Figure 5: Postsynaptic pathway of gliotransmission by slow inward currents. The transient increase of gliotransmitter concentration in the perisynaptic space (a) triggers a slow inward (depolarizing) current (SIC) in the postsynaptic neuron ((b), (c)). Such SIC adds to postsynaptic currents triggered by presynaptic spikes ((d), (e), cyan triangle marks gliotransmitter release/SIC onset) and may dramatically alter postsynaptic firing (f). In general postsynaptic firing frequency increases with both SIC amplitude (g) and frequency (h). In this latter case, however, SICs as ample as 30 pA (similar to what reported in several experiments) need to impinge on the postsynaptic neuron at unrealistically high rates (≫0.1 Hz) in order to trigger a sensible change in the neuron’s firing rate (black data points). Lower, more realistic SIC rates may affect neuronal firing only for larger SIC amplitudes (e.g., 45 pA, grey data points). The entity of SIC-mediated increase of postsynaptic neuronal firing further depends on the neuron’s state of depolarization at SIC timings which is set by synaptic inputs (blue and cyan data points). Data points and error bars: meanSTD out of simulations with presynaptic Poisson-distributed spike trains. Parameters as in Table 1 except for , ms, ms, and M.