Objective      To investigate whether sympathetic sprouting occurs in dorsal root ganglion (DRG)  in rats with autologous nucleus pulposus (NP) herniation

so as to provide a new research direction for the diagnosis and treatment of intervertebral disc hernia.       Methods      A total of 110 male SD rats were randomly divided into three groups: a normal group (n=10)

an operation group and a sham group (n

=10 at each point time after surgery). In operation group

autologous NP of intervertebral disc of the rat proximal tails was transplanted onto the surface of L5 DRG. The rats in the sham group received the same operation but without NP transplantation. The pain threshold of the ipsilateral hind paw was assessed on different days after surgery. Then the rats were sacrificed and fixed by perfusion of 4% paraformaldehyde. The ipsilateral L5 DRGs were taken out

fixed

and sectioned at a thickness of 30 μm to perform immunohistochemical staining with tyrosine hydroxylase (TH) antibody

and the images from the selected sections were captured with an optical microscope. The density of sympathetic nerves was estimated by measuring the nerve length using image analysis software.       Results      After transplantation of autologous NP

distinct mechanical allodynia and thermal hyperalgesia were found in the operation group. The paw withdrawl threshold (PWT) and thermal withdrawl latency (TWL) in the operation group were significantly lower than those of the sham group or normal group on days 7

  14

and  20 (P0.05). Meanwhile

immunohistochemical staining results showed that the density of sympathetic nerves in the operation group was significantly higher than that of the sham group or normal group on days 5

7

  14

and 20 (P0.05). In the DRGs from the operation group

the density (19.70±2.67 mm/mm

2

) of sympathetic nerves was significantly higher than that (2.75±2.20 mm/mm

2

) of the sham group and that (1.11±1.07 mm/mm

2

) of the normal group on day 20 after surgery (P0.01).       Conclusion      Sympathetic sprouting occurs in the DRG of the rats with autologous NP herniation and may lead to lower limb pain caused by intervertebral disc hernia.