Participation of Golgi neuron processes in the cerebellar glomeruli: An electron microscope study

SummarySynaptic relations, within the cerebellar isles, of Golgi II neuron axons and dendrites have been studied in the cat. Golgi axon endings can be identified with some probability in the outer (cortical) zone of the cerebellar glomeruli in normal material. They can well be recognized in the chronically isolated folium in which mossy fibers have completely degenerated. The Golgi axons are very thin preterminal fibers with small enlargements containing synaptic vesicles and contacting the preterminal intraglomerular parts of the granule cell dendrites as well as their terminal spheroid protrusions. The spheroid protrusions of the granule dendrites are the main postsynaptic loci of the granule neuron having their main synapse with the mossy fiber — generally of central position in the glomerulus — and additional synapses, more often on their outer surface, with the Golgi axons. No significant difference is seen between the two contacts, from which one is known to be excitatory (mossy) and the other inhibitory (Golgi ax.). The Golgi cell has also descending dendrites, known from light microscopy to be engaged in the cerebellar isles. By tracing these dendrites from the cell bodies and using their characteristic short finger-like processes as a criterion for their identification, the synapses between mossy endings and Golgi dendrites could be identified under the EM. They are broad contacts between a dendrite passing along one side of the mossy ending, with several synaptic attachment plaques and with small dendritic processes protruding into invaginations of the mossy ending. — The cerebellar glomerulus is thus a complex synaptic apparatus with two different axonal elements (mossy and Golgi endings) and often two dendritic elements (granule and Golgi dendrites) involved. — The possible functional significance of the Golgi cell is discussed in the light of these findings and the new discoveries by Eccleset al. (1964b, 1966) on its inhibitory nature.

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