Worm Breeder's Gazette 2(2): 34
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Starting with the published anatomy of the ventral nerve cord (White et al., 1976), we have developed a model for contractile wave propagation in C. elegans. This model attempts to rationalize the known circuitry of the ventral cord with several known features of C . elegans movement, most notably the ability of waves to propagate at different rates and in opposite directions, and the ability of the animal to reverse immediately from an existing waveform. The central features of the model are that the O motor neurons act inhibitorily to keep dorsal and ventral sides in anti-coordination, that both the A and the B motor neurons act excitatorily to facilitate wave propagation, that the A motor neurons are active during backward movement while the B motor neurons are active during forward movement, that the long, 'undifferentiated' portions of the A and B motor neurons adjacent to their neuromuscular outputs are stretch sensors, and that the alpha and interneurons act as 'command fibers' for the A and B motorneurons respectively. This model accounts satisfactorily for several otherwise difficult features of movement, and seems in accord with what is known about sensory inputs that can affect movement; it also makes an interesting suggestion about the lineage division which separates the VA and VB motorneurons. Building on Stretton's (personal communication) report of a commissural 'repeat unit' in Ascaris and Sulston's (1976) lineage study of the C. elegans central cord, we have examined the notion that the motor neurons of C. elegans and Ascaris might be very similar. Under this assumption, we predicted that the commissure repeat unit of Ascaris should contain Ascaris homologs of 1 DA, 1 DE, 1 DD, 2 VD and 2 DAS cells. By initial stimulation near the lateral line and by later use of preparations from which broad muscle strips had been removed to expose the commissures, we stimulated individual commissures or commissure pairs in Acaris and determined the nature of any observed effect on muscles (dorsal or Ventral, excitatory or inhibitory). The results strongly suggest that the DD and VD cells are inhibitory, whereas the DA and DAS cells are strongly excitatory and the DB cells are weakly so. These results are predicted by the model.