Neurosecretion and shell regeneration in Helisoma duryi (Mollusca: Pulmonata)

Abstract

The distribution of cells that stain positively with paraldehyde fuchsin (PAF) in the brain of Helisoma duryi has been mapped. Two cell groups occur in the visceral ganglion, one of which (group 1) has been shown to contain electron-dense secretory granules resembling neurosecretory material. Backfilling experiments and serial sectioning show that group 1 cells send axons into the intestinal and left pallial nerves.PAF-positive material is depleted from group 1 cells between 24 and 48 h after shell removal and has reappeared by 72 h. PAF-positive material accumulates in the axons by 24 h and disappears by 48 h; shell regeneration is apparently complete within 15 days. Tissue injury alone or shell removal from a non-regenerating area does not cause depletion of stainable material in these cells. No change in stainability occurs in other PAF-positive cells in the brain during shell regeneration. It is suggested that this cycle of activity may indicate involvement of the group 1 neurosecretory cells in the control of shell regeneration.