The networks of nerves and muscles responsible for forward and backward movements in C. elegans offer unique advantages for investigating the functional relationships among cells in integrated cellular networks. The first advantage is that John Sulston and his colleagues identified the interneurons, motor neurons and muscle cells that compose the networks (Sulston, et al., 1983). Second, John White and colleagues determined the synaptic patterns that interconnect the network (White et al., 1986). Finally, the C. elegans community has generated mutations that cause specific alterations in the cellular networks. A model based on the connectivity pattern and laser ablation results suggests that distinct sets of interneurons and excitatory motor neurons are dedicated to forward and backward movement, respectively. These two circuits converge upon two classes of inhibitory motor neurons and four longitudinal strands of body wall muscles and create antiphasic contractile muscular waves that travel along the dorsal and ventral axes of the body. We will report results from the analysis of movies showing locomotion patterns of animals. These movies allows us to quantitatively characterize the traveling wave in terms of amplitudes, dorsal and ventral deflections, frequency and velocity of the wave progression and the forward and backward velocity of the animal's progression. We will compare wild-type locomotion characteristics with those exhibited by three uncoordinated mutants (
unc-4,
unc-55, and
cnd-1) that are known to make specific alterations in the network that result in movement defects that are predicted by the model. The connectivity model can also be used to predict epistatic relationships for double mutant combinations (for example
unc-55 mutants exhibit a ventral asymmetric pattern of backward movement, whereas
unc-4 exhibits a dorsal asymmetric pattern of backward movement). We find that
unc-4 masks the defect of
unc-55 mutants, which is predicted by the model neural circuit. However the model's predictions for forward movement are not as accurate. We will discuss possible explanations for the resiliency of forward movement and the vulnerability of backward movement to genetic perturbations.