Immunoreactive calcitonin cells in the nervous system of polychaete Perinereis aibuhitensis

We examined immunoreactive calcitonin (iCT) cells in the nervous system of the polychaete Perinereis aibuhitensis using immunohistochemical methods. We found the most iCT cells (53-70 cells) in the cerebral ganglion. We also detected iCT cells (4-6 cells) in the subpharyngeal ganglion. Furthermore, it was noted that iCT cells were present bilaterally in each segment of the ventral nerve cord. These results suggest that iCT cells play some functional roles in the nervous system. Next, the molecular weight (MW) of the iCT substance was examined using the western blotting method. Cerebral ganglia were collected from 200 individuals. These ganglia were homogenized and centrifuged. The separated supernatants were treated with 66% acetone and then dialyzed to remove low MW substances (less than 2,000) at 4°C. After lyophilization, the sample was reconstituted with 1 M acetic acid and then fractionated with an ultrafiltration membrane system into MWs of 3,000 to 10,000. Thereafter, the specimen was separated by SDS-polyacrylamide gel electrophoresis and analyzed by western blotting with anti-salmon calcitonin (CT) antiserum. Our results indicated that the MW of the iCT substance was close to that of teleost fish CT (3.5 kDa). The annelid Capitella teleta has two genes encoding CT-like peptides. This suggests that the iCT substance in P. aibuhitensis includes amino acid residues similar to fish CT and belongs to the CT family.