An Experimental Swallow Evoked Potential Protocol to Investigate the Neural Substrates of Swallowing

Advancement in dysphagia intervention is hindered by our lack of understanding of the neural mechanisms of swallowing in health and disease. Evoking and understanding neural activity in response to normal and disordered swallowing is essential to bridge this knowledge gap. Building on sensory evoked potential methodology, we developed a minimally invasive approach to generate swallow evoked potentials (SwEPs) in response to repetitive swallowing induced by citric acid stimulation of the oropharynx in lightly anesthetized healthy adult rats. The SwEP waveform consisted of 8 replicable peaks within 10 milliseconds immediately preceding the onset of electromyographic swallowing activity. Methodology refinement is underway with healthy rats to establish normative SwEP waveform morphology before proceeding to models of advanced aging and age-related neurodegenerative diseases. Ultimately, we envision that this experimental protocol may unmask the pathologic neural substrates contributing to dysphagia to accelerate the discovery of targeted therapeutics.

Width and neurophysiologic properties of tissue bridges predict recovery after cervical injury

ObjectiveTo assess whether preserved dorsal and ventral midsagittal tissue bridges after traumatic cervical spinal cord injury (SCI) encode tract-specific electrophysiologic properties and are predictive of appropriate recovery.MethodsIn this longitudinal study, we retrospectively assessed MRI scans at 1 month after SCI that provided data on width and location (dorsal vs ventral) of midsagittal tissue bridges in 28 tetraplegic patients. Regression analysis assessed associations between midsagittal tissue bridges and motor- and sensory-specific electrophysiologic recordings and appropriate outcome measures at 12 months after SCI.ResultsGreater width of dorsal midsagittal tissue bridges at 1 month after SCI identified patients who were classified as being sensory incomplete at 12 months after SCI (p = 0.025), had shorter sensory evoked potential (SEP) latencies (r = −0.57, p = 0.016), and had greater SEP amplitudes (r = 0.61, p = 0.001). Greater width of dorsal tissue bridges predicted better light-touch score at 12 months (r = 0.40, p = 0.045) independently of baseline clinical score and ventral tissue bridges. Greater width of ventral midsagittal tissue bridges at 1 month identified patients who were classified as being motor incomplete at 12 months (p = 0.002), revealed shorter motor evoked potential (MEP) latencies (r = −0.54, p = 0.044), and had greater ratios of MEP amplitude to compound muscle action potential amplitude (r = 0.56, p = 0.005). Greater width of ventral tissue bridges predicted better lower extremity motor scores at 12 months (r = 0.41, p = 0.035) independently of baseline clinical score and dorsal tissue bridges.ConclusionMidsagittal tissue bridges, detectable early after SCI, underwrite tract-specific electrophysiologic communication and are predictors of appropriate sensorimotor recovery. Neuroimaging biomarkers of midsagittal tissue bridges may be integrated into the diagnostic workup, prediction of recovery, and patients' stratification in clinical trials.

Test-Retest Reliability of the Vestibular Sensory-Evoked Potential (VsEP) in C57BL/6J Mice

Background: The vestibular sensory-evoked potential (VsEP) is an electrical potential that provides a direct test of vestibular function in animals. VsEP recordings are carried out using subcutaneous stainless steel electrodes placed over the nuchal crest (noninverting), behind either the left or right pinna (inverting), and at the hip (ground). A noninvasive head clip is used to secure the head to a mechanical shaker for delivery of a linear vestibular stimulus measured in units of jerk (g/msec). Frequent repositioning of the noninvasive head clip and skin electrodes may be necessary during recording for particular protocols; however, the test-retest reliability of the VsEP response (latency, amplitude, and threshold) has not been determined. Purpose: The purpose of this study was to determine the possible effects of frequent repositioning of the noninvasive head clip and skin electrodes on VsEP response parameters (latencies, amplitudes, and thresholds). We hypothesize that the VsEP response will remain stable and reliable with such repeated measurements in a given animal across time. Research Design: Linear VsEP responses were recorded from ten C57 mice (ages: 2.45 mo ±0.20; weights: 17.94 g ±1.51). Two standard threshold protocols and four repeated VsEP measurements at +6 dB re: 1.0 g/msec were performed, with four selected time points of head clip repositioning. In addition, three novice investigators performed measurements of noninverting electrode placement and head clip positioning. Results: VsEP response latency, amplitude, and threshold means did not significantly change with frequent repositioning of the head clip and skin electrodes; however, increased variability was observed. Conclusions: The findings demonstrate that repositioning does not introduce significant changes in mean parameter values of the recorded VsEP response waveform; however, mean absolute difference calculations demonstrated that frequent repositioning increased response variance. For VsEP protocols requiring frequent repositioning, standardized electrode montage, optimal placement of the noninverting electrode at the nuchal crest, and increased sample size are suggested.

General and Electrophysiological Toxic Effects of Manganese in Rats following Subacute Administration in Dissolved and Nanoparticle Form

In an attempt to model occupational and environmental Mn exposures and their possible interaction, young male Wistar rats were exposed to Mn by oral administration in dissolved form (MnCl2·4H2O, 14.84 and 59.36 mg/kg b.w.) and by intratracheal application of MnO2nanoparticles (2.63 mg/kg b.w.). After 3 and 6 weeks oral, or 3 weeks oral plus 3 weeks intratracheal, exposure, general toxicological, and electrophysiological tests were done. Body weight gain was significantly reduced after 6 and 3 plus 3 weeks exposure, but the effect of the latter on the pace of weight gain was stronger. Organ weights signalized systemic stress and effect on lungs. Changes in evoked electrophysiological responses (cortical sensory evoked potential and nerve action potential) indicated that the 3 plus 3 weeks combined exposure caused equal or higher changes in the latency of these responses than 6 weeks of exposure, although the calculated summed Mn dose in the former case was lower. The results showed the importance of the physicochemical form of Mn in determining the toxic outcome, and suggested that neurofunctional markers of Mn action may indicate the human health effect better than conventional blood Mn measurement.