The integration of antagonistic reflexes revealed by laser ablation of identified neurons determines habituation kinetics of the Caenorhabditis elegans tap withdrawal response.

Abstract

Previously, we described the circuitry that underlies the tap withdrawal response of the nematode Caenorhabditis elegans. In response to a light mechanosensory stimulus a worm will withdraw, usually by initiating backward locomotion, but occasionally with increased forward locomotion. The form of an animal's response is a product of the balance between two antagonistic reflexes: backward locomotion (reversals) triggered by anterior mechanosensory input and forward locomotion (accelerations) triggered by posterior mechanosensory input. During habituation of this reflex, the frequency of forward and backward locomotion in response to tap is modulated by both experience and interstimulus interval; reversals are more frequent early in a habituation series and at longer Inter stimulus intervals. Single-cell laser microsurgery was used to study each of the subcomponents of the intact behavior during habituation training. Groups of intact or laser-ablated worms were habituated at either a 10-s or a 60-s inter stimulus interval and the kinetics of habituation in each group was analyzed. We demonstrate that each component of the behavior habituates and does so with kinetics that are consistent with the decrement observed in the intact animal.