Developmental changes of synapses in the cerebellar cortex of the rat. A quantitative analysis.

Synaptogenesis in the molecular layer of the vermis cortex in Wistar rats between 1 and 25 days after birth was investigated. After staining with OSO4, the following parameters were measured: the density of synaptic profiles; the percentage of the neuropil area occupied by synapses; the mean diameter of the boutons; and the numerical density of synapses in a defined volume. The detailed topographical analysis enabled us to show the following: the first synapses appear diffusely in the molecular layer; after the 10th day a synaptic gradient is present between the depth and the surface area (this gradient can be found by the count of the synapses and by studying the spatial distribution of the synaptic area); this gradient is no longer seen at the 25th day, when the density of synapses is relatively uniform throughout the whole molecular layer.