Gastrin- and cholecystokinin-like immunoreactivities in the nervous system of the earthworm

Abstract

The distribution of cholecystokinin and gastrin-like immunoreactive cell bodies and fibers in the nervous system of 2 annelid worms, Lumbricus terrestris and Eisenia fetida, has been studied by means of immunohistochemistry. The cerebral ganglion contains 170–250, the subesophageal ganglion contains 120–150, and the ventral ganglia contain 50–75 cholecystokinin immunoreactive cells, that represent 8–12%, 8–10% and 4–5% of the total cell number, respectively. The anti-gastrin serum stained 330–360 nerve cells in the cerebral, 32–46 in the subesophageal and 7–25 in the ventral cord ganglia, representing 15–16%, 2–3% and 0.5–2% of the total cell number. Immunopositivity was found with both antisera in the enteric nervous system, where the stomatogastric ganglia and the enteric plexus contain immunoreactive cells and fibers. Immunopositive cells were found in the epithelial and subepithelial cells, as well as in nerve cells innervating the muscular layer of the gastrointestinal tube. Various epidermal sensory cells also displayed strong immunoreactivity. According to our findings and the results of several functional studies, it is suggested that in annelids cholecystokinin- and gastrin-like peptides may be involved in digestive regulation, sensory processes and central integrating processes.