Dorsal root ganglion

Dorsal root ganglion

A posterior root ganglion (or spinal ganglion) (also known as a dorsal root ganglion), is a cluster of nerve cell bodies (a ganglion) in a posterior root of a spinal nerve.

This structure is critical in the processing of the pain signal from the peripheral nervous system to its position in the central nervous system.

1st order neuron: small, finely myelinated afferents; soma in dorsal root ganglion (no synapse). Enter cord at dorsolateral tract (zone of Lissauer). Synapse: substantia gelatinosa (Rexed II).

The dorsal root ganglion (sensory) is also located in the foramen within the nerve root sheath.

In the “STIR” image the dorsal root ganglion may enhance on fat suppression images.

In extreme lateral lumbar disc herniation pain tends to be more severe (may be due to the fact that the dorsal root ganglion may be compressed directly) and often has more of a burning dysesthetic quality.

Compression of the dorsal root ganglion may result in a slower recovery from discectomy and overall less satisfying outcome than with the more commonplace paramedian disc herniation.


In a study, Sanz et al. identified a metalloproteinase-dependent mechanism necessary to promote growth in embryonic dorsal root ganglion cells (DRGs). Treatment of embryonic DRG neurons with pan-metalloproteinase inhibitors, tissue inhibitor of metalloproteinase-3, or an inhibitor of ADAM Metallopeptidase Domain 10 (ADAM10) reduces outgrowth from DRG neurons indicating that metalloproteinase activity is important for outgrowth.

The IgLON family members Neurotrimin (NTM) and Limbic System-Associated Membrane Protein (LSAMP) were identified as ADAM10 substrates that are shed from the cell surface of Dorsal root ganglion (DRG) neurons. Overexpression of LSAMP and NTM suppresses outgrowth from DRG neurons. Furthermore, LSAMP loss of function decreases the outgrowth sensitivity to an ADAM10 inhibitor. Together this findings support a role for ADAM-dependent shedding of cell surface LSAMP in promoting outgrowth from DRG neurons 1).

Dorsal root ganglion (DRG) are promising sites for recording sensory activity. Current technologies for DRG recording are stiff and typically do not have sufficient site density for high-fidelity neural data techniques.

In acute experiments, Sperry et al. demonstrated single-unit neural recordings in sacral DRG of anesthetized felines using a 4.5 µm-thick, high-density flexible polyimide microelectrode array with 60 sites and 30-40 µm site spacing. They delivered arrays into DRG with ultrananocrystalline diamond shuttles designed for high stiffness affording a smaller footprint. They recorded neural activity during sensory activation, including cutaneous brushing and bladder filling, as well as during electrical stimulation of the pudendal nerve and anal sphincter. They used a specialized neural signal analysis software to sort densely-packed neural signals.

They successfully delivered arrays in five of six experiments and recorded single-unit sensory activity in four experiments. The median neural signal amplitude was 55 μV peak-to-peak and the maximum unique units recorded at one array position was 260, with 157 driven by sensory or electrical stimulation. In one experiment, they used the neural analysis software to track eight sorted single units as the array was retracted ~500 μm.

This study is the first demonstration of ultrathin, flexible, high-density electronics delivered into DRG, with capabilities for recording and tracking sensory information that is a significant improvement over conventional DRG interfaces 2).

C2 root ganglion.

Sacral dorsal root ganglion.

Dorsal root ganglion stimulation.


1)

Sanz RL, Ferraro GB, Girouard MP, Fournier AE. Ectodomain shedding of Limbic System-Associated Membrane Protein (LSAMP) by ADAM Metallopeptidases promotes neurite outgrowth in DRG neurons. Sci Rep. 2017 Aug 11;7(1):7961. doi: 10.1038/s41598-017-08315-0. PubMed PMID: 28801670.
2)

Sperry ZJ, Na K, Jun J, Madden LR, Socha A, Yoon E, Seymour J, Bruns TM. High-density neural recordings from feline sacral dorsal root ganglia with thin-film array. J Neural Eng. 2021 Feb 5. doi: 10.1088/1741-2552/abe398. Epub ahead of print. PMID: 33545709.
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