Detection of Small Fiber Neuronal Activity with Optically Pumped Magnetometers

The pain experience is a complex process that involves the activation of multiple neuronal signaling pathways that originate in the peripheral nervous system and are transmitted to the central nervous system. In the peripheral nervous system, specialized peripheral nociceptor (unmyelinated C fibers and lightly myelinated A-Delta; fibers) depolarization results in afferent transmission of noxious signals. Small Fiber Neuropathy (SFN) can result in chronic neuropathic pain with significant lifetime morbidity if not promptly treated. Current technological and operator limitations may delay SFN diagnosis and prolong appropriate treatment. Therefore, there is an unmet need for robust and non-invasive ways to accurately measure small fiber function. It is well known that the propagation of action potentials along a nerve is the result of ionic current flow which, according to the Ampere Law, generates a small magnetic field that is detectable by magnetometers such as superconducting quantum interference device (SQUID) Magnetoencephalography (MEG) systems. Optically pumped magnetometers (OPM) are an emerging class of quantum magnetic sensors with a demonstrated sensitivity of 1 fT/SQRT;Hz level, capable of cortical action potential detection. However, they have not as of yet been implemented for peripheral nerve action potential detection. We demonstrate for the first time, compelling evidence that OPM can detect the magnetic signature of travelling peripheral nerve action potentials that indicate OPM use as a potential technique for SFN diagnosis.

Compound nerve action potential conduction changes in nerve trunk due to tension at various strains and strain rates

This study investigated compound nerve action potential (CNAP) changes of nerve trunk subjected to stretch at various strains and strain rates. An animal model of rapid stretch injury to nerve based on traffic accidents was developed in order to study CNAP changes of nerve trunk subjected to acute stretch. 18 bullfrogs were dissected and the sciatic nerves’ trunks were obtained. The nerve trunk was stretched by 6%, 12% or 18% of its length and the tensile strain rates were 30s-1 and 50s-1 respectively. The results showed that at 6% strain and 30s-1 strain rate, the amplitude, action potential duration and conduction velocity of CNAP had a slight change. When the strain and strain rate continued to be increased, the amplitude, conduction velocity and area under the curve would be decreased while the action potential duration would be increased. At 18% strain and 50s-1 strain rate, CNAP conduction was almost completely blocked. The different strains or strain rates had a significant effect on nerve signal conduction. Under the same strain, a higher strain rate would increase the probability of nerve conduction block. These findings are of great significance to study the injury mechanism of rapid nerve stretch and to evaluate the nerve functional damage level in traffic accidents.

Focal Vibration Alters Human Digital Sensory Nerve Action Potentials: A Pilot Study

Introduction. We studied the impact of vibratory stimulation on the electrophysiological features of digital sensory nerve action potential (SNAP). Methods. The antidromic digit 3 SNAP was recorded in 19 healthy adults before, during, and after applying a vibration to either 3rd or 5th metacarpal phalangeal joint (MCPJ) at 60 Hz and amplitude of 2 mm. 100% supramaximal stimulus intensity was performed in 5 subjects (randomly selected from the 19 subjects) where the SNAP sizes were recorded. Results. The amplitude of digit 3 SNAP declined to 58.9 ± 8.6 % when a vibration was applied to MCPJ digit 3. These impacts did not change by increasing the electrical stimulus intensity. The SNAP regained its baseline value immediately after the cessation of vibration stimulation. The magnitude of size reduction of digit 3 SNAP was less when vibration was moved to from MCPJ of digit 3 to MCPJ of digit 5. Discussion. The marked drop of the SNAP size during vibratory stimulation reflects the decreased responsiveness of Aβ afferents to electrical stimulation, which deserve further investigation in the study of focal vibration in neurorehabilitation.

The effect of evocalcet on vagus nerve activity of the gastrointestinal tract in miniature pigs

Evocalcet is a novel calcimimetic agent with fewer gastrointestinal (GI) adverse effects compared to cinacalcet. Although it is thought that cinacalcet induces GI side effects through the direct stimulation of the calcium receptor (CaR) expressed in the GI tract, the differences in the direct stimulatory effects of these two drugs on the GI tract have not been reported. In this study, we analyzed the difference in the GI effects of these two calcimimetic agents using miniature pigs by detecting vagus nerve stimulation after oral administration of the agents. Although cinacalcet induced vomiting in miniature pigs, evocalcet never induced emetic symptoms. A significant increase in the vagus nerve action potentials was observed after the administration of cinacalcet. Although the increase of that after the administration of evocalcet was mild and not significant in comparison to that in the vehicle group, it was not significantly different from the vagus nerve action potentials after cinacalcet treatment.

Detailed insight into transtympanic electrocochleography (TT-ECochG) and direct cochlear nerve action potential (CNAP) for intraoperative hearing monitoring in patients with vestibular schwannoma – methodology of measurements and interpretation of results

<b>Background:</b> The aim was to present the methodology and interpretation of intraoperative hearing monitoring with simultaneous Transtympanic Electrocochleography (TT-ECochG) and direct Cochlear Nerve Action Potential (CNAP) measurements during vestibular schwannoma removal. <br><b>Materials and Methods:</b> Detailed methodology of measurements and interpretation of results are presented in three exemplary patients who underwent tumor removal via middle fossa approach (MFA) with the use of intraoperative monitoring of hearing with TT-ECochG and direct CNAP performed in real time. In addition, all responses were automatically recorded and stored along with surgical information and subjected to detailed analyses and calculation after surgery. <br><b>Results:</b> The following changes in TT-ECochG and direct CNAP responses were observed: Patient #1 – TT-ECochG and CNAP responses with minor, but transient, morphology changes (hearing was preserved); Patient #2 – CNAP responses changed significantly but, temporarily, from triphasic into biphasic responses later, with marked but partially reversible desynchronization of CNAP; changes in TT-ECochG responses were also observed but, at the end, returned to baseline (surgery-related deterioration of hearing); Patient #3 – irreversible changes of TT-ECochG and direct CNAP (complete loss of hearing). <br><b>Conclusions:</b> A combination of TT-ECochG and direct CNAP allows for real-time monitoring of auditory function during vestibular schwannoma resection and surgical manipulation which contribute to the risk of hearing loss. Therefore, the surgeon can be instantly informed about changes which could increase the possibility of preserving the patient’s hearing