Neurons contain neurotransmitters, which are chemicals that trigger signals to pass messages.
Until recently, neuroscientists believed neurons were the only brain cells transmitting message signals. Glial cells were thought to serve only as support. In the mid-1990s, however, Parpura and Haydon were among the first researchers to discover that glial cells are much more important to the brain's communication network than previously thought. This release of glutamate is controlled by increased levels of calcium in the astrocytes. Exactly how much calcium was needed to cause the glutamate release was unclear.