Regional Distribution of Immunoreactive-Thyrotrophin-Releasing Hormone and Substance P, and Indoleamines in Human Spinal Cord

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Abstract
The regional distributions of thyrotrophin-releasing hormone (TRH) and substance P in postmortem human spinal cord were determined by radioimmunoassay in fresh tissue taken from 22 patients who died without known neurological disease. Dorsal, ventral, and intermediolateral spinal cord regions were obtained from different segmental levels (lumbar L1, 2, 3 and 4; thoracic groups T1-3, T4-6, T7-9, and T10-12) together with selective regions of grey matter of lumbar spinal cord. The effects on peptide levels of (a) the age of the patient, (b) the postmortem time interval, and (c) freezing the tissue samples prior to assay were assessed. Levels of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in regional lumbar and thoracic tissue using HPLC with electrochemical detection. Substance P was found in the highest concentration in the dorsal spnal cord, with no significant segmental differences. In contrast, TRH was present in higher levels in the ventral rather than the dorsal spinal cord, with segmental differences. There was a significant difference in the 5-HT/5-HIAA ratio between dorsal and ventral spinal cord, with the highest ratio in the ventral spinal cord. There were no significant differences in substance P, TRH, or 5-HT levels in spinal cords between 5 and 20 h postmortem or from patients aged between 5 and 90 years. Freezing the tissue (-80.degree. C for 24 h) prior to assay significantly reduced TRH and substance P levels compared to samples assayed immediately without prior freezing. The levels and distribution of peptides and indoleamines in human spinal cord are compared with those previously reported in the rat and other species and the possible roles of these substances in the control of motor function and autosomic control are discussed.