Acute Effects of Pharmacological Neuromodulation on Leg Motor Activity in Patients With SCI Treated With EES

In a current first-in-man study, called Stimulation Movement Overground (STIMO) (NCT02936453; CER-VD: 04-2014; Swissmedic: 2016-MD-0002), epidural electrical stimulation (EES) of the spinal cord is applied to enable individuals with severe spinal cord injury (SCI) to complete intensive locomotor neurorehabilitation training. In this clinical feasibility study, it was demonstrated that EES results in an immediate enhancement of locomotor functions and that when applied repeatedly as part of a neurorehabilitation program, EES can progressively improve leg motor control in individuals with severe SCI. Mechanistically, EES acts trans-synaptically upon spinal circuitries through the electrical stimulation of proprioceptive fibers. It is assumed that this stimulation does not increase the level of availability of monoamine neurotransmitters below the SCI level, which are essential for lower extremity movement generation. Specifically, in a non-injured individual, dopamine and serotonin synthesized in the brain and brainstem are released by fibers diffusely innervating the spinal cord, serving to critically mediate excitability of motor neurons and interneurons in lumbar and sacral spinal level. Spinal cord injury would partially or entirely disrupt these modulation pathways, resulting in a detrimental lack of crucial neurotransmitters below the injury level. This lack of endogenous neurotransmitters could potentially be compensated for by pharmacological agents promoting the neurochemical environment necessary for locomotion.