QUANTIFICATION OF THYROTROPIN-RELEASING-HORMONE CHANGES AND SEROTONINCONTENT CHANGES FOLLOWING GRADED SPINAL-CORD INJURY

Thyrotropin-releasing hormone (TRH) and serotonin (5-HT) are well know n as neurotransmitters of descending bulbo-spinal tracts. 5-HT uptake caudal to (5-HT decreased) graded spinal lesions has been measured in rats and dogs and significantly correlated with the degree of cord inj ury. We studied 5-HT content via high-pressure liquid chromatography a nd radioimmunoassay measurements of TRH in dog spinal cord, both rostr al and caudal, to 6 week T6 spinal transection (T) (n = 7) or T6 hemis ections (H) (n = 7). Sham controls (n = 7) were used. Mean 5-HT conten t values were (pmol/mg): rostral sham 1.25 +/- 0.02, caudal sham 1.35 +/- 0.17, rostral T 2.65 +/- 0.36, caudal T 0.19 +/- 0.06, rostral H 2 .1 +/- 0.22, and caudal H 1.0 +/- 0.31. A significant decrease in 5-HT caudal to transection versus control (P < 0.001) was seen. A trend fo r decreased 5-HT caudal to hemisection versus control (P < 0.1) was al so seen. Mean TRH levels (pg/mg protein) were:: rostral sham 40.02 +/- 18.47, caudal sham 30.61 +/- 10.03, brainstem sham 18.9 +/- 5.13, ros tral T 52.4 +/- 21.34, caudal T 3.52 +/- 1.87, brainstem T 19.25 +/- 4 .11, rostral H 43.45 +/- 18.61, caudal H 14.24 +/- 5.7, and brainstem H 21.89 +/- 1.23. Significant decreases for caudal. TRH transection ve rsus controls (P < 0.001) and for caudal TRH hemisection versus contro ls (P < 0.02) were seen. A significant difference between caudal hemis ection and caudal transection TRH levels (P < 0.001) was seen. The rat io of the percentage of drop between H and T was 60%, which is near th e predicted ideal of 50%. Significant increases for rostral 5-HT trans ection versus control (P < 0.02) and rostral 5-HT hemisection versus c ontrol (P < 0.02) were seen. The increase in TRH above a transection w as not statistically significant. The increase in 5-HT rostral to the level of injury may result from blockade of transport. The decrease in measured TRH below the level of injury correlated with the severity o f injury. These results suggest that TRH measurements are superior to 5-HT content for correlating the degree of long tract injury. (C) 1995 Academic Press, Inc.