Immunohistochemical localization of substance P in postmortem rat and human spinal cord

The stability of substance P-like immunoreactivity was examined in postmortem rat and human spinal cord using radioimmunoassay and indirect fluorescence immunohistochemistry. The distribution of fluorescence in rat and human spinal cord was unchanged at intervals up to 48 hours (h) and 87 h, respectively. Fine linear fluorescent fibers were seen only in rat spinal cord processed at time intervals up to two h postmortem; they were never observed in human spinal cord, which was routinely obtained more than 6 h postmortem. The content of substance P-like material in human spinal cord nd its immunohistochemical appearance was not affected by age, the nature of the terminal illness, or autopsy delay. However, no correlation was found between intensity of fluorescent staining and content as measured by radioimmunoassay. It may be possible to use postmortem analysis of substance P in diseases of the central nervous system, but radioimmunoassay and immunohistochemistry should be used concurrently.