CGRP-like immunoreactivity in A11 dopamine neurons projecting to the spinal cord and a note on CGRP-CCK cross-reactivity.

Using the indirect immunofluorescence technique and double labelling procedures combined with retrograde tracing it could be demonstrated that the A11 dopamine cell group, located at the border between the diencephalon and mesencephalon of the rat brain and some of which project to the spinal cord, contains calcitonin gene-related peptide (CGRP)-like immunoreactivity. Thus, another catecholamine group in the rat brain has been shown to have a coexisting peptide. One of the CGRP antisera used in the present study also stained cholecystokinin (CCK) containing neurons in various brain areas. Absorption and displacement experiments using immunohistochemistry and radioimmunoassay showed that this cross-reactivity was confined to the C-terminal portion of the peptide molecule. Therefore, the present results suggest that CGRP antisera used for immunohistochemistry and radioimmunoassay should be tested for possible cross-reactivity with CCK.