Origins and distribution of calcitonin gene-related peptide-containing nerves in the wall of the cerebral arteries of the guinea pig with special reference to the coexistence with substance P.

The origins and overall distribution of calcitonin gene-related peptide-like immunoreactivity (CGRPI) in the wall of the cerebral arteries were investigated in the guinea pig by using whole-mounts. Two types of CGRPI fibers were seen; one forming dense fiber bands, located among the periadventitial nerves, and the other forming a meshwork. CGRPI fibers in the periadventitial nerves often leave these nerves to form a meshwork, of a density that varies according to the diameter or location of the blood vessel. The present study showed that CGRPI fibers in the walls of the carotid arterial system originated from the trigeminal ganglion, and those in the vertebrobasilar arterial system from other origins besides the trigeminal ganglion. We also examined the coexistence of this peptide with substance P-like immunoreactive (SPI) structures in a single neuron system. Double staining immunocytochemistry showed that the patterns of the running of CGRPI and SPI fibers in the wall of the cerebral arteries were similar, and this method also demonstrated the presence of neurons containing both CGRPI and SPI structures in single cells of the trigeminal ganglion, which is the major origin of these fibers in the cerebral arteries.