Magnesium ion (Mg²⁺) is involved in a wide variety of biochemical reactions, and a multitude of physiological functions are known to require Mg²⁺. Many previous works suggest that Mg²⁺ is involved in various neuronal diseases, such as migraine, Alzheimer's disease and Parkinson's disease. Therefore, Mg²⁺ dynamics in neurons may play key roles for maintaining normal neuronal functions. In facts, in neurons, main excitatory neurotransmitter glutamate induced intracellular Mg²⁺ concentration [Mg²⁺]_i increase (Shindo et al. 2010). However, it has not been revealed whether neuronal activity under physiological condition modulate [Mg²⁺]_i in neurons. This study aimed to explore the relationship between neural activity and [Mg²⁺]_i dynamics.
To monitor [Mg²⁺]_i dynamics during neural activation, we developed the combined system of neuronal stimulation and fluorescent imaging of cultured neurons. In concrete, we cultured rat hippocampal neurons on glasses coated with electrically conductive and optically transparent indium-tin oxide (ITO) films, and simultaneously visualized [Mg²⁺]_i and [Ca²⁺]_i dynamics by fluorescent dyes KMG-104-AM, a highly selective fluorescent Mg²⁺ probe, and fura red, a fluorescent Ca²⁺ probe, respectively, during neural stimulation through ITO electrodes.
We observed transient [Ca²⁺]_i increase in response to stimulation, indicating our experimental system clearly stimulates enough to trigger neural activation, and we simultaneously detected the [Mg²⁺]_i increase. Taken together, we concluded that neuronal activity accompanied the [Mg²⁺]_i increase in rat hippocampal neurons.