Lumbar radiculopathy and its neurobiological basis

Table 2 Hypothetic mechanisms of neuropathic pain and target molecules involved in radiculopathy

Symptoms/signs	Type of pain	Mechanism	Molecules/channels
Spontaneous shooting pain	neuropathic	Spontaneous ectopic DRG neuron activity	Na channels
Spontaneous ongoing pain	Inflammatory	Inflammation surrounding or within DRG	TNF-α, IL-1/6
Positive straight-leg raise test	Inflammatory, mechanical, ischemic	Induction of ectopic neuron activity or ischemia when a sensitized and constricted nerve root stretches	ASIC3, Piezo2, 5-HTR
Sensory deficit	Neuropathic	Apoptosis or phenotype shift of DRG neurons	?
Heat allodynia	Neuropathic	Reduced threshold to heat	TRPV1
Cold allodynia	Neuropathic	Reduced threshold to cold	TRPM8
Static Mechanical allodynia	neuropathic	Reduced threshold to mechanical	ASIC3?, Piezo2?
Dynamic Mechanical allodynia	neuropathic	Reduced threshold to mechanical	ASIC3?, Piezo2?
Soreness	Inflammatory, ischemic	Increased protons	ASIC3, TNF-α, IL-1, IL-6

TNF-α: Tumor necrosis factor α; DRG: Dorsal root ganglia; ASIC: Acid-sensing ion channel; IL: Interleukin.