Surface and membrane morphology of Bergmann glial cells and their topographic relationships in the cerebellar molecular layer.

The cerebellar Bergmann glial cells of Swiss albino mouse, teleost fish and human have been examined by means of freeze-fracture and ethanol-cryofracturing techniques for scanning electron microscopy and freeze-etching and thin sectioning techniques for transmission electron microscopy in order to study the outer surface, membrane morphology and topographic relationship with Purkinje cells, parallel and climbing fibers and stellate axons. Freeze-fracture and ethanol-cryofracturing techniques exposed the somatic outer surface and lamellated processes surrounding the Purkinje cells. Transmission electron microscopy showed a granular substance filling the extracellular space separating Bergmann glial cell cytoplasm from dark Purkinje cells. This substance was absent in the vicinity of clear Purkinje cells. Freeze-etching replicas showed a multilayered ensheathment of Bergmann glial lamellar processes surrounding parallel fibers. The P face of Bergmann glial cell plasma membrane exhibited orthogonal arrays or assemblies of intramembrane particles (IMPs) and high density distribution of round IMPs 6-15 nm in diameter, whereas the E face was characterized by a smooth surface and low density distribution of IMPs. Rod intramembrane particles, 20-30 nm in length, were also found in the plasma membrane P and E faces. The fractured Bergmann glial cell cytoplasm was observed encapsulating the parallel fiber varicosities, or the bundles of non-synaptic segments of parallel fibers and enclosing the climbing fiber and stellate axonal synapses with Purkinje dendrites.