Structure of the synaptic junctions in the rat sensorimotor cortex, freeze-etching study of axodendritic synapses

The intramembranous structure of axodendritic synapses in the rat sensorimotor cortex was studied by means of freeze-etched replicas and thin sections. In thin sections, symmetric synaptic junctions were located on dendritic shafts. Examination of freeze-etched preparations supported the notion that the postsynaptic dendritic shaft membrane exhibited the same structure as the surrounding non-junctional membrane on both fracture faces. In thin sections, asymmetric perforated and non-perforated synapses were found on dendritic spines and dendritic shafts. In freeze-etched replicas, the postsynaptic membrane of the dendritic spine and some of the dendritic shaft synapses were characterized by perforated and non-perforated aggregates of intramembranous particles at the extracellular half (E-face). These aggregates are accepted as a freeze-etch equivalent of perforated and nonperforated asymmetric synapses seen in thin sections. The intramembranous characteristics of axodendritic synapses in the rat sensorimotor cortex are discussed in terms of synaptic contact zone plasticity.