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.

A Cellular Model of Wave Propagation in C. elegans

D. Russell, L. Byerly

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