Conventional and high resolution scanning electron microscopy of outer and inner surface features of cerebellar nerve cells.

This paper provides an exploration into the inner and outer surfaces of vertebrate cerebellar neurons utilizing secondary electron (SE-I and SE-II) topographic contrasts. SE-I enriched chromium coated, cryofractured Rhesus monkey cerebellum staged within the condenser/objective stage of SEMs equipped with high brightness LaB6 and field emission emitters generated quality images of intact and fractured nerve cells studied at intermediate and high magnifications. These images were compared with conventional SE-III images of gold-palladium teleost fish cerebellar neurons and transmission electron micrographs of mouse cerebellar nerve cells obtained either by thin-sections or freeze-etch replicas. Chromium coated Rhesus monkey granule and Golgi cell surfaces revealed smooth, accurately delineated profiles of true cell surface features, which lacked the SE-III dominated brilliance of conventional teleost fish gold or gold-palladium, decorated neurons. Chromium coated fractured nerve processes showed the outer smooth surface of interconnected anastomotic networks or ER tubules, vesicles and cisterns. Cross fractured presynaptic endings of parallel fibers in the molecular layer exhibited spheroidal synaptic vesicles and SE-I edge brightness contrast delineated their limiting plasma membranes. Fractured synaptic endings showed a homogeneous extravesicular material surrounding the synaptic vesicles. The presynaptic dense projections appeared as columnar shaped structures. The postsynaptic membrane and associated postsynaptic density showed a discontinuous surface formed by round subunits 25-35 nm in diameter. The neuroglial cytoplasm ensheathing nerve process exhibited a smooth discontinuous surface. The surface of the myelin sheath showed a mixed population of globular structures 10-30 nm in diameter, apparently corresponding, according to freeze-etch images, to protein and phospholipid microdomains.