Invertebrate nervous systems are structurally less elaborate than those of vertebrates. This simplicity along with the accessibility of their nervous system have permitted detailed electrophysiological and morphological studies resulting in the construction of functional circuit diagrams. Dr. Stretton has used Ascaris summ, a large nematode parasite of pigs, as a model system to understand the neural circuits controlling locomotion. Their relatively simple movements are coordinated by a motor nervous system that contains approximately 77 neurons distributed within the ventral nerve cord along the length of the worm. He has found that along with the classic neurotransmitters that operate within the nematode nervous system are a large number of immunoreactive neuropeptide-like substances. These data indicate that previously unknown elaborate communication system exists in these simple organisms similar to that reported in more complex animals. Dr. Stretton along with Dr. Wright, his postdoctoral fellow, will isolate, clone, and sequence the gene that encodes two bioactive neuropeptides. Since each neuropeptide is a potentially potent chemical messenger with unique target- responses, they will characterize which motor nervous system neurons are likely to express individual peptides. The results obtained using this simple system will enhance our understanding of the neurochemical basis of locomotion and its coordination. Moreover, studies on the basic neurobiology of nematodes may provide a rational basis for the design of controls on these parasites found in man, domesticated animals and cultivated plants.
