Investigation of a possible site of action for the molluscicide frescon

Interest in molluscicides has been generated by the prevalence of the widespread human disease, schistosomiasis. The molluscicide Frescon, developed by Shell Research Ltd., is highly specific against aquatic snails. It has been used with considerable success in several tropical countries where the snail is the intermediate host to the schistosome parasite. It has been reported that Frescon has a profound effect on the electrophysiological activity of the isolated SDail brain, raising the possibility that this organ may be a site of action of this molluscicide. The present experiments were undertaken to explore this possibility. The molluscicidal {in vivo) and the 'neurotoxic' {in vitn.o) activities of ten Frescon analogs were compared in order to determine if a relation exists between the lethal effects in vivo, and the disruption of the electrophysiological activity in vitn.o. Also, the brains of Frescon-poisoned snails were examined to see if a relation exists between symptoms of poisoning and abnormal central nervous activity. It was found that those Frescon analogs which were capable of disrupting the normal electrophysiological activity of the isolated brain were also molluscicidal. The single analog which was not molluscicidal also had no effect on the electrophysiology of the isolated brain. However, the brains removed from Frescon-poisoned snails exhibited normal electrophysiological activity upon examination. Therefore, it was concluded that the central nervous system is not a likely site of action of Frescon. The correlation of molluscicidal effectiveness of the Frescon analogs to their ability to disrupt the in vit/io central nervous activity suggests that excitable tissue other than nervous tissue may be a site of action. In view of this finding, and in consideration of other observations, it is possible that snail musculature is a target of Frescon.