Figure 1.

The inhibitory circuit of cerebellar granular layer. In the granular layer of the cerebellar cortex, granule cells receive excitatory inputs from the mossy fibers and are inhibited by Golgi cells. The synaptic contacts among granule cell (GrC) dendrites, mossy fiber (MF) terminals, and Golgi cell (GoC) axon and dendrites are enwrapped into a glial sheet, originating a peculiar anatomical structure known as cerebellar glomerulus. Each glomerulus is characterized by one mossy fiber rosette and several granule cell and Golgi cell dendrites, as well as Golgi cell axons. Each granule cell dendrite contacts different glomeruli, receiving inputs from different mossy fibers. GrC axon ascends in the molecular layer, where it originates the parallel fibers (pf), that form excitatory synapses on GoC dendrites (Palkovits et al., 1971; Palay and Chan-Palay, 1974; Hámori and Somogyi, 1983). Mossy fiber terminals contact granule cell dendrites as well as Golgi cells, that therefore inhibit granule cells in a feedforward loop. Parallel fibers originating from granule cell axons, activates Golgi cells, giving rise to a feedback inhibition on granule cells.