Fluoride exposure decreased learning ability and the expressions of the insulin receptor in male mouse hippocampus and olfactory bulb.

Fluoride is one of the common environmental pollutants. Internal exposure to fluoride is related to the lowered cognitive function and intelligence, particularly for children. Determination of protein content in brain tissue is a means to reflect the functional development of the central nervous system. Insulin and insulin receptor (IR) signaling systems are associated with cognitive ability. The present research focused on the assessment of the expressions of IR protein and mRNA in hippocampus and olfactory bulb (OB), as well as learning and memory ability of male Kunming mice. Mice were exposed to 50, 100, and 150 mg/L NaF for 90 continuous days. The results showed that learning and memory abilities as well as protein content of male mice brain was significantly decreased by fluoride. Fluoride could inhibit the protein and mRNA expressions of the IR in the hippocampus and OB of mice. IRs mainly distributed in the olfactory nerve layer of the outermost layer of the OB, and most distributed in the hippocampal cornu ammon 3 (CA3) region, followed by the dentate gyrus (DG) and cornu ammon 1 (CA1) regions. These findings suggested that inhibition of the IR protein and mRNA expressions in the hippocampus and OB by fluoride might in part affect learning and memory ability in male mice.