Freeze-fracture of developing neuronal plasma membrane in postnatal cerebellum.

The structure of the plasma membrane of two neuronal cell types was quantitatively assessed in freeze-fracture replicas of rat cerebellar cortex from 2 to 73 postnatal days. The measurement of the number and size of intramembrane particles (IMP) in different regions of the Purkinje cells and of the granule cell showed that between 2 and 21 postnatal days there was a differential increase in the number of IMP; several regions of the cell characterized by a different pattern of synaptic interconnections showed differences in particle size and in particle number: neuronal processes had lower numbers of IMP than perikarya, whereas dendrite spines contained fewer IMP than dendritic trunks. These differences in IMP content appeared at the time at which specific synaptic contacts are established in these various regions of the cells.