Abstract
The dorsal root ganglia (DRG) contain cell bodies of primary afferent neurons, which are frequently studied by recording extracellularly with penetrating microelectrodes inserted into the DRG. We aimed to isolate single- and multi-unit activity from primary afferents in the lumbar DRG using non-penetrating electrode arrays and to characterize the relationship of that activity with limb position and movement. The left sixth and seventh lumbar DRG (L6-L7) were instrumented with penetrating and non-penetrating electrode arrays to record neural activity during passive hindlimb movement in 7 anesthetized cats. We found that the non-penetrating arrays could record both multi-unit and well-isolated single-unit activity from the surface of the DRG, although with smaller signal to noise ratios (SNRs) compared to penetrating electrodes. Across all recorded units, the median SNR was 1.1 for non-penetrating electrodes and 1.6 for penetrating electrodes. Although the non-penetrating arrays were not anchored to the DRG or surrounding tissues, the spike amplitudes did not change (<1% change from baseline spike amplitude) when the limb was moved passively over a limited range of motion (~20 degrees at the hip). Units of various sensory fiber types were recorded, with 20% of units identified as primary muscle spindles, 37% as secondary muscle spindles, and 24% as cutaneous afferents. Our study suggests that non-penetrating electrode arrays can record modulated single- and multi-unit neural activity of various sensory fiber types from the DRG surface.
Highlights
Since the pioneering studies of Sir Edgar Adrian[1,2], neuroscientists have been measuring the bioelectrical activity of primary afferent neurons to understand the neural code for touch[3,4,5], proprioception[6,7], and other sensory systems
We observed that non-penetrating electrode arrays could record modulated, single-unit activity at the dorsal root ganglion (DRG) surface
While signal to noise ratios (SNRs) was generally lower than for units recorded by penetrating electrodes, it was possible to isolate many single units via non-penetrating recordings
Summary
Since the pioneering studies of Sir Edgar Adrian[1,2], neuroscientists have been measuring the bioelectrical activity of primary afferent neurons to understand the neural code for touch[3,4,5], proprioception[6,7], and other sensory systems. Et al and Prochazka, et al were the first to demonstrate single neuron action potential recordings from DRG of freely moving cats, providing the first measurements of muscle and cutaneous afferent activity during normal locomotion[13,14]. Penetrating arrays in spinal roots to target DRG are subject to mechanical failure as electrodes can be damaged by contact with surrounding vertebral bone during the implantation procedure For both long-term investigations of somatosensory function in experimental animals, and potentially for neuroprosthetic applications in people, stable recordings from primary sensory afferents in the DRG are essential. Electrodes placed on the surface of the DRG would be in close proximity to the most superficial cell bodies
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