Aloin attenuates NMDA receptor by modulating calcium response on substantia gelatinosa neurons of the trigeminal subnucleus caudalis in mice

Aloe vera extracts, particularly aloin, have been widely used in traditional Chinese medicine for their anti-inflammatory and detoxifying properties. Recent studies suggest that aloin may also exert neuroprotective effects, though its specific mechanisms remain unclear. Glutamate excitotoxicity, a critical factor in neurodegenerative and pain-related disorders, is mediated primarily by <i>N</i>-methyl-D-aspartic acid (NMDA) receptors, which regulate calcium influx and neuronal excitability. Meanwhile, substantia gelatinosa (SG) of the trigeminal subnucleus caudalis (Vc) plays a central role in processing orofacial pain, where glutamate is a key excitatory neurotransmitter. Using whole-cell patch-clamp electrophysiology and calcium imaging techniques in mice SG neurons of the Vc, we examined aloin's effects on glutamate receptor-mediated responses. Aloin selectively inhibited NMDA-induced responses without affecting AMPA or kainate receptor activity. The suppression of NMDA-mediated currents by aloin was linked to changes in Ca²⁺ influx but occurred independently of voltage-gated sodium channels and action potential generation. Calcium imaging revealed that aloin reduced NMDA-induced intracellular calcium influx, supporting its role in mitigating NMDA-mediated excitotoxicity. Furthermore, aloin significantly suppressed the spontaneous firing activity of SG neurons, suggesting its broader regulatory effects on neuronal excitability. Our findings demonstrate that aloin attenuates NMDA receptor-induced excitatory signaling by regulating calcium response. This specificity highlights aloin's potential as a therapeutic candidate for conditions involving glutamate excitotoxicity and orofacial pain regulation.