In Vitro Model to Investigate Communication between Dorsal Root Ganglion and Spinal Cord Glia.

Junxuan Ma,Leo R Quinlan,Mauro Alini,Marianna Peroglio,Sibylle Grad,Vaibhav Patil,Abhay Pandit,David P Finn

doi:10.3390/ijms22189725

Abstract

Chronic discogenic back pain is associated with increased inflammatory cytokine levels that can influence the proximal peripheral nervous system, namely the dorsal root ganglion (DRG). However, transition to chronic pain is widely thought to involve glial activation in the spinal cord. In this study, an in vitro model was used to evaluate the communication between DRG and spinal cord glia. Primary neonatal rat DRG cells were treated with/without inflammatory cytokines (TNF-α, IL-1β, and IL-6). The conditioned media were collected at two time points (12 and 24 h) and applied to spinal cord mixed glial culture (MGC) for 24 h. Adult bovine DRG and spinal cord cell cultures were also tested, as an alternative large animal model, and results were compared with the neonatal rat findings. Compared with untreated DRG-conditioned medium, the second cytokine-treated DRG-conditioned medium (following medium change, thus containing solely DRG-derived molecules) elevated CD11b expression and calcium signal in neonatal rat microglia and enhanced Iba1 expression in adult bovine microglia. Cytokine treatment induced a DRG-mediated microgliosis. The described in vitro model allows the use of cells from large species and may represent an alternative to animal pain models (3R principles).

Highlights

Low back pain (LBP) is often associated with intervertebral disc (IVD) degeneration [1]
Degenerative IVD is characterized by increased levels of pro-inflammatory cytokines [2], such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, which are observed in disc tissue from discogenic pain patients [2,3,4]
Viable neurons were distinguished from other types of cells by a depolarization-triggered acute and significant rise in intracellular calcium (Figure 1A,B)

Summary

Introduction

Low back pain (LBP) is often associated with intervertebral disc (IVD) degeneration [1]. Degenerative IVD is characterized by increased levels of pro-inflammatory cytokines [2], such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, which are observed in disc tissue from discogenic pain patients [2,3,4]. The dorsal root ganglion (DRG) contains the cell bodies of primary sensory neurons [9], which transduce nociceptive stimuli into electrical action potentials (AP), which can be transmitted from the periphery (DRG) to the central nervous system [10] (spinal cord and brain) This process can be affected by pro-inflammatory cytokines and develop a maladaptive response for producing nociceptive or pain signals [11]. IL-6 was shown to potentiate spontaneous discharge and response to capsaicin, bradykinin, prostaglandin E2 (PGE2), heat, and electrical field stimulation in primary adult mouse DRG neurons [14]

Methods

Discussion

Conclusion