Dose-dependent developmental fluoride exposure leads to neurotoxicity and impairs excitatory synapse development

Abstract

Developmental fluoride exposure has been implicated in cognitive deficits and neurotoxicity, yet the mechanisms underlying these effects remain unclear. Here, we investigated the dose- and time-dependent impacts of sodium fluoride (NaF) on neuronal morphology, viability, oxidative stress, and synaptic function using both in vitro and in vivo mouse models. Cultured primary embryonic mouse cortical neurons were exposed to varying concentrations of NaF (0–200 μg/ml). Acute exposure led to neuronal swelling at higher concentrations (≥ 50 μg/ml), while prolonged exposure reduced neuronal viability. Notably, NaF dose-dependently elevated reactive oxygen species (ROS) production, implicating oxidative stress as a key mechanism of fluoride-induced neurotoxicity. Synaptic development was also impaired, as evidenced by reduced density and co-localization of excitatory synapse markers with prolonged 2 μg/ml NaF exposure. To extend these in vitro findings, pregnant mice were exposed to 50 mg/L NaF in drinking water, and offspring brain functions were evaluated postnatally. Whole-cell patch-clamp recordings in layer V pyramidal neurons in the prefrontal cortex revealed reduced frequency and amplitude of miniature excitatory post-synaptic currents (mEPSCs), indicating impaired synaptic function. Morphological analysis showed decreased dendritic spine density and head diameter. These findings suggest that fluoride exposure during critical period of brain development disrupts synaptic integrity and function through excitatory synapse impairments.