Analysis of interneurons based on their synaptic organization in the cerebellar cortex of the cat.

Abstract

The geometrical regularity of the cerebellar cortex of mammals provides us with favorable opportunities for electron microscopic analysis of various kinds of neurons which have been identified by the light microscope as upper stellate, basket, Golgi and granule cells. It has been revealed that the synaptic organization on the surface of the soma of each neuron is specific for each type of cell mentioned above.Upper stellate cells: This type of cell is characterized by its location in the upper molecular layer, its size and shape, and the specific configuration of the nucleus featuring deep invagination. Most conspicuous is the structure of the peculiarly shaped cytoplasmic inclusions. The axon terminals of this neuron contain flattened synaptic vesicles indicative of an inhibitory function (UCHIZONO 1965, 1966, 1967) of this neuron. It must be emphasized that almost no synapse is found on the surface of the soma of the stellate cell.Basket cells: The surface of the soma of basket cells is found to have abundant synapses, excitatory and inhibitory, the former usually exceeding the latter in number. The filamentous nature of the axoplasm and membranous bodies in the axons is also remarkable. The terminal boutons of the axons contained flattened vesicles. Deep invagination of the nucleus is also characteristic of this cell.Golgi cells: Synaptic supply on the surface of Golgi cells is relatively poor. Small numbers of synapses of both S-type (excitatory) and F-type (inhibitory) are found on the neuron soma. The complex invagination of the nucleus is remarkable. Axon terminals of this neuron contain flattened vesicles indicating the inhibitory nature of this cell.Granule cells: No difficulty is encountered in identifying this type of neuron. An enormous number of granule cells are tighly packed in the granule cell layer of the cortex. No synapse is found on the neuron soma. Cerebellar glomeruli consisting of granule cell dendrites, mossy fiber terminals and Golgi cell axons are easily identified by their location and their morphological characteristics of the excitatory and inhibitory synapses of the axon terminals of the component neurons. Terminals of the axon of granule cells (parallel fibers) contain spheroid synaptic vesicles (S-type) indicating the excitatory nature of the neuron.