Axon demyelination contributes to the loss of sensory and motor function following injury or disease in the central nervous system. Numerous reports have demonstrated that myelination can be achieved in neuron/oligodendrocyte co-cultures. However, the ability to selectively treat neuron or oligodendrocyte (OL) cell bodies in co-cultures improves the value of these systems when designing mechanism-based therapeutics. We have developed a microfluidic-based compartmentalized culture system to achieve segregation of neuron and OL cell bodies while simultaneously allowing the formation of myelin sheaths. Our microfluidic platform allows for a high replicate number, minimal leakage, and high flexibility. Using a custom built lid, fit with platinum electrodes for electrical stimulation (10-Hz pulses at a constant 3 V with ~190 kΩ impedance), we employed the microfluidic platform to achieve activity-dependent myelin segment formation. Electrical stimulation of dorsal root ganglia resulted in a fivefold increase in the number of myelinated segments/mm² when compared to unstimulated controls (19.6 ± 3.0 vs. 3.6 ± 2.3 MBP+ segments/mm²). This work describes the modification of a microfluidic, multi-chamber system so that electrical stimulation can be used to achieve increased levels of myelination while maintaining control of the cell culture microenvironment.

Neuronal activity promotes myelination in vivo and in vitro. However, the molecular events that mediate activity-dependent myelination are not completely understood. Seven, daily 1 h sessions of patterned electrical stimulation (ESTIM) promoted myelin segment formation in mixed cultures of dorsal root ganglion (DRG) neurons and oligodendrocytes (OLs); the increase in myelination was frequency-dependent. Myelin segment formation was also enhanced following exposure of DRGs to ESTIM prior to OL addition, suggesting that ESTIM promotes myelination in a manner involving neuron-specific signaling. Cyclic adenosine monophosphate (cAMP) levels in DRGs were increased three-fold following ESTIM, and artificially increasing cAMP mimicked the ability of ESTIM to promote myelination. Alternatively, inhibiting the cAMP pathway suppressed ESTIM-induced myelination. We used compartmentalized, microfluidic platforms to isolate DRG soma from OLs and assessed cell-type specific effects of ESTIM on myelination. A selective increase or decrease in DRG cAMP levels resulted in enhanced or suppressed myelination, respectively. This work describes a novel role for the cAMP pathway in neurons that results in enhanced myelination.

Study design: Postintervention. Objectives: To determine the effectiveness of the Praxis multifunctional implantable functional electrical stimulation (FES) system (Neopraxis Pty. Ltd, Lane Cove, NSW, Australia) to provide standing and stepping ability and bladder and bowel management for individuals with motor complete thoracic level spinal cord injuries (SCI). Setting: Pediatric orthopedic hospital specializing in SCI. Subjects: Three males, ages 17 and 21 years, with motor-complete thoracic level SCI and intact lower motor neurons to the muscles targeted for stimulation. Methods: Each subject was successfully implanted with the Praxis FES system. All three subjects received electrodes for upright mobility and the first two subjects received additional electrodes for stimulated bladder and bowel management. Following training, subjects were evaluated in their ability to use FES for nine mobility activities. Acute and chronic experiments of the effect of stimulation on bowel and bladder function were also performed. Results: All three subjects could independently stand up from the wheelchair and could walk at least 6 m using a swing through gait pattern. Two subjects were able to independently perform swing through gait for 6 min and one subject was able to independently ascend and descend stairs. Suppression of reflex bladder contractions by neuromodulation (subject 1) and stimulated contractions of the rectum (subject 2) were observed in acute experiments. When stimulation was applied over the course of several weeks, a positive effect on bowel function was measured. Stimulated bladder contractions were not achieved. Conclusion: The feasibility of using the Praxis FES system for upright mobility and aiding aspects of bladder and bowel function was demonstrated with three subjects with thoracic level SCI.

Oligodendrocyte (OLG) death plays a major role in white matter dysfunction and demyelination following injury to the CNS. Axonal contact, communication, and neuronal activity appear to promote OLG survival and function in cell culture and during development. The application of electrical stimulation to mixed neural cultures has been shown to promote OLG differentiation and the formation of myelin in vitro. Here we show that OLG viability can be significantly enhanced in mixed cortical cultures by applying biphasic pulses of electrical stimulation (ESTIM). Enhanced survival via ESTIM requires the presence of neurons and is suppressed by inhibition of voltage-gated sodium channels. Additionally, contact between the axon and OLG is necessary for ESTIM to promote OLG survival. This report suggests that patterned neuronal activity could repress delayed progression of white matter injury and promote CNS repair in neurological conditions that involve white matter damage.

Our object is to develop a reliable, implantable and closed-loop functional electrical stimulator (FES) hybrid system for safe prolonged standing in paraplegic individuals. Open-loop FES systems rapidly induce muscle fatigue that limits paraplegic standing to less than 20 and typically 10 min. Since December 1991, a paraplegic male (CS: 23 years old, T₁₀ level, Asia: A) has been implanted with the first Nucleus FES-22 channel stimulating system (Cochlear Ltd., Lane Cove, N.S.W., Australia). Epineural platinum disc electrodes (2.5 mm) were placed on branches of the femoral, gluteal and sciatic nerves, which can be activated to produce controlled lower extremity movements for exercise and standing. No medical complications have occurred during these 5½ years of implantation. The ankles are stabilized with Andrews'' ankle-foot braces, the knees are free to flex. With bilateral knee goniometers fitted to sense a 10° angle flexion, this hybrid closed-loop stimulation system allows the patient to achieve safe uninterrupted standing for over 60 min. The stimulator has needed to be activated ''on'' for 8% (range: 3–17%) of the standing times, preventing muscle fatigue, with little or no changes found in the vital signs. The patient can manipulate and transfer objects at arm length up to 2.2 kg with good stability. New, less obstrusive sensors are currently being tested for a safer and more reliable closed-loop system.