In Vivo Electrophysiological Measurements on Mouse Sciatic Nerves

The overall goal of this method is to determine major nerve conduction properties on SCIC nerves of living mice. The mouse to be tested is placed on its stomach. Please take into consideration that you have to be familiar with the anatomy of the SCIC nerve here indicated in blue, the sensing electrodes indicated in black is installed at a position where the gastro muscle has its maximum diameter.

The reference electrodes indicated in red is just placed beneath the sensing electrodes. Now the point of distal stimulation has to be marked. We arbitrarily chose the defined and constant distance of four millimeters.

The place of proximal stimulation is at a distance of 16 millimeters from the sensing electrode. This means that we have a gap of exactly 12 millimeters between the points of proximal and distal stimulation of the STIC nerve. The stimulation using the needle electrodes is subsequently performed firstly at the proximal stimulation site and afterwards at the position of distal Stimulation.

Hi, my name Is Alexander Schultz. I work at the Ance Institute for H Research in Gina, Germany under the supervision of Dr.Helen Morrison. In collaboration with Professor Reinhard Power from the Institute of Molecular Cell Biology from Gina University Hospital, we established a method by which we are able to perform electrophysiological measurements on sky nerves of living mice.

These recordings are a powerful tool used to characterize mouse models of neuromuscular diseases. So let's get Started. This is the equipment you Would need to perform the measurements.

Three needle electrodes for ECG recordings. One needle electrode for stimulation, ring electrodes for sensing, and as reference hair, remove the cream an electric razor, a feedback controlled heating plate, a recal thermo probe, a mouse piece for anesthesia And contact gel. The mice are Anesthetized by continuous isof fluorine inhalation for initiation of the anesthesia.

We applied 3%isof fluorine in a hundred percent oxygen. Later during the measurements, it is sufficient to work with 2%isof fluorine in a hundred Percent oxygen. In order to reduce Skin resistance during the measurements, we completely remove the fur from the hind limbs of the tested mice.

This is achieved by an electric Razor. In addition, we use a commercially available hair removal cream. At the end, The cream is completely removed and the skin is cleaned using 70%ethanol.

In The Next step, we, we install three electrodes for ECG recordings, one electrode under the skin of each fallen and one electrode under the skin in the neck area. Taking ECG recordings during the measurements allows monitoring of at least one vital parameter. Both Hind limbs are fixed on the ground by adhesive tape after an approximate placement of the ring Electrodes.

For Optimal signal conductivity, we use contact gel reducing transfer resistance between the skin and the ring electrodes. The sensing Electrodes labeled in black is placed at the position where the gastrocs muscle has its maximum diameter. The reference electrodes indicated in red is placed just beneath the sensing electrodes.

Then the exact positions for sciatic nerve stimulation are defined and marked in a distance of four millimeters to the sensing electrodes. The distal stimulation will take place in a distance of 16 millimeters to the sensing electrodes. The proximal stimulation will be carried Out here.

Here you see the user interface of a program for data acquisition and analysis. In the first row, the ECG recording is visualized. In the second row.

You can see the repetitive pulses from the stimulator. In the third row, the response signals detected by the sensing electrode will appear using a sampling rate of 50 kilohertz. Now we can start the actual recordings.

The stimulation needle is firstly injected at the position of proximal stimulation. The correct positioning of the needle, or more specifically, the proper stimulation of the STIC nerve, can be monitored by an appropriate muscle response downstream of the STIC nerve. In the area of the sensing electrodes, the signals detected by the sensing electrodes are visualized in the user interface.

Simultaneously, please try to achieve clear biphasic response curves of constant maximum Amplitude. Afterwards, the distal Stimulation is performed in the same manner. In the left upper corner, you can see the simultaneous recordings from the standing electrodes in the user Interface.

In the Upper row, you see a representative image of a single square wave pulse of oh 0.1 milliseconds duration, which is applied by the stimulation needle electrodes every 200 milliseconds in the lower row, a corresponding neuromuscular response curve is shown. The data analysis comprises the determination of the latency and the amplitude of the recorded signals. For this purpose, it is recommended to average multiple response curves from one stimulation site.

The latency of the signal is the time between stimulation onset, and the beginning of the response curve. Or more precisely the inflection point of the, the time difference between the latencies following proximal and distal stimulation can now be used to calculate the nerve conduction velocity. For this purpose, you also need to know the spatial distance between proximal and distal stimulation in our case 12 millimeters.

In addition, the amplitude of the response curve can be quantified in order to determine the so-called compound motor action potential. It represents the magnitude between maximum positive and negative turnaround points of the signal. For some applications, it can be also helpful to measure the duration of the signal amplitude lasting from the first inflection points to the last one of the response curve.

The nerve conduction velocity is highly dependent on rapid signal propagation enabled by myelination. Therefore, demyelinating diseases generally show decreased conduction velocities. The compound motor action potential correlating with the number of functional axons and neuromuscular junctions is an indicator for axonal damage when significantly Reduced.

We have Just shown you an easy and reliable way to determine major nerve conduction properties in mice. When doing this procedure, it is of great importance to reduce skin resistance by complete hair removal and cleaning of the skin. Then you will record signals with an optimal signal to noise ratio.

Furthermore, it is important to identify the maximum stimulus response for appropriate data acquisition. This can be achieved by gentle movement of the stimulation needle in a way that you can detect biphasic response curves. Thanks for watching and good luck with your experiments.