially the basic knowledge of the reproduction system and the availability of parameters to measure effects on reproduction (electro-physiology, endocrinology and histology) make this snail an interesting model species for toxicological studies as well as for biomonitoring studies.
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