Substance P-saporin down-regulates substance P receptor immunoreactive sensory dorsal root ganglion neurons innervating the lumbar intervertebral discs in rats.
METHODS
To examine changes in substance P receptors on dorsal root ganglion cells innervating the rat lumbar intervertebral discs using immunohistochemistry and a retrograde neurotracing method.


OBJECTIVE
We evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptors.


BACKGROUND
The rat L5/6 intervertebral disc is multi-segmentally innervated from the L1-L6 dorsal root ganglions. Substance P and the neurokinin-1 receptor contribute to inflammatory pain transmission. Substance P immunoreactive-sensory nerve fibers in human intervertebral discs and immunoreactive-dorsal root ganglion neurons innervating rat intervertebral discs have been reported to be important in the transmission of discogenic low back pain. In the current study, we evaluated the effects of intradiscal administration of substance P-saporin, a toxin selective for cells expressing substance P receptor.


METHODS
Sixteen rats were used (control group, n = 8; substance P-saporin group, n = 8). To detect dorsal root ganglion neurons innervating the L5/6 intervertebral disc, neurotracer (fluoro-gold crystals) was placed into the intervertebral disc. Seven days after fluoro-gold application, the L5/6 intervertebral disc was exposed and injected with 175 ng of sterile substance P-saporin (substance P-saporin group, n = 8). Fourteen days after the first operation, each dorsal root ganglion was harvested, sectioned, and processed for neurokinin-1 immunohistochemistry using rabbit antibody to neurokinin-1. The numbers of fluoro-gold labeled neurons, and fluoro-gold labeled and neurokinin-1 immunoreactive neurons were counted in both groups.


RESULTS
Neurons innervating the L5/6 intervertebral discs, retrogradely labeled with fluoro-gold, were distributed throughout dorsal root ganglions from L1 to L6 in both groups. Of fluoro-gold labeled neurons, the proportion of neurokinin-1 immunoreactive neurons was 35% in the control group. However, the proportion of neurokinin-1 immunoreactive neurons was 8% after administration of substance P-saporin into the intervertebral discs (substance P-saporin group). Substance P-saporin significantly decreased the ratio of neurokinin-1 immunoreactive neurons.


CONCLUSIONS
Substance P-saporin decreased the ratio of neurokinin-1 immunoreactive neurons innervating the disc related to discogenic low back pain. Substance P-saporin may be a useful tool to investigate the mechanism of discogenic low back pain.
Ohtori
Seiji
S
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan. sohtori@faculty.chiba-u.jp
Inoue
Gen
G
Koshi
Takana
T
Ito
Toshinori
T
Doya
Hideo
H
Moriya
Hideshige
H
Takahashi
Kazuhisa
K
D000818:Animals; D015536:Down-Regulation; D005727:Ganglia, Spinal / Q000187:drug effects*; D007403:Intervertebral Disc / Q000294:innervation; D008159:Lumbar Vertebrae; D008297:Male; D009474:Neurons / Q000187:drug effects; D009498:Neurotoxins / Q000008:administration & dosage*; D018377:Neurotransmitter Agents / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000187:drug effects*; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D013373:Substance P / Q000008:administration & dosage / Q000031:analogs & derivatives*
D009498:Neurotoxins; D018377:Neurotransmitter Agents; D018040:Receptors, Neurokinin-1; D054789:Ribosome Inactivating Proteins, Type 1; C468274:substance P-saporin; D013373:Substance P; D000076985:Saporins