Volume 16, Number 12,
Issue of June 15, 1996
pp. 4017-4031
Copyright ©1996 Society for Neuroscience
A Dynamic Network Simulation of the Nematode Tap Withdrawal
Circuit: Predictions Concerning Synaptic Function Using Behavioral
Criteria
Received Oct. 16, 1995; revised March 22, 1996; accepted March 29, 1996.
Stephen R. Wicks1,
Chris J. Roehrig1, and
Catharine H. Rankin2
1 Program in Neuroscience and 2 Department
of Psychology, University of British Columbia, Vancouver, British
Columbia, Canada V6T 1Z4
The nematode tap withdrawal reflex demonstrates several
forms of behavioral plasticity. Although the neural connectivity that
supports this behavior is identified (Integration of mechanosensory
stimuli in Caenorhabditis elegans, Wicks and Rankin, 1995, J
Neurosci 15:2434-2444), the neurotransmitter phenotypes, and hence
whether the synapses in the circuit are excitatory or inhibitory,
remain uncharacterized. Here we use a novel strategy to predict the
polarity configuration, i.e., the array of excitatory and inhibitory
connections, of the nematode tap withdrawal circuit using an
anatomically and physiologically justifiable dynamic network simulation
of that circuit. The output of the modeled circuit was optimized to the
behavior of animals, which possessed circuits altered by surgical
ablation by exhaustively enumerating an array of synaptic signs that
constituted the modeled circuit. All possible polarity configurations
were then compared, and a statistical analysis was used to determine
whether, for a given synaptic class, a particular polarity was
associated with a good fit to behavioral data. The results from four
related experiments were used to predict the polarities of seven of the
nine cell classes of the tap withdrawal circuit. In addition, the model
was used to assess possible roles for two novel mechanosensory
integration neurons: DVA and PVD.
Key words:
Caenorhabditis elegans;
mechanosensory;
habituation;
lesion;
inhibition;
reflex