RESUMEN
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 α3, α4 and α7 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 α3, α4 and α7 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 α3, α4 and α7 nAChR subunits in rat brains of highfluoride 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.
RESUMEN
Objective To observe the influence of coal burning fluorosis on learning and memory ability in rats and reveal its possible mechanisms. Methods Healthy 48 SD rats were divided into control, low-fluoride and high-fluoride group. All rats in fluoride exposed groups were fed with the eom polluted by drying processes with burning coal containing high level of fluoride obtained from the endemic fluorosis area to produce the animal model of fluorosis. The experiment period were 3,6 mouths, respectively. The ability of leaning and memory was measured by Morris test and cholinesterase activity detected by photometric method at 3 or 6 month after experiment, respectively. Results Fluoride contents signifieantlly influenced the escape latency, the numbers of crossing the platforms and the time of staying the platforms(the value of F was 29.29,6.47,6.50, respectively, P<0.01).In addition, the numbers of crossing the platforms and the time of staying the platforms were influenced by the exposed time(the value of F was 16.11,45.59, P<0.01). Furthermore, the fluoride contents and the exposed time had an interaction between the numbers of crossing the platforms and the time of staying the platforms (the value of F was 4.67,5.68, P<0.05 or<0.01). Three months after the experiment, the mean values of escape latency [(14.71± 4.85)s] of rats in highly fluoride exposed group were significantly prolonged as compared with controls [(9.28±4.22)s]; 6 month after the experiment, the mean values of escape latency[(12.42±8.03)s, (17.48± 8.05)s] of rats in both groups exposed to fluoride were significantly prolonged as compared to controls [(7.04± 3.29)s, P<0.05]. The decreased numbers of crossing the platforms[(1.62±0.87)number] and the declined time of staying the platforms[(16.70±5.02)s] were found in the rats exposed to high fluoride as compared to controls [(3.53±1.67 )number, (23.33±5.35)s, P<0.05]. The fluoride contents obviously influenced the activities of acetylcholinesterase and butylcolinesterase (the value of F was 12.83,13.27, P<0.01). On the other hand, the times of breeding also influnced the activities of butylcolinesterase (the value of F was 16.26, P<0.01). In 3 months of the experiment, the activities of butylcolinesterase [(0.55±0.12)kU/g] in low fluoride exposed group were significantly decreased in comparison with controls[(0.73±0.10)kU/g, P<0.05]. The activities of acetylcholinesterase[(0.62±0.42)kU/g] and butylcolioesterase[(0.58±0.10)kU/g] in high fluoride group were significantly decreased as compared to eontrois[(1.41±0.52), (0.73±0.10)kU/g, P<0.05]. The correlation analysis showed that there was a negative correlation between the cholinesterase and the escape latency(r=-0.68, P< 0.01), and a positive correlation between the cholinesterase and the time of staying the platforms(r=0.57, P< 0.01). Conclusions The ability of learning and memory in rats with coal buring fluorosis was decreased, which might be connected to the decreased activity of cholinesterase in a dose-effect correlation.