Axonal transport of substance P in the vagus and sciatic nerves of the guinea pig

The axonal transport and apparent subcellular distribution of substance P-like immunoreactive material (SPLI) were examined in nerves of guinea pigs by means of a sensitive radioimmunoassay and by immunohistofluorescence. Crushes or ligations were made at various levels above and below the nodose ganglion of the vagus, on the sciatic nerve, and on the central process of the S1 spinal ganglion. From the relative rates of accumulation of SPLI in the adjacent segments, it was concluded that the bulk of the substance P produced in the sensory ganglion cells was being exported toward the terminal regions of their peripheral branches. The average velocity of transport of SPLI in the peripheral direction was calculated to be 1 mm/h in the sciatic nerve and 1.25 mm/h in the vagus. The removal of SPLI from regions of nerve distal to a ligature indicated that only 26% of the peptide in vagus nerve and 17% of the peptide in sciatic nerve was available for rapid transport. It was therefore estimated that the mean velocity of the moving fraction was 5-6 mm/h. Stop-flow experiments with local cooling and rewarming in vivo suggested that some SPLI may have been transported as rapidly as 10 mm/h. The behavior of SPLI during ultracentrifugation of nerve and ganglion extracts indicated that this peptide was normally present both in a soluble form and in association with particles but was transported primarily in the latter form.