Objective:To study the effects of fluoride on apoptosis and oxidative stress levels of spinal cord nerve cells in rats.Methods:A total of 54 6-week-old Sprague-Dawley female rats, weighing 150 - 200 g, were selected and fed for 1 week. They were divided into a control group [given deionized water containing 0 mg/L sodium fluoride (NaF)], a low fluoride group (given deionized water containing 50 mg/L NaF), and a high fluoride group (given deionized water containing 100 mg/L NaF) using a random number table method, with 18 rats in each group. All groups received standard feed. After 4, 8, and 12 weeks of fluoride exposure, six rats were selected from each group to observe the occurrence of dental fluorosis, and the motor function of hind limbs in rats was evaluated based on the Basso-Beattie-Bresnahan (BBB) score. Then the rats were anesthetized with 5% chloral hydrate via intraperitoneal injection and euthanized by cardiac puncture. Spinal cord tissue of the rats was collected to detect the activities of oxidative stress factors such as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), as well as the contents of malondialdehyde (MDA) and catalase (CAT). After 12 weeks of fluoride exposure, morphologic changes in rat spinal cord neurons were observed using Nissl staining, and apoptosis of spinal cord nerve cells was detected using the TdT mediated dUTP nick end labeling (TUNEL) cell apoptosis detection kit. The Western blotting was used to detect the expression of B-lymphoblastoma-2 (Bcl-2) gene related X protein (Bax), Bcl-2 promoter (Bad), and Bcl-2 protein in rat spinal cord tissue; immunofluorescence staining was used to observe the expression of Bax and Bcl-2 protein in spinal cord neurons.Results:After 12 weeks of fluoride exposure, rats in both the low fluoride and high fluoride groups developed varying degrees of dental fluorosis; the differences of BBB scores of rats in the control, low fluoride, and high fluoride groups were statistically significant ( F = 14.09, P < 0.001). The differences of SOD [(124.04 ± 4.87), (96.66 ± 15.01), (91.12 ± 15.87) U/mg prot] and GSH-Px activitives [(561.92 ± 59.65), (456.83 ± 29.51), (385.07 ± 74.87) U/mg prot], MDA [(9.96 ± 1.50), (16.64 ± 2.05), (20.80 ± 3.37) nmol/mg prot] and CAT contents [(8.97 ± 1.05), (6.39 ± 0.97), (6.42 ± 0.83) nmol/mg prot] among the control, low fluoride, and high fluoride groups were statistically significant ( F = 11.17, 14.19, 30.12, 14.52, P < 0.05). Among them, the SOD, GSH-Px activities, and CAT content in the low fluoride and high fluoride groups were lower than those in the control group, while the MDA content was higher than that in the control group ( P < 0.05). The GSH-Px activity in the high fluoride group was lower than that in the low fluoride group, and MDA content was higher than that in the low fluoride group ( P < 0.05). The intact neuronal structures and clear visible nuclei were seen, and Nissl bodies were uniformly stained in the spinal cord neurons of the control group rats, with more numbers, and no apoptotic cells were observed; the staining of Nissl bodies in the spinal cord neurons of rats was uneven in the low fluoride and high fluoride groups, with fewer numbers, and more apoptotic cells. There were statistically significant differences in the apoptosis rate of spinal cord nerve cells and the expression levels of Bax, Bad, and Bcl-2 protein in the spinal cord tissues of rats in the control, low fluoride, and high fluoride groups ( F = 272.81, 35.53, 17.57, 92.50, P < 0.05). The results of immunofluorescence staining showed that there were statistically significant differences in the fluorescent intensity of Bax and Bcl-2 proteins in the spinal cord neurons of rats in the control, low fluoride, and high fluoride groups ( F = 12.67, 22.14, P < 0.05). Conclusion:Chronic fluorosis induces a decrease in antioxidant enzyme activity, an increase in lipid peroxidation levels, and an increase in neuronal apoptosis in the spinal cord of rats.