Ontogeny of substance P-containing fibers in the taste buds and the surrounding epithelium. I. Light microscopic analysis.

Ontogeny of the substance P-like immunoreactive (SPI) structures in the circumvallate papillae of the rat taste buds was examined by means of indirect immunofluorescence method. SPI fibers in the lamina propria first appeared at gestational day 20, and their quantity increased up to postnatal day 10. On the other hand, SPI fibers in the epithelium were first seen on gestational day 21 and in the taste buds at postnatal day 2-4. These fibers increased remarkably in number after postnatal day 5 and reaching their maximum at postnatal day 20, and thereafter numbers decreasing slightly.