Electrophysiological Methods to Assess Peripheral Pain Block in an Anesthetized Rat

In vivo electrophysiological recordings from the lumbar region of the rat spine can be used to study the activation of sensory neural signals in the hindlimbs, as well as the efficacy of therapeutic interventions that interrupt ascending pain signals. Here, we describe the surgical procedures (laminectomy and sciatic nerve exposure), data collection, and analysis of two complementary electrophysiological signals: local field potential recordings and wide dynamic range single neuron recordings. Both differentiate activation of nerve fiber subclasses based on conduction velocity relative to an electrical stimulation pulse. Local field potentials (LFP) can differentiate between A α/β and C nerve fibers but cannot detect Aδ activity. They provide information about the global activation of the whole sciatic. Following electrical direct stimulation of the sciatic nerve using a J-cuff style bipolar electrode, area under the curve measurements of the two troughs corresponding to each component are calculated. Wide dynamic range (WDR) single neuron recordings assess the activity of a subset of sciatic activation, and can differentiate Aα/β, Aδ, and C fiber types. Electrical stimulation can be applied directly to the sciatic as with LFP, or via needle electrodes placed in the plantar surface of the hindpaw. This higher-frequency signal yields high signal-to-noise action potential spikes. Spike counts within predefined latency windows reflect the level of activity of the various fiber types. To date, these techniques have been used to assess the temporal properties of three different pain block modalities: Direct current electrical nerve block using a custom-made Carbon Separated Nerve Interface Electrode (CSINE), Kilohertz Frequency Alternating Current, and photobiomodulation using an 830 nm laser. This surgical preparation has been used for nerve block interventions for up to 5 h.