Ultrastructural immunocytochemical localization of substance P in the cat small intestine

The immunocytochemical peroxidase-antiperoxidase technique was used to identify substance P (SP) in the cat small intestine at the ultrastructural level in the nerve plexuses. In the myenteric plexus the SP containing fibres form synapses with the other nerve terminals and run parallel to the circular muscle. The SP in these fibres is present in the vesicles of 80 to 120 nm or 150 to 250 nm in diameter. The results support the contention that SP containing nerve terminals are present in the enteric nervous system.