Subchronic fluoride intake induces impairment in habituation and active avoidance tasks in rats

Since clinical case reports suggest that sodium fluoride (NaF) intoxication may impair learning and memory, the objective of the present study was to evaluate the effects of NaF on two memory tasks: open-field habituation and two-way active avoidance. Adult male rats were exposed to NaF in drinking water at three concentrations for 30 days: 1.54 (control, tap water), 50 and 100 ppm NaF (corresponding to an intake of 0.10+/-0.005, 5.15+/-0.14, and 10.77+/-0.39 mg/kg of NaF, respectively). At day 30, the rats were placed in an open-field and retested after 24 h (test session) to measure habituation. In the two-way active avoidance task, another three groups of rats were trained in a 30-trial training session and tested again 24 h later (test session). Dental fluorosis was also evaluated. Habituation was impaired by 50 and 100 ppm, but not by 1.54 ppm NaF. Moreover, 100 ppm NaF reduced the number of avoidance responses in the active avoidance task. No locomotor impairment was observed. Mild dental fluorosis in rat incisor teeth was found in the 50 and 100 ppm NaF groups. Overall, these results suggest that moderate intoxication with sodium fluoride has potentially deleterious effects on learning and memory.