Immunohistochemical localization of endothelin-1 in the nervous system of the earthworm Eisenia foetida

Abstract

The distribution of a substance that resembles endothelin-1 (ET-1) was examined immunohistochemically in the nervous system of the earthworm, Eisenia foetida, using antiserum against ET-1. In the cerebral ganglion, ET-1-like immunoreactivity was demonstrated in two to three pairs of neurons located in the peripheral portion. These immunoreactive neurons projected axons toward the neuropile located in the central portion of the ganglion. Immunoreactive fibers were distributed in the neuropile and proceeded posteriorly to the subesophageal ganglion through the circumpharyngeal connective. In the subesophageal ganglion, no immunoreactive cell bodies were detected, although the immunoreactive fibers were found in the neuropile. In each segmental ganglion, two to eight immunoreactive neurons were observed on each side of the caudo-ventral portion and these neurons sent axons ipsilaterally to the fiber tracts. The pattern of distribution of the immunoreactive neurons in the segmental ganglion was almost identical from one segment to the next. No immunoreactivity was detected in the nerve tracts that emerge peripherally from the cerebral, subesophageal, and segmental ganglia or in other organs, such as the digestive tract and the integument. Specific immunoreactivity to antiserum raised against corticotropin-releasing factor (1–20) was not detected in the nervous system of Eisenia.