Can ongoing immune activation and inflammatory lipid mediators amplify nerve hyperexcitability after sensory ganglion injury?

Sensory-ganglion injury can create a locally inflammatory milieu that promotes abnormal sensory-neuron firing. The strongest support concerns immune-cell–neuron signaling; lipid-mediated mechanisms are biologically coherent but less directly demonstrated in injured ganglia.

Immune activation and hyperexcitability

• In peripheral nerve-injury models, resident CX3CR1-positive dorsal root ganglion (DRG) macrophages proliferate and activate, increasing TNF and IL-1β production. Macrophage expansion also contributes to maintenance of mechanical hypersensitivity, with depletion reversing this phenotype in mice.
• The most direct mechanistic evidence comes from injury-primed DRG macrophage conditioned-medium experiments. Exposure increased spontaneous firing, evoked action potentials, and Naᵥ1.7/Naᵥ1.8 current density in small DRG neurons.
• This sensitization required soluble TNF and neuronal p38 signaling. p38-dependent trafficking of Naᵥ1.7 and Naᵥ1.8 channels to the neuronal membrane provides a specific explanation for lowered firing thresholds and ectopic activity.

Inflammatory lipid mediators

• Prostaglandins, particularly PGE₂ and PGI₂, can activate neuronal EP/IP receptors. PGE₂–EP signaling increases cAMP–PKA activity; related PKA/PKC pathways can enhance sodium and calcium-channel activity, sensitize TRPV1, and reduce potassium-current and afterhyperpolarization restraints.
• Leukotrienes and arachidonic-acid–related reactive lipids may further sensitize nociceptors through cysteinyl-leukotriene receptors, P2X3-related signaling, ASIC, and TRPA1 pathways.
• These effects plausibly amplify firing, but direct evidence linking measured ganglionic eicosanoids to electrophysiologic hyperexcitability after injury is not established.

Bottom line

• Ongoing DRG immune activation is moderately supported as an amplifier of post-injury hyperexcitability, most clearly through macrophage-derived TNF, neuronal p38 activation, and increased Naᵥ1.7/Naᵥ1.8 membrane trafficking. Inflammatory lipid mediators are credible interacting amplifiers, but their causal role in injured sensory ganglia remains mechanistically plausible rather than directly demonstrated.