To study the expression of silent information regulator (SIRT) in brains of rats with chronic fluorosis and reveal the correlation between SIRT1 and the ability of learning and memory of rats.

Sixty SD rats were selected and their body weight was (100 ± 20) g, according to the body mass of the rats, random number table method was used to divide rats into control group, low and high fluoride groups, experimental period was 3 and 6 months (ten rats in each experimental period, half males and half females). In control group, the rats were fed with drinking water containing no more than 0.5 mg/L fluoride; the rats in low and high fluoride groups were fed drinking water containing 5.0 and 50.0 mg/L fluoride, respectively. All of rats were fed the same standard food containing no more than 0.6 mg/kg fluoride. Three degree method was used to check the formation of dental fluorosis. Rat urinary fluoride was determined via the fluoride electrode method; Morris water maze method was used to detect the ability of learning and memory of rats (the escape latency time, the number of crossing the platform and stay time in platform quadrant); the protein and mRNA expression levels of SIRT1 were detected by Western blotting and Real-time PCR, respectively.

In the experimental period of 3 and 6 months, no dental fluorosis was observed of rats in control group, but there were different degrees of dental fluorosis in low and high fluoride groups, especially in high fluoride group. The urinary fluorine contents [(1.60 ± 0.09), (1.91 ± 0.16) mg/L; (1.94 ± 0.19), (2.31 ± 0.18) mg/L] of rats fed with low and high fluoride for 3 or 6 months were significantly higher than those in control group [(1.08 ± 0.15), (1.09 ± 0.17) mg/L, P < 0.05]. The escape latency time [(18.36 ± 2.80) s] of rats in the high fluoride group at the end of 3 months was higher than that of control group [(6.68 ± 3.01) s, P < 0.05], the number of stay time in platform quadrant [(12.91 ± 3.25) s] was lower than that of control group [(19.97 ± 3.30) s, P < 0.05]. The escape latency time [(15.46 ± 4.56), (28.16 ± 4.00) s] of rats in low and high fluoride groups at the end of 6 months were all higher than that of control group [(6.62 ± 2.31) s, P < 0.05]; the number of crossing the platform and stay time in platform quadrant [(2.25 ± 1.71) times, (12.73 ± 3.55) s; (1.40 ± 1.15) times, (9.26 ± 1.72) s] of these rats were significantly lower than those of the control group [(4.00 ± 1.58) times, (19.53 ± 4.36) s, P < 0.05]. The expression levels of protein [(73.84 ± 9.68)%, (73.23 ± 4.51)%; (53.30 ± 17.63)%, (54.69 ± 18.71)%] and mRNA [(70.33 ± 4.89)%, (66.27 ± 3.38)%; (37.72 ± 4.89)%, (44.15 ± 1.74)%] of SIRT1 in the hippocampus and cortex of rats fed with high fluoride for 3 or 6 months were significantly lower than those in control group [(100.00 ± 13.51)%, (100.00 ± 13.60)%; (100.00 ± 15.37)%, (100.00 ± 12.19)%; (100.00 ± 2.65)%, (100.00 ± 4.34)%; (100.00 ± 3.40)%, (100.00 ± 4.52)%, P < 0.05]. Whereas, the decreased expression levels of protein [(77.65 ± 14.51)%, (71.51 ± 8.27)%] and mRNA [(57.78 ± 1.96)%, (63.76 ± 2.16)%] of SIRT1 in the hippocampus and cortex of rats in the low fluoride group were only observed at the end of 6 month of experiment (P < 0.05). The expression of protein of SIRT1 in the hippocampus and cortex of rats in 3 or 6 months was negatively correlated with the escape latency time of rats (r=-0.598 5,-0.493 2;-0.782 6,-0.777 3, P < 0.05), and it was positively correlated with the number of crossing the platform (r= 0.547 7, 0.523 3; 0.720 5, 0.715 4, P < 0.05).

The decrease of the ability of learning and memory in rats with chronic fluorosis may be related to the decreased expression of SIRT1 influenced by chronic fluorosis.

Fluorine; Rats; Brain; Silent information regulator; Learning; Memory