We analyzed synaptic connections between basket cells (BCs) and granule cells (GCs) in acute cerebellar slices from mice. BCs were voltage-clamped in the whole-cell patch clamp configuration, whereas single GCs were stimulated in the cell-attached mode. GC-mediated EPSCs in BCs were characterized by i) rapid kinetics, ii) rather asynchronous release, and iii) marked paired-pulse facilitation¹. Decay time constants were approximately 0.8 ms (n=5 cells), facilitating the analysis of release events occurring at high frequencies. The delay between presynaptic action potential and the start of the EPSC was rather variable in given connections (typically 0.6 to 2.0 ms). Furthermore, the compound EPSCs were often composed of several separable current components, and EPSCs were often followed by additional asynchronous events. These characteristics indicate a rather loose coupling between Ca²⁺ channels and release machinery. The marked paired-pulse facilitation dropped from a paired-pulse ratio of 2.4 ± 0.1 (n=8) at an interstimulus interval (ISI) of 5 ms to unity at ISIs of ~500 ms. Fluctuation analyses were performed by analyzing the charge of the first 5 ms of EPSCs recorded at different extracellular Ca²⁺ concentrations. GC-BC connections were characterized by a quantal size (q) of approximately 110 fC, a binominal parameter N of ~1.3, and a release probability (p) of ~0.4 (at 2 mM [Ca²⁺]_o). Our data help to establish the GC-BC synapse as a model system for studying conventional excitatory synapses at the quantal level. Supported by the DFG (GRK Interneuro, 1097)

¹Bao et al. 2010, J Neurosci