Figure 1. Target cell-specific short-term enhancement and suppression at parallel fiber synapses.

(A) A simplified circuit of the cerebellar cortex shows excitatory synapses made by granule cell (GrC) parallel fibers (PFs) onto Purkinje cells (PCs) and Golgi cells (GCs). Arrows indicate that mossy fibers (MFs) provide a major source of excitatory input to the cerebellar cortex and PCs are the sole output from this region. ML, molecular layer; PL, Purkinje cell layer; GrL, granular layer. (B, H) Fluorescent images of a PC (B) and a GC (H) filled with Alexa 594. Postsynaptic responses to PF burst stimulation (10 stimuli, 50 Hz) were recorded in current clamp (C, F, I, L). PFs were activated with an extracellular electrode placed either in the ML (C, D, I, J, black traces) or the GrL, (F, G, L, M, red traces). EPSCs evoked at 0.5 Hz prior to and following a PF burst were recorded in voltage-clamp, at a holding potential of −70 mV in a representative PC (D, G) and a GC (J, M), using a K-based internal solution. (E, K) Time course of change in synaptic strength following PF bursts (at t = 0 s) evoked by ML (black) or GrL stimulation (red). Responses shown are normalized to the average EPSC amplitude prior to burst stimulation.