This article details a method for electrophysiological recording from polymodal C-fibers in the sciatic nerve of anesthetized rats. The procedure involves surgical exposure of the nerve, application of stimuli, and monitoring of action potentials.
Take an anesthetized rat and make an incision on its thigh to expose the sciatic nerve, a peripheral nerve providing sensory and motor supply to the lower limbs.
Apply a physiological solution to keep the exposed tissue moistened.
Suture the incised skin to a metal hoop, creating a chamber for electrophysiological measurements.
Place a platform under the nerve to enhance the visibility of the nerve. Apply liquid paraffin to prevent the nerve from drying.
Place a reference electrode subcutaneously to establish a baseline electrical activity.
Remove the membranous nerve covering to expose the C-fibers. Suspend a single fiber over a recording electrode.
Apply mechanical and thermal stimuli to the foot and observe the fiber's response to both, confirming it as a polymodal C-fiber.
Implant stimulus electrodes on the foot for targeted single-fiber stimulation.
The stimulation generates action potentials that travel along the fiber and are monitored by the recording electrode.
To begin this procedure, prepare and disinfect all surgical instruments, prior to surgery. Then, prepare one to two liters of normal Ringer's extracellular solution, and store at four degrees Celsius until use. To expose the sciatic nerve trunk for recording first, cut open the anesthetized rat skin and muscles on the dorsal part of the thigh. Then, perform a blunt dissection along the femoral biceps.
Carefully isolate the sciatic nerve trunk using ophthalmic scissors and a glass separation needle, and keep the tissue moist using Ringer's solution. Next, fix the animal on a homemade metal hoop by sewing the skin into the slot around it.
Pull the skin up slightly, to establish a fluid bath. Expose 1 centimeter of sciatic nerve trunk at the proximal side. Place a small brown platform under the nerve trunk to enhance the contrast in order to observe the fine nerve trunk clearly. Subsequently, apply some warm liquid paraffin on the top of the nerve trunk to prevent drying of the fiber surface. Remove the fluid if there is an exudation around the nerve trunk.
To perform recording, select a platinum filament as the recording electrode. Heat and create a small hook at the very end. Afterward, attach the electrode to a micromanipulator. In the bath, place a reference electrode next to the subcutaneous tissue. Split the spinal dura and the Pia mater, and obtain the sciatic nerve. Under a stereomicroscope at 25% magnification, pick up a fine fascicle and suspend the proximal end of the axon on the hook of the recording electrode.
Identify the receptive field of a single nociceptive C fiber using a mechanical stimulus and thermal stimulus. If the firing of the nerve fiber responds to the mechanical stimuli and hot water, then, consider it as a polymodal non-receptive C fiber.
Next, insert two needle stimulus electrodes with a two-millimeter interval into the skin of the identified field for the delivery of electrical stimuli. Display the waveform of an action potential on the oscilloscope and employ a computer A/D board with a signal sampling rate of 20 kilohertz. Then, record the spikes using data acquisition software and analyze it later with professional software.
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