The origin of chondrocytes in the nucleus pulposus and histologic findings associated with the transition of a notochordal nucleus pulposus to a fibrocartilaginous nucleus pulposus in intact rabbit intervertebral discs.
METHODS
Intact rabbit lumbar intervertebral discs were examined histologically.


OBJECTIVE
To demonstrate the origin of chondrocytes in the nucleus pulposus, and to document histologic findings associated with the transition of a notochordal to a fibrocartilaginous nucleus pulposus.


BACKGROUND
A human nucleus pulposus undergoes a chronological transition from a notochordal to a fibrocartilaginous nucleus pulposus. However, the origin of chondrocytes forming fibrocartilage in the nucleus pulposus and the mechanisms of transition remain unknown.


METHODS
Hematoxylin-eosin- and safranin O-stained slides obtained from 125 intact rabbit intervertebral discs were observed with light and polarized light microscopy.


RESULTS
Of the 125 intervertebral discs examined, 58 had a notochordal nucleus pulposus. The remaining intervertebral discs had a nucleus pulposus with fibrocartilage lamellas or fibrocartilage fibers. All forms of fibrocartilage lamellas and fibers found in the nucleus pulposus were formed by chondrocytes that had originated and migrated from the cartilage endplate. The origin of chondrocytes proceeded in a centripetal direction from the periphery toward the center of the cartilage endplate. The newly formed fibrocartilage lamellas and fibers, therefore, initially involved replacement of the peripheral regions of the nucleus pulposus, followed by replacement of the central region. This centripetal sequential replacement mechanism decreased the size of the notochordal tissue while increasing the lamellar structure of the intervertebral disc.


CONCLUSIONS
Chondrocytes in the intact rabbit nucleus pulposus originated and migrated from the cartilage endplate. The chondrocytes changed notochordal nucleus pulposus into fibrocartilaginous nucleus pulposus by depositing fibrocartilage lamellas and fibers in a centripetal direction.
Kim
Ki-Won
KW
Department of Orthopedic Surgery, St. Mary's Hospital, the Catholic University of Korea, Seoul, Korea.
Lim
Tae-Hong
TH
Kim
Jesse G
JG
Jeong
Soon-Taek
ST
Masuda
Koichi
K
An
Howard S
HS
D000818:Animals; D002356:Cartilage / Q000033:anatomy & histology / Q000166:cytology*; D019070:Cell Lineage; D002465:Cell Movement; D019902:Chondrocytes / Q000166:cytology*; D007403:Intervertebral Disc / Q000033:anatomy & histology / Q000166:cytology*; D008859:Microscopy, Polarization / Q000379:methods; D009672:Notochord / Q000166:cytology*; D011817:Rabbits