The function of cerebellar Golgi cells revisited

Abstract

The inhibitory interneurons of the cerebellar cortex have received very little attention compared to the granule and Purkinje cells, and Golgi cells are no exception. Theoretical considerations of the function of Golgi cell functions have evolved little since from the late sixties and experimental studies were sparse until the last few years. Recent modeling and in vivo experimental studies by our group, combined with in vitro experimental studies by others, have provided new insights into the properties of these cells which necessitate a revisiting of their function. The connectivity of the Golgi cell The anatomical facts are rather simple. The numerically most important input to the cerebellum is the mossy fiber system (Murphy and Sabah, 1971; Brodal and Bjaalie, 1997). If we limit ourselves to this input, the anatomy of cerebellar cortex can be described as a two-layered network. The input layer, corresponding to the granular layer, processes the incoming mossy fiber signals and transmits them by the parallel fiber system to the output layer, consisting mainly of the Purkinje cells. In both layers activity is controlled by inhibitory neurons, the Golgi cells in the input layers, and the basket and stellate cells in the output layer. Mossy fibers activate both the excitatory granule cells and the inhibitory Golgi cells (Fig. 1A). The granule cell axon forms the parallel fibers, which not only transmit information to the output layer, but also provide additional excitatory input to Golgi cells. Each Golgi cell in turns inhibits the many granule cells present within the range of its axonal arbor (Eccles et al., 1966) with probably some overlap between adjacent Golgi cells. The combination of the parallel fiber excitation of Golgi cells with their inhibition of granule cells constitutes a feedback inhibition circuit (Fig. 1C). The direct excitation of Golgi cells by mossy fibers (Fig. 1B) provides a feed-forward connection. It should be noted, however, that the existence of mossy fiber contacts onto Golgi cells couldwere not be confirmed found in electron microscopal reconstructions of cerebellar glomeruli (Jakab and Hamori, 1988).