The distribution of putative neurosecretory cells in the central nervous system of the North American medicinal leech Macrobdella decora

Nerve cells that displayed a distinct Tyndall blue–white effect were observed in the supra- and sub-oesophageal ganglia, the ventral nerve cord ganglia, and the posterior ganglion of the Gnathobdellid leech Macrobdella decora. These cells formed four anatomically distinct groups in the supraoesophageal ganglion and occupied characteristic and analogous positions in the other ganglia. Light microscopy of these blue–white cells revealed histochemical properties not seen in other nerve cells. The perikarya of the four groups of blue–white cells in the supraoesophageal ganglion were examined with the electron microscope and found to contain large membrane-bounded electron-dense granules similar to those observed in proven neurosecretory cells. Tracts from two of these cell groups possibly form primitive neurohemal organs. A neurosecretory role for the blue–white cells is suggested.