AUTORADIOGRAPHIC ANALYSIS OF I-125 SUBSTANCE-P BINDING IN RAT SPINAL-CORD FOLLOWING CHRONIC CONSTRICTION INJURY OF THE SCIATIC-NERVE

Using receptor binding and autoradiographic techniques, changes in Bolton-Hunter labeled I-125-substance P (I-125-BH-SP) binding were determined in laminae I/II, V and X of rat lumbar spinal cord after chronic constriction injury (CCI) of the sciatic nerve. When compared to the sham-operated side of the control group, SP binding significantly increased ipsilateral to the CCI in laminae I/II at 5, 10 and 20 days after injury and in lamina V at 5 days after injury. Scatchard analysis was performed on the I-125-BH-SP binding to the NK1 receptor in laminae I/II of rats 5 days after generation of the CCI. A significant decrease in the K(d) of I-125-BH-SP binding was observed in laminae I/II ipsilateral to CCI when compared with the control side (ipsilateral to sham surgery). There was no significant change in the B(max) in laminae I/II ipsilateral to CCI. The changes in I-125-BH-SP binding in the rat spinal cord that occurred after CCI were found in areas of the spinal cord that receive terminations of nociceptive primary afferent fibers. The increased affinity of the NK1 binding site that we report could result in an increase in SP receptor activation in laminae I/II. Such central changes in SP binding may contribute to the neuropathic pain syndrome observed in rats with the CCI.