Figure 4.

Perforant path recruits strong inhibition in GCs that occludes GC sensitivity to perforant path inputs. A, Voltage-clamp response of a GC clamped at −40 mV to a single pulse delivered to the middle molecular layer at varying stimulus strengths. B, Same as A but for a FS interneuron (FS IN). C, The IPSC/EPSC ratio as a function of stimulus strength for GCs (black) and FS INs (gray). Dotted line shows where IPSC/EPSC = 1. Ratios are significantly different for GCs compared with FS INs (p ≤ 0.01, n = 8 for FS INs, n = 6 for GCs, F test, see Materials and Methods). D, Voltage-clamp response of a GC clamped at −40 mV to a single pulse delivered to the middle molecular layer in control (Ctrl), 10 μm DNQX, and wash conditions (left). IPSC amplitude is significantly reduced by 10 μm DNQX (right). The difference in amplitudes was significant between control and drug conditions but not between control and wash conditions (p ≤ 0.01, n = 7, one-way ANOVA with repeated measures, Dunnett's test). Stim, Stimulus. E, Blocking inhibition reverses sensitivity of GCs and FS INs to perforant path inputs. Input–output curves for middle molecular layer (MML) fibers to GC and FS IN synapses (left) and outer molecular layer (OML) fiber synapses (right) in the presence of 5 μm bicuculline and 1 μm CGP55845. Compare with Figure 2 in absence of bicuculline and CGP55845.