Modulation of motor patterns by sensory feedback during earthworm locomotion

Role of sensory feedback to motor pattern activity concerning locomotion in the earthworm, Eisenia fetida, was investigated. We have previously reported that bath application of octopamine induces fictive locomotion in the earthworm. In this study, we have examined the role of sensory feedback during fictive locomotion by analyzing electrical activities from the cut end and intact first lateral nerves of the ventral nerve cord (VNC). From the cut end recordings, motor activity associated with fictive locomotion was measured. A mixture of sensory and motor activities was measured from the intact first lateral nerve using en passant recordings, and sensory activity was separated by subtraction of the cut end recording (mainly motor activities) from the intact first lateral nerve recording. We estimated the effect of sensory feedback from the earthworm body wall by comparing recordings that made when the preparation was in-contact with a substrate or suspended above it. Motor pattern activities and the coefficient of variation for inter-spike-interval of motor outputs were increased under suspended conditions during circular muscle contraction. These results indicate that sensory feedback modulates the pattern of motor activity in the earthworm during locomotion.