Interactions between two antagonistic reflexes in the nematode Caenorhabditis elegans.

1. Antagonistic reflexes that use the same final common path cannot be activated simultaneously; as a consequence one reflex often inhibits the expression of the other. Results of experiments with two antagonistic reflexes in Caenorhabditis elegans showed that the reflex inhibition in this simple animal is the same as in more complex organisms. Thus C. elegans can serve as a model system for studying the neural mechanisms underlying these behavioral patterns. 2. In adult C. elegans tail-touch normally elicits forward movement, while tap normally elicits backward movement. When tail-touch is delivered 1 s before a tap, reversals to the tap are inhibited and the magnitude of any reversal that does occur is reduced. 3. The relative magnitude of the 2 stimuli, tail-touch and tap, affects the amount of inhibition observed. 4. The effectiveness of tail-touch as an inhibitory stimulus can be varied as a result of experience. Habituating the response to tail-touch decreased the inhibition of reversal to tap following a tail-touch. 4. The tail-touch induced inhibition of reversal to tap diminishes over an interval of at least 10 s; however, following the inhibition an enhancement of responding to tap is seen. 6. Inhibition of reversal to tap is present in worms of all stages of development including newly hatched worms.