Proceedings of The Physiological Society

Future Physiology (Leeds, UK) (2017) Proc Physiol Soc 39, PC11

Poster Communications

An improved method that allows simultaneous recording of stimulus evoked A and C fibre conduction in mouse sciatic nerve

A. M. Brown1, L. R. Rich1

1. Life Sciences, University of Nottingham, Nottingham, United Kingdom.

The area under the stimulus evoked compound action potential (CAP) recorded from isolated nerve trunks is indicative of the number of conducting axons, a phenomenon that has been used advantageously in investigations of injury mechanisms in central white matter, where the ratio of post- and pre-insult CAP area offers an index of injury, against which neuroprotective strategies can be compared. Equivalent studies to those described above are lacking in peripheral nerves, although peripheral nerves are affected by chronic hypoglycaemia, and as susceptible to diabetic neuropathy. These considerations led us to carry out preliminary studies on the effect of aglycemia on sciatic nerve. In the absence of exogenously applied glucose Schwann cell glycogen is broken down to lactate, which is shuttled to the large myelinated A fibres to support conduction; the unmyelinated C fibres do not benefit from the presence of glycogen (Brown et al, 2012). All procedures were carried out in accordance with the Animals (Scientific Procedures) Act 1986 under appropriate authority of project and personal licenses. Adult male CD-1 mice were killed by cervical dislocation and decapitated. Sciatic nerves were dissected, placed in a perfusion chamber, superfused with aerated aCSF containing 10 mM glucose. A Grass S88 double pulse stimulator was employed to deliver two independent stimuli to the nerve. The sciatic nerve contains two morphologically distinct axons; large myelinated A fibres, and small unmyelinated C fibres. The A fibres have a lower threshold for recruitment than the C fibres, thus the 1st stimulus of up to 15 V was used to recruit the A fibres, whereas the 2nd stimulus of up to 150 V was used to recruit the C fibres. In the metabolic studies that we routinely carry out it is beneficial to monitor the amplitude of the responses in real time. During acquisition we opened a separate viewing window, which allowed real time monitoring of the A peak. The small C peak can be occluded in electrical noise, thus we used a running average of the traces to increase the signal to noise ratio in order to visualize the C peak profile over extended periods of time. We are currently investigating the ability of substrates to support conduction in the sciatic nerve. Thus the method we describe can be used for the extended type of experiment required in these studies. 10 mM glucose supports A and C fibre conduction of over 8 hours, but omitting glucose from the aCSF causes C peak then A peak failure. For C peaks 10 mM glucose supports conduction for 8 hours but 10 mM fructose causes the peak to fail after about 6 hours. This method allows for extended duration experiments to be conducted that allow the experimenter to view real time amplitudes of the A and C peak, and record the A and C peak simultaneously to compare their metabolic profiles.

Where applicable, experiments conform with Society ethical requirements