Lumbar radiculopathy and its neurobiological basis

Table 1 Animal models of lumbar radiculopathy

Injurycomponent	Model	Species	Injury site	Pain behaviors	Motor function
Mechanical	Chronic gradual nerve root compression (Cornefjord et al[24])	Porcine	Preganglion	NA	NA
	chronic compression of dorsal root ganglion produced by intervertebral foramen stenosis (Hu et al[25])	Rat (SD)	Dorsal root ganglion	Heat hyperalgesia 5-35 d after surgery	NA
	Compression strain of nerve root (Winkelstein et al[26])	Holtzman rats	Preganglion	Mechanical allodynia	NA
	Stainless rod -induced lumbar radiculopathy(Takayama et al[32])	Rat (SD)	Preganglion	NA	NA
Chemical	Autologus nucleus pulposus-induced lumbar radiculopathy (Olmarker et al[28])	Porcine	Preganglion	NA	NA
	Autologus nucleus pulposus-induced lumbar radiculopathy (Yabuki et al[29])	Rat (SD)	Preganglion	NA	NA
	Autologus nucleus pulposus-induced lumbar radiculopathy (Otani et al[30])	Dog	Preganglion	NA	NA
	Autologus nucleus pulposus-induced lumbar radiculopathy (Shamji et al[16])	Rat (SD)	Dorsal root ganglion	Mechanical allodynia	Marked gait asymmetry, preference to bear weight on the contralateral limb
Mechanical + chemical	Spinal nerve root irritation with chromic gut ligatures (Kawakami et al[27])	Rat(SD)	Preganglion	Prolonged thermal hyperalgesia 2 to 12 wk	Immeditaely paresis resolved in 2 wk, totally recovered in 6 wk
	Chronic compression of lumbar dorsal root ganglion with SURGIFLO™(Gu et al[31])	Rat(SD)	Dorsal root ganglion	Mechanical allodynia and thermal hyperalgesia up to 4 or 5 postoperative week	NA

NA: Not available.

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.