Fig. 9.

Interactions between glutamatergic and GABAergic synaptic inputs. A, Schematics of the experimental conditions: one extracellular stimulation pipette (stim IN) was positioned in the molecular layer near the Purkinje cell layer (PCL) to stimulate presynaptic INs, and another one (stim GC) was placed in the granular cell layer to stimulate ascending axons from granule cells or climbing fibers. The postsynaptic IN is recorded in whole-cell configuration using a physiological Cl⁻ concentration (Cl_i = 15 mm). B, Current-clamp experiment (V_m ∼ −70 mV). Superimposed traces (10 in eachpanel) show that the probability for a successful glutamatergic stimulation to induce an action potential increases fromp = 0.43 to p = 0.72 (n = 60 trials in each condition;p < 0.01) if it occurs 30 msec after a successful GABAergic stimulation. Therefore, 30 msec after a GPSP, the excitability of the cell is increased. C, Synaptic currents recorded under voltage-clamp conditions for the same cell as in B. The two panels show superimposedtraces of postsynaptic currents induced by stim GC and stim IN, respectively. Exponential fits to the decays of the synaptic currents gave time constants of 1 and 7 msec, respectively. The marked differences in the time courses of decay for the two sets of traces demonstrate that stim GC and stim IN respectively induce only EPSCs and only GPSCs. Note that at the time chosen for the second stimulus, GABAergic currents have fully subsided, so that shunting inhibition does not play a role here.