Human Dorsal Root Ganglia

Abstract

Sensory neurons with cell bodies situated in dorsal root ganglia convey information from external or internal sites of the body such as actual or potential harm, temperature or muscle length to the central nervous system. In recent years, large investigative efforts have worked toward an understanding of different types of DRG neurons at transcriptional, translational, and functional levels. These studies most commonly rely on data obtained from laboratory animals. Human DRG, however, have received far less investigative focus over the last 30 years. Nevertheless, knowledge about human sensory neurons is critical for a translational research approach and future therapeutic development. This review aims to summarize both historical and emerging information about the size and location of human DRG, and highlight advances in the understanding of the neurochemical characteristics of human DRG neurons, in particular nociceptive neurons.

Keywords: DRG; MRI; immunohistochemistry; nociceptor; satellite cells.

FIGURE 1

(A) Representative HE stained micrograph section of a thoracic human DRG (medical dissection course, ethics approval obtained from The Southern Adelaide Clinical Human Research Ethics Committee, OFR no.: 55.17) with a thick protective layer of connective tissue demonstrating the predominant localization of cell bodies in the periphery of the ovoid DRG cross-section. (B) Cell bodies of sensory neurons containing lipofuszin (1) and a nucleus with a prominent nucleolus (2), surrounded by satellite cells (3). Bundles of nerve fibers (dashed line) are predominantly present in the center of the ganglion. The HE staining method results in shrinkage of the cell bodies which disconnects them from the layer of satellite cells. (C) Immunohistochemistry micrograph for CD163 with counterstaining for hematoxylin shows the presence and distribution of macrophages (arrows) in DRG.

FIGURE 2

(A) HE micrograph section of a thoracic human DRG in higher magnification shows a high number of neuronal somata of different sizes in the periphery of DRG, next to the thick connective tissue covering. (B) Schematic representation of the HE micrograph figure highlighting the variety of different structures and cell types in human DRG. Connective tissue layers (Reina et al., 1996) (1), fibroblasts (2), capillaries (Kutcher et al., 2004) (3), basement membrane (Johnson, 1983) (4) between nerve cells (5) and satellite cells (Hanani, 2005) (6). The pseudo-unipolar process (Rudomin, 2002) (7) originates from sensory neurons with prominent nuclei containing a singular nucleolus (Berciano et al., 2007) (8) and sometimes lipofuszin (Moreno-Garcia et al., 2018) (9). Non-neuronal cells in DRG include T- and B-lymphocytes (10) and macrophages (11) (Graus et al., 1990a).