Does cholecystokinin-like immunoreactivity in rat primary sensory neurons represent calcitonin gene-related peptide?

Using immunohistochemistry, calcitonin gene-related peptide (CGRP)- and cholecystokinin (CCK)-like immunoreactivity (LI) were found in many of the same spinal and trigeminal ganglion cells and motoneurons in the spinal cord and hypoglossal nucleus, as well as in fibers with an overlapping distribution in the spinal cord (dorsal horn, bundle ventral to the central canal) and in the spinal trigeminal nucleus. CCK-LI in all these structures disappeared after preadsorption of CCK antisera with CGRP at 10(-4) M and almost completely at 10(-5) M. CCK peptide in concentrations up to 10(-4) M, on the other hand, did not influence CGRP staining. The present findings raise the possibility that some CCK-LI in primary sensory neurons in rat may represent CGRP or a similar peptide.