A Study Of Neural Control Of The Rolling Wave Underlying Aplysia Locomotion

The rolling wave of neural activity which is responsible for locomotion is a type of rhythmic movements in a number of vertebrates and invertebrates.The neural network that regulates rhythmic behavior is classified as the central pattern generator(CPG).In Aplysia californica,the escape locomotion,accompanied with rolling waves,is an excellent model system for this research.How this activity is generated has primarily been studied in the situation where it results from sequential activation of segmental ganglia or networks.Aplysia are however different since locomotion is mediated by neurons that are contained within a single ganglion(pedal ganglion).Previous work has studied the involvement of neurons on the dorsal surface of the pedal ganglion in Aplysia,we focused our research on neurons on the ventral side of the pedal ganglia.We identified p1 cluster neurons on the ventral side of the pedal ganglion with backfill and we also verified that they actually can cause the foot muscles to contract in semi-intact preparations.We recorded the firing pattern of cells in the p1 root cluster,and found the neurons showing different phase relationship relative to the bursting activity of the motor nerve PPCN which is used to monitor locomotion programs.We found motoneurons in this cluster that fire at a similar phase are often electrically coupled.On the root of the p7 nerve,we recorded interneurons which are electrically-coupled with the similar phase cells.Different firing patterns of the motor neurons may be the neural basis underlying rolling waves observed in actual locomotor behavior.Moreover,the electrical coupling may be the mechanism underlying the temporal difference between rhythmic bursts.Thus,we have a preliminary understanding of the neural control of the Aplysia rolling wave.These findings provide a basis to the future studies aimed to discover the entire CPG of locomotion.