Figure 6.
Decay times of inhibitory synaptic conductances profoundly affect Purkinje neuron excitability. A, Constant current pulse (1 s, 200 pA) evoked spike firing in a Purkinje neuron with slow (12.5 ms decay time, black) and fast (8.5 ms decay time, blue) inhibitory conductances (E rev = −82 mV) (Chavas and Marty, 2003) injected through a conductance clamp amplifier during the train. The fast conductance is reflected by the shorter inhibition time window [see expanded timescale, right panel; 99 (fast conductance) and 102 (slow) overlaid sweeps at −65 mV]. B, The cumulative distribution for first spike latencies after conductance injection is significantly displaced to the right for longer-lasting conductances (n = 9, time course of the conductance injection is shown below). C, Injecting an excitatory conductance (E rev = 0 mV, τrise = 0.3 ms, τdecay = 3 ms, conductance fixed at 20% above threshold, typically 12–18 nS) to induce a single spike with a concurrent sliding inhibitory conductance (fixed at 15 nS) with either slow (left, black) or fast (right, blue) kinetics. Sweeps are separated by 4 ms, and those shown in the top panel correspond to conductances depicted as thick lines in the lower panel. The cell is prevented from firing by the inhibition time window, which is reduced from ∼50 to ∼20 ms for the fast conductance injection (measured over 50–60 trains of injections, alternating between fast and slow conductance injection). D, Summary of the duration of the inhibition windows for fast (blue) and slow (black) conductance injections.