Types and distribution of synapses upon basket and stellate cells of the mouse cerebellum: An electron microscopic study

The consistent identification of nerve terminals in the molecular layer of the mouse cerebellum has permitted electron microscopic study of the spatial and numerical distribution of synapses upon the soma and dendrites of stellate cells at three depths in the molecular layer. The number of boutons synapsing per 100 μ of cell perimeter, or general synaptic density (G.S.D.) has been found to vary among stellate cells located at different depths in the molecular layer. It has also been found that the G.S.D. of the dendrites is greater than that of the cell bodies of these cells. The specific synaptic densities, or number of boutons of specific type (such as parallel fiber, climbing fiber etc.) synapsing upon 100 μ of cell perimeter, have been found to vary significantly for each type of terminal among upper, lower, and very low stellate cells in the molecular layer. Very low stellate cells receive almost exclusively Purkinje collateral synapses upon their cell bodies (the dendrites have not been identified) whereas low stellate cells (basket cells) receive upon both their cell bodies and dendrites mostly parallel fiber synapses and in decreasing order lesser amounts of basket‐stellate, Purkinje collateral and climbing fibers. Uppermost stellate cells, however, receive only parallel fiber and a few stellate terminals. The distribution of synapses upon stellate cells found in the mouse agrees with physiological data reported in the cat.