Novel distribution of calcitonin gene-related peptide in rodent subcommissural organs

For the first time we showed the presence of CGRP immunoreactivity in the SCO of golden hamsters, Wistar rats and Mongolian gerbils. In hamsters, the intense CGRP-like immunoreactivity was detected in the whole SCO, including Reissner's fiber- and granule-like structures at the ventricular surface of the SCO. The CGRP-positive hypendymal cells were frequently in contact with local blood vessels and some of them were situated intimately to the leptomeningeal space. In the SCOs of rats and gerbils, only the supranuclear area and apical cytoplasm of the ependymal cells were positive for CGRP, whereas the basal pole of the cells and the hypendyma were CGRP-negative. The existence of CGRP in rodents SCO was confirmed by the expression of CGRP mRNA in rat SCO by RT-PCR. The present results indicate that the SCOs of rodent species contain CGRP that may be in part synthesized by ependymocytes themselves. A species difference in the CGRP distributions of rodents SCOs may therefore imply its different synthesis rates or release pathways.