Substance P in the vagus nerve

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Abstract
The presence of immunoreactive substance P (I-SP) in the vagus nerve of 5 species was demonstrated by radioimmunoassay. Different amounts of SP per unit weight were found: Guinea pig > cat > rabbit, rat and cattle. Infranodose ligations of the vagus nerve of cats and rabbits caused an accumulation of I-SP proximal but not distal to the ligation. The results obtained by radioimmunoassay and immunohistochemistry indicate a somatofugal axoplasmic transport of SP. Double ligation experiments revealed that about 37% of I-SP of the cat vagus nerve are mobile. The transport rate of this mobile I-SP was found to be 170 mm per day. Locally applied colchicine resulted in a similar accumulation of I-SP as after ligations. This is evidence favouring the involvement of microtubuli in the axoplasmic transport of SP. Immunohistochemical data show that SP-fibers account for about 10% of the axons in the cat vagus nerve. Most of these SP-fibers seem to be unmyelinated. Supranodose extracranial ligations of the cat vagus nerve led to an accumulation of I-SP on both sides of the ligature. Part of the SP-fibers are, therefore, afferent and their cell bodies are located in the nodose ganglion. The presence of efferent SP-fibers cannot be excluded.