Freeze-fracture cytochemistry of neuronal membranes: inhomogeneous distribution of filipin-sterol complexes in perikarya, dendrites and axons.

Vibratome slices of cerebellar cortex fixed in a glutaraldehyde solution containing filipin, a sterol-specific probe, were freeze-fractured to study the distribution of filipin-sterol complexes in neuronal plasma membranes. These complexes appear as 25-30 nm protuberances or pits in the fracture face of plasma membranes, and their density was low in dendrites of Purkinje and granule cells. In contrast, the plasma membranes of neuronal perikarya showed an abundant filipin labeling, 4-6 times greater than in dendrites. Parallel fibers, the axons of granule cells also had significantly more filipin-sterol complexes than granule cell dendrites, but fewer than granule cell perikarya. The results reveal difference in the organization of specific regions of neuronal plasma membranes, which are also characterized by a different pattern of synaptic contacts.