Schematic diagram of an axodendritic synapse for each class of GC. (A) Time-course analysis of two elements during the maturation of the first glutamatergic contact onto newborn GCs. The NMDAR/AMPAR ratios are shown in red. Functional release sites (blue) are indicated as either single or multiple. Both class 4 and class 5 neurons showed a high NMDAR/AMPAR ratio with multiple release sites. (B) Developmental changes in a single axodendritic synapse. Top: Transmitter vesicular events (circle) per action potential gradually changed from single to multiple events. Each event occurred independently, but seemed to become integrated together in mature GCs (gray). Bottom: Differences observed in the number of axodendritic synapses. During maturation, the number of synapses (red circles) impinging onto newborn GCs increased in parallel with the appearance of perforated synapse (red doughnut-like shape). At the later stages of maturation, perforated synapses then divided, with a spillover of transmitter occurring at adjacent synapses (gray).