Abstract

Objective: To observe the learning and memory changes in coal-burning type of fluorosis rats, detect the expressions of neuronal nicotinic acetylcholine receptor(nAChR) at mRNA and protein levels in rat brains and to reveal the mechanism of changed learning and memory ability.

Methods: Twenty-four healthy SD rats, weighting 100 – 120 g, were randomly divided into three groups(8 in each). Control group was fed with normal diet, and low- and high-dose fluoride groups were fed with corn polluted with high fluoride (fluoride were 11.30,104.20 mg/kg, respectively) during drying processes with local burning-coal from the areas of endemic fluorosis to established rat model of chronic fluorosis. After exposed to fluoride for 6 months, behavioral changes were measured by Morris water maze. Animals were sacrificed, the brain was taken, after homogenizing the fluoride content of brain tissue was determined by fluoride ion selective electrode. The 3, 4 and 7 nAChR subunits at mRNA and protein levels were analyzed by real-time PCR and Western blotting, respectively.

Results: For rats in low- and high-fluoride groups, the escape latency time [(12.42 ± 8.03),(17.48 ± 8.05)s] was significantly longer than that in the control [(7.04 ± 3.29)s, all P< 0.05]. For rats in high-fluoride group, the numbers of crossing the platforms (1.62 ± 0.87) and the time of staying at the platforms [(16.70 ± 5.02)s] were significantly decreased as compared to that of control[3.53 ± 1.67, (23.33 ± 5.35)s, all P < 0.05]. The fluoride content in rat brain tissue in low- or high-fluoride groups [(1.14 ± 0.04), (1.79 ± 0.04)mg/kg] was significantly higher than that of control [ (0.52 ± 0.05) mg/kg, all P < 0.05]; in addition, the amount of fluoride in brain tissue of high-fluoride group was significantly higher than that of low-fluoride group (P < 0.05). In high-fluoride group, the mRNA expressions of 3, 4 and 7 nAChR subunits in rat brains (1.51 ± 0.20,1.45 ± 0.06,1.63 ± 0.08) were significantly lower as compared to controls (1.79 ± 0.11,1.66 ± 0.14,1.83 ± 0.06, all P< 0.05); whereas there were no significant changes in mRNA levels of these receptor subunits of the rat brains between low-fluoride group(1.65 ± 0.17,1.59 ± 0.09,1.71 ± 0.03) and controls (all P > 0.05). Furthermore, the protein levels of 3, 4 and 7 nAChR subunits in rat brains of high fluoride group (0.58 ± 0.13,0.16 ± 0.03,1.41 ± 0.38) and low-fluoride group(0.56 ± 0.23,0.08 ± 0.02,0.51 ± 0.16) were significantly lower than those of controls ( 1.48 ± 0.42,0.57 ± 0.21,2.56 ± 0.26, P<0.05 or < 0.01).

Conclusions: Decreased ability of learning and memory in coal-burning type of fluorosis rats may be associated with declined expressions of nAChR at proteins and mRNA levels, which might be the main mechanism of the behavior change.

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