The cornea is not innervated by substance P-containing primary afferent neurons

The contribution of substance P-containing primary afferent neurons to the innervation of two pain sensitive organs, the skin and the cornea, was investigated in rats. A combined fluorochrome tracing-immunohistochemical method was used. While 8.4% of the sensory neurons innervating the skin of the neck display substance P immunoreactivity, the cornea lacks any substance P-immunostained primary afferents.