Ultrastructure of dorsal root ganglia

Abstract

Dorsal root ganglia (DRG) contains thousands of sensory neurons that transmit information about our external and internal environment to the central nervous system. This includes signals related to proprioception, temperature, and nociception. Our understanding of DRG has increased tremendously over the last 50 years and has established the DRG as an active participant in peripheral processes. This includes interactions between neurons and non-neuronal cells such as satellite glia cells and macrophages that contribute to an increasingly complex cellular environment that modulates neuronal function. Early ultrastructural investigations of the DRG have described subtypes of sensory neurons based on differences in the arrangement of organelles such as the Golgi apparatus and the endoplasmic reticulum. The neuron-satellite cell complex and the composition of the axon hillock in DRG have also been investigated, but, apart from basic descriptions of Schwann cells, ultrastructural investigations of other cell types in DRG are limited. Furthermore, detailed descriptions of key components of DRG, such as blood vessels and the capsule that sits at the intersection of the meninges and the connective tissue covering the peripheral nervous system, are lacking to date. With rising interest in DRG as potential therapeutic targets for aberrant signalling associated with chronic pain conditions, gaining further insights into DRG ultrastructure will be fundamental to understanding cell–cell interactions that modulate DRG function. In this review, we aim to provide a synopsis of the current state of knowledge on the ultrastructure of the DRG and its components, as well as to identify areas of interest for future studies.

Transcriptional Profiles of Non-neuronal and Immune Cells in Mouse Trigeminal Ganglia

“…It is presumed that transcriptional changes in sensory ganglion non-neuronal cells could eventually lead to production of plethora of mediators. It has been shown that these mediators can sensitize sensory neurons (Ji et al, 2016;Donnelly et al, 2020;Gazerani, 2021) by direct communication with sensory neurons (Kim et al, 2016) and/or by regulating a plethora of neuronal channels, which could result in changing neuronal excitability and gating properties (Domoto et al, 2021;Haberberger et al, 2023;McGinnis and Ji, 2023).…”

“…Multiple reports assigned critical roles in nociceptive signal transmission to dorsal root ganglion (DRG) glial (Huang et al, 2013;Donnelly et al, 2020;Gazerani, 2021;McGinnis and Ji, 2023) and immune cells, especially macrophages and neutrophils (Ji et al, 2016;Yu et al, 2020;Domoto et al, 2021;Lesnak et al, 2023). It is suggested that ganglion non-neuronal cells are capable of sensitizing neurons (Ji et al, 2016;Donnelly et al, 2020;Gazerani, 2021) by directly communicating with them and changing their gating properties (Domoto et al, 2021;Haberberger et al, 2023;McGinnis and Ji, 2023).…”

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing

“…200 The size of DRG also varies across species (in accordance with body size) as human DRG have approximately 4- to 5-fold more neurons per ganglion compared with the same ganglia in rodents. 85 In general, sensory neurons are concentrated near the DRG periphery while the center contains intersecting columns of nerve fibers, although this appearance can vary depending on the plane of section. 84,85 The numbers of sensory neurons may vary considerably in paired DRG for a given spinal cord segment.…”

“…85 In general, sensory neurons are concentrated near the DRG periphery while the center contains intersecting columns of nerve fibers, although this appearance can vary depending on the plane of section. 84,85 The numbers of sensory neurons may vary considerably in paired DRG for a given spinal cord segment. 246 Neurons in DRG range in size from 10 to over 100 µm in diameter (depending on age 172 and species), and neurons of all sizes are interspersed in the neuron-rich regions of sensory ganglia, with the bigger neurons frequently concentrated near the capsule.…”