In Vivo Electrophysiological Measurements on Mouse Sciatic Nerves

Summary

Measurements of nerve conduction properties in vivo exemplify a powerful tool to characterize various animal models of neuromuscular diseases. Here, we present an easy and reliable protocol by which electrophysiological analysis on sciatic nerves of anesthetized mice can be performed.

Abstract

Electrophysiological studies allow a rational classification of various neuromuscular diseases and are of help, together with neuropathological techniques, in the understanding of the underlying pathophysiology¹. Here we describe a method to perform electrophysiological studies on mouse sciatic nerves in vivo.

The animals are anesthetized with isoflurane in order to ensure analgesia for the tested mice and undisturbed working environment during the measurements that take about 30 min/animal. A constant body temperature of 37 °C is maintained by a heating plate and continuously measured by a rectal thermo probe². Additionally, an electrocardiogram (ECG) is routinely recorded during the measurements in order to continuously monitor the physiological state of the investigated animals.

Electrophysiological recordings are performed on the sciatic nerve, the largest nerve of the peripheral nervous system (PNS), supplying the mouse hind limb with both motoric and sensory fiber tracts. In our protocol, sciatic nerves remain in situ and therefore do not have to be extracted or exposed, allowing measurements without any adverse nerve irritations along with actual recordings. Using appropriate needle electrodes³ we perform both proximal and distal nerve stimulations, registering the transmitted potentials with sensing electrodes at gastrocnemius muscles. After data processing, reliable and highly consistent values for the nerve conduction velocity (NCV) and the compound motor action potential (CMAP), the key parameters for quantification of gross peripheral nerve functioning, can be achieved.

Introduction

Electrophysiological measurements are an indispensable tool for investigating the functional integrity of peripheral nerves in both clinical and laboratory environments. In humans, a large number of neuromuscular disorders and neuropathies diagnostically rely on electrophysiological measurements. By measuring nerve properties as conduction velocity or potential amplitudes of the signal, it is possible to characterize the rough origin of peripheral nerve diseases.

The nerve conduction velocity is highly dependent on rapid signal propagation enabled by myelination. Therefore, demyelinating processes generally show decreased conduction velocit....

Protocol

The present study was performed according to the Protection of Animals Act of the Federal Republic of Germany (Tierschutzgesetz der Bundesrepublik Deutschland) and was approved by the Thuringian State Office for Food Safety and Consumer Protection (Thüringer Landesamt für Lebensmittelsicherheit und Verbraucherschutz).

1. Setting Up the Measurements

1. Anesthetize the mice by isoflurane/O₂ inhalation - for initiation of anesthesia 3%, for maintenance 2% isoflurane in 100% oxygen (Figure 1). Confirm sufficient anesthesia by testing simple reflexes such as movement reflexes and testing of sensitivity for lo....

Results

We conducted a series of in vivo electrophysiological measurements on sciatic nerves of 12 mice in total for this study: 6 animals of each gender. The measurements were performed with the presented protocol and delivered the following results:

Both male and female mice display a mean sciatic nerve conduction velocity of approximately 20 m/sec (Figure 5). This is consistent with other measurements in the literature. Furthermore, it shows that there are no relevant diff.......

Discussion

The described protocol provides an easy and reliable method to determine sciatic nerve conduction properties on anesthetized mice without the need to expose the nerve of interest. Nevertheless, this experimental procedure causes tissue injury by needle puncture. It is therefore a reasonable option to sacrifice the animals after finishing the recordings. However, compared to other more invasive procedures, which require the exposure of the nerve prior to recordings, tissue damage is comparably small ^3,14. There.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Concentric Needle Electrodes (Stimulation)	Natus Medical Incorporated, San Carlos, CA, USA	9013S0901
Digital Ring Electrodes (Recording)	Natus Medical Incorporated, San Carlos, CA, USA	9013S0302
ToM - Tower of Measurement (A/D converter)	GJB Datentechnik GmbH, Langewiesen, Germany
AtisaPro, data acquisition and analysis software	GJB Datentechnik GmbH, Langewiesen, Germany
HSE-Stimulator T	Hugo Sachs Elektronik, Hugstetten, Germany