Distribution of Eisenia tetradecapeptide immunoreactive neurons in the nervous system of earthworms

A detailed mapping of Eisenia-tetradecapeptide-immunoreactive neurons in th e central and peripheral nervous system combined with quantitative morpholo gical measurements was performed in Eisenia fetida and Lumbricus terrestris . In Eisenia, most labelled neurons were observed in the ganglia of the ventr al cord (20.38% of the total cell number of the ganglion) and 15.67% immuno reactive cells occurred in the brain, while 6% of the neurons could be show n in the subesophageal ganglion. In the case of Lumbricus, most immunoreact ive cells were found in the subesophageal ganglion (16.17%) and in the vent ral ganglia (12.54%). The brain contained 122 ETP-immunoreactive cells (5.6 %). The size of the immunoreactive cells varied between 35-75 mu m. A small number of Eisenia-tetradecapeptide immunoreactive fibres were seen to leav e the ventral ganglia via segmental nerves, and labelled processes could al so be observed in the stomatogastric system and the body wall. Labelled axo n branches originating from the segmental nerves formed an immunoreactive p lexus both between the circular and longitudinal muscle layer and on the in ner surface of the longitudinal muscle layer. This inner plexus was especia lly rich in the setal sac. Among the superficial epithelial cells the body wall contained a significant number of immunoreactive cells. Only a few Eisenia-tetradecapeptide immunoreactive neurons and fibres occur red in the stomatogastric ganglia. In the enteric plexus the number of immu noreactive neurons and fibres decreased along the cranio-caudal axis of the alimentary tract. Eisenia-tetradecapeptide immunoreactive cells were also present among the epithelial cells in the alimentary canal. Some of these c ells resembled sensory neurons in the foregut, while others showed typical secretory cell morphology in the midgut and hindgut.