Corpuscular bodies in the palate of the rat. 2. Innervation and central projection

The source of innervation of the corpuscular bodies in the palate and the central projections of the afferent fibres of the entire palate was studied in rats by transganglionic transport of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) and with substance P (SP) immunohistochemistry. WGA-HRP injected into the incisal papilla was taken up by the nerve fibres that terminated in the corpuscles. Retrogradely labelled neurons were observed in the trigeminal ganglion as well as anterogradely labelled terminals in the dorsolateral part of the spinal trigeminal nucleus and in the lateral part of the nucleus of the solitary tract. No labelling could be found in the geniculate ganglion, the facial nerve and the hypoglossal nucleus. Following WGA-HRP injection in the intermolar area and in the soft palate, labelling was only restricted to the trigeminal ganglion. The lamina propria of the entire palate and the corpuscle-enriched area of the incisal papilla and the soft palate were richly innervated by SP-containing fibres. Numerous SP-containing fibres were also observed in the nerve plexus at the base of the corpuscle. In addition, SP-positive neurons were identified in the trigeminal ganglion and SP-labelled terminals in the sensory trigeminal nuclear complex and in the solitary tract nucleus. On the basis of our morphological observations we conclude that the palatal corpuscular bodies are involved in taste perception which is of trigeminal origin.