Xylene Impairs Neuronal Development by Dysregulating Calcium Homeostasis and Neuronal Activity in Developing Hippocampal Neurons

Xylene is an aromatic hydrocarbon widely used as a solvent and emitted from numerous commercial products in industrial or indoor settings. Epidemiological studies of occupational exposure indicate that xylene primarily targets the central nervous system, producing neurobehavioral impairments and other neurological disorders. Both environmental and occupational exposure to volatile organic compounds, therefore, raise concerns about neurodevelopmental risk; however, the specific neurotoxicity of xylene in developing neurons remains poorly characterized. Here, we investigated the effects of xylene (2 or 5 mM) on developing mouse hippocampal neurons, with a focus on Ca²⁺ homeostasis, presynaptic function, and electrophysiological activity. We assessed Ca²⁺ homeostasis with selective inhibitors of voltage-gated Ca²⁺ channels and organelle-specific Ca²⁺ indicators. Presynaptic activity was evaluated in transgenic mouse pups expressing a genetically encoded pH sensor within the synaptic vesicle lumen. Xylene suppressed cytosolic Ca²⁺ transients by inhibiting P/Q-type Ca²⁺ channels, thereby reducing Ca²⁺ uptake into the endoplasmic reticulum. It also decreased Ca²⁺ influx at both presynaptic and postsynaptic sites, impairing synaptic vesicle exocytosis and endocytosis. Electrophysiological and morphological analyses further showed reduced spontaneous firing and hindered synaptic maturation. Collectively, these findings provide mechanistic insight into the neurotoxic actions of xylene and underscore its potential hazard to brain development and function.