Temporal correlation between neuronal tail ganglion activity and locomotion in the leech, Hirudo medicinalis

Intracellular and extracellular recordings were performed in the posterior ventral nerve cord of restrained crawling preparations of the medicinal leech, Hirudo medicinalis. Short-latency neuronal activities in the tail ganglion nerves correlated with different phases of crawling behavior. Eight neurons with characteristic activation patterns during crawling were identified morphologically and physiologically in the tail ganglia of 23 preparations. The axons of four of these neurons projected through posterior tail brain nerves; four ascending interneurons had projections in the connectives or in Faivre's nerve. These interneurons are suitable candidates for carrying information between the front end and the tail end of the animal to coordinate the behavioral components during a crawling step.