Differential localization of vasopressin‐ and oxytocin‐immunoreactive cells and conventional neurosecretory cells in the ganglia of the earthworm Pheretima hilgendorfi

Abstract Cells containing arginine vasopressin (AVP)‐ and oxytocin (OXT)‐like substances were immunohistochemically visualized in the cerebral, subesophageal, and ventral nerve cord ganglia of the earthworm Pheretima hilgendorfi . Whether these anti‐AVP– and anti‐OXT–reactive cells are identical with classical aldehyde fuchsin (AF)‐positive neurosecretory cells was tested in serial sections. In all ganglia, groups of scattered neuronal cell bodies and axons strongly reactive to AVP and OXT antisera were observed, but AF‐positive cells consisting of type a (dark blue) and type b (purple) cells were predominantly present in the cerebral and subesophageal ganglia. In the cerebral and subesophageal ganglia anti‐AVP– and anti‐OXT–reactive cells were generally larger than AF‐positive cells. Some AF‐positive cells were reactive either to anti‐AVP or anti‐OXT serum, but some failed to react to either serum. Anti‐AVP– and anti‐OXT–reactive cells were not immunoreactive to OXT and AVP antisera, respectively. Electron microscopic observations showed that the granules of type a cells were larger and less electron dense than those of type b cells and anti‐AVP–reactive cells. The present cytological observations clearly showed that AVP‐ and OXT‐like substances were widely present in the ganglionic cells of the earthworm