Vertigo is one of the most common clinical symptoms. However, the chemical processes involved in the pathological mechanism of vertigo remain to be fully understood. In this study, we investigate the dynamic changes in the magnesium (Mg 2+ ) concentration in medial vestibular nucleus (MVN) of guinea pigs following vertigo induced by vestibular ice water stimulation with an electrochemical detection method consisting of in vivo microdialysis and on-line selective electrochemical detection. Electrochemical detection of Mg 2+ was accomplished based on the current enhancement of Mg 2+ towards the electrocatalytic oxidation of NADH at the electrodes modified with the polymerized film of toluidine blue O (TBO). Selectivity for the on-line electrochemical detection against Ca 2+ was achieved by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca 2+ . The basal level of the extracellular Mg 2+ in the MVN of guinea pigs was determined to be 759.7 ± 176.2 M(n = 16). Upon ice water irrigation of the left external ear canal, the concentration of Mg 2+ in the MVN decreases significantly, reaches 72 ± 6% (n = 8) of the basal level, and maintains for at least 1000 s. Control experiments reveal that neither warm water irrigation of the external ear canal nor ice water irrigation of the auricle induces the decrease in the concentration of Mg 2+ in the MVN. These results demonstrate that the extracellular Mg 2+ in the MVN decreases significantly following vertigo induced by vestibular ice water stimulation. This demonstration suggests that Mg 2+ might play an important role in the pathological mechanism of vertigo.
