Dual innervation of substance P-containing neuron system in the wall of the cerebral arteries.

The present study has shown the presence of substance P-like immunoreactive (SPI) fiber plexuses both in the carotid and vertebrobasilar systems in the Mongolian gerbil, suggesting that the origins of SPI fibers in these two systems differ. The present study further demonstrated in the guinea pig, using experimental manipulations, the dual origin of SPI fibers in the cerebral arteries; one from the trigeminal ganglion (TG) that mainly innervates the carotid system, and the other that separates from the TG and mainly innervates the vertebrobasilar system.