This article details the methodology for trans-spinal direct current stimulation (tsDCS) in rat models, focusing on the measurement of motoneuron activity. It outlines the procedures for electrode placement and the recording of electrical properties during stimulation.
Begin by placing a saline-soaked sponge on the thoracic-12 vertebra of a rat prepared for the procedure.
Position an electrode on it for trans-spinal direct current stimulation or tsDCS, which involves applying a direct current across the spinal cord.
To measure the intracellular recording of a target motoneuron during tsDCS, insert a microelectrode into the spinal cord at the location of its origin.
Assess the motoneuron's baseline membrane potential and the frequency of electrical impulses to ensure the microelectrode is securely placed for accurate measurements during tsDCS.
Apply anodal tsDCS, where positively charged ions enter the neuron as the current flows from the anode through the tissue to the cathode.
Apply cathodal tsDCS, where negatively charged ions enter the neuron as the current flows in the reverse direction.
Record the changes in the motoneuron's electrical properties during anodal and cathodal tsDCS.
To place the trans-spinal direct current stimulation electrodes, place a saline-soaked sponge on the dorsal side of the TH-12 vertebra, and use fine manipulation to press the sponge with an active trans-spinal direct current stimulation electrode. Then, mount a custom-pulled microelectrode onto the micromanipulator, allowing a 1 to 2-micron stepping movement and stereotaxic calibration, and drive a micropipette tip into a selected patch in the PR at a 15 to 20-degree medial-lateral angle.
To record the motor neuron membrane and firing properties, in the bridge mode of the intracellular amplifier, stimulate the respective nerve branches to identify the motor neuron on the basis of the all-or-nothing appearance of the antidromic action potential.
In the discontinuous current clamp mode of the intracellular amplifier with a current switch rate mode of 4 to 8 kilohertz, use a 0.5-millisecond intracellular depolarizing current pulses to evoke an orthodromic action potential in a motor neuron.
To calculate the cell input resistance, stimulate a motor neuron with 40 short 100-millisecond pulses of hyperpolarizing 1 nanoamp current. To determine the rheobase value as the minimum amplitude of the depolarizing current required to elicit a single spike, stimulate a motor neuron with 50-millisecond square wave pulses at increasing amplitudes.
Then, inject 500-millisecond square wave pulses of depolarizing current at increasing amplitudes in 0.122 nanoamp steps to evoke rhythmic discharges of motor neurons. For trans-spinal direct current stimulation, start the polarization procedures by trans-spinal application of direct current, while maintaining a stable penetration of the motor neuron.
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