Overall distribution of substance P-containing nerves in the wall of the cerebral arteries of the guinea pig and its origins



The overall distribution of substance P-like immunoreactivity (SPI) in the wall of the cerebral arteries and their origins were investigated in the guinea pig by using whole-mounts.

Two types of SPI fibers were seen: one forming dense fiber bands and lo-cated among the periadventitial nerves, and the other forming a meshwork. The SPI fibers located in the periadventitial nerves often leave these nerves to form a meshwork of SPI fibers of varying density according to the diame-ter or location of the blood vessels.

The present study suggests that: (1) SPI fibers located on the circle of Willis and its branches originate from SPI cells in the trigeminal ganglion; (2) SPI fiber's of the rostral one-third of the basilar artery originate partly from trigeminal SPI cells; and (3) SPI fibers in the caudal two-thirds of the basilar artery originate exclusively from other SPI cells, apart from the tri-geminal ganglion.