Modulation of synchronous calcium oscillations in hippocampal neurons by photostimulation of astrocytes with femtosecond laser

A large body of evidence indicates that astrocytes play an important role in a range of brain functions through calcium (Ca²⁺) signaling. Experimentally evoking Ca²⁺ signaling is a useful technique for investigating the functions of astrocytes. However, conventional stimulation methods typically have poor spatio-temporal precision, and some are invasive. Our group has developed a technique to overcome these problems, in which astrocytes are photostimulated with a femtosecond laser. In the current study, we applied this method to a hippocampal neural network to explore astrocytic functions in detail. The results revealed that applying photostimulation to astrocytes in a cultured hippocampal astrocyte-neuron network caused the following changes: (i) Synchronous Ca²⁺ oscillations in neurons were induced; (ii) spontaneous Ca²⁺ synchrony instantaneously emerged; and (iii) high-frequency spontaneous Ca²⁺ synchrony was regulated. Thus, astrocytic Ca²⁺ signaling evoked by photostimulation was found to modulate synchronous Ca²⁺ oscillations in hippocampal neurons. We propose that photostimulation with a femtosecond laser will serve as a powerful tool in investigating astrocytic functions at the network level.