Quantification of changes in serotonin uptake with spinal cord injury

The high-affinity uptake of [3H]serotonin was studied using spinal cord preparations obtained from normal dogs, dogs made paraplegic by midthoracic transection, and dogs made monoplegic by midthoracic hemisection. Measurements were made at 1, 4, and 8 weeks after surgery. Lumbar spinal cord was removed at the above time periods and a myelin-free synaptosomal fraction was obtained by centrifugation and used for studying high-affinity serotonin uptake. At 1 week, there were no significant differences for Km values (nM) among any of the three groups (138 +/- 20, 128 +/- 22, and 118 +/- 20). The Vmax values (pmol/min/mg of protein) at 1 week for the control group (4.9 +/- 0.6) versus the hemisected group (4.3 +/- 0.7) were not significantly different. The Vmax values at 1 week for the completely transected group (2.3 +/- 0.3; P less than 0.01) were significantly reduced by 53 +/- 7%. At 4 weeks, the Vmax values for the hemisected (1.8 +/- 0.2; P less than 0.05) and transected groups (0.6 +/- 0.2; P less than 0.05) were significantly different as compared to the control group. The mean percent drop in Vmax after hemisection was 56 +/- 4%, close to the predicted value of 50%. The mean percent drop in Vmax after transection was 86 +/- 2%. At 8 weeks the mean Vmax values for the hemisected (1.9 +/- 0.3; P less than 0.05) and transected (0.4 +/- 0.4; P less than 0.05) groups were not significantly different compared to their respective 4-week values. It appears that serotonin uptake can be used to quantitate roughly the degree of spinal cord injury.