Peptide-containing Neurons Projecting to the Tongue of the Rat: Retrograde Tracing and Immunocytochemistry.

The origin and neuropeptide content of nerve fibres in the rat circumvallate papilla was studied by retrograde tracing in combination with immunocytochemistry. An injection of the retrograde tracer True Blue into the circumvallate papilla resulted in the appearance of labelled nerve cell bodies in the superior cervical, the stellate, the thyroid, the nodose, the jugular, the petrosal, the otic, the trigeminal and the dorsal root ganglia at level C2. Most of the True Blue-labelled nerve cells in the superior cervical ganglia contained neuropeptide Y. The majority of labelled cell bodies in the thyroid ganglia contained vasoactive intestinal peptide. In the jugular and trigeminal ganglia, the majority of the labelled nerve cell bodies stored calcitonin gene-related peptide. A small number of neurons in the medial reticular formation of the central nervous system was labelled. Tracer injections deep into the tongue tissue beneath the circumvallate papilla gave rise to True Blue-labelled neurons in the hypoglossal nucleus.