Intervertebral disc degeneration model and the rule of migration associated with chondrocytes in the nucleus pulposus in rat cervical disc

Abstract

To develop a scientific and reproducible degenerative disc rat model for the study on the cervical disc and study the rule of migration associated with the chondrocytes in the nucleus pulposus. The degenerative cervical disc animal model was developed in 40 infancy SD rats by means of forelimb amputation. Thirty-six normal rats in the same age served as the control. When the rats in the experimental group were 3, 6, 9 and 12 months (named E3, E6, E9 and E12 group respectively) and in the control group were 4, 8, 12 and 16 months (named C4, C8, C12 and C16 group respectively) postoperatively, the vertebral columns from C4-5 to C6-7 were removed and observed under radiographic and histological examination after the rats were sacrificed. Light microscopy revealed that aging rat undergoes a chronological transition from a notochordal to a fibrocartilaginous NP. The chondrocytes found in mature nucleus pulposus originate and migrate from the cartilage endplate. The origin of chondrocytes proceeded in a centripetal direction from the periphery toward the center of the NP. In the periphery of NP, chondrocytes migrate along collagen fibers; in the center part of NP, chondrocytes migrate from endplate to NP in a parallel or vertical direction. Overload on the cervical spine elicited by this surgical intervention accelerated the process and resulted in cervical intervertebral disc degeneration thereafter. The availability of this experimental model should be valuable for comprehensive understanding of the pathogenesis of cervical degeneration. The degeneration process of the bipedal rats'discs is in agreement with that of human beings. Chondrocytes in the rat NP originated and migrated from the cartilage endplate. There are different rules of the chondrocytes migrating from endplate associated with different period of degeneration and different region of nucleus pulposus.