Type 1 and 2 synaptic junctions: differences in distribution of concanavalin A binding sites and stability of the junctional adhesion.

Two classes of synaptosomes have been distinguished in subcellular fractions from rat forebrain. They differ in morphology and distribution of concanavalin A binding sites. Morphological examination suggests that the two classes correspond to the type 1 (excitatory) and type 2 (inhibitory) synapses of intact brain tissue. Under the conditions of incubation employed in this study, type 1 synaptosomes show splitting of the synaptic junctions, but the type 2 junctions are apparently stable. The chemical differences illustrated by the differences in concanavalin A binding sites suggest that type 1 and type 2 synaptic junctions differ fundamentally in supramolecular structure rather than being superficial variants of basically similar structures.