THE INTEGRATION OF ANTAGONISTIC REFLEXES REVEALED BY LASER-ABLATION OF IDENTIFIED NEURONS DETERMINES HABITUATION KINETICS OF THE CAENORHABDITIS-ELEGANS TAP WITHDRAWAL RESPONSE

Previously, we described the circuitry that underlies the tap withdraw al response of the nematode Caenorhabditis elegans. In response to a l ight mechanosensory stimulus a worm will withdraw, usually by initiati ng backward locomotion, but occasionally with increased forward locomo tion. The form of an animal's response is a product of the balance bet ween two antagonistic reflexes. backward locomotion (reversals) trigge red by anterior mechanosensory input and forward locomotion (accelerat ions) triggered by posterior mechanosensory input. During habituation of this reflex, the frequency of forward and backward locomotion in re sponse to tap is modulated by both experience and interstimulus interv al; reversals are more frequent early in a habituation series and at l onger Inter stimulus intervals. Single-cell laser microsurgery was use d to study each of the subcomponents of the intact behavior during hab ituation training. Groups of intact or laser-ablated worms were habitu ated at either a 10-s or a 60-s inter stimulus interval and the kineti cs of habituation in each group was analyzed. We demonstrate that each component of the behavior habituates and does so with kinetics that a re consistent with the decrement observed in the intact animal.