About this trial

This trial is recruiting individuals with spinal cord injuries to study the effects of the drug 5-hydroxytryptophan (5-HTP) on spinal cord function. 5-HTP is a commonly used over-the-counter dietary supplement; it is broken down in the body to become serotonin. Serotonin is a chemical necessary for nerve signal transmission and therefore important for motor function in the spinal cord. The study will also look at the effect of carbidopa, a drug which may enhance the effects of 5-HTP. The study will measure nerve cell activity, reflexes and changes in motor performance during leg cycling in response to a single administration of drugs in 4 study segments: 1) carbidopa only (50mg); 2) 5-HTP (50mg) combined with carbidopa (50 mg); 3) 5-HTP (100 mg) combined with carbidopa (50mg); or 4) a placebo. Blood and serum samples will be obtained to measure levels of serotonin, serotonin related molecules, and cortisol. Each participant will receive all 4 interventions given in a randomized order; neither participant nor doctor will know which medication is given. If included in the trial, participants will complete a total of four lab visits.