The cerebellum of the frog Rana ridibunda. An electron microscopic study.

An electron microscopic study of neuronal types and different synaptic contacts has been made in the cerebellum of the frog Rana ridibunda. The Purkinje cells have a pear-shaped cell body and in their cytoplasm the organelles show a special arrangement because of the great amount of microtubules they contain. The granule cells are small, rounded neurons with a large nucleus surrounded by a thin rim of cytoplasm. The stellate cells are interneurons of the molecular layer whose large nuclei show a single finger-like invagination of its nuclear envelope. The afferent tracts to the cerebellum end either as climbing fibers or mossy fibers. The axon terminals of climbing fibers are large and the synaptic complexes exhibit all the features of a type-I Gray synapse. The mossy fibers reach the granular layer and synapses between them and granule cell dendrites are by far the most abundant. The parallel fibers establish synaptic contacts on the spines arising from the spiny branchlet units of the Purkinje cells and with the perikaryon and dendrites of stellate cells. The stellate cell axons cross the molecular layer and establish type-II Gray synapses on the Purkinje cells.