The ontogeny of substance P fibers in the mouse trigeminal nerve.

The putative neurotransmitter substance P was localized in the embryonic and neonatal mouse trigeminal nerve by indirect immunofluorescence. Central terminals in the nucleus caudalis gave a positive substance P-like immunofluorescence (SPLI) reaction of E13-E14. SPLI subsequently appeared in the peripheral mucous and cutaneous nerves at E16-17 at which time trigeminal nucleus cell bodies were also positive. These findings indicate the early development of primary afferent nociceptive pathways.