title: Investigation of dichotomizing sensory nerve fibers projecting to the lumbar multifidus muscles and intervertebral disc or facet joint or sacroiliac joint in rats.
abstract: METHODS
  Immunohistological analysis of dichotomizing sensory nerve fibers projecting to the lumbar multifidus muscles and intervertebral disc (IVD), facet joint (FJ), or sacroiliac joint (SIJ) in rats.
  
  
  OBJECTIVE
  To elucidate dichotomizing sensory nerve fibers projecting to the lumbar multifidus muscles and to IVDs, FJs, or SIJs.
  
  
  BACKGROUND
  Clinically, the origin of low back pain remains unknown. Multiple studies have identified lumbar muscles, IVDs, FJs, and SIJs as sources of low back pain. Pain may originate directly from lumbar muscles or be referred from the spine, or both. Dorsal root ganglion (DRG) neurons with dichotomizing axons have been reported in several species and are thought to be related to referred pain.
  
  
  METHODS
  We used 2 neurotracers, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) and fluorogold (FG), in this double-labeling study involving 30 Sprague Dawley rats. DiI was applied to lumbar multifidus muscles in all rats. Simultaneously, FG was applied to the anterior left portion of L5-L6 IVDs in the IVD group (n = 10), to the left L5-L6 FJs in the FJ group (n = 10), and to the left SIJs in the SIJ group (n = 10). Fourteen days after surgery, left DRGs from L1 to L6 were harvested, sectioned, and observed under a fluorescence microscope.
  
  
  RESULTS
  We verified the existence of double-labeled DRG neurons (i.e., dichotomizing sensory nerve fibers) projecting to lumbar multifidus muscles and to IVDs, FJs, or SIJs, depending on the group. The proportion of double-labeled cells in all DiI-labeled DRG neurons was higher in the FJ group (6.8%) and SIJ group (7.1%) than in the IVD group (3.1%) (P < 0.05).
  
  
  CONCLUSIONS
  Our results document the presence of dichotomizing sensory nerve fibers projecting to lumbar multifidus muscles and to IVDs, FJs, and SIJs. Referred low back muscle pain may reflect disorders of lumbar posterior structures, such as FJs and SIJs, rather than disorders of lumbar anterior structures, such as IVDs.
authors.affiliation: School of Medicine, Chiba University, Chiba, Japan.
authors.forename: Tomotaka
authors.initials: T
authors.lastname: Umimura
authors.forename: Masayuki
authors.initials: M
authors.lastname: Miyagi
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Ishikawa
authors.forename: Hiroto
authors.initials: H
authors.lastname: Kamoda
authors.forename: Ken
authors.initials: K
authors.lastname: Wakai
authors.forename: Takafumi
authors.initials: T
authors.lastname: Sakuma
authors.forename: Ryo
authors.initials: R
authors.lastname: Sakai
authors.forename: Kazuki
authors.initials: K
authors.lastname: Kuniyoshi
authors.forename: Nobuyasu
authors.initials: N
authors.lastname: Ochiai
authors.forename: Shunji
authors.initials: S
authors.lastname: Kishida
authors.forename: Junichi
authors.initials: J
authors.lastname: Nakamura
authors.forename: Yawara
authors.initials: Y
authors.lastname: Eguchi
authors.forename: Nahoko
authors.initials: N
authors.lastname: Iwakura
authors.forename: Tomonori
authors.initials: T
authors.lastname: Kenmoku
authors.forename: Gen
authors.initials: G
authors.lastname: Arai
authors.forename: Sumihisa
authors.initials: S
authors.lastname: Orita
authors.forename: Miyako
authors.initials: M
authors.lastname: Suzuki
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sakuma
authors.forename: Gou
authors.initials: G
authors.lastname: Kubota
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Oikawa
authors.forename: Gen
authors.initials: G
authors.lastname: Inoue
authors.forename: Yasuchika
authors.initials: Y
authors.lastname: Aoki
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Toyone
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Takahashi
authors.forename: Seiji
authors.initials: S
authors.lastname: Ohtori
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D005727:Ganglia, Spinal / Q000502:physiology*; D007403:Intervertebral Disc / Q000294:innervation*; D017116:Low Back Pain / Q000209:etiology; D008159:Lumbar Vertebrae / Q000294:innervation; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012446:Sacroiliac Joint / Q000294:innervation*; D011984:Sensory Receptor Cells / Q000502:physiology*; D021801:Zygapophyseal Joint / Q000294:innervation*