Effects of experimental spinal cord transection on substance P receptors: a quantitative autoradiography study

The autoradiographic localisation of Substance P (SP) receptors was investigated in the rat spinal cord following cordotomy at the thoracic 8-9 level. The binding of [125I]-BH-SP was measured in discrete gray matter structures above (C6-C7 level) and below (L2-L3 level) the injury site, and expressed in fmol/mg protein. There was a statistically significant increase in SP receptor density 1 week after cordotomy in the dorsal horn and in the central canal of lumbar region, in laminae 3-4-5 and also in the ventral horn of cervical spinal cord. Elevated SP receptor density was also noted in cervical ventral horn at 3 weeks after thoracic cordotomy, whereas the increase seen at 1 week was normalized at 3 weeks everywhere else. Since SP concentration has been reported to show a similar localized increase below a spinal transection, the present results are consistent with an up-regulation of SP receptors. A similar direct relationship between SP receptors and SP content appears to occur also in the ventral horn above the injury site.