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In severe cases of sensorineural hearing loss where the numbers of auditory neurons are significantly depleted, stem cell-derived neurons may provide a potential source of replacement cells. The success of such a therapy relies upon producing a population of functional neurons from stem cells, to enable precise encoding of sound information to the brainstem. Using our established differentiation assay to produce sensory neurons from human stem cells, patch-clamp recordings indicated that all neurons examined generated action potentials and displayed both transient sodium and sustained potassium currents. Stem cell-derived neurons reliably entrained to stimuli up to 20 pulses per second (pps), with 50% entrainment at 50 pps. A comparison with cultured primary auditory neurons indicated similar firing precision during low-frequency stimuli, but significant differences after 50 pps due to differences in action potential latency and width. The firing properties of stem cell-derived neurons were also considered relative to time in culture (31-56 days) and revealed no change in resting membrane potential, threshold or firing latency over time. Thus, while stem cell-derived neurons did not entrain to high frequency stimulation as effectively as mammalian auditory neurons, their electrical phenotype was stable in culture and consistent with that reported for embryonic auditory neurons.

A workshop, entitled Return-to-Duty Assessment Methods and Standards: Developing a Research Agenda, was held at the Hilton Garden Inn, Frederick, MD, on 19-20 September 2012. Sponsored by the U.S. Army Medical Research and Materiel Command?s (USAMRMC) Military Operational Medicine Research Program (MOMRP), the workshop objectives were 1) to ensure that MOMRP RTD research programs are targeting the most important gaps and current Department of Defense (DoD) needs, 2) to establish a dialog among the various key performers and stakeholders, and 3) to synchronize the efforts of various RTD and fitness-for-duty programs across the DoD. The underlying intent was to address the development of RTD standards and assessment tools focused on the most common injuries across DoD: neurosensory injury (e.g., concussion), musculoskeletal injury (e.g., training-related), and psychological injury (e.g., PTSD, depression). This report contains the workshop presentations, comment highlights, and break-out group notes., The original document contains color images.