5-3. Golgi Cells

Golgi cells are large neurons that extend their dendrites like a bouquet into the molecular layer and also extend their descending dendrites to the granular layer. Golgi cells have broadly branching axons in the granular layer (Color Plate X A). It is now apparent that Golgi cells exert extensive control of spatio-temporal signal organization and information storage in the granular layer (see D’Angelo, 2008). It is also apparent that they play unique roles in computational aspects of cerebellar function (Chapter 9).

The molecular layer dendrites of each Golgi cell receive ~4,800 excitatory inputs from parallel fibers, and the same cell’s descending dendrites in the granular layer receive ~230 excitatory mossy fiber terminals (Pellionisz and Szentágothai, 1973). Through such inputs, each Golgi cell recorded in the C₃ zone has a localized receptive field in the forelimb skin (Ekerot and Jörntell, 2001a,b). The major excitatory inputs from parallel fibers to Golgi cells are mediated by both AMPA and NMDA receptors (Dieudonné, 1998) and mGluR2 (Watanabe et al., 2003). Interestingly, parallel fiber-induced mGluR2 activation hyperpolarizes Golgi cells via G-protein-coupled inward K⁺ channels, as contrasted to the depolarizing action mediated by mGluR1 on Purkinje cells. mGluR2 is expressed also in the somata and axons of Golgi cells whose axon terminals can be activated by glutamate released from mossy fiber terminals (Ohishi et al., 1994). Golgi cells also receive inhibitory synapses from Lugaro cells (see below) but not from Purkinje cells or other Golgi cells. Morphological evidence suggests that climbing fibers might make contact with Golgi cells (Palay and Chan-Palay, 1974; Sugihara et al., 1999) but its functional significance is unclear (see Chapter 8, “Multiplicity and Persistency of Synaptic Plasticity”).