Home > Conscious > Chapter 7 > 7.2. The Importance of Astrocytes



Figure 7-3. The astrocyte. [Source: Wikipedia]

Astrocytes are a class of glial cells. For many years, glial cells have been thought to play only a supporting role in brain functions, until the discovery that astrocytes can release neurotransmitters to influence synaptic transmission directly. In 2009, Halassa and colleagues demonstrated that inhibiting neurotransmitter release from astrocytes attenuated the accumulation of sleep pressure (Halassa et al., 2009). Since then, a growing number of studies have confirmed the importance of astrocytes in sleep (Florian et al., 2011; Frank, 2013; Pelluru et al., 2015).

In fact, as early as 1895, the founder of modern neuroscience, Santiago Ramón y Cajal, have speculated that astrocytes could regulate sleep by using their processes (projections from the cell body) to invade the synapse, thereby blocking the signal transmission between neurons (Figure 7-4). According to recent studies, astrocytes can indeed obstruct synaptic transmission, but not by invading the synapse. Rather, the ATP (adenosine triphosphate) released from astrocytes may break down into adenosine, which plays a pivotal role in sleep (see Section 7.4).


Figure 7-4. Cajal's speculation on sleep. The astrocyte's process may invade the synapse, thus blocking signal transmission between neurons. [Source: Tso and Herzog, 2015]