Effects of implantation of iodine-125 seeds in the intervertebral foramina on histological changes in dorsal root ganglion and pain threshold in rats

Objective To evaluate the histologic changes of dorsal root ganglion (DRG) and pain threshold following implantation of iodine-125(125I) seeds in the lumbar intervertebral foramina in rats.Methods Thirtysix adult male SD rats aged 6 months weighing 220-250 g were randomly assigned into 3 groups (n =12 each):group sham operation (group A) and groups low and high radioactive 125I seeds (groups B and C).125I seeds of 0.4 and 0.8 mCi were implanted in L4,5 and L5,6 intervertebral foramina in groups B and C respectively.Paw withdrawal threshold to von Frey filament stimulation (MWT) and paw withdrawal latency to thermal nociceptive stimuli (TWL) were measured 2 days before (T1,baseline) and at 2,7,14,30 and 60 days after implantation (T2-6) in 6 animals in each group.The remaining 6 animals in each group were sacrificed at 14 and 60 days after 125I seeds implantation for microscopic examination of L5 DRG.Results MWT and TWL were significantly decreased after 125I seeds implantation at T4 compared with the baseline values at T1 in both groups,and returned to the baseline in group B and were significantly increased in group C at T6.The neurons were severely injured in DRG in groups B and C in a time-and dose-dependent manner.Conclusion Implantation of 125I seeds in intervertebral foramen can induce radiation resection of DRG. Key words: Iodine radioisotopes; Injections, spinal; Pain threshold; Ganglia, spinal; Neurons