Localization and changes of substance P in spinal cord of paraplegic cats

Female cats were transected at the T 12 region of the spinal cord and sacrified by perfusion through the aorta after 5 days, 2, 5, 8 or 12 weeks. Tissue from above and below the lesion was postfixed, dehydrated and embedded in paraffin. 5 μ sections were incubated for substance P immunoreactivity by the peroxidase-anti-peroxidase (PAP) immunohistochemical method. Spinal cord sections of normal cats showed a small amount of peroxidase-positive staining in the dorsal horn in laminae I, II and III of Rexed. Starting at 5 days after transection, there was a sharp increase in the amount of substance P-staining below the lesion in the form of punctate bodies and long varicosities. Above the lesion in the region of the substantia gelatinosa the number of stained bodies was fewer and the intensity of staining around the dorsal horns was less than that in sections obtained from below the lesion. This pattern was repeated when sections from animals sacrificed at later times were stained for substance P. The results confirm the presence of substance P in the spinal cord nerve tracts. Its accumulation in the dorsal horn below the transection lends credence to its role as a transmitter or modulator of afferent neuronal activity, and suggests its rostral direction by axoplasmic flow.