Spinal cord potentials evoked by cutaneous afferents in the monkey

Area of Science:

• Neuroscience
• Spinal Cord Physiology

Background:

• The lumbosacral spinal cord processes sensory information from the hindlimb via myelinated afferent fibers.
• Previous studies in cats identified N1 and N2 potentials in response to afferent fiber stimulation.

Purpose of the Study:

• To investigate spinal cord potentials evoked by stimulation of myelinated afferent fibers in the monkey hindlimb.
• To characterize a newly observed potential, termed the N3-wave, and determine its origin and properties.

Main Methods:

• Recording of surface and intracellular cord potentials in the monkey lumbosacral spinal cord.
• Stimulation of cutaneous and mixed nerves of the hindlimb.
• Utilizing subtraction techniques, stimulus-response strength grading, conduction delay measurements, and selective fiber blockade (anodal block of A-alpha-beta fibers).

Main Results:

• A novel potential, the N3-wave, was identified, occurring later than N1 and N2 potentials.
• The N3-wave originates from neural circuitry intrinsic to the lumbosacral spinal cord, as it persists after spinal cord transection.
• The N3-wave is evoked specifically by Adelta fibers and shows distinct field potential characteristics.
• A late burst discharge in spinal neurons, including spinothalamic tract neurons, corresponds in time to the N3-wave.

Conclusions:

• The N3-wave is a distinct spinal cord potential generated by Adelta fibers.
• Its intrinsic spinal origin suggests a role in local processing of Adelta fiber input.
• The N3-wave can potentially serve as a valuable monitor of the central effects of Adelta fibers within the spinal cord.