Cytological approach to morphogenesis in the planarian blastema. II. The effect of neuropeptides.

The regeneration blastema consists of three cell types, undifferentiated cells, regenerative cells, and differentiated cells all of which can be identified by their ultrastructural characteristics. Quantitative changes in the numbers of these cells within the blastema offer important clues about the detailed process of regeneration. When decapitated worms were allowed to regenerate in neuropeptide-containing tap water, the undifferentiated cells accumulated rapidly and initiated blastema formation. These cells were then replaced with regenerative cells, and subsequently with differentiated cells. In the non-treated regenerating worms, the proportion of undifferentiated cells was much lower than in the neuropeptide-treated ones. The results of this study indicate that neuropeptides have a remarkable effect on the early stage of regeneration in planarians. Immunoelectron microscopy using a gold-conjugated anti-neuropeptide antiserum revealed the presence of neuropeptides in some kinds of parenchymal cells in the post-blastemal area.