The protein brain-derived neurotrophic factor (BDNF) is known to promote cell survival, improve synaptic function, and induce neuronal morphological changes. Consequently, BDNF plays a major role in neuroplasticity and the ability of the central nervous system to adapt and recover following injury. Regardless of the molecular mechanisms by which this occurs (which are poorly understood), potentiating the expression of BDNF following spinal cord injury has been shown to improve functional outcomes in animals.(1, 2) It is well documented in both animal and human literature that the production BDNF increases with physical exercise in healthy populations and individuals with chronic disease or disability. (3) The literature suggests that this increase is proportional to the intensity of exercise, though the parameters of exercise to maximize this effect are poorly understood. (2, 4-6) From animal research, it has been postulated that serotonin (5HT) plays a role in the mechanism of increase in BDNF expression, (7-9) with findings that specifically demonstrate potentiation of the exercise-induced expression with antidepressant treatment(10)and a blunted response when monoaminergic signaling is blocked.(11) A specific genetic variation in the BDNF gene, found in approximately 30% of the population has also been noted as an important factor in the proper release of BDNF with associated deficits in motor learning. (12, 13) Initial evidence also suggests that this polymorphism may have an impact of the relationship between exercise and BDNF. (14, 15) The objective of this study is the evaluate the response of serum concentrations of brain-derived neurotrophic factor ([BDNF]s) to an acute bout of exercise in ambulatory people with incomplete spinal cord injury; additionally, to examine the effect of pharmacological agents that alter serotonergic (5HT) transmission on this exercise-induced change in [BDNF]s. To achieve this objective we will investigate [BDNF]s during a treadmill test alone and in combination with two commonly used medications; escitalopram oxalate , a selective-5HT reuptake inhibitor (SSRI) and cyproheptadine (CYPRO), a 5HT antagonist.