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 sens orimotor cortex was studied by means of freeze-etched replicas and thi n sections. In thin sections, symmetric synaptic junctions were locate d on dendritic shafts. Examination of freeze-etched preparations suppo rted the notion that the postsynaptic dendritic shaft membrane exhibit ed the same structure as the surrounding non-junctional membrane on bo th fracture faces. In thin sections, asymmetric perforated and non-per forated 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 p erforated and non-perforated aggregates of intramembranous particles a t the extracellular half (E-face). These aggregates are accepted as a freeze-etch equivalent of perforated and nonperforated asymmetric syna pses seen in thin sections. The intramembranous characteristics of axo dendritic synapses in the rat sensorimotor cortex are discussed in ter ms of synaptic contact zone plasticity.