Figure 5.

Short-term synaptic plasticity is physiologically set by the rate of gliotransmitter release from the astrocyte. (A) The rate of glutamate or ATP release from the astrocyte could differently affect basal synaptic release probability. In particular, a threshold frequency for the release of these gliotransmitters could exist (blue vertical line) beyond which a depressing synapse could turn into facilitating (right, green area) or vice versa, a facilitating synapse could become depressing (left, magenta area). Adapted from De Pittà et al. (2011). (B) In basal conditions, synaptic release is due to sporadic neuronal network firing and the possible frequency of Ca²⁺ fluctuations beyond the threshold for exocytosis (dashed red line) in the astrocyte (top trace). In this fashion plastic changes in paired-pulse ratio could be inherently regulated by astrocytic gliotransmitters, as shown here for the case of an originally facilitating synapse under the effect of astrocytic glutamate exocytosis (20 trials with identical input statistics). Adapted from Berry et al. (2011). The color code for the raster plot is the same as in Figure 4C.