PROTEOGLYCAN ULTRACYTOCHEMISTRY AND CONVENTIONAL AND HIGH-RESOLUTION SCANNING ELECTRON-MICROSCOPY OF VERTEBRATE CEREBELLAR PARALLEL FIBER PRESYNAPTIC ENDINGS

The parallel fiber ''en passant'' synaptic endings of mouse cerebellar molecular layer have shown by means of transmission electron microscopy, the presence of an electron dense extravesicular material in samples perfused with Alcian blue. This alcianophilic material was digested in cerebellar tissue previously treated with testicular hyaluronidase, suggesting the presence of hyaluronic acid or chondroitin 4- or 6-sulphate. Freeze-fractured Rhesus monkey cerebellar cortex prepared for conventional scanning electron microscopy also revealed the presence in fractured synaptic varicosities of parallel fibers of a high mass density material, in which the synaptic vesicles are embedded. Examination of cryofractured primate cerebellar cortex coated with thin chromium films, 1-2 nm thick, in the high resolution field emission scanning electron microscope showed the SE-I topographic contrast of an extravesicular material deposited in axoplasmic matrix of fractured parallel synaptic endings. The precise localization of this material corresponds to that observed in transmission electron microscopy and conventional freeze-fracture scanning electron microscopy. These electron microscopic findings tend to agree with the omnipresence in several vertebrates of a presynaptic axoplasmic material, which seems to be proteoglycan in nature.